Major project report

EMERGING APPROACH TO HARNESS ENERGY FROM SOLID

WASTE:PLASMAGASIFICATION

Major Project Report

Submitted by

SAKSHI

For the partial fulfillment of the requirements of the degree of

MASTER OF TECHNOLOGY

in

Renewable Energy Engineering and Management

Department of Energy and Environment

TERI University

June 2013

DECLARATION This is to certify that the work that forms the basis of this project, entitled “Emerging approach to

harness energy from solid waste: Plasma Gasification” is an original work carried out by me and

has not been submitted anywhere else for the award of any degree.

I certify that all sources of information and data are fully acknowledged in the project report.

i

CERTIFICATE This is to certify that Sakshi has carried out her major project in partial fulfillment of the requirement for the degree

of Master of Technology in Renewable Energy Engineering and Management on the topic “Emerging approach

to harness energy from solid waste: Plasma Gasification” during January 2013 to May 2013. The project was

carried out at Solena-ABSi India Private Limited.

The report embodies the original work of the candidate to the best of our knowledge. Date:

Dr. Gaurav Mishra Dr. V.V.N Kishore

(External Supervisor) (Internal Supervisor)

General Manager, Head of the Department,

Solena-ABSi India Private Limited, Department of Energy and Environment

Suite -304, 3rd

Floor PinnacaleClaridges TERI University, New Delhi

Business Towers, Surajkund

ii

ACKNOWLEDGEMENT I take this opportunity to express my sincere thanks and deep gratitude to almighty and all those

people who extended their whole-hearted co-operation and have helped me in the project successfully.

I am extremely thankful to Dr. Gaurav Mishra for giving me this priceless opportunity of working

with Solena-ABSi India Private Limited (SAIP). I am deeply thankful to Dr. Gaurav Mishra for his

persistent guidance and also sharing his knowledge and valuable time with me. I feel obliged to him

for his constant support, encouragement and regular inflow of ideas. I am very grateful to him for his

deep interest and enthusiasm towards my project, which helped me immeasurably towards the

accomplishment of the objectives.

I am grateful to all staff members of SAIP for their support and good wishes. I truly could not have

imagined working in a more congenial and creative atmosphere without their support.

I wish to express my heartfelt thanks and respect to Dr. V.V.N Kishore, TERI University for his

inputs, valuable assistance and helping me at each step by providing me with valuable inputs all

throughout the training period. I would like to thank all the other faculties in the Department of

Energy and Environment Studies for their help and co-operation in successful completion of this

project.

Lastly, I offer my regards to my parents, brother, friends and all of those who supported me in any

respect during the completion of the project.

iii

TABLE OF CONTENTS LIST OF

Figures.......................................................................................................................... v

LIST OF Tables....................................................................................................................... vi

LIST OF

ABBREVIATIONS..................................................................................................... vii

ABSTRACT............................................................................................................................. viii

1. INTROUCTION............................................................................................................... 1

1.1. Waste Generation Scenario in India.......................................................................................... 1

1.2. Collection and Potential MSW............................................................................................... 3

1.3. Potential from Urban MSW India......................................................................................... 4

1.4. Methods to Recover Energy.................................................................................................... 6

2. LITERATURE REVIEW AND METHODOLOGY............................. 9

3. GASIFICATION........................................................................................... 11

3.1 Classification of Gasification..................................................................................................... 12

3.2 Gasifying agents: .................................................................................................................... 12

3.3 Basic Gasification Reactions...................................................................................................... 13

3.4 Components of gasification system: ......................................................................................... 14 4

.

PLASMA

GASIFICATION................................................................................................. 17

4.1 Plasma...................................................................................................................................... 17

4.2 Torch................................................................................................................................ 18

4.3 Working of plasma torches.................................................................................................... .. 19

4.4 Types of Plasma torches........................................................................................................... 20

4.5 Lifetime of Plasma torches......................................................................................................... 21

4.6 Plasma gasifier/reactor 22

4.6.1 Materials of construction 22

4.6.2. Updraft gasifier 22

4.6.3 Efficiency 23

4.7 Controlling parameters 23

4.7.1 Moisture content 23

4.7.2. Residence time 24

4.7.3. Gasifying agents 24

4.7.4. Gasifying agents biomass ratio 24

4.7.5. Air fuel ratio and equivalent ratio 24

4.7.6 Reaction temperature 25

5. PLANT PROCESS AND WORKING......................................... 27

5.1 Feedstock preparation island 27

5.1.1. Waste reception and sorting 28

5.1.2 Waste handling 28

5.1.3 Waste processing 28

5.2 Size reduction and blending 28

5.2.1 Waste drying 29

5.2.2 Waste blending 29

5.3 Gasification island 29

5.4 Syngas conditioning 31

5.5 Power generation island 32

5.6 Balance of plant and waste heat recovery 32

5.7 Plant energy load 33

5.8 Working principle of plasma gasification 33

5.9 Highlights of plasma gasification 35

6. RESULTS AND DISCUSSION 37

7. CONCLUSIONS AND RECOMMENDATIONS 39

iv

LIST OF FIGURES Figure 1-1: MSW to Energy Technologies and Pathways (EAI, 2013) ..............................................7 Figure 3-1: Diagrammatic Representation of Classification ........................................................... 13 Figure 4-1: Plasma Flash (Phoenix Solutions Co.) ........................................................................ 18 Figure 4-2: Cross-section of a typical plasma torch (http://commons.wikimedia.org/wiki/File:Plasma_Welding_Torch.svg) ......................................... 19 Figure 4-3: A Generic Plasma Torch Design ................................................................................. 19 Figure 4-4: Pictorial representation of different arc torches (Phoenix solutions co.) ......................... 21 Figure 5-1: Schematic Diagram for Waste Processing ................................................................... 28 Figure 5-2: Process Layout .......................................................................................................... 31 Figure 5-3: Mass balance for the plant ......................................................................................... 32 Figure 5-4: Schematic of the Whole Process (Recovered Energy, Inc.) ........................................... 33

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LIST OF TABLES Table 1-1: Population Growth and Impact on Overall Urban Waste Generation and Future Predictions Until 2041 ....................................................................................................................................3 Table 1-2: State-wise MSW Generated and Corresponding Power Potential .....................................4 Table 2-1: Commercial plants based on plasma gasification technology ………………………….10 Table 3-1: Main Reactions in Homogeneous and Heterogeneous Phase during Solid Waste Gasification Process (Arena, 2012) .............................................................................................. 13 Table 4-1: Classification on operating and range basis .................................................................. 20 Table 6-1: Economics for Plasma Gasification Plant ..................................................................... 38

vi

LIST OF ABBREVIATIONS MSW - Municipal Solid Waste

ST - Steam Turbine

GT - Gas Turbine

C/C - Cleaning - Cooling System

T - Tons

TPY - Tons per year

TPD - Tons per day

NGO - Non-governmental Organization

RDF - Refuse Derived Fuel

SVOCs - Semi Volatile Organic Compounds

HRSG - Heat Recovery Steam Generator

ASR - Automotive Shredded Residues

RM - Raw Material

NEERI - National Environmental Engineering Research Institute

ULBs - Urban Local Bodies

PPA - Power Purchase Agreement

MoEF - Ministry of Environment & Forests

MSWM- Municipal Solid Waste Management

WTE - Waste to Energy

EIA - Environmental Impact Assessment

PP - Pre-processing

AD - Anaerobic Digestion

ICE - Internal Combustion Engine

RE - Reciprocating Engine

MNRE - Ministry of New and Renewable Energy

CV - Calorific Value

MW - Mega Watt

MJ - Mega Joule

kg - Kilogram

gm - Gram

Yr. - Year

Rs. - Rupees

hrs. - Hours

vii

ABSTRACT One of the most compelling challenges of 21st century is finding a way to meet sustainable

development in terms of energy as well as environment. From a recent study it has been found that

solid waste generated at domestic level is the single largest component of all wastes generated in our

country. A number of research studies have shown that somewhere 300 to 600 gm. of solid waste is

generated per person per day in our country.

Decomposition of solid waste produces waste that includes gases, of which methane and carbon

dioxide are the major constituents. Methane is a hazard because it is flammable and explosive as well

as greenhouse gases, which contribute towards global warming. Decomposition of waste in landfill

site produces contains trace gases that are detrimental to public health and the environment. Leachate

from the dumping site enters into the surface/ground water leading to water pollution.

Gasification is one of the means of transforming biomass and/or other solid waste so that they can be

so that it can be more easily utilized as a renewable source to extract energy and fuels. This project

aims at studying emerging approach to harness energy from solid waste using Plasma Gasification.

Plasma gasification is an enabling technology for transforming such waste into valuable Syngas and a

vitrified slag by means of thermal energy generated by plasma. The inference results in presenting a

promising technology for processing waste and generating power.

Keywords: Plasma Gasification, MSW, Syngas, Power

viii

1

CHAPTER 1

INTRODUCTION

Waste is anything, which is unacceptable to an owner and directly has no monetary value but its

proper utilization can make a business. Municipal Solid Waste (MSW) includes waste from

households, nonhazardous solid waste from industrial commercial, institutional establishment

(excluding bio-medical waste in present context), Market waste, Yard waste, Agriculture waste &

Street Sweepings. Industrial and community hazardous waste and infectious waste is not considered

as MSW and should be collected and processed separately. MSW (Management and Handling) Rules

2000 defines MSW as commercial and residential wastes generated in municipal or notified areas in

either solid or semi-solid form excluding hazardous wastes but including treated biomedical wastes. Various other definitions related to MSW, which are defined in MSW Rules 2000, are given in MSW management encompasses the functions of collection, transfer and transportation, processing

and recycling, and disposal of MSW.

1.1. Waste Generation Scenario in India Municipal solid waste management (MSWM) is one of the major environmental problems of Indian

cities. Improper management of municipal solid waste (MSW) causes hazards to inhabitants. Various

studies reveal that about 90% of MSW is disposed of unscientifically in open dumps and landfills,

creating problems to public health and the environment. In the present study, an attempt has been

made to provide a comprehensive review of the characteristics, generation, collection and

transportation, disposal and treatment technologies particularly “Plasma Gasification” of MSW Rapid industrialization and population explosion in India has led to the migration of people from

villages to cities, which generate thousands of tons of MSW daily. The MSW amount is expected to

increase significantly in the near future as the country strives to attain an industrialized nation status

by the year 2020 (Sharma and Shah, 2005; CPCB, 2004; Shekdar et al., 1992, Kansal et al., 1998;

Singh and Singh, 1998; Gupta et al., 1998).

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The quantity of MSW generated depends on a number of factors such as food habits, standard of

living, degree of commercial activities and seasons. Data on quantity variation and generation are

useful in planning for collection and disposal systems. With increasing urbanization and changing life

styles, Indian cities now generate eight times more MSW than they did in 1947. Presently, about 90

million t of solid waste are generated annually as byproducts of industrial, mining, municipal,

agricultural and other processes. The amount of MSW generated per capita is estimated to increase at

a rate of 1–1.33% annually (Pappu et al., 2007; Shekdar, 1999; Bhide and Shekdar, 1998). A host of

researchers (Siddiqui et al., 2006; Sharholy et al., 2005; CPCB, 2004; Kansal, 2002; Singh and Singh,

1998; Kansal et al., 1998; Bhide and Shekdar, 1998; Dayal, 1994; Khan, 1994; Rao and Shantaram,

3

1993) have reported that the MSW generation rates in small towns are lower than those of metro

cities, and the per capita generation rate of MSW in India ranges from 0.2 to 0.5 kg/ day. It is also

estimated that the total MSW generated by 217 million people living in urban areas was 23.86

million T/yr in 1991, and more than 39 million t in 2001 (Sharholy et al., 2008).

India is the second most populous nation on the planet. The Census of 2011 estimates a population

of 1.21 billion, which is 17.66% of the world population. The average per capita waste generation in

India is 370 grams/day. 70% of India‟s urban population generates 130,000 TPD or 47.2 million

TPY at a per capita waste generation rate of 500 grams/day. This implies the total MSW generated

by urban India could be as much as 188,500 TPD or 68.8 million TPY. This number matches the

projection (65 million TPY in 2010) (Kumar, et al., 2010). Table 1-1gives future predictions of

waste generation and population growth until 2041(Anneppu, 2012).

Table 1-1: Population Growth and Impact on Overall Urban Waste Generation and Future

Predictions Until 2041

Year Population (Millions) Per capita Total waste generated Thousand tons/yr

2001 197.3 0.439 31.63 2011 260.1 0.498 47.30 2021 342.8 0.569 71.15 2031 451.8 0.649 107.01 2036 518.6 0.693 131.24 2041 595.4 0.741 160.96

1.2. Collection and Potential of MSW

The collection of MSW is the responsibility of corporations/municipalities. The predominant system of

collection in most of the cities is through communal bins placed at various points along the roads, and

sometimes this leads to the creation of unauthorized open collection points. Efforts to organize house-to-

house collection are just starting in many megacities such as Delhi, Mumbai, Bangalore, Madras and

Hyderabad with the help of NGOs. It has been observed that many municipalities have employed private

contractors for secondary transportation from the communal bins or collection points to the disposal sites.

Others have employed NGOs and citizen‟s committees to supervise segregation and collection from the

generation source to collection points located at intermediate points between sources and dumpsites. In

addition, the welfare associations on specified monthly payment arrange collection in some urban areas.

A sweeper who sweeps the roads manually is allotted a specific area.

4

The sweepers put the road wastes into a wheelbarrow, and then transfer the waste to dustbins or

collection points (Colon and Fawcett, 2006; Nema, 2004; Malviya et al., 2002; Kansal et al., 1998;

Bhide and Shekdar, 1998).

In most cities, a fraction of MSW generated remains uncollected on streets, and what is collected is

transported to processing or disposal sites. The collection efficiency is the quantity of MSW collected and

transported from streets to disposal sites divided by the total quantity of MSW generated during the same

period. Many studies on urban environment have revealed that MSW collection efficiency is a function of

two major factors: manpower availability and transport capacity. The average collection efficiency for

MSW in Indian cities and states is about 70% (Rathi, 2006; Siddiqui et al., 2006; Nema, 2004; Gupta et al.,

1998; Maudgal, 1995; Khan, 1994). The collection efficiency is high in the cities and states, where private

con- tractors and NGOs are employed for the collection and transportation of MSW. Most of the cities are

unable to provide waste collection services to all parts of the city. Generally, overcrowded low-income

settlements do not have MSW collection and disposal services (Sharholy et al., 2008).

1.3. Potential from Urban MSW in India

MNRE estimates that there exists a potential for generating 1500 MW of power from Municipal solid

waste in the country. The potential is likely to increase with further economic development. Table

1-2 gives state-wise power potential and MSW generated as per 2011 Census (Annepu, 2012).

Table 1-2: State-wise MSW Generated and Corresponding Power Potential

S.No. City MSW Generated

Calorific value Power

(TPD) (MJ/k

g) Production

potential (MW)

1 Greater Kolkata 11,520 5.0 129.9

2 Greater Mumbai 11,124 7.5 186.6

3 Delhi 11,040 7.5 186.8

4 Chennai 6,118 10.9 149.0

5 Greater Hyderabad 4,923 8.2 91.0

6 Greater Bangalore 3,344 10.0 74.9

7 Pune 2,602 10.6 61.8

8 Ahmadabad 2,518 4.9 27.9

9 Kanpur 1,756 6.6 35.9

10 Surat 1,734 4.1 16.1

5

11 Kochi 1,366 2.5 7.6

12 Jaipur 1,362 3.5 10.7

13 Coimbatore 1,253 10.0 28.0

14 GreaterVishakhapatn

am 1,194 6.7 18.0

15 Ludhiana 1,115 10.7 26.8

16 Agra 1,021 2.2 5.0

17 Patna 945 3.4 7.3

18 Bhopal 877 5.9 11.7

19 Indore 867 6.0 11.7

20 Allahabad 815 4.9 9.0

21 Meerut 804 4.6 8.2

22 Nagpur 801 11.0 19.8

23 Lucknow 743 6.5 10.9

24 Srinagar 713 5.3 8.5

25 Asansol 706 4.8 7.7

26 Varanasi 706 3.4 5.3

27 Vijayawada 688 8.0 12.3

28 Amritsar 679 7.7 11.7

29 Faridabad 667 5.5 8.3

30 Dhanbad 625 2.5 3.5

31 Vadodara 606 7.5 10.1

32 Madurai 543 7.6 9.2

33 Jammu 534 7.5 8.9

34 Jamshedpur 515 4.2 4.9

35 Chandigarh 486 5.9 6.4

36 Pondicherry 449 7.7 7.8

37 Jabalpur 380 8.6 7.3

38 Bhubaneswar 356 3.1 2.5

39 Nasik 329 11.6 8.5

40 Ranchi 325 4.4 3.2

41 Rajkot 317 2.9 2.0

42 Raipur 316 5.3 3.8

43 Thiruvanthapuram 308 10.0 6.9

44 Dehradun 247 10.2 5.7

45 Guwahati 246 6.4 3.5

46 Shillong 137 11.5 3.5

6

47 Agartala 114 10.2 2.6

48 Portblair 114 6.2 1.6

49 Aizwal 86 15.8 3.0

50 Panji 81 9.3 1.7

51 Imphal 72 15.8 2.5

52 Gandhinagar 65 2.9 0.4

53 Shimla 59 10.8 1.4

54 Daman 23 10.8 0.6

55 Kohima 20 11.9 0.5

56 Gangtok 19 5.2 0.2

57 Itnagar 18 14.3 0.6

58 Silvassa 11 5.4 0.1

59 Karavati 5 9.4 0.1

Total 81,407 1,292

1.4. Methods to Recover Energy

Basically two methods are being followed for energy recovery from the organic fraction of MSW

(biodegradable as well as non-biodegradable).

(i) Thermo-chemical conversion: This process entails thermal de-composition of

organicmatter to produce either heat energy or fuel oil or gas; and

(ii) Bio-chemical conversion: This process is based on enzymatic decomposition of

organicmatter by microbial action to produce methane gas or alcohol.

The Thermo-chemical conversion processes are useful for wastes containing high percentage of

organic non-biodegradable matter and low moisture content. The main technological options under

this category include Incineration, Pyrolysis, Gasification and Combustion.

The bio-chemical conversion processes, on the other hand, are preferred for wastes having high

percentage of organic biodegradable matter and high level of moisture content, which aids microbial

activity. The main technological options under this category are Anaerobic Digestion, also referred to

as Bio-methanation. Figure 1-1 pictorially shows different technologies and pathways for MSW

conversion to energy.

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! Municipal Solid Waste (MSW)

Collection & Transportation from Point of Generation

Cans,!Tins,!Pipes,!etc.!

Storage & Segregation

Inerts (sand, stones,

Ferrous & Non – Ferrous

Recyclables

etc.)

Organic (Hydro –

Metals, Plastics

Carbon Materials)

Landfill

Broken Glass -

Ceramics, Concrete

Containers,

Aggregates, Recycled

Glass, Cups,

Glass Countertops

etc.

High Moisture Biodegradables (kitchen Low Moisture Organics (Polythene, Rubber Tires

Wastes, etc.) etc.)

Anaerobic Digestion

Gasification!

Pyrolysis!

Incineration/

Combustion

Figure 1-1: MSW to Energy Technologies and Pathways (EAI, 2013)

8

9

CHAPTER 2

LITERATURE REVIEW AND METHODOLOGY

In order to bring an environment friendly solution for increasing waste and process it into power to

curb energy scarcity there is need for a technology, which is technically and economically viable.

Plasma gasification is one such technology pertaining to which research has been carried out in

different parts of the world and researchers are continuing on the same to advance this technology. To

bring the available information on technology into one umbrella and conclusions, recommendations to

address issues from own analysis this study has been carried out.

Gomez et al., 2009, give a review of thermal plasma technology for the treatment of waste. Initially,

the plasma concept was proposed to treat particular categories of waste, mainly hazardous, with the

aim of vitrifying the entering material (Wang et al., 2009; Moustakas et al., 2005). A similar

technological approach was then proposed to process solid waste with the aim of energy recovery,

using plasma reactors where the plasma jet directly impacts the refuse (Minutillo et al., 2010).

Further, a different approach is proposed to apply plasma process for energy recovery, in which the

plasma jet is used to process the syngas produced by a former waste gasification step (Morrin et al.,

2010) and to vitrify the solid residues from gasification (NNFCC, 2009) (Lombardi et al., 2012).

Various types of gasification technologies exist like Biomass gasification, Waste gasification and

Plasma gasification amongst those plasma gasification is a key enabling thermochemical technology

which has been used in past only for Steam cycle power, presently power via IGCC power or

reciprocating engines i.e. syngas production which can be used for multiple end purposes as

required and future can be explored for the generation of biofuels like ethanol, propanol and FT

liquids or hydrogen separation –fuel cell, refinery, vehicle. Since plasma gasification leaves no

waste other saleable by-products like inert vitrified slag can be used for road construction and

particulate recovered after syngas cleanup are recyclable.

10

Plasma gasification is different from other types of gasification in the view that it can process any

type of waste whether it‟s MSW, hazardous waste, agro residue, plastics, tires, and industrial waste

etc.

Table 2-1: Commercial plants based on plasma gasification technology

Capacity Waste processed Location of plant Type of plant

220 TPD MSW+ASR Utashinai city, Japan Waste to Power

78 TPD Hazardous Waste Pune city, India Waste to Power

950 TPD Industrial Waste Teeside , UK Waste to Power

24 TPD MSW+Sludge Mihama-Mikata,Japan Waste to Power

166 TPD MSW+ Sludge Yoshi, Japan Waste to Power

Source: Westinghouse Plasma Corp.

Since this technology can process any type of waste leaving virtually no tar or soot gives it an edge

over other waste processing technologies. In terms of financial viability also when compared to

incineration (Mass burning)

2.1. Methodology

This section covers the methodology used for the development of study in harnessing energy

fromsolid waste using plasma gasification. A literature search on Plasma gasification technology was

done to determine the current status of Plasma gasification commercialization, identify near-

commercial processes and collect reliable gasification data. Secondary data mostly in the form of

journals, reports, articles and primary knowledge gathered from learning have been used. MSW

(Handling and Management) Rules 2000 have been used for defining waste. While the economic

analysis of the plant, has been done by using assumption and excel as a tool.

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CHAPTER 3

GASIFICATION

Gasification is a thermo-chemical process that converts biomass into gas initial by subjecting it to elevated

temperature in an oxygen lean combustion environment. The thermal energy required to drive the gasification

reaction can be provided from outside the gasifier through several means but is often generated by combusting a

portion of biomass/coke.

Gasification process consists of mainly four stages:

Drying: This is the first stage of the gasification where water (moisture) from the fuel getsconverted to

water (steam).

Pyrolysis: Pyrolysis, the second stage releases the volatile components of the organiccompounds at low

temperature zone of about 400-600 ° C and results in char consisting of fixed carbon and the inorganic

compounds in the feed. It involves release of three kinds of products, namely, solid charcoal, liquid tars,

and gases.

Oxidation: A heterogeneous reaction takes place in the oxidation zone between solidcarbonized fuel and

gasifying agent producing carbon dioxide and releasing a substantial amount of heat.

Reduction: Last stage of gasification, a number of high-temperature chemical reactions takesplace in the

absence of oxygen or under a reducing atmosphere.

12

The principal gasification reactions that take place are:

C + O2 CO2 -393 kJ/mol

C + H2

CO + H2 +131 kJ /mol

C + CO2

2CO +172 kJ/mol

C + 2H2

CH4 -74 kJ/mol

CO + H2O

2 + H2 -41 kJ/mol

CO + 3H2

CH4 + H2O -205 kJ/mol

The Third equation describes the “Boudouard reaction” whereby hot carbon in the form of coke can convert CO2

to CO. This conversion is important in gasification as CO2 is of low value in Syngas and should be restricted to a

minimum to increase the over- all efficiency of the installation. The CO/CO2 ratio increases with higher

temperatures and is considered an important regulation parameter for control of the gasification process. (Lemmens

et al.,2007)

3.1. Classification of Gasification Gasification is broadly classified as Direct and Indirect gasification. If the process does not occur with the help of

an oxidizing agent, it is called indirect gasification and needs an external energy source.If the process occurs with

the help of oxidizing agent, it is called direct gasification. Figure 4-1 explains direct and indirect gasification

pictorially.

3.2. Gasifying agents:

• Steam: Gasification with steam “reforming” results in a hydrogen and carbondioxide rich

“synthetic” gas (Syngas)

• Air: Gasification with air produces a high-N2, low Btu fuel gas

• Enriched oxygen: Gasification with enriched oxygen produces a high Btu mixtureof carbon

monoxide and hydrogen

13

Figure 3-1: Diagrammatic Representation of Classification

3.3. Basic Gasification Reactions Gasification, or „„indirect combustion‟‟, in particular, is the con- version of solid waste to fuel- or synthesis-gases

through gas- forming reactions: it can be defined as a partial oxidation of the waste in presence of an oxidant

amount lower than that required for the stoichiometric combustion. Basically, part of the fuel is combusted to

provide the heat needed to gasify the rest (auto- thermal gasification), as in the case of air gasification, or heat

energy is provided by an external supply (allo-thermal gasification), as in the case of plasma torch utilization. The

result is not a hot flue gas as in the conventional direct combustion of wastes but a hot fuel gas („„producer gas‟‟ or

„„Syngas‟‟), containing large amounts of not completely oxidized products that have a calorific value, which can

be utilized in a separate process equipment, even at different times or sites. The organic content of the waste is

converted mainly to carbon monoxide, hydrogen and lower amounts of methane, although the Syngas is generally

contaminated by undesired products such as particulate, tar, alkali metals, chloride and sulphide (Heermann et al.,

2001;Knoef, 2005).

14

Diminishing landfill volume and high costs associated with traditional incineration technologies strongly increase

the interest on the application of the gasification process to MSW: the evidence that gas is easier to handle (and to

burn) than a solid waste makes it a candidate to become the advanced thermal treatment of the near future, for both

the un- sorted residual dry fraction left downstream of separate collection and that produced from mechanical

treatment of MSW (Heermann et al., 2001; Malkow, 2004; DEFRA, 2007a) (Arena,2012) Table 4-1 represents the

basic heterogeneous and homogeneous reactions.

Table 3-1: Main Reactions in Homogeneous and Heterogeneous Phase during Solid

Waste Gasification Process (Arena, 2012)

Oxidation reactions

"111 MJ/kmol

1 C + ½ O2 ?CO Carbon partial oxidation

2 CO + ½ O2 ?CO2 "283 MJ/kmol Carbon monoxide oxidation

3 C + O2 ?CO2 "394 MJ/kmol Carbon oxidation

4 H 2 + ½

O H O " 242 MJ/kmol Hydrogen oxidation

5 n 2

? 2 m /2 H2

CnHm partial oxidation

CnHm + /2 O2MnCO + Exothermic

Gasification reactions involving steam

6 C + H2O MCO + H2 +131 MJ/kmol Water–gas reaction

7 CO + H2O MCO2 + H2 "41 MJ/kmol Water–gas shift reaction

8 CH4 + H2O MCO + 3 H2 +206 MJ/kmol Steam methane reforming

9 CnHm + n H2O MnCO + (n + m

/2) H2 Endothermic Steam reforming

Gasification reactions involving hydrogen

"75 MJ/kmol

10 C + 2H2 MCH4 Hydrogasification

11 CO + 3H2 MCH4 + H2O "227 MJ/kmol Methanation

Gasification reactions involving carbon dioxide

12 C + CO2 M2CO +172 MJ/kmol Boudouard reaction

13 CnHm + nCO2 M2nCO + m

/2 H2 Endothermic Dry reforming

Decomposition reactions of tars and hydrocarbonsa

14 pCxHy ?qCnHm + rH2 Endothermic Dehydrogenation

15 CnHm ?nC + m

/2 H2 Endothermic Carbonization

a Note that CxHy represents tars and, in general, the heavier fuel fragments produced by thermal cracking and CnHm represents

hydrocarbons with a smaller number of carbon atoms and/or a larger degree of unsaturation than CxHy.

3.4. Components of gasification system:

A gasification system is made up of three fundamental elements: (1) the gasifier, helpful in producing

the combustible gas; (2) the gas clean up system, required to remove harmful compounds from the

combustible gas; (3) the energy recovery system. The system is completed with suitable sub-systems

helpful to control environmental impacts (air pollution, solid wastes production, and wastewater). A

sufficiently homogeneous carbon-based material is required for a correct and efficient gasification

process.

15

3.5. Gasifier

The gasifier is a reactor in which the conversion of a feedstock into fuel gas takes place. There are

three fundamental types of gasifier:

(i) Fixed bed: Also called “dense phase” reactors (updraft, downdraft, cross-draft, etc.), the

biomass feedstock occupies maximum reactor volume (0.3-0.8)

(ii) Fluidized bed: Also called “lean phase” reactors, the biomass occupies very little reactor

volume (0.05-0.2)

(iii) Entrained-bed: It operates with feed and blast in co-counter flow. Residence time in these

processes is short (a few seconds).

16

17

CHAPTER 4

PLASMA GASIFICATION

By means of high temperature gasification, solid waste can be converted into a valuable synthesis gas

and a vitrified slag. The Syngas can be used for efficient production of energy due to its high caloric

content or as a raw material for the production of chemical substances (Malkow, 2004) (e.g., the

production of methanol, Fischer Tropsch diesel, hydrogen). The vitrified slag should be inert for

leaching processes and as a consequence applicable as, for example, a building material additive

(Lombardi et al., 2002)

In case of plasma gasification, the heat source of the gasifier is one or more plasma arc torches that

produce a very high temperature plasma gas (up to 15,000 °C). The plasma torch is an independent

heat source, which allows control of temperature independently from fluctuations in the feed quality

and supply of air/oxygen/steam needed to gasify the feed. (Lemmens et al., 2007)

4.1. Plasma Plasma is a high temperature, ionized, conductive created in the plasma torch. Plasma is created by

the interaction of the gas with an electric arc. This interaction dissociates the gas into electrodes and

ions, enabling the gas to become that are thermally and electrically conductive. The conductive

property of the ionized gas in the arc to the incoming process gas, and in turn to process or reactor.

This state is called Plasma and will exist in the immediate confines of the arc in the torch. As the gas

exits the torch, it has recombined into its neutral (non-ionic) state although it still maintains its

superheated properties. Figure 5-1 shows plasma flash

18

Figure 4-1: Plasma Flash (Phoenix Solutions Co.) 4.2. Plasma Torch A plasma torch is a device in which a flowing gas is passed through an electric arc, producing plasma.

Plasma is a mixture of ions, electrons and neutral particles produced when stable molecules are

dissociated (in this case by an electric arc). The electric arc is formed between two electrodes, the

anode (+) and cathode (-)

1. Electric arc

2. Gas plasma

3. Nozzle protection

4. Shield gas

5. Electrode

6. Nozzle construction

Figure 4-2: Cross-section of a typical plasma torch (http://commons.wikimedia.org/wiki/File:Plasma_Welding_Torch.svg)

19

Plasma torches and arcs convert electrical energy into intense thermal (heat) energy. Plasma torches

and arcs can generate temperatures up to 10,000 ° F. When used in a gasification plant, plasma

torches and arcs generate this intense heat, which initiates and supplements the gasification reactions,

and can even increase the rate of those reactions, making gasification more efficient. Figure 4, above

shows various components of a typical plasma torch.

4.3. Working of plasma torches

The working of plasma torch differs based on their kinds, but their working in principle is same for

all. In general, the gas enters the torch body through a tube, travels up the length of the cathode and

out through the anode throatmeanwhile passing through the generated arc and becoming plasma.

Figure 4-3: Generic plasma torch design

20

Many different types of gases have been used with plasma torches; Air, O2 (Kato et al., 1996 and

Mitani, 1995), N2, H2, Ar (Stouffer, 1989), CH4, C2H4 and C3H6 to name a few. The first object the

gas encounters when entering the plasma torch is the cathode. Typically, cathodes are thin, pointed

rods made of tungsten or copper, although some are flat-ended depending on the application (Chan et

al., 1980). They are electrically connected to the negative power supply of the torch. After travelling

up along the cathode, the gas then encounters the electric arc, becomes plasma and passes out of the

torch through the anode throat. The anode is generally constructed from copper or tungsten, like the

cathode. It has a nozzle upstream of the throat to accelerate the flow, ejecting the gas-plasma mixture

at high velocity out of the torch. (scholar.lib.vt.edu/theses/available/etd-71998-13553/.../Sec3.pdf

4.4. Types of Plasma torches On the basis of operating mode Plasma arc torches are available in generally two arc modes and

different power ranges.

Two widely used plasma torch types are Transferred and Non-Transferred Mode. It may be applied at

almost any angle. A hermetic seal may be applied around the steel shroud of the torch, if it is needed.

Figure 4-4 shows two types of troches.

Transferred Arc Torch Transferred Arc Plasma Torch, with one internal electrode, transfers the arc of the plasma jet to the

melt, resulting in a localized and very high heat.

Non-Transferred Arc Torch

Non-Transferred Plasma Arc Torch, houses both front and rear internal electrodes, creating a jet of

plasma constrained to the end of the torch, while allowing the jet to be moved inside the furnace.

Table 4-1: Classification on operating and range basis

Type Operating Range Reference

Gases

Transferred Ar, N2, He, 50KW and http://www.phoenixsolutionsco.com/psctorches.ht

ml

H2, CH4, O2, 3,000KW

C3H8

Non- Air, N2, O2, 50KW and

transferred H2, CO, CO2 2,000KW

21

Advantage of Non-Transferred Mode:

• Moveable Jet inside the furnace, which transferred mode, does not offer.

• Heat from a Non-transferred mode is much more dispersed than transferred arc suited for

wide range of applications.

Figure 4-4: Pictorial representation of different arc torches (Phoenix solutions co.)

4.5. Lifetime of Plasma torches Torch uses various types of electrodes made from different metals such as Copper (Cu), Hafnium

(Hf), Tungsten (W), etc.

The electrodes‟ lifetime depends on a variety of factors:

• Material of the electrode and the purity of that material

• The type of gas used and level of gas consumption

• Current

• Technological aspects of the exploitation and other parameters and can last up to hundred

hours. The plasma torches that are generally installed in furnaces and reactors normally have Copper (Cu)

electrodes and work on air to produce the torch. Electrodes‟ life in this case is 300 hours. Plasma

22

torches with Tungsten (W) electrodes that work on Argon (Ar) have electrodes‟ life expectancy of

900 hours.

4.5.1. Efficiency The degree of efficiency of plasma torches has two components: electrical and thermal. Electrical

degree of efficiency of plasma torches depends on the source of power supply, and the thermal degree

of efficiency depends on the configuration of plasma torches. Its typical aggregate degree of

efficiency is 60-80% under non-transferred mode.

4.6.PlasmaGasifier/Reactor The plasma rector does not discriminate between types of waste. The only variable is the amount of

energy that it takes to destroy the waste. Consequently no sorting of waste is necessary and any type

of waste, other than nuclear waste can be processed. But in general practice metals/glass are sorted

out before raw material is fed to the gasifier.

4.6.1. Material of construction Gasifiers/Reactors can be constructed with different materials, which in turn decide the life of

operation. To have longer working life, Stainless Steel (SS 304) is preferred as outer sheath with

internal cast able linings of different Refractory grades. The grades and heat transfer rates decides

respective thickness. Alumina based cast able is used for the construction of plasma gasifier.

4.6.2.Updraft Gasifier

Counter-flow gasification, the updraft configuration has been in use since the oldest times and is the

simplest form of gasifier; used for gasification. Biomass is introduced at the top of the reactor, and a

grate at the bottom of the reactor supports the reacting bed. Air or oxygen and/or steam are introduced

below the grate and diffuse up through the bed of biomass and coke. Complete dissociation of

feedstock takes place at the bottom of the bed, liberating CO2 and H2O. These hot gases (~2000 °C)

pass through the bed above, where they are reduced to H2 and CO and cooled to 1750 °C. Continuing

up the reactor, the reducing gases (H2 and CO) gasify the descending dry biomass and finally dry the

incoming wet biomass, leaving the reactor at a low temperature (~1200°C).

23

The Advantages of updraft gasification are:

• Simple, low cost process

• Able to handle biomass with a high moisture and high inorganic content as in municipal solid

waste and has higher carbon conversion efficiency

• Proven technology, with well-defined zones for various reactions.

The primary Disadvantage of updraft gasification is:

• In low temperature gasification syngas contains high tar, which in turn requires extensive gas

cleanup before engine, turbine or synthesis applications but due to the use of plasma torches

(high temperature gasification), virtually no or zero tar results.

4.6.3. Efficiency

Efficiency is high because hot gases pass through the entire fuel bed and leave at lower temperature.

The sensible heat of hot gas is used for the reduction, Pyrolysis, and drying procedures.

4.7. Controlling parameters 4.7.1. Moisture content

Moisture content is crucial in the gasification process, as any increase in the fuel‟s moisture content

means that more energy is required for water evaporation and steam gasification reactions, which in

turn lowers the gasifier‟s operating temperature. Bed temperatures remain more or less stable with

moisture contents below 15%(C et al., 2009). Even so, the moisture level of the biomass depends on

the gasifier in which it is to be processed: in updraft type reactors it may be as high as 50% (EG et

al.,2012).

Syngas composition is linked to biomass moisture content. Thus, the molar fraction of CO increases for

dry fuels, while for moister fuels the molar fraction of CO2 increases, reducing the calorific power of

the Syngas and, therefore, process efficiency, according to tests conducted in an updraft fixed bed

gasifier with air (P et al., 2011).

24

4.7.2. Residence time The residence time in each type of reactor, which is the average period for which the biomass

particles remain inside the gasifier, should be long enough to ensure that the reactions in the

gasification process take place satisfactorily, generating the expected Syngas. This is linked to the

degree of fluidization of the beds, with the time being shorter as there is more stirring in the bed.

The reactors with the longest residence times are fixed bed gasifier(L.et al., 2008). An optimum time

of 1.6 s is proposed for this type of gasifier(J et al., 2009).

4.7.3. Gasifying agents Air is the most commonly used gasifying agent, as it is obviously economical. Using air produces a

Syngas of less calorific power, due mainly to its high N2 content (L.et al., 2008). Steam as a gasifying

agent produces a Syngas with a moderate calorific power, and its costs are somewhere between air

and oxygen. Oxygen is the gasifying agent required for more advanced applications, and also the most

expensive one (AF et al., 2011). CO2 may also be used as a gasifying agent, as can a mixture of all the

above (L.et al., 2008).

4.7.4. Gasifying agent–biomass ratio The gasifying agent ratio is the ratio of the gasifying agent to the biomass feedstock used in the

reactor. In a fluidized bed reactor with steam (with the latter being used as gasifying agent and fluidizer), it

was observed that by keeping the temperature constant at 750 °C and increasing the steam/biomass

ratio, the production of H2, CO2 and CH4 increases.

4.7.5. Air–fuel ratio and equivalent ratio (ER) The air–fuel ratio is the ratio between the air and fuel used, which is considerably lower than in

combustion process, which operate with excess stoichiometric air, whereas gasification involves

default air values:

rair-fuel = (mol of air/mol of fuel)

The air–fuel ratio is considered to have the greatest influence on the final calorific value of the syngas

generated (C et al., 2011). Suitable values of the ER for gasification fall within the 0.2–0.4 range,

thereby enabling the generation of tars and char to be controlled (L.et al., 2008).

25

By increasing the ER and keeping the biomass flow constant, the gasifier‟s temperature increases, as

there is more oxygen per volume of biomass for conducting the partial combustion reactions, which

are the ones that generate the necessary energy (C et al., 2009).

Hosseini et al. (M et al., 2012) used thermodynamic analysis to demonstrate the effect on energy

efficiency of increasing the ER with different biomass moisture levels. They found that efficiency

decreased with the same trend regardless of whether air or steam was used as the gasifying agent.

4.7.6. Reaction temperature The reaction temperature is one of the more important parameters. According to Enami et al. (L tabaet

al., 2012) it is the most significant parameter in gasification, so it needs to be controlled accurately,as

depending on the type of fuel it can cause problems of ash build-up or sintering. Reducing the

temperature to control this unwanted phenomenon leads to lower char conversion (reducing process

efficiency) and a higher concentration of tars in the Syngas generated (limiting its use in certain

electricity conversion equipment) (A mez-Barea et al., 2011).

Raising the temperature increases the concentration of CO and H2 in the Syngas and reduces that of

CO2, CH4 and H2O,(L taba et al., 2012,FSalvae, 2012).

An increase in reactor temperature leads to an increase in H2 and CO contents and a decrease in CO2

and CH4 contents in the syngas generated (J et al., 2009). This is an important finding, as H2 and CO

are the components with the greatest bearing on syngas quality. An increase in temperature improves

the quality of the Syngas.

4.7.7. Pressure Depending on the pressure used, there are two types of gasification process: at atmospheric pressure

or pressurized (at higher pressures). The latter are more efficient, although they also imply high

investment costs.

An increase in the operating pressure of gasifier reduces the amount of char and tar in the Syngas

generated. Furthermore, the Syngas is obtained already pressurized for subsequent use in end

conversion equipment, such as engines or turbines (L.et al., 2008).According to Klimantos et al.,

combined-cycle gasification systems based on pressurized cycles coupled to hot gas cleaning systems

are one of the most promising options, recording efficiencies of more than 40% (P et al., 2009). The

greater commercial avail- ability of gas turbines would favor this type of solution.Pressurized systems

are used in large plants, but they are uneconomical at small scale (AF et al.,2011). (Ruiz et al., 2013)

26

27

CHAPTER 5

PLANT PROCESS AND WORKING

Various steps to achieve gasification within the gasifier can be described as follows:

5.1. Feedstock Preparation Island A feedstock-conditioning island is built on the front-end to prepare the raw feedstock entering the plant and make it

suitable for use in the reactors. This first island typically includes biomass shredders that physically render biomass

into a given size appropriate for being delivered into the reactor; biomass dryers to remove moisture; biomass storage

areas and finally, biomass conveyor belts.

5.1.1. Waste Reception and Sorting Waste is received via road transport and be delivered in compacted or loose, unsorted, bulk form.

Waste will enter the plant via an entry weighbridge that will record and log the volume of incoming

waste and type.

Waste is to be unloaded inside a purpose designed staging/storage area by either direct tipping from

the delivery trucks or by forklift trucks. The MSW will be delivered to a common storage area for

subsequent sorting and/or size reduction.

MSW, either loose or compacted will be sorted and classed via a waste separation system to ensure

inorganic material is identified. MSW recyclables such as glass and metal will be separated for re-

cycling via the waste sorting system located upstream of the RDF production system.

For sorting purposes, MSW will be fed through a sorting machine that incorporates conveying belts

tilted in an inclined position. At specific points, vibration devices distribute the waste over the

available area of the conveyor belt. After the vibrating section, the waste passes through a rapping

28

section where flat or light material will remain on the conveyor belt, unaffected by the vibration of the

rapping device, while rolling or heavier material move through the effect of gravity across the down-

slope of the conveyor and are removed at right-angles to the direction of the conveyor.

Separation chain curtains will provide further sorting of heavy rolling material from light rolling

material; for example glass bottles from metal cans, or mineral elements from wood. For total

removal of ferric materials magnetic conveyors will be installed running right angles to the main

conveyor, which will collect the ferric material and deposit it for recycling.

5.1.2. Waste handling

The incoming waste is weighed in and then deposited on the tipping floor from the trucks that are

used to pick-up and or transfer MSW. The only separation that is required will be large oversized

pieces that won‟t fit into the shredder need pre-processing. Hazardous waste and medical waste

are handled separately and not co-mingled with normal waste. Any oversized material is shredded

and then conveyed to storage.

5.1.3. Waste processing Through the use of a rigorous preprocessing, segregation and drying system segregating out inert

material and drying the waste to no more than 15% water content carry out conversion of MSW and

local biomass resources into RDF. The small percentage of inert material segregated prior to

gasification (such as glass, metals, debris, etc.) would be properly handled them through recycling and

sales for commercial reuse. Below figure 7, shows the waste processing mechanism.

Figure 5-1: Schematic Diagram for Waste Processing

5.2. Size Reduction and Blending The sorted MSW will undergo shredding/compaction to achieve a uniform particle size, as well as

drying. As part of the compaction process, the RDF will be blended to achieve a homogeneous

feedstock.

29

5.2.1. Waste Drying Once the MSW has been sorted, it will be conveyed to a drying system, for essential removal of at

least 80-85% of the moisture contained in the waste. To achieve this level of moisture removal, heat

will be transferred to forced draft fin and tube heaters located in the drying section. The waste is

conveyed through the dryer and before exiting the dryer is compacted into pellet form. The waste in

an RDF state is discharged from the RDF system into a common storage area where it is transferred

by front-end loaders to the waste feed conveying system for feeding to the plasma gasifier.

5.2.2. Waste Blending To further ensure the performance of the Plasma Gasification Reactor is maximized, the waste is

passed through a blending unit. Catalysts are fed into the inlet of the waste-blending machine, the

purpose of which is primarily to stabilize any molten slag derived from any inorganic/inert waste that

enters the reactor/gasifier prior to it being discharged to the molten slag-vitrifying unit. Stabilizing the

molten slag will prevent it from solidifying in the reactor/gasifier, thus alleviating operational

difficulties such as oxygen lance burning to free a blockage. Once the molten slag is vitrified a non-

leaching slag is produced. The flux material will be either pneumatically conveyed or mechanically

conveyed from a storage silo directly to the waste-blending machine.

Blending the waste to a homogenized state, while not essential, increases the stability of the plasma

reactor/gasifier and in doing so maximizes the efficiency of the gas cooling/cleaning system and

subsequent power generation.

5.3. Gasification Island The feedstock-receiving island feeds the biomass feedstock into the Gasification Island, which

comprises the plasma reactor to produce the Bio-Syngas. The reactor vessel houses plasma torches

that generate an extremely high temperature plasma jet that heats a catalytic bed whose purpose is to

provide uniform heat distribution. The resultant even distribution of high temperature from the

catalytic bed dissociates the organic materials (the biomass feedstock is fed onto the top of the

catalytic bed) into basic gases while at the same time melting the inorganic materials into an inert and

non-leachable “slag”. This process of thermal depolymerization of organic materials and melting by

means of high temperature plasma energy is the basic principle of technology. Figure 8, given below

is the simplified form of the process layout occurring in plasma gasification.

The plasma reactor operates under an oxygen–deprived, controlled atmosphere, which means that

there is a minimum and controlled sub-stoichiometric amount of oxygen admitted and, therefore, no

30

burning (complete oxidation) takes place and no toxic ash is created, no bottom and fly ashes, and no

carcinogenic molecules e.g. dioxins/furans/other SVOCs are produced. Thus, the plasma reactor is

neither an incinerator nor a combustion system. It is a gasification/vitrification system operating under

extremely high temperatures and sub-stoichiometric conditions that breaks all organic molecular

bonds.

In the Bed Gasification Zone is further divided into four distinct zones (zone B1 – B4) as described

below:

• In the drying zone (B-1), remaining feed moisture leaves the fuel and enters the gas phase.

• In the devolatilization zone (B-2), feed mass enters the gas phase in proportion to the volatile

fraction. All the molecules contained in the feedstock are broken into their elemental compounds

(C, N, O, H, S, and Cl), which subsequently form the Bio-Syngas molecules, i.e., CO, H2, H2O, N2,

HCl, and H2S. All non-carbon feed components enter the gas phase along with sufficient carbon to

match the specified volatile matter. Remaining carbon will be converted into CO in the

gasification zone.

• In the gasification zone (B-3), the reactions

(i) C + H2O→CO + H 2 and

(ii) C + CO2 →2 CO are assumed to proceed to completion until one of the reactants is

exhausted. Because reaction (i) is known to be faster, this reaction is given precedence and is assumed

to occur until one of the reactants is depleted. If any carbon is left after completion of reaction (i),

reaction (ii) takes place. In addition, the reversible "water-gas shift reaction" reaches equilibrium very

fast at the temperatures existing in the gasifier. This balances the concentrations

of carbon monoxide, steam, carbon dioxide, and hydrogen (CO + H2O↔CO2 + H2).

• The oxidation zone (B-4) is defined as the region in which all the oxidizer oxygen is consumed,

unless sufficient carbon is not present. Since all non-carbon feed and coke components are

assumed to enter the gas phase in the devolatilization zone, only carbon oxidation is considered.

31

Figure 5-2: Process Layout

5.4. Syngas Conditioning Island When inserted into the reactor, the organic fraction of biomass is then converted into syngas while its

inorganic/ inert fraction is melted into vitrified slag. Upon exiting the reactor, the syngas enters the

Syngas conditioning island through a syngas duct that is the interface between the two Islands. The

Syngas is free of tar, soot, or medium to long chain hydrocarbon.

Entering the syngas-conditioning island, the syngas is rapidly cooled and filtered to ensure that any

remaining volatile metals, and/or particulate matter are removed and deposited into the vitrified slag.

Moreover, any acidic gases such as hydrogen chloride (HCl) and hydrogen sulfide (H2S) are separated

to meet both the gas turbine manufacturer‟s fuel-gas specifications and air emission regulations and at

the same time ensure the gas turbine is protected from possible damage.

Cooling of the syngas is achieved via a gas/liquid heat exchanger, which recovers the sensible energy

of the syngas and generates steam. Once the syngas is cooled, it is passed through a scrubbing system

for acid gas removal.

This syngas treatment process removes acid gases and ensures that the syngas meets or exceeds the

fuel gas specifications required by the manufacturer of the power generating equipment. This process

typically involves a hydrogen chloride absorption system; and, in a majority of cases, a hydrogen

sulfide removal system. Since these pollutants are removed from the syngas stream, in which they are

32

much more concentrated than they would be in an exhaust flue gas, the gas clean-up process is more

efficient and costs less than post-combustion clean-up methods employed in most steam- boiler

plants.

5.5. Power Generation Island Once the syngas has been cleaned, it is passed through a series of filters and moisture separators to

„condition‟ it before it is compressed and delivered to the gas combustion turbine in combined cycle

where it is used as fuel to drive the electrical power generator. The equipment used in the Power

Generation Island consists of commercial off-the-shelf components like Gas turbines.

5.6. Balance of Plant and Waste Heat Recovery When the syngas is used for power generation application after the syngas has been combusted with

excess air in a gas turbine generator, the temperature of the combustion products (i.e. the exhaust gas)

is high because of the combustion process. The large flow of hot exhaust gases is passed through a

heat recovery steam generator (HRSG) where the heat energy in the exhaust gases is used to generate

steam. Part of this steam generated by the HRSG is then used to drive a steam turbine for generating

additional electrical energy, while the other part is sold for commercial purposes. Both the HRSG and

the steam turbine are commercially available. In figure 9, mass balance for the plant of 100 TPD has

been calculated and shown.

Once the steam has given up its energy in the steam turbine, it is circulated through a steam condenser

where it is condensed back to liquid state for re-circulation back through the same process. Having

released its sensible energy to produce steam in the HRSG, the cool exhaust gas from the gas turbine

is safely discharged to the atmosphere.

Figure 5-3: Mass balance for 100 TPD plant

33

5.7. Plant Energy Load Electrical energy is required to power the plasma torches and all the upstream and downstream

equipment. This power load is taken from the power generated by the plant itself thus making it

totally energy self-sufficient.

5.8. Working principle of plasma gasification

The waste is injected into the upper part of the plasma gasifier or reactor and piles up in the body

of the reactor. The plasma torches located at the bottom of the reactor generate a flame that is

between 2500-3000°C.

Figure 5-4: Schematic of the Whole Process (Recovered Energy, Inc.)

The organic material does not burn because of partial oxygen environment. The organic matter is

transformed to a gas composed primarily of carbon monoxide and hydrogen. This gas called syngas

contains substantial energy that can be used in a variety of ways.

34

The hot gas rises up through the waste piled in the gasifier and begins the gasification process on

the material piled in the gasifier. By the time the waste has reached the bottom of the reactor, the

high temperature, oxygen starved environment has totally transformed all organic compounds into

gas.

The gas that exits from the top of the gasifier primarily consists carbon monoxide, hydrogen, and

water along with small amounts of hydrogen chloride, hydrogen sulfide, particulates, carbon

dioxide and inerts in the gas. Because of high temperature, the base elements of the gas cannot

form toxic compounds such as furans, dioxins in the reactor.

As the gas exits the reactor it first goes to a gas reformer and then it is cooled in a series of high

temperature heat exchangers. The sensible heat is reduced to about 200°C and is used to generate

high-pressure steam that is fed to a steam turbine to produce electricity.

The high temperatures from the plasma torches liquefy all inorganic materials such as metals, soil,

glass, silica, etc. All metals other than non-metals, becomes vitrified or molten glass. The metal

and glass flow out of the bottom of the reactor at as the metal and glass flow from the reactor; they

are quenched in a water bath. Metals are separated from the glass. Figure 10, below explains the

process of plasma gasification diagrammatically.

No waste is left as all of the waste has been recycled to metal, glass or has been converted to fuel gas

All of the feedstock is converted to syngas and recycled to metal or glass as vitrified slag, which is

another saleable product.

The fuel gas is passed through cyclone mainly for particulate removal. After particulate removal the

fuel gas enters the heat exchanger, where approximately 80-85% heat is recovered for steam

generation.

After exchanging heat with water syngas passes through a series of scrubbers where the HCL is

scrubbed out to form aqueous HCL. The clean HCl water is further concentrated to 15-20% for

commercial sale.

The H2S in the gas is scrubbed out to make fertilizer grade sulfur using a biological or alternatively

can be converted into sodium bisulfite.

The gas then goes to the gas turbine to produce electricity.

35

5.9.Highlights of the Plasma Gasification

Advantages

• Renewable Feedstock Flexibility: Feedstock can be mixed, such as municipal solid

waste,biomass, tires, hazardous waste, agro residue, e-Waste, auto shredder waste, which

makes plasma gasification solution a 100% biomass based.

• Reclamation of landfill areas: It reduces the need for land filling of waste since no waste

isproduced during or after process. It is not incineration and therefore doesn‟t produce

leachable bottom ash or fly ash.

• Multiple Uses Syngas: It produces Syngas, which can be combusted in a gas turbine

orreciprocating engines to produce electricity or can be processed into chemicals, fertilizers,

or transportation fuels using different routes

• Low environmental emissions: No generation of dioxins/furans as environmental threats

ascarcinogenic gases. Generation of high temperature by plasma torches results in virtually no

or zero tar/soot. Because of high temperature maintained inside the reactor no formation of

dioxins/furans.

• Conversion of Fixed Carbon to Energy: Complete dissociation of molecules, thusunlocking

the greatest amount of energy from waste. It has ability to gasify fixed carbon along with

volatile, which gives plasma gasification an edge over other available technologies. Hence,

almost 98% carbon conversion is achieved.

• Handle high moisture content: Can handle moisture content of up to 25%.

• Vitrification of glass/metals: The vitrified glass/metals get converted to slag, which can beused

as construction aggregate, road fill material as another saleable product.

• Energy efficiency: Plasma gasification solution is an efficient means of extracting

energyfrom biomass. It allows for efficiencies three times greater than traditional biomass

gasification.

Disadvantages

• Energy Intensive: Highly energy intensive as compared to other gasification technologies

asit consumes around 10 % of total power production as parasitic load.

• Skilled Labor: Plasma gasification technology requires skilled labor for its operation

andmaintenance

• High O&M Cost: Higher operation and maintenance cost as compared to other

technologiesavailable for gasification.

36

37

CHAPTER 6

RESULTS AND DISCUSSION

The present study shows that Plasma gasification, as a WTE conversion technology is a viable option

in terms of both technical and economical. To support this technology from technology point of view,

like it can handle moisture content of upto 25%. It gives carbon conversion efficiency of 98% with

virtually no or zero tar/soot. Unique characteristic of plasma gasification is that it is 100% biomass

based feedstock process resulting in syngas, which has multiple end uses like bio-power, bio-fuel.

Plasma gasification generally has two end products syngas and vitrified slag both of which has

commercial value. This technology is self-sufficient and has greater efficiency as compared to other

gasification with better temperature control.

Return on investment for a 100 TPD plant with a power output of 8MW is 20% considering RDF cost

at a price of Rs.2.5/kg, which is fairly a good number. But if the tipping is provided by government

cost of RDF would lesser than this ROI would certainly increase up to 25 %.

6.1. Economics of plasma gasification plant

Below given is the cost for 100 TPD for an output of 8MWfor 24 hrs running

Selling price of electricity as per PPA =Rs 6/kWh

Insurance cost = Rs 5000000/yr

Yearly operation=8000 hrs

Raw material cost (RDF) =Rs 2.5/kg

Capital cost is Rs.10 Cr/MW

Total Investment Rs.80 Cr

38

Table 6-1: Economics for Plasma Gasification Plant (All figures in crores)

Capital Cost 10/MW

Investment 80

Sale of electricity to the grid 28.80

Cost of production

Raw material 8.40

O&M cost 3.20

Manpower cost 5.00

Insurance cost 5.00

Total 12.6

Unit cost of electricity 2.625/kWh

Profit/Revenue 16.20

Investment 80

ROI 20%

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CHAPTER 7

CONCLUSIONS

From this study it can be concluded that Plasma gasification seems to be a promising WTE solution for

processing waste to power. Besides the technology benefit of Plasma gasification process, there is the

clear environmental benefit here, which is the reduction of need for land filling. This prolongs the life of

our existing landfills, which in turn reduces the need to find new sites for land filling purposes.

Moreover, the other factor that is now important is the reduction in net CO2 emissions that result from

use of waste containing biomass (e.g. MSW) rather than fossil fuels to provide electricity or hot water.

This environmental benefit is now recognized through different economic instruments in many

countries. Apart from this technology benefit and environmental benefit being associated with this

plasma gasification it is also economically viable to set such facility that too without large land

requirement. No technology is fully competent with out government support and financial aid. For this

waste-to-energy as a sector to grow government should introduce the concept of tipping fee like in other

parts of the world.

Recommendation:

There is a huge gap between demand and supply mainly in India for this technology. Large capacity

systems are available but in order to make this technology advanced and widely accepted smaller

capacity systems of pico range i.e. 1-2 MW should be encouraged particularly for rural areas. Such

kind of technology advancement can cater to huge gap.

40

41

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