cpcb paper guideline

FINAL REPORT

ON

DEVELOPMENT OF GUIDELINES FOR WATER CONSERVATION IN PULP AND

PAPER SECTOR

Sponsored by

CENTRAL POLLUTION CONTROL BOARD

Delhi

Submitted by:

{Environment Group} NATIONAL PRODUCTIVITY COUNCIL

New Delhi (March, 2006)

TABLE OF CONTENT

SL. NO. TITLE PAGE NO

Chapter 1: Background 1.1 Introduction 1 1.2 Objective of the study 2 1.3 Scope of work 2 1.4 Methodology 3

Chapter 2: Industry Profil;e: Pulp and Paper 2.1 Status of Pulp and Paper Mills in India 5 2.2 Classification of Pulp and Paper Mills in the country 11

Chapter 3: Manufacturing Processes 3.1 Generalised Paper /Paper board making process 16 3.2 Different industrial processes in pulp and paper sector 17 3.3 Chemical recovery from black liquor 36

Chapter 4: Water consumption pattern in other countries 48 Chapter 5: Present Water consumption pattern prevailing

in pulp and paper sector in India

5.1 Background 52 5.2 Water consumption Scenario 52 5.3 Water consumption: Norms/Standards for paper and pulp 52 5.4 Water consumption: Latest Trends 54

Chapter 6: Unit Process/operation specific water consumption factors

6.1 Background 58 6.2 Existing Water Consumption Status 62

Chapter 7: Formulation of Standards for water consumption by different categories of pulp and paper manufacturing units

7.1 Background 79 7.2 Proposed categaries of pulp anf paper mills for standards 78 7.3 Proposed types of Water consumption standards 82 7.4 Development of category specific water consumption standards 83 7.5 Proprosed category specific wastewater discharge standards 90

Chapter 8: Water conservation options identified for different categories of pulp and paper mills

92

Conclusion 115

Annexure I: Copy of Questionnaire Annexure II: List of pulp and paper mills in India Annexure III: Compilation of Questionnaire data

STUDY TEAM

PROJECT ADVISOR Dr. A. K. Saxena, Group Head TEAM LEADER Mr. Rajat Gupta, Senior Consultant TEAM MEMBERS Mr. K. K. Sinha, Senior Consultant

Ms. Shukla Pal, SeniorConsultant Mr. S. Baskaran, Consultant From other Regional Offices Mr. Kaliprasad V, Senior Consultant, RPMG, Hyderabad

Mr. Hemantha S S, Consultant, RPMG Bangalore SECRETARIAL ASSISTANCE Mrs. H. K. Sarna Mr. R.K. Ahuja LABORATORY ASSISTANCE Mr. S. K. Jain, Laboratory Analyst Mr. Bhupinder Singh Yadav

ACKNOWLEDGEMENT

National Productivity Council (NPC) places on record its sincere thanks to the Central Pollution Control Board for entrusting the study on “ Development of Guidelines for Water conservation in Pulp and Paper sector”. NPC is grateful to Shri P. M. Ansari, Additional Director, CPCB and Shri S. K. Gupta, Senior Environmental Engineer, CPCB for their cooperation and assistance at various stages of the project in collecting information from State Pollution Control Boards and in selecting representative pulp and paper mills. NPC is also thankful to all State Pollution Control Boards for providing list of operating pulp and paper mills in their respective states. NPC places on record its sincere thanks to all the management of following pulp and paper mills for their full cooperations during conduction of field studies in their mills:

1. M/s Tehri Pulp & Paper Ltd, Muzaffarnagar 2. M/s Shreyan Industries Ltd., Ahmedgarh 3. M/s HNL, Kottayam 4. M/s ITC (PSPD) Ltd., Bhadrachalam 5. M/s Seshasayee Paper & Boards Limited, Erode 6. M/s Indo Afrique Paper Mills (P) Ltd., Pune 7. M/s Pudumjee Pulp & Paper Mills Ltd. Pune 8. M/s. Shalimar Paper Mills (p) Ltd., Muzaffarnaga 9. M/s The Simplex Mills Co. Ltd. (Paper Division), Gondia 10. M/s KAWATRA PAPER Mills Ltd., Dadri

NPC also extends its thanks to various pulp and paper associations for providing information on pulp and paper mills operating in India. Last but not the least, NPC is thankful to all those who have been associated with the project studies either directly or indirectly.

National Productivity Council, New Delhi

EXECUTIVE SUMMARY

The pulp and paper industry is one of India's oldest and core industrial sector. The socio-economic importance of paper has its own value to the country's development as it is directly related to the industrial and economic growth of the country. Although paper has many uses, its most important contribution to modern civilization is its use as a medium to record knowledge. Paper manufacturing is a highly capital, energy and water intensive industry. It is also a highly polluting process and requires substantial investments in pollution control equipment. In India, around 905.8 million m3 of water is consumed and around 695.7 million m3 of wastewater is discharged annually by this sector1. India’s current average fresh specific water consumption of about 150 m3/tonne of product is far above the global best specific water consumption of 28.66 m3/tonne (for large scale wood based pulp and paper mill) and this large gap is primarily attributed to the use of obsolete technology / equipments and poor water management practices. The large water requirements and consumption by the Indian pulp and paper industries has led to, water fast becoming a scarce commodity and lowering of the groundwater table and thus increased pumping costs and more importantly water shortage in many regions. Realizing the importance of water and excessive usages of water by pulp and paper sector, Central Pollution Control Board (CPCB) has taken initiative to develop the water conservation guidelines and water consumption standards and entrusted National Productivity Council to undertake the study to address these issues. India produces 5.96 million tones of paper per year (2003 – 2004) through 309 paper manufacturing mills at a capacity utilization of approximately 60 percent. The number of paper manufacturing mills has increased consistently from just 17 in 1951 to around 600 in Year 2002 with an annual installed capacity of 6.2 million to meet the increasing demand. However since 2001 – 02, the number of mills have fallen sharply to 309 in the year 2004 primarily due to increased environmental regulatory pressure, water shortage etc. The profile of Indian pulp and paper sector including the various aspects like product consumption pattern, operational scale, state wise industry inventory, production process used, raw material used is presented in the Figures E-1 to E-3 and tables E-1 to E-3.

Table E-1: Consumption pattern of paper and paper board products in India

Type of paper Main varieties % of total consumptions

Cultural paper cream woven, maplitho, bond paper, Chromo paper

41%

Industrial paper

kraft paper, paper board – paper board - single layer board, multilayer board, duplex board,

43%

1 Source: Estimated by CSE based on the wastewater discharged data published by CPCB in "Water quality in India (Status and trends) 1990 - 2001".


Specialty paper Security paper, grease proof paper, electrical grades of paper

4%

Newsprint glazed, non-glazed 12%


66

227

20

57

187 174

21

62

322

12 12

0

50

100

150

200

250

Cultrual -

high grade

Cultural -

low grade

Industrial

New

sprint

Pulp

Specialty

Figure E-2: Distribution of Pulp and Paper Mills Based on Products Manufactured

No ofMills

Production, 104TPA

Table E-2: Distribution of Pulp and Paper Mills (Number of Mills) Based

on Pulping Processes and Operational Scale No of Mills Installed Capacity,

million tonnes/yr Sl. No

Pulping Process

Large Scale

Small Scale

Grand Total

Large Scale

% Small Scale

%

1 Chemical Soda Process 29 26 54 0.666 4.26 0.106 18.2

8 2 Hydro Pulping 92 113 219 12.80

7 81.88 0.462 80.07

3 Kraft/Sulphite process 34 2 36 2.169 13.87 0.010 1.65

Table E-3 : Summary of classification of pulp and paper sector in

different categories Large/Medium scale Small Scale Sl.

No Product type Agro

based Integrated 2

Paper Mill3

Wastepaper

Wood based

Agro

Integrated Paper Mill

Waste paper

Total

1. Cultural - high

15 1 15 14 7 1 12 65

2 Integrated refers to mill using wood, agro residue and waste paper as raw material 3 Paper Mill refers to mill using pulp produced from other mills to produce directly paper and paper products


Large/Medium scale Small Scale Sl. No

Product type Agro

based Integrated 2

Paper Mill3

Wastepaper

Wood based

Agro

Integrated Paper Mill

Waste paper

Total

grade 2. Cultural -

low grade 2 1 8 1 1 7 20

3. Industrial 19 2 50 18 1 90 1874. Newsprint 1 1 15 2 2 215. Pulp 4 46. Specialty 2 4 3 3 12 Total 39 3 2 92 21 26 1 4 114 309

In order to develop water conservation measures for different types of industries in the pulp and paper sector and also the water consumption / discharge standards, 10 mills were identified (in consultation with CPCB) in accordance with the above referred distribution of pulp and paper mills based on operational scale, raw material used, pulping process, end product etc. Detailed studies were conducted in these 10 mills to identify the water conservation measures and also to generate the water consumption profile. The detailed studies in conjunction with the data from questionnaire survey, literature search and international water consumption norms have been used to develop water consumption standards in the country. Existing Water Consumption Norms / Standards: India In India so far, no standards have been set for water consumption by any agency. However CPCB has prescribed standards in terms of wastewater discharge for different categories of pulp and paper industry. The wastewater discharge quantum with additional 21 % (towards evaporation losses) is generally used to give a fair picture of water consumption. The wastewater discharge standard of 150 and 50 m3/tonne of product for small agro and wastepaper based mills respectively and 200 m3/tonne for large scale mills prescribed by CPCB do not appear appropriate as it does not cater to different categories of pulp and paper manufacturing mills prevailing in India presently. Further, this standard in the current scenario seems to have outdated as the current average water consumption is itself 150 m3/tone of product. As per Corporate Responsibility for Environment Protection (CREP)-2002, following water discharge standards have been agreed upon by different pulp and paper manufacturing associations: A. Large scale pulp and paper mills:

Less than 140 cum/tonne of paper within 2 years Less than 120 cum/tonne of paper in 4 years for mills installed before

1992 Less than 100 cum/tonne of paper in 4 years for mills installed after

1992


B. Small scale pulp and paper mills: Less than 150 cum/tonne of paper within 3 years

This standard is also discharge specific but takes into consideration the operational scale and the age of the mill. This standard also does not differentiate on the basis of pulping process, raw material used, end product etc. Centre for Science & Environment through their Green Rating Project has reported significant reduction in water consumption in large-scale Indian paper mills and average figure has been reduced to 135 m3 per tonne paper in the year 2002 due to increasing awareness regarding water conservation, ever increasing pressure from government regulatory agencies and also due to increasing water scarcity in many regions. The CSE finding gives an indication that most of the industries are already achieving the water consumption norms as agreed upon by them under CREP programme – 2002. Existing Water Consumption Norms / Standards: World In developed countries, most of the pulp and paper manufacturing mills are wood based, however, due to environmental implications, trend is changing towards use of recycled fibre as is the case with India. The average water consumption for wood based large pulp and paper industries primarily producing paper & paper board products from 6 regions / countries namely United States, Australia, Europe, Canada Finland & Spain have been compiled from various documents available on the web and the same is presented in the Table E-4 below : Table E-4: Region / Country Specific Average Water Consumption in

Large Scale Wood Based Pulp and Paper Mills Sl.No.

Region / Country

Average Specific water

consumption (m3/T of product)

Source

1 U.S. 64 (Average value in

the year 2000)

Appendix “W” of Report on Status of Pulp & Paper in US by Michiel P. H. Brongers and Aaron J. Mierzwa

2.

Australia 28.66 ( Average value

for the year 2003)

APIC Public Eco-efficiency Report 2003

3.

Europe 40


4.

Canada 67


5 Finland 40 Pulp Fact - Environmental Implications of


Sl.No.

Region / Country

Average Specific water

consumption (m3/T of product)

Source

. the Paper Cycle” by Nigel Dudley, Sue Stolton and Jean-Paul Jeanrenaud WWF International 1996

6.

Spain 30 Pup Fact – Environmental Implications of the paper Cylcle by Nigel Dudley, Sue Stolton and Jean Paul, Jean Renaud – WWF International 1996

The average water consumption for wood based large pulp and paper industries primarily producing paper & paper board products in developed countries varies from 30 – 70 m3/tonne of Product. Whereas average water consumption in waste paper based pulp and paper mills in developed countries varies from 8 – 10 m3/Tonne of product. Current Water Consumption: A Revisit - Questionnaire Response In order to review present water consumption levels in pulp and paper sector in India, questionnaires were circulated to all the pulp and paper manufacturing mills. Based on the questionnaire responses by industries (44 mills responded out of total of 309), specific fresh water consumption range (excluding domestic) has been compiled and is as given below:

S.No. Raw Material End Product Specific Water Consumption

(M3/T of product) Min Max Remark

Large Scale category

1 Integrated Cultural high grade including newsprint 105 202

2. Wood Based Cultural grade including newsprint 68 168

3. Wood Based Newsprint only 74 There is only one mill

4. Wood Based Rayon pulp 130 Only one mill in this category responded

5 Agro Based Cultural - high grade 73 -do-

6 Agro Based Cultural - low grade including newsprint 46 -do-

3 Waste paper Newsprint 29 -do- Medium Scale category

1 Agro Residue Cultural – high grade 102 219

2 Agro Residue Industrial grade 28 Only one mill in this category responded

3 Waste Paper Based Cultural – high grade 40 -do-

4 Waste Paper Newsprint 16 -do-



(M3/T of product) Min Max Remark

based

5 Waste paper Based Industrial grade 5.5 35

One mill reported 5.5 m3/T & operating with zero discharge system

Small Scale category

1 Agro Residue Cultural - high grade 156 Only one mill in this category responded

2 Agro Residue Industrial 7 Straw board making

mill

3 Waste paper Cultural - high grade 18 Only one mill in this category responded

4 Waste paper Cultural - low grade 14 25 5 Waste Paper Industrial 7 80

Current Water Consumption: In depth Study Findings Keeping in view, the above mentioned variation prevailing in Indian pulp and paper sector, ten representative mills were selected in consultation with CPCB official for carrying out detailed field studies. During the field studies, detailed water balance, material balance (with respect to fibre and water) audits were carried out. And based on studies, specific water consumption in each mill was estimated. The specific fresh water consumption estimated in each representative mill is as given in table E-5 below:

Table E-5: Specific Water Consumption in Selected Field Study Mills Mill Code

Operational Scale & Raw Material

End Product Water consumption,

m3/T Large Scale 1 Wood & Wastepaper based Newsprint

manufacturing 80

2 Wood & wastepaper Based Cultural – high grade

77

3 Wood, Agro& wastepaper Cultural – high grade

67

Medium Scale 4 Agro & waste paper based Cutural – high

grade 80

5 Agro & waste paper based Industrial grade 47 6 Waste paper based Cultural – high

grade 48

Small Scale 7 Agro & waste paper Cultural – high

grade 110

8 Agro & wastepaper based Industrial grade 93


Mill Code

Operational Scale & Raw Material

End Product Water consumption,

m3/T 9 Waste paper based Cultural – low

grade 13

10 Waste paper based Cultural – low grade

129

Proposed standards for water consumption in pulp and paper sector Based on the detailed pulp and paper mill’s inventorisation and observations from the dry and detailed field studies conducted during the course of this study, it became evidently clear that water consumption varies significantly depending upon the raw material used, scale of operation and the end product. Realizing these variation it was clear that one or two general standards would not suffice for the entire pulp and paper sector. Accordingly, considering the prevailing characteristics of Indian pulp & paper mills in the country, following six categories of pulp and paper mills with respect to water consumption pattern have been proposed for formulation of standards:

A. Large scale Wood based and integrated pulp and paper mills manufacturing cultural grade paper & paper board and / or Newsprint

B. Small/Medium Scale Agro based pulp and paper mills manufacturing high grade cultural paper

C. Small/Medium Scale Agro based pulp and paper mills manufacturing industrial grade paper

D. All wastepaper based pulp and paper mills manufacturing high grade cultural paper with “De-inking”

E. All wastepaper based pulp and paper mills manufacturing cultural grade paper without De-inking

F. All medium / small scale waste paper based mills manufacturing industrial grade paper

While developing the water consumption standards for the above referred categories following factors have been considered.

The standards developed should ensure continuous reduction in water consumption.

The standards should be such that they trigger technological interventions as well as reuse / recycling opportunities and thus lead to quantum reduction in water consumption in long term.

The standards should be India specific and practicable and feasible to implement.

The standards should also even out the huge water consumption disparities among the similar type of mills in short term.


Considering all the above factors, three levels of standards have been formulated. The three levels are

• Benchmark Standard: This standard refers to minimum water consumption required after implementation of best available technology (economically viable and currently practiced / demonstrated in India), recycle and reuse practices. This standard has been developed by identifying the various mill operations involved in each specific category and also identifying the least water consumption actually achieved by any of the mills studied in that particular category. The total of water consumption in each of the mill operation / process would be the benchmark standard for that specific category.

The idea of developing this standard is to ensure o Quantum reduction in water consumption: No mill in the

above referred categories is currently operating at this level. To achieve this level most of the mills would need to undertake certain technological modifications and complex recycling / reuse measures to achieve the quantum reduction in the water consumption and comply with these standards

o Development of feasible standards: Further these standards reflect the feasible and demonstrated mill operation specific water consumption norms already practiced in one or the other industry in India and thus expected to be appreciated and followed by industries.

Since complying with these standards would need technological and complex recycling / reuse systems interventions, which require significant time and resources at the industries end, it is proposed that these standards to be considered for implementation after four years from the acceptance year of this report.

• Best Achieved Standard: This standard refers to the minimum water consumption already achieved by a mill (or can be achieved by implementation of simple recycling / reuse measures) simple in the specific category.

This standard is developed with the perspective of bringing the other mills to the currently best achieved and demonstrated level in the country. This standard can be achieved by implementation of simple water recycling and reuse practices and minor technological changes. This standard is proposed to be considered for implementation from two years from the acceptance year of this report. The three years grace period is proposed to enable other industries to undertake technologies feasibility (technical, economical, environmental etc) and implementation.

• Relaxed Standard: This standard provides 20 % relief over the best achieved standard in each specific category. This standard is proposed


for immediate reduction in water consumption by most of the high water consuming industries and thus bridge the huge gap between best performing and worst performing mills in a short time. It is estimated that this standard can be achieved by other industries in each categories by implementing simple reuse, recycling and other minor modification.

This standard is proposed to be implemented after six months from the acceptance of this report. The six months grace period is proposed to enable other industries to undertake the reuse, recycling and other minor modifications. The process of developing above referred benchmark standards would also identify mill operation / process or section specific water consumption benchmark figures that can be used by the industries for continuous improvements.

The consolidated proposed water consumption/wastewater discharge* standards for each category of the pulp & paper mills are compiled and tabulated below in table E-6:

Table E-6: Proposed Water Consumption/Wastewater Discharge Standards

Proposed water consumption/wastewater discharge standard in m3 / Tonne of product

Sl Category Description

Benchmark Best achievable

Relaxed

1 Large scale Wood based and integrated pulp and paper mills manufacturing Newsprint, Cultural grade paper and paper board

63 / 50 67 / 53 80 / 63

2 Small/Medium Scale Agro based pulp and paper mills manufacturing cultural grade paper

38 / 30 80 / 63 95 / 75

3 Small/Medium Scale Agro based pulp and paper mills manufacturing industrial grade

18 / 15 47 / 37 56 / 44

4 All wastepaper based pulp and paper mills manufacturing high grade cultural paper and / or news print with “De-inking”

19 / 15 41 / 32 49 / 38

5 All waste paper based pulp & paper mills manufacturing high grade cultural paper without “De-inking”

9 / 7 13 / 10 15 / 12

6 All Medium / Small scale wastepaper based pulp and paper mills manufacturing industrial grade paper

6 / 5 6 / 5 7 / 6


* Wastewater discharge standards have been evolved with an assumption that around 21% of the input fresh water is lost as vapour in fourdreineir machine (drier section) and in boiler section and the balance is discharged as wastewater. Further, it is recommended to reuse this wastewater as much as possible for irrigation purpose. Water Conservation Options Evolved and Recommended to Achieve Quantum Reduction in Fresh Water Consumption in Pulp and Paper Sector The high water consumption in Indian pulp and paper industry is mainly due to obsolete process technology, poor water management practices and inadequate wastewater treatment. In order to evolve techno economically feasible option, detailed field studies were carried out as mentioned earlier. Depending upon the category and scale of operations, water conservation options have been recommended. They are briefly described below: Low – cost improvements

• General Housekeeping Measures: General housekeeping measures deals with low-cost improvements like leak detection, repair, production scheduling, use of press type tap, auto close valve hose to reduce wastage due to negligence, etc

• Using better quality raw material to achieve desired brightness: Manipulation of raw material quality enables use of lesser quantity of bleaching chemicals, hence requires less water quantity for bleaching and washing

• Dry de-dusting of straw for removal of fines and dust / Dry depithing of Bagasse / Dry debarking of Wood

• Collection of black liquor spills in a common tank: This reduces fresh water consumption required for floor washing.

Design stage procedures (new plant/equipment)

• Use of Better pulp washing technology: Various technologies available in decreasing specific water consumption are potcher washing, hydraulic washing, vacuum drum washing, Pressure washing, diffusion washing, chemi or belt washing, twin roll press washing. Among all, potcher washing has maximum specific water consumption (55 - 60 m3/BDMT bleached pulp) and twin wire roll press has minimum specific water consumption (26 m3/BDMT bleached pulp). However, a


twin wire roll press washer for a 300 OD TPD fiberline costs approx. 1081 million INR. Where as a vacuum drum washer would cost only 10 – 25 million INR, hydraulic washer would cost 2.5 million (works good with lower capacity). Therefore, techno-economic feasibility is required before identification of suitable washer in the individual mill.

• Use of More Efficient Deinking Plant : The clarified water is reused in different mill operations: Helicopulper, H D Cleaner, Pulp Dilution, Centricleaner, Pressure screen

• Membrane filtration technique in deinking process instead of conventional floatation method: Membrane separation technology is a potentially attractive method for the removal of flexographic ink residues from the wash filtrate effluent of deinking mills and thereby enabling recycle of wash filtrate

• Installation of Indirect & More Efficient Heat Transfer System for Blow Heat Recovery In Digestor Section: This avoids generation of contaminated wastewater (in direct heat transfer, waste gases are directly injected to water) and enables reuse of cooling wastewater.

• Replacing barometric leg (direct) condensor cooling by surface (indirect) condensor cooling: The wastewater from barometric leg is generally discharged to ETP and cannot be completely recycled back

Process modifications including recycle/reuse

• Optimum use of cooling wastewater: A. Collection of once-through cooling water and reuse it in different

process operation B. Converting once-through system into a closed –loop system by

installing a cooling tower • Recovery and re-cycling of clean water from vacuum pumps • Installation of Vacuum flume tank to recycle vacuum pump sealing

water • Replacement of water seals in Process Pumps: Mechanical seal

pumps can be used to avoid usage of sealing water. Also seal less pumps are extensively used in chemical industries which can also be used pulp and paper manufacturing mill.

• Use of modified design of nozzle in Decker thickener shower • Use of efficient Decker thickener/ vacuum drum showers • Use of efficient shower system and Regular monitoring of low pressure

and high pressure showers and in the paper machine section • Use of Enzymatic deinking process • Recovery of bleaching chemicals through membrane separation &

reuse (closed loop bleaching): For Mills with Elemental Chlorine free bleaching process.

• Reuse of secondary condensate in raw material preparation section, Brown Stock Washing / Bleach Washing


• Reuse of Spout cooling wastewater • Reuse of barometric leg wastewater: This wastewater is suitable for

reuse in Brown stock washing. • Reuse of wastewater from DM plant (regeneration & sandfilter

backwash), softner (regeneration & sandfilter backwash) for ash conditioning / quenching

Process redesign which includes improvement in quality and management of paper machine wastewater

• Choosing right type of saveall system: There are different technologies to clarify paper machine white water like polydisc saveall, Krofta saveall, sedimentation type saveall, drum filter, inclined or Hill screens, etc. Depending upon the usage of clarified water and quality required, type of saveall needs to choosen. In large scale mills, polydisc saveall is advantageous. The clear filtrate generated from the saveall can be directly used in high pressure paper machine showers.

• Optimum use of paper machine clarified wastewater in sections other than paper machine: Various application areas are :Decker thickener showers, Vacuum washers, Centricleaner reject dilution, Pulp dilutions before bleaching stage, Johnson screen showers, etc. this requires provision of sufficient storage capacity. A modified storage capacity similar to ‘Stawford” separator helps in further separation of solids and fibres from the clarified water

• Use of back or recycled water in low pressure showers: Various locations in paper machine section where back water can be used are: Wire section - Breast roll, wire turning and wire-return rolls, knock – off shower, trim knock – off shower, wire cleaning shower ( low pressure).,Press section - Cleaning of rolls

Total system closure with zero liquid effluent

• Tertiary treatment of wastewater for recycling: In tertiary treatment, Aluminum oxide, ferric oxide and poly electrolytes assist coagulation of waste in the effluents, which are then sand filtered. The quality of treated wastewater after the tertiary treated is fit for recycling back completely to the system especially in wastepaper based mills and partially for other mills.

However, there is a limitation to continuous recycle of wastewater within the plant for a long period as it leads to slime generation. This is prevented by optimized addition of biocide and chemicals in the water at regular intervals.


Conclusion Existing standards are passé. The questionnaire responses, CSE’s green rating project and the detailed field studies have clearly indicated that the majority of industries in-fact actually performing better than both the existing standards and the CREP standards they have agreed to. Common standard not far-sighted It has also clearly emerged from the in depth studies that water consumption varies significantly based on the scale of operation, raw material used and the end products manufactured. Hence a common standard for all type of industries would not be prudent and accordingly standards have been developed for six categories of pulp and paper industries considering operational scale, raw material used and the end product manufactured. Recommended standards a challenge already conquered While comparing with the existing standards, the currently recommended standards may seem to be a challenging task to achieve but actual practice these have already been achieved in totality by an Indian enterprise (Best achieved standard) or partially i.e. at a mill process level by one or the other Indian enterprise (benchmark standard). Hence the proposed standards are practical and feasible to achieve. The industries may refer to the water conservation measures identified under the study to achieve the water consumption standards. Let’s not stop, we need to go further The currently developed and recommended water consumption standards are still comparably high in light of the latest world wide trends on water consumption. The currently developed standards should be treated as short term applicable for about 8 years. It is further recommended that these standards should again be revisited after 6 years.

***************

Final report on water conservation in Pulp and Paper Sector Page No.1


CHAPTER 1

BACKGROUND 1.1 INTRODUCTION The pulp and paper industry is one of India's core sector industries. The average production in the year 2003 – 2004 is 5.96 million tonnes per annum. The socio-economic importance of paper has its own value to the country's development as it is directly related to the industrial and economic growth of the country. Although paper has many uses, its most important contribution to modern civilization is its use as a medium to record knowledge. Paper represents the perfect adjustment of a basic material to any use and purpose. Paper manufacturing is a highly capital, energy and water intensive industry. It is also a highly polluting process and requires substantial investments in pollution control equipment. In India, around 905.8 million m3 of water is consumed and around 695.7 million m3 of wastewater is discharged annually by this sector1. Looking into the serious nature of pollution, the pulp and paper industry in India has been brought under the 17 categories of highly polluting industries. In global comparison on specific water consumption (the global best specific water consumption is 28.66 m3/tonne for large scale wood based pulp and paper mill), India is still far behind ( India’s average fresh water consumption in pulp and paper sector is 150 – 200 m3/tonne of product) and this is largely attributed to the use of obsolete technology / equipments and poor water management practices. At the same time, water has been increasingly becoming a scarce commodity and several industries are experiencing acute water shortages especially during non-monsoon periods. While most large industries are located near abundant water supply source (the rivers), The majority of small / medium scale agro residue/waste paper based mills are in clusters and have to depend on groundwater. The continuous exploitation of ground water by these industries has led to lowering of the groundwater table and thus increased pumping costs and more importantly water shortage in many regions. This has forced many industries to curtail their production levels and some closed down their mills for want of adequate amounts of water. However, in large scale mills, the situation is slightly better with regard to water conservation and environmental compliance because of better technology / equipment employed by them, large scale of operation and also access to latest information / developments. Despite this, water management is very poor in pulp and paper industry and it requires immediate attention as its excess use is affecting the water availability particularly during non-monsoon.

1 Source: Estimated by CSE based on the wastewater discharged data published by CPCB in "Water quality in India (Status and trends) 1990 - 2001".



Central Pollution Control Board (CPCB) has therefore approached National Productivity Council (NPC) to develop suitable guidelines for water management in different types of pulp and paper mills through out the country. 1.2 OBJECTIVE OF THE STUDY The objective of the study is to evolve appropriate guideline for conservation of water based on the existing water management practices and identify optimum recycle/reuse options for water. 1.3 SCOPE OF WORK For the above objective, following scope of work has been defined: (i) Inventorisation of pulp and paper manufacturing mills through out the country (ii) Classification of the mills in different categories according to scale of

operation, raw material usage, products manufactured (iii) Selection of 10 representative mills for detailed studies (iv) Preliminary survey of the selected mills, followed by detailed studies. Detail

study comprises of:

• Collection of background data regarding the raw material consumption, product output, installed and operating capacity of existing process and utilities etc.

• Study of the manufacturing process.

• Identification of the sources and characterisation of the wastewater generated from each process operation

• Compilation of material balance for complete process

• Identification of the water conservation, waste recycling/reuse options, if any adopted by the mill

• Compilation of the water balance for the complete mill and

• Generation of water recycle/ reuse and other conservation options with or without mild treatment.

(v) Cost benefit analysis for optimum reuse and recycling of waste water in terms of reduction in pollution load reaching ETP and fresh water consumption for each type of pulp and paper industry

(vi) Evolve limits for water consumption and discharge from the processes assuming the optimum water consumption level for each type of industry

(vii) Formulation of guidelines for water conservation for each type of pulp and paper industry



1.4 METHODOLOGY The following methodology is being adopted to accomplish the above said scope of work: Phase I (i) Questionnaire for seeking information on the type of product, scale of

operation, production process, water management practices followed, etc was prepared in consultation with CPCB officials and Pulp and Paper manufacturing Association’s members. A copy of questionnaire is placed as Annexure I.

(ii) The inventorisation of pulp and paper mills and other relevant information on pulp and paper mills was compiled through various agencies, research institutes, pulp and paper manufacturing associations, state pollution control boards, and associated bodies.

(iii) Questionnaires were sent to around 622 pulp and paper manufacturing mills through out the country.

(iv) Responses received from the Questionnaire survey has been compiled. Based on the responses, typical wastewater characteristics from pulp and paper mill has been generated.

(v) Literature survey was carried out with respect to production process, water consumption, wastewater generation, etc for different types of pulp and paper mills has been procured from pulp and paper manufacturing associations, printed matters and internet.

(vi) Based on the literature survey and questionnaire survey, criteria for selection of representative mills has been developed.

Phase II (vii) Based on the information obtained from Pulp and paper mill associations and

other Institutions, pulp and paper mills through out the country have been classified according to scale of operation, raw material usage and product manufactured.

(viii) Ten representative mills were identified as per the criteria developed in consultation with CPCB and based on the questionnaire responses.

(ix) Detailed studies at the individual mill were carried out as given below:

− Background data with respect to raw material consumption, product output, installed and processing capacity, existing process and utilities, etc. were collected from stores and inventory, raw material preparation section, pulp mill section, chemical recovery section, stock preparation section, paper machine section, utilities department, engineering department, projects, quality control and technical services department.

− The manufacturing process was studied in a detailed manner. Following general process related information were collected:



- Yield - Cooking temperature and time - Cycle time - Makeup chemical type and amount - Bleaching stages and time - Temperature and charge to bleaching towers - Dilution factor in washing - Black liquor solids content before and after evaporation - Black liquor quantity - Product target data

This was followed by collection of specific process related details, engineering drawings and verifying them by conducting a shop floor walk through. Simultaneously, different input and output streams were identified at each process step

− Different sources of wastewater generation was identified and marked. Sampling and monitoring of wastewater at these points was carried out. The samples were analysed for relevant parameters for characterization of inlet process water and wastewater stream.

− Material balance for the complete process was compiled. TSS balance was also carried out to ascertain the fiber loss from the process.

− Water conservation measures as adopted by the mills were identified and the total water saved per unit of the product was computed.

− Water balance for the complete mill along with the water used in the utility was made.

− Water conservation techniques/technologies were identified and techno-economic feasibility of the identified technologies/techniques were studied. The impact of implementation of these were also ascertained so as to determine the effect on the pollution load.

Phase III (x) On the basis of the studies carried out in all the ten mills, limits for water

consumption level for each type of industry was established. (xi) Subsequently, general guidelines for water conservation for each type of pulp

and paper industry were evolved.



CHAPTER 2

INDUSTRY PROFILE : PULP AND PAPER 2.1 STATUS OF PULP AND PAPER MANUFACTURING MILL IN INDIA Growth Pattern The pulp and paper mill sector in India is one of the oldest industries. The first paper manufacturing mill was commissioned in 1812 in the eastern state of West Bengal. At the time of independence (1947) there were less than 20 mills in India with a total annual capacity of 100,000 tonnes. The number of paper manufacturing mills has increased from just 17 in 1951 to around 600 in Year 2002 with an annual installed capacity of 6.2 million tonnes and has then fallen to 309 in year 2004. The reason has been non-availability of techno –economic solution for black liquor recovery/treatment for agro based pulp and paper manufacturing process. Due to regulatory pressure, several small/medium scale agro based pulp and paper manufacturing mills have been forced to closed down in recent years. The capacity utilization is estimated at around 60-65 percent of the total installed capacity. The growth of paper mills from 1950 onwards along with average installed capacity is as given in the Table 1. Table 1: Number of paper mills in India with installed capacity during 1950 to 20042 Year No of

Mills Installed Capacity (million tonnes/ annum)

Actual Production (million tonnes/ annum)

1950 – 51 17 0.137 1970 – 71 55 0.768 1980 – 81 137 1.816 1990 – 91 325 3.304 1999 – 01 600 6.2 2001 – 02 594 8.500 2003 – 04 309 7.8 5.6

In India, the average size of a pulp and paper mill is only about 25,000 tonnes per annum (tpa) when compared to 85,000 tpa in Asia and about 300,000 tpa in Europe and North America. The low capacity utilisation in the industry is due to high incidences of sickness in many small / medium mills and thus most of these are operating either at lower capacity or closed. The state wise distribution of the closed mills during 1999 to 2002 is given in Table 2 below. 2 Source: IARPMA & indiastat.com



Table 2:No of mills closed between 1999 and 20023

State-wise Number of Paper Mills Closed Down in India (01.01.1999 to 31.10.2002) State No. of Sick Paper Mills Andhra Pradesh 3 Bihar 1 Chattisgarh 1 Goa 0 Gujarat 11 Haryana 0 Kerala 2 Karnataka 2 Madhya Pradesh 2 Maharashtra 18 NCT Delhi 9 Orissa 0 Punjab 7 Rajasthan 0 Tamil Nadu 7 Uttar Pradesh 13 West Bengal 4 Total 80

Product Portfolio Indian industries produces different types / grades of paper for variety of uses. The paper and paperboard product segment constitutes of cultural paper, industrial paper and specialty paper. Cultural paper comprises of writing and printing paper, Art/Media paper, Bond paper, Copier paper, Cream wove, Maplitho, Ledger paper, etc. Industrial paper comprises of Duplex Board/Paper, Kraft Paper, Other Board/Paper. The major types of paper that are produced in the country along with main varieties and their consumption pattern (demand indicator) are presented in the Table 3 below:

Table 3: Consumption pattern of paper and paper board products in India Type of paper Main varieties % of total

consumptions Cultural paper cream woven, maplitho, bond paper, 41%

3 Source: (www.indiastat.com)



Type of paper Main varieties % of total consumptions

Chromo paper Industrial paper

kraft paper, paper board – paper board - single layer board, multilayer board, duplex board,

43%

Specialty paper Security paper, grease proof paper, electrical grades of paper

4%

Newsprint glazed, non-glazed 12% In India, the cultural varieties (writing and printing paper) account for about 41% of the production, specialty papers including coated papers for about 4% and newsprint for about 12 %. This leaves about 43% for kraft and boards. The world consumption of paper and paperboard at present has been estimated to be over 300 million tonnes a year which includes 30% of cultural papers, 14% of newsprint, and the balance of kraft / packaging paper and specialty paper. State wise Distribution of Pulp & Paper Mills The statewise distribution of pulp and paper mills (including further distribution based on raw material used) in the country from 2000 to 2004 is given in Table 4 through Table 6. Figure 1 depicts the present distribution of pulp and paper mills in India. Annexure II gives the list of industries operating in 2004

Table 4: No of pulp and paper mills as on 20004

State-wise Number of Paper Mills in India (As on June 2000)

States/Uts No. of Paper Mills

Andhra Pradesh 22 Assam 4 Bihar 9 Chandigarh 8 Gujarat 68 Haryana 15 Himachal Pradesh 15 Jammu & Kashmir 1 Kerala 7 Karnataka 17 Madhya Pradesh 21

4 Source: IARPM



State-wise Number of Paper Mills in India (As on June 2000)

States/Uts No. of Paper Mills

Maharashtra 115 Meghalaya 1 Delhi 6 Nagaland 1 Orissa 9 Pondicherry 3 Punjab 37 Rajasthan 8 Tamil Nadu 22 Uttar Pradesh 100 West Bengal 26 India 515

Table 5: No of Pulp and Paper Mills as on 20025

State Agro based Waste Paper Wood Based Grand Total Andhra Pradesh 17 20 5 42Assam 1 2 3Bihar 4 3 7Chattisgarh 2 7 9Gujrat 4 91 2 97Haryana 7 9 1 17Himachal Pradesh 1 5 1 7Jammu & Kashmir 1 1Jharkand 2 2Karnataka 2 15 3 20Kerela 10 2 12Madhya Pradesh 3 26 1 30Maharashtra 13 83 4 100Nagaland 1 1Orissa 1 2 3 6Pondicherry 1 6 7Punjab 16 59 75Rajasthan 1 9 10Tamil Nadu 2 33 2 37Uttar Pradesh 32 64 1 104Uttaranchal 8 7 1 16West Bengal 8 14 4 26Grand Total 122 466 33 622

5 Source: (www.indiastat.com)



Table 6: No of Pulp and paper mills as on 20046 State Agro Wastepaper Wood PaperMill Integrated Sub Total

Andhra Pradesh 6 6 4 16 Assam 1 1 Bihar 1 1 2 Chattisgarh 3 1 4 Gujarat 2 46 1 49 Harayana 7 4 1 1 13 Himachal Pradesh 1 1 2 J & K 2 2 Karnataka 1 8 3 12 Kerela 9 2 11 Madhya Pradesh 2 7 1 10 Maharastra 107 53 1 4 1 69 Nagaland 1 1 Orissa 4 2 6 Pondicherry 5 5 Punjab 9 11 1 21 Rajasthan 8 8 Tamil Nadu 22 2 2 26 Uttar Pradesh 17 20 1 38 Uttaranchal 4 1 1 6 West Bengal 2 5 7 Total 65 213 21 6 4 309

6 Source: (IPPTA) 7 Out of 10 Agro based mills, 9 have now shifted to waste paper based.



2.2 CLASSIFICATION OF PULP AND PAPER MILLS IN THE COUNTRY At present, around 3098 pulp and paper manufacturing mills are operating in the country. Out of these, 198 mills are operating under large scale category with actual capacity of 5.2 million tonnes per annum and 111 mills are operating under small scale category with actual capacity of 0.3 million tonnes per annum. (a) Based on Scale of operation The pulp and paper mills based on the scale of operation are classified as those having an installed capacity of 25,000 tonnes per year & above as large scale and less than 25,000 tonnes but greater than 5,000 tonnes per year as medium scale and up to 5000 tonnes per year as small scale. The distribution of large/medium and small scale pulp and paper mills in the country is given below in Table 7. Table 7: Distribution of Large/Medium and Small scale pulp and Paper Mills Sl. No

Scale of operation No of Mills Actual Capacity, million tonnes per annum

1 Large/Medium Scale 198 5.2 94.5% 2 Small Scale 111 0.3 5.5%

(b) Based on Raw material Usage The pulp and paper industry is segmented as wood/forest-based, agro-based and waste paper based with the former accounting for 21 %, agro-based 71 %, waste paper based 7% wood based and integrated for 1 % of the total actual production. The number of pulp and paper mills under each classification is given below in Table 8 Table 8: Distribution Pulp and Paper Mills Based on Raw Material Used Agro Integrated Wastepaper Wood

No of Mills 66 3 219 21

% No. of Mills 21 1.0 71 7 Production, million TPA 1.0 0.14 2.8 1.6 % Production 18.0 2.5 50.5 28

In Large/medium Scale Category. In the large/Medium scale category, 63% of the mills are wastepaper based, 25% agro based, 11% wood based and 1% integrated pulp and paper mills 8 Source: IPPTA Directory, 2004



Category No of Mills % Production, million TPA

%

Agro 49.0 24.6 0.89 16.8 Integrated 2.0 1.0 0.1 1.8 Wastepaper 126.0 63.3 2.5 47.2 Wood 21.0 11.1 1.8 34.2

In Small Scale category, In the small-scale category, 83.6 % of the mills are wastepaper based, 15.3 % agro based, and 0.1% integrated pulp and paper mills

Category No of Mills % Production, million TPA

%

Agro 17.0 15.3 0.0460 18.4 Integrated 1.0 0.1 0.0015 1.6 Wastepaper 93.0 83.6 0.2025 80

(c) Based on Products manufactured The Indian paper industry is classified broadly into two categories based on product manufactured:

• Paper and Paper board products

• Newsprint The number of pulp and paper mills producing Paper and Paper board and Newsprint along with actual production in the country is given in Table 9 below: Table 9: Distribution of Pulp and Paper Mills Based on Raw Material Used

Category No of Mills % Production, million TPA %

Cultural - high grade 66 21.3 2.27 41 Cultural - low grade 20 6.5 0.57 10.2 Industrial 187 60.5 1.74 31.4 Newsprint 21 6.8 0.62 11.2 Pulp 3 1 0.22 4 Specialty 12 3.9 0.12 2.2

In the Large/Medium Scale category, 28% are involved in manufacture of high quality cultural paper and paper board while only 7.5% are involved in low quality cultural paper, 1.51 % only pulp, 3% only specialty paper and rest industrial and newsprint grade paper as shown below:



Category No of Mills % Production, million TPA % Cultural - high grade 56 28.28 2.24 42 Cultural - low grade 15 7.57 0.55 10.4 Industrial 97 48.98 1.55 29 Newsprint 21 10.60 0.62 11.5 Pulp 3 1.51 0.22 4.1 Specialty 6 3.03 0.11 2 In Small Scale Category, maximum mills (about 81%) are involved in the production of industrial grade paper followed by 9% high grade cultural paper manufacturing, 4.5% are involved in low grade cultural paper manufacture, 9% are involved in high quality Cultural grade paper, 5.45% specialty and rest industrial grade as shown below:

Category No of Mills % Production, TPA % Cultural - high grade 10 9.0 32879 13.1 Cultural - low grade 5 4.5 16734 6.7 Industrial 90 81.1 194970 78.0 Specialty 6 5.4 5415 2.2

(i) Paper and Paper board products The major producers of paper in the country along with their installed capacities are given in Table 10. Table 10: Major players in paper board product segment Major players Capacity in

tpa (FY2002) Product mix

AP Paper Mills 98,500 creamwove, maplitho, kraft Ballarpur Industries 2,47,500 maplitho,creamwove, bond,others Hindustan Paper Corp. 2,00,000 creamwove ITC Bhadrachalam 1,82,500 duplex board, maplitho, kraft, security

paper, MG poster Orient Paper & Industries 1,61,000 creamwove, kraft, maplitho, duplex

board Sinar Mas 1,10,000 coated writing & printing paper The West Coast Paper Mills

1,19,750 creamwove, maplitho, kraft, MG poster



(ii) Newsprint In the News print segment around 21 mills in Large scale category (4 in central public sector, 2 in state public sector and 15 in private sector) with an installed capacity of about 0.658 million TPA are operating. The major mills in the newspaper/newsprint segment with their production capacities are given in Table 11. Table 11: Major mills in Newsprint segment

Company Capacity Million tpa Hindustan Newsprint 0.1 NEPA 0.08 TNPL 0.18 Rama Newsprint 0.15

(d) Based on Pulping Process Generally speaking, the pulp and paper industry divides itself along pulping process lines: chemical pulping (e.g., kraft chemical pulping), mechanical pulping, and semi-chemical pulping. The pulping process affects the strength, appearance, and intended use characteristics of the resultant paper product. Pulping processes are the major source of environmental impacts in the pulp and paper industry; each pulping process has its own set of process inputs, outputs, and resultant environmental impacts. The different types of products resulting from various pulping processes are listed as below:

• Bleached Paper grade Kraft and Soda / Unbleached Kraft: Bleached or unbleached kraft process wood pulp usually converted into paperboard, coarse papers, tissue papers, and fine papers such as business, writing and printing.

• Paper grade Sulfite: Sulfite process wood pulp with or without bleaching used for products such as tissue papers, fine papers, and newsprint.

• Semi-chemical: Pulp is produced by chemical, pressure, and mechanical (sometimes) forces with or without bleaching used for corrugating medium (for cardboard), paper, and paperboard.

• Mechanical pulp: Pulp manufacture by stone groundwood, mechanical refiner, thermo-mechanical, chemi - mechanical, or chemi-thermo - mechanical means for newsprint, coarse papers, tissue, molded fiber products, and fine papers.

• Non-wood Chemical pulp: Production of pulp from textiles (e.g., rags), cotton linters, flax, hemp, tobacco, and abaca to make cigarette wrap papers and other specialty paper products.

• Secondary Fiber Deink: Pulps from waste papers or paperboard using a chemical or solvent process to remove contaminants such as inks, coatings and pigments used to produce fine, tissue, and newsprint papers.



• Secondary Fiber Non-deink: Pulp production from wastepapers or paperboard without deinking processes to produce tissue, paperboard, molded products and construction papers.

• Fine and Lightweight Papers from Purchased Pulp: Paper production from purchased market pulp or secondary fibers to make clay coated printing, uncoated free sheet, cotton fiber writing, and lightweight electrical papers.

The distribution of pulp and paper mills in the country based on pulping processes is given in Table 12 and Table 13 based on number of mills and installed capacity. Table 12: Distribution of pulp and paper mills based on pulping processes ( number of mills)

No of Mills Sl. No Pulping Process Large Scale Small Scale Grand Total

1 Chemical Soda Process 29 26 54 2 Hydro Pulping 92 113 219 3 Kraft/Sulphite process 34 2 36

Table 13: Distribution of pulp and paper mills based on pulping processes (installed capacity)

Sl. No.

Installed Capacity, million tonnes/yr

Pulping process Large Scale % Small Scale % 1 Chemical Soda Process 0.666 4.3 0.106 18.3 2 Hydro Pulping 12.807 81.9 0.462 79.9 3 Kraft / Sulphite process 2.169 13.9 0.01 1.7

Grand Total 15.642 0.578



CHAPTER 3

MANUFACTURING PROCESSESS This section describes the major industrial processes within the pulp and paper industry, including the materials and equipment used, and the processes employed. This section specifically describes the details of commonly used production processes, associated raw materials, the products produced, and the materials recycled. This discussion, coupled with schematic drawings of the identified processes, provide a concise description of where wastes may be produced in the process.

3.1 Generalised Paper/Paper board making process In general, paper is manufactured by applying a liquid suspension of cellulose fibers to a screen, which allows the water to drain, and leaves the fibrous particles behind in a sheet. The liquid fibrous substrate formed into paper sheets is called pulp. Processes in the manufacture of paper and paperboard can, in general terms, be split into three steps: pulp making, pulp processing, and paper/paperboard production. Paperboard sheets are thicker than paper sheets; paperboard is normally thicker than 0.3 mm. Generally speaking, however, paper and paperboard production processes are identical. First, a stock pulp mixture is produced by digesting a material into its fibrous constituents via chemical, mechanical, or a combination of both. In the case of wood, the most common pulping material, chemical pulping actions release cellulose fibers by selectively destroying the chemical bonds in the glue-like substance (lignin) that binds the fibers together. After the fibers are separated and impurities have been removed, the pulp may be bleached to improve brightness and processed to a form suitable for paper-making equipment. Currently, one-fifth of all pulp and paper mills practice bleaching. At the paper-making stage, the pulp can be combined with dyes, strength building resins, or texture adding filler materials, depending on its intended end product. Afterwards, the mixture is dewatered, leaving the fibrous constituents and pulp additives on a wire or wire-mesh conveyor. Additional additives may be applied after the sheet-making step. The fibers bond together as they are carried through a series of presses and heated rollers. The final paper product is usually spooled on large rolls for storage. A typical process for the manufacture of paper is shown in Figure 2.



Figure 2: A typical process for Paper manufacture Raw material Wastewater Water Chemicals Water Water Wastewater Alum, Rosin Water Additives Wastewater

3.2 Different industrial processes in pulp and paper sector Based on the type of raw material used, the manufacturing processes are classified into

− Wood Based Pulp and Paper manufacturing Process

− Agro residue based Pulp and Paper manufacturing Process

− Secondary fibre based Pulp and Paper manufacturing Process Figure 3 shows the schematic diagram of different manufacturing processes of pulp and paper making from raw material sources.

Raw material Preparation section

Pulping Section

Pulp Washing & Bleaching Section

Stock Preparation system

Paper Machine

Finished Paper



Chipping

Figure 3: Generalisedl Process of Paper making from different types of raw material

Timber

Agro residue

Wastepaper

Mechanical Pulping

Chemical Pulping

De- Inking

Chemical Additives

Product

Hydro- Pulping

Washing & Bleaching

Paper making



3.2.1 Wood Based Pulp and paper manufacturing Process Pulp Production: Various Methods of Pulping

Wood consists of two primary components: cellulose and lignin. Cellulose, which is the fibrous component of wood, is used to make pulp and paper. Lignin is the “glue” that holds wood fibers together. Pulping is the process, which reduces wood to a fibrous mat by separating the cellulose from the lignin. Pulping processes are generally classified as chemical, mechanical, or semi-chemical.

Mechanical Pulp (yield 90%): Mechanical pulp uses mechanical abrasion to separate cellulose fibres which are held together by lignin. In the process called “Groundwood”, wet wood is ground by large stones. In Thermo mechanical pulping (TMP), metallic plates rub steam heated chips at high speeds, separating fibers. Mechanically produced pulp has a higher proportion of broken cell fragments (called 'fines') among the fibres. Thus, when used to make paper, the long fibres form the matrix of the sheet within which the fines are trapped. Paper derived from mechanical pulps, therefore, tend to be denser and is often a component of newsprint and other printing papers. However, because mechanical pulps are not chemically processed they still contain lignin and other natural wood substances, and paper with a high component of mechanical pulp tends to yellow quickly in sunlight. Mechanical pulping processes all use a lot of electrical energy and water. However, they also provide 80-90% recovery of total fibre. Mechanical pulp processes are cheaper to operate than more sophisticated chemical based systems. There are also fewer environmental issues, such as chemical contamination of sites and unpleasant smells.

Chemical Pulp (yield 50%): Chemical pulping achieves fiber separation by dissolving the lignin that cement the fibers together. In chemical pulping, fibres are less likely to be damaged than in other pulping processes. Chemical pulp is more expensive then mechanical pulp, but it has better strength and brightness properties. There are three chemical pulping methods known as Soda, Kraft (or Sulfate), and Sulfite. The choice of the chemical pulping method depends upon the type of raw material available and the product end use.

1. Soda Pulping

Soda pulp is the original chemical pulp and is produced by cooking chips of (usually) deciduous woods in a solution of caustic soda under pressure. This leaves a relatively pure cellulose pulp which is then washed and bleached. Soda pulp produces relatively soft, bulky papers (as a filler with other pulps) used in books, magazines and envelopes. Caustic soda dissolves most of the lignin in wood while having little effect on the cellulose. Cooking liquor is recovered during the washing process. Currently this process is primarily used for agro residue based material pulping.



2. Kraft / Sulfate Pulping

In a chemical pulping process, heat and chemicals are added to wood chips in a pressure cooker called the digester. In the kraft process, an aqueous solution of sodium hydroxide and sodium sulfide, known as white liquor, selectively dissolve the lignin and make it soluble in the cooking liquid. After 2 to 4 hours, the mixture of pulp, spent pulping chemicals and wood waste is discharged from the digester. The pulp is washed to separate it from the black liquor - the pulping chemicals and wood waste. Kraft pulping is a low yield process - only 45% of the wood used becomes pulp. The pulp, called brownstock at this point in the process, is ready to be bleached. Softwood pulp from a conventional cooking process contains about 4.5% lignin. This lignin will be removed and the pulp will be brightened during the bleaching process. In response to concerns about the amount of organic waste in the effluent, as conventional pulping processes remove only about 95% of the lignin from the pulp, there are few mills that have started extended / oxygen de-lignification for further lignin removal. Today, a well run oxygen de-lignification system can remove 55% of the lignin from the unbleached pulp. Figure 4 shows the oxygen delignification tower installed in one of pulp and paper mill in India.

The kraft process is applicable to almost any wood and produces a pulp with strong fibres, but which also takes more bleaching that other chemical pulps. It is suitable for even quite resinous pine species. Kraft pulp is used where strength, wear and

Fig 4: Oxygen De-lignification Tower



tear resistance and colour are less important. the most obvious examples are brown paper bags, cement sacks and similar sorts of wrapping paper.

3. Sulfite Pulping

Sulfite pulping uses sulfurous acid and an alkali to produce pulps of lower physical strength and bulk, but exhibits better sheet formation properties. The yield on the basis of chipped wood is again about 45 percent. These pulps are blended with ground wood for newsprint and are used in printing, bond papers, and tissue. Sulfite pulping was originally designed with a recovery system similar to the older soda process still used in some plants. Environmental pressures have often forced these plants to develop a recovery process. The pulp produced is made up of longer, stronger and more pliable fibres and is favoured where strength properties are particularly important.

Chemical pulping requires significant quantities of energy, mostly for process heat but uses less electrical energy than mechanical processes. However, many modern kraft pulp mills are totally self-sufficient in energy, with combustion of residues and waste products meeting all heat and electrical energy needs.

Semi-Chemical Pulps Semi-chemical pulps are essentially mechanical pulps that have been pre-treated with a sulphite or sodium hydroxide liquor to improve breakdown and reduce energy requirements during processing. Pulps tend to retain some of the properties of mechanical pulp, including good yields of fibre, but are also suitable for better classes of paper manufacture.

Pulp & Paper Manufacturing Process In general, pulping process is described in following 3-steps: Step 1: Pulping

Raw Material Preparation The wood logs are fed to a log chain conveyor and from log chain conveyor, the wood is fed to the chipper by means of a belt conveyor (Figure 5). The wood after chipping goes to a cyclone. The chips from the cyclone are fed on the vibrating screen where oversize chips are removed and the accepted chips go to the silo via a conveyor belt. The oversized chips are fed back to the crusher.

Digester House The chips from the silo are fed in the Digester through a belt conveyor. There are two types of digestion processes employed; Batch digestion carried out in spherical digestors and Continuous digestion process carried out in a pandia type digester. A shuttle conveyor helps in filling up the digester. The chips in a vertical digester provided with liquor circulation pumps and pre heaters. In this process, wood is cooked in a “digester” at elevated pressure (upto 11 bar) with a solution of the appropriate chemicals, which dissolve the lignin and leave behind the cellulose. The



cooking process results in emissions of a variety of hazardous air pollutants including formaldehyde, methanol, acetaldehyde, and methyl ethyl ketone. The cooked material is blown into a blow tank provided with blow heat recovery system. The blown material from the blow tank is taken into the unbleached knotters where the uncooked chips are removed.

Step 2: Pulp Washing After the wood is pulped, the pulp that is created is washed to remove the dissolved lignin and chemicals. In the washing process, the pulp is passed through a series of washers and screens. The washing process occurs at high temperatures (above room temperature), which generates a large volume of exhaust gases containing hazardous air pollutants which are released to the atmosphere. The liquid that results from the washing process contains lignin as well as the chemicals used to separate the lignin from the cellulose. The chemical recovery processes are used to recover these chemicals. Step 3: Pulp Bleaching After washing, if a white product is desired, the pulp must be bleached to remove color associated with remaining residual lignin. The three general approaches to bleaching are: Elemental Chlorine Bleaching is the process currently in place at some existing bleaching plants, and uses chlorine (Cl2) and twice hypochlorite to brighten the pulp. In addition, Sodium hydroxide with or without peroxide is used for extraction of chlorine from the pulp. When elemental chlorine and hypochlorite react with the lignin, they form chlorinated pollutants such as chloroform, dioxins, and furans in the wastewater stream. Elemental Chlorine Free Bleaching (ECF) replaces chlorine with chlorine dioxide as a bleaching agent and hypochlorite in no longer used. The use of ECF bleaching results in reduced levels of chlorinated pollutants in the wastewater stream. Figure 6 shows a ClO2 plant installed in one of Indian pulp and paper mill.

Fig 5: Chipper Section



Totally Chlorine Free (TCF) bleaching uses no chlorinated bleaching agents to bleach the pulp. Instead, bleaching agents such as oxygen and peroxide are used. TCF bleaching eliminates chlorinated pollutants in the wastewater stream. Typically, in the bleaching process, the bleaching chemicals are injected into the pulp, and the resulting mixture is washed with water. This process occurs several times and generates a large volume of liquid waste. Additionally, vents from the bleaching sections emit hazardous air pollutants including chloroform, methanol, formaldehyde, and methyl ethyl ketone9. Figure 7 shows bleached and unbleached pulp.

9 Source: EPA Fact sheet – The Pulp and paper Industry, The Pulping Process and Pollutant Releases to the Environment, November 1997

Fig 6:ClO2 Plant



Depending on the bleaching chemicals used, the waste stream from the bleaching process may contain chlorine compounds and organics. The mixture of chemicals may result in the formation of a number of toxic chemicals (such as dioxins, furans, and chlorinated organics). Different types of equipment/technologies used for bleaching are listed below: 1. Batch process: Potcher washing is the oldest technology (shown in Figure 8)

used in batch washing. Potcher consists of a series of beaters or engines used in washing and preparing pulp. This process consumes huge quantity of water.

2. Continuous countercurrent processes: Different continuous processes are

highlighted below: a. Hydraulic drum washing: A hydraulic drum washer does not require Barometric leg and works on hydraulic principle therefore has minimum operating costs. A sketch of hydraulic drum is shown in Figure 9 below:

Fig 7: Bleached and unbleached pulp

Fig 8: Potcher washer



Figure 9: Hydraulic Washer

b. Vacuum Drum washing: In vacuum drum washing, each stage consists of a rotating screen drum which has a partial vacuum applied to interior. The drum sits in a tank where pulp is diluted with wash water. The vacuum draws a pulp mat against the surface and wash water through the mat. The drum rotation advances the washed pulp mat to the next dilution tank. Wash water discharged from this wash stage is sent to the previous washing stage. c. Pressure washing: Pressure washing is similar to vacuum drum, but differs by spraying water under pressure through the pulp mat as the drum rotates. d. Diffusion washing: Diffusion washing is a counter flow process that takes place in one or more stages. Pulp flow is upward and is carried on a perforated plate. Water flows downward through a series of baffles.

Rubber roll of 500 mm diaDoctor's Knife

Washed Pulp consistency = 10%

Unwashed Pulp

Perforation of 25 mm40# wire over the drum

200 mm



e. Chemi or Belt washing: A Chemi or belt washer10 is perhaps the simplest washing system in terms of design. It offers excellent washing with reduced water usage. Belt washing is a counter flow process where pulp enters the washer area on a wire belt. Washing takes place under a series of showers. Clean water enters on the opposite end from the pulp and is sprayed vertically through the pulp. The used wash water is then collected and reapplied to the dirtier pulp by the next washing head. Countercurrent to the direction that the pulp moves. This process is continued through at least seven stages until the wash water is saturated with liquor after washing immediately coming pulp. The wash water is then sent to the recovery process. Diffusion washing and belt washing can reduce the amount of water used per tonne of pulp in brownstock washing by 50% or more according to published data. f. Twin roll press washer Twin wire roll press washer works on the general principle of dewatering, displacement and pressing. It consists of a twin-wire dewatering unit which allows controlled washing of the pulp. The two-sided dewatering and strong turbulence of the washer facilitate two to three times higher capacities per unit of width than conventional washer technologies. An additional main feature of this technology is that the ash and fines removal can be controlled depending on the targeted levels. This technology can be used for high consistency pulp washing and resulting in reduced water consumption. Figure 10 shows a twin wire roll press washer installed in one of pulp and paper mill in India.

10 Source: U.S. EPA, 1993b. Pollution Prevention Technologies for the Bleached Kraft Segment of the U.S. Pulp and Paper Industry

Fig 10: Twin wire press roll washer



3.2.2 Agro Based Pulp and paper manufacturing Process The process of pulp and paper making from agro-based residues is described below: The various production stages are as given below:

(i) Raw material preparation: Dedusting, depithing, leaf removal (ii) Pulping section: Cooking, beating, pulp washing, refining, bleaching,

cleaning and, thickening (iii) Stock preparation: Blending, pulp conditioning (iv) Paper machine: Refining, Centricleaning, dewatering, drying of paper

Raw material preparation The agro residue based raw material (RM) is procured by the mills from nearby farms. In some mills raw material is screened at the site itself. The dust from the screening section is disposed of as solid waste along with municipal waste. In very small mills, bagasse is not depithed. The prepared agro raw material is then conveyed to spherical digesters. Figure 11 through 13 below shows a raw material preparation sections of agro residue based pulp and paper mill.

Fig 11: Raw material Preparation section



Pulping Section Pulping comprises of cooking or digestion followed by washing, bleaching and centricleaning. Cooking

Fig 12: Wheat straw washing section

Fig 13: Wheat straw washing section



There are two types of digestion processes employed similar to wood pulping; Batch digestion carried out in spherical digesters and Continuous digestion process carried out in a pandia type digester. Figure 14 and 15 shows batch and continuous digesters Also unlike wood pulping two different chemical pulping processes are employed, namely, Kraft process and soda process. The agro residue is chemically digested in a digester at 150 – 160oC and 6 – 7 atm pressure for about six hours. Charging and discharging takes 1.5 hours and 0.5 hours respectively. The cooking in small agro-based mills is done with caustic soda (NaOH) and steam. The quantity of NaOH charged, varies from 6 to 14 percent of raw material, depending on the type of agro residue. For every tonne of agro residue, about 1.5 – 2.0 tonnes of steam is used, depending on the pulp required (hard cooked or soft cooked). During digestion, solid to liquid (bath ratio) in the range of 1:3 to 1:4 is maintained.

Fig 14: Spherical (Batch) Digester



Blow tank After cooking, the content of the digester is discharged, under pressure, either into a blow tank where the pressure is released or directly into potchers. Water is added to reduce the pulp consistency from an inlet value of 12 – 14 percent to about 3 – 4 percent, so that it can be pumped to the washing and cleaning section. Washing The pulp is then pumped to the washers for washing with fresh water in the final stage and backwater in the previous stages. The washing operation takes about four to six hours. The wash water called black liquor, which has total solids content of around 7-10% due to residual alkali and lignin. This liquor is mostly discharged to drains as chemical recovery has so far been economically unviable. Screening The washed pulp contains sand and uncooked agro residue as impurities. The impurities are removed through screening and centricleaning. The rejects from the screening (Johnson and / or Hill screen) are normally drained out. After screening, which is carried out at 1% consistency, the pulp is thickened to about 4% for next operation, namely bleaching. The filtrate, called back water, generated during thickening operation, is generally collected and used for pulp washing (previous operation). The pulp for making unbleached kraft paper (for packaging purpose) is not bleached and is taken directly for stock preparation.

Fig 15: Pandia digestor (Continuous digester)



Bleaching The bleaching in small mills is carried out using calcium hypochlorite (hypo), which is added in two stages in order to provide sufficient retention time for hypo and to minimize the fibre degradation. Fifty percent of the hypo is added in the screened pulp storage chest and the rest is added in the bleacher. A retention time of about two hours is provided in the storage chest. After bleaching, the pulp is washed, partly with fresh water and partly with white water (paper machine back water). The wash water from bleaching operation contains chloro-lignates and residual chlorine preventing the wash water from direct reuse. A typical vacuum drum bleach washer is shown in Figure 16 Stock Preparation The bleached pulp is mixed with the long fibre pulp, comprising mainly rags and wastepaper pulp. The mix depends upon the agro residue being processed and the type of paper to be manufactured. The mix pulp is blended with additives and fillers in the blending chest. The chemicals added to the blending chest are rosin, alum, talc, dye (optional), optical whitener and high gum. The chemicals (additives, fillers etc) solutions are prepared and added manually in every batch.

Fig 16: Conventional vacuum drum washer after bleaching



Paper machine The blended pulp is again centricleaned to remove impurities and finally fed to the paper machine through a head box. From the dewatering and paper making angle, the machine has three principal stages:

• The gravitational and vacuum dewatering stage (wire part)

• The mechanical dewatering stage (press rolls part)

• The thermal drying stage (indirect steam dryers) On the wire part of the paper machine, the dewatering of pulp takes place by gravity and vacuum. The water from the wire mesh is collected in a fan pump pit and is continuously recycled to dilute the pulp fed into the paper machine centricleaner. In some mills, the wire is continuously washed with fresh water showers. The water is collected and fibre is recoverd through Krofta saveall. The clear water from saveall is recycled back to different consumption points. Excess is discharged to drain. After the wire part, the edge cutting operation is carried out to obtain paper of a definite width. The edge cuts of the pulp web falls in the couch pit and are recycled to the machine chest. Towards the end of the wire part of the machine, the consistency of pulp rises to about 20 per cent. Further dewatering is carried out by press rolls to raise the consistency to about 55%. The paper is finally dried through an indirect steam dryer to about 94% solids and is collected in rolls as the final product. Figure 17 shows a typical paper machine section.

Fig 17: Paper machine section



3.2.3 Waste paper pulping Secondary fibre recycling or wastepaper pulping is another important sector. Figure 18a and b shows wastepaper storage yards.

Fig 18 b: Wastepaper Storage Yard

Fig 18 a: Wastepaper Storage Yard



The repulping of recycled paper and deinking is described below.

Recycled paper, newsprint and magazine is charged in Hydraulic pulper (Figure 19 ) with adding water and it is being processed till waste paper is converted into slurry form with high consistency pulp. The hydro pulped pulp is cleaned in High density cleaner followed by turbo separator for heavy weight and light weight impurities respectively. Then it is continuously forwarded to centricleaner after passing through screen. At centricleaner, the sand is separated due to centrifugal force. The pulp is then taken to Decker thickener where the wastewater is removed and pulp is thickened. The thickened pulp is processed to a chest through refiner by which the pulp is thickened. The thickened pulp is processed to a chest through refiner by which the pulp becomes finer as per process requirement. Then it is transferred to machine chest where addition of dye, chemical takes place. This pulp then is fed to the machine chest (Flow sheet is shown in Figure 20).

Fig 19: Hydropulper used for pulping wastepaper/recycled material



Fig 20: A typical process in pulp manufacture from wastepaper/recycled material

Waste paper

Cloudy Filtrate Helico Pulper

Paper m/c back water Dumping Poir Reject

Constant Level Chest

H D Cleaner

Horizontal Screen

Reject Diabole Screen To Reject handling system

SR Box

Clear Filtrate Clear Filtrate

Pr. Centricleaner

Reject Sec. Centricleaner

Reject Tert. Centricle aner

Reject

Accept Accept

Clear Filtrate Algus Thickener

SR Box

Dewaterer Clear & Cloudy Filtrate Tank

Screw Press

Plug Screw

Shredder

Pre Heater Mixer

In Feeder Screw conveyor

Disperser

Storage



Deinking process: Deinking is a recycling technique that can produce high quality recycled pulp from recovered papers. Ink detachment is an important step. Flotation method is commonly used for this purpose. Flotation Deinking which makes ink particles hydrophobic by means of a collector in a flotation cell. The air bubbles generated at the bottom of the cell carry the ink particles to the surface where they are confined in foam which is removed. Paper Making Papermaking is common to all types of categories. 3.3 CHEMICAL RECOVERY FROM BLACK LIQUOR Another very important process in line with the chemical pulping mills is the recovery of the pulping chemicals from the concentrated black liquor generated from the pulp washing process. The entire chemical recovery process from spent cooking liquor of Kraft and Soda process is described separately in the following section. The recovery of chemicals in the spent cooking liquor in general is described below. The weak black liquor from brown stock washers goes through the following steps: a. Concentration in multiple – effect evaporators b. Incineration in recovery furnaces/boiler with addition of salt cake to make up

loss c. Dissolving smelt from furnace in water to form green liquor. d. Causticising of green liquor with lime to form white liquor which, after settling

and filtering is ready for next cooking cycle. e. Burning of lime mud to recover lime. Figure 21 shows a flow diagram of the process.

Pulping AreaBlack Liquor

White LiquorRecausticising Green LiquorEvaporator, Recovery Boiler

Lime (CaO) Lime Mud (CaCO3) to Cement

Fig 21 : Schematic diagram of chemical recovery flow process



3.3.1 Chemical Recovery: Kraft Process Conventional Chemical recovery Process comprises of mainly soda recovery, Causticising and lime kiln plant. Weak Black liquor generated from the brown-stock washing is concentrated to 70% solids in multiple effect evaporator and is mixed with flue gas residue from Soda recovery boiler. The thick concentrated black liquor is then preheated in super heater and is injected via high-pressure spray guns into the soda recovery boiler. Hot air is injected into the boiler. Combustion process is initiated by fuel oil. Once, required temperature is attained, fuel oil supply is cut off. The heat generated by the combustion reaction of black Liquor is used for generation of steam. Flue gases from the boiler passes through superheater, economizer and ESP and is then let off to atmosphere. Molten Sodium carbonate is tapped from the bottom section of the boiler (Figure 22 & 23). The molten sodium carbonate is send to the Recausticising Plant for production of white Liquor. Molten sodium carbonate is dissolved in weak white liquor generated by washing of lime mud. The resultant green liquor is clarified and is mixed with lime in a slaker. The slurry is clarified through slaker clarifier, from where clear white liquor overflows and the underflow, lime mud is washed in four-stage counter current washer with Process condensate (vapour condensate from multi effect evaporator). Weak white liquor is generated from the first stage washer as depicted in Figure 24.

Fig 22: Conventional Chemical



Weak Black Liquor, 18% solidssteam condensate To Boiler

LP Steam 150 o C, 20 T/h Falling film

Evaporator (7 effects) Process condensate

Foul condensate To causticisation Plant

LP Steam High

Concentrated Black Liquor

storage

70% solids

To ETP

steam condensate To Boiler

SRB Flue gas residue Ash TankSalt slurry (ClO2 Plant)

LP Steam through 73% Solids

Ambient airguns

Pr Air Heater Soda Recovery Boiler (SRB)

Flue gas Super Heater

Economiser

Sec Air molten smelt AshTo atmosphere ESP

Fresh water Spout Cooling System Wastewater to ETP

Weak White LiquorDissolver

Green Liquor60% carbonate, 20% Na2S, 20% NaOH

Fig 23: Soda Recovery Process



Green Liquor from SRBProcess Condensate from SRB

Clarifier

Underflow

Dreg Washer

To

Lagoon

Filtrate

Constant Overhead tank

(Weak White Liquor)

Process Condensate

Lime from Lime Kiln Slaker Impurities Landfill

Slurry Wastewater to ETP

Causticiser 8 Nos in series

overflow

White Liquor

Clear White liquor

Clarifier

Underflow

(Mud)

Fig 24 : Re –Causticisation process



Lime mud sludge generated from the recausticising plant is either utilized in cement industries or sent to landfill facility or to lime kilns. In lime sludge burning process ( lime kilns), lime i.e CaO is regenerated from CaCO3. Figure 25 shows one such lime sludge burning plant installed within a pulp and paper mill.

Fig 25: Lime sludge burning plant



3.3.2 Chemical Recovery: Soda Process Process description of non-conventional chemical recovery Black Liquors from agro residue based mills pose problem in chemical recovery process in conventional system due to following reasons:

• High viscosity of the liquor resulting in low heat transfer

• Low concentration of black liquor (7 – 10%) compared to wood based (14 – 17%)

• Higher silica content causing fouling and sealing at evaporators

• Low combustibility In order to overcome the above-mentioned limitations, conventional recovery process has been modified and instead of chemical recovery boiler, Fluidised bed reactor is used. Also, the non-conventional recovery process does not generate Power. A typical non-conventional chemical recovery plant installed and being operated successfully in one of the Agro residue based pulp and paper mill in India is shown in Figure 26. The process of chemical recovery from a non-conventional process is briefly described below; The black liquor generated from brown stock washing operation, also called weak black liquor (WBL) contains 8% solids and has a residual alkali of 4.5 gpl. This weak black liquor is concentrated to 25% solids in a multiple effect evaporator called semi concentrated black liquor (SBL). The semi concentrated black liquor is then burnt in a fluidized bed reactor at a temperature of 650oC to produce soda ash. In order to maintain a temperature of 650oC, fresh water is injected through three cooling guns at top chamber of the fluidized bed reactor. The flue gases containing considerable amount of heat is used for preheating the strong black liquor. The product is cooled by passing it through a double sludge water-jacketed product cooler and passing part of fluidizing air through it. The flow sheet for chemical recovery process is depicted in Figure 27. Figure 28 & 29 shows the schematic of a fluidising process and Fluidised Bed reactor respectively.



Fig 26: Non conventional chemical recovery plant for Agro

Weak Black Liquor 8% solids

Steam

Multiple Effect Evaporator

Combined (Process) C d t

Steam condensate To Boiler

Semi Concentrated Black Liquor 25% solids

Exhaust gases to atmosphere

Economiser45% solids

Fresh water (cooling)Fluidised Bed reactor Hot flue gases

thro guns Sodium carbonate pellets

Fig 27: Process flow sheet for Non Chemical Recovery process



]

Source: “An Experience in Running a fluid bed recovery system for agriculture residues black liquor at M/s Shreyans Industries Limited, Sangrur”, IPPTA Vol 9, No-3, Sept. 1997

Fig 28: Schematic of Fluidised bed process



Fig 29: Schematic of Fluidised Bed reactor

Source: “An Experience in Running a fluid bed recovery system for agriculture residues black liquor at M/s Shreyans Industries Limited, Sangrur”, IPPTA Vol 9, No-3, Sept. 1997



3.4 ENVIRONMENT IMPACT / CONCERNS OF PULP AND PAPER

MANUFACTURING PROCESS The major environmental concerns from a pulp and paper manufacturing process are contaminated effluents and malodorous gases. Pulping often releases a range of pollutants, including organic products which cause eutrophication in water, aluminum salts and sometimes also generation of sulphur dioxide. Both of the two main pulping methods - mechanical and chemical pulping - can cause pollution. Most papers require bleaching. When bleaching is carried out with chlorine or hypochlorite, it may generate dioxin. These pollutants have direct impacts on freshwater and marine ecosystems near pulp mills. Pollutants can also have direct effects on human health, through impacts on pulp workers, as a result of people eating contaminated fish, and through air pollution. The various contaminants/components that cause environment concerns in pulp and papermaking are enumerated below:

• Liquid effluents The different sources of liquid effluent from a pulp and paper industry are as given below:

Section / Equipment Typical Sources Raw material preparation Wet depithing of bagasse Wet debarking Wet cleaning of straw and grasses Chip wash water Pulping Blow condensate Leaks and spills of black liquor Gland cooling water from refiners,

pumps, etc. Unbleached pulp wash (Black Liquor) Centricleaner rejects containing high

concentration of fiber, grit or sand Filtrate from pulp thickening Bleaching Bleach wash water containing chloro-

lignin in case of chlorine or hypochlorite bleaching

Stock Preparation and paper machine Leaks and spills of chemicals and additives

Floor wash Spills of pulp Centricleaner rejects containing fibers,

grit or sand White water overflow



Wire section and press section felt wash water

Utilities Boiler blow down Softener regeneration discharges Chemical recovery Evaporator condensate Weak liquor from dregs washer Weak liquor from mud washer Gland cooling and mud washer Foul condensates

‘The major concerns from these effluent are:

o pulping liquors containing VOCs ( terpenees, alcohols, phenols, methanol, acetone)

o bleaching effluents chlorinated hydrocarbons like dioxins and furans chloroform other chlorinated compounds

o nonyl phenol ethoxylates (NPE) used as nonionic surfactants in some papermaking processes break down to nonylphenol, (NP), a suspected endocrine

disrupter o discharge color

• Air emissions Air pollution mainly occurs from digesters blow tanks, steam boilers, chemical recovery boilers and limekiln. The major concerns from these emissions are as given below:

o hazardous air pollutants (HAPs) and other toxic substances, including: reduced sulfur compounds (hydrogen sulfide, mercaptans, and

alkyl disulfides) VOCs (acetaldehyde, methanol, propionaldehyde, methyl ethyl

ketone, phenols, terpenes, etc.) o odor (including sulfides generated during chemical recovery of kraft

process "black liquors") o acid gases (sulfuric, hydrochloric, hydrofluoric) o emissions from boilers and lime kilns (including particulates, and sulfur

and nitrogen oxides) • Solid waste Solid waste is generated in the form of sludge, ash, wood waste, screening, centricleaner rejects, sand and grit. The main source of solid waste is wastewater sludge from primary and secondary clarifier. Ash from boilers is also significant.



The other major waste that is generated in good quantity is lime sludge from recausticisation process of chemical recovery plant. The major concerns with these wastes is their disposal.



CHAPTER 4

WATER CONSUMPTION PATTERN IN OTHER COUNTRIES

In developed countries, most of the pulp and paper manufacturing mills are wood based, however, due to environmental implications, trend is changing towards use of recycled fibre. This has been possible due to more efficient collection activity and development in process technologies. However, all the pulp, paper and board products cannot be produced from recovered fibres due to technical, environmental or health requirements. The average water consumption for wood based large pulp and paper industries primarily producing paper & paper board products from 6 regions / countries namely United States, Australia, Europe, Canada Finland & Spain has been compiled from various documents available on the web and the same is presented in the Table 14 below: Table 14: Region / Country specific Average Water Consumption in large scale

wood based Pulp and Paper mills Sl.No.

Region / Country

Average Specific water consumption

(m3/ tonne of product)

Source

1 U.S. 64 (Average value in the

year 2000)

Appendix “W” of Report on Status of Pulp & Paper in US by Michiel P. H. Brongers and Aaron J. Mierzwa

2. Australia 28.66 (Average value for the

year 2003)


3. Europe 40


4. Canada 67


5. Finland 40 Pulp Fact - Environmental Implications of the Paper Cycle” by Nigel Dudley, Sue Stolton and Jean-Paul Jeanrenaud WWF International 1996

6. Spain 30 Pup Fact – Environmental Implications of the paper Cylcle by Nigel Dudley, Sue Stolton and Jean Paul, Jean Renaud – WWF International 1996



Water consumption in these countries have been found to be much lower then in developing countries like, India, Pakistan, China, etc. The best performances in few industries employing close cycle have even touched the specific water consumption of around 20 m3/tonne of paper. Realizing the huge costs of, energy, water, chemicals and environment from virgin paper production, the recent trends have been to shift to paper recycling i.e. producing paper from waste paper. Beyond saving trees, making new paper from old takes a fraction of the energy and chemicals used in virgin paper production and thus expanding the recycling of used paper has enormous potential to bring environmental and economic benefits. The specific water consumption in various European and Scandinavian countries varies from 8 to 10 m3 / tonne of paper. A few industries in Netherlands in fact claim of only 4.4 m3 of water consumption per tonne of paper production from waste paper. A brief scenario of pulp and paper industries in few of the developed countries is given below: UNITED STATES OF AMERICA11: US, is one of the largest producers of pulp and paper (around 38% of the world production share). It has more than 300 pulp mills and more than 550 paper mills to support its production. Due to the fierce competition within the pulp and paper industry, many companies merged resulting in a smaller total number of pulp and paper mills, and significantly increased production capacity per mill. Furthermore, factories in US are no longer allowed to "run a river through their plant" and dump the processed water back into the environment without cleaning it first. There is a clear trend of decreasing the amount of process water, recycling and reusing the water in closed-loop systems, and cleaning the water before releasing. A typical pulp mill uses about 64 m3 (17,000 gal) of water per tonne of bleached pulp produced, which is a decrease from approximately 379 m3 (100,000 gal) per metric tonne in the 1940s.(3) Today, the pulp and paper industry in US uses a lower volume of process water, recycles and reuses more water, and cleans water before releasing it, all in an effort to reduce costs as well as respond to increasingly strict environmental regulations. AUSTRALIA1: In Australia, five major papermaking facilities, four large saw mills and numerous smaller wood processing plants are operating. The Australian paper industry is acutely aware of the need to minimise its water use. In 2001-02 the industry used an average of 28.66 kilolitres per tonne of paper production. This represents a 62 per cent reduction in water use since 1990. The Australian paper industry’s water use compares favorably to the industry elsewhere in the world. EUROPE12: In Europe, around 60% of the pulp and paper produced comes from mills certified in one of the major eco-management schemes. Recovered paper 11 Source: APIC Public Eco-efficiency Report 2003 12 Source: EUROPA - Forest-Based industries - Pulp and paper manufacturing, http://europa.eu.int/comm/enterprise/forest_based/pulp_en.html



forms more than 40% of the raw materials used in paper production in Europe with the packaging sector the biggest consumer. Newsprint, sanitary and household papers, are produced from recovered paper. However, printing and writing papers - which represent 40% of total paper and board production - mostly rely on virgin fibres. Levels of paper recycling has increased in Europe, however performance varies greatly from one country to another due to differences in market and industry structures, population density, education, transportation distances, etc. CANADA13: Canadian pulp and paper industry is a cornerstone of the Canadian economy. Canada is a leading producer of high quality, recycled content paper products. Today, 22 mills across Canada are capable of recycling, and 62 mills use recovered paper in whole or in part as a source of fibre. Water consumption per tonne of pulp is less than half of what it was 20 years ago. Since 1990, the pulp and paper industry has invested over $6 billion in pollution prevention technologies, resulting in the virtual elimination of dioxins and furans. These reached non-measurable levels in 1995. TSS (Total Suspended Solids) and BOD (Biological Oxygen Demand), two leading indicators of mill effluent pollution have also dropped drastically. In this decade, levels of BOD have dropped ten fold and TSS, by more than half. The use of elemental chlorine in bleaching had dropped to 87% between 1988 and 1999. Further, a level of dioxins and furans in mill effluent has gone down by 99%. DUTCH14: In Dutch, fresh water consumption in wastepaper based pulp and paper mill is at present 8.4 m3/tonne of production. The production process in Dutch operates in water system closure. In water system closure, water system is basically divided in two large process water cycles, which are separated by the thickener: the Stock Preparation (SP) cycle with comparatively contaminated water and the Paper Machine (PM) cycle with comparatively clean water. The current paper production process in Dutch is as given below:

13 Source: Pulp and operations in Canada, http://www.cppa.org/english/info/work.htm 14 Source: Towards Water System Closure in the Paper Industry & Assessment of an improved separation of the stock preparation and paper machine based on the quality of the paper production, environmental impacts and economic aspects” by Leo Breedveld, Wiely Luttmer, Henk Senhorst Institute of Inland Water Management and Waste Water Treatment RIZA, P.O. Box, 17, NL-8200 AA, Lelystad, the Netherlands



The current production process is further improved by inserting an extra thickener in the process. As a result, an extra water cycle is created between refiner and cleaner as shown in below. The new cycle comprises refiner and thickener, while the PM cycle comprises cleaner and paper machine.

The improved process reduces the fresh water consumption further to 4.4 m3/tonne of production.



CHAPTER 5:

PRESENT WATER CONSUMPTION PATTERN PREVAILING IN PULP AND PAPER SECTOR IN INDIA

5.1 Background Pulp and paper sector is one of the water intensive industry. Water is one of the major inputs without which it is impossible to produce pulp and paper. Apart from large volume of water that is consumed at each and every process stage of paper manufacturing, water is also required for utility sections like boilers and co-generation plants to generate steam and power. Off late, water, the most sought out commodity is depleting very fast and already started giving alarming signals in many parts of the country. The demand for water in a specific industry depends on the quality of paper and type of raw material used and the extent of recycling adopted in the mill. 5.2 Water Consumption Scenario The most water consuming category is wood based and agro based integrated pulp and paper mills. The average water consumption15 (in 1998) by a integrated pulp and paper mill in India was 200 m3 per tonne of paper, varying from 175 m3 to as high as 415 m3 of water per tonne of paper. Average water consumption16 in wood based and waste paper based Indian pulp and paper industry as reported by Central Pollution Control Board (CPCB) and MoEF (Ministry of Environment & Forests) is given below:

Wood based mills: 150 - 200 m3 / tonne Waste paper based mills: 75 -100 m3/ tonne

5.3 Water Consumption/ Wastewater discharge: Norms / Standards For Paper And Pulp

1. CENTRAL POLLUTION CONTROL BOARD (CPCB)

So far, no water consumption standard has been set for water consumption by CPCB. Standards are prescribed in terms of wastewater discharge for different categories of pulp and paper industry as given below: A. Small Pulp & Paper Industry: As per Standards, pulp and paper mill established before January, 1992

Agro based are allowed to discharge 200 cu.m /tonne of product. And for wastepaper based pulp and paper mills are allowed to discharge 75 cum/tonne of product

15 Source: CSE ‘s Green Rating Project report for pulp and paper sector for second time, 2004. 16Source: Environmental management in selected industrial sectors - status and need, CPCB & MoEF, February, 2003.



And those mills established after January, 1992 Agro based mill are allowed to discharge 150 cum/tonne of product and that

wastepaper based mill is 50 cum/tonne of product B. Large Pulp and Paper Industry above 24000 tonne/annum Large pulp and paper mills are allowed to discharge 200 cum/tonne of product whereas newsprint-manufacturing mill are allowed to discharge 175 cum/tonne of product. 2. CHARTER ON CORPORATE RESPONSIBILITY FOR ENVIRONMENTAL

PROTECTION (CREP)

Central Pollution Control Board has issued a directive in the form of Corporate Responsibility for Environment Protection to 17 most polluting industries. Pulp and paper industry is one among them. CREP for Pulp and paper industry is as given below: Large scale pulp and paper mills has agreed to comply with following standards with respect to wastewater discharge quantity:

Less than 140 cum/tonne of paper within 2 years Less than 120 cum/tonne of paper in 4 years for mills installed before 1992 Less than 100 cum/tonne of paper in 4 years for mills installed after 1992

Small-scale pulp and paper mills have agreed to comply with following standard with respect to wastewater discharge: Less than 150 cum/tonne of paper within 3 years In addition, all the pulp and paper mills have agreed to utilize the treated effluent for irrigation wherever possible. 3. NORMS FOR PAPER AND PULP INDUSTRY ISSUED BY KARNATAKA

STATE POLLUTION CONTROL BOARD (KSPCB)

KSPCB has set norms for maximum consumption of fresh water by the pulp and paper mill. As per the norms, different categories of pulp and paper mill can consume fresh water upto the maximum limit as given below: A. Small Pulp and Paper Mills

Agro – residue based mill can consume upto a limit of 200 cum/tonne of paper

Wastepaper based mills can consume upto a limit of 75 cum/tonne of paper B. Large Pulp and Paper Mills

All large scale mill can consume upto a limit of 250 cum/tonne of paper



5.4 Water Consumption: Latest Trends With increasing awareness regarding water conservation, ever increasing pressure from government regulatory agencies and also due to increasing water scarcity many large industries have taken proactive steps like regular water auditing, technology modifications etc for reducing the water consumption. These efforts have also been reflected in the CSE’s finding through their green rating project in pulp and paper sector, water consumption has come down significantly in large-scale Indian paper mills and average figure has been reduced to 135 m3 per tonne paper in the year 2002. However, this figure is still very high when compared to the average water consumption in US and European pulp and paper mills as indicated in chapter 4. In view of the large water requirements, most of the large mills had setup their production facility close to perennial water sources. In many of the cases the easy and cheap availability of the water had in fact caused the excessive water usages and thus high specific water consumption figures. In small-scale industries, despite being dependent on ground water have high specific water consumption primarily due to use of obsolete technologies. The latest / current water consumption pattern in different categories of Indian pulp and paper mills (based on scale of operation, raw material used and the final product manufactured) as arrived through industries response to the questionnaire is compiled and is as tabulated below in Table 15: The details of questionnaire data is compiled and is given in Annexure III. Table 15: Water consumption in pulp and paper sector as per Questionnaire survey


(M3/ tonne of product) Min Max Remark

Large Scale category

1 Integrated Cultural high grade including newsprint 105 202

2. Wood Based Cultural grade including newsprint 68 168

3. Wood Based Newsprint only 74 There is only one

mill

4. Wood Based Rayon pulp 130

Only one mill in this category responded

5 Agro Based Cultural - high grade 73 -do-

6 Agro Based Cultural - low grade including newsprint 46 -do-

3 Waste paper Newsprint 29 -do- Medium Scale category

1 Agro Residue Cultural – high grade 102 219




(M3/ tonne of product) Min Max Remark

2 Agro Residue Industrial grade 28


3 Waste Paper Based Cultural – high grade 40 -do-

4 Waste Paper based Newsprint 16 -do-

Waste paper Based Industrial grade 5.5 35

One mill reported 5.5 m3/ tonne, operating

with zero discharge

system Small Scale category

1 Agro Residue Cultural - high grade 156


2 Agro Residue Industrial 7 Straw board making mill

3 Waste paper Cultural - high grade 18


4 Waste paper Cultural - low grade 14 25 5 Waste Paper Industrial 7 80

With the background information generated through above referred literature and questionnaire survey, detailed studies were undertaken in ten representative industries from various categories of pulp and paper manufacturing mills with the intention of identifying current water consumption levels, developing further water conservation measures and water conservation guidelines for use by different industries. The current water consumption pattern as identified through extensive water and fiber balance study in above mentioned 10 industries is as tabulated in Table 16:



Table 16: Overall water consumption (excluding domestic) in ten representative mills Water

consumption, m3/ tonne

Large Scale 1 Wood & Wastepaper based Newsprint

manufacturing 80


77


67

Medium Scale 4 Agro & waste paper based Cultural – high

grade 80


grade 48


grade 110

8 Agro & wastepaper based Industrial grade 93 9 Waste paper based Cultural – low

grade 13


129

During the detailed study efforts were also made to quantify / standardize the mill process / operation specific water consumption figures for various category pulp and paper manufacturing industries. The unit process / operation specific water consumption figures as developed during the detailed studies in 10 representative pulp and paper mills are discussed in the next chapter. 5.4 Waste Water Discharge: Latest Trends Through extensive detailed field studies in ten representative mills, wastewater discharge quantities (excluding domestic) have been estimated for different categories of pulp and paper manufacturing mills and are compiled below in table 17.



Table 17: Compilation of Water consumption figures from Questionnaire response Waste Water

discharge, m3/ tonne

Large Scale 1 Wood & Wastepaper based Newsprint

manufacturing 65


58


58

Medium Scale 4 Agro & waste paper based Cultural – high

grade 61


grade 36


grade 95

8 Agro & wastepaper based Industrial grade 76 9 Waste paper based Cultural – low

grade 11


100

From the above, it has been observed that wastewater discharge to fresh water consumption ratio varies between 0.72 and 0.86.



CHAPTER 6

UNIT PROCESS / OPERATION SPECIFIC WATER CONSUMPTION FACTORS

6.1 Background

Ten representative mills were studied in different categories of pulp and paper sector as mentioned in Chapter 2. Methodology adopted for estimation of specific water consumption In order to determine the existing specific water consumption, detailed water balance were prepared for both overall plant as well as individual unit process/operation/equipment wise. The following methodology was followed in preparing a detailed water balance:

a. Detailed study of the production process through available process flow sheets, shop floor walk through, detailed discussions with plant personnel.

b. Identification of unit processes/operations/equipments using fresh water c. Identification of sources of back water generation and their characteristics d. Measurement of metered fresh water intake volume inlet to the plant and

metered effluent discharged out e. Detailed fiber and water balance across the whole production process: The

requires estimation of moisture content of input raw material and output product and pulp consistencies at various stages of production processes

f. Measurement of unit process/operation fresh water consumption and wastewater discharge

g. Estimation of ratio of recycled water used to fresh water consumption The above mentioned methodology required extensive waste water monitoring (24 hours for 3 days), measurement of inlet water to the mill (using Ultrasonic flowmetre as well as mill’s water metre), collection of corresponding production related data, measurement of pulp consistencies at various stages of production, collection of data on chemical addition, steam used etc in the process. Prior to wastewater monitoring, preparatory work like identification of channels carrying wastewater from individual unit processes and the total, cleaning of the channels, removal of foams from the wastewater, fixing of weirs wherever required, etc. The impeller-based instrument was used for monitoring wastewater flow through channel. Fresh water flow through closed pipes was measured using ultrasonic flowmetres. The above information was used to construct a water balance diagram and material balance (fibre + water) charts, showing water use in different parts of the process (A typical water balance and material balance diagram constructed is shown in Figure 30 & 31). Further a detailed breakdown of unit process/operation fresh as well as recycled water use was made. Based on them, water conservation options were evolved.



The current specific water consumption factors and further water conservation potential, unit operation/process wise for different categories of pulp and paper sector estimated is described in subsequent section.



Digestor House

Bleach Plant

PULP MILL

Anaerobic lagoon

PM 1-4

Raw Water

WTP

Turbo generator, Compressor Cooling

Hypo Preparation

DM Plant Boiler House

SRP

Cooling Tower

PM 5

WPPS

Per Water

ETP

Pith press filtrate 4000 m3/d

River water (raw)

River water (treated)

Per water

Water along with. pulp

Paper m/c back water

Wastewater

9500 m3/d

500 m3/d 500 m3/d

7500 m3/d

12000 m3/d 6000 m3/d

5000 m3/d

6000 m3/d

14000 m3/d 5000 m3/d

15000 m3/d

1000 m3/d

500 m3/d

1200 m3/d 2200 m3/d

1800 m3/d

3000 m3/d

Under sludge 100 m3/d

300 m3/d

2200 m3/d

1900 m3/d

100 m3/d 3500 m3/d

21000 m3/d

2000 m3/d

18000 m3/d

3000 m3/d

Fig 30 : Typical Water Balance



Wheat straw /Bagasse 52.0 MT OD

12.8 m3

Caustic flakes 6500 Kg Caustic lye 0.0 m3 Digester

Black Liquor 141.8 m3 12.74% 26.3 MTSteam (condenses) 25.2 m3 179.9 m3

Flash vapours to atmosphereBlack Liquor 289.3 m3 Blow tank

5.30% 26.3 MT469.2 m3

Black liquor 1003.7 m3

26.3 MT1646.4 m3 1.57%

Johnson Screen 10.25 MT

642.6162 m3 WW to ETPHill

Screen 402

1424.7

4%

399.1534Fresh water 430.0 m3 2.82% 10.25 MT

2 STAGE COUNTER CURRENT

BSW 26.3 MT

243.4629 m3

9.42% 252.5 m3

HD TowerPulp Mill thickener ww 739.1 m3 2.58% 26.3 MT

991.6 m3

Fresh water + Pulp Mill thickener ww 379.0 m3

Centrifugal Screen1.88% 26.3 MT

1370.5 m3Pulp Mill Thickner ww

28.0 m3

Centricleaner (3 stage)

Tert C.C reject 28 m3 R

1.88% eThickner ww c

Fresh water 700.0 m3 Thickner 1071.027 m3 y2.56% 26.3 MT c

999.5 m3 lBleaching ww e

Backwater

1078.0 m3

Bleaching CEPH 1933.281 m3

Cl2 10.40% 26.3 MTCaustic 2.0 m3 226.2 m3

PeroxideHyposolution 80.0 m3

Paper m/c B/w 5.62% 26.3 MT214.8 m3 H D Tower 441.0 m3

Paper m/c B/w412.5 m3 2.99% 26.3 MT

853.5 m3

Wastepaper pulp 0.0Blending chest

7.5 MT 33.8 MT

Fig 31: Typical Material balance chart



6.2 Existing Water Consumption Status Based on the detailed studies as mentioned above in various categories of pulp and paper industries, the unit operation wise specific water consumption figures have been evolved and the same are elaborated below: 6.2.1 Raw material preparation Section In raw material preparation section water is primarily used for de-pithing, wet cleaning (in case of agro residues), log washing, chipping (in case of wood). Existing Water consumption status in raw material preparation section for various categories of pulp and paper mills has been generated, compiled and presented below in Table 18 in terms of specific fresh water consumption and specific total water consumption17.

Table 18: Specific Water Consumption – Raw Material Preparation Section

Specific water consumption (m3 / tonne of product)

Cat Cod

e

Category Description

Fresh water

Total water

Remarks

A Medium Scale Agro & Waste paper based Industrial paper manufacturing mill

0 0 It is a bagasse-based mill and only dry de-pithing is carried out, so no water is used.

B Medium Scale Agro & Waste paper based Cultural – high grade paper manufacturing mill

0.2 7.58 Process condensate from chemical recovery plant is used for washing of agro residues viz., wheat/rice straw and fresh water is used only

C Large scale wood and wastepaper based newsprint manufacturing mill

0.7 0.7 No recycling practiced

D Large scale wood and wastepaper based Cultural – high grade paper and paper board manufacturing mill

0.3 0.3 No recycling practiced

E Large scale Wood, Agro and wastepaper based (Integrated) Cultural – high grade paper and paper board manufacturing mill

0 13.5 Recycled water is used for depithing of bagasse and log washing and no fresh water is consumed in this section

17 Includes fresh as well as recycled water. This is the maximum water consumption needed for the specific process / operation.




Cat Cod

e


Fresh water

Total water

Remarks

F Small Scale Waste paper based Cultural – low grade paper manufacturing mill

- - Wastepaper based mill and does not warrant any raw material preparation

G Medium Scale Wastepaper based Cultural – high grade paper manufacturing mill

- - Wastepaper based mill and does not warrant any raw material preparation

H Small Scale Agro – residue based Industrial paper manufacturing mill

0 0 Dry dedusting of wheat straw and dry depithing of bagasse

I Small Scale Agro- residue based Cultural – high grade paper manufacturing mill

0 0 Dry depithing of bagasse

J Small Scale Wastepaper based Cultural – low grade paper manufacturing mill

- - Wastepaper based mill

Observations 1. Agro residue based pulp and paper mills using bagasse as raw material: It may be noticed from the above table that two mills using bagasse as raw material (category code A & E) has huge difference in water consumption. The variation is due to de-pithing technology. De-pithing of bagasse can be carried out by both dry and wet method. Wet de-pithing has following advantages over dry de-pithing process: a. Maximum removal of pith is possible in wet de-pithing around 90 % when compared to dry de-pithing process which removes only 46 – 50% of the total pith present in bagasse b. Other impurities like sand is also removed in the wet de-pithing process c. Removal of residual sugar content Pulp and paper mills involved in the manufacture of unbleached paper and paper board need not remove 90% of the pith and hence can go for dry depithing. However, those involved in the manufacture of Cultural papers have to remove maximum pith in order to avoid excessive use of bleaching chemicals. Further, those mills with continuous digesters need to remove sand or any such impurities in order to avoid damage to the screw feeder.



Dry depithing can be improvised by increasing the mesh size of the perforations in the dry depither from standard 6mm to 8 mm. This can result in pith removal from 50% to 66 - 73% of the total pith content Efforts should be made to purchase the bagasse having low sugar content and using dry de-pither as a precedent to wet depithing. 2. Agro residue based pulp and paper mills using wheat/rice straw: The water consumption variation in mills processing rice / wheat straw as raw material (Code B and H) is primarily due to the sand & chlorides present in them (farm sand sticked to raw material). Presence of Sand & chloride in the agro residue effects the chemical recovery from the waste pulping liquor (black liquor). Mills not adopting chemical recovery process can go for dry de-dusting, however others with chemical recovery plant needs wet de-dusting of agro residue. The acceptable chloride content (as NaCl) in the agro residue is below 0.2%. Mills processing wood needs water for log washing to remove the sand adhered with the wood logs. Most of the mills uses recycled water however a few large scale mills having log washing section far away from rest of the plant, uses fresh water with the recycling provision. 6.2.2 Pulping section: Agro Residue and Wood Based

The major processes in pulping section are the actual digestion of the raw material (agro residue, woodchips etc), pulp washing and pulp bleaching. In pulping section water is primarily required for following unit processes /operations:

(a) Blow heat recovery system (b) Brown stock washing (c) Bleaching, washing and bleach chemical preparation (d) Decker thickener showers (e) Pulp dilution at different stages

Other than the above water is also required for pump gland cooling/sealing, and floor washing. However there could be few areas which are either not pertinent or no water is used depending upon the type of raw material used and / or type of pulping process employed. The specific water consumption for different water use areas (e.g. brown stock washing, pulp dilution etc.) in pulping section for pulp mills studied in various categories is presented in the table below. The specific water consumption has been expressed as fresh water per tonne of product, total water consumption per tonne of product and also as fresh water consumption per tonne of bleached pulp as this particular data can be used more reliably18 as benchmark by industries for comparing water consumption in pulping section. The water consumption pattern for pulping section is as given below in Table 19:

18 Water consumption per tonne of finished product would be a misleading figure because of variety of raw materials (wood, agro residue, waste paper, imported pulp etc) used in varying proportions.



Table 19: Specific Water Consumption – Pulping Section

Specific Water consumption Cat cod

e

Category Description Fresh

Water, (m3/tonne of finished product)

Fresh water

(m3/BDMT of

bleached pulp)

Total water

(m3/tonne of finished product)

Remarks

A Medium Scale Agro & Waste paper based unbleached Kraft paper manufacturing mill Brown stock washing

16.20 20.25 27.20 Recycled water is used

Pulp dilution 4.40 5.47 18.40 -do- Pump gland cooling

0 0 5 Recycled water is used for pump gland cooling

Sub Total 20.6 50.6 B Medium Scale Agro & Waste paper based bleached writing & printing

paper manufacturing mill Brown stock washing

8.84 12 8.8419

Bleaching & washing

12.6 17.4 70.90 Save-All filtrate is reused in Bleach washing.

Sub Total 21.5 79.6 C Large scale wood and wastepaper based newsprint manufacturing mill Chemical Pulping (CP)

Brown stock washing

0 0 2.4020 Recycled water is used

Pulp dilution 0 0 3.50 -do- Centricleaning (Fibre saver)

0.26 2

Bleaching & washing


19 The figure is on a lower side as only partial washing is taking place in the brown stock washing section and remaining washing is achieved in bleaching section. This also causes relatively higher water consumption figure for bleaching operation. 20 Comparatively less water consumption (w.r.t. integrated mills producing high grade cultural paper) because of relatively less stringent washing requirements for news print grade paper.




e



Fresh water

(m3/BDMT of

bleached pulp)

Total water


Remarks

Bleach pulp dilution

0 0 2.40 -do-

Chemi- Mechanical Pulping (CMP) Hill Screen 0.13 0.12 0.13 Bleaching & washing

0 0 8.50 Recycled water is used

Non process like pump gland cooling, sealing, AC plant cooling, agitator, compressor, raffinator cooling, etc.

7.90 - 7.90

Sub Total 9.90 27.90 D Large scale wood and wastepaper based paper and paper board

manufacturing mill Brown stock washing

4 10 4 Better brown stock washing technology

Bleaching & washing

6.60 16.60 6.60 Better bleach washing technology

Pulp dilution 5 4 5 Non process like pump gland cooling, sealing, floor washing

3.76 - 3.76

Sub Total 19.36 19.36 E Large scale Wood, Agro and wastepaper based (Integrated) paper and

paper board manufacturing mill Brown stock washing

6.90 9.60 6.90




e



Fresh water

(m3/BDMT of

bleached pulp)

Total water


Remarks

Bleaching & washing

14 23.90 17.30 Recycled water is also used

Pulp dilution 0 0 18 –do- Non process like pump gland cooling, sealing

5.70 - 16.50 -do-

Sub Total 27.4 58.7 H Small Scale Agro – residue based Industrial paper manufacturing mill

Potcher washing

0 - - Recycled water is used

I Small Scale Agro- residue based Cultural – high grade paper manufacturing mill Brown stock washing

11 16.3 11

Bleaching & washing

5.89 8.75 41.79

Pulp dilution 0 0 39.2 Recycled water is usedCentrifugal Screen shower, Decker thickener shower

14.1 20.9 14.1

Pump gland cooling, floor washing

9 9

It may be noted from the above table that the water consumption varies significantly from industry to industry for the same unit processes using similar raw materials. These variations are caused by type of technology being used, water management practices etc. The minimum water consumption for different unit processes / operation in the pulping section for various categories of pulp and paper mills is compiled below.



6.2.3 Pulping section: Waste Paper Based Wastepaper pulping The major processes in waste paper pulping section are the hydro pulping, de-inking and sand / silica removal. In waste paper pulping section water is primarily required for following unit processes /operations:

(a) Hydropulper (b) De-inking plant (floatation cells) (c) Decker thickener shower (d) Pulp dilution (e) Centricleaning

Other than the above water is also required for pump gland cooling/sealing, and floor washing. The specific water consumption for different water use areas (e.g. hydro pulping, de inking, dilution, centricleaning etc brown stock washing, pulp dilution etc.) in waste paper pulping section of pulp mills studied in various categories is presented in the table below. The specific water consumption has been expressed as fresh water per tonne of product, total water consumption per tonne of product and also as fresh water consumption per tonne of waste paper pulp as this particular data can be used more reliably as benchmark by industries for comparing water consumption in waste paper pulping section. Specific water consumption factors have been compiled and given below in Table 20.

Table 20: Specific Water Consumption – Waste Paper Pulping Section

Specific Water consumption

Cat Code


Fresh water m3/tonne of finished product

Fresh water m3/BDMT of waste paper pulp

Total water m3/tonne of finished product

Remarks

A Medium Scale Agro & Waste paper based unbleached kraft paper manufacturing mill

Hydropulper 0 0 16.40 Recycled water is used

Decker thickener

7 35 14 -do-

Sub Total 7 30.40 B Medium Scale Agro & Waste paper based bleached writing & printing

paper manufacturing mill Hydropulper 0 0 4.76 -do-




Cat Code





Remarks

Decker thickener

2.50 68.50 2.50

Sub Total 2.50 7.26 C Large scale wood and wastepaper based newsprint manufacturing mill De-Inking Plant (DIP)

Process (Pulper, Screens etc)

4.40 23 13.10 Recycled water is used

Non process like pump gland cooling, agitator cooling, etc.

1.50 - 1.50


manufacturing mill Wastepaper

pulping (Process)


Wastepaper pulping (non process like pump gland cooling, etc.)

0.75 - 0.75

Imported pulp pulping

1.60 3.7 1.60


paper board manufacturing mill Hydropulper 0 0 4.80 Recycled water is

used Pulp dilution 0 0 1.50 -do- Sub Total 0 6.30 F Small Scale Waste paper based Cultural – low grade paper manufacturing

mill




Cat Code





Remarks

Waste paper pulping, cleaning

0 31 Recycled water is used

Pulp dilution 5 -do- G Medium Scale Wastepaper based Cultural – high grade paper

manufacturing mill De inking Plant:

Thickener, back water tank make up

9.6 23.2 9.6

Wastepaper/ Imported pulp pulping, cleaning

1.66 27.33

Pulp dilution 0 0 16.6 Pump gland

cooling 3.3 3.3

H Small Scale Agro – residue based Industrial paper manufacturing mill Waste paper

pulping 0 46.5 Recycled water is

used Decker

thickener 0 79.5 -do-


Wastepaper pulping

0 5.12 -do-

Decker thickener

0 1.38 -do-


Wastepaper pulping, cleaning,

0 29.8 Recycled water is used

Potcher washing

0 55.18 Recycled water is used



6.2.4 Stock Preparation and Papermaking

Paper machine section The major processes in stock preparation and paper making section are the chemicals preparation, Pulp dilution, paper making. In this section water is primarily required for following unit processes /operations.

(a) Chemical preparation (b) Pulp dilution (c) Centricleaning (d) Felt cleaning shower (e) Wire section high pressure shower (f) Couch press roll lubrication tower (g) Felt lubrication shower (h) Pick up roll lubrication (i) Breast roll shower (j) Broke pit showers, couch pit showers, etc (k) Thickener showers Other than these water is also required for refiner gland cooling, compressor cooling/sealing, pump gland cooling/sealing, rewinder drum cooling, paper roll and pope reel cooling, Floor washing, etc

The specific water consumption for different water use areas (e.g. chemical preparation, paper machine, showers vacuum sealing etc) in stock preparation and paper making section for pulp mills studied in various categories is presented in the Table 21 below. The specific water consumption has been expressed as fresh water per tonne of finished product and total water consumption per tonne of finished product. Table 21: Specific Water Consumption – Stock Preparation and Paper Making

Section Specific water

consumption (m3 / tonne of product)

Category

Code


Fresh water

Total water

Remarks

A Medium Scale Agro & Waste paper based unbleached Kraft paper manufacturing mill

Chemical preparation 0.50 0.50 Paper machine

Showers 10 10

No recycled water is used




Category

Code


Fresh water

Total water

Remarks

Vacuum pump sealing

5 5

Pump gland cooling, Floor washing

1.92 1.92

Sub Total 17.42 17.42 B Medium Scale Agro & Waste paper based bleached writing & printing

paper manufacturing mill Chemical preparation 21.50 21.50 Paper machine

Showers 10.50 10.50 Vacuum pump

sealing, compressor cooling, pope reel cooling

6.30 6.30


Sub Total 38 38 C Large scale wood and wastepaper based newsprint manufacturing

mill Chemical

Preparation 2.90 2.90

Stock preparation & Paper machine (Process)

16.10 16.10

Showers 4.40 4.40 Broke thickener 0.88 0.88 Others white water

silo make up, saveall filtrate tank make up, water conservation tank make up

6.4 6.40

Vacuum flume tank make up (vacuum pump sealing)

4.40 4.40

Pump gland cooling, AC plant cooling, etc.

1.90 1.90



manufacturing mill Chemical preparation 0.08 0.08 Showers 14.40 14.40





Category

Code


Fresh water

Total water

Remarks

Cooling tower make up, pump gland cooling/ sealing, rewinder drum cooling, COL, cooling cylinder water, etc

24.12 24.12

Pulp sheeting 1 1


paper board manufacturing mill Stock Preparation 2.35 9.95 Recycled water is used

Showers 21.28 22.18 Pump gland cooling,

dryer surface condenser, hot press cooling, rewinder break cooling, etc.

5.28 19.58

Sub Total 28.20 51.71 Recycled water is used F Small Scale Waste paper based Cultural – low grade paper

manufacturing mill High & Low Pressure

showers 11 11 No recycled water is used

Vacuum pump sealing

1.5 1.5 -do-

G Medium Scale Wastepaper based Cultural – high grade paper manufacturing mill

Chemical Preparation

2.38 1.96

High & Low Pressure showers

21.6 23.3

Back water tank make up

3.3 3.3

Pump gland cooling, vacuum pump sealing, rewinder cooling, Floor washing

4.59 4.59




Category

Code


Fresh water

Total water

Remarks

H Small Scale Agro – residue based Industrial paper manufacturing mill High & Low pressure

showers 90.65 90.65

Vacuum pump sealing/cooling

5.75 5.75


Showers 47.58 47.58 Pump gland cooling,

pope reel cooling, rewinder cooling, floor washing

3.95 3.95

Back water tank make up

0.17 0.17


Showers 64 64 Vacuum pump

sealing 60 60

6.2.5 Chemical recovery Plant

The major processes in chemical recovery plant are concentration of black liquor through multi effect evaporator, salt recovery by black liquor burning, generation of pulping liquor etc. In chemical recovery plant the water is primarily required for following unit processes /operations:

(a) For maintaining barometric leg in the evaporator (Old evaporators without surface condenser) and in the lime kiln

(b) Vacuum pump sealing, centrifugal pump gland cooling/sealing (c) Spout cooling (d) Evaporator tube cleaning (e) Lime kiln dryer bearing and roller cooling (f) Floor washing



Other than the above water is also required for pump gland cooling/sealing, and floor washing. However there could be few areas which are either not pertinent or no water is used depending upon the type of recovery process employed. The specific water consumption for different water use areas (e.g. For maintaining barometric leg in the evaporator, Vacuum pump sealing, centrifugal pump gland cooling/sealing brown stock washing, pulp dilution etc., Spout cooling, Evaporator tube cleaning, Lime kiln dryer bearing and roller cooling etc) in Chemical recovery section for pulp mills studied in various categories is presented in the Table 22 below. The specific water consumption has been expressed as fresh water per tonne of finished product and total water consumption per tonne of finished product.

Table 22: Specific Water Consumption – Chemical Recovery Section Category Specific fresh

water consumption, m3/tonne of finished product

Specific total water consumption, m3/tonne of finished product

Remarks

B Medium Scale Agro & Waste paper based bleached writing & printing paper manufacturing mill

Pump gland cooling/sealing, etc

0.42 0.42

Sub Total 0.42 0.42 C Large scale wood and wastepaper based newsprint manufacturing mill

Pump gland cooling/sealing, etc

11.10 11.10


manufacturing mill Soda recovery boiler

& evaporator

Spout cooling 0.2 0.2 Pump gland cooling,

floor washing, cooling tower make up, tube cleaning

3.6 3.6

Causticisation Barometric leg 0.56 0.56 Vacuum pump

sealing 0.425 0.425

Pump gland cooling, floor washing

0.496 0.496

Lime kiln Vacuum pump

sealing 0.84 0.84



Category Specific fresh water consumption, m3/tonne of finished product

Specific total water consumption, m3/tonne of finished product

Remarks

Moisture trap 0.24 0.24 Pump gland cooling,

bearing 7 roller cooling

0.068 0.068


paper board manufacturing mill Evaporator & reboiler

Pump gland cooling & cooling tower make up

1.44 8.07 Recycled water is used

Spout cooling 0.11 0.11 Causticisation Plant

Pump gland cooling, slaker roller cooling

0.08 2.65 Recycled water is used

Sub Total 1.63 10.83 Mill A, F, G, H, I, J does not have chemical recovery plant and are therefore not appearing in the above table.

6.2.6 Utilities

Utilities (a) DM plant (b) Chemical recovery plant: reactor cooling, product cooling, etc.

Scrubber (Boiler House) Other than these water is also required for pump gland cooling/sealing, and floor washing. Water consumption pattern in Utility section is as given below in Table 23:



Table 23 : Specific Water Consumption – Chemical Recovery Section Category Specific fresh water

consumption, m3/tonne of finished product

A Medium Scale Agro & Waste paper based unbleached kraft paper manufacturing mill

DM Plant, cooling tower make up 2.21 Sub Total 2.21 B Medium Scale Agro & Waste paper based bleached writing & printing paper

manufacturing mill DM Plant, Boiler House

DM Plant Feed + Back wash 6.80 Boiler scrubber 10.52 Sub Total C Large scale wood and wastepaper based newsprint manufacturing mill

DM Plant, Boiler House, Miscellaneous DM Plant Feed + Back wash 2.50 Boiler house: cooling water make up, compressor, ID

Fan’s bearing, pump gland cooling & sealing, etc. 19.4

Miscellaneous like road washing, etc. 1.50 Sub Total 20.90 D Large scale wood and wastepaper based paper and paper board manufacturing

mill DM Plant, Coal Fired Boiler, Softener

DM Plant Feed + backwash 4.19 Pump gland cooling, spreader cooling, etc. 0.83 Coal fired boiler- cooling tower make up, dust

suppression, etc. 1.60

Softener regeneration + Sand filter backwash 4.83 Sub Total 11.45 E Large scale Wood, Agro and wastepaper based (Integrated) paper and paper

board manufacturing mill Water treatment plant

Chemical preparation Sand filter backwash & regeneration

DM Plant, Boiler House DM Plant + Backwash 6.28 Pump gland cooling Sub Total 14.74 F Small Scale Waste paper based Cultural – low grade paper manufacturing mill DM Plant, Cooling Tower 4.5 G Medium Scale Wastepaper based Cultural – high grade paper manufacturing

mill Softening Plant, Cooling Tower, DG Set, & others 5 H Small Scale Agro – residue based Industrial paper manufacturing mill



Category Specific fresh water consumption, m3/tonne of finished product

None I Small Scale Agro- residue based Cultural – high grade paper manufacturing mill DM Plant/Boiler House 3.94 J Small Scale Wastepaper based Cultural – low grade paper manufacturing mill Softener Plant/Boiler House, Wastage 3.7



CHAPTER 7

FORMULATION OF STANDARDS FOR WATER CONSUMPTION / WASTEWATER DISCHARGE BY DIFFERENT CATEGORIES OF

PULP AND PAPER MANUFACTURING MILLS 1. BACKGROUND Based on the detailed pulp and paper mill’s inventorisation and observations from the dry and detailed field studies conducted during the course of this project, there are various salient features about pulp and paper sector in India that would be useful in developing water consumption standards in the country. These salient features are discussed below in detail. Primarily three distinct level / range of “scale of operation” in the whole pulp and paper sector across the country and these may be defined as

Large scale : > 25000 TPA of production, Medium scale : between 5,000 and 25000 TPA Small scale : < 5000 TPA

Large-scale pulp and paper sector in India exhibits following distinct features:

• Most of the large-scale mills are either wood based or integrated mills and some yet significant number of only wastepaper based mills.

• There are few large-scale newsprint manufacturing mills but also involved in manufacturing high-grade paper and paperboard.

• There is only one large scale mill manufacturing only newsprint

• Nearly all mills manufacture high-grade paper and paper board.

• All the large-scale mills have already undergone modernization and have reduced their fresh water consumption substantially.

• All of them have installed chemical recovery plant.

Medium Scale pulp and paper mills in India exhibits following distinct features:

• All medium scale mills are either agro based and / or only waste paper based mills.



• Maximum mills in this category are involved in industrial grade paper production

• There are some agro and waste paper based medium scale mills involved in the manufacture of high grade cultural paper production

• Very few agro based medium scale mills have chemical recovery plant.

• There is not significant difference in water consumption due to use of chemical recovery plant.

• Technological level is similar to that of large scale and small scale mills in respect of waste paper based mills

• Significant variations in water consumption exist among waste paper based mills, with or without de-inking process, manufacturing cultural grade paper.

Small Scale pulp and paper mills in India exhibits following distinct features:

• All small-scale mills are either agro based and / or only waste paper based mills.

• Maximum mills in this category are involved in industrial grade paper production

• There are very few agro based small scale mills involved in the manufacture of high grade cultural paper production

• Most of the small scale wastepaper based mills are involved in industrial or low grade paper manufacture

• None of the agro based small-scale mills have chemical recovery plant.

• Significant variation / difference in water consumption in high grade and low grade paper manufacturing exists

• Technological level is at par with most of the medium scale mills both in high grade and low-grade paper manufacturing facilities.

2. PROPOSED CATEGORIES OF PULP & PAPER MILLS FOR STANDARDS Keeping the above referred salient features and characteristics of Indian pulp & paper mills prevailing in the country in view, following categories of pulp and paper mills with respect to water consumption pattern are considered for formulation of standards:

A. Large scale Wood based and integrated pulp and paper mills

manufacturing cultural grade paper & paper board and / or Newsprint

B. Small/Medium Scale Agro based pulp and paper mills manufacturing high

grade cultural paper



C. Small/Medium Scale Agro based pulp and paper mills manufacturing

industrial grade paper

D. All wastepaper based pulp and paper mills manufacturing high grade

cultural paper with “De-inking”

E. All wastepaper based pulp and paper mills manufacturing cultural grade

paper without De-inking

F. All medium / small scale waste paper based mills manufacturing industrial

grade paper

Category A represents all the large-scale mills which primarily uses wood and or agro residue along with recycled fibre. In India, all such large-scale mills manufacture high-grade cultural paper including newsprint and none are involved in manufacture of industrial grade alone. Further, all of them have installed chemical recovery mill. Water consumption pattern in all the mills under this category is of similar order due to similar mill operations/processes being carried out with similar scale of operation. Category B represents Medium and small-scale agro residue based mills involved in the manufacture of high-grade cultural grade paper. This category does not differentiate between mills with wet or dry raw material preparation, with or without chemical recovery, type of agro residues used. Category C represents medium and small-scale agro residue based mills involved in the production of industrial or low-grade paper. This category does not differentiate between mills with wet or dry raw material preparation, with or without chemical recovery, type of agro residues used. This mills in this category will not be having bleaching and post bleaching wash processes and thus allowing large extent of waste water recycling (may require simple physico-chemical treatment). Category D represents all waste paper based mills irrespective of production scale involved in the manufacture of high-grade cultural paper including newsprint with “de inking”. The major mill operation / processes being employed are hydro pulping, de-inking, pulp bleaching (may or May not) and papermaking. Category E represents all waste paper based mills irrespective of production scale involved in the manufacture of high-grade cultural paper without “de inking”. The major mill operation / processes being employed are hydro pulping, pulp bleaching (may or May not) and papermaking. Category F represents all the small-scale wastepaper based mills involved in the manufacturing of industrial low-grade paper. The major operations in mills of this category are primarily hydro pulping and paper making with water recycling system. The various types of paper products referred in the above-mentioned categories are detailed below:



High grade Cultural Paper: Bond paper, Copier Paper, Writing & Printing, Paper with brightness above 60 Also includes specialty paper like tissue paper, security paper, etc Low grade Cultural paper: Art paper/media paper, Creamwove, etc Industrial grade: Duplex Board/Paper, Kraft paper Newsprint

3. PROPOSED TYPES OF WATER COMSUMPTION STANDARDS Based on detailed studies in ten representative mills, based on the literature survey and also questionnaire response, mill operation/process wise water consumption standards have been formulated. While developing the standards following factors have been considered.

The standards developed should ensure continuous reduction in water consumption.

The standards should be such that they trigger technological interventions as well as reuse / recycling opportunities and thus lead to quantum reduction in water consumption in long term.

The standards should be India specific and practicable and feasible to implement.

The standards should also even out the huge water consumption disparities among the similar type of mills in short term.

Considering all the above factors, the standards have been formulated in terms of

• Benchmark Standard: This standard refers to minimum water consumption required after implementation of best available technology (economically viable and currently practiced / demonstrated in India), recycle and reuse practices. This standard has been developed by identifying the various unit operations involved in each specific category and also identifying the least water consumption actually achieved by any of the mills studied in that particular category. The total of water consumption in each of the unit operation / process would be the benchmark standard for that specific category.

The idea of developing this standard is to ensure o Quantum reduction in water consumption: No mill in the above-

referred categories is currently operating at this level. To achieve this level most of the mills would need to undertake certain technological modifications and complex recycling / reuse measures to achieve the quantum reduction in the water consumption and comply with these standards

o Development of feasible standards: Further these standards reflect the feasible and demonstrated unit operation specific water



consumption norms already practiced in one or the other industry in India and thus expected to be appreciated and followed by industries.

Since complying with these standards would need technological and complex recycling / reuse systems interventions, which require significant time and resources at the industries end, it is proposed that these standards to be considered for implementation after four years from the acceptance year of this report.

• Best Achieved Standard: This standard refers to the minimum water consumption already achieved by a mill (or can be achieved by implementation of simple recycling / reuse measures) simple in the specific category.

This standard is developed with the perspective of bringing the other mills to the currently best-achieved and demonstrated level in the country. This standard can be achieved by implementation of simple water recycling and reuse practices and minor technological changes. This standard is proposed to be considered for implementation from two years from the acceptance year of this report. The three years grace period is proposed to enable other industries to undertake technologies feasibility (technical, economical, environmental etc) and implementation.

• Relaxed Standard: This standard provides 20 % relief over the best-achieved standard in each specific category. This standard is proposed for immediate reduction in water consumption by most of the high water consuming industries and thus bridge the huge gap between best performing and worst performing mills in a short time. It is estimated that this standard can be achieved by other industries in each categories by implementing simple reuse, recycling and other minor modification.

This standard is proposed to be implemented after six months from the acceptance of this report. The six months grace period is proposed to enable other industries to undertake the reuse, recycling and other minor modifications. The process of developing above referred benchmark standards would also identify unit operation / process or section specific water consumption benchmark figures that can be used by the industries for continuous improvements. 4. DEVELOPMENT OF CATEGORY SPECIFIC WATER COMSUMPTION STANDARDS The unit operation / process specific water consumption figures developed during the detailed field studies have been used to develop the water consumption standards for above referred categories of the pulp & paper mills. The category specific water consumption standards development for all categories is detailed in the tables 24 to 29 in the following pages.



CATEGORY A: Large scale Wood based and integrated pulp and paper mills manufacturing high grade cultural paper and paper board and / or Newsprint,

Table 24: Water Consumption Standards for Category A

Sl Unit Processes/Operations Specific fresh water consumption, m3/ tonne of product

(Minimum required)

Remarks

1 Raw material Preparation 0 100% recycled water can be used as this process does not require quality water

2 Pulping Section a

Brown stock washing

4 Counter current washing, Best technology to achieve min limit: Twin roll wire press washer and extended delignification using oxygen after digestion

b Bleaching and washing

6.6 Recycle of waste bleach liquor partly, Use of recycled water, Best technology to achieve min limit: Twin roll wire press washer

c Pulp dilution 5 d Other non process like pump

gland cooling, floor washing, etc.

3.76

3 Waste paper 6.32 100% recycled water can be used 4 Stock Preparation

(Chemical preparation) 0.08

5

Paper machine

16.1 Self cleaning showers, well maintained pressurised showers, Use of recycled water in low pressure showers, 100% recycling of vacuum pump sealing wastewater, recycling of pump gland cooling

6 Chemical Recovery

6.52 Using surface condenser in the multiple effect evaporator replacing barometric leg, recycling pump gland cooling waste water,etc

7 Utilities

11.45 Installation of cooling tower to recycle cooling water from pumps, compressors, turbines, etc.

Total

60

Other Miscellaneous (5% of total)

3

Overall (Benchmark Standard)

63

Benchmark Standard : 63 m3/ tonne of product Best Achieved standard : 67 m3/ tonne of product (M/s Seshasayee Paper and

Paper board Ltd., Erode) Relaxed Standard : 80 m3 tonne of product



CATEGORY B: Small/Medium Scale Agro based pulp and paper mills manufacturing high-grade cultural paper with or without chemical recovery

Table 25: Water Consumption Standards for Category B


(Minimum required)

Remarks

1 Raw material Preparation 0.2 100% recycled water can be used as this process does not require quality water

2 Pulping Section a Brown stock washing 11 Counter current washing, Use of recycled

water b Bleaching and washing 5.89 Recycle of waste bleach liquor partly, use of

recycled water c Pulp dilution 0 Use of recycled water d Other non process like pump


0 Recycling gland cooling wastewater

3 Waste paper pulping 0 100% recycled water can be used 4 Stock Preparation


5 Paper machine 16.1 Self cleaning showers, well maintained pressurised showers, Use of recycled water in low pressure showers, 100% recycling of vacuum pump sealing wastewater, recycling of pump gland cooling

6 Chemical Recovery 0.42 Using surface condenser in the multiple effect evaporator replacing barometric leg, recycling pump gland cooling wastewater,etc

7 Utilities 2.2 Installation of cooling tower to recycle cooling water from pumps, compressors, turbines, etc.

Total 36 Rounded off


2


38

Benchmark Standard : 38 m3/ tonne of product Best Achieved standard : 80 m3/ tonne of product (M/s Shreyan Industries) Relaxed Standard : 95 m3/ tonne of product Present consumption in other mills ranges from 110 to 160 m3/tonne of product



CATEGORY C: Small/Medium Scale Agro based pulp and paper mills manufacturing industrial grade paper with or without chemical recovery

Table 26 : Water Consumption Standards for Category C

Sl Unit Processes/Operations Specific fresh water consumption, m3/ tonne of

product (Minimum required)

Remarks

1 Raw material Preparation 0 Dry depithing, dry dedusting can be practiced

2 Pulping Section a Brown stock washing 11 Counter current washing, Use of recycled

water c Pulp dilution 0 Use of 100% recycled water d Other non process like pump


0 Recycling gland cooling wastewater

3 Waste paper pulping 0 100% recycled water can be used

4 Stock Preparation (Chemical preparation)

0.08


6 Chemical recovery 0.42 7 Utilities 2.2 Installation of cooling tower to recycle

cooling water from pumps, compressors, turbines, etc

Total 17 Rounded off


1


18

Benchmark Standard : 18 m3/ tonne of product Best Achieved standard : 47 m3/ tonne of product (M/s Tehri Pulp and Paper Ltd) Relaxed Standard : 56 m3 / tonne of product Present consumption in other mills ranges from 60 to 100 m3/tonne of product



CATEGORY D: All wastepaper based pulp and paper mills manufacturing high-grade cultural paper and / or Newsprint with “De-inking”

Table 27: Water Consumption Standards for Category D

Sl. Unit Processes/Operations Specific fresh water consumption, m3/ tonne of product

(Minimum required)

Remarks

1 Waste paper pulping 9.6 100% recycled water can be used 2 Stock Preparation


3

Paper machine


4 Utilities

5 Installation of cooling tower to recycle cooling water from pumps, compressors, turbines, etc.

Total 18


1


19

Benchmark Standard : 19 m3/ tonne of product Best Achieved standard : 41 m3/ tonne of product (M/s Pudumjee Pulp and

Paper: anticipated after implementation of simple recycle/reuse options)

Relaxed Standard : 49 m3/ tonne of product Present consumption in other mills ranges from 98 to 110 m3/tonne of product



CATEGORY E: All waste paper based pulp & paper mills manufacturing cultural grade paper without “De-inking” Table 28: Water Consumption Standards for Category E


(Minimum required)

Remarks

1 Waste paper pulping 2.32 100% recycled water can be used

2 Stock Preparation (Chemical preparation)

0.08


4 Utilities 2.2 Installation of cooling tower to recycle cooling water from pumps, compressors, turbines, etc.

Total 8 Rounded off


1


9

Benchmark Standard : 9 m3/ tonne of product Best Achieved standard : 13 m3/ tonne of product (M/s Indo Afrique paper Mill) Relaxed Standard : 15 m3/ tonne of product Present consumption in other mills ranges from 115 to 129 m3/tonne of product



CATEGORY F: All Medium / Small scale waste paper based pulp & paper mills manufacturing industrial grade paper

Table 29: Water Consumption Standards for Category F

Sl. Unit Processes/Operations Specific fresh water consumption, m3/ tonne of product

(Minimum required)

Remarks

1 Waste paper pulping 0 100% recycled water can be used 2 Stock Preparation


3

Paper machine


4 Utilities

2.2 Installation of cooling tower to recycle cooling water from pumps, compressors, turbines, etc.

Total 5.6


0.4


6

Benchmark Standard : 6 m3/ tonne of product Best Achieved standard : 6 m3/ tonne of product (M/s Paper Packaging (P) Ltd.) Relaxed Standard : 7 m3/ tonne of product Present consumption in other mills ranges from 6 to 80 m3/tonne of product



The consolidated proposed water consumption standards for each category of the pulp & paper mills are compiled and tabulated below in Table 30.

Table 30: Proposed Water Consumption Standards Proposed water consumption standard

(m3/ tonne of paper)


Benchmark Best achievable

Relaxed


63 67 80


38 80 95


18 47 56


19 41 49


9 13 15


6 6 7

5. PROPOSED CATEGORY SPECIFIC WASTEWATER DISCHARGE STANDARDS From the water balance studies carried out at different representative pulp and paper, it has been found that the ratio of wastewater discharge to fresh water consumption (only process) varies between 0.72 and 0.86. Considering an average ratio of 0.79, following waste water discharge standards based on the above water consumption standards proposed (Table 31).



Table 31: Proposed Water Consumption Standards

Proposed wastewater discharge standard in m3 / Tonne of product


Benchmark

Best achievable

Relaxed


50 53 63


30 63 75


15 37 44


15 32 38


7 10 12


5 5 6

It is further recommended to use the treated wastewater as much as possible for irrigation purpose.



CHAPTER 8

WATER CONSERVATION OPTIONS IDENTIFIED FOR DIFFERENT CATEGORIES OF PULP AND PAPER MILLS

The high water consumption in Indian pulp and paper industry is mainly due to obsolete process technology, poor water management practices and inadequate wastewater treatment. Water once used is generally thrown without any further use, even if the water is not much contaminated. Segregation of wastewater from various processes into clean wastewater, (that can be reused) and contaminated water is therefore one of the very important step to be taken towards water conservation. This would avoid the uncontaminated water getting contaminated after mixing and is discharged as effluent. Another important step towards water conservation would be rainwater harvesting. This would help the industries to meet a substantial part of their annual water requirement even as demand on local sources is minimised. In order to evolve techno economically feasible option, detailed field studies were carried out as mentioned in earlier chapter. Depending upon the category and scale of operations, water conservation options have been recommended. They are as detailed below: I. General Housekeeping Measures 1. Instituting a repair and replacement system to reduce water loses from valve leaks: Good maintenance of seals, flanges and water pumps can substantially reduce the fresh water consumption. Large quantities of water are wasted as spills and overflows. A preventive maintenance schedule needs to be developed. 2. Monitoring and follow up of automatic shut down procedure for the water turbines when pulping or paper machine sections are out of production. It has been observed that auto-shut down procedure of water turbines is not strictly followed with the result water turbines remain in operation while pulping and paper machine sections are down. 3. Installation of Press type taps to avoid leakages from all taps inside plant: Press type taps will avoid water wastage through open taps due to negligence of a worker. Cost of a single press type tap ranges between Rs 50 to 100. 4. Auto close valve for hosepipes: Press type clutches in the hosepipes, similar to one used for delivering oil in Petrol pump stations. This would prevent water loss due to negligence. Cost of one such hosepipe is Rs. 1000/-. 5. Daily reporting of water consumption and drain losses from individual sections like pulp mill, wastepaper pulping section, paper machine sections, utility, etc). This allows rapid identification of non-routine conditions so that prompt remedial action can be taken. This requires installation of online flowmetres. Further, monitoring of



water use/drain losses can be done over a specific financial periods and management can place a specific target to the individual sections. This would motivate the plant supervisors, operators and would encourage them to improve the standards. The standards achieved should be reviewed time to time to enable continuous improvement. II. Common Measures 1. Use of Better pulp washing technology instead of obsolete technologies like potcher washing Conventional potcher washing consumes huge quantity of water as it is a batch process. Compared with this continuous countercurrent processes consume less water. Usually three washings are applied in these processes. It is suggested to use fresh water only at the last stage (i.e. at third stage) and recycle the effluent in first and second washings. This system not only reduces water consumption but also allows recycle of wastewater to some extent leading to saving of bleaching chemicals. Some of the continuous processes are as detailed below: a. Hydraulic drum washing: A hydraulic drum washer does not require Barometric leg and works on hydraulic principle therefore has minimum operating costs. A hydraulic drum would cost around Rs. 2.5 Lakhs including civil costs. A sketch of hydraulic drum is shown in Figure 32 below For a 30 TPD pulping mill



Figure 32: Schematic design of a hydraulic washer b. Vacuum Drum washing: In vacuum drum washing, each stage consists of a rotating screen drum which has a partial vacuum applied to interior. The drum sits in a tank where pulp is diluted with wash water. The vacuum draws a pulp mat against the surface and wash water through the mat. The drum rotation advances the washed pulp mat to the next dilution tank. Wash water discharged from this wash stage is sent to the previous washing stage. For a 30 TPD pulping mill, a vacuum drum washer would cost around Rs. 20 – 25 Lakhs including civil costs. c. Pressure washing: Pressure washing is similar to vacuum drum, but differs by spraying water under pressure through the pulp mat as the drum rotates. d. Diffusion washing: Diffusion washing is a counterflow process that takes place in one or more stages. Pulp flow is upward and is carried on a perforated plate. Water flows downward through a series of baffles. e. Chemi or Belt washing: A Chemi or belt washer is perhaps the simplest washing system in terms of design. It offers excellent washing with reduced water usage. Belt washing is a counter flow process where pulp enters the washer area on a wire belt. Washing takes place under a series of showers. Clean water enters on the opposite end from the pulp and is sprayed vertically through the pulp. The used wash water is then collected and reapplied to the dirtier pulp by the next washing head. Countercurrent to the direction that the pulp moves. This process is continued through at least seven stages until the wash water is saturated with liquor after washing immediately coming pulp. The wash water is then sent to the recovery process. Diffusion washing and belt washing can reduce the amount of water used per tonne of pulp in brownstock washing by 50% or more according to published data.

Rubber roll of 500 mm diaDoctor's Knife

Washed Pulp consistency = 10%

Unwashed Pulp

Perforation of 25 mm40# wire over the drum

200 mm



Capital equipment Costs – including all support facilities21 : $ 10.2 to $ 12.3 MM Operating Cost reduction compared to vacuum drum washing: $4.67 per Tonne of pulp Payback period : 4.25 to 4.9 years. Due to long pay back period, Chemi washer is more feasible in a new installation or when new washer is required to replace a vacuum drum washer that has reached the end of its service life. f. Twin roll press washer: Twin wire roll press washer consists of a twin-wire dewatering unit which allows controlled washing of the pulp. The two-sided dewatering and strong turbulence of the washer facilitate two to three times higher capacities per unit of width than conventional washer technologies. An additional main feature of this technology is that the ash and fines removal can be controlled depending on the targeted levels. This technology can be used for high consistency pulp washing and resulting in reduced water consumption. The cost (rough estimate) for 300 OD TPD fiberline (excluding cost of civil construction, land and detail engineering design cost) can be as follows:

1. Brown stock washing & Screening including ODL- price SEK 65 million or 413 million INR

2. Bleach plant- price SEK 45 million or 286 million INR 3. Instruments electrical DCS- price SEK 35 million or 222.28 million INR 4. Tanks & pressure vessels- price SEK 25 million or 159 million INR

2. Optimum use of cooling wastewater. In every mill, cooling with water is required at various sites like pump gland cooling/sealing, steam turbine cooling, compressor cooling, refiner gland cooling, rewinder brake cooling, etc. In most of the industries, fresh water is being used for pump jacket cooling on once through basis. This water is most of the time non-contaminated. There are different alternatives in which this water use can be optimized as described below: A. Collection of once-through cooling water and reuse it in different process operation: Collection involves installation of several small sumps or tanks from which water is subsequently pumped to process water tanks. It is also possible to directly use the water for specific applications like shower systems. The higher temperature of cooling wastewater is advantageous to the shower system as it increases the water drainage property of the web. B. Converting once-through system into a closed –loop system: This requires installation of cooling tower, a temperature controller and a cartridge filter to remove

21 Source: U.S. EPA, 1993b. Pollution Prevention Technologies for the Bleached Kraft Segment of the U.S. Pulp and Paper Industry.



any suspended particles present in the waste cooling water. Further, periodic injection of fresh water is required as a make up for the evaporation loss. One such figure of a closed loop re-circulation system is shown in Figure 33.

Figure 33: Temperature controlled re – circulation system 3. Recovery and re-cycling of clean water from vacuum pumps. In most of the industries, fresh water is used for sealing/cooling in vacuum pumps of paper machine section. Vacuum pumps are used to supply vacuum to vacuum drum pulp washers, wire section, press section and dryer section of the paper machine. Vacuum pumps are typically liquid ring pumps which use water for sealing and cooling. Water usage is continuous and high depending upon the size of the pump. The wastewater is mostly non-contaminated and suitable for recycling back after passing through a cartridge filter. At present, the wastewater from this source is either discharged outside directly or sent to ETP. This filtered water can also be used in the pulp mill for pulp dilution, decker thickener showers, brown stock washing, etc. This requires similar arrangement as discussed in Option 2. 4. Installation of Vacuum flume tank to recycle vacuum pump sealing water Sealing wastewater from all the vacuum pumps in paper machine section is collected in a tank and by the action of centrifugal action, suspended particles are separated from it. 50% of the clear filtrate goes back to vacuum pump as sealing water and rest is collected in water conservation tank. In the water conservation tank, fresh water is added as make up and is recycled back to the plant for different uses as mentioned above. The schematic diagram for flume tank water usage and water conservation tank is shown in Figure 34 below:



Figure 34: Schematic of vacuum sealing wastewater recycling through Flume

tank Saving in fresh water consumption by this option has been estimated to be 14.3 m3/tonne of product. 5. Replacement of water seals in Process Pumps Seal water used in various pumps can be eliminated by replacing with mechanical face and lip seals. Seal water flows are typically not very high, but are continuous and can add up to large volumes over time. Replacing water seals with mechanical seals usually increases energy consumption due to friction. Sealless pumps are commonly used in Chemical industries. An example of a sealless pump is a diastolic tube pump where magnetically coupled pump transmits power from the motor to the pump with a magnetic pump. Pumps with braided packing seals and a self – lubricating compound are also available. These lubricants have a colloidal mixture of lubricants amalgamated with Aragraphe fibers. Replacement of water lubricated seals not only reduces water consumption but also reduces the occurrence of equipment damage, maintenance time and wastewater generation. In some mills, pressurized air has been found to be used instead of water as sealing agent in vacuum pumps. 6. Use of efficient Decker thickener/ vacuum drum showers: It was found that in most of pulp and paper mills, Decker thickener as well as vacuum drum shower contained drilled perforation instead of nozzles. This results in large consumption of fresh water. An optimum nozzle design (e.g. Needle jet type,

Paper machine Flume tank water to vacuum pump sealing

Flume tank

Fresh water

To Water Conservation tank

Waste water (Hot)

Water Conservation tank

Freshwater make up

Flume tank water To Process



flat type, etc) with maintenance of appropriate pressure in the pipeline ensures optimum water consumption. Also with the passage of time, nozzle diameter gets widen due to corrosion. It is therefore recommended to monitor the functioning of showers regularly maintaining required pressure in the showers. Further by installing oscillating showers at bleaching and high pressure nozzles at pulp and paper sections improve the washing efficiency and reduce quantity of water required for washing. 7. Use of efficient shower system and regular monitoring of low pressure and high-pressure showers and in the paper machine section Paper machine showers are one of the largest users of fresh water in any pulp and paper mill, it is necessary to optimize water use in paper machine shower system. Design of an efficient shower system depends on the total number of shower nozzles, type of nozzle: needle jet, flat type, etc, the locations of the nozzles, jet angles and the distance between nozzles. Figure 35 depicts efficient paper machine shower system. For new plants, it is advisable to have only optimum numbers of paper machine felt/wire to minimize the water use. Further, It has been observed during field studies that most of the pulp and paper mills do not have any pressure gauge attached to the showers. Further, nozzle shape gets deformed due to corrosion and other reasons with time. This results in large consumption of fresh water. Fig 35: Efficient design of a paper machine shower

system



8. Use of High-pressure low volume showers: It is known fact that high-pressure showers consume lesser quantity of water and therefore can save water. 9. Use of back or recycled water in low-pressure showers: Clarified paper machine wastewater can be used in low pressure showers used as felt sprays after passing through a multiplex filter unit or so depending upon the quality of clarified paper machine wastewater achieved in the saveall. The various locations where this water can be used are: Wire section: Breast roll, wire turning and wire-return rolls, knock – off shower, trim knock – off shower, wire cleaning shower (low pressure). Press section: Cleaning of rolls The characteristics of recycled water that can be used in the paper machine section is as given below22:

Solids content (mg/l) Recommended use

0-50 Equivalent to filtered fresh water and can be used anywhere

50-75 Can be used in fixed orifice nozzles of 1 mm diameter and larger

75-100 Can be used in fixed orifice nozzles of 1.5 mm diameter and larger

100-200 Can be used in fixed orifice nozzles of 3 mm diameter and larger

10. Use of self-Cleaning showers in paper machine section It has been found that mills having self-cleaning showers in low-pressure showers only in paper machine section have been consuming fresh water 55 to 60% less23. 11. Choosing right type of saveall system There are several proven technologies to clarify paper machine wastewater or also called white water. Some of the popular ones used in the industry are listed here: A. Poly disc filtration system: Polydisc filtration system uses a number of hollow discs to achieve a high surface are of filtration. They produce two different qualities of filtrate. The filtrate initially

22 Source: A Good practice guide ‘ Practical Water Management in Paper and Board Mills” produced by accepta, www.accepta.com 23 Source: A paper on “ Water conservation in pulp and paper industry” by (Late) S. G. Rangan, Past President of IPPTA



produced has relatively high-suspended solids content is called cloudy filtrate and can be re-used for pulp dilutions. The next stage filtrate is produced once a mat of fibres has been built up on the disc surface which acts as a filter medium. The suspended solid concentrations in this filtrate is much less and can be easily used for variety of applications like paper machine showers, pump gland cooling/sealing, vacuum pump sealing, etc. Cloudy filtrate is suitable for use in pulp dilution, etc whereas clear filtrate is suitable for use in self-cleaning showers. Figure 36 &37 depicts the schematic diagram and a view of polydisc saveall system.

Fig 36: Clear/Cloudy Filtrate recycling system

Fresh water make upConsistency control Clear Filtrate

Filter drainsCloudy Filtrate Paper m/c 4 white water

make up

White WaterTank Clear Filtrate 250 Cu. M 100 Cu. M Centricleaner Reject

dilution

Excess to ETP

For Screen Dilution For Pulper Dilution To Showers

Fig 37: Polydisc Saveall



The saving in fresh water consumption by this system is expected to be 13.3 m3/Tonne or 26.6 m3/ tonne of pulp. B. Krofta / Gravity sedimentation type saveall: Krofta saveall is based on dissolved air floatation principle where as other on works on sedimentation. This has been effectively used in wastewater treatment system and has been also found very effective in fibre separation from the paper machine wastewater. Flocculating agents are used in both the system. Figure 38 depicts a krofta saveall installed in one of the pulp and paper mill in India.

Figure 38: Krofta saveall installed in a wastepaper-based mill C. Drum filters Drum filters use a rotating cylinder covered with a mesh that acts as the filtration medium. The filtrates produced contain suspended solids concentrations of 120 – 150 mg/l. These types of filters are frequently used in broke pulp thickening, decker thickeners, etc. D. Inclined / Hill Screens Inclined/Hill screens provide a simple separation system for the recovery of fibre and clarification of paper machine wastewater. However, they are less frequently used



due to lower quality of filtrate produced. Figure 39 depicts a Hill screen used in a mill in UK24 Figure 39: Hill Screen used for clarification of paper machine wastewater in a mill in UK 12. Optimum use of paper machine clarified wastewater in sections other than paper machine In order to make maximum use of paper machine clarified wastewater, it is important to have a sufficient storage capacity. The requirement of backwater in other sections is not regular and is often intermittent. The various applications of this water are

Decker thickener showers Vacuum washers Centricleaner reject dilution Pulp dilutions before bleaching stage, etc Johnson screen showers, etc.

Further, clarified water storage tank can be modified to enable further separation of fibres from the filtrate. One such design has been suggested by Arjo Wiggins5 called ‘Stowford ‘ separator. Figure 40 depicts stowford separator used as filtrate storage tank.

24 Source: A Good practice guide ‘ Practical Water Management in Paper and Board Mills” produced by accepta, www.accepta.com 5 Source: A Good practice guide ‘ Practical Water Management in Paper and Board Mills” produced by accepta, www.accepta.com



Figure 40t: The ‘Stowford’ separator that can be used as clarified wastewater

storage tank 13. Recycling of treated effluent for use within the mill for non-process In most of the mills, fresh water is used for the following purposes:

Plantation Gardening Floor washing & toilet flushing

Since quality of water is not essential for these activities, treated wastewater from ETP can be used. This will reduce fresh water consumption The saving in fresh water consumption by this system is expected to be 50 - 100 m3/d



14. Tertiary treatment of wastewater for recycling In order to recycle the wastewater completely back to the system, biologically treated wastewater requires to undergo a number of treatment processes to achieve nearly inlet water quality. In a pulp and paper mill, color removal is an important requirement to use the finally treated wastewater as process water. Figure below gives schematic diagram of treatment process. The wastewater after primary treatment involving physio-chemical separation is given secondary treatment. Secondary treatment uses microorganisms to accelerate the natural decomposition of organic waste. The two main methods used are aerated stabilisation and activated sludge treatment - both are known as aerobic treatments. The efficiency of these two systems varies widely, depending on climate, influent quality, pulp type, fibre source and mill practice. In ideal conditions, activated sludge performs better at reducing BOD and removing suspended solids. Other methods include anaerobic processes like USAB processes followed by aerobic systems have been successfully been used in the pulp and paper industry. The secondary treated wastewater is then sent to tertiary treatment plant. In tertiary treatment, Aluminum oxide, ferric oxide and polyelectrolytes assist coagulation of waste in the effluents, which are then sand filtered. Figure: Schematic diagram for tertiary treatment process The quality of treated wastewater after the tertiary treated is fit for recycling back completely to the system especially in wastepaper based mills and partially for other mills. III. Measures specific to individual category A. Small/Medium Scale wastepaper based Cultural – high-grade paper manufacturing mill 1. Using better quality raw material to achieve desired brightness: Manipulation of

raw material quality enables use of lesser quantity of bleaching chemicals, hence requires less water quantity for bleaching and washing.

Secondary treatment (e.g Aerobic / Anaerobic process)

Filtration process e.g, Rapid Sand Bed Filter, PSF, etc.

Activated carbon process

Membrane process or ion exchange, etc



B. Small/Medium Scale waste paper based Industrial and Cultural – low-grade paper manufacturing Mills Such mills can operate in closed loop water system. Following water conservation options can be adopted to achieve a nearly closed loop water system:

1. Segregation of different streams: First step is to segregate high COD stream from low COD stream. Wastewater generated from Vibratory screens, Centricleaners, Decker thickener, etc are high COD containing wastewater and those generated from paper machine section i.e. shower wastewater, vacuum pump sealing wastewater, floor washing, etc are low COD containing stream. The COD and BOD values of two streams are approximately as given below: High COD stream: COD = 25,000 to 30,000 mg/l, BOD = 10,000 to 12,000 mg/l Low COD Stream: COD = 2000 to 3,000 mg/l, BOD = 900 to 1000 mg/l 2. The two streams are to be treated separately. On such scheme is depicted in Figure below. :



Air

ChemicalSludge Drying Bed

High COD Stream Flash Mixer

Collection Sump

PumpPrimary Clarifier

Upflow Anaerobic FilterSludge

Low COD streamTreated Effluent

Equalisation cum Activated Sludge Process Secondary ClarifierNeutralisation Tank Primary Clarifier

Sludge

Filtrate



3. The final treated effluent will have following characteristics: pH: 7.0 – 8.0, TSS: 2000 – 2500 mg/l, COD: 80 – 120 mg/l, BOD: 20 – 30 mg/l 4. The treated effluent is suitable for recycling back in the process for following unit operation/process:

Hydropulper: For preparing wastepaper slurry Decker thickener: For washing and thickening of wastepaper slurry Centricleaning Vibratory screen showers

5. A part of treated effluent can be discharged out which can again be used for land irrigation, gardening, etc. Use of Fresh water will be limited to paper machine showers, for steam generation in the Boilers and for chemical preparation only. Fresh water requirement will be equal to the amount of water vapour lost during drying and the evaporation losses. C. Small/Medium Scale Agro based Cultural – high-grade paper manufacturing mill 1. Dry dedusting of straw for removal of fines and dust: Dry dedusting of straw will not only reduce water consumption for washing of raw material but also would avoid wastewater generation. A dry dedusting system would require Vibratory/ rotary screens, conveyers & dust handling system required. 2. Collection of black liquor spills in a common tank Black Liquor spills can be collected in tank and recycled back to the system. This reduces fresh water consumption required for floor washing. 3. Recycling of chlorine wash backwater completely into the system: After passing the unbleached pulp through a chlorination tower, it is washed in a conventional vacuum drum thickener cum washer. The filtrate generated from this washer contains mainly organo chlorine compounds. It has been observed that recycling of this filtrate completely back to the system with occasional bleeding does not effect the quality of bleached pulp produced. This not only saves fresh water consumption but also reduces AOX containing wastewater generation. This would result in saving of saving in fresh water consumption by 1.4. m3/ tonne of product 4. Recycling of part of the bleach wash back water into the system. Similar to chlorine wash backwater wash water generated from the Hypochlorite washer, Alkali extraction washer, etc can be partly recycled back to the system. Complete recycle is not possible. This would result in saving of saving in fresh water consumption by 76 m3/ tonne of product.



D. Small/Medium Scale Agro based Industrial grade paper manufacturing 1. Dry depithing of Bagasse: Pulp and paper mills involved in the manufacture of unbleached paper and paperboard need not remove 90% of the pith and hence can go for dry depithing. This will not only reduce fresh water consumption for washing of raw material but also would avoid wastewater generation. Not only this, wastewater generated from wet depithing of Bagasse is more difficult to treat. E. Large/Medium Scale wastepaper based high-grade Cultural paper manufacturing mills 1. Use of More Efficient Deinking Plant Use of efficient Floatation system for deinking and reuse of back water generated from thickener washer and screw press in the deinking process again. This requires use of good flocculating aid at optimized quantity. Figure 41 depicts the one such scheme.

Figure 41: Recycling system in deinking plant The clarified water is reused in different unit operations:

• Helicopulper

• H D Cleaner

• Pulp Dilution

• Centricleaner

• Pressure screen

Cleaned pulpConsistency = 0.7%

Fresh water

Fresh water DNT

Thickener

Wastewater Boseidon System (DAF)Clear water

for reuseScrew Press Sludge

Sludge Decanter

Pulp Consistency = 30%



This results in saving in Fresh water consumption by 76.5 m3/ADMT of DIP pulp 2. Manipulation of raw material quality To achieve desired brightness in the finished product, better quality wastepaper can be used. This reduces use of water for washing and bleaching. 3. Enzymatic deinking process Enzymatic deinking has been proved as environmental friendly solution for recovered paper recycling. Enzyme in deinking reduces conventional chemical use. This would reduce washing water usage. Figure 42 below depicts one of the schemes for enzymatic deinking:

Figure 42: Enzymatic deinking system (one stage)

WastepaperEnzyme

Backwater

13 - 16% ConsistencyPulper

Vacuum filter

Coarse screen

High Density Cleaner

screw press

Bleaching chemical

Perforated screen Centricleaner kneader

Floatation cellsStorage Tower



4. Membrane filtration technique in deinking process instead of conventional floatation method25 Water-based inks used in flexographic news printing remain one of the most troublesome contaminants and present a unique challenge to the deinking operation. Most newspaper deinking plants are designed to remove the oil-based inks most commonly used in newsprint publication. These facilities tend to rely on froth flotation for ink removal. However, it is well established that the conventional flotation process is ineffective at removing flexographic inks. Under alkaline repulping conditions, flexographic inks form colloidal dispersions of small hydrophilic particles (<5 µm) stabilized by the ionized binder via an electrostatic mechanism. Flexographic ink particles dispersed in the pulp suspension are then too small and/or too hydrophilic to float at a good rate in flotation cells. Since flexographic inks form very small hydrophilic dispersions under alkaline repulping conditions, they are particularly well suited for removal by washing deinking technology. However, large quantities of filtrate are produced by washing which cannot be directly recycled to the process without detrimental effects on brightness of the deinked pulp or discharged to the environment. However, the deinking efficiency of a wash deinking process is strongly dependent on removal of the ink from the washer effluent. Therefore, the wash effluent must be clarified of the flexographic pigments. In practice, most deinking plants have some process water clarification as part of a washing stage. Dissolved air flotation (DAF) is one of the most common types of process water clarification used in deinking mills. However, the presence of flexo-printed materials in the furnish seriously impacts DAF clarification and necessitates significantly higher levels of coagulant to achieve a proper clarified water quality. Membrane separation technology is a potentially attractive method for the removal of flexographic ink residues from the wash filtrate effluent of deinking mills. One such scheme is shown in Figure 43.

25 Source: Flexographic Newspaper Deinking: Treatment of Wash Filtrate Effluent by Membrane Technology B. CHABOT, G.A. KRISHNAGOPALAN and S. ABUBAKR, JOURNAL OF PULPAND PAPER SCIENCE: VOL. 25 NO. 10OCTOBER 1999



Figure 43: Membrane based de-inking system H. Large/Medium Wood based high-grade Cultural Paper and Paperboard manufacturing Mill 1. Dry debarking of Wood 2. Recovery of bleaching chemicals through membrane separation & reuse (closed loop bleaching) For Mills with Elemental Chlorine free bleaching process Results have proven that both the coagulation/flocculation and the ultra/ nanofiltration technologies26 can be considered as an available kidney to remove organic materials from the alkaline bleach plant effluents. In closed-loop bleach plant operation, the build-up of COD in the bleaching stages leads to an increased chemical consumption. By using membrane filtration, this negative effect could be strongly reduced in an ECF sequence where EOP stage filtrate can be recycled to the post oxygen washing system. The risk for scaling of calcium carbonate (EO and EOP stages) and calcium oxalate (Ql or Do stages)

26 Source:FAIR-CT96-1360: Separation Methods for Closed-Loop Technology in Bleached Kraft Pulp Manufacture, November 2000, Final Report Abstract



would increase by increased closure. Addition of magnesium would be recommended in order to avoid the formation of calcium oxalate. This would result in saving of saving in fresh water consumption by 18.7 m3/BDMT of bleached pulp or 6.6 m3/ tonne of product 3. Indirect & More Efficient Heat Transfer System for Blow Heat Recovery In Digester Section In most of the mills, blow heat recovery system consists of direct heat transfer system as depicted below. In this system, hot water generated is contaminated due to lignin presence in the flash vapors. If instead of direct injection of fresh water into the dirty accumulator, indirect heat transfer is installed, hot water produced can be used for other operations in the pulp mill like bleach washing, pulp dilution after bleaching operation etc. Condensate generated can be either drained to ETP or can be recovered by installing online conductivity meter in the condensate collection pipe. And only pure condensate can be sent back for recovery to boiler house. Measures in Chemical recovery Section 1. Replacing barometric leg (direct) condenser cooling by surface (indirect) condenser cooling In older plants, multiple effect evaporators work on barometric leg principle. Barometric leg requires around 3000 ~ 400 m3/d of water. The wastewater from

Blow tank

Flash vapor Primary Condenser

Secondary y CondenserFlash vapor +

condensate

Condensate

Dirty Accumulator

Fresh Water

Overflow Hot water to Hot water tank

Vapors to atmosphere



barometric leg is generally discharged to ETP. Replacing barometric leg with surface condenser. 2 Reuse of secondary condensate in raw material preparation section: Combined condensate of chemical recovery plant can be used for washing in final brown stock washer and in raw material wet cleaning system. 3. Secondary Condensate from Soda Recovery Plant to be Used For Brown Stock Washing / Bleach Washing Secondary condensate can be used in brown stock washing. This would result in saving of fresh water consumption by 200 m3/d. 4. Reuse of Spout cooling wastewater: Spout cooling water is a non contact water and is therefore not contaminated back after passing through cooling system 5. Reuse of barometric leg wastewater: In the old plants, vacuum in the evaporators, Limekiln is generated by barometric leg condensers which uses large amount of fresh water for cooling. Since cooling of the vapours is done by direct contact with the water, the wastewater sometimes is contaminated with organics present in the vapour in case of multiple effect evaporators in Chemical recovery section. This wastewater is suitable for reuse in Brown stock washing. Further, instead of using fresh water for cooling in the barometric leg, backwater can be used. However in case of limekiln section, the wastewater is not contaminated and can be recycled back after passing through cooling system. 6. Reuse of vacuum pump sealing wastewater: Vacuum pump sealing wastewater from Chemical recovery plant and causticisation plant is non-contaminated wastewater and can recycled back. Measure in Utility Section 1. Reuse of wastewater from DM plant (regeneration & sand filter backwash), softener (regeneration & sand filter backwash) for ash conditioning / quenching Since ash conditioning/quenching is a physical process and it does not require very good quality water, DM plant regeneration and sand filter backwash can be used. Saving in fresh water consumption, m3/ tonne of product= 1.68 2. Reuse of Water Drained from Pressure Sand Filters & Activated Carbon Filters It has been observed in some of the mills that during back-washing/regeneration of Pressure sand bed filter (PSF) & activated carbon filter (ACF), first the filters are taken out of service line and the water present in the filters are being drained to ETP. This water is raw fresh water and can be directly taken to raw water storage tank. This requires installation of an additional pipeline. 3. Re use of Backwash water from PSFs & ACF



The backwash water from PSF & ACF contains only suspended particles and instead of discharging it to the ETP, it can be reused for gardening, plantation, etc. This will lead to a saving of about 86.4 m3/day of raw water consumption.

Limitation In Continuous Recycle/Reuse Of Wastewater A. Product quality specifications often limit the extent of recycling. For example food grade products have an upper limit for chloride ion concentration. This limits the maximum recycling of paper machine wastewater. B. Continuous water recycling system also causes slime formation. This can be prevented by optimized addition of biocide and chemical. C. Closing the paper machine white water system can cause increase in temperature and this requires use of suitable material of construction, greater use of plastics



CONCLUSION

Existing standards are passé. The questionnaire responses, CSE’s green rating project and the detailed field studies have clearly indicated that the majority of industries in-fact actually performing better than both the existing standards and the CREP standards they have agreed to. Common standard not far-sighted It has also clearly emerged from the in depth studies that water consumption varies significantly based on the scale of operation, raw material used and the end products manufactured. Hence a common standard for all type of industries would not be prudent and accordingly standards have been developed for six categories of pulp and paper industries considering operational scale, raw material used and the end product manufactured. Recommended standards a challenge already conquered While comparing with the existing standards, the currently recommended standards may seem to be a challenging task to achieve but actual practice these have already been achieved in totality by an Indian enterprise (Best achieved standard) or partially i.e. at a mill process level by one or the other Indian enterprise (benchmark standard). Hence the proposed standards are practical and feasible to achieve. The industries may refer to the water conservation measures identified under the study to achieve the water consumption standards. Let’s not stop, we need to go further The currently developed and recommended water consumption standards are still comparably high in light of the latest world wide trends on water consumption. The currently developed standards should be treated as short term applicable for about 8 years. It is further recommended that these standards should again be revisited after 6 years.

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