PRODUCTION AND GASIFICATION OF WASTE PELLETS Farokh

UNIVERSITY OF BORÅS
SCHOOL OF ENGINEERING
PRODUCTION
AND
GASIFICATION OF WASTE PELLETS
Farokh SAHRAEI-NEZHAD
Sara AKHLAGHI-BOOZANI
This thesis comprises 30 ECTS credits and is a compulsory part in the
Master of Science with a Major in Energy and Material Recovery, 120 ECTS credits
No. 6/2010
i

PRODUCTION AND GASIFICATION OF WASTE PELLETS
Farokh Sahraei, e-mail: x080291@student.hb.se, farokh156@gmail.com
Sara Akhlaghi, e-mail : x080157@student.hb.se, akhlaghi.sara@yahoo.com
Master thesis
Subject Category: Technology
University of Borås
School of Engineering
SE-501 90 BORÅS
Telephone +46 033 435 4640
Examiner: Professor Tobias Richard
Supervisor, name: Professor Tobias Richard
Supervisor, address: University College of Borås, School of Engineering
SE-501 90, BORÅS
Client: Borås Energi och Miljö AB,
Date: 03-03-2011
Keywords: Gasification, Municipal solid waste treatment, Renewable Energy,
Syngas, Waste treatment, Sustainable waste management, Waste Pellet
ii

Abstract
Thermo-chemical processing of waste materials including gasification is considered as an
effective waste treatment method in modern communities. Through this process, Green House
Gases are significantly reduced alongside the emergence of value added products (renewable
fuels), sustainable development targets are met.
In this study, the gasification of municipal solid waste materials has been investigated.
Syngas is a gasification product which is made up of carbon monoxide, hydrogen and
methane. Syngas can be used for power production, automotive fuel and production of
chemicals. Product gas through gasification is considered as a sustainable alternative transport
fuel for petroleum based fuel which can improve the domestic support of energy for the
independent countries.
In the gasification process, the energy content in carbonates material like municipal solid
waste is converted into a gas phase fuel. The conversion is affected by several parameters
such as gasification agent, operating temperature, reactor design, heating method, moisture
content and particle size of feedstock. It has been found out that gasification performance;
product gas yields, chemical composition and heating value of product gas are significantly
impacted by the gasification agent and operating temperature of the gasifier.
The kinetic mechanism of the gasification reaction and energy balance have been applied in
order to design the gasifier and to predict the operational behavior of the process. Also the
shrinking un-reacted particle model (SUMP) has been selected for waste particles gasification
modeling. By this way, designed parameters and optimal conditions of a gasification process
are achieved. This study presents the correlation between the reactor temperature, size of the
fed particles and the particles residence time.
The findings of this study shows that a waste gasifier can be an indirect heated, atmospheric
pressure, bubbling fluidized bed, steam gasifier which can be connected to a bubbling
fluidized bed waste boiler. The gasifier would be run at temperature of 650°C with steam as
gasifying agent and fluidized media by 1.84 ton/ton of feed supported by a connected boiler
with circulating sand with flow rate of 12.38 ton/ton of feed. The residence time of the
particles has been found to be around 318 second.
Accordingly, the combination of waste gasifier and waste boiler can be considered as an
efficient method for waste treatment process to produce renewable energy.
iii

Acknowledgements
We hereby acknowledge to numerous persons in contributing and assisting the work of this
thesis. Firstly we would like to sincerely acknowledge our supervisor and examiner professor
Tobias Richards for his valuable guidance and constant support during this research project.
The project is exists because of his vision and his guidance in right direction.
We are truthfully grateful to Borås Energi och Miljö AB staff especially Mr. Per Karlsson and
Ms. Pauline Salomonsson Lindberg at Reyavarket site, as well as Mr. Claes Ranweg and Mr.
Hans Skoglund at Sobacken site of Borås Energi och Miljö. Their supports have been very
helpful in many ways.
We would also like to thank Dr. Claes Breitholtz and Margareta Lundberg in research and
development department of the Metso Power Company and Mr. Ove Johanzon at Sodra Cell
Varo gasification plant in Varbarg (Sweden) for their technical support and useful advice.
Finally our program director at school of engineering Dr. Peter Therning is gratefully
acknowledged for his support.
Farokh Sahraei Nezhad
Sara Akhlaghi Boozani
iv

Contents
Abstract................................................................................................................................ 3
Acknowledgements .............................................................................................................. 4
List of tables ......................................................................................................................... 7
List of charts ........................................................................................................................ 8
List of figures ....................................................................................................................... 9
Abbreviations...................................................................................................................... 10
Chapter 1, Introduction ..................................................................................................... 13
Aim of this project ............................................................................................................ 13
Methods and materials ...................................................................................................... 13
Background review ........................................................................................................... 14
Gasification products and application ............................................................................... 14
Syngas market .................................................................................................................. 15
Syngas market terend ........................................................................................................ 15
Feedstock of gasification .................................................................................................. 16
Incineration versus gasification of waste ........................................................................... 17
Process and general comparison .................................................................................... 17
Emission and pollutants ................................................................................................ 17
Pollutants ...................................................................................................................... 17
Ash and slag, residues handling .................................................................................... 18
Gas clean up procedure ................................................................................................. 18
Economic...................................................................................................................... 18
Benefits of gasification ..................................................................................................... 19
Drawback of gasification of waste .................................................................................... 20
Chapter 2, Feedstock preparation ..................................................................................... 21
Production of waste pellet ................................................................................................. 21
Benefits and drawbacks of pelletization of waste materials ........................................... 22
Pelletization steps ............................................................................................................. 23
Size reduction steps ...................................................................................................... 23
Metal separation ........................................................................................................... 24
Drying .......................................................................................................................... 24
Pelletizing ..................................................................................................................... 25
Cooling ......................................................................................................................... 27
Chapter 3, Gasification ...................................................................................................... 28
Gasification of municipal solid waste ................................................................................ 28
Gasification main steps ..................................................................................................... 28
Drying .......................................................................................................................... 28
Pyrolysis and de-volatilization ...................................................................................... 28
Gasification reactions ................................................................................................... 29
Key factors for gasification of waste ................................................................................. 31
Gasification agent ......................................................................................................... 31
Temperature ................................................................................................................. 32
Pressure ........................................................................................................................ 33
Moisture ....................................................................................................................... 33
Heating rate .................................................................................................................. 33
Heating method ............................................................................................................ 34
Feedstock heating value ................................................................................................ 34
Waste particle size and preparation steps ...................................................................... 35
v

Ashes ............................................................................................................................ 35
Pollutants level ............................................................................................................. 35
Gas utilization ............................................................................................................... 35
Types of gasifier ............................................................................................................... 36
Fixed bed gasifier ......................................................................................................... 36
Fluidized bed gasifier .................................................................................................... 37
Entrained flow gasifier .................................................................................................. 38
Kinetic of waste pellet gasification ................................................................................... 40
Selecting a modeling for waste particles gasification ..................................................... 40
Residence time of the particles ...................................................................................... 42
Heat required for gasification of waste Pellet .................................................................... 46
The assumptions ........................................................................................................... 49
Chapter 4, Cost estimation of the project .......................................................................... 52
Chapter 5, Results and Discussion ..................................................................................... 53
Pre-treatment of gasification waste feedstock by pellet production ................................ 53
Gasification of pelletized waste in gasifier combined to the boiler .................................... 55
Cost estimation of the project: .......................................................................................... 60
Conclusions ...................................................................................................................... 61
Further works ................................................................................................................... 62
References ........................................................................................................................... 63
vi

List of tables
Table 1. The contributions of authors .................................................................................... 12
Table 2. Analysis of various gasification feedstock ............................................................... 16
Table 3. Effect of temperature on gas composition of MSW gasification [2, 45, 47, 48]. ....... 32
Table 4. Effect of heating method on heating value of product gas[2, 3]. .............................. 34
Table 5. Summarized characteristics of different gasifier [7, 8] ............................................. 39
Table 6. Experiential models for char gasification kinetics .................................................... 41
Table 7. Summarized assumptions, formulas of estimating residence time ............................ 44
Table 8. Residence time of particles at different temperatures ............................................... 45
Table 9. Summarized the heat balance calculations ............................................................... 46
Table 10. Operational data of boilers in Borås Energy Plant ................................................. 48
Table 11. Product gas composition at reactor temperature of 650 °C [64, 65]........................ 48
Table 12. The carbon consumption for the reactions paths considered for assumption 3 ........ 49
Table 13. Summarized energy demand/supply calculations ................................................... 50
Table 14. Design parameters of the gasifier .......................................................................... 51
Table 15. Summary of design parameters of the gasifier ....................................................... 58
Table 16. Purchased cost of equipment ................................................................................. 60
Table 17. Price list of equipment .......................................................................................... 60
vii

List of charts
Chart 1.Worldwide gasification capacity by products, data taken from [3] ............................ 15
Chart 2. World Market of Gasification GWth per year. [3] .................................................... 15
Chart 3. (a), (b) Effect of gasification agent on composition and heating value of product gas.
[42, 45] ................................................................................................................................. 31
Chart 4. The syngas main components as a function of temperature. [2, 48] .......................... 32
Chart 5. Effects of pressure on gas composition at 1000°C[3] ............................................... 33
Chart 6. Average heating value of gasification feedstock ...................................................... 34
Chart 7. Effects of gasification temperature on residence time .............................................. 55
Chart 8. Bed material at different temperatures ..................................................................... 56
Chart 9. Energy demand considering assumption 3 ............................................................... 56
Chart 10. Bed material and steam flow rate at different temperatures .................................... 57
Chart 11. Effect of moisture content of feed on sand flow rate .............................................. 57
Chart 12. Effects of gasification temperature on gasifier bed volume .................................... 58
viii

List of figures
Figure 1. (a), (b) Biomass pellet, (c), (d) Refused derived fuel pellet (RDF) [23] .................. 21
Figure 2. A Hook shredder [28]. ........................................................................................... 23
Figure 3 (a), (b). Mechanism of milling of waste material [29]. ............................................ 23
Figure 4 (a), (b). Pelleting mechanism in flat die pellet mill [32] .......................................... 25
Figure 5. Pelleting mechanism in ring die pellet mill[25] ..................................................... 26
Figure 6. Schematic of biomass gasification[1] ..................................................................... 29
Figure 7. Summary of biomass gasification reactions[1] ....................................................... 30
Figure 8. Updraft gasifier [1]. ............................................................................................... 36
Figure 9. Downdraft gasifier [1]. .......................................................................................... 36
Figure 10. Schematics of bubbling fluidized bed [48] .......................................................... 37
Figure 11. BFB gasifier [7]. .................................................................................................. 37
Figure 12. Schematics of circulating fluidized bed[48] ......................................................... 38
Figure 13. CFB gasifier [7]. .................................................................................................. 38
Figure 14. Entrained flow gasifier [14] ................................................................................. 38
Figure 15. Single char particle conversion models. ............................................................... 42
Figure 16. Schematic of waste pellet production. .................................................................. 53
Figure 17. Flow diagram of the waste pellet production (made by Super Pro) ....................... 54
Figure 18. Trap-door and steam collector of waste boiler in Borås Energi ach Miljö site ....... 57
Figure 19. Bottom ash screw and ash elevator in Borås Energi ach Miljö site ...................... 59
Figure 20. Bottom ash screw Borås Energi ach Miljö site ..................................................... 59
Figure 21. Rejected bottom ash (larger than 2mm) ................................................................ 59
ix

Abbreviations
YH2
YCO
YCH4
Cross section of the cylindrical or cubic gasifier
Total reacting surface area per unit of mass
Reference state of the conversion
Heat Capacity
Diameter
Activation energy )
Structural profile
Particle Height
Gas enthalpy
kinetic coefficient of the reaction
Enthalpy
Mass of carbon in waste pellet sample
Mass flow rate of feed
Mass flow rate of bed material
Mass flow rate of steam
Order of reaction
Pressure
Heat duty
Gas constant
Char reactivity per unit of surface reacting
Char reactivity of a waste pellet sample
Temperature
Steam velocity
Minimum steam velocity
Volume
Carbon conversion at time t
Carbon composition of waste (% wt. dry basis)
Percentage of Hydrogen in raw product gas
Percentage of Carbon monoxide in raw product gas
Percentage of methane in raw product gas
Heat of reaction
Density
Volumetric flow rate
Residence time
x

BFB Bubbling Fluidized Bed
CFB Circulating Fluidized Bed
CPM California Pellet Mill
DME Dimethyl Ether
EF Entrained Flow
FB Fixed Bed
FT Diesel Fischer-Tropsch Diesel
GHG Green House Gases
HHV High Heating Value
HRSG Heat Recovery Steam Generator
IGCC Integrated Gasification Combined Cycle
LHV Low Heating Value
MSW Municipal Solid Waste
PMSC Progressive Model with Shrinking Core Model
PMSP Progressive Model with Shrinking Particle Model
RDF Refused Derived Fuel
SMR Steam Methane Reforming
SNG Synthesis Natural Gas
SUCM Shrinking Un-reacted Core Model
SUPM Shrinking Un-reacted Particle Model
UCM Uniform Conversion Model
xi

Table 1. The contributions of authors
Chapter Part of the project Contributor s Page
1 Introduction Farokh Sahraei 13
1 Gasification products and application Farokh Sahraei 14
1 Syngas market Farokh Sahraei 15
1 Feedstock of gasification Farokh Sahraei 16
1 Incineration versus gasification of the waste Farokh Sahraei 17
1 Benefits and drawback of gasification of waste
2 Feedstock preparation
2
Benefit and drawback of pelletization of
waste materials
2 Pelletization steps
3 Gasification
3 Gasification reactions
3 Key factors for gasification of the waste
3 Types of gasifier
3 Kinetic of waste pellet gasification
3
Heat required for gasification of waste Pellet
and design parameters
4 Costs estimation
5 Results and discussion
5 Conclusions
xii
Farokh Sahraei 19
Farokh Sahraei 21
Sara Akhlaghi
Farokh Sahraei
22
Sara Akhlaghi 23
Farokh Sahraei 28
Farokh Sahraei 29
Farokh Sahraei 31
Sara Akhlaghi 36
Sara Akhlaghi
Farokh Sahraei
Sara Akhlaghi
Farokh Sahraei
40
46
Farokh Sahraei 52
Farokh Sahraei
Sara Akhlaghi
Farokh Sahraei
Sara Akhlaghi
53
61

Chapter 1, Introduction
People are not going to stop producing waste. Thermo chemical processing is an effective
way to treat municipal solid waste material and it has achieved a great attraction in modern
communities. Furthermore, gasification of waste materials has the potential to offer a major
impact on the ability for communities to meet the sustainable development targets[1].
Gasification of the waste is considered as a renewable and sustainable method in an effective
and environmental friendly way. It can meet the targets to reduce Green House Gases at the
first rank[2], and produces a valuable renewable fuel which can improve demand of the
sustainable energy present to different sectors of society.
In the gasification process, the energy content in the waste materials is converted into a gas
phase fuel [3]. The conversion is affected by several parameters where one of the important is
the preparation of the feedstock to achieve increased conversion efficiency. Pellet production
as an option for pretreatment of waste, has highly influence on waste gasification.
Gasification of waste offers numerous benefits with few drawbacks. It has the potential to
increase the overall efficiency of electricity generation compared to conventional waste
incineration[1]. On the other hand, excluding some of the disadvantages for waste
incineration process; waste combustion has a slightly higher thermal efficiency than
gasification [4-6].
Aim of this project
The aim of this project is a theoretically investigation of the possibilities to improve the
efficiency of the waste boilers by waste gasification. Consequently in this research project the
focus is to use waste pellet (mainly municipal solid waste) as raw material to the gasification
process. The study has been carried out to assess the feasibility of gasifying feed as
homogeneous structure as possible in order to fulfill the renewable fuel production, and also
sustainable management of waste materials adapted to the city of Borås (Sweden).
Methods and materials
This investigation has been done based on literature review, some calculations; and analysis
of the results of those calculations which were carried out. The data used for cost estimation
of the project was achieved through connection with the related industries.
13

Background review
Society always needs to use fuels for different purposes. The first fuel that human used was
wood for heating their homes. Wood was also used in the form of charcoal and later the coke
was used instead of the charcoal. When the population increased the shortage of this fuel
became a problem so the needs of using fuel from other sources become important. At the end
of the eighteenth century gas was produced and used from coal. In the twentieth century, the
gas usage became more significant in the market particularly for heating [2, 3, 7].
Gasification is a technology that becomes more important when humans faces with the lack of
fossil fuels and also the damages from the burning of these fuels, because fossil fuels like
coals produce CO2 and the emission is one probable causes of global warming. Hence for the
emission of CO2 some pretreatments need to be done on the coal or other feedstock like
biomass. The advantages of using gasification is that CO is produced instead of CO2, and also
the energy content of the products are increased and they can be used in other application
such as high efficiency power generation in gas turbine, fuel production and chemical
manufacturing[8, 9].
In the period of 1900-1940 the usage of gasification technology increased. It then halted for a
couple of decades before the interest was reactivated in the 1980´s, particularly for
environmental problems such as global warming[8]. Some landmarks in the early history of
gasification are:
• Coal gas first patented for lighting in 1804 [9].
• Westminster Bridge (London) illuminated with town gas light on New Year’s Eve
using wooden pipe for gas delivery in 1813[9].
• Baltimore, Maryland becomes first U.S city to light street with town gas in 1816 [3].
• Town gas lightning in factories replaces candles and lanterns, making the night shift
possible and enabling the industrial age in 1800s[9].
Gasification products and application
The product from the gasification process is a product gas mainly includes carbon monoxide
(CO) and hydrogen (H2) and less percentage of methane (except for nitrogen, water and CO2).
When the concentration of CO and H2 is high, the product is named syngas. Syngas is
colorless, odorless and very flammable[2]. The application of syngas could be as following:
Electricity production
Syngas and product gas can be fired in gas turbines and gas engines to generate electric
power. For the gas turbine application, high level of gas cleaning is required in order to
remove particles, alkali, sulphur and tar in comparison with gas engine. The efficiency of a
gas turbine is higher compared to a gas engine [ 3]
. In addition, electricity production of syngas
is more efficient than directly combustion in a boiler to produce heat for the electricity
production purposes. They also can be used as fuel in Integrated Gasification Combined
Cycle (IGCC) to further increase the electricity production.
14

Automotive fuel
Bio-based automotive fuels like synthetic fuels including methanol, ethanol, DME, FT-diesel,
synthetic natural gas (SNG) and hydrogen are all alternatives as automotive fuels. The
produced gas from gasification of waste is more appropriate for SNG application considering
its methane percentage. Also syngas is more suitable for Fischer-Tropsch products (gas to
liquids) and methanol because of high percentage of CO and H2 [1, 10, 11].
Production of chemicals
The hydrogen content in syngas can be used to produce a wide range of chemicals, ammonia
and fertilizers. Hydrogen can react with nitrogen available in the air to form ammonia (NH3).
Some other products are lube oils, and waxes[2]. The CO content could be used to produce
renewable plastics[1, 4].
Syngas market
According to statistic data from the energy market, syngas are increasingly being used for
different applications. Worldwide gasification capacity is shown in Chart 1 by different
products. As it can be seen, there is significant demand in the world for power production
using syngas at the first rank and chemical and automotive fuel in the second rank [12].
Syngas market terend
Chart 1.Worldwide gasification capacity by products, data taken from [3]
Nowadays, market demand for gasification products has a rapid growth in the world. Based
on the Simback report in 2007 (Chart 2), gasification planned capacity had an increased by
110 GWth per year in 2010 and by 150 GWth in 2014. Thus syngas as one of the energy carrier
can be one of the major players in energy market in the future. [3]
Chart 2. World Market of Gasification GWth per year. [3]
15

Feedstock of gasification
A wide range of carbon content feedstock can be converted to syngas through the gasification
process. The feedstock should have a high ratio of carbon-to-nitrogen, quite little sulfur, and
low moisture content. According to heating value, the feedstock can be divided into two main
categories which are high heat values feedstock such as coals, oil, black liquor, lignin, and
low heating value materials like municipal solid waste (MSW), biomass, petroleum coke (pet
coke), high-sulfur fuel oil, and any other low grade carbon content feedstock [1, 2].
The chemical composition of the feedstock might be the main limited factor of selecting the
feed for gasification process. The chemical compositions of the feed have great effect on the
quality of the product gas, design of the process and gas clean up procedure. In Table 2, there
are some comparisons between different feedstock’s and their produce gas composition in
different plants. It also shows differences between properties of coal, biomass and waste
materials as following:
1. Coals have higher heating value and carbon content than biomass and waste material.
2. MSW and coal have more ash and sulfur in comparison with biomass.
3. MSW has lower oxygen content, higher nitrogen and ash content than biomass since
oxygen content of biomass is higher than coal except in Anthracite coal.
4. MSW has high alkaline and chlorine content which leads to produce corrosive gas. In
contrast, chlorine content of biomass is rather low except the forest biomass materials
coast close to the sea however they have rather high alkali content which must be reduced
before a gas turbine application.
5. MSW is non-uniform in comparison with coal and biomass. MSW has different physical
properties, densities and morphologies that makes it difficult feed for gasification[4].
The municipal solid waste was compared for energy content, chemical composition and water
content using proximate analysis, with the same of biomass and coal in Table 2. The analyses
(C, H, O, N and S) are made on dry ash material.
Feedstock Region
Anthracite
coal [2, 3]
Lignite coal
[2, 3]
Brown
coal[2, 3]
Biomass [2,
3]
MSW[13]
MSW[14]
Ruhr,
Germany
Dakota,
USA
Rhein,
Germany
Typical
Biomass
Borås,
Sweden
Asian
Countries
Table 2. Analysis of various gasification feedstock
LHV
MJ/kg
Carbon
%
mass
Hydrogen
%
mass
16
Oxygen
%
mass
Nitrogen
%
mass
Sulphur
%
mass
Water
%
mass
36.2 91 3.6 2.5 1.4 0.7 4.5 6
Ash
%
mass
26.7 71 4.3 23.2 1.1 0.4 36.9 10.2
26.2 67.5 5 26.5 0.5 0.5 60 2.7
19.6 54 6 30.9 0.3 0.1 20 1.5
18.05 45.9 6.2 24.1 1.1 0.48 38.8 21.7
8.4 36.7 7.2 21.1 1.5 0.04 35 25.4

Incineration versus gasification of waste
Waste incineration, as one of the current options for waste management, has a great of interest
in the most modern cities. Incineration of the waste is a method for turning the waste material
to electrical energy and heat. The other option is gasification which is an advanced method for
converting waste to energy [15]. The common mistaken is claimed that gasification is just
another name for incineration [16]. Those two methods have advantages and drawbacks. The
main differences of both methods are discussed in the following.
Process and general comparison
During the waste incineration process, partial or total oxidation of carbonations
matters is take place. Heat is released from incineration whereas gasification is a
process whereby organic materials are decomposed through thermal cracking into
useful products as well as more valuable gases used for different purposes[1].
Gasification offers the highest controllability whereas incineration offers higher heat
application efficiency [2, 6].
Emission and pollutants
Pollutants
The incineration process is designed to maximize the conversion of feedstock to CO2
and H2O whereas gasification is designed to maximize the conversion of feedstock to
CO and H2. Both processes convert carbonaceous materials to gases but the
composition of gases before cleanup is different. The gasification resulting gas
consists mainly of H2, CO, H2S, NH3, and particles while the composition of flue gas
from the combustion process are CO2 , H2O, SO2, CH4 and particulates[2, 17].
Combustion processes operate with excess oxygen or air. It means that the combustion
agent has to be added to waste as input and the waste burns. The result of these sorts
of chemical reactions are mainly heat and CO2 and H2O which can emitted to the
environment while, the air emission can raise the level of Green House Gases and
other air pollutants. The gasification processes operate with a limited amount of
oxygen[2].
Syngas is burned with significant little NOX emissions[6]. So emission of NOx will be
decreased when produce gas is burned in gasification of waste compared to
incineration.
Release of sulfur and nitrogen oxides in the atmosphere are led to acid raining[6]. In
case of using syngas for chemicals these acid-rain are not produced but sulfur may be
entered with feedstock into the gasifier and is converted to H2S, also nitrogen in the
feed is converted to diatomic nitrogen (N2) instead of NH3.
The toxic and carcinogenic pollutants like dioxin and furan may be produced during
organic materials combustion. In gasification process there is no production of furans
and dioxins because the gasification process is performed at high temperature so furan
or dioxin will be cracked that caused precursors in the feedstock. The other reason is
17

elated to control amount of oxygen in the gasifier which restricted formation of free
chlorine from HCl [2, 6].
Ash and slag, residues handling
Solid residues of both processes are different. Particles from gasification are char and
inert slag but bottom ash and fly ash are leftover of combustion. The leftover of
gasification at low temperature is char which has value and can be sold. Char consists
of un-reacted carbon and the mineral matter existed in the waste. The major utilization
of char is as a source of activated carbon. Activated carbon may be used for decolorization
and waste water treatment [1, 6].
High temperature gasification above the melting point of mineral matters is resulting
of formation of glassy state non-hazardous and inert slag. Those not vaporized molten
slag are suitable for use in fields of road and construction industry and also as an
abrasive materials used for sand blasting[2].
In other hands, about the 30% of input to the waste incineration is converted to the
ash[18] which is consists of high amount of mineral matter and less amounts of unreacted
carbon. Those sort of by products must be safely treated and disposal as
hazardous waste[16]. Therefore, combustion as a waste treatment method is makes a
solid waste but a sort of hazardous solid waste.
Gas clean up procedure
Economic
In gasification cleanup of the syngas is performed in order to use that as a fuel,
chemicals and energy sourced but treated flue gas from combustion will be discharged
to the atmosphere. As mentioned, the sulfur contents in gasification feedstock are
recovered as a byproduct in form of sulfur or sulfuric acid. In contrast sulfur content in
combustion fuel converts to SO2 and must be removed from the flue gas. Cleaned
syngas is mainly consisted of H2 and CO but cleaned fuel gas consists of CO2 and
H2O [1]. A cleaned syngas free from sulfur and nitrogen oxides is ready for different
applications such as combusted in a gas turbine to produce electric power or it can be
burned in a steam boiler to produce hot water or steam. The syngas can be used as a
base for new chemicals like automotive fuel. Although the product gas without any
cleaning may use for gas fired steam boiler combined with steam turbine to produce
electricity [2].
The steam cycle has a higher operational reliability but requires higher investments.
The gasifier engine has a higher efficiency but lower reliability [5, 6]. Gasification of
waste using heat recovery system has an increscent up to 50% in electricity output in
comparison with waste incineration process [4, 5].
18

Benefits of gasification
1. Flexibility in wide range of feedstock
Ability to process a wide range of carbonaceous feedstock and convert them to the
syngas among high heat values feedstock such as coals, oil, wood and wide range of
low-value carbon content material like municipal solid waste, biomass, agricultural
wastes, petroleum coke (pet coke), high-sulfur fuel oil, refinery residuals, refinery
wastes, hydrocarbon contaminated soils, and any other carbon content feedstock [2].
This range of flexibility increases the economic value of these resources and decreases
costs by providing industry with a broader range of feedstock options [1, 2, 19].
2. Flexibility in wide range of product
The syngas which is produced by gasification process can be converted into numerous
valuable products, ranging from electricity, heat, steam to fuels in gas and liquid phase
(FT Diesel), chemicals such as Acetic anhydride (Acetic Acid), methanol, ammonia,
Fertilizer (Urea) and hydrogen[19].
3. Low cost of cleaning equipment
The application of gasification technology is produced less volume of flue gas in the
process. So it reflects in a decreased size and cost of equipment related to off-gas
cleaning system and increases opportunities for added revenues [2, 20].
4. Clean products
gasification process has the ability to remove contaminants in the feedstock and
produce a clean syngas product.
5. Almost zero emissions
The system based on gasification process can meet the strictest environmental
regulations pertaining to emissions of sulfur oxide SOx (sulfur dioxide SO2),
particulate matter, and toxic compounds other than coal contaminates such as mercury,
arsenic, selenium, cadmium, etc.. Further, gasification provides an effective means of
capturing and storing or sequestering carbon dioxide (CO2), a greenhouse gas. The
carbon dioxide produced during gasification is present at much higher concentrations
and at higher pressures than in streams produced from conventional combustion,
making them easier to capture[2, 16].
The vision is to convert synthesis gas into pure hydrogen using the waster gas shift
reaction and use the hydrogen as an ultra-clean fuel with an exhaust gas of nothing but
water [7].
6. Energy security
By making better use of available and domestic biomass renewable rich energy
resources such as biomass and MSW, gasification can decrease dependency on
petroleum, fossil fuel and other imports energy sources[6].
High efficiency by combined with power cycle
The systems based on gasification process can be integrated with other processes and
technologies for power production, mainly combustion, gas turbines cycle and also
19

solid oxide fuel cells[1]. The integrated systems are significantly efficient, and result
in more value from each unit of raw material and feedstock[19].
Waste incineration plant consumes high quality fuel for its operation; it is possible to
apply gasification process as the first stage of thermal treatment to minimize the
consumption of auxiliary fuel [20]. Accordingly, the combination of waste
gasification and waste incineration has the potential to increase the overall efficiency
of both waste gasifier and waste boiler compared to conventional waste incineration
process.
Drawback of gasification of waste
Waste gasification technology is still in a premature stage and not common technique for
MSW. That is the major drawback of gasification process. Numbers of problems associated
with gasification for waste materials are as following.
1. Tar formation, gas reforming and gas cleaning. The gas reforming procedure can be
one of the complex and expensive stage of the process as well as the gas cleaning
steps of hot product gas[4].
2. Not fully conversion of inorganic content. Inorganic content of waste materials are not
fully converted at rather low temperature less than 800°C and lower content of
oxidizing agent therefore, all materials may be not reacted. But in case of combine
waste gasifier and waste combustor that is not matter, whatever is not reacted in
gasifier will react in the combustion unit but the gas yield will be less[19].
3. Alkali content of waste materials at high temperature gasification. At temperature
higher than 700 C, alkali metal is problematic when it reacts with chlorine gives
sodium chlorine which is corrosive[19].
20

Chapter 2, Feedstock preparation
All type of biomass among waste material is required preparation process because of variety
in physical, chemical and morphological characteristics[1]. The different characteristics of
municipal solid waste materials make a necessity to pretreatment the feedstock for gasifier.
Pelletization is one of the pretreatment methods for make the feeds uniformed.
When the materials in small size are compressed into cylinder shape they called pellets. Pellet
is produced of wide ranges of biomass materials and used for different purposes. Finland and
Sweden are the two leading countries in pelletizing technology in Europe [21, 22]. The
process of pellets manufacturing was first developed for the livestock feed industry [23].
Special focus here is on municipal solid waste as feedstock for gasification process. The
property of this waste stream varies with lifestyle, season, location, trends of sorting of the
waste materials which make them heterogeneous. The waste streams are varied in size, type,
shape, density. Therefore, they behave differently when they are entered to the reactor. And
prediction of reactor condition is become difficult. For an efficient gasification process, a
homogeneous waste mixture and uniform structure and density is required, thus control of the
system will be much better [24-27].
Production of waste pellet
Production of biomass pellet is common. Although a wide range of biomass and agricultural
residues are pelletized for different thermal proposes. However when the feedstock is waste
material, the process is more difficult as mentioned earlier. Steps of production of waste pellet
include size reduction, metal separation, drying, pelletizing, cooling, storage and transport.
Figure 1, illustrates pelletized biomass and RDF (refused derived fuel) respectively. The
major composition of RDF is plastic and paper.
a b
c d
Figure 1. (a), (b) Biomass pellet, (c), (d) Refused derived fuel pellet (RDF) [23]
21

Benefits and drawbacks of pelletization of waste materials
The benefits of pelletization can be explained as following:
1. It can provide the homogenous feed, which makes easier controlling of the flow rate of
a reactor, prediction of conditions, and controlling of the system.
2. Less storage place is needed. Waste materials are compressed as pellets, required less
space compare to untreated waste [24].
3. There is a limitation on keeping untreated municipal solid waste in the waste bag more
than 3 days when they are collected at the waste collection center because of the risk
of firing and bacterial pollutant. This is especially important in the summer season
when the heat demand of the city is lower than available waste at the plant. By waste
pelletization, it is possible retained them more for the next demand.
4. Pelletization of waste material is efficient way of loading, unloading and handling
them from waste collection center to the plant. Hence the cost of transportation and
material handling would be decreased.
5. Amount of extra dust in the feedstock could be decreased and the feed becomes more
stable as a result of pelletization.
6. Distribution of the waste and odor problems in the environment would be controlled
better by waste pelletization [21].
Drawback of pelletization is that when the density by compaction is increased, the active
surface area will be decreased then reaction rate will be decreased and the reaction time
will be increased.
22

Pelletization steps
Size reduction steps
If the dimension of input waste material is larger than a certain range, size reduction step is
required [20]. This range for most of the pellet mills is 30-50mm [25]. The size reduction
process can involve one or more steps like grinding, shredding, crushing or milling. A
shredder has the ability to significantly reduce the size of the large waste materials with a
maximum size of 2700 mm[28]. A Hook shredder used in Sobacken recycle center, Borås,
Sweden is Figure 2.
Figure 2. A Hook shredder [28].
Size reduction is typically performed in hammer mills (Figure 3) which is appropriate for
waste material with rather low energy cost compares to other size reduction method [29]. It
can reduce the size of the material to 80mm. Hammer mills use rotating hammers or knives to
provide an extremely high hammer tip speed, as well as a minimum clearance between the
hammer and the screen which determines the size of the outgoing material. A hammer mill
includes a rotor with rods for the hammers and a motor for rotating the rotor. As the rotor
turns, the hammers are free to swing on the rods and the waste materials are fed into the
hammer mills and are crushed. This gives an energy efficient grinding process[30, 31].
a
Figure 3 (a), (b). Mechanism of milling of waste material [29].
23
b

Metal separation
All sorts of ferric and non-ferric metals must be detected and are removed from the waste
stream via magnetic separation. Separated metals can be recycled. The reason is that even a
very small amount of metal could destroy the pellet mill equipment.
Drying
To achieve a good quality of the pellet, the moisture content of the feedstock is one of the
important factors. The moisture content of the waste materials is rather high and it has
influenced on gas composition and the energy balance of the process[20]. From gasification
point of view, high moisture content is required more energy for evaporation. On the other
hand, depending on the process design and the desired produced gas, controlling the amount
of moisture is necessary. It should be in the range of 10-15%. One of the reason for this range
is, when the wet produced pellet is dried, some cracks are appeared in the pellet due to lack of
water and the pellet becomes fragile [32]. In addition, if the moisture content is less than that
range, the pellets are denser and loosed their quality, also in the pelletizing step, the friction
between the feedstock and the dies in the pellet mills increase and could cause blockage of the
holes in the dies [21, 22, 33, 34].
To achieve the desired moisture content, different dryers can be used. There are a lot of dryers
that can be classified in different categories. Based on methods of heat transfers, they can be
conduction, convection, radiation and electromagnetic field [35, 36]. About 85% of industrial
dryers are convective [35]. In convective dryers, drying medium and materials have direct
contact with each other but in conductive dryers materials dry with indirect heating [35, 36].
They can also be continuous or batch based on the mode of operation [36]. Another category
can be based on the vessels that used for drying the materials such as tray, fluidized bed,
rotating drum, pneumatic spray [35]. Also different sources can be used for providing the
necessary heat in the form of hot air, flue gas and superheated steam for evaporating the
moisture from the materials [36].
In case of municipal solid waste as a feedstock, some emissions release during the drying, due
to volatile organic compounds. Usually when the temperature of the feedstock is more than
100°C, these emissions happen[34].
Another matter is the risk of firing in the dryers due to the explosion of combustible gases that
might release during the drying. If the high temperature and enough oxygen exist explosion
can be happened. When the concentration of oxygen is more than 10%, it could be dangerous
[34].
Many factors can be influenced on the selection of the dryers. For example depending on the
desired quality of the product, the size of materials that used, the energy demand is needed for
drying, the safety of the dryers and impacts of them on the environment, and the residence
time of the dryers [34-36]. The residence time of continuous dryers can be varied from few
minutes to two hours [35]. As mentioned above most of the dryers are convective, also most
of them are continuous with atmospheric pressure and hot air as a medium drying [35, 36].
24

Rotary cascade dryer is one of the common dryer that used in the commercial and industrial
scale for drying biomass. This dryer consist of cylindrical shell with the diameter between 1m
to 6 m inside the shell. There are some vanes that elevate materials and flood them through
the cylinder. This dryer has a little slope that materials can move through the cylinder while
rotating [34].
For instance, the Vandenbroek Company uses a rotary drum dryer for drying municipal solid
waste. Drying medium is hot air that co-currently contacts with the materials. This dryer has
multi-pass system which consists of 10 drying passes. The temperature of the hot air is
between 200 - 800°C. The temperature of the final product is not to be exceeding 90 °C due to
the possibility of firing in this temperature[37].
There are also other dryers that can be used for drying biomass. Perforated floor bin dryers are
usually used in small scale with batch system that is appropriate for feedstock like grains. The
bed conveyor dryer is similar to the perforated dryer but with a continuous system feeding. In
this type, the feedstock is carried out on the conveyor with bands and the drying medium is
fed by fans in the dryer [34].
Fluidized bed steam dryers are more advanced in comparison with the other dryers mentioned
and can be used for drying e.g. biomass. They are expensive but in large scales they can be
appropriate [34].
Pelletizing
Production of pellet consists of compaction and densification of crushed waste in the form of
pellets. This part is the most energy demanding part. For having the better quality of the
pellets, such as hardness and stability, sometimes in order to attaching the feedstock binders
are added[26]. Increasing the feed temperature decreases the energy demand, however
temperatures higher than 100°C, cause more emissions of volatile organic compounds [38].
Two common pellet mills are the flat die pellet mill and the ring die pellet mill [26, 37, 39,
40].
The flat die pellet mill, Figure 4, consist of two main parts: roller and perforated die. The
roller parts are made from alloy metals which are tight (severe) and cannot be broken easily.
This part can have one or more (two or three) pair of rollers. The perforated die parts include
holes in order to compress and compact the material and make the pellet. The diameter of the
holes could be changed due to different requirements. The materials are pressed between the
rollers and the flat die and come out from the holes in the die part in the form of pellet [32,
39].
a b
Figure 4 (a), (b). Pelleting mechanism in flat die pellet mill [32]
25

In the ring die pellet mill, Figure 5, materials are pressed between the roller and the ring die
into the holes on the ring die. On the outside of the ring die a stationary knives cut the pellets
to the desired length [26, 37, 40].
Figure 5. Pelleting mechanism in ring die pellet mill[25]
In the following there are some comparisons between these two pellet mills that can be
affected on the selection of them for different feedstock.
1. The diameter size of the ring die pellet mill is limited due to the limitation of the ring
die mould, so the pressure is limited, but in the flat die there is no limitation of
diameter size from moulds, so in this type by increasing the diameter size the press
power of the rollers are increased, also the service life of the machine can be extended
[39].
2. The material in the ring die pellet mill is distributed by high-speed rotation of the
roller that has a centrifugal distribution. The materials are non-uniform fed, but in the
flat die the materials are entered the equipment vertically by their own weights and
they are equally distributed [39].
3. The ring die has high-speed rotation with high rate of damaging of the materials when
they are exiting but the flat die has low-speed rotation with low breakage rate [39].
4. The ring dies pellet mill are usually used for high bulk density materials but flat die
can handle rather low bulk density materials[41].
5. The capacity of the ring die is much bigger than the flat die.
6. The ring die has a complex structure in comparison with the flat die, so flat die usually
used in home or small workshops[26].
7. In the ring die pellet mill ease of maintenance and operation, only straight forces on
the die which makes the machine more efficient in comparison with flat die. Also less
wear parts even on rollers and dies is another advantages of ring die pellet mill [19].
8. Investment cost in ring die pellet mill is lower than flat die[41].
26

Cooling
The cooling process is a very simple procedure where ambient air sometime is cooled by a
coolant which is flowed over the hot pellets. According to the pelletization procedure, the
temperature of the produced waste pellet is between 80 to 100°C [25] and the moisture
content is about 15% which makes the pellet slightly forgeable. Cooling is needed to reduce
the temperature to 5°C higher than ambient temperature and also about 3 % - 5 % reduction of
the moisture [42]. Therefore the final moisture content of produced pellet would be in range
of 10-12%. The reasons are that high amounts of moisture in the produced pellets lead to
deformation of the pellet when they are dried and caused low stability during handling and
transportation. In other hands, high amounts of energy are needed to evaporate the waste in
the feed materials within gasification process.
There are two basic structures for coolers, horizontal and vertical. The flow in both is counter
current. This means that the airflow is in the opposite direction of the feed [42, 43]. In the
horizontal cooler, pellets are conveyed on a perforated steel mesh by a transmission belt
where cool air stream passes through. In the vertical type, pellets fall by gravity into a
chamber through where air is sucked upwards by a fan [42]. The cooler is based on the air
flow through columns of hot and moist pellets, which result in evaporation of moisture from
the pellets. For moisture evaporation, heat is taken from the pellets leading to cooling of
pellets. To achieve the necessary cooling effect, air pressure and volumetric flow rate of
coolant, length of column and the residence time will play an important role [35].
27

Chapter 3, Gasification
Gasification in general is a process to extract a gas from mixed carbonates materials. In other
words, gasification is a process that involves a series of reactions to convert carbon-based
material in form of liquid and solid into a gaseous combustible product called syngas or
synthesis gas. Syngas is mainly composed of carbon monoxide CO and hydrogen H2[1, 2].
Gasification of municipal solid waste
Municipal solid waste (MSW) materials have a rather high carbon content and heating value
resembled to biomass material [13] as indicated in Table 2. The analyses (C, H, O, N and S)
are made on dry ash material.
In MSW gasification, the energy content in solid waste is converted to energy rich gas fuel.
The remaining material parts that could not be converted in to syngas, such as metal, glass,
rock and concrete are vitrified to produce’s slag [1, 43]. Some factors have influenced on
carbon conversion rate and product gas yields. Factors like density, size and shape of the
waste particle, reactor temperature, type and amount of gasification agent, design of gasifier
and heat transfers rate [1, 44].
Gasification main steps
Drying
As the first step of gasification feedstock is heated below temperatures of 200°c and the water
content in the fuel is released by evaporation.
Pyrolysis and de-volatilization
Wet feedstock + Heat → Dry feedstock + Steam
When dried feedstock is exposed with high temperature in the range of 300°C to 700°C [1]
pyrolysis and de-volatilization of feedstock are takes place [4].
Dry feedstock + Heat → Char + Volatiles Components
In this step, non-condensable volatile components of feedstock are released when the material
is heated and cracked. They form pyrolysis gases and the remaining solid material is called
char and its organic part consists mainly of carbon. The composition of products gas is
depended upon temperature and methods of heat support to the rector [1].
During direct heated gasification, thermal decomposition, the light hydrogen rich volatile
hydrocarbons components are release in presents of insufficient amount of oxygen. Then a
gas product and solid carbon (char) and also other components like tars, phenols and
hydrocarbon gases are formed [1, 4, 20].
In indirectly heated gasification, steam is used as a heating source but steam plays an
important another rule as hydrogenation agent. If hydrogen is added to the system formation
28

of hydrogen and carbon monoxide will be accelerate. It means that steam plays as a catalytic
for gasification reactions at relatively low temperatures. Formation of methane is promoted by
the hydrogenation process within the gasification reactor at the same low temperature. [2]
The amount of volatile components are varies. It is depending on the source of the raw
materials and contains mainly H2O, H2, N2, O2, CO2, CO, CH4, H2S, NH3, and C2H6. In
addition to these compounds, there are also a slight amount of unsaturated hydrocarbons such
as acetylenes, olefins, aromatics and Vanillin Syring aldehyde Conifer aldehyde, Whiskylactone,
tars and char. The Figure 6, represents the different steps during biomass gasification
as well as the products of each reaction [1, 2, 4].
Gasification reactions
Figure 6. Schematic of biomass gasification[1]
The following stoichiometric reactions take place in a gasifier when oxygen is present [1, 43].
(1) C + O2 → CO2 (∆H= -405.9 kJ/mol Exothermic)
(2) C + 1/2O2 → CO (∆H= -123.1 kJ/mol Exothermic)
(3) H2 + 1/2O2 → H2O
Inorganic materials in the char + Heat → Slag
Depending on the gasification process, the reactions are carried out in presence of insufficient
amount of oxygen. Most of the supplied oxygen into the gasifier is consumed by the reactions
(1), (2) and (3). Results of char combustion are ash, un-reacted inorganic material. They can
be melted into liquid slag. Slag can be solidified and formed clinker [2]. In the combustion
step, CO2 and H2O are formed when the syngas is burned to supply the necessary thermal
energy for the endothermic reactions.
By combustion of char carbon, the amount of necessary energy for the gasification reactions
is directly provided. In some cases, the required energy is supplied indirectly by combusting
fuels separately from outside the gasifier[2, 4].
29

The principal gasification reactions (4) and (5) are water-gas reactions which are endothermic
and accrue at high temperatures and low pressures.
(4) C + H2O = CO + H2 (∆H=131.3 kJ/mol. Endothermic)
(5) C + 2H2O = CO2 + 2H2
Reaction (6) is known as the Boudourd reaction, which is endothermic and is much slower
than the combustion reaction (1) at the same temperature in the absence of a catalyst[2].
(6) C + CO2 = 2CO (∆H= 159.7 kJ/mol. Endothermic) Boudouard reaction
(7) C + 2H2 = CH4 (∆H= -87.5 kJ/mol. Exothermic)
Reaction (7) mainly is an exothermic and very slow reaction which is called hydrogasification.
(8) CO + H2O = H2 +CO2 (∆H= - 40.9 kJ/mol. Exothermic)
Reaction (8) is called water-gas shift reaction, is important especially where H2 production is
desired. Optimum yield is obtained at low temperatures (up to 260°C) in the presence of a
catalyst. It is noticeable that the pressure has no effect on increasing hydrogen yield[1].
(9) CH4 + H2O = CO + 3H2 (∆H= 206.3 kJ/mol. Endothermic)
Reaction (9) is called steam methane reforming (SMR) reaction which is proceeds very
slowly at low temperatures in the absence of catalysts. Also during the reactions (4) through
(9) the heat necessary for drying the solid fuel, breaks up chemical bonds, is provided and
resulted in the raising in temperature of the reactor to make gasification process. The
following chemical and thermal reactions may take place
(10) C + H2O = 1/2CH4+1/2CO2
Reactions (4) to (10) are equilibrium reactions which mean that they can go either way.
Reaction (10) is relatively thermal neutral, suggesting that gasification could proceed with
little heat input but methane formation is slow relative to reactions (4) and (5) unless
catalyzed. Summary of gasification reactions are shown in Figure 7[1].
Figure 7. Summary of biomass gasification reactions[1]
30

Key factors for gasification of waste
The following parameters as key factors for gasification of waste materials have significant
impact on gasification performance, chemical composition and heating value of product gas.
Gasification agent
The gasification agent has a significant effect on the system performance and product gas
composition[45]. According to the gasification process, one of the medium substances such as
air, oxygen, steam and CO2 can promote the gasification process.
Due to high percentage of nitrogen in the air, gasification of biomass with air have rather high
amount of nitrogen in product gas contains e.g. 47.5% by volume dry basis, and low heating
value approximately 5.5 MJ.Nm 3 . In case of oxygen, the product syngas contains low amount
of nitrogen e.g. 22.5 % by volume dry basis depending on the purity of the oxygen, but the
oxygen separation from air has a high energy demand and thus is associated with a high cost.
Early experimental works by different researchers confirm that gasification of solid fuels like
biomass and MSW with pure steam can improve the heating value of the syngas from ~15
MJ/Nm 3 up to 30 MJ/Nm 3 [45, 46] by reducing the nitrogen content in the syngas depending
on purity of the steam and ratio of steam to oxygen[46]. When steam is used as gasification
agent, a significant raise is observed in yield of hydrogen and carbon monoxide and methane
as indicated in Chart 3[11, 45]. Steam agent can provide heat which is needed to maintain the
gasifier temperature. Required steam can be generated through a boiler or a heat recovery
steam generator (HRSG). Effect of gasification agent on heating value and average
composition of the produced gas of the Güssing biomass gasifier is presented in Chart 3[47].
The Güssing biomass gasifier plant is working at 850-900°C with a feed composition of 50%
C, 6% H, 44% O2 (% wt. dry basis) and 20% moisture content [20, 24, 45, 47].
(a)
(b)
Chart 3. (a), (b) Effect of gasification agent on composition and heating value of product gas. [42, 45]
31

Temperature
The effect of reactor temperature on gasification is a key factor of the process. The higher
temperatures promote the reaction rate, yield of the produced gas, hydrogen content and the
complete conversion of char. The lower temperatures promote methane formation, char, tar
also volatile content [2, 11]. At increasing temperatures less methane is formed as well as less
concentration carbon dioxide.
As it is observed in Chart 4 and Table 3, the content of CO is decreased from 500°C to 650°C
and then increased again at 900°C. It means that the maximum concentration of carbon
monoxide and hydrogen can be obtained at temperature of 900°C. Also, gradually increased
temperature may lead to increase of hydrogen and high heating value of product gas at
equilibrium condition for biomass gasification.
Table 3. Effect of temperature on gas composition of MSW gasification [2, 45, 47, 48].
Temperature °C H 2 mol % CO mol % CO 2 mol % CH 4 mol % HHV MJ/m 3
500 5.56 33.5 44.8 17.50 12.3
650 16.6 30.5 31.8 11.00 15.8
900 32.5 35.5 18.3 4.50 15.1
Chart 4 shows the yield of the main components of synthesis gas as a function of temperature
from municipal solid waste gasification [2, 48].
Chart 4. The syngas main components as a function of temperature. [2, 48]
Consequently, the gasification temperature can control the concentration of the desired
product such as methane, hydrogen or carbon monoxide. However, it must be considered that
the reaction kinetic, fuel composition and eventual catalytic material also have a high impact
when the optimum operation conditions are determined[49].
32

Pressure
Operating pressure of a gasifier is selected according to process requirement and products
applications. For instance, the pressure of syngas used for ammonia production should be in
range of 130-180 bars. Also applied gas turbine for power production needs the product gas in
the range of 20 bars. Therefore, gasifier may operate at the same pressure [3]. Effects of
different pressures on the composition of product gas at 1000°C are shown in Chart 5. As it
indicates, increasing pressure makes a gradual increase in CH4 and CO2, and slight decrease
in CO and H2 contents in product gas.
Chart 5. Effects of pressure on gas composition at 1000°C[3]
In industrials application of syngas for power or chemicals production, when a high pressure
is desired, it is preferable that the gasifier is pressurized to reduce energy consumption, for
reducing equipment size, and decreasing agglomeration of the ashes inside the reactor [1].
It is noticeable that majority of gasifiers are working in the sub atmospheric pressure range
since in case of leakage, the outside air will move into the reactor, therefore no potential
hazardous gases will come out. Furthermore, applying high pressure generally has influences
on reactor materials, gasifier joints, isolation issues and feedstock feeding equipment which is
lead to an increase on the cost of a rector and the whole system.
Moisture
The moisture level has various impacts on reactions temperature and composition of syngas as
well as on the energy balance of the process. Appropriate range of moisture content is
recommended 10-15% [4].
Heating rate
The effect of the heating rate can be seen on volatiles separation during the pyrolysis and the
de-volatilization step. A higher heating rate significantly increases a higher porous of char in
the steam gasification of biomass as a result of the volatile matters has been rapidly released.
Consequently, the increase of the reaction rate of char, as well as volatile yield and also the
conversion of biomass can be expected. On the other hand, low heating rate allows char
particles to react with volatiles[2]. The heating rate doesn’t influence the elemental
composition of char[50].
33

Heating method
The gasification process involves a series of endothermic and exothermic reactions, so the
required heat should be supplied. Gasifies are classified as autothermal or allothermal
depending on how the heat is supplied. In the autothermal method or direct heated gasifier,
the necessary heat is provided by exothermic reactions paths through a partial oxidation of the
feedstock inside the reactor. But in case of allothermal or indirect heated gasifier, the heat
needed is provided by an external source. The heating value of product gas by allothermal
method is greater than autothermal as it is shown in Table 4 [2, 3, 24].
Table 4. Effect of heating method on heating value of product gas[2, 3].
Producer gas Gasification Agent
34
HHV of Product Gas
(MJ/Nm 3 )
Aautothermal (Direct heated ) gasification Air 4-6
Pure oxidation gasification O2 10-12
Allothermal (Indirect heated) gasification Steam 15-20
Feedstock heating value
The heating value in general term refers to the amount of heat releases from the combustion
reaction which is indicated by weight unit for solid fuel (MJ/kg) or volume unit for gas fuel
(MJ/Nm 3 ). There are high and low heating values for the fuels:
The High Heating Value (HHV) is the amount of heat released from the complete combustion
reaction where the energy released during water condensation is taken into account[51].
The Low Heating Value (LHV) is the amount of heat released from the combustion reaction
where the energy released during water condensation is not taken into account[51]. In other
word, it is the heat released from the combustion reaction where the water produced is steam.
Heating value of feedstock depends on the amount of moisture and combustible organic
material [14]. In Chart 6, the heating value of different biomass and coal is presented. As it
indicates, the highest value is related to the coal and the rest which are corresponded to the
biomass is in the range of 14-20 (MJ/kg) [2, 3, 51].
Chart 6. Average heating value of gasification feedstock

Waste particle size and preparation steps
Type of gasifier determines density, size and shape of the waste particle. They influence the
heat transfer within the gasifier bed. For instance, in case of an entrained flow reactor the
feedstock has to be in range of hundreds of µm and for a fluidized bed reactor, it should be in
the range of a few mm, larger particles are accepted in fixed bed gasifier[4] however, the
higher ranges lead to un-treat feed particles in the process[1, 44].
Ashes
The composition and melting point of the ash have great impact on ash behavior particularly
at high temperatures, and on the accumulation rate in the reactor. Moreover the amount of
ashes can be influenced on the ash discharge system and type of the gasifier[52].
Pollutants level
Pollutants can be classified into tar, particles and heavy metals. Level of tars is one of the
limiting factors in the gasification process. Tars refer to condensable organic or inorganic
compounds which are present in raw product gas. Tars make fouling or inactivating of
catalytic filters[49]. The particles like mineral substances in fuel, un-reacted solid materials
and part of fuel entrained with gas products, outcome as pollution.
Pollutants can be removed by cyclones, filters or scrubbers. Feedstock like MSW has quite
low level of heavy metals content. If they are present in high amount, they must be removed
through e.g. filtration[20].
Gas utilization
In order to utilize gasification produces, gas cooling and gas cleaning procedures are required.
The quality of syngas is depended on mentioned gasification key factors and applied gas
cleanup technology as well as feed composition. Cleaning process from the producer gas
stream involves removing unwanted components including particulates, alkali, tars, sulfur,
and ammonia. A gas cleaning system may consist of cyclone separation, gas cooling system,
low temperature gas cleaning, high temperature gas cleaning, acid removal, sulfur recovery,
CO2 removal, gas reforming and Fischer Tropsch synthesis.
Obtained product gas through biomass gasification can be upgraded to hydrogen-rich
synthesis gas. The synthetic gas can be further converted to liquid (Fischer Tropsch synthesis)
or gaseous fuels and chemicals, including fuels such as methanol, dimethyl ether (DME), and
synthetic diesel. However, the raw product gas contains both gas and particle impurities
which can have negative affects to both catalysts and hot-gas filters [53].
35

Types of gasifier
Based on the reactor design they are fixed bed, fluidized bed and entrained bed gasifier. In the
following the types of the gasifier will be explained [1, 20].
Fixed bed gasifier
Updraft gasifier
In this simple type of gasifier (Figure 8), the feedstock is fed from the top of the gasifier and
passed through the different zones in the gasifier such as drying, pyrolysis, oxidation and
reduction zones. Gasification agent is injected from the bottom. The produced gas leaves the
gasifier from the top in the converse direction of the feedstock.
One of the advantages of this type is high thermal efficiency due to internal heat exchange
that gives a low temperature of the exit gas. Another advantage is that rather large size of the
feedstock in range of 100-200mm can be used. The main drawbacks of this type are high
amounts of tars and pyrolysis products which they are not combusted therefore, for power
production application expansive gas cleaning is required [1, 20, 54].
Downdraft gasifier
The feedstock in the downdraft gasifier is fed from the top (Figure 9), but the produced gas is
exit from the bottom in the same direction of the feedstock. Gasification agent injects from
the top or from the sides of the gasifier. In this type the feedstock passes the zones mentioned
above in the updraft gasifier with some different in the locations of the zones. The content of
tar in the produced gas is relatively low and it is appropriate for engine applications. When
gas passes the oxidation zone small ash particles enter to the gas and caused high dust and ash
content of the gas, also increased the temperature of the exiting gas which is lead to the low
efficiency of the gasifier and that is the drawback of this gasifier. There is some limitation for
the feedstock used for this type. For example the moisture content should be less than 25%,
also in the range size of 40-100mm[1].
Heat transfers between feedstock and medium agent in fixed bed gasifier is not optimal due to
different zones that are in these types. Also they are usually used in small scale plant for
production of power and heat [1, 2, 54].
Figure 8. Updraft gasifier [1].
36
Figure 9. Downdraft gasifier [1].

Fluidized bed gasifier
Using fixed bed gasifier have limitations like high ash content, hot spots and limitation in
using small particles due to blocking and increasing the pressure drop. To overcome the
problems of fixed bed gasifier and use gasifier in large scale plant, fluidized bed gasifiers
were developed. The bed materials behave as a fluid in contact with medium agent which is
steam, air or oxygen to increase the reaction rates and heat transfers. Usually sand is used as
bed material to provide good contact with the feedstock. The different zones in fixed bed
gasifier cannot be distinguished here due to compact mixing of the materials. The temperature
is rather similar in the whole bed and can be controlled in the range of 700-900°C [1, 2].
Particles are become suspended and fluidized at minimum fluidization velocity (µ mf) by
means of the inlet velocity of medium agent µ0 which is an important parameter for designing
the fluidized bed gasifier[55, 56].
In comparison with fixed bed gasifier, the fluidized bed gasifier has several benefits. The
fluidized bed gasifier has high heat transfers and reaction rates due to the fast mixing and also
they have identical temperature in the bed without hot spots. The fluidized bed gasifier can
accept different particles size with different shapes.
Also these types of gasifiers have drawbacks. They have rather high content of dust and tar in
produced gas. They have also low conversion efficiency due to their operating temperature
range. The fluidized bed gasifier requires power consumption for fluidizing media and they
have complex operation. There are two types of fluidized bed gasifier according to the
condition of the suspension when it is small is related to bubbling fluidized bed and when it is
high related to circulating fluidized bed[1, 56].
Bubbling fluidized bed gasifier
Bubbling fluidized bed (BFB) gasifier (Figure 10 and Figure 11) is commonly used in
industry. In the structure of this gasifier, the freeboard above the bed is separated from the
fluidized bed reaction zone. Fluidization rate in this type is in the range of 2-3m/s[55, 57]
which is low and avoids from some of the fines entrainment [1, 58]. BFB gasifier is possibly
the lowest capital cost option among the advanced waste gasification technology.
Figure 10. Schematics of bubbling fluidized bed [48]
37
Figure 11. BFB gasifier [7].

Circulating fluidized bed gasifier
In the circulating fluidized bed (CFB) gasifier (Figure 12 and Figure 13), there is no
separation between the freeboard and fluidized bed reaction zone. There is just a small bed
left of the material. The fluidization rate in this type is in the range of 5-10 m/s which is
higher than bubbling fluidized bed that lead to particles exit with produced gas. The particles
are removed from the produced gas by means of a cyclone also char particles are recycled to
the gasifier in order to improve the char conversion rate [58].
Figure 12. Schematics of circulating fluidized bed[48]
Entrained flow gasifier
38
Figure 13. CFB gasifier [7].
The feedstock for entrained flow gasifier (Figure 14) has to be very small and pulverized. The
common feedstock for entrained flow gasifier is coal due to its slurry property. For biomass
becomes difficult and costly due to the required pretreatment for pulverizing them.
Operational conditions for this type of gasifier are at high temperature range of 1300-1600°C
and high pressure between 25-60 bar, short residence time approximately 1 second with large
capacity more than 100 MW.[1, 20]
High temperature and pressure improve the heat transfers between the feedstock and medium
agent also avoid from the present of methane and tar in produced gas. But leads to decreasing
the thermal efficiency of the gasifier due to the high temperature of the produced gas. The
product gas should be cooled before used for power generation. That is the reason why it is
more efficient to convert the produced gas in chemicals instead of power applications[20].
Figure 14. Entrained flow gasifier [14]

Summarized characteristics of different gasifiers are present in Table 5. As it can be seen, the
fixed beds reactors can accept shredded material in range of 100 to 200 mm whereas the
feedstock size required for fluidized beds should be in range of few millimeters. The required
range for entrained flow gasifier is less than < 0.5mm which means that the feedstock is
required high preparation [7, 8, 24, 33]
Table 5. Summarized characteristics of different gasifier [7, 8]
Gasifier type Updraft Downdraft CFB BFB EF
Temperature (°C) 700-900 700-1200 700-900 700-900 1250-1600
Pressure (bars) ≥ 1 ≥ 1 1-30 1-30 25-60
Tar content high low moderate moderate very low
Ash condition
dry ash or
slagging
dry ash or
slagging
39
Dry ash or
agglomeration
Dry ash or
agglomeration
Feedstock very critical critical Less critical Less critical
Application
Applicable
Feedstock size
Heat and
power
Heat and
power
Heat and power,
chemicals
100 to 200 mm A few millimeter
Heat and power,
chemicals
Slagging
only for fines
particles
chemicals
less than <
0.5mm

Kinetic of waste pellet gasification
Knowledge of the kinetic mechanism of the gasification reactions is applied to design the
gasifier. Modeling is useful for prediction of the operation behavior of reactor in order to
achieve optimal conditions of the gasification process [48, 59]. Using the kinetic modeling of
gasification process, time and cost of the project can be saved since experimental operation of
the system, particularly in large-scale, are costly and complicated. The kinetic modeling can
be challenging due to the variability in properties, compositions, reactivity of different raw
materials and also different parameters such as: residence time, reaction rate and it can
support research and optimization of experiments and finally it can be carried out in an
industrial scale [48, 49, 60].
Selecting a modeling for waste particles gasification
The main focus is on the kinetic of the fluidized bed gasifier to get a model and formula for
estimating the reaction rate and residence time of a particle in the gasifier based on gas-solid
reaction in char conversion part. The model of the gasifier and the equations are simplified in
order to be used in related to the conservation of energy and mass which defines boundary
conditions matched to the sources of the energy.
Char particle usually consist of ash and carbon which is produced after de-volatilization part.
The reaction (4) among the gasification reactions is selected as a basis for the kinetic
modeling calculation. The main reason is the reaction (4) is the slowest one in comparison
with other reactions in gasification process.
(4) C + H2O = CO + H2 (∆H=131.3 kJ/mol. Endothermic)
The reaction rate is affected by pressure, temperature, size, porosity and concentration of the
reactants and products [49, 61, 62].
In chemical reaction, usually one reactant is selected as a basis for the calculations which is
called “limiting reactant”. The limiting reactant here is the steam which reacts with char in the
water gas reaction and with the product gas [23, 61]. Char reactivity of a waste pellet sample
can be defined as [49]:
Where is the mass of carbon in the waste pellet sample, Xc is the conversion of the char at
time t. Kinetic formula of the char reactivity defined as [49]:
Where ρ is the mass concentration of the reactant gas and is the kinetic coefficient of the
reaction and n is the order of reaction. Values of and n are achieved by experiments.
40

Another definition for the reactivity is per unit of surface reacting:
Coefficients and are both dependence on the temperature according to the Arrhenius
equation [49] which is . In this equation, A is the pre-exponential factor, R is
the gas constant, T is the temperature and is the activation energy.
For indicating the changes of reactivity during char conversion, the new parameter is defined
as a total reacting surface area per unit of mass, which is also related rm and rA by the
following expression:
During the conversion of char, the surface area of the waste pellet particles is changed
continuously because of expansion and coalescence of the pores. To describe the variation of
the surface area, there is an equation which is relates the surface area to the reference state of
the conversion and structural profile :
The parameter is described via structural model that is used to show the pore system
changes during conversion of char particles. The values of the parameters that are used in the
different models for expression of are usually obtained experimentally. Table 6 and
Figure 15 show some models of the [49] .
Table 6. Experiential models for char gasification kinetics
Model name Abbreviation
Uniform conversion model UCM 1
Shrinking models or grain model SCMs (SUPM and SUCM) GM
41

Figure 15. Single char particle conversion models.
In Figure 15, black is the color of not converted carbon and white color is the full converted
ash. Intermediate colors are intermediate states. The classical models are (a, b, c). Types d
and e are extensions of (b) and (c) for porous char, allowing reaction to take place within the
shrinking core/particle, showing an extreme behavior of the ash formed [49].
Residence time of the particles
By using and substituting all of the five equations above, the equation (1) converts to the
following equation;
Where
Using equation (6) in gas-solid non-catalytic reaction is a standard way to evaluate this
reaction measurement and modeling char particle. Local conversion ( ) here is used instead
42

of due to in kinetic regime is empirical. In some cases, the local conversion(x) is
not equal to ( ; this equation is just a way to get for reactor modeling not for a char
particle modeling. Based on different feed, heating rate and temperature the char reactivity is
varied. It depends on size, porosity and catalytic activity.
In this project, the equation (6) with some assumptions (Table 7) is used in order to estimate
the particles residence time in the gasifier.
The gasification agent here is steam. According to the endothermic gasification reactions, the
surface temperature of the particle is rapidly decreased so it takes heat from the surrounding,
giving a rather constant surface temperature and because the steam cannot go so much in the
particle the heat transfers inside the particle can be negligible causing the reaction to occur on
the surface of the particles. Another reason that can be influenced on the assumption of
happening reaction on the surface is that the particles here are in the form of pellets and they
are dense material that caused steam doesn’t go further inside the particles.
The model that would be more appropriate for this case is shrinking unreacted particle model
(SUMP) which the reactions are happened at the surface of the materials. The mechanism of
this model presents in Figure 15[49].
By substituting from equation (7) in equation (6), and also by using the partial pressure
of the limiting reactant (steam) instead of mass concentration (ρ), due to the solid
concentration of the another reactant which is char is constant and can be negligible. Then by
integrating and simplifying the equation, the residence time of the steam gasification can be
described as:
43

By having the values of the different parameters used in equation (8), the residence time can
be calculated. The values here are obtained according to the availability and conditions of the
gasifier and the following assumptions.
is initial surface area of the particles per unit of mass. Mass here is considered as a
molecular weight of the carbon. Due to the high porosity of the particles the value of is
higher than just for one single particle. The value of the surface area is assumed between 10
to 1000 times bigger than . The parameters of the kinetic coefficient formula are
usually measured experimentally. By using the atmospheric pressure gasifier, partial pressure
of the gas reactant is assumed 90 % of the total pressure.
The order of the reaction is usually in the range of 0.5-0.7 [59, 63]and the average of this
range consider here. Conditions, assumptions and values for estimating the parameters of the
equation (8) are summarized in Table 7.
Parameter
Abbreviation
Temperature T
Table 7. Summarized assumptions, formulas of estimating residence time
Unit Formula Value Assumption
°C
44
650
K 923
pressure P Pa - 91183.5
Order of
reaction
Conversion
fraction
Kinetic
coefficient
n - - 0.5 [63]
x - - 0.85
k A -
0.00000403
[61]
Temperature value is based on the
condition of the required gasifier.
90% of the total atmospheric pressure
considered for partial pressure.
The average between the range of 0.4-
0.7 is considered.[63]
The value consider by experimental
data for biomass conversion rate
Value of
calculated experimentally

Gas constant R J/mol k - 8.314 [61] -
Exponential
factor
Activation
energy
Initial surface
Area
Particle
diameter
Particle
height
Residence
time
A - - 810 [61] -
E a J/mol - 146718 [61] -
A m
0
m 2 /kg
45
0.0518
100*0.0518=5.
D m - 0.016
H m - 0.032
t sec 318.75
18
-Shape of particles is cylindrical.
-Due to porosity of the particles surface
area is 100-1000 times bigger than of
one particle surface area.
-Reaction happens at the surface area
of the particle.
Value consider according of the pellet
pretreatment
Value consider according of the pellet
pretreatment
The available data considering here for estimating the residence time and the result of
calcuations for residence time at differnt temperature ranges are persented in Table 8.
Table 8. Residence time of particles at different temperatures
Reactor Temperature
(°C)
Residence Time
(sec)
500 13,023
550 3,253
600 925
650 318
700 119
750 49

Heat required for gasification of waste Pellet
The residence time of the particles in the reactor and heat balance calculations are the main
parameters considered for design of the gasifier[56]. Using the following heat balance
between the required heat for gasification (equation 9) and supported heat from the boiler in
the form of hot sands (equation 10), the flow rate of the required sand can be calculated. Then
the specific volumetric flow rate of the sand as well as the volume bed of the gasifier reactor
can be calculated roughly.
It is noted that the heat for pyrolysis compare to the heat demand of evaporation and steam
gasification reaction can be neglected. The results are reflected in Table 9.
Table 9. Summarized the heat balance calculations
Parameter Formula Assumption Value
- Initial feed temperature 15
- Wet feed temperature after heating 100
- Designed temperature for feed, sand, steam, reactor 650
- Initial sand temperature 800
- Initial inlet steam temperature from boiler to gasifier 490
- Average of between temperatures 25C to 100C 4.198 [51]
- Average of between temperatures 100Cto 650 C 2.238 [51]
- Average of different of compositions in waste 1.62 [51]
- Sand here consider as silica sand 0.84 [51]
Here at temperature 100 2257.03 [51]
46

Mass flow rate of feed
(kg/s)
- Steam Enthalpy at temperature 650 3816.6 [51]
- Enthalpy of steam at temperature of 490 C 3467.39 [51]
-
The initial value of for endothermic gasification
reaction is 131300 kJ/k mol that converts to kJ/kg by
dividing the molecular weight of carbon (12g)
The initial value of for exothermic methane formation
reaction is 87.5kJ/mol that converts to kJ/kg by dividing
the molecular weight of carbon (12g)
47
10941.67[51]
7291.67 [50]
- Considering 1 ton/h feed rate 0.278
(kg/s) 1.84
- At steam temperature of 490°C 0.2841 [51]
(kg/m 3 ) Considering Silica sand 1325
U mf (m/sec)
-
Umf=0.01(µ/ρ gd g)((27.2 2 +0.0408Ar) 0.5 -27.2)
where Ar=ρ g(ρ p-ρ g)g(d p 2 /µ 2 ) [55]
The value here considered by of the gas in BFB
gasifier[56]
- Gasifier diameter 2 [63]
1.95
2 [51]
Cross section of the cylindrical gasifier 3.1415
W*L Cross section of the cubic gasifier 4
Y(% wt. dry basis) The carbon content in waste stream in Borås [13]
0.459

In this project the required heat for the gasification process is provided by hot sands from the
available BFB waste boilers in Borås Energi och Miljö plant by thermal capacity of each
20MW operating at 49bar. The operational data of boilers are shown in Table 10.
Table 10. Operational data of boilers in Borås Energy Plant
Parameters Waste Boiler
1
48
Waste Boiler
2
Wood Chip
Boiler 1
Wood Chip
Boiler 2
Boiler name Pav107 Pav207 K111 K121
Sand and bed temperature (°C) 785 788 793 790
Generated steam temperature (°C) 403 405 486 488
By means of empirical equations for product gas [64, 65] the compositions of product gas are
estimated and presented in Table 11.
Table 11. Product gas composition at reactor temperature of 650 °C [64, 65]
Parameter Formula Value(%)
(12) 29
(13)
20
(14) 15.87

The assumptions
According to the lack of data in this project, the following assumptions are made to simplify
the equations in heat balance.
In the first assumption, it is considered that all of the carbon content in the feed is left after the
pyrolysis step and then transferred in the gasification reactions step mainly by the water-gas
steam gasification (Reaction 4).
Reaction (4) C + H2O = CO + H2 (∆H=131.3 kJ/mol. Endothermic)
In the second assumption, approximately 85% of carbon content in total feed is taking into the
account after pyrolysis and undergoes steam gasification (reaction 4). The rest (15% of carbon
content) in the form of volatile components is not denoted.
The third assumption is based on a mixture of two reactions paths. The first reaction path is
reflected in the second assumption and another is based on the reaction (7) which is called
hydro-gasification where the methane is formed through a very slow exothermic reaction.
Reaction (7) C + 2H2 = CH4 (∆H= -87.5 kJ/mol. Exothermic)
Thus the amount of released heat from exothermic reaction as supported heat in energy
balance. In comparison with the second assumption, 85% of carbon content is consumed for
mentioned reactions. The carbon consumption for reactions paths (4) and (7) by assumption
1,2 and 3 are shows in Table 12.
Table 12. The carbon consumption for the reactions paths considered for assumption 3
Assumption Calculations Value(%)
1
2
3
Reaction (4) C + H2O = CO + H2
Total carbon content in the feed is undergoes only to the reaction (4)
The 85% of carbon content is undergoes only to the reaction (4) and 15% of
that is not reacted.
Reaction (7) C + 2H2 = CH4
Reaction (4) C + H2O = CO + H2
The 85% of carbon content is undergoes to the reaction (4) and (7) also 15% of
that is remained un reacted.
49
100
85
17.85
67.15

Using the percentage of methane in raw product gas as 15.87%, the percentages of consumed
carbon in reactions (7) and (4) are achieved respectively with values of 17.85% and 67.15%
of total (0.85%) remaining carbon after pyrolysis step.
These values are used in the heat balance calculations in Table 13 in order to find out the
amount of required hot sand together with bed material as heat source for gasification as well
as correspondence bed volume of gasifier.
Table 13. Summarized energy demand/supply calculations
Heat Formula
Heat of
evaporation
Heat of
endothermic
gasification
reaction
Heat of feed
heated up
Heat of sand
Steam inlet
heating to
gasifier
temperature
Heat of
exothermic
methane
formation
reaction
Considering 0.9 for the dry content, 85% and 67.15% for the carbon
fraction and Y as the carbon content in waste stream in Borås for
(0.459% wt. dry basis) [13, 64, 65]
Considering 0.9 for the dry content, 17.85 % for the carbon fraction
and Y as the carbon content in waste stream in Borås for (0.459% wt.
dry basis) [13, 64, 65]
50
Value
(kJ/kg)
106.80
(Considering assumption 1)
1255.56
(Considering assumption 2)
1067.22
(Considering assumption 3)
830.55
) 257.18
(Considering assumption 1)
2134.48
(Considering assumption 1)
1946.15
(Considering assumption 1)
1560.12
514.94
149.35

Design parameters
By substituting the related formulas in Table 9 and Table 13 in equations 9, 10, and the heat
balance, equation 11, the flow rate of the sand and required heat can be calculated. The
designed parameters considering assumption 1,2 and 3 are presented in Table 14.
Table 14. Design parameters of the gasifier
Parameter Formula Assumption Value
Mass flow rate of
bed material
(kg/s)
[56]
51
(Considering assumption 1)
(Considering assumption 2)
(Considering assumption 3)
(Considering assumption 1)
(Considering assumption 2)
(Considering assumption 3)
(Considering assumption 1)
(Considering assumption 2)
(Considering assumption 3)
16.94
15.45
12.38
0.013
0.012
0.009
4.07
3.71
2.97

Chapter 4, Cost estimation of the project
Cost estimation of the project was also carried out by the study estimation method. This
method uses the purchase cost of major equipment which is designed in the process. Then
each price of equipment is roughly sized and the approximate cost is determined [66].
In case of availability of data, relevant program like Capcost, Superpro, Aspen Icarus can be
applied for economic analysis of the project. It will illustrate whether the project is worth to
be purchased and economic. However, the capital cost of the project must consider many
costs other than purchased cost of the equipment which are out of this project scope.
The most accurate purchase cost of equipment is obtained from supplier’s quotation. In this
project several manufacturers of required equipment were met or contacted by phone, email in
order to obtain the purchased cost of equipment during February to December 2010.
52

Chapter 5, Results and Discussion
According to the earlier discussions and calculations, the results are categorized in two parts
includes pre-treatment of gasification feedstock by pellet production, gasification of pelletized
waste in gasifier combined to the boiler which has been discussed as following.
Pre-treatment of gasification waste feedstock by pellet production
Due to the available equipment provided in Sobacken waste collection center for city of
Borås, Sweden, the following plan (Figure 16) would be considered for the production of
waste pellet at the Sobacken site.
Figure 16. Schematic of waste pellet production.
The total received waste material in different sizes is crushed to 80mm in two steps by using
the available Hook shredder and Hammer mill. This ultimate size is not adequate for waste
pellet production, consequently another extra size reduction step is recommended so that the
particle waste can be crushed into 30-50mm needed for the pellet mill. As a result of this, an
extra hummer mill should be an option which can be added to the system.
The waste stream of Borås city is contained approximately 10% metal which would be
destroyed the pellet mill, therefore the metal separation from this waste is inevitable.
53

For drying municipal solid waste, the prominent model is the rotary dryer according to the
mechanism of agitating and mixing materials in these dryers, and also the rather high
efficiency of the process. The added dryer is reduced the waste moisture from 40% to 15%
which is adequate moisture content for the gasification process. In this project, source of
energy for providing the heat as drying medium can be supported by small combustion unit
which is fed by biomass connected to the dryer. However issues related to emitted flue gas
filtration, air pre-heating and transition of combusted air are remained to be determined.
The crushed and dried MSW enters the pellet mill and turns into waste pellets. Due to the fact
that, the waste materials are varied in size, shape, properties and bulk density, the ring die
pellet mill could be more appropriate for making uniform output according to its mechanism.
On the other hand, the capacity of ring die pellet mill is bigger than flat die pellet mill.
Accordingly, the bulk density of the produced pellet will increase usually from 300 to 700
kg/m3. This makes its temperature reach to 80-100°C. To increase the stability and durability
of the pellets, they need to be cooled to the ambient temperature. Usually for cooling the
waste material, the counter current cooler is more appropriate due to its higher efficiency. The
horizontal structure of the cooler is commonly used in industrial scales. It is expected that 3-
4% of the moisture content is reduced during the cooling process and then the waste pellet is
prepared to storage or transfer to the gasification plant. The whole proposed model is
illustrated in Figure 16. Ultimately designed parameter would be as following.
Size and shape of produced waste pellet would be cylindrical pellet with 16mm in diameter
and 32mm in length. Moisture content of produced pellet after the cooler should be 10-12%.
Density of produced pellet is 700 kg /m3.
The produced waste pellet has to be transported in 13 km from Sobacken to the gasification
plant which is located on Borås Energi ach Mjlö site (Ryavarket). Flow diagram of the waste
pellet production is presented in Figure 17.
Figure 17. Flow diagram of the waste pellet production (made by Super Pro)
54

Gasification of pelletized waste in gasifier combined to the boiler
Gasification of pelletized waste materials can be performed by two different scenarios
according to the available equipment in the Borås Energi och Miljö.
1. Retrofitting of existent waste BFB boiler with a new BFB gasifier
2. Design a new combined waste boiler with waste gasifier
The first scenario has been focused in this report so based on earlier discussion, the gasifier
would be indirect heated, atmospheric pressure, bubbling fluidized bed, steam gasifier which
can be joined to the bubbling fluidized bed waste boiler running in Borås Energi och Miljö
site at Ryavarket.
Estimation of particle residence time is based on kinetic calculation by considering the
slowest reaction which is reaction (4) among the gasification reactions.
According to the effect of temperature on gas composition and deducing trend of methane
yield (Chart 4) and considering high corrosion of waste boiler equipment at high temperature
due to alkali contents of waste material in one side, and restriction for decreasing the reactor
temperature because of un-reacted particles on the other side, consequently it was decided to
keep the bed temperature in the range of 650-700°C, so the result of the kinetic calculation is
reflected in residence times at different temperature range which can be seen in Chart 7.
Considering the design temperature of 650°C, the corresponding residence time will be 318
sec. Consequently tar cracking would be necessary because the gasifier operating temperature
is less than 800°C.
Chart 7. Effects of gasification temperature on residence time
The thermal capacity of the gasifier can be determined based on heating value and feed rate of
waste material. The feed rate was determined to 1 ton/h, and considering 11.78 MJ/kg waste,
the thermal capacity of gasifier can be determined in range of 3.27MWh. Due to lack of
experimental design data, three assumptions (Table 12) are made to find out the design
parameters (Table 14). Thus three results for the flow rate of the circulating sand from boiler
into the gasifier and also steam as a fluidized media are achieved through those assumptions.
The results are reflected in the following graphs and tables.
55

The value of the third assumption is more reliable compare to the empirical cases according to
waste boiler specification, so investigation related to the carbon left after the pyrolysis is
remained to be established to get the idea about more realistic and reliable data as it can be
seen in Chart 8.
Chart 8. Bed material at different temperatures
The heat demand for the gasification reactions, heating the feed and steam from initial
temperature level up to gasifier temperature is supported by hot bubbled sand at 800°C from
waste boiler to the gasifier. There is a possibility to transfer 29000 GJ energy from silica sand
at 800°C from waste boiler according to 26 ton available sand with heat capacity of sand for
0.84 kJ/kgK which can provide process heat demand, although the bed temperature may be
dropped from the initial level. Chart 9 is presents the effect of gasifier temperature on energy
demand for 1 ton of waste pellet per hour.
Chart 9. Energy demand considering assumption 3
The steam is chosen as gasification agent. The steam can play the role of fluidized media for
gasifier. According to the amount of sand considered in assumption 3, two options for steam
extraction can be selected. In the first option the required steam can be provided by waste
boiler steam collector at 400°C. Then the steam has to be heated up to 650°C which is the
gasifier temperature. In the second option the steam is taken from steam collector of biomass
boilers with a temperature of 490°C. In this case, the amount of circulation sand needed for
heating the steam from 490°C to 650°C will be significantly reduced from 18.6 to less than 14
ton bed material/ ton of feed as it is illustrated in Chart 10.
56

Chart 10. Bed material and steam flow rate at different temperatures
In case of increasing of the amount of moisture in the feedstock, more energy should be
supplied by circulating sand in order to evaporate feed water content. As it can be seen in
Chart 11, for moisture content of 10% to 50% the amount of required sand for 1 ton of feed/h
is not so exceed than initial level. It is expected that the amount of moisture content effects on
composition of product gas the same as steam (gasification agent).
Chart 11. Effect of moisture content of feed on sand flow rate
The gasifier designed place has to be as close as possible to the waste boiler due to easy
transfer of incoming and returning bed material from-to the waste boiler to the gasifier. The
suitable place for the gasifier can be located down side of boiler next to existence trap-door
and bottom ash screw which is illustrated in Figure 18.
Figure 18. Trap-door and steam collector of waste boiler in Borås Energi ach Miljö site
57

The generated steam from biomass boiler K121, at 488°C (see Table 10) is the best choice as
can be seen in Chart 10. The extraction point has to be at the steam collector of the two
biomass boilers. The capacity of steam generation of biomass boiler is 27 ton/h in each boiler.
They can produce 10% extra steam. It means that 5.7 ton/h steam can be extracted from steam
collector of biomass boilers (Figure 18).
Although the steam extraction point is located 30meter from the designed place of the gasifier
the cost of steam transport pipes constriction will be more than the first option. It is noticeable
that the temperature and pressure drop in this range of distance is negligible.
The gasifier bed volume has been calculated and the obtained result is shown in Chart 12. The
gasifier volume is 2-3 times bigger than bed volume [63]. It means that the gasifier volume
should be in range of 6-9m 3 . The gasifier designed parameters are summarized in Table 15.
Value
Parameter
Chart 12. Effects of gasification temperature on gasifier bed volume
Table 15. Summary of design parameters of the gasifier
Sand flow rate
(ton/ton of feed)
Bed volume of
gasifier (m 3 )
Assumption 1 16.94 4.07
Assumption 2 15.45 3.71
Assumption 3
12.38 2.97
58
Steam flow rate
(ton/ton of feed)
Residence
time (Sec)
1.84 318

Bottom ash and parts of bed material have been extracted by the bottom ash screw at the
down part of the boiler. The mechanism of separation is based on size of particles. The
particles smaller than 2mm are passed through basket screw, recycling to the boiler by ash
elevator while those larger than 2mm are collected as bottom ash and collected in the ash
container. The energy content of those is transfer to the district heating water through heat
exchanger. In this project, separation of returned sand from boiler after heat transfer should be
taking into consideration.
Figure 19. Bottom ash screw and ash elevator in
Borås Energi ach Miljö site
59
Figure 20. Bottom ash screw Borås Energi ach
Miljö site
The rejected bottom ash (Figure 21), screw bottom ash (Figure 19 and 20) and down trap-door
of the waste boiler (Figure 18) are two options for extraction points of bed materials from
boiler to the gasifier. However indirectly heated BFB waste gasifier and also steam injection
at 49bar from the boiler to the atmospheric gasifier are at an early stage of development since
feeding and discharging system of bed materials are more complicated and would be
remained an open issue to further development.
Figure 21. Rejected bottom ash (larger than 2mm)

Cost estimation of the project:
The equipment required for the production and gasification of waste pellet project are
summarized in Table 16 and 17.
Table 16. Purchased cost of equipment
Equipment Supplier Specification
Hammer mill
Metal separator
Dryer
Ring die pellet mill
Pellet cooler
BFB gasifier
IQR Systems AB
http://www.iqr.se
MESUTRONIC GmbH
http://www.mesutronic.de
Torkapparater AB
http:// www.torkapparater.se
CPM - California Pellet Mill
http://www.cpmeurope.nl
The Kahl Group
http://www.akahl.de
Metso Power
http://www.metso.com
Table 17. Price list of equipment
60
Output particle size 30-50mm
Metal separator
Quicktron-A Model
Maximum capacity 3.5 ton/h
Outlet moisture 10-12%
Combustion unit as a source of energy for drying process
Model 7932-9 Power 315 kW Capacity 3-5 ton waste/h
Energy consumption 20-60kwh/ton of waste
horizontal cooler with cooling surface 36 m²
Including internal material feeding system and gas
cleaning system
Equipment Approximate cost (SEK)
Hammer mill 750,000
Metal separator 120,000
Dryer with Combustion unit as a source of
energy for drying process
5,610,000
Ring die pellet mill 1,720,000
Pellet cooler 970,000
BFB gasifier 45,000,000
Total Approximate Cost (SEK) 54,170,000

Conclusions
Municipal solid waste material as an energy source can be used as feed for gasification
process in order to produce renewable energy.
Gasification of waste material enable the introduction of new fuel source for generates carbon
neutral option for the energy market. The gasification of waste material can play an important
role in the future of energy market.
Syngas is a gasification product which can be used for power production, automotive fuel and
production of chemicals. Production of transport fuel through gasification is considered as a
sustainable alternative for petroleum based on fuel and can be improved domestic support of
the energy for the independent countries.
Different alternatives should be looked upon but special focus is on systems which can be
developed in city of Borås in Sweden. The research has been conducted on the following
conclusions:
1. Production of waste pellet is appropriate option for convert heterogeneous
structure of waste material to homogeneous one which might be fulfilled the
requirements for feedstock pretreatment reflected on gasification efficiency.
2. Waste pellet production process needs major equipment like, hammer mill, rotary
dryer with small combustion unit as a heat source of drying process, ring die pellet
mill, pellet cooler and other auxiliary equipment.
3. The considered physical properties of produced pellets are cylindrical shape with
16mm in diameter and 32 mm in length with a density of 700 kg/m 3 .
4. The moisture content of the produced pellet as a feed for gasification process is
recommended in the range of 10-12% in order to enhance pellet hardness, stability
and durability also for effective gasification process.
5. A hybrid system of waste gasifier and waste boiler offers significant operation and
environmentally advantages for both gasifier and boiler. This approach may also
allow of the BFB gasifier operates with waste pellet, nevertheless the same major
uncertainties is exist in how to integrate the two system and processes. Therefore
the best approach for the process integration remains to be established.
6. Leaving unconverted feed from the gasifier can be combusted in the jointed waste
boiler.
7. The gasifier is indirect heated, atmospheric pressure, bubbling fluidized bed, steam
gasifier which can be joined to the bubbling fluidized bed waste boiler. This
combination has the potential to increase the overall efficiency of the system
61

compared to conventional waste incineration. Considering the above mentioned
advantages this method was selected as basis for this research.
8. The kinetic mechanism of the gasification reaction and energy balance have been
applied in order to design the gasifier and to predict the operational behavior of the
process by using the shrinking un-reacted particle model (SUMP) for waste
particles gasification modeling.
9. Combing the waste gasifier with the boiler substantially increases the efficiency of
energy recovery and fuel conversion of the waste material.
10. The thermal capacity of the gasifier for 1 ton feed/h is calculated as 3.27 MWh.
11. The reactor is designed at temperature of 650°C, pressure of less than 1 bar
because of safety reasons. The residence time of particles is found in order of 318
sec.
12. The gasification agent and fluidized media by 1.84 ton/ton of feed supported by
connected boiler with circulating sand in range of 12.38 ton/ ton of feed.
13. Initial cost estimation of equipment’s for pretreatment stage and gasification of
pelletized waste is estimated in range of 55 MSEK.
14. It is clear that more research is needed to determine the cost effectiveness of the
project.
Further works
Because of the above detailed discussion it is clear that further development work is necessary
to establish and would be benefit for filling the data gap identified in this report.
1. Technical issue related to combination of BFB gasifier and BFB boiler
2. Upgrading of raw gas in order to use in automotive fuel application
3. Efficiency analysis of using syngas in gaseous or liquid phase
4. Analysis of gas composition obtained from waste pellet gasification in lab scale
5. Cost efficiency and probability of the project
62

References
1. Knoef, H. and J. Ahrenfeldt, Handbook biomass gasification. 2005, Enschede: BTG
Biomass Technology Group. 378 s.
2. Higman, C. and M.v.d. Burgt, Gasification. 2nd ed. ed. 2008, Burlington, MA:
Elsevier Science. 1 v.
3. Higman, C., M.v.d. Burgt, and Elsevier Science Publishers., Gasification. 2003,
Boston: Elsevier/Gulf Professional Pub. x, 391.
4. Rezaiyan, J. and N.P. Cheremisinoff, Gasification technologies : a primer for
engineers and scientists. 2005, Boca Raton, FL CRC Press,. 336.
5. Morris, M. and L. Waldheim, Energy recovery from solid waste fuels using advanced
gasification technology. Waste Management, 1998. 18(6-8): p. 557-564.
6. Quaak, P., et al., Energy from biomass a review of combustion and gasification
technologies. 1999, Washington, D.C.: World Bank. xvii, 78 s.
7. Zafar, S., Gasification of Municipal Solid Wastes. Energy Manager, 2009. 2(1): p. 47
– 51.
8. Kakaras Emmanuel, et al. (2005) Co-gasification of Lignite and RDF in Greece.
9. Lieuwen, T.C.Y., Vigor Yetter, Richard A., Synthesis gas combustion fundamentals
and applications. 2010, Boca Raton: CRC Press. 1 online resource (xii, 403 ).
10. Zhang, W., Automotive fuels from biomass via gasification. Fuel Processing
Technology, 2010. 91(8): p. 866-876.
11. He, M., et al., Hydrogen-rich gas from catalytic steam gasification of municipal solid
waste (MSW): Influence of catalyst and temperature on yield and product
composition. International Journal of Hydrogen Energy, 2009. 34(1): p. 195-203.
12. Penniall, C.L. and C.J. Williamson, Feasibility study into the potential for gasification
plant in the New Zealand wood processing industry. Energy Policy, 2009. 37(9): p.
3377-3386.
13. SP, Typical Proximate and Ultimate Analysis of MSW in Borås, in F918576. 2009, SP
Sveriges Tekniska Forskningsinstitut Borås (SWEDEN). p. 4.
14. De Filippis, P., et al., Prediction of syngas quality for two-stage gasification of
selected waste feedstocks. Waste Management, 2004. 24(6): p. 633-639.
15. Venendaal, R. and H.E.M. Stassen, Comparison of two new waste gasification
facilities with a modern waste incineration plant. Biomass for Energy, Environment,
Agriculture and Industry, Vols 1-3, 1995: p. 1528-1537, 2426.
16. Bébar, L., et al., Analysis of using gasification and incineration for thermal processing
of wastes. Applied Thermal Engineering, 2005. 25(7): p. 1045-1055.
17. Zhao, W., et al., A new gasification and melting incineration process of MSW with cocurrent
shaft furnace. Journal of Environmental Sciences, 2009. 21(Supplement 1): p.
S108-S111.
18. Porteous, A., Municipal solid waste energy recovery - a comparison between mass
burn incineration and gasification options. Power Generation by Renewables, 2000.
2000(15): p. 113-130, 331.
19. Jay Ratafia-Brown, L.M., Jeffrey Hoffmann, Massood Ramezan, MAJOR
ENVIRONMENTAL ASPECTS OF GASIFICATION-BASED POWER GENERATION
TECHNOLOGIES. 2002, National Energy Technology Laboratory (NETL).
20. Letellier, C., C.U.o Technology, Comparative study of gasification technologies for
fuels production. 2008, Göteborg: Chalmers University of Technology. 91 bl.
63

21. Uslu, A., A.P.C. Faaij, and P.C.A. Bergman, Pre-treatment technologies, and their
effect on international bioenergy supply chain logistics. Techno-economic evaluation
of torrefaction, fast pyrolysis and pelletisation. Energy, 2008. 33(8): p. 1206-1223.
22. Lestander, T.A., B. Johnsson, and M. Grothage, NIR techniques create added values
for the pellet and biofuel industry. Bioresource Technology, 2009. 100(4): p. 1589-
1594.
23. Di Giacomo, G. and L. Taglieri, Renewable energy benefits with conversion of woody
residues to pellets. Energy, 2009. 34(5): p. 724-731.
24. Belgiorno, V., et al., Energy from gasification of solid wastes. Waste Management,
2003. 23(1): p. 1-15.
25. CPM. California Pellet Mill Catalog. 2010 [cited 2010 20-08-2010]; Available from:
http://www.cpmeurope.nl.
26. Baker, E.V. (2006) Grass Pelleting – The Process.
27. Vinterba, J., Biomass and Bioenergy in The First World Conference on Pellets. 2002,
Biomass and Bioenergy p. 513–520.
28. SA, S. Hook shredder XLC 2005 [cited 2010 2010-11-01]; Available from:
http://www.sidsa.ch.
29. IQR. Hammer mill stationary units. 2006 [cited 2010 2010-11-01]; Available from:
http://www.iqr.se/en/products/stationary/stationaryriggs.aspx.
30. Chester D. Rogers, W.L.M., Hammermill. 1995, The Toro Company. p. 1.
31. Fleenor, J.A., Hammermill having sealed hammers. 1997, Vermeer Manufacturing
Corporation.
32. KG, A.K.G.C., KAHL Pelleting Presses. 2010, Amandus Kahl GmbH & Co. KG.
33. Zafar, S. (2009) Waste Pelletization. manages the renewable energy advisory firm
BioEnergy Consult in Aligarh, India. .
34. Cummer, K.R. and R.C. Brown, Ancillary equipment for biomass gasification.
Biomass & Bioenergy, 2002. 23(2): p. 113-128.
35. Mujumdar, A.S., Handbook Of Industrial Drying. 2 ed. Vol. 2. 2004: Marcel Dekker
Ltd. 730.
36. Christopher G. J. Baker , P.B., Industrial Drying Of Foods, ed. 1. Vol. 1. 2002:
Springer. 309.
37. AG, A. Waste pelleting - From waste to environmental friendly new products. 2010;
Available from:
http://www.andritz.com/ANONID19D2F9EF712CF9EF/ft_waste_pelleting_2008.
38. Mehrdad Arshadia, R.G., Paul Geladia, Sten-Axel Dahlqvistc, Torbjörn Lestandera,
The influence of raw material characteristics on the industrial pelletizing process and
pellet quality. Fuel Processing Technology, 2008. 89: p. 1442-1447.
39. Anyang Gemco Energy Machinery Co., L. Flat Die Pellet Mill, Pelleting Press,
Pelletizer, Granulator. 2010 [cited 2010 08-2010]; Available from:
http://www.biodiesel-machine.com/flat-die-pellet-mill.html.
40. Anyang Gemco Energy Machinery Co., L. Ring Die Pellet Mill for Feed, Biomass
Wood Pellets. 2010 [cited 2010 08-2010]; Available from: http://www.biodieselmachine.com/ring-die-pellet-mill.html.
41. Chettiar, R.C.o.M., Briquettes & Pellets forms of solid fuel in Biomass Pellet. 2009,
Muthaiya Chettiar Research, Centre, Chennai, India: Chennai, India.
42. Thomas, M., D.J. van Zuilichem, and A.F.B. van der Poel, Physical quality of pelleted
animal feed. 2. contribution of processes and its conditions. Animal Feed Science and
Technology, 1997. 64(2-4): p. 173-192.
64

43. Hau, J.L.R.R., Rex B. Thorpe, and Adisa Azapagic, A Thermodynamic Model of the
Outputs Gasification of Solid Waste. INTERNATIONAL JOURNAL OF
44.
CHEMICAL REACTOR ENGINEERING, 2008. 6(2008).
Bridgwater, A.V., The Technical and Economic-Feasibility of Biomass Gasification
for Power-Generation. Fuel, 1995. 74(5): p. 631-653.
45. Colpan, C.O., et al., Effect of gasification agent on the performance of solid oxide fuel
cell and biomass gasification systems. International Journal of Hydrogen Energy,
2010. 35(10): p. 5001-5009.
46. Bi, X.T.T. and X.H. Liu, High density and high solids flux CFB risers for steam
gasification of solids fuels. Fuel Processing Technology, 2010. 91(8): p. 915-920.
47. Bolhar-Nordenkampf, J.P., T.Hofbauer, H.Aichernig, C., Analysis of thermoelectric
generators replacing low temperature heat exchangers in the biomass CHP plant
Gussing. Proceedings of the 8th Biennial Conference on Engineering Systems Design
and Analysis, Vol 4, 2006: p. 305-313.
48. Wang, Y. and C.M. Kinoshita, Kinetic-Model of Biomass Gasification. Solar Energy,
1993. 51(1): p. 19-25.
49. Gomez-Barea, A.L., B., Modeling of biomass gasification in fluidized bed. Progress in
Energy and Combustion Science, 2010. 36(4): p. 444-509.
50. Fushimi, C., et al., Effect of heating rate on steam gasification of biomass. 1.
Reactivity of char. Industrial & Engineering Chemistry Research, 2003. 42(17): p.
3922-3928.
51. Van Wylen, G.J., R.E. Sonntag, and C. Borgnakke, Fundamentals of classical
thermodynamics. 4. ed. ed. 1994, New York: Wiley. xii, 852 s.
52. Gómez-Barea, A., et al., Plant optimisation and ash recycling in fluidised bed waste
gasification. Chemical Engineering Journal, 2009. 146(2): p. 227-236.
53. Eva Gustafsson, M.S., and Mehri Sanati, Physical and Chemical Characterization of
Aerosol Particles Formed during the Thermochemical Conversion of Wood Pellets
Using a Bubbling Fluidized Bed Gasifier. Energy & Fuels, 2007. 21: p. 3660–3667.
54. Goswami, D.Y., Alternative energy in agriculture. 1986, Boca Raton, Fla.: CRC
Press. 2 vol.
55. Grace, J.R., Modelling and simulation of two-phase fluidized bed reactors. Chemical
Reactor Design Technology, ed. ASI. Vol. 110 . In: (2nd ed.),, ASI Ser., ser. E. 1986,
NATO. 245-289.
56. Yang, W.-C., Handbook of fluidization and fluid-particle systems. Chemical
industries, 91. 2003, New York: Deeker. viii, 861 s.
57. Octave Levenspiel, D.K., Fluidization Engineering. Chemical Engineering Series, ed.
S. Edition. 1991, NY: John Wiley & Sons.
58. Marano, J.J. and J.P. Ciferno (2002) Benchmarking Biomass Gasification
Technologies for Fuels, Chemicals and Hydrogen Production.
59. Antal Michael, J., The Effects of Residence Time, Temperature, and Pressure on the
Steam Gasification of Biomass, in Biomass as a Nonfossil Fuel Source. 1981,
AMERICAN CHEMICAL SOCIETY. p. 313-334.
60. Dupont, C., et al., Study about the kinetic processes of biomass steam gasification.
Fuel, 2007. 86(1-2): p. 32-40.
61. Mann, M.D., et al., Modeling reaction kinetics of steam gasification for a transport
gasifier. Fuel, 2004. 83(11-12): p. 1643-1650.
62. Ahmed, I.I. and A.K. Gupta, Pyrolysis and gasification of food waste: Syngas
characteristics and char gasification kinetics. Applied Energy, 2010. 87(1): p. 101-
108.
65

63. Perry, R.H. and D.W. Green, Perry's chemical engineers' handbook. 8. ed. / ed. 2008,
New York: McGraw-Hill. 2732 s. med var.pag.
64. Neves D, T.H., Seeman M, Ideias P, Matos A, Tarelho L, Gómez-Barea A., A
database on biomass pyrolysis for gasification applications, in Proceedings of the
17th European Biomass Conference & Exhibition. 2009: Hamburg, Germany. p. 1018-
1028.
65. Larsson A., P.D., Neves D., Seemann M., Thunman H., ZERO DIMENSIONAL
MODELING OF INDIRECT FLUIDIZED BED GASIFICATION, in The 13th
International Conference on Fluidization. 2011, 2010 ECI Conference: Gyeong-ju,
Korea. p. 112.
66. Richard Turton, R.C.B., Wallace B. Whiting, Joseph A. Shaeiwitz Analysis, Synthesis
and Design of Chemical, ed. 3. 2009: Prentice Hall.
66