advancement in cement technology

8/9/2019 Advancement in Cement Technology

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T3 146

Indian Cement Industry: A Technology Perspective

Dripto Mukhopadhyay

Indian cement industry has passed through many ups and down. It was under strict

government control till 1982. Subsequently, it was partially decontrolled and in 1989, the

industry was opened for free market competition along with withdrawal of price and

distribution controls. Finally, the industry was completely de-licensed in July 1991 under the

policy of economic liberalization and the industry witnessed spectacular growth in production

as well as capacity. Over time, the industry has also witnessed spread of the plants in several

regions of the country as presented in Table 1- 2, which were previously concentrated in

close proximity to the raw material.

Fig 1. Capacity, Production and Capacity Utilization in Indian Cement Industry

0

50

100

150

200

250

1950 1980 1900 2000 2009CapacityandproductioninM

T

Capacity Production


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Table 1: Distribution of Cement Plants with Installed Capacity above 0.50 MnT

StateInstalled Capacity above 0.5 Million Tonnes

No. of Plants Percentage Share

Andhra Pradesh 32 21.33

Assam 1 0.67

Bihar 1 0.67

Chhattisgarh 8 5.33

Gujarat 11 7.33

Haryana 2 1.33

Himachal Pradesh 5 3.33

Jharkhand 3 2.00

Karnataka 8 5.33

Madhya Pradesh 11 7.33

Maharashtra 9 6.00

Meghalaya 1 0.67

Orissa 4 2.67Punjab 2 1.33

Rajasthan 18 12.00

Tamil Nadu 17 11.33

Uttar Pradesh 8 5.33

Uttarakhand 2 1.33

West Bengal 7 4.67

Table 2: Distribution of Cement Plants with Installed Capacity Less than 0.5 MNT

State

Installed Capacity less than 0.5 Million Tonnes

No. of Plants Share in %

Andhra Pradesh 3 9.09

Assam 1 3.03

Chhattisgarh 2 6.06

Delhi 1 3.03

Gujarat 3 9.09

Haryana 1 3.03

Himachal Pradesh 1 3.03

Jammu & Kashmir 1 3.03

Jharkhand 2 6.06

Karnataka 3 9.09Kerala 2 6.06

Madhya Pradesh 1 3.03

Maharashtra 1 3.03

Meghalaya 3 9.09

Punjab 1 3.03

Rajasthan 2 6.06


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Technologies Adopted by Indian Cement Industry

Generally cement manufacturing process involves following stages:

1. Quarrying raw materials

2.

Crushing

3.

Pre-homogenization and raw meal grinding

4.

Pre-heating

5.

Precalcining

6.

Clinker production in the rotary kiln

7.

Cooling and storing

8.

Blending

9.

Cement grinding

10.

Storing in the cement silo

India is the second largest cement producing country in the world with a distinction of

operating plants with varying capacity and varying technologies. Some of the modern plants

can be compared to the best plants in the world in terms of variety, quality and energy

efficiency. Indian cement industry remained proactive in adopting technological

advancements taking place all over the world. The share of energy inefficient wet process

plants had slowly decreased from 94.4% in 1960 to 61.6% in 1980. Currently, the share of

wet process is only about 1% according to industry sources.

During the 80's and 90's, major technological advancements took place world over in design

of cement plant equipment/systems primarily in the following major areas:

a)

Pre-calcination

b)

High pressure grinding

c)

Automation in process control

d) High efficiency particle separation

e) Clinker cooling

These resulted in significant transformation of the production process globally. The Indian

cement industry closely followed the international trend. Energy conservation has been the

prime objective that propelled major technological changes in the industry. A few recent

technologies that helped Indian cement industry to consolidate in sustained energy savings

are broadly discussed below.

Raw Material Grinding: Raw material grinding is a critical mechanical operation that

determines the sizing of equipment in cement plant. This process consumes about 20% of


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total energy consumed in the plant. Depending on the raw materials physical characteristics,

various grinding systems are used in Indian cement industry:

a) Ball mills

b)

Vertical Roller Mills (VRM)

c)

Ball mills with high pressure grinding rolls.

d)

High pressure grinding rolls

e) Horizontal roller mills

Vertical roller mills have been widely accepted for combined grinding and drying of moist

raw materials due to their excellent drying capacity and low energy consumption. While a

number of plants are still using ball mills, many have installed pre-grinders like roller press to

improve energy efficiency. Here, the extent to which the roller press is loaded determines the

efficiency of the grinding circuit. Use of roller press alone as a finish grinding equipment to

give the final product is also a new development.

Horizontal roller mill is yet another improvement in grinding systems incorporating the

advantages of vertical roller mill and roller press. An additional advantage with the horizontal

roller mill is its low space requirement. A compact horizontal roller mill with an in-built

separator is now in the process of development. This kind of a mill would eliminate many

small conveyors carrying material to separator and from separator.

The efficiency of the grinding circuit and power consumption of the mill fan largely depend

on the performance of the classifier. Perhaps classifier is the part that has undergone

maximum changes and has been the target part for efficiency improvement. A variety of high

efficiency classifiers are employed in grinding circuits.

Pyro-processing: Pyro-processing section in a cement plant comprises pre-heater, rotary

kiln and clinker cooler. This section is considered as the main element of cement plant as

cement clinker formation takes place in kiln. This section determines the size of a cement

plant as well as sizes of all other equipment. With the introduction of pre-calciners in 80's,

the size of cement plant had considerably increased. With technology upgradation, a kiln size

of 7000 tpd is considered as an economic size which was at the level of 600 tpd in 70s.

Pre-heaters can be classified into the following 5 categories irrespective of the manufacturer.

Pre-heater without calciner

Inline calciner with air passing through the kiln

Inline calciner with external tertiary air duct


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Separate line calciner

Separate line calciner with inline calciner

Cyclones are basic units in a pre-heater system. Efficiency of cyclones depends on pressure

drop and change of temperature of gas across each stage. Introduction of Low Pressure drop

(LP) cyclones has brought the pressure drop across each stage to around 50 mm WG from

around 150 mm WG in conventional cyclones. A typical 6 stage pre-heater with LP cyclones

will have a pre-heater exhaust gas temperature of around 2500C and draught of around 500

mm WG. This in turn leads to decrease in pre-heater fan power consumption. The reduced

temperatures at pre-heater exhaust contribute to environmental improvement.

The burners also play an important role in determining the thermal efficiency of the pyro

processing system. There has been a continuous effort on operating the burners with the least

possible primary air. Multi-channel burners that consume only 5% primary air are being used

in many plants. This leads to a direct thermal energy saving of 15 kcal/kg clinker. These

modern burners also facilitate easy flame control in the process.

Clinker cooler is also critical for the production process. It has dual functions, i.e. reducing

the temperature of the clinker to an acceptable level for further transport as well as grinding

and recover energy from the heat of the hot clinker by heating the cooling air. Mainly two

types of clinker coolers are used at present in cement industry. They are:

a) Grate cooler

b) Planetary cooler

Conventional grate coolers are still used by many plants due to comparatively higher thermal

efficiency though they account for several bottlenecks. There have been a number of design

improvements in grate coolers in recent times, mainly on grate plate to improve the

efficiencies simultaneously reducing the cooling air intake. More and more cement plants

with conventional grate coolers are retrofitting the coolers with high efficiency coolers. This

has resulted in low electrical energy consumption in cooling air fans and also in cooler ID

fan.

Cement Grinding: Cement grinding is another energy intensive operation. Cement

grinding consumes around 25-30% of the total energy consumed in a cement plant. Typical

cement grinding systems in use are:

Open circuit mills

Closed circuit mills


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Roller press with open circuit ball mill

Roller press with closed circuit ball mill.

Roller press in finished mode

Vertical roller mill

Horizontal roller mill

For many years Ball Mills were in use in open circuit and closed circuit mode. In recent past,

roll press as has been introduced and this has led to substantial reduction in energy

consumption. Use of vertical roller mill for cement grinding is also very recent and the

performance results are reported to be encouraging. Horizontal roller mills combine the

advantages of roll press and vertical roller mill. These mills are reported to be highly energy

efficient. Horizontal roller mills are best suited for slag grinding.

Separator is crucial equipment in cement mill section as it has direct bearing on production

and quality of cement and energy consumption. High efficiency separators are used in

modern cement plants and old plants are also going for a retrofit. Apart from these, auxiliary

items like mill liners and diaphragms have also been improved continuously over time and

these items in different designs are available contributing to energy reduction in cement

grinding.

Table 3: Technology of Indian Cement Industry at a Glance

Low Technology Plants Modern Plants Global Technology

Mining and

Material HandlingConventional Computer aided Computer aided

Crushing Two stage Single stageIn-pit crushing &

conveying

Conveying of

Limestone

Dumpers/Ropeway/

TippersBelt conveyors

Pipe conveyors, Belt

conveyors

GrindingBall Mills with / without

conventional classifier

VRMs, Roller Presses

with dynamic classifierVRMs, Roller Press

Pyro-Processing

Wet

Dry

-5/6 stage pre-heater

- High efficiency coller

Multi-channel burner

Dry

6 stage pre-heater

High efficiency coller

Multi-channel burner

Semi Dry

Dry

-4 stage pre-heater

- conventional coller

- Single channel burner

Co-processing WDF

Co-generation of power

Low Nox/SO2 emission

technology

Blending &

Storage

Batch Blending silosContinuous Blending

silos

Continuous Blending

silos

Multi-chamber silos


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T3 156

Fig 7. Trend of Thermal Energy Consumption in Indian Cement Industry

Source: Adopted from Raina, S. J. (2002), Energy Efficiency Improvement in Indian Cement Industry, National

Council for Cement & Building Materials, paper prepared for IIPEC Programme.

Production of blended cement is also another outcome of the new researches in theindustry.

Blended cements are hydraulic binders in which a part of portland cement is replaced by

other hydraulic or non-hydraulic materials. They display some superior properties directly

related to durability apart from normal properties of Portland cement. It has been found that

fly ash generated in thermal power plants and slag generated in steel plants is suitable for

manufacture of blended cements. Fly ash or slag is inter-ground with cement clinker to

produce blended cement. Many developed countries started using such blended cements in

large quantities in construction of critical structures such as rocket launch pads, sea water

jetties, large dams etc. Production of blended cements directly increases the plant capacity

without any need for creating additional clinker making capacity. This reduces the limestone

usage and fuel usage in cement plants and in turn lessens the greenhouse gases emissions.

Increasing scarcity of good quality coal and power at an attractive price and an ever

increasing energy cost to total production cost are forcing the Indian cement industry to look

for alternate fuels. Use of cheap alternate fuels like lignite, pet coke, rice husk, groundnut

shells etc. is in practice now. In some European cement plants the cost of fuel is reported to

be zero due to the use of 100% waste fuels. In fact, in many cases the cement plants are paid

Dry Process Kilns

120 TPD 4-ST KilnsPC Kilns

Wet to Dry Conversion

5-Stage PC Kilns

6-Stage PC Kilns & MultiChannel Burners

High Efficiency Coolers

700

900

1100

1300

1500

1700

1960 1970 1980 1900 2000

KCAL/KGCL


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for burning the municipal and industrial wastes in such places. Indian cement industry should

also look for such alternatives. However, this requires development of infrastructure at

cement plant site as well as waste generation and collection infrastructure.

advancement in cement technology

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