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PROYECTO FIN DE CARRERA
THE IMPLICATION OF OPERATION OF
GAS TURBINES FUELLED BY LHV, IN
CONTEXT TO GASIFICATION
PROCESSES.
AUTOR: FRANCISCO QUESADA BUENO.
MADRID, Septiembre de 2007
UNIVERSIDAD PONTIFICIA COMILLAS
ESCUELA TÉCNICA SUPERIOR DE INGENIERÍA (ICAI)
INGENIERO INDUSTRIAL
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ABSTRACT
Biomass, in the energy production industry, refers to living and recently dead
biological material and biodegradable wastes which can be used as fuel putting it
under a process called gasification.
There are numerous different gasification processes and raw materials that can be
used. The properties of the fuel obtained depend on the gasification technology and
the type of raw material used.
Fuels can be classified into three categories depending upon their heating value: high
heating value HHV, medium heating value MHV and low heating value LHV fuels.
The heating value is the amount of heat obtained by burning an unit quantity of fuel.
Nowadays, gas turbines work combusting fuels like kerosene, natural gas or liquid
petroleum in the combustion chamber. That fuels are fossil fuels with a high heating
value.
Today, the world is facing the problem of increased price and shortage of fossil fuels
along with the effect of using these fuels on the environment. In the future, to make a
truly sustainable energy system, we would have to replace fossil fuels with biomass
or other renewable fuels.
The aim of this project is to investigate the practical implications of operating modern
gas turbines on biofuels, the problem is that biofuels are mostly low heating value.
The amount of fuel injected in the combustion chamber will need to be much higher
and this may cause several problems, like the unbalance between compressor and
turbine that may leads to high speeds of shafts, increased pressure ratios of
compressors that can cause compressor surging and overload in the fuel system.
For this study, the GT-500 turbine has been used, it is a 20 MW power production gas
turbine unit designed and manufactured by Siemens. This turbine is designed for
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working with high heating value fuels. This thesis is based on the feasibility study
and thermodynamic analysis of GT-500 gas turbine by using low heating value fuels.
The working of the gas turbine GT-500 with low heating value fuels would need
several changes in the machine. This changes need to be as simple as possible and
after them, the efficiency and life of the machine have to be at appropiate levels.
This specific work includes the pre studies on types of gasification processes,
properties of the fuel after those processes, classification of fuels and the type of
gasifiers that can possibly be used in the preceding sections.
The composition of the fuels from various sources has been collected, different
thermodynamic properties have been calculated and it has been observed that the
values of various properties differed for different fuel compositions. The complete
fuel list is in appendix A.
The chapter 6 and 7 includes the thermodynamic analysis of the Siemens gas turbines
SGT-500 by using Siemens software GT Perform. GT perform is a computer program
that simulates the behaviour of the Siemens turbines. It allows to change many input
parameters and gives the output values that show the working point and state of the
machine like pressures, temperatures and flows. In these chapters, the results obtained
by GT perform are shown.
There are many parameters that can be changed in the machine, with numerous
combinations: limitations, vane guides angles, extractions and injections of air and so
on. Many simulations were to be made to see the problems of using low heating value
fuels and understand how the changes of the parameters affect to the working state of
the turbine.
The results suggest the changes that have to be made in the machine to avoid the
unbalance between compressor and turbine and keep the machine in a safe and
efficient working point.
When using low heating value fuels, the amount of fuel in the combustor has to be
much higher and this means that the fuel system needs to be bigger also. The chapter
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8 introduces the new dimensions of the fuel system for low and medium heating
values gases.
The conclusions suggest that is possible to use low heating value fuels in turbines
designed for been powered with high heating value fuels but several changes in the
machine are needed. Those changes are simple and because of them, the machine can
work at nearly normal conditions.
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RESUMEN
Cuando se habla de biomasa, en la industria de producción de energía, nos referimos
a material biológico vivo o recientemente muerto y a desechos biodegradables, que
pueden ser usados como combustible, después ser sometidos a un proceso llamado
gasificación.
Existen diferentes procesos de gasificación así como diversas materias primas que
pueden ser usadas. Las propiedades del combustible obtenido dependen de la
tecnología de gasificación y del tipo de materia prima usada.
Los combustibles pueden ser clasificados en tres categorías dependiendo de su poder
calorífico: combustibles de alto poder calorífico HHV, combustibles de poder
calorífico medio MHV y combustibles de bajo poder calorífico LHV. El poder
calorífico, es la cantidad de calor obtenido al quemar una unidad de masa de
combustible.
Actualmente, las turbinas de gas funcionan quemando combustibles como queroseno,
gas natural o petróleo liquido. Todos ellos son combustibles fósiles, con un alto poder
calorífico.
En estos días, el mundo se enfrenta al problema derivado del alto precio y escasez de
los combustibles fósiles, así como al efecto que tiene en el medio ambiente el uso de
dichos combustibles. En el futuro, para conseguir un sistema energético
verdaderamente sostenible, deberíamos cambiar los combustibles fósiles por biomasa
u otros combustibles renovables.
El objetivo de este proyecto es investigar las implicaciones prácticas de hacer
funcionar las actuales turbinas de gas con biocombustibles, el problema es que los
biocombustibles son en su mayoría de bajo poder calorífico. La cantidad de
combustible inyectado en la cámara de combustión tendría que ser mucho mayor, y
esto puede causar diversos problemas, como la sobrecarga en el sistema de
combustible y el desequilibrio entre compresor y turbina que a su vez puede provocar
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altas velocidades en los ejes y relaciones de compresión elevadas que pueden causar
que el compresor se cale.
Para este estudio, se ha usado la turbina SGT-500, que es una turbina de gas de
producción de energía eléctrica de 20 MW de potencia, diseñada y construida por
Siemens. Esta turbina ha sido diseñada para funcionar con combustibles de alto poder
calorífico. Este proyecto tiene como objetivo el estudio de viabilidad y análisis
termodinámico de SGT-500 cuando se usan combustibles de bajo poder calorífico.
El correcto funcionamiento de la turbina de gas SGT-500 con combustibles de bajo
poder calorífico, requiere varios cambios en la máquina. Es necesario que estos
cambios sean tan simples como sea posible y que después de realizarlos, la eficiencia
y vida de la máquina se mantenga a niveles aceptables.
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Este proyecto incluye pre-estudios sobre tipos de procesos de gasificación, las
propiedades del combustible obtenido después de dichos procesos, la clasificación de
los combustibles y el tipo de gasificadores que podrían ser usados para obtener el
combustible.
Se ha recopilado de diversas fuentes la composición de numerosos biocombustibles
usados en la actualidad. Se han estudiado las diferentes propiedades termodinámicas
y se ha observado como varia el valor de estas propiedades en función de la
composición del combustible. En el anexo A se recoge la lista completa de
combustibles.
Los capítulos 6 y 7 incluyen el análisis termodinámico de la turbina SGT-500 de
Siemens usando el software GT-Perform. GT perform es un programa informático
que simula el comportamiento de las turbinas Siemens. Permite modificar muchos
parámetros y devuelve los valores que muestran el punto de trabajo y el estado de la
maquina tales como presiones, temperaturas y flujos. En estos capítulos, se muestran
los resultados obtenidos con GT perform.
Hay muchos parámetros que pueden ser modificados en la turbina con múltiples
combinaciones: limitaciones, ángulos de guía de las paletas, extracciones e
inyecciones de aire, etc. Se tuvieron que realizar muchas simulaciones para poder ver
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los problemas que conlleva usar combustibles de bajo poder calorífico y comprender
como las modificaciones en los parámetros afectan al estado de funcionamiento de la
turbina.
Los resultados sugieren los cambios que se deben de hacer en la máquina para evitar
el desequilibrio entre compresor y turbina y mantenerla en un punto de
funcionamiento eficiente y seguro.
Cuando se usan combustibles de bajo poder calorífico, la cantidad de combustible
inyectado en la cámara ha de ser mucho mayor y esto significa que el sistema de
combustible necesita ser más grande. El capitulo 8 introduce las nuevas dimensiones
del sistema de combustible para su uso con combustibles de bajo y medio poder
calorífico.
Las conclusiones sugieren que es posible usar combustibles de bajo poder calorífico
en turbinas diseñadas para ser alimentadas con combustibles de alto poder calorífico
pero es necesario realizar diversos cambios en la máquina. Esos cambios son simples
y gracias a ellos la máquina funcionaria en puntos muy cercanos a los del
funcionamiento con combustibles de alto poder calorífico.
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TABLE OF CONTENTS
ABSTRACT ..................................................................................................................3
ABBREVATIONS ....................................................................................................111
LIST OF TABLES ...................................................................................................133
LIST OF FIGURES ...................................................................................................14
1.INTRODUCTION ...................................................................................................15
1.2 SGT-500 Gas Turbines ......................................................................................17
2. OBJECTIVES ........................................................................................................19
3. METHOD OF ATTACK .......................................................................................20
4. PRE-STUDIES.......................................................................................................21
4.1 Biomass gasification ..........................................................................................21
4.1.2 Types of Gasifier.........................................................................................23
4.1.3 Updraft gasifier/counter-current fixed bed gasifier (UDG). .......................25
4.1.4 Downdraft gasifier or co-current fixed bed gasifier (DDG). ......................27
4.1.5 Fluidized-bed gasifier (FBG)....................................................................288
4.1.6 Circulating fluid-bed gasifier (CFBG)........................................................31
4.1.7 Entertained flow gasifier (EFBG).............................................................322
4.1.8 Comparison of gasifiers ..............................................................................34
5. CLASSIFICATION OF BIOMASS FUELS .......................................................36
5.1 Composition.......................................................................................................36
5.2 Basic fuel properties ..........................................................................................38
5.2.1 Stoichiometric Air-fuel-ratios.....................................................................38
5.2.2 Heating values.............................................................................................39
5.2.3 Wobbe indices.............................................................................................41
5.2.4 Flow ratios ..................................................................................................41
5.2.5 Stoichiometric adiabatic flame temperatures..............................................42
5.2.6 Molecular ratios ..........................................................................................43
6. GT PERFORM.......................................................................................................44
6.1 SGT-500 Parameters..........................................................................................45
7. RESULTS OBTAINED BY GT PERFORM ......................................................46
7.1 Base or reference case........................................................................................47
7.1.1 Simulation of several LHV fuels ................................................................48
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7.1.2 Utilization of two representative fuels, how the parameters affect. ...........52
7.1.3 Turbine Inlet temperature limitation v.s. power output limitation..............55
7.2 Power needed for compressing the fuel .............................................................57
7.2.1 Power and efficiency without fuel compressor power................................57
7.2.2 Power and efficiency with fuel compressor power.....................................58
7.3 Simulations of medium heating value MHV fuel. .............................................60
7.3.1 Results of reference case vs. MHV fuel......................................................61
7.3.2 Effect of increasing gamk2 .........................................................................63
7.3.3 Using a pressurized gasifier. .......................................................................66
7.4 Simulations with LHV and MHV fuels .............................................................69
7.4.1 Results in compressors maps. .....................................................................69
8. FUEL SYSTEM .....................................................................................................74
8.1 SGT-500 Fuel system ........................................................................................75
9. CONCLUSIONS....................................................................................................83
10. REFERENCES.....................................................................................................84
11. APPENDIX...........................................................................................................84
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ABBREVATIONS
LHV Low heating value
MHV Medium heating value
HHV High heating value
GT Gas Turbine
LPC Low pressure compressor
HPC High pressure compressor
LPT Low pressure turbine
HPT High Pressure turbine
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PT Power turbine
UDG Updraft gasifier
DDG Downdraft gasifier
FBG Fluid bed gasifier
CFBG Circulating Fluid bed gasifier
EFG Entrained flow gasifier
PIK Pressure ratio, compressor
PIT Pressure ratio, turbine
N Speed
G Mass flow
NNORM Normalized speed
GK Compressor (inlet) mass flow
Shaft#1 Power turbine Shaft
Shaft #2 Low pressure turbine shaft
Shaft# 3 High Pressure Turbine shaft
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LIST OF TABLES
Table 1: Comparison of gasifiers................................................................................................. 34
Table 2: Advantages and disadvantages of different gasifiers..................................................... 35
Table 3 Maximum, minimum and average molar concentrations of the found biomass
gasification product gases between 3 and 10 MJ/m..................................................................... 37
Table 4 Calculated adiabatic flame temperatures of the collected gasification product
gases.............................................................................................................................................. 43
Table 5:- GT-500 parameters....................................................................................................... 45
Table 6 Two representative fuels from Appendix A...................................................................... 52
Table 7 Explanation of figure 15.................................................................................................. 53
Table 8: Standard fuel operating conditions................................................................................ 76
Table 9: Fuel system for standard gas.......................................................................................... 77
Table: 10 MHV fuel operating conditions.................................................................................... 78
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Table 11: Fuel system for MHV gas............................................................................................. 79
Table 12: Operating conditions of SGT-500 for LHV.................................................................. 80
Table 13: Fuel system for LHV gas.............................................................................................. 81
LIST OF FIGURES
Figure 1: GT-500.......................................................................................................................... 18
Figure 2 (a) and 2(b): Updraft gasifier........................................................................................ 25
Figure 3 (a) & 3 (b): Downdraft gasifier..................................................................................... 27
Figure 4 (a) & 4 (b): Fluidized Bed Gasifier............................................................................... 29
Figure 5(a) and 5(b): Circulating Fluidized Bed Gasifier ........................................................... 31
Figure 6: Entrained Flow Gasifier............................................................................................... 33
Figure 7: Occurrences of heating value for biomass gasification product gases in the
range between 3 and 10 MJ/m³ for the fuels in appendix A. ................................................ 40
Figure 8: Occurrences of heating value for all low calorific value fuels attained from
literature ............................................................................................................................... 40
Figure 9 :The mass flow ratio for a variety of different fuels. To visualize the much
higher mass flow going through the turbine not only the gases from Appendix A,
but all acquired fuel compositions were used....................................................................... 42
Figure 10: Molecular ratios of the gasification product gases from Appendix A........................ 43
Figure 11: SGT-500 parameters................................................................................................... 45
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Figure 12: The effect of decrease in heating values on power output and efficiency.................. 48
Figure 13: The effect of decrease in heating values on speeds of LPC and HPC........................ 51
Figure 14: The effect of decrease in heating values on pressure ratio........................................ 51
Figure 15: Effect of change of parameters on gas # 22.............................................................. 54
Figure 16: Effect of change of parameters on gas # 66 ............................................................... 54
Figure 17: TIT vs. PO limitation.................................................................................................. 56
Figure 18: Power output and efficiency without calculating power needed to
compress the fuel................................................................................................................... 58
Figure 19: power output and efficiency with the power needed to compress the fuel................. 59
Figure 20: Result of refrence case vs MHV fuel .......................................................................... 61
Figure 21: Result of refrence case with MHV fuel....................................................................... 61
Figure 22: Speed of shaft2 and shaft 3 using MHV fuel............................................................... 63
Figure 23: Pressure ratio of LPC and HPC using MHV fuel ...................................................... 65
Figure 24: The gasifier integrated with the unit........................................................................... 66
Figure 25: Gasifier vs. bleeding after low pressure compressor................................................. 67
Figure 26: Low pressure compressor efficiency map................................................................... 70
Figure 27: Low pressure compressor speed map......................................................................... 71
Figure 28: High pressure compressor efficiency map.................................................................. 72
Figure 29: High pressure compressor speed map........................................................................ 73
1. INTRODUCTION
Fossil fuels supply most of the energy consumed today. The combustion of fossil
fuels causes the emission of greenhouse gases and sulfuric, carbonic, and nitric acids,
which fall to earth as acid rain and has adverse impact on the environment. The fossil
fuels may also cause the global warming. Today we are facing the problem of
increased price and shortage of fossil fuels along with its effect on the environment.
A possible solution to the problems with fossil fuels is to utilize renewable energy
sources such as wind, solar, tidal, geothermal and biomass for power generation.
Biofuels can be obtained by the gasification of biomass. There are numerous different
gasification processes and raw materials that can be used. The properties of the fuel
obtained depend on the gasification technology and the type of raw material used.
One very important physical property of the fuel is the heating value, that represents
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the intensity of the combustion and it is defined as the amount of heat produced by
combustion of a unit quantity of fuel.
The fuels obtained by the gasification of biomass can be classified into three
categories depending upon their heating values, the high heating value HHV, medium
heating value MHV and low heating value LHV fuels. There are other important
characteristics to take into account like the composition, tar formation, wobbe index,
laminar flame temperature and flammability limits. All these properties decide the
fuels which are convenient to be used.
Gas turbines are essential in power generation. Energy is extracted in the form of
shaft power, compressed air and thrust, in any combination. They are versatile and
can be used in a number of applications such as transports and industries. Nearly
every aircraft in the world is powered by gas turbines as well as some ships,
helicopters and locomotives. There are also prototypes of cars that are powered by
gas turbines. Industrial gas turbines range in size is very wide, from truck-mounted
mobile plants that are used as auxiliary power units to enormous, complex systems
that can generate a huge amount of electric power. Gas turbines for electric
generation are usually used in peaking power plants, supplying power during peak
demand due to their ability to be turned on and off within minutes.
Gas turbine is a very sensitive machine. Small changes in the fuel properties may
cause disturbances in operation and failure of its components as result.
The operation of gas turbines with LHV fuels leads to increased fuel flow which may
provoke the unbalance between compressor and turbine, and overload in the fuel
system of conventional gas turbine. The increased fuel flow causes the increase in
pressure ratios and speed of the shafts which may ultimately lead to compressor
surge.
This specific work includes the pre studies on classification of fuels and the type of
gasifiers that can possibly be used in the preceding sections.
In Chapter 4, the fundamentals of gasifiers for biomass gasification are reported. The
chapter 5 covers the classification of fuels.
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The chapter 6 and 7 includes the thermodynamic analysis of the Siemens gas turbines
SGT-500 by using Siemens software GT Perform. In these chapters, the results
obtained by GT perform are shown. The results suggest the changes that have to be
made in the machine to avoid the unbalance between compressor and turbine and
keep the machine in a safe and efficient working point.
The chapter 8 introduces the new dimensions of the fuel system for low and medium
heating values gases.
This thesis emphasizes on the use of low heating value biomasses for power
generation, specifically for the gas turbines.
1.2 SGT-500 Gas Turbines
The SGT-500 is a heavy duty industrial gas turbine designed and manufactured for
various industrial applications requiring high thermal efficiency and reliable trouble-
free operation. It has a limit of 4000 to 160000 hours time between overhaul TBO, an
output limit of 20.7 MW and turbine inlet temperature limit of 500 °C to 880 °C.
It is suitable for indoor, outdoor and onshore applications. It can be adjusted to
offshore environments and requirements common in the oil & gas industry with pre-
designed standard function modules. The gas turbine operates on a simple open cycle
utilizing a three shaft concept. The shaft number 1 corresponds to power turbine,
shaft number 2 corresponds to low pressure compressor and shaft number 3 to high
pressure compressor as shown in the figure 1.
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Figure 1: GT-500
The gas generator has 10 stage low pressure LP and 8 stage high pressure HP axial
flow compressor sections providing an overall compression ratio of 12.6. The LP and
HP compressors are driven by a 2-stage LP and a single stage HP axial flow turbine.
Seven can-type combustors are located in the annular space between the concentric
casings extending from the HP compressor exit diffuser duct. These combustors are
capable of burning a wide band of fuels. For power generation, the power turbine is a
three stage axial flow turbine extracting the output power from the exhaust flow
across the operating speeds 3000 rpm (50 Hz) and 3600 rpm (60 Hz). In mechanical
drive applications, the power turbine can be either a three stage axial flow turbine
extracting the output power from the exhaust flow across an operating speed range
2200 to 3600 rpm or single stage operation in the 5000 to 6300 rpm range. The
minimum operating speed can be decreased provided load vs. speed of driven
equipment are within certain limits.
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2. OBJECTIVES
The objective of this thesis work are summarized as under
• The literature study aiming of suitability of integrated gasifier.
• To classify the biomass fuels suitable for gas turbine applications and to study
their thermodynamic properties.
• Investigation of operational problems using LHV fuels.
• Optimization of gas turbine based on in house code GT perform.
• To document the design change which will be necessary to keep the speeds
and pressure ratio of gas turbine within limits to avoid compressor surging.
• To calculate the new dimensions of the fuel system to be able to manage a
higher fuel flow keeping constant the press
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3. METHOD OF ATTACK
In the first step, a study about the gasification techniques and types of gasifier will
lead to the classification of fuels on the basis of their properties like Wobbe index,
heating value, air fuel ratio, adiabatic flame temperature etc. will be done.
In the next step, the simulations on GT Perform will be performed. GT perform is a
program developed by Siemens that simulates the behaviour of the Siemens gas
turbines. In this project, a version of the program will be used where only the SGT-
500 gas turbine is available.
The first approach to the program will be to use it under all standard conditions and
by the use of standard fuel which is natural gas in our case. After having a base case
with standard fuel and standard conditions, a number of simulations will be made for
a number of syngases (e.g. gasified biomass) and under different operating
conditions.
It is necessary to understand the parameters that one can change in the program (and
also in the machine). These parameters include the turbines flow constants, the
injection and extraction of air at several points of the machine and also the type of
load or limitations of the machine. These parameters have rules and limitations, it is
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not possible to use any value, some of the parameters can be changed freely while the
others are locked. Two different fuels will be selected, one with LHV and another one
with MHV to see how the change of parameters affects the behaviour of the machine
in each case.
In order to address the unbalance between compressor and turbine, the first approach
is bleeding of the compressed air after low pressure compressor. The second approach
is leading the compressed air after high pressure compressor to a pressurized gasifier.
In order to examine the performance of the compressor and draw the working points
of the map of compressor will be defined and the surge limits will be inspected.
The final work will be to set of recommendation regarding the re-designing of the
fuel system using MHV and LHV gases.
4. PRE-STUDIES
The aim of this part is to gain better understanding of the gasification process for
different biomass. The gasification process of biomass can result in different qualities
of gases with low or high heating values. Different types of gas cleaning processes
are being used for removal of tar in order to use it in Gas Turbines.
Based on the fuel composition, it is obtained the values of the physical properties
such as heating value, wobbe index, molecular weight and combustion properties
such as flammability limits, ignition delay or laminar flame speed; these properties
make fuels suitable or not for using them in the turbine.
4.1 Biomass gasification
Gasification is a process to convert a solid to a gas that can be used in modern power
generation applications such as a heat engine or gas turbine.
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Biomass has great potential as a renewable and relatively clean feedstock for
producing modern energy carriers, such as electricity and transportation fuels.
Currently, biomass gasification is considered as one of the most promising thermo
chemical technologies.
Biomass gasification, also known as incomplete combustion of biomass resulting in
production of combustible gases consisting of Carbon monoxide (CO), Hydrogen
(H2) and traces of Methane (CH4). This mixture is called synthetic gas. Synthetic gas
can be used to run internal and external combustion engines, can be used as substitute
for fossil fuels in direct heat applications and can be used to produce methanol, in an
economically viable way. Since any biomass material can undergo gasification, this
process is much more attractive than ethanol production or biogas where only
selected biomass materials can be used as raw material.
However under present conditions, economic factors seem to provide the strongest
argument of considering gasification. In many situations where the price of petroleum
fuels is high or where supplies are unreliable the biomass gasification can provide an
economically viable.
The combustion products from complete combustion of biomass generally contain
nitrogen, water vapor, carbon dioxide and surplus. However in gasification where
there is a surplus of solid fuel (incomplete combustion) the products are combustible
gases like Carbon monoxide (CO), Hydrogen (H2) and traces of Methane.
In a gasifier, biomass undergoes three processes:
1. Pyrolysis or devolatilization is a thermal decomposition process that occurs at
moderate temperatures with a high heat transfer rate to the biomass in the
absence of oxygen. In practice, it is not possible to achieve a completely
oxygen-free atmosphere. Because some oxygen will be present in any
pyrolytic system, nominal oxidation will occur. Pyrolysis produces
combustible gases, including carbon monoxide, hydrogen and methane. The
pyrolysis gases require further treatment.
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When biomass decomposes at elevated temperatures, three primary products
are formed: gas, bio-oil and char. At high temperatures the bio-oil vapors are
decomposed in secondary products like gas and polymeric tar.
2. The combustion process occurs as the volatile products and some of the char
reacts with oxygen to form carbon dioxide and carbon monoxide, which
provides heat for the subsequent gasification reactions.
3. The gasification process occurs as the char reacts with carbon dioxide and
steam to produce carbon monoxide and hydrogen in the presence of
gasification agent. The resulting gas is called producer gas or syngas. Syngas
is primarily carbon monoxide and hydrogen (more than 85 percent by
volume) and smaller quantities of carbon dioxide and methane. Syngas can be
used as a fuel to generate electricity or steam. When mixed with air, syngas
can be used in internal and external combustion engines with few
modifications. The gasification process requires heat and an oxidant such as
oxygen (O2) or steam (H2O). Heat addition can occur directly by partial
oxidation of the fuel or indirectly using some means of high rate indirect heat
transfer.
4.1.2 Types of Gasifier
There are basically five types of gasifiers used. Fixed bed gasification processes can
be divided into two different process designs
• Counter-current fixed bed ("up draft")
• The co-current fixed bed ("down draft")
Moving bed gasification processes can be classified into three process designs.
• Fluidized bed
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• Entrained flow
• Circulating Fluid-Bed
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4.1.3 Updraft gasifier/counter-current fixed bed gasifier (UDG).
Figure 2 (a) and 2(b): Updraft gasifier
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Biomass enters through a lock-hopper and flows down against the flow of air and that
is why it is named as counter-current gasifier. The air is introduced to the biomass
through grates at bottom of furnace. High temperatures are generated initially where
the air first contacts with the char, but combustion gases enter a portion of excess
char, where any CO2 and H20 is reduced to CO and H2. As the air rises to lower
temperature zone, they meet the descending biomass and pyrolyze the incoming
biomass in the range 200 to 500 C. The counter flow arrangement is tolerant to
biomass moisture (up to 40 or 50%M) since drying process occurs by produced gas,
however the produced gas has the tar content 5 to10 percent and is suitable for staged
combustion. The dirty product gas of the UDG means that it is not applicable for most
applications that require clean gas, such as synthetic fuel, chemical or gas turbine
applications. It is best only for heat applications, such as boiler firing. [SCHL96]
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4.1.4 Downdraft gasifier or co-current fixed bed gasifier (DDG).
Figure 3 (a) & 3 (b): Downdraft gasifier
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Biomass enters through an open top in an air-blown system or through a lock-hopper
in an oxygen-blown system. The open top DDG design is simple and low-cost. Air is
introduced to gasifier through a set of nozzles. The drying zone contains un-reacted
fuel. In the pyrolysis zone, the fuel reacts with oxygen. Most of the volatile
components of the fuel are burned in this zone and provide heat for continued
pyrolysis reactions. The open top design ensures uniform access of air to the pyrolysis
region. In combustion zone, hot combustion gases from the pyrolysis region react
with the charcoal to convert the carbon dioxide and water vapor into carbon
monoxide and hydrogen. The inert char and ash, which constitute the next zone, are
normally too cool to cause further reactions; however, since this zone is available to
absorb heat or oxygen as conditions change, it serves both as a buffer and as a
charcoal storage region. Below this zone is the grate. The presence of char and ash
serves to protect the grate from excessive temperatures. Adding blast to the char zone
is an excellent approach for achieving low tar gas (<100 mg tar/Nm3). The downdraft
gasifier is useful for small scale applications, and may have a practical upper limit of
5 MW [SCHL96].
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4.1.5 Fluidized-bed gasifier (FBG).
The FBG gasifier is well known for reliable performance, isothermal operation, and
suitability to large scale application. It can accommodate much greater quantity and,
normally, a much lower quality of fuel.
Figure 4 (a) & 4 (b): Fluidized Bed Gasifier
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The bed material can either be sand or char, or some combination which is pre heated
to a temperature of 1000 ºF. The fluidizing medium is usually air; however, oxygen
and/or steam are also used. Air, steam or oxygen blends are delivered through a flow
distributor into a fluidized bed of sand. The fluidized bed gives rapid heating of
reactant gases in addition to excellent mixing of biomass solids and inert media. The
inert fluidizing media is typically comprised of silica, mullite, or olivine sand. The
fluidized bed system is made in such a way that the ash particles are carried out of the
bed with the gas stream. This ash is then removed from the gas stream by a special
ash removal system. Tar production is moderately high at ~1% to 2%, but less than a
fixed bed updraft gasifier. In any case, the FBG is quite robust for both pyrolysis and
gasification, but secondary processing of the generated gas may be required for more
critical applications besides strictly thermal energy supply. [SCHL96].
31
4.1.6 Circulating fluid-bed gasifier (CFBG).
Figure 5(a) and 5(b): Circulating Fluidized Bed Gasifier
32
In CFBG, pulverized fuel is added to the bottom of the pyrolysis chamber. A stream
of circulating sand particles takes the coke particles with it, after which they are
separated by a primary cyclone and re-circulated. CFBG is a fast fluidization process
and speed up the gasification process. The formation of a fast fluidized bed depends
on the following conditions: (a) small particle materials (b) high operating gas
velocity (c) continuous solid circulation. CFBG circulate the char continuously which
increases the residence time of char and hence less char loss. The higher velocity
regime gives an alternative approach to increasing char residence time to promote
higher efficiency gasification. These features enhance heat and mass transfer, raise
reaction rate, and strengthen fast pyrolysis. This both facts make the productivity of
the CFBG much higher and gas quality much better than other kind of air blown.
[SCHL96].
33
4.1.7 Entertained flow gasifier (EFBG)
They are commonly used for coal because of finer particle sizes and higher operating
temperatures. However, entrained flow gasifiers are not practical for biomass for
several reasons including operating temperature limiting properties of biomass ash
and the impracticality of generating finely ground biomass feedstock. Biomass also
has a lower energy density and higher moisture holding capacity, which makes it
impractical to slurry feed biomass gasifiers. Certain types of biomasses can form slag
that is corrosive for ceramic inner walls. Several commercial designs are available for
coal, but these will not work with more than 10 to 15% biomass in a coal blend.
[SCHL96]
Figure 6: Entrained Flow Gasifier
34
4.1.8 Comparison of gasifiers
The table 1 shows the comparison between different types of gasifiers based on their
operating temperatures, tars content in the products, their application areas and their
operational control.
Parameters Co-current Counter-
Current
Fluidized bed Circulating
Bed
Entrained
bed
Temp C 700 - 1200 700 -900 < 900 < 900 1500
Tars Low Very high intermediate intermediate absent
Scale < 5 MW < 20 MW 10 < MW< 100 20 < MW > 100 MW
Feed Stock Very critical Critical Less critical Less critical Very fine
particles
Control easy Very easy intermediate intermediate Very
complex
Table 1: Comparison of gasifiers
35
The table 2 shows the advantages and disadvantages of different types of gasifiers.
Name Advantages Disadvantages
Updraft Mature for Heat
Small Scale Applications
Can Handle High Moisture
No Carbon in Ash
Feed size limits
High Tar Yields
Scale limitations
Slagging potential
Downdraft Small scale applications
Large particulates
Low tars
Moisture sensitive
Scale limitations
Feed size limits
Producer gas
Fluidized Bed Large scale applications
Direct and indirect Heating
Feed characteristics
Can produce syngas
Medium tar yields
High particle loading
Circulating Bed Large scale applications
Feed characteristics
Can produce syngas
Medium tar yields
High particle loading
Entrained flow Can be scaled
Can produce syngas
Potential for low tar
Large amount of carrier gas
Particle size limits
Higher particle loading
Potentially high S/C
Table 2: Advantages and disadvantages of different gasifiers
36
5. CLASSIFICATION OF BIOMASS FUELS
The composition of the fuels from various sources has been collected, different
thermodynamic properties have been calculated and it has been observed that the
values of various properties differed for different fuel compositions. Calculation of
the heating values differed from source to sources. The complete fuel list is in
appendix A.
5.1 Composition
There is variety of different gasification techniques, which yield gases that can be
very different in composition. The composition of the product gases depend strongly
on the variable parameters of the gasification process like pressure and equivalence
ratio and the gasification technique used.
The gasification product gases are basically a mixture of H2, CO, and N2 and can also
contain CH4, CO2, and H2O. Some further minor species may be present also, but
their effect is neglected in this study due to their small fraction.
During the literature study that preceded the calculations composition data of
interesting fuels was collected from various sources. Some of the sources also
included additional fuel properties like heating value and molecular weight. To ensure
consistency in data, only the compositions of the fuels were used and all other fuel
properties were derived from the composition. This way the fuel properties and their
quantitative change with change of composition can be compared.
A total of 68 fuels mixtures was found and included in a spreadsheet (Appendix A).
The processes that yielded these fuels were very different. 25 of them are biomass
gasification product gases whose LHV was in the interesting range between 3 and 10
MJ/m³. It should be noted that none of those in that range had a LHV of more than 8
MJ/m³. Unless indicated otherwise the discussion in this study refers to these biomass
gasification product gases only.
37
The upper and lower limits of the molar fractions of the different species together
with their average value can be found in table 3.
Species Minimum molar
concentration
Maximum molar
concentration
Average molar
concentration
H2 0.096 0.251 0.167
CO 0.108 0.315 0.193
CH4 0.000 0.132 0.032
CO2 0.000 0.289 0.105
H2O 0.000 0.097 0.015
N2 0.278 0.733 0.488
Table 3 Maximum, minimum and average molar concentrations of the found biomass gasification
product gases between 3 and 10 MJ/m
According to the obtained composition datasets, CO is in average the most abundant
combustible species contained in the fuels. Its volumetric heating value is higher than
that of H2. Due to the fact that CH4 is in average a rather minor species CO is usually
the main contributor to the volumetric heating value of the fuel.
On the other hand it should be noted that the CH4, even though usually contained in
rather small fractions compared to the other two combustibles, can also be a major
contributor to the heating value due to its high volumetric heating value (34 MJ/Nm³
compared to 10.2 MJ/Nm³ for H2 and 12.0 MJ/Nm³ for CO).
A problem concerning the direct combustion of gasification product gases in a gas
turbine is the tar-content of the fuel. Also, other minor species may lead to corrosion
problems in the fuel system. This study primarily focuses on the combustibility
characteristics of the fuels and thus does not consider these effects.
38
5.2 Basic fuel properties
In order to provide an overview over the differences in the fuel properties and for
easy implementation of new composition sets a spreadsheet has been developed to
calculate a series of fuel properties from the composition.
Standard conditions with 101325 Pa pressure and 288.15 K temperature were
assumed. Some of the properties of biomass fuel are as under:
• Molecular weight
ii MWxMW ∑=
The molar weight MW of the fuels varies between 21.5 and 27.2 kg/kmol. This strong
variation is mostly due to the low molecular weight of hydrogen.
• Density
The density ρ was approximated with the ideal gas law:
TR
pMWfuel
⋅⋅
=ρ
It varies between 0.91 and 1.15 kg/m³, which is rather high compared to ρCH4 = 0.68
kg/m³.
5.2.1 Stoichiometric Air-fuel-ratios
These measures are the ratio of the amount of air and fuel needed to theoretically
achieve complete combustion without excess oxygen. Due to the high amount of
dilutive components this figure is significantly lower for gasification product gases
than for natural gas fuels in use today.
39
Volumetric: icombistoichv axFA ∑= ,,)/(
In this equation “a” is a stoichiometric factor that quantifies how many oxygen
molecules are needed to oxidize a molecule of the combustible fraction i. It has a
value of 0.5 for H2 and CO and a value of 2 for CH4.
Mass-based: fuel
airstoichvstoichm FAFA
ρρ
⋅= ,, )/()/(
The values for the volumetric stoichiometric air-fuel-ratio vary between 0.7 and 2.0,
while the value for pure methane is 9.5. These low values indicate that combustor and
turbine will have to accommodate a significantly higher volume flow than in natural
gas combustion.
5.2.2 Heating values
The different definitions of heating values are a measure for the heat release that is
achieved in combustion of a given fuel.
They can be formulated either based on mass or on volume. Both values were
calculated, but in the further studies only the volumetric heating values will be used,
as the fuels looked are in gaseous state.
The higher heating value describes the total thermal energy release in the combustion,
whereas the lower heating value neglects the heat of vaporization that the water
vapour in the flue gas contains. Due to the fact that this part of energy contained in
the combustion products has no direct implications on the gas turbine process only
the lower heating value will be considered later in this study. It ranges from 3.25
MJ/m³ and 7.77 MJ/m³ with an average of 5.10 MJ/m³.
Volumetric LHV: voliivol LHVxLHV .∑=
40
Mass-based LHV: ρ
volmass
LHVLHV =
Volumetric HHV: OH
OHvapOHCHHvolvol MW
hxxxLHVHHV
2
2242 )2(
ρ⋅+++=
0
1
2
3
4
5
6
7
3,5 4
4,5 5
5,5 6
6,5 7
7,5 8
8,5 9
9,5
and
larger
LHV_v (MJ/m³)
Occ
urre
nce
Figure 7: Occurrences of heating value for biomass gasification product gases in the range between
3 and 10 MJ/m³ for the fuels in appendix A.
0
1
2
3
4
5
6
7
3,5 4
4,5 5
5,5 6
6,5 7
7,5 8
8,5 9
9,5
and
larger
LHV_v (MJ/m³)
Occ
urre
nce
Figure 8: Occurrences of heating value for all low calorific value fuels attained from literature
41
Fig 7 shows the frequency distribution of the heating values for the biomass
gasification product gases in 3-10 MJ/m³ range. It can be clearly seen that most gases
are in the 4.5 to 6 MJ/m³ range.
Fig 8 also includes the other gases found in the literature. The distribution is similar
to the seen for biomass gases, with a few more gases in the upper LHV range.
5.2.3 Wobbe indices
The Wobbe index is a figure which is important when designing a fuel system. For a
given valve setting two gases with the same Wobbe index will release the same
amount of heat.
Inferior:
ref
volLHVWI
ρρ
=inf
Superior:
ref
volHHVWI
ρρ
=sup
5.2.4 Flow ratios
In order to give an estimation of the expected additional mass flow in the turbine two
formulas to calculate the turbine-compressor-mass-flow ratio were derived. The first
one takes the overall λ as a constant compared to a reference case (e.g. natural gas
combustion), whereas the second one determines a ratio for the same power output as
in a base case. The latter formula is more practical as the turbine should be utilized to
its full capacity to provide cost-efficient operation.
Constant-λ mass flow: stoichmC
T
FAm
m
,)/(1
φ+=&
&
Constant-Power mass flow: LHV
LHV
FAm
m ref
refstoichm
ref
C
T ⋅+=,,)/(
1φ
&
&
42
0,8000
0,9000
1,0000
1,1000
1,2000
1,3000
1,4000
1,5000
1,6000
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00
LHV_v (MJ/m³)
MF
_T/M
F_C
const. λ const. Power
Figure 9 :The mass flow ratio for a variety of different fuels. To visualize the much higher mass
flow going through the turbine not only the gases from Appendix A, but all acquired fuel
compositions were used
5.2.5 Stoichiometric adiabatic flame temperatures
Individually, H2 and CO have higher adiabatic flame temperatures at stoichiometric
conditions than CH4 (2383K and 2385K as compared to 2220K at ambient state). The
dilutive components in turn lower the flame temperature.
The stoichiometric adiabatic flame temperatures of the 25 GPGs were calculated for
both ambient state and compressor outlet state. For this the Chemkin equilibrium
reactor model with the GRI-Mech 3.0 mechanism was applied. The upper and lower
limits as well as the average values of the results are given in table 4.
Property Minimum Maximum Average
Tad,st (p=1atm,T0=298K) (K) 1677 2125 1887
Tad,st (p=12atm, T0=650K) (K) 1958 2374 2149
43
Table 4 Calculated adiabatic flame temperatures of the collected gasification product gases.
5.2.6 Molecular ratios
Apart from the minimum and maximum molar concentrations of the different species
in the fuels as given in Table 3, it is also important to know in which boundaries their
molecular ratios vary.
0,0
0,5
1,0
1,5
0,0 0,5 1,0 1,5 2,0
H2:CO ratio
CH
4:C
O r
atio
Figure 10: Molecular ratios of the gasification product gases from Appendix A.
Figure 10 shows how the mass flow ratio for a variety of different fuels. To visualize
the much higher mass flow going through the turbine not only the gases from
Appendix A, but all acquired fuel compositions were used.
The H2:CO ratio varies between 0.37 and 1.73. This means that there is always
hydrogen present next to CO in the mixtures and that the CO oxidization will be able
to follow the fast wet CO combustion pathway with the determining reaction CO +
OH → CO2 + H, which makes the CO combustion much more rapid than in the dry
case. The average value for this ratio is 0.92.
44
The CH4:CO ratio ranges between 0 and 1.192. The average value is at a low 0.2,
though.
6. GT PERFORM
Siemens has developed GT Perform computer program for thermodynamic
simulations of gas turbines. The program can simulate different gas turbines like GT-
500, GT-600, GT-700 and GT-800. For this thesis the GT-500 simulator was used.
The program optimizes the compressors, turbines and combustion chamber of open
cycle gas turbines GT-500. It simulates the open cycle gas turbines, without any
integration of additional cycles like co-generation or combined cycle. It doesn’t
calculate the power needed to compress the fuel. The simulations can be done at any
operating conditions, ambient or elevated.
Input design requirements of the program include the type and composition of fuel,
Inlet and outlet pressure losses, type of application (either power generation or
mechanical drive), percentage of base load, type of injection to combustion chambers,
power turbine speed and different parameters of compressors and turbines like
pressure loss co-efficient, temperature, pressure, mass flow, turbine constants,
injection and extraction of air at different points etc. The fuel properties are input as
composition, gas constant, heating value and specific heat.
The program output includes the temperature, pressure, pressure ratios, speed of
shafts, mass flow of the fuel in combustion chamber, mass flows at compressors and
turbines, electric power output, compressor and turbine efficiency, shaft power and
heat rate etc.
It works with International SI and US units. It is compatible with all versions of
windows.
45
6.1 SGT-500 Parameters
The figure 11 explains some of the parameters of interest of GT-500 used in GT
Perform.
Figure 11: SGT-500 parameters
S.No Parameter Meaning
1 GAMK2 or GAMK LPC Air extraction after low pressure compressor.
2 GAMK3 or GAMK HPC Air extraction after high pressure compressor.
3 GAMT2 or GAMT LPT Air injection before low pressure turbine.
4 GAMT3 or GAMT HPT Air injection before high pressure turbine.
5 GINTE2 or GINTE LPT Air injection after low pressure turbine.
6 GINTE3 or GINTE HPT Air injection after high pressure turbine.
7 HPT constant High pressure turbine constant.
8 PT constant Power turbine constant.
Table 5:- GT-500 parameters
46
GAMK2 of 0.025 means that 2.5% of total flow is extracted after low pressure
compressor. The HPT and PT constants change the turbine capacities (“flow
numbers”). Only the flow numbers of the high pressure turbine (HPT) and the power
turbine (PT) can be altered in the SGT-500 without surplus effort (a washer is
changed, altering the guide vane angles).
47
7. RESULTS OBTAINED BY GT PERFORM
The results obtained by GT perform by simulating biogases with alteration of GT-500
parameters are presented in the following sections. A step by step approach is
presented.
7.1 Base or reference case
The first approach to the program is to simulate the gas turbine SGT-500 under
standard conditions and with a standard fuel “natural gas” as base case.
The SGT-500 has the following limitations for speed and power output
• Maximum low pressure (LP) shaft speed = 5900 rpm
• Maximum high pressure (HP) shaft speed = 7300 rpm
• Maximum electrical power output = 20.7 MW (generator limitation)
The limitations on speed are obligatory to avoid from compressor surge, while the
power output is limited due to generator.
The reference or base case has the following standard conditions in GT Perform.
• Power Generation, 50 Hz, with gear
• Inlet and outlet pressure losses = 0 mbar
• Power factor = 1.0
• Fuel is standard natural gas (LHV = 46 798 kJ/kg), fuel temp = 25°C
• Load 100 % of base load (TIT = 850°C)
• Air pressure 1.01325 bar (“Site elevation = 0 meter”)
• Ambient air temperature 15°C
• Relative air humidity is 60 %
• No water/steam injection
The results of the base case are presented in appendix C and D.
48
7.1.1 Simulation of several LHV fuels
The next measure is to simulate the gas turbine with several LHV fuels from
appendix A and to compare the results with the base case.
In the figures 12, 13 and 14, all the values are normalized with respect to base case.
The base case is represented by the points (1, 1). If the value on x-axis is “7.99”, the
fuel flow needed with biomass fuel in combustor is 7.99 times the fuel flow of the
base case.
The heating value decreases in x-axis with an increase in fuel ratio. The fuel ratio is
mass flow of the bio-fuel with respect to natural gas under same conditions.
Figure 12: The effect of decrease in heating values on power output and efficiency
The graph in figure 12 is unusual because it shows that the lower heating value of the
fuel provides higher power output and efficiency. This has an explanation.
49
The total input power (PI) supplied to the combustor is due to the heating value and
the enthalpy of the fuel.
E = Enthalpy
H.V = Heating value
PE = Power due to the enthalpy.
P H.V = Power due to the heating value of the fuel.
PI = Input power supplied to combustor
Po = Output power
PI = PE + P H.V (1)
PE = E * fuel flow (2)
P H.V = H.V * fuel flow (3)
PI = [H.V+E] *[fuel flow] (4)
The enthalpy for high heating value fuels is neglected because it is negligible as
compared to the heating value.
The enthalpy can’t be neglected for LHV bio-fuels because the values of the enthalpy
and heating value are in the same scale, while PE increases according to equation (2)
with an increase in fuel flow. As a consequence the input PI and output power Po also
increases.
The output power Po in figure 12 is constant for fuel ratio equal to or greater than
5.66. This is because of the power output PO limitation of GT Perform.
50
If Po is constant then PI has to be nearly constant. If we assume that PI is constant and
PE is increasing, then according to equation (4), PH.V has to decrease.
The efficiency is defined as:
Eff = PO / P H.V (5)
In equation (5), the power output PO is constant and PH.V is decreasing, that’s why the
efficiency is higher with low heating values in figure 12.
The power and efficiency is increasing in figure 12 because the program doesn’t take
into account the power needed to compress the fuel, and in the case of LHV fuels, the
fuel flow is very high. The fuel introduced in the combustor is assumed to be
compressed. The power needed to compress that fuel is not added in the figure 12.
The power output is constant in figure 12 because the gas turbine has a power
limitation of 20.7 MW. This limitation can be removed in program but it is needed as
a safety measure for the electric generator.
In the figure 13, the speeds of the shaft 2 (low pressure compressor and turbine) and
shaft3 (high pressure compressor and turbine) are presented.
These speeds are normalised with respect to base case. The speed at point (1, 1)
represents the base case.
51
Figure 13: The effect of decrease in heating values on speeds of LPC and HPC
In the figure 14, the efficiency and pressure ratio are normalized with respect to base
case.
Figure 14: The effect of decrease in heating values on pressure ratio
52
It is observed in figure 13 that the speed of low pressure compressor and high
pressure compressor initially increases with increase in fuel ratio (decrease in heating
value) up to interval (1-6) and gradually decrease afterwards. This has an explanation
also with the reference of pressures graph (figure 14).
When the fuel flow in combustor is up to six times higher than the base case, the flow
going through the turbine increases, this crafts the turbine to run with high speed, but
when the fuel flow is further increased, the power output of the gas turbine hits its
maximum value of 20.7 MW and further increase in fuel flow through combustor will
drop the speeds and increase the pressure ratio of low and high pressure compressor.
7.1.2 Utilization of two representative fuels, how the parameters affect.
The following simulation is performed to know the effect of the parameters listed in
table 5 on the speeds and pressure ratios of low and high pressure compressor, power
and efficiency of GT-500 .The fuels selected are listed in table 6.
The selected fuels are the following:
S.No Fuel from Appendix A Heating Value
MJ/KG
Mass flow of fuel
kg/s
1 Fuel #22 9.36 6.5
2 Fuel #66 3.36 16.7
Table 6 Two representative fuels from Appendix A
The composition of fuels is listed in Appendix A. These fuels are selected because of
their heating values.
The parameters listed in table 5 are increased than their standard values and the
results are represented in figure 15 and 16. The table 7 explains the terminologies
represented in figure 15 and 16.
53
S.No Parameter Explanation The constant
parameters
1 Ref No change in parameters All
2 Hpt Hpt constt increased 4 times 3 - 9 (from
serial no)
3 Hpt pt Both Hpt and Pt constants increased 4
times
4 - 9
4 Gamk 2 Gamk2 increased 4 times, 5 - 9
5 Gamk 3 Gamk 3 increased 4 times 4 and 6-9
6 Gamt 2 Gamt 2 increased 4 times 4,5,7,8,9
7 Gamt 3 Gamt 3 increased 4 times 4,5,6,8,9
8 Ginte 2 Ginte 2 increased 4 times 4,5,6,7,9
9 Ginte 3 Ginte 3 increased 4 times 4 - 8
Table 7 Explanation of figure 15
The fuel flow in combustor at “ref” is used as reference. This reference value is used
to normalize the fuel ratio. The power, efficiency, speeds and pressure ratio are
normalized with respect to base case.
54
Figure 15: Effect of change of parameters on gas # 22
Figure 16: Effect of change of parameters on gas # 66
55
The figure 15 shows that there is no significant effect on the speed and pressure ratio
of low and high pressure compressor by change of parameters listed in table 5.
The figure 16 shows that the extraction after high pressure compressor decreases the
efficiency of GT-500 and that the efficiency has an inverse relation with fuel flow for
a specific fuel. Also we know from the equation 6 that:
Power output = efficiency * HV * fuel flow (6)
The power output is constant for a specific fuel, when the fuel flow increases the
efficiency decreases.
7.1.3 Turbine Inlet temperature limitation v.s. power output limitation
There could be two types of constrains applied on GT Perform for operation of GT-
500 gas turbine. One limitation is on the turbine inlet temperature TIT of high
pressure turbine, it’s maximum limit is 850 ºC. Another limitation is on power output
PO, it’s maximum limit is 20.7 MW. Both the limitations are praticle limitations on
GT-500 gas turbine, even they can be removed from the GT Perform but it is
recommended to work in these limitations. Only one limit can be used at a time.
Normally the turbine inlet temperature limitation is used in GT Perform simulations.
In all the simulations performed previously, the limitation to turbine inlet temperature
TIT=850ºC was used. It means that the gas turbine can offer as much power as
possible but the turbine inlet temperature can’t exceed the limit of 850ºC.
Turbine Inlet temperature limit is replaced by power output limit. It means that the
output power can not be higher than a specific value; it is a limit introduced in the
total output power of the gas turbine unit. In a specific case as shown in figure 12,
when power output is exceeding its maximum limit, the power output limit of 18
MW is used.In this case the power turbine PT constant is increased from 254 to 260
and high pressure turbine HPT constant from 948 to 970.
56
The results are the following:
Figure 17: TIT vs. PO limitation
By utilizing the PO limitation, the power and efficiency of GT-500 are lower but the
speeds and pressure ratio of LPC and HPC are much closer to the base case.
If the speeds and pressure ratio of LPC and HPC are too high with TIT limitation, it
would be better to use the P.O. limitation. The better speed and pressure ratios of
LPC and HPC can be obtained at the cost of low output and efficiency to avoid
compressor surge problem and to avoid imbalance between compressor and turbine.
57
However practically, it is difficult to set a limitation on the power out put of gas
turbine, which needs to change the generator.
If we assume that the power needed for compressing the fuel is obtained from the
power output of the machine, then the results obtained so far are not realistic because
the power needed to compress the fuel has been ignored. So the simulations and
results obtained after this work will accommodate the power needed to compress the
biomass and hence the results are realistic.
7.2 Power needed for compressing the fuel
As a lot of power is needed to compress the biogas in a separate fuel gas compressor,
it should be calculated. If the biogas is assumed to be at atmospheric pressure, it
should be compressed to at least 18.5 bar; it is the gas pressure for which the fuel gas
control valve and governor are designed for. The efficiency of the compressor is
assumed to be 75%. The power needed for the biogas compressor must be calculated
outside GT Perform, since it is not possible to add components to the program. The
calculations are in Appendix B
7.2.1 Power and efficiency without fuel compressor power
The figure 18 shows the results that were obtained earlier, when the power needed for
compressing the fuel wasn’t taken into account.
58
Figure 18: Power output and efficiency without calculating power needed to compress the fuel
7.2.2 Power and efficiency with fuel compressor power
This graph shows the results after calculating the power needed to compress the fuel.
It is assumed that the power needed for compressing the fuel is taken from the power
output of the unit.
59
Figure 19: power output and efficiency with the power needed to compress the fuel
Figure 19 represents the realistic results. The low heating value of biomass fuel gives
the less efficiency and less power output. In spite of that, the efficiency in the fuel
ratio interval (1-10) is quite good. It is higher than 90% of the efficiency of the
reference case, and also in the interval (1-6) the efficiency is even higher than the
reference case.
60
7.3 Simulations of medium heating value MHV fuel.
Since it is interesting to see the running lines of the compressors, it is good to run at
say three different load points (say 20%, 60% and 100% of base load) and plot the
pressure ratios for the LP and HP compressors vs. the speed of respectively shaft
using a high heating value fuel as reference.
The speeds and pressure ratios for the compressors are kept as close as possible to the
base case (SGT-500 running on natural gas).
It is recommended to use a gas with moderate LHV (i.e. a medium calorific value
(MCV) gas), since otherwise the gas turbine will hit the power output limitation
resulting in a reduction of the firing temperature. The increased mass flow through
the turbine due to the low heating value of the gas will of course lead to increased
pressure ratios over the compressors and increased shaft speeds. The surge margin
will hence reduce. To overcome this, it is necessary to change the turbine capacities
(“flow numbers”). Only the flow numbers of the high pressure turbine (HPT) and the
power turbine (PT) can be altered in the SGT-500 without too much effort (a washer
is changed, altering the guide vane angles). In this project, it is recommended by
siemens to open up the HP-turbine to a higher flow number maximum up to 270
without affecting the turbine efficiency (254 is the reference flow number of the
HPT).
Afterwards, the PT flow number is decreased to reduce the LPT pressure ratio and
shaft speed. The PT flow number should not be lowered < 900 since this lowers the
gas turbine performance. The results obtained are shown here.
61
7.3.1 Results of reference case vs. MHV fuel
Figure 20: Result of refrence case vs MHV fuel
Figure 21: Result of refrence case with MHV fuel
62
As can be seen from Figure 20, the pressure ratio increased for the LPC even
though the HPT and PT constants are rematched. It might therefore be necessary
to bleed off some air from the compressor(s). This is done by changing
(increasing) the “GAMK” values. The GAMK expresses how much air is bled off
as percent of the flow into the compressor. The GAMK is used since some air is
bled off for cooling the discs and for sealing air purpose and also to account for
air leakages. The GAMT and GINTE are used to model the disc cooling etc.
To be accurate in the modeling, the GAMT and GINTE mass flows of the
reference case in kg/s are calculated and for the other cases, they have been kept
the same as reference case.
The reason is that the disc cooling areas are constant, and since the GAMT and
GINTE are expressed as percentages, increase of the mass flow in the turbines
will also increase the cooling flows, which isn’t the case since the disc cooling
areas are fixed.
It is exercised to start increasing the GAMK2, which is the GAMK for the low
pressure compressor. Increase of the bleed off after the low pressure LP
compressor can decrease the pressure ratio and speed of the LP compressor.
63
7.3.2 Effect of increasing gamk2
The graph of figure 22 shows the speeds in absolute value. The bar “bio*” shows the
results when the bio fuel is used with no changes in the parameters. The bar “bio
hpt*” shows the result when the hpt constant is increased. The bar “bio hpt pt*”
shows the result when the hpt constant is increased and the pt constant is decreased.
Figure 22: Speed of shaft2 and shaft 3 using MHV fuel
64
It can be seen that the increase in “gamk 2” doesn’t affect the speed of compressors.
It is observed that the speeds are within the specified range. They are quite near to the
base case and also far away from the limits: 5900 rpm for shaft 2 and 7300 for shaft
3.
65
Figure 23: Pressure ratio of LPC and HPC using MHV fuel
The graph in figure 23 shows the pressure ratio in absolute value:
It is noticed that the increase of gamk2 decreases the pressure ratio of the low
pressure compressor. It is an acceptable way out when the pressure ratio of the LPC is
too high. The increase of gamk2 increases the pressure ratio of the high pressure
compressor HPC; it is also favorable because the pressure ratio in HPC is lower than
the base case for LHV fuel.
66
7.3.3 Using a pressurized gasifier.
An alternative option is to integrate the gas turbine with pressurized biomass gasifier
as shown in figure 24. It would then be an advantage to extract air from the high
pressure compressor (increase GAMK3) and use this air in the gasifier. The energy
needed for the gas compression could then be drastically reduced, and one would
merely need a booster compressor to increase the biogas pressure somewhat before
injecting it into the gas turbine. This point is therefore to model how a large
extraction of air after the HP compressor affects the gas turbine performance and the
power demand for the booster compressor. The booster compressor+ gasifier
efficiency has been assumed to be 60%.
Figure 24: The gasifier integrated with the unit
67
Figure 25: Gasifier vs. bleeding after low pressure compressor
The results of three types of simulations are compared in figure 25, i.e. standard or
base case, the bleeding after low pressure compressor and bleeding after high
pressure compressor with integrated gasifier.
It is obvious from figure 25 that the results are superior with the integration of a
gasifier because the speeds and pressures of compressors are very close to the base
case and the power and efficiency are even higher. The incorporation of gasifier is an
expensive solution but the results are remarkable.
The bleeding of air after low pressure compressor is simple and cheap solution but the
results are not remarkable because the energy is lost as compressed air.
68
These simulations are performed with a MHV fuel, and the results are appealing. It is
needed to do the same study with a LHV fuel to perceive if the results are still good
enough.
It is also necessary to observe the results of speeds and pressure ratios of LPC and
HPC and efficiency of GT-500 in the compressor and efficiency maps provided by
Siemens.
69
7.4 Simulations with LHV and MHV fuels
In section 7.3 it was concluded that there are two key solutions by the use of medium
heating value fuels, to get high enough efficiency and power output and to keep the
pressure ratios and speeds within limitations.
1. Bleeding air after low pressure compressor: increase in gamk2.
2. Integration of a pressurized gasifier after high pressure compressor.
Now, the last step in this regard is to manipulate the above two conclusions with the
LHV fuels. The results are shown in actual compressor maps obtained by Siemens.
7.4.1 Results in compressors maps.
There are two types of compressor maps
• Efficiency maps.
• Speed map.
The inputs in the maps are pressure ratio and fuel flow. The value of the flow is not
the absolute; it is a value in characteristic, using a reference value.
In these maps, both solutions (bleeding and gasifier) are presented, with both medium
and low heating value fuels.
70
• LOW PRESSURE COMPRESSOR
Figure 26: Low pressure compressor efficiency map
The figure 26 represents the efficiency of LPC for base case, bleeding after low
pressure compressor, and integration of gasifier after high pressure compressor, for
medium and low heating value gases. Figure 27 shows that all the points are in same
area of graph. All the points are really close to each other and they are far away from
the surge margin. They are all in the same blue area.
71
Figure 27 shows the speed of the low pressure compressor LPC.
Figure 27: Low pressure compressor speed map
The figure 27 represents the speed of LPC for base case, bleeding after low pressure
compressor, and integration of gasifier after high pressure compressor for medium
and low heating value gases. Figure 27 shows that all the points are in same area of
graph. Figure 26 and 27 shows that there will be no problems in the low pressure
compressor by the utilization of LHV fuels.
Now, the results are plotted in high pressure compressor map.
72
• HIGH PRESSURE COMPRESSOR
Figure 28: High pressure compressor efficiency map
Figure 28 is the map of efficiency of the high pressure compressor. The points are not
as close as in the low pressure compressor but they are in the same area in moderate
working range.
The next map shows the speed in the high pressure compressor
73
Figure 29: High pressure compressor speed map
Figure 29 is the speed map of high pressure compressor; the points are not in the
same area and they are far away from the surge margin. It shows that there will be no
problems in the high pressure compressor by the utilization of LHV fuels.
74
8. FUEL SYSTEM
The fuel system includes all components needed to control fuel during start-up and
operation. It consists of the values and pipes listed in table 3.The fuel system must
supply clean, accurately metered fuel to the combustion chambers. All fuel systems
have basically the same components; how these specific units do their jobs differs
radically from one system to another.
A complete gas turbine fuel system more specifically comprises a fuel distribution
control system, a fuel purge system, a purging air supply system and a fuel nozzle
wash system in which, fuel distribution is controlled to be done uniformly to a
number of fuel nozzles with enhanced reliability of fuel distribution, and residual oil
in fuel pipings and nozzles.
A gas turbine fuel purge system comprises a number of fuel supply pipings for
supplying fuel to a number of fuel nozzles via a header; and a drain piping connected
to plurality of fuel supplying pipings and a purging air supply piping for supplying air
to each said sealing connection pipe.
The Gas Turbine Fuel Control system provides a unique approach to integrated and
stand-alone fuel control for new and retrofit applications and can be configured for
the control of any gas turbine and speed control is used to position the fuel control
valve at the minimum fuel flow requirement and still maintains the power turbine
speed requested.
Many industrial machines are delivered suitable to burn either gaseous fuel or liquid
fuels. Thus, a fuel system is frequently a part of the installation.
75
8.1 SGT-500 Fuel system
The fuel system helps to define requirements for proper fuel flow and placement to
ensure optimum combustion performance and to design and build fuel nozzles,
valves, pipes and injection systems.
The table 5 shows the system designed for SGT-500 operating with Natural Gas. In
our case using LHV fuel, the gas volume flows increase i.e. the velocities in the
system becomes very high, the dimensions of all of values and pipes in table 5 has to
be changed to reduce velocities. This is due to avoid high pressure drops in the
system, but also sound problems that might occur at high media velocities.
According to the recommendations of Siemens, the pressure losses in the fuel system
of LHV operated gas turbines is kept on the same level as for standard gas or slightly
higher. This of course means that valves and pipes have to increase in diameter. The
values in table 5 represent physical dimensions of equipment in the fuel system and
they are constant for a specific fuel system, but with LCV gas it will not be possible
to utilize the standard fuel system, so we have to design a larger system to handle
LCV gas.
The operating conditions of SGT-500 with standard fuel are as under in table 8 and
the table 9 shows the fuel system of base case.
76
`
Parameters Values
Fuel Temperature 25 ºC
Individual gas constant 464.66 J/kg,K
Ratio of specific heat 1.2859
Minimum safe fuel gas
pressure 16.33
Compressor pressure 12 bars
Fuel mass flow 1.14 kg/s
Value Area 586.55 mm2
Nozzle Pressure drop 6.96 bars
Value pressure ratio 0.87
Table 8: Standard fuel operating conditions
77
Pipes or valves
Area / diameters
[mm2] [mm]
STANDARD FUEL
Pipe to gas filter 77.9mm
Gas filter area 3,000 mm2
Pipe to inner system and
S.O.V. 1 52.5mm
Pipe to S.O.V. 2 52.5 mm
Pipe to governor valve 52.5 mm
Pipe to S.O.V. 3 Dual fuel
only 52.5 mm
Pipe to hose 52.5 mm
Hose to manifold 52.5 mm
Manifold 43.1 mm
Pipe to burner 22.3 mm
Burner stem outer pipe inner
diameter 64.0 mm
Burner stem inner pipe outer
diameter 40.0 mm
No of burners 7
Burner effective area (Each) 134mm2
Table 9: Fuel system for standard gas
78
Table 10 shows the operating conditions of SGT-500 for MHV gas =18 kj / kg and
the table 11 shows the fuel system for this new fuel system.
Parameters values
Fuel Temperature 25 ºC
Individual gas constant 321.39 J/kg,K
Ratio of specific heat 1.29
Minimum safe fuel gas
pressure 18 bar
Compressor pressure 12 bars
Fuel mass flow 2.92 kg/s
Value Area 568.9 mm2
Nozzle Pressure drop 7.01 bars
Value pressure ratio 0.599
Table: 10 MHV fuel operating conditions
79
Table 11: Fuel system for MHV gas
Table 12 shows the operating conditions of SGT-500 for low heating value gas = 7 kj
/ kg and the table 13 shows the fuel system for this new fuel system.
Pipes or valves
Area / diameters
[mm2] [mm]
MHV FUEL
Pipe to gas filter 109.1 mm
Gas filter area 4,200 mm2
Pipe to inner system and
S.O.V. 1 73.5mm
Pipe to S.O.V. 2 73.5mm
Pipe to governor valve 73.5mm
Pipe to S.O.V. 3 Dual fuel
only 73.5mm
Pipe to hose 73.5mm
Hose to manifold 73.5mm
Manifold 60.3 mm
Pipe to burner 31.2 mm
Burner stem outer pipe inner
diameter 89.6 mm
Burner stem inner pipe outer
diameter 56.0 mm
No of burners 7
Burner effective area (Each) 188 mm2
80
Parameters values
Fuel Temperature 25 ºC
Individual gas constant 348.89 J/kg,K
Ratio of specific heat 1.359
Minimum safe fuel gas
pressure 18.5 bar
Compressor pressure 11.65 bars
Fuel mass flow 7.1 kg/s
Value Area 2344.44 mm2
Nozzle Pressure drop 7.21 bars
Value pressure ratio 0.78
Table 12: Operating conditions of SGT-500 for LHV
81
Pipes or Valves
Area / diameters
[mm2] [mm]
L.H.V. FUEL
Pipe to gas filter 183.065mm
Gas filter area 16567.5 mm2
Pipe to inner system and
S.O.V. 1 123.375mm
Pipe to S.O.V. 2 126 mm
Pipe to governor valve 126 mm
Pipe to S.O.V. 3 Dual fuel
only 126 mm
Pipe to hose 126 mm
Hose to manifold 126 mm
Manifold 103.44 mm
Pipe to burner 53.52 mm
Burner stem outer pipe inner
diameter 153.6 mm
Burner stem inner pipe outer
diameter 96mm
No of burners 7
Burner effective area (Each) 740.015mm2
Table 13: Fuel system for LHV gas
82
In the first step the pressure drop that one have to deal within the governing valve was
calculated, if the fuel system is connected to a gas pipe with a certain pressure.
The idea is to calculate how the pressure drops are distributed in the fuel system when
it is connected to a gas pipe with a certain pressure. In other words the given pressure
could be at any value (not too high) and to calculate how the pressure drop is
distributed in the fuel system.
According to the recommendations of Siemens, the pressure losses in the fuel system
are kept on the same level as for standard gas or slightly higher or lower. This of
course means that valves and pipes have to increase in diameter.
The values in the table 5 represent physical dimensions of equipment in the fuel
system, and they are constant for that fuel system. The table 6 represents the same
dimensions in the case of MHV gas and table 7 shows the same in the case of LHV
gases.
83
9. CONCLUSIONS
It is possible to use LHV fuels in gas turbine by implication of simple changes in the
unit. The investigation of operational problems using LHV fuels suggests two
possible solutions. To simulate these solutions, an in house code GT Perform was
used.
It is concluded that the unbalance between compressor and turbine can be countered
by two ways. The first solution suggests the bleeding of air after low pressure
compressor, it is a very simple solution but it causes an efficiency drop.
The second solution suggests to integrate a pressurised gasifier after extraction of air
after high pressure compressor. This is a superior solution for the reasons:
• The gas turbine only needs simple modifications.
• The fuel obtained is already pressurised.
• More power output and efficiency of unit is obtained
Both Solutions, bleeding after low pressure compressor and integrating a gasifier after
high pressure compressor are simulated and the results can be seen in this thesis. The
results show that in both solutions the gas turbine works near to standard working
points. The speed and pressure ratio of compressor are within the limits to avoid
surge limit.
It is calculated to increase the diameter of all of the pipes and valves of the fuel
system by 1.4 times if an MHV gas with a heating value of 18 kj/kg is used, and to
increase the diameter of pipes by a factor of 2.35 times, if a LHV gas of heating value
7 kj/kg is used.
84
10. REFERENCES
[SARA01] Herb Saravanamuttoo, ”Gas Turbine Theory” , Jan 2001
[BOYC06] Meherwan P Boyce , ”Gas Turbine Engineering Handbook”, April 28,
2006.
[LEFE98] Arthur Lefebvre , “Gas Turbine Combustion”, Sep 1998.
[SCHL96] Martin D. Schlesinger , “Fuels and Furnaces”, 1996.
[KERR92] Jack L. Kerrebrock , “Aircraft engines and gas turbines”, 1992.
[KOST85] A. Kostyuk and V. Frolov , “Steam and gas turbines”, 1985.
[GLAS97] Irvin Glassman , “Combustión”, 1997.
85
11. APPENDIX
• Appendix A, Complete fuel list
# FUEL
Composition
x (volume
fractions)
H2 CO CH4 CO2 O2 N2 H2O
1 Hydrogen 1.000 0.000 0.000 0.000 0.000 0.000 0.000
2 CO 0.000 1.000 0.000 0.000 0.000 0.000 0.000
3 Methane 0.000 0.000 1.000 0.000 0.000 0.000 0.000
11 Syngas GE [1] Schwarze Pumpe 0.619 0.262 0.069 0.028 0.000 0.022 0.000
13 Syngas GE [1] Opti Nexen 0.318 0.635 0.004 0.036 0.000 0.005 0.002
16 Syngas GE [1] Vresova 0.468 0.150 0.116 0.245 0.000 0.021 0.000
24
Biogas [3] (average gas,
wikipedia.org) 0.010 0.000 0.600 0.350 0.003 0.006 0.031
30
GPG [4] Carbon Black Plant
(Wood) 0.060 0.063 0.000 0.028 0.000 0.323 0.480
31 Coke Oven Gas 0.540 0.074 0.306 0.020 0.004 0.056 0.000
32
Blue Water Gas (mostly from
coal) 0.490 0.410 0.008 0.047 0.000 0.045 0.000
33 Carburretted Water Gas 0.370 0.305 0.210 0.056 0.004 0.055 0.000
44 GPG Ptasinski [5] Sludge 0.192 0.056 0.004 0.147 0.000 0.415 0.186
45 GPG Ptasinski [5] Manure 0.171 0.038 0.002 0.147 0.000 0.396 0.246
47
StatIFA [6] Fin Lahti Kymijärvi
Plant 0.059 0.046 0.034 0.129 0.000 0.402 0.330
54 GPG Mississippi [9] FERCO 0.262 0.382 0.189 0.151 0.000 0.016 0.000
56 GPG Mississippi [9] Princeton 0.294 0.392 0.174 0.131 0.000 0.009 0.000
58 GPG Mississippi [9] Univ. Vienna 0.315 0.227 0.152 0.274 0.000 0.032 0.000
34 Coke producer Gas 0.110 0.290 0.005 0.050 0.000 0.545 0.000
38 GPG Ptasinski [5] Coal 0.158 0.324 0.001 0.009 0.000 0.503 0.005
5 Syngas GE [1] Cinergy 0.248 0.395 0.015 0.093 0.000 0.022 0.227
6 Syngas GE [1] Tampa 0.372 0.466 0.001 0.133 0.000 0.025 0.003
7 Syngas GE [1] El Dorado 0.354 0.450 0.000 0.171 0.000 0.021 0.004
8 Syngas GE [1] Pernis 0.344 0.351 0.003 0.300 0.000 0.002 0.000
9 Syngas GE [1] Sierra Pacific 0.145 0.236 0.013 0.056 0.000 0.493 0.057
10 Syngas GE [1] ILVA 0.086 0.262 0.082 0.140 0.000 0.430 0.000
12 Syngas GE [1] Sarlux 0.227 0.306 0.002 0.056 0.000 0.011 0.398
14 Syngas GE [1] Exxon Singapore 0.445 0.354 0.005 0.179 0.000 0.016 0.001
15 Syngas GE [1] Motiva Delaware 0.320 0.495 0.001 0.158 0.000 0.022 0.004
17 Syngas GE [1] Tonghua 0.103 0.223 0.038 0.145 0.000 0.482 0.009
86
19
Syngas S [2] DOW Plaquemine
(USA) 0.414 0.385 0.001 0.185 0.000 0.015 0.000
20 Syngas S [2] Nuon Power (NL) 0.123 0.248 0.000 0.008 0.004 0.426 0.191
21
Syngas S [2] Elcogas Puertollano
(E) 0.107 0.292 0.000 0.019 0.003 0.537 0.042
22 Syngas S [2] ISAB Energy (I) 0.313 0.285 0.000 0.032 0.000 0.001 0.369
23 Syngas S [2] Elettra GLT (I) 0.090 0.163 0.146 0.136 0.000 0.410 0.055
25 GPG [4] Lurgi (Brown Coal) 0.250 0.160 0.050 0.140 0.000 0.400 0.000
26 GPG [4] Lurgi (Bituminous) 0.248 0.172 0.041 0.110 0.000 0.429 0.000
27 GPG [4] Winkler (Lignite) 0.120 0.220 0.010 0.100 0.000 0.550 0.000
28 GPG [4] Wellman-Galusha (Coke) 0.150 0.290 0.030 0.030 0.000 0.500 0.000
29 GPG [4] Blast furnace gas 0.090 0.040 0.050 0.220 0.000 0.600 0.000
39 Blast furnance Gas 0.025 0.240 0.000 0.175 0.000 0.560 0.000
70 GPG Nimbkar [10] Rice hulls 0.096 0.161 0.010 0.000 0.000 0.733 0.000
68
GPG Nimbkar [10] Pressed
sugarcane 0.165 0.165 0.000 0.130 0.000 0.540 0.000
65
GPG Nimbkar [10] Wheat Straw
pellets Downdraft 0.180 0.155 0.000 0.125 0.000 0.540 0.000
67 GPG Nimbkar [10] Coconut shells 0.125 0.215 0.000 0.130 0.000 0.530 0.000
66 GPG Nimbkar [10] Coconut husks 0.183 0.180 0.000 0.125 0.000 0.512 0.000
71 GPG Nimbkar [10] Cotton stalks 0.117 0.157 0.034 0.000 0.000 0.692 0.000
52 StatIFA [6] Swi Xylowatt Gasifier 0.140 0.180 0.020 0.130 0.000 0.530 0.000
62 GPG Mississippi [9] USEPA 0.100 0.148 0.049 0.128 0.000 0.575 0.000
48 GPG Ptasinski [5] Grass/plants 0.232 0.146 0.018 0.145 0.000 0.362 0.097
42 GPG Ptasinski [5] Treated Wood 0.213 0.194 0.010 0.112 0.000 0.409 0.062
43
GPG Ptasinski [5] Untreated
Wood 0.227 0.177 0.013 0.126 0.000 0.381 0.076
64
GPG Nimbkar [10] Wood
Downdraft 0.180 0.195 0.025 0.125 0.000 0.475 0.000
41 GPG Ptasinski [5] Straw 0.225 0.205 0.010 0.113 0.000 0.384 0.063
57 GPG Mississippi [9] Carbona 0.217 0.238 0.007 0.094 0.000 0.444 0.000
61
GPG Mississippi [9] Univ.
Zaragosa 0.160 0.215 0.033 0.144 0.000 0.448 0.000
50 StatIFA [6] Swe Värö Gasifier 0.103 0.151 0.073 0.159 0.000 0.435 0.079
51 StatIFA [6] Swe Värnamo Plant 0.175 0.108 0.067 0.155 0.000 0.495 0.000
55 Producer gas [8] 0.180 0.220 0.030 0.060 0.000 0.510 0.000
53 Wikipedia [7] Woodgas 0.140 0.270 0.030 0.045 0.006 0.509 0.000
49
StatIFA [6] Fin BIONEER
Process 0.110 0.300 0.030 0.070 0.000 0.490 0.000
40 GPG Ptasinski [5] Vegetable Iols 0.251 0.275 0.001 0.003 0.000 0.467 0.003
60
GPG Mississippi [9] Univ.
Brussels 0.100 0.160 0.090 0.180 0.000 0.470 0.000
69 GPG Nimbkar [10] Corn cobs 0.165 0.186 0.064 0.000 0.000 0.585 0.000
63 GPG Mississippi [9] IGT 2 0.191 0.111 0.132 0.289 0.000 0.278 0.000
87
# FUEL Dens. Air/Fuel ratio heating value
kg/m³ kg_air/kg_fuel MJ/kg
1 Hydrogen 0.08 34.05902778 119.9503968
2 CO 1.14 2.451374509 10.10282042
3 Methane 0.65 17.12294264 50.02119701
11 Syngas GE [1] Schwarze Pumpe 0.47 6.883042987 24.18924651
13 Syngas GE [1] Opti Nexen 0.82 3.285318759 12.8283503
16 Syngas GE [1] Vresova 0.75 4.042882675 13.53317739
24 Biogas [3] (average gas, wikipedia.org) 1.05 6.396470188 18.70192689
30 GPG [4] Carbon Black Plant (Wood) 0.85 0.406986183 1.558095817
31 Coke Oven Gas 0.43 11.85383366 37.2927242
32 Blue Water Gas (mostly from coal) 0.65 4.017364373 15.12507718
33 Carburretted Water Gas 0.68 6.195376838 20.50388548
44 GPG Ptasinski [5] Sludge 0.95 0.77249147 2.790701159
45 GPG Ptasinski [5] Manure 0.95 0.635775406 2.291761473
47 StatIFA [6] Fin Lahti Kymijärvi Plant 1.01 0.666268452 2.196927838
54 GPG Mississippi [9] FERCO 0.87 4.501799918 15.13104499
56 GPG Mississippi [9] Princeton 0.83 4.654638171 15.77655588
58 GPG Mississippi [9] Univ. Vienna 0.91 3.527230217 11.71978969
34 Coke producer Gas 1.05 1.11376978 4.351662158
38 GPG Ptasinski [5] Coal 0.98 1.391195875 5.448658719
5 Syngas GE [1] Cinergy 0.84 2.342840935 8.9201337
6 Syngas GE [1] Tampa 0.83 2.830375778 10.89906229
7 Syngas GE [1] El Dorado 0.87 2.567175354 9.902497233
8 Syngas GE [1] Pernis 0.97 2.036945056 7.759234017
9 Syngas GE [1] Sierra Pacific 0.99 1.217826104 4.599045737
10 Syngas GE [1] ILVA 1.10 1.716929053 5.945351749
12 Syngas GE [1] Sarlux 0.77 1.954717903 7.52960899
14 Syngas GE [1] Exxon Singapore 0.78 2.92329369 11.00993089
15 Syngas GE [1] Motiva Delaware 0.90 2.536761069 9.845702757
17 Syngas GE [1] Tonghua 1.10 1.210682516 4.371206479
19 Syngas S [2] DOW Plaquemine (USA) 0.82 2.729990942 10.39103987
20 Syngas S [2] Nuon Power (NL) 0.94 1.10520121 4.335205583
21 Syngas S [2] Elcogas Puertollano (E) 1.02 1.091360835 4.321235159
88
22 Syngas S [2] ISAB Energy (I) 0.68 2.459024536 9.362808101
23 Syngas S [2] Elettra GLT (I) 1.04 2.249298915 7.241755529
25 GPG [4] Lurgi (Brown Coal) 0.94 1.808923042 6.298981625
26 GPG [4] Lurgi (Bituminous) 0.93 1.756104983 6.198600049
27 GPG [4] Winkler (Lignite) 1.07 0.98934739 3.76513297
28 GPG [4] Wellman-Galusha (Coke) 0.99 1.5866996 5.876469252
29 GPG [4] Blast furnace gas 1.16 0.792430022 2.559972425
39 Blast furnance Gas 1.23 0.603264803 2.452112277
70 GPG Nimbkar [10] Rice hulls 1.03 0.802953709 3.023852684
68 GPG Nimbkar [10] Pressed sugarcane 1.05 0.878151929 3.355913171
65
GPG Nimbkar [10] Wheat Straw
pellets Downdraft 1.03 0.907993235 3.449644057
67 GPG Nimbkar [10] Coconut shells 1.09 0.86971728 3.392682041
66 GPG Nimbkar [10] Coconut husks 1.03 0.986926962 3.769159165
71 GPG Nimbkar [10] Cotton stalks 1.00 1.146057005 4.071000468
52 StatIFA [6] Swi Xylowatt Gasifier 1.07 1.047761037 3.846836267
62 GPG Mississippi [9] USEPA 1.09 1.134418328 3.921174822
48 GPG Ptasinski [5] Grass/plants 0.94 1.336684041 4.839116921
42 GPG Ptasinski [5] Treated Wood 0.96 1.304542858 4.863678277
43 GPG Ptasinski [5] Untreated Wood 0.94 1.348917645 4.972160027
64 GPG Nimbkar [10] Wood Downdraft 1.02 1.302854692 4.74434339
41 GPG Ptasinski [5] Straw 0.94 1.389742673 5.186784564
57 GPG Mississippi [9] Carbona 0.97 1.391860229 5.266568152
61 GPG Mississippi [9] Univ. Zaragosa 1.05 1.351326463 4.891381384
50 StatIFA [6] Swe Värö Gasifier 1.07 1.430113688 4.814408369
51 StatIFA [6] Swe Värnamo Plant 1.02 1.504861504 5.03713029
55 Producer gas [8] 0.97 1.491818986 5.425544592
53 Wikipedia [7] Woodgas 1.01 1.469919766 5.425836557
49 StatIFA [6] Fin BIONEER Process 1.05 1.404356209 5.231476645
40 GPG Ptasinski [5] Vegetable Iols 0.87 1.693163051 6.482005977
60 GPG Mississippi [9] Univ. Brussels 1.11 1.56425676 5.205586062
69 GPG Nimbkar [10] Corn cobs 0.93 1.815508314 6.267586053
63 GPG Mississippi [9] IGT 2 1.06 2.180198878 7.020889823
89
• APPENDIX B, POWER NEEDED TO COMPRESS THE
FUEL
Assumptions:
Atmospheric pressure = 1.013 bar
Final pressure = 18.5 bar
Biogas = perfect gas.
P = power for compressing fuel.
p= pressure
m’ = flow.
P = m’ * ∆h
P = m’ * Cp * (T2-T1)
T2/T1 = (p2/p1) ((γ-1)/ γ)
P = m’ * Cp * T1 ((p2/p1) ((γ-1)/ γ) -1)
90
• APPENDIX C, RESULT SHEETS
PARAMETER UNITS
STANDARD
GAS bio43 bio40 bio10
HEATING VALUE MJ/kg 46.798 4.97 6.48 5.94
FUEL FLOW IN CC kg/sec 1.1394 11.6997 9.107 9.9813
N of Shaft # 1 ( PT) rpm 3600 3600 3600 3599.9998
N of Shaft # 2 (LPT) rpm 5304.7295 5536.9912 5592.5928 5559.3931
N of Shaft # 3 (HPT) rpm 7064.1035 7099.3735 7140.1064 7115.4785
LPC Pressure ratio x 4.238988095 4.61022333 4.59251539 4.59890819
HPC Pressure ratio x 2.932551663 3.05229504 3.04794121 3.04445979
POWER MW 16.9128 20.6998 20.6999 20.6998
EFFICIENCY x 0.317184536 0.35598773 0.35076633 0.34913436
POWER AFTER FUEL
COMP. MW 16.3431 14.84995 16.1464 15.70915
EFF. AFTER FUEL
COMP x 0.306500318 0.25538411 0.27360584 0.26495928
PARAMETER UNITS bio45 bio66 bio71 bio 22
HEATING VALUE MJ/kg 2.291 3.355 4.07 9.361
FUEL FLOW IN CC kg/sec 23.1668 16.7498 13.8792 6.4453
N of Shaft # 1 ( PT) rpm 3600 3599.9995 3600 3600
N of Shaft # 2 (LPT) rpm 5405.0796 5466.7817 5530.1372 5616.8975
N of Shaft # 3 (HPT) rpm 6993.5732 7055.0854 7095.6143 7158.6289
LPC Pressure ratio x 4.686743401 4.64420405 4.62282878 4.57653365
HPC Pressure ratio x 3.090635784 3.07124693 3.06926463 3.03181936
POWER MW 20.6998 20.6996 20.7004 20.7002
EFFICIENCY x 0.390009343 0.36834926 0.36645436 0.34309087
POWER AFTER FUEL
COMP. MW 9.1164 12.3247 13.7608 17.47755
EFF. AFTER FUEL COMP x 0.171764035 0.21931796 0.24360424 0.28967777
91
• APPENDIX D, RESULT SHEETS CHANGING
PARAMETERS (DEFINITIONS AT THE END).
Parameters B.L 100 B.L 100 bio* bio hpt* bio hpt pt
*
Standard bf 24
Heating value 46.798 18.7 18.7 18.7 18.7
GAMK 2 0.0042 0.0042 0.0042 0.0042 0.0042
GAMK 3 0.025 0.025 0.0242 0.0245 0.0255
GAMT 2 0.0041 0.0041 0.004 0.004 0.0042
GAMT 3 0.007 0.007 0.0068 0.0068 0.0072
GINTE 2 0.0009 0.0009 0.0009 0.0009 0.0009
GINTE 3 0.0051 0.0051 0.0049 0.005 0.0052
FUEL FLOW 1.1463 2.9737 2.9766 3.0035 2.9163
FLOW NO OF
HPT 254 254 254 270 270
FLOW NO OF PT 948.3 948.3 948.3 948.3 910.3
N of Shaft # 2 5310.4194 5370.188 5373.5967 5324.4507 5165.9243
N of Shaft # 3 7066.7427 7079.5889 7082.1812 6926.375 6860.8301
LPC PR 4.24476905 4.33843269 4.3413936 4.41235689 4.19917094
HPC P.R 2.93259394 2.9585504 2.96114761 2.74676777 2.7603535
TOTAL PR 12.448184 12.8354718 12.8555073 12.1197197 11.5911962
POWER
OUTPUT 17.2122 18.2224 18.2597 18.1972
17.5727
Power for fuel 0.5722 1.4824 1.4897 1.4972 1.4627
Power after fuel
comp 16.64 16.74 16.77 16.7 16.11
EFFICIENCY 0.32085647 0.32769274 0.32769274 0.32769274 0.32222905
NEW EFF 0.31018996 0.30103479 0.30128047 0.29733582 0.29540765
92
Parameters gamk2
0.01
gamk2
0.15
gamk2
0.20
gamk2
0.25 gamk2 0.30
Heating value 18.7 18.7 18.7 18.7 18.7
GAMK 2 0.01 0.015 0.02 0.025 0.03
GAMK 3 0.0258 0.0258 0.026 0.0262 0.0263
GAMT 2 0.0042 0.0043 0.0043 0.0043 0.0044
GAMT 3 0.0071 0.0072 0.0073 0.0073 0.0074
GINTE 2 0.0009 0.0009 0.0009 0.0009 0.0009
GINTE 3 0.0052 0.0053 0.0053 0.0053 0.0053
FUEL FLOW 2.9036 2.8928 2.8822 2.8717 2.8615
FLOW NO OF
HPT 270 270 270 270 270
FLOW NO OF
PT 910.3 910 910 910 910
N of Shaft # 2 5160.3906 5155.3574 5151.3438 5147.3584 5143.8066
N of Shaft # 3 6857.1987 6852.7104 6849.3569 6846.2114 6842.8276
LPC PR 4.16452823 4.13600474 4.10777734 4.07935255 4.052013423
HPC P.R 2.76528025 2.76922159 2.7733061 2.77758153 2.781804896
TOTAL PR 11.5160876 11.4535136 11.392124 11.3307343 11.27191078
POWER
OUTPUT 17.371 17.217 17.0557 16.893 16.7415
Power for fuel 1.451 1.447 1.4457 1.433 1.4315
Power after fuel
comp 15.92 15.77 15.61 15.46 15.31
EFFICIENCY 0.31992371 0.31827129 0.31644907 0.31457638 0.312866462
NEW EFF 0.29320047 0.29152223 0.28962576 0.28789148 0.286114478
93
Parameters gasif gamk3
0.06*
gasif gamk3
0.04* bleed lhv gasif lhv
Heating value 18.7 18.7 7.757 7.757
GAMK 2 0.0042 0.0042 0.03 0.0044
GAMK 3 0.06 0.04 0.0242 0.067
GAMT 2 0.0043 0.0041 0.004 0.0043
GAMT 3 0.0073 0.007 0.0067 0.0072
GINTE 2 0.0009 0.0009 0.0009 0.0009
GINTE 3 0.0053 0.0051 0.005 0.0052
FUEL FLOW 2.8404 2.9196 7.4347 7.1254
FLOW NO OF
HPT 254 254
270 270
FLOW NO OF
PT 948.3 948.3
910 910
N of Shaft # 2 5219.6074 5306.1831 5251.0552 5103.5615
N of Shaft # 3 7027.3657 7057.5269 6860.4507 6812.4712
LPC PR 4.126135018 4.250789578 4.259968417 4.13945914
HPC P.R 2.892814429 2.930785484 2.837611788 2.74051644
TOTAL PR 11.93614291 12.45815239 12.0881366 11.3442558
POWER
OUTPUT 16.0305 17.2931 18.9121 16.9504
Power for fuel 0.190166754 0.175278994 3.71735 0.53638744
Power after fuel
comp 15.84033325 17.11782101 15.19475 16.4140126
EFFICIENCY 0.301804672 0.316743631 0.327931032 0.30667397
NEW EFF 0.298224421 0.313533189 0.263473123 0.29696941
94
Definitions
• B.L. 100 standard : machine using standard fuel at 100% of base load
(B.L.).
• B.L. 100 b.f. 24: machine using bio fuel #24 (M.H.V fuel) at 100% of
base load.
• Bio*: machine using bio fuel #24 at 100% of B.L. and keeping flows of
gamt and ginte constant.
• Bio hpt*: machine using bio fuel #24 at 100% of B.L., keeping flows of
gamt and ginte constant and increasing h.p.t constant.
• Bio hpt pt*: machine using bio fuel #24 at 100% of B.L., keeping flows
of gamt and ginte constant , increasing h.p.t constant and decreasing
pt constant.
• Gamk2 + number: machine using bio fuel #24 at 100% of B.L.,
keeping flows of gamt and ginte constant , increasing h.p.t constant ,
decreasing pt constant and beeding air after low pressure compressor
in an amount equal to “number*total flow in low pressure compressor” .
• Gasif gamk3 + number : machine using bio fuel #24 at 100% of B.L.,
keeping flows of gamt and ginte constant , increasing h.p.t constant ,
decreasing pt constant and beeding air after high pressure compressor
in an amount equal to “number*total flow in high pressure compressor”
to be used in a gasifier .
95
• Bleed lhv: machine using low heating value fuel at 100% of B.L.,
keeping flows of gamt and ginte constant , increasing h.p.t constant ,
decreasing pt constant and beeding air after low pressure compressor
in an amount equal to “0.15*total flow in low pressure compressor”
• Gasif lhv: machine using low heating value fuel at 100% of B.L.,
keeping flows of gamt and ginte constant , increasing h.p.t constant ,
decreasing pt constant and beeding air after high pressure compressor
in an amount equal to “0.067*total flow in high pressure compressor” to
be used in a gas
