Production Optimization of SRP wells using PROSPER software
Major project report
1. 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
2. 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
3. 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, 3
rd
Floor PinnacaleClaridges TERI University, New Delhi
Business Towers, Surajkund
ii
4. 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
5. 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
6. 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
7. 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
v
8. 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
9. 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
10. 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
11. 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).
12. 2
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,
13. 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.
14. 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
16. 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.
17. 7
! Municipal Solid Waste (MSW)
Collection & Transportation from Point of Generation
Cans,!Tins,!Pipes,!etc.!
Storage & Segregation
Inerts (sand, stones, Ferrous & Non – Ferrous
Recyclablesetc.) 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)
19. 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.
20. 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.
21. 11
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.
22. 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
23. 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).
24. 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/kmol1 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 oxidationCnHm + /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/kmol10 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 hydrocarbons
a
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.
25. 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).
27. 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
28. 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)
29. 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
30. 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
31. 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
32. 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).
33. 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).
34. 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).
35. 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)
37. 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
38. 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.
39. 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
40. 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.
41. 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
42. 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
43. 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.
44. 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.
45. 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.
47. 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
48. 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 material8.40
O&M cost3.20
Manpower cost 5.00
Insurance cost5.00
Total12.6
Unit cost of electricity 2.625/kWh
Profit/Revenue 16.20
Investment 80
ROI 20%
49. 39
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.
51. 41
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