final report of plasma gasification

7/29/2019 Final Report of plasma gasification

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A PROJECT REPORT ON PLASMA

GASIFICATION OF PLASTIC WASTE FOR

GENERATIONOFSYNGAS

SUBMITTED BY -:

Anirmoy Debnath

&

Utkarsh Sharma

Of

National Institute of Technology, Durgapur

UNDER GUIDANCE OF Dr. BISWAJIT RUJ (CMERI,DURGAPUR)


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ACKNOWLEDGEMENT

We have taken efforts in this project. However, it would not have

been possible without the kind support and help of many individuals.We would like to extend our sincere thanks to all of them.

We are highly indebted to Dr.B.Ruj for his guidance and constant

supervision as well as for providing necessary information regarding

the project. Without his esteemed support, it would not have been

possible.

We would also like to thank Dr. P.K.Chatterjee for allowing us to

work on such an upcoming technology.

We have gathered extensive knowledge in the field of mentioned

topic of project which surely benefit us in near future.

Anirmoy Debnath

Utkarsh Sharma


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CONTENTS

1. Introduction

2. History of Plasma Technology3. Types of Waste

4. Plasma Technolgy

5. Detailed Theory

6. Process Description

7. Experimental Process

8. Observations9. Model Development

10. Advantages of Plasma Technology

11. Conclusion

Bibliography


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INTRODUCTION

A factor common to all developed countries is the generation of excessive amounts of waste

per capita. As societies developed, the amount of waste material generated has increased to a

level that is becoming unmanageable .This, together with the increasing awareness of the

general public for the damage caused to the environment, explains the need to plan for and

implement sustainable and integrated strategies for handling and treating wastes.

Plasma gasification is a technologically advanced and environmentally

friendly process of disposing of waste and converting them to usable by-products. It is a non-

incineration thermal process that uses extremely high temperatures in an oxygen starved

environment to decompose completely the input waste material into very simple molecules.

The products of the process are a combustible gas, known as synthesis gas, and an inert

vitreous material, known as slag. Furthermore, it consistently exhibits much lower

environmental levels for both air emissions and slag leachate toxicity than competing

technologies, e.g. incineration.

Standard gasification technologies operate the reactor in the 400850C

range. They do not use any external heat source and rely on the process itself to sustain the

reaction. Normal gasifiers are really partial combustors, and a substantial portion of the

carbon is combusted just to support the reaction. Their gasification process produces a fuel

gas similar to the gas produced by the plasma process, although it is much dirtier and

contains char, tars and soot. The lower temperatures cannot break down all the materials.

With standard gasification, many materials must be sorted out of the waste stream before

reaching the reactor and landfilled or processed in other ways. Because of the low

temperature used, the gas that is produced by a standard gasifier has tars that are difficult to

remove and other contaminants that must be further cleaned. The char residue is up to 15% of

the weight of the incoming material and must still be landfilled.

In addition to these drawbacks, most standard gasification systems cannot feed

heterogeneous waste, e.g. municipal solid waste, directly from the truck. Plasma gasification

uses an external heat source to gasify the waste, resulting in very little combustion. Almost

all of the carbon is converted to fuel gas. Plasma gasification is the closest technology

available to pure gasification. Because of the temperatures involved, all the tars, char and

dioxins are broken down. The exit gas from the reactor is cleaner, and there is no ash at the

bottom of the reactor.


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In this work, the basic energy & mass balance of plasma gasification of the

plastic & polymeric waste is being discussed upon due to the fact that this fraction is linked

to a greater extent to the energy terms of analysis. On the other hand, the plasma treatment of

the inorganic fraction of the solid waste results in its vitrification that is of great importance,

mainly for its environmental performance and not for its energetic characteristics. More

specifically, the objective of this work is the development of a mass & energy model that can

describe the plasma gasification process.

HISTORY OF PLASMA TECHNOLOGY

Plasma as a method to generate heat is a proven, well-demonstrated commercial

technology at work around the world. In the 19th century, plasma technology was

developed and used in Europe for the metals industry. At the beginning of the 20th

century, the chemical industry used plasma heaters to extract acetylene gas from natural

gas. In the early 1960s, the United States National Aeronautics and Space

Administration used plasma technology to simulate the high temperatures that orbiting

space vehicles would encounter when reentering earths dense atmosphere. In the 1980s,

large-scale plasma heater processes were built and commissioned for a variety of

industrial applications, particularly for metals and chemicals.

Although plasma technology has a long track record, its application to waste disposal is

limited. During the past twenty years, the use of plasma technology for waste

disposal has undergone extensive research and small-scale development. It has been

tested and evaluated on many types of wastes, including automobile shredder residue,sludges, asbestos fibers, medical waste, and MSW. This R&D effort is continuing and

some small-scale commercial plasma facilities for disposing of waste have been

operating for more than a decade.


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TYPES OF WASTE

First, it presents an overview of four types of waste that are currently being addressed with

Plasma Technology worldwide:

MSW includes most household trash, such as paper, plastic, metals, and organic

Waste.

Hazardous waste includes various toxic industrial wastes.

Medical waste is a specific type of hazardous waste. It may be disposed through

incineration or subjected to autoclaving, microwaves, radio waves, with the

disinfected waste being landfilled.

Incinerator ash is the residue from a WTE plant.

PLASMA TECHNOLOGY

Second, the Report discusses plasma technology and the differences between Plasma

Technology and state-of-the-art WTE. A plasma arc facility is a system consisting of

three parts: (1) the plasma reactor, (2) environmental controls, and (3) a power

generation unit (optional).

The plasma reactor is an enclosed chamber into which the waste is fed.

Plasma torches provide the heat, 3000C or higher, in the chamber which converts

organic material to a gas and inorganic material into a glassy slag. The plasma

facility may generate electric power, using the fuel gases produced in the reactor.

These fuel gases may be combusted in a waste-heat boiler, or cleaned and fed into a

combustion turbine or other combustion device. However, the plasma facility must

be large enough, in terms of waste throughput,to justify the cost of a powergeneration unit. The environmental controls on a plasma facility will be located

downstream of the reactor and may include scrubbers, a carbon injection system, or a

baghouse, whether or not the facility is generating electricity.


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WASTE AND WASTE DISPOSAL

Understanding the use of plasma arc gasification and vitrification technology for waste

disposal first requires some understanding of the types of waste that require disposal and the

methods typically used to dispose of the waste. Waste is a very general term that can be

sub-divided in many different ways. For the purposes of this report, we will focus on the four

types of waste that are currently being disposed in one or more plasma arc facilities

worldwide. The four types of waste are:

1. Municipal Solid Waste (MSW),

2. Hazardous Waste,

3. Medical Waste, and

4. Incinerator Ash.

These wastes differ from each other and disposing of each presents a somewhat different set

of problems.

MUNICIPAL SOLID WASTE (MSW)

MSW consists of everyday items such as product packaging, grass clippings, furniture,

clothing, bottles, food scraps, appliances, and batteries. Taken as a whole, MSW is highly

variable. That is, MSW includes many different types of materials paper, metal, plastic,

vegetable matter, glass, and animal wastes. Heterogeneity is a key characteristic of MSW.

HAZARDOUS WASTE

Hazardous waste is a broad category of wastes that includes, but is not limited to,industrial

wastes, radioactive wastes, and toxic substances. Because of the dangers of handling,transporting, and disposing of hazardous waste, their management is carefully regulated by

the USEPA. Because of the danger to human health and the environment,hazardous wastes

must be destroyed or rendered harmless. Although hazardous wastes include a wide variety of

materials, the facilities that transport, store, and dispose of these wastes typically manage a

relatively narrow range of materials, such as hazardous chemical wastes or medical wastes

(see below). Facilities are designed to handle specific types of hazardous wastes.The

individual hazardous wastes are more homogeneous than MSW. The primary means of land


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disposal of liquid wastes is deepwell injection.Thermal treatment includes both energy

recovery and incineration.

Medical WasteMedical waste is one specific type of hazardous waste.Medical waste is defined as any solid

waste generated in the diagnosis, treatment, or immunization of human beings or animals,in

research pertaining thereto, or in the production or testing of biologicals. It includes, but is

not limited to, body organs, tissue, blood-soaked bandages, needles used to give shots or

draw blood, and discarded surgical instruments.Like other hazardous wastes, the disposal of

medical wastes is carefully regulated.These wastes are also relatively homogeneous. Other

methods of sterilization include subjecting it to high-frequency radio waves, microwaves, or

steam auto-claving. For facilities that disinfect the material, the residue is typically landfilled.

INCINERATOR ASH

The combustion of the MSW in these waste-to-energy WTE plants results in an ash which

must then be disposed. The amount of ash produced represents approximately 25 percent of

the amount of MSW disposed in the WTE plant. The ash from a WTE plant is less

heterogeneous than the MSW.Assuming that 25 percent of the 35 million tons of MSW

disposed in WTE plants became ash, approximately 8.75 million tons of ash .

Table 1 summarizes the characteristics of the four types of waste discussed above.

Table 1

Four Types of Waste

Type of Waste Typical Constituents Conventional Disposal

Facilities

MSW (2) Household trash, paper, plastic,

metals, organics

Landfills, WTE plants

Hazardous (3) Chemical waste, radio-active

material, heavy metals.

Incineration, deepwell injection

Medical (4) Body parts, tissue, blood. Incineration, microwaves, auto-

claving

Ash (5) Incinerator ash Landfilling


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To understand the advantages and issues of disposing of these types of waste in a plasma arc

facility, it is necessary to understand some basic principles of plasma technology.

DETAILEDTHEORY

The Plasma cell used for the generation of syn gas consisted of

1. A voltage regulator

2. Screw feeder mechanism

3. Furnace

4. Scrubber

5. Blower

The idea was to produce a syngas (synthetic gas) from the gasification of the plastic waste.

The plasma heat is used to provide the heat for gasification, to produce the syngas. The

syngas product is combusted in a gas engine or turbine generator on-site to produce

electricity. Some of the thermal energy in the gas stream can be also recovered in a steam

boiler and the steam can be used to produce additional electricity.

The electrical energy of the torches goes into the plasmawhich transfers its energy to the

substances to be treated, thereby triggering a dual simultaneous reaction process in the

plasmachemical reactor: the plastic wastes are thermally decomposed into their constituent

elements (syngas with more complete conversion of carbon into gas phase than in

incinerators), and the inorganic materials are melted and converted into a dense, inert, non-

leachable vitrified slag, that does not require controlled disposal. Therefore, it can be viewed

as a totally closed treatment system.


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PROCESSDESCRIPTION

The block diagram presented in Fig. 1 includes the main sections of a plasma waste treatment

plant. The waste feed sub-system is used for treatment of each type of waste in order to meet

the inlet requirements of the plasma furnace. For example, for a waste material with high

moisture content, a drier will be required. However, a typical feed system consists of a

shredder for solid waste size reduction prior to entering the plasma furnace.

The plasma furnace is the central component of the system where gasification/vitrification are

taking place. One graphite electrode, as a part of the transferred arc torche, extend into theplasma furnace. An electric current is passed through the electrodes, and an electric arc is

generated between the tip of the electrodes & the conducting receiver, i.e. the slag in the

furnace bottom. The gas introduced between the electrode and the slag that becomes plasma

can be oxygen, helium or some other, but the use of air is very common due to its low cost.

The gas cleaning sub-system has to achieve the elimination of acid gases (HCl, SOx),

suspended particulates, heavy metals and moisture from the synthesis gas prior to entering the

energy recovery system. The energy recovery system can be based on a steam cycle, gas

turbine cycle or a gas engine. Depending on the quality of the produced synthesis gas, the


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best option can be one of the above energy recovery scenarios. In addition, alternatively, the

energy recovery system can be a chemical fuel production unit, such as for hydrogen or

methanol.

EXPERIMENTALPROCESS

The first step was input of plastic waste which is free from dust and crushed uniformly. Feed

is regulated through a mechanism where screw rotates and places the feed just near the

plasma torch that is produced in the plasma gasifier. This mechanism ensures a uniform feed

rate into the furnace so that the gases are produced uniformly.

The gasifier consists of two carbon rods with high voltage applied at one rod while other

one at ground potential. A proper short distance is maintained between the ends for the

generation of arc which produces a very high temperature. The feed when comes in contact

with the arc, it gets converted into basic molecular components. In a oxygen controlled

environment, a variety of gases are being produced which consists of many combustible

gases. This gaseous mixture so produced is called as syn gas and a glassy slag is developed

at the bottom which is taken out after hardening at the end of the process.

The various analysis such as mass balance, energy balance, gas mixture ratio, etc were

carried out on the results obtained from model of gasifier so that a rough idea of efficiency

of gasifier model is obtained and hence its applicability in the areas of industrial usage and

removal of plastic waste .


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OBSERVATIONS

Many runs were carried out but unfortunately due the various problems such as Gas analyzer

not calibrated, no flow rate of syngas recorded etc, all the runs were abandoned. Mainly 2-3

successful runs were there whose detailed readings are shown below:-

Temperature Distribution across the Furnace

(Part-I situated at the top of the reactor)

Thermocouple distance & temperature from electrode rod DISTANCE FROM

CARBON PLATE(mm)

POSITION TEMPERATURE(C) DISTANCE(mm) 380

1st 505 25

2nd 490 100

3rd 450 175

440

450

460

470

480

490

500

510

0 20 40 60 80 100 120 140 160 180 200

Temperature(C)

Distance(mm)


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(Part-II situated at the middle of the reactor)


CARBON PLATE(mm)

POSITION TEMPERATURE(C) DISTANCE(mm) 220

1st 665 25

2nd 620 100

3rd 570 175

(Part-III situated at the bottom of the reactor)


CARBON PLATE(mm)

POSITION TEMPERATURE(C) DISTANCE(mm)60

1st 792 25

2nd 767 100

3rd 668 175

560

580

600

620

640

660

680

0 20 40 60 80 100 120 140 160 180 200

Temperature(C)

Distance(mm)


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The core temperature that was recorded is 3500C.

Energy meter readings

a) Initially (Arc starts) 384.4 kWhr

b) At feeding start 389.4 kWhr

c) When feeding stops 397.2 kWhr

d) Time for which feeding is done 45 min

Feed Rate 5kg/hr (42 volts)

Voltage is adjusted through a variac for getting a constant feed rate as screw-feed mechanism

is operated using it.

Gas analyzer was being used to get the components present in the syngas generated. It was

calibrated using gas cylinders of constant composition. It showed the reading of CO, H 2 and

hydrocarbons present mainly consisting of methane and ethane.

660

680

700

720

740

760

780

800

0 20 40 60 80 100 120 140 160 180 200

Temperature(C)

Distance(mm)


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CO (%) H2 (%) CnHn (%)

6.5 16.3 26.4

6.2 15.8 27.4

5.8 15.7 33.46.0 17.1 35.0

4.8 13.7 51.4

4.2 9.6 14.8

2.7 7.6 12.0

1.7 4.8 9.0


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MODELDEVELOPMENT

MODELLING OF GASIFICATION PROCESS

The central part of the plasma gasification process is the plasma furnace. The thermo-

chemical conversion process that takes place inside the plasma furnace can be described well

by the term gasification, and the model development will be based on the chemical

reactions that describe better the gasification process. During the plasma gasification process,

various chemical reactions take place that are difficult to be reproduced by a simple

equilibrium model. Nevertheless, models based on thermodynamic equilibrium have been

used widely, and they are convenient enough for process studies on the influence of the most

important waste and process parameters. The following simplified chemical conversion

formulas describe the basic gasification process.

C(s) +H2O=CO+H2O (Heterogeneous water gas shift reactionendothermic)

C(s) +CO2=2CO (Boudouard equilibriumendothermic)

C(s) +2H2=CH4 (Hydrogenating gasificationexothermic)

CH4+H20=CO+3H2 (Methane decompositionendothermic)

CO+H2O=CO2+H2 (Water gas shift reactionexothermic)

For the development of a model approach, the number of independent reactions has to be

determined by applying the phase rule, as described by Tassios. In the case where no solid

carbon remains in the equilibrium state, only two independent reactions need to be considered

for the equilibrium equations. In the case of some remaining solid carbon, i.e. soot, in the

gasification products, three independent reactions have to be considered in the equilibrium

calculations.


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An important point in the modeling procedure is whether equilibrium is reached in the plasma

gasification process, i.e. whether the operating conditions allow the chemical reactions to

reach an equilibrium state. As far as the gasification temperature is concerned, it is stated that

equilibrium is not achieved when the gasification temperature is sufficiently below 800C

(common gasifiers), while it is reached for higher temperatures like those of plasma

gasification.

Thermoselect plant, which is a similar process to plasma gasification, the residence times for

the gas phase and also for the molten phases are sufficient for equilibrium to be attained, i.e.

for the solids it is about 12 h and for the gas phase 24 s at about 1200C. In addition, Chen

et al.presented that in such processes, a significant increase of gas yield is noted between 2

and 3 s (as a result of a tar cracking reaction), and after that time period, equilibrium is

assumed to be attained. Consequently, plasma gasification is studied in this work based on

equilibrium terms in order to describe the process and to present its energetic performance in

relevance to the main operational parameters, e.g. moisture, oxygen and temperature.

The thermodynamic data that are required for development of the equilibrium gasification

model are the Gibbs energies of formation at 298 K, the enthalpies of formation at 298 K and

the temperature dependent heat capacities Cp, which are required to evaluate the change ofthe equilibrium constants with temperature.


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Waste material is described by its ultimate analysis (CXHYOZ), and the global gasification

reaction is written as follows:

CHXOY + wH2O + mO2 + 3.76mN2 = n1H2 + n2CO+ n3CO2+ n4H2O+ n5CH4+ n6N2+ n7C

(1)

where w is the amount of water per kmol of waste material, m is the amount of oxygen per

kmol of waste, n1,n2, n3, n4, n5, n6 and n7 are the coefficients of the gaseous products and soot

(all stoichiometric coefficients in kmoles).The equilibrium is, thus, calculated considering the

components CH4, CO, CO2, H2, H2O and C (soot).


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ADVANTAGES OF PLASMA TECHNOLOGY

Compared to non-plasma methods the advantages of plasma gasification can be summarized

as follows:

Energy for gasification is supplied by plasma rather than energy liberated from

combustion and thus it is independent of the treated substances, providing flexibility,

fast process control, and more options in process chemistry.

No combustion gases generated in conventional auto-thermal reactors are produced.

The temperature in the reactor can be easily controlled by control of plasma power

and material feed rate.

As sufficiently high temperatures and homogeneous temperature distribution can be

easily maintained in the whole reactor volume, production of higher hydrocarbons,

tars and other complex molecules is substantially reduced.

High energy density and high heat transfer efficiency can be achieved, allowing

shorter residence times and large throughputs.

Highly reactive environment and easy control of composition of reaction products.

Low thermal inertia and easy feedback control.

Much lower plasma gas input per unit heating power than the gas flow of classical

reactors and thus lower energy loss corresponding to the energy necessary for heating

of plasma to reaction temperature; also lower amount of gases diluting produced

syngas.

Smaller plants than for conventional reactors due to high energy densities, lower gas

flows, and volume reduction.


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CONCLUSIONS

The research of plasma gasification has been started as a response for a need of

more efficient utilization of waste plastic mass for energy and fuel production. Classical ways

of waste mass gasification, based on partial combustion, do not produce synthesis gas with

quality demanded by advanced technologies of fuel and energy production, mostly due to

contamination of syngas by CO2, methane, tars and other components. The necessity of

production of clean syngas with controlled composition leads to technologies based on

external energy supply for material gasification. Plasma is medium with the highest energy

content and thus substantial lower plasma flow rates are needed to supply sufficient energy

compared with other media used for this purpose. This result in minimum contamination of

produced syngas by plasma gas and easy control of syngas composition.

The experiments with gasification of plastic mass from municipal wastes, plastic chips &

polyethylene were performed on the reactor. The composition of produced syngas was close

to the calculated equilibrium composition, determined for the case of complete gasification.

The heating value of produced syngas was in good agreement with calculated equilibrium

values .This is substantially lower than the tar content in most of non-plasma gasifiers, where

the tar content for various types of reactors varies in the range from 10 mg/N-m3 to 100 g/N-

m3

[Hasler 1999, Jun Han 2008].

It has been experimentally verified that for small particles and higher feeding rates all

supplied material was gasified. Heating value of produced syngas was for the highest

material feed rates more than two times of power of plasma torch. In case of gasification

with carbon dioxide as oxidizing medium, most of power needed for gasification process

was power for dissociation of CO2. The process can be used as an energy storageelectrical

energy is transferred to plasma energy and then stored in produced syngas. This can beutilized for storage of energy produced by sources of electrical energy with large

fluctuations of energy production. Moreover, the process offers utilization and

transformation of CO2 generated by industrial technologies. If energy balances of plasma

gasification are compared with the conventional auto-thermal reactors, where only very low

power is supplied to ignite the process of partial combustion,in Thermal Plasma Gasification

the energy gain in plasma systems is smaller. However, the LHV of produced syngas for

autothermal reactors is usually between 35% and 60% of its theoretical value, and moreover,

quality of produced syngas is low especially due to the production of tars and other


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contaminants. Thus, plasma can offer advantages if high quality syngas with high heating

value is needed. Moreover, possibility of electrical energy storage can be utilized in

combination with new renewable power production technologies.


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BIBLIOGRAPHY

1. Thermal Plasma Gasification of Biomass-Milan Hrabovsky (Institute of Plasma Physics

ASCR,Czech Republic).

2. Solid Waste Plasma Gasification: Equilibrium Model Development & Exergy

Analysis(A. Mountouris *, E. Voutsas, D. Tassios), School of Chemical Engineering,

Laboratory of Thermodynamics and Transport Phenomena, National Technical

University of Athens,9 Heroon Polytechniou Street, Zographou Campus, 15780

Athens, Greece.

3. A Review of the Options for the Thermal Treatment of Plastics(Environment and

Plastics Industry Council (EPIC)),December 2004.

4. Kinetics modeling of biomass gasification under thermal plasma conditions.

Application to a refractory species: the methane. (H. Lorcet1, D. Guenadou

1, C.

Latge2, M. Brothier

3, G. Mariaux

4, A. Vardelle

4)

1CEA, DEN, DTN/STPA/LPC, F-13108, Saint-Paul-lez-Durance, France

2CEA, DEN, DTN, F-13108, Saint-Paul-lez-Durance, France

3CEA, DEN, DEC/SPUA/LCU, F-13108, Saint-Paul-lez-Durance, France

4SPCTS UMR CNRS 6638, ENSIL University of Limoges, 16 rue Atlantis, 87068,

Limoges Cedex , France.

final report of plasma gasification

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