Afstudeerverslag van: J.T. Drenth
Afstudeerhoogleraar: Prof. Ir. J. Klein Woud Afstudeerbegeleider: Dr. Ir. L.J.M.J. Blomen
Blomenco B.V.
I4)-PPo
9 Li /oz.
FINAL REPORT
Systematic Analysis of Gas Turbine
- Fuel Cell
Combinations for Electric Power Generation
with very high Efficiency
faculteit der WerIctuigbouwkunde en Marine= Techniek van de, Technische Universiteit Delft, bestaat het laatste, onderdeel van dc studie uit ecn afstudeeropdracht.
Mijn afstudeeropdracht stond ,grotendeels in het teken van een gezamenlijke EU-studic naar de systematische analyse van verschillendc gasturbine-brandstofcel combinaties gericht op hetopweldcen van eleIctriciteit met een hoog rendemcnt. Alhoewel het een gezamenlijk onderzoek betrof van vijf
verschillende bedrijven was op voorhand een duidelijke afbalcening gemaakt voor wat betreft de
specifielce bijdrage van de afzonderlijke partners. Mijn bijdrage is totstandgekomen viaBlomenco BY.
dat de hoofdmoot van het onderzoek voor
haar rekening nam. Dit bedrijf fungeerde tevens als coordinator voor de gehele studie en was verantwoordclijk voor de eindrapportage naar de EU toe. Omdubbele rapportage, aan EU en aan TUD, te vermijden is overeengekomen dat een complect
EU-eindrapport ook mocht dienen als mijn afstudeerverslag. Het navolgcnde doet dan ook verslag van de
gehele studie. Op de hoofdstulcken 14, 19 en 20 na beschrijft dit verslag mijn onderzoelcsbijdrage.
Omdat rapportage aan de EU door Blomenco B.V. en partners in het Engels diende te geschieden, is dit verslag in de Engelse taal geschreven.
Zonder het geduld en de aandacht van anderen was dit rapport waarschijnlijk nooit in deze vorm tot stand gekomen. Reden waarom ik vooral mijn afstudeerbegeleider op deze plaats hartelijkwil bedanken voor de tijd die hij in mij heeft geinvesteerd. Dit ondanks zijn eigen drukkewerlczaamheden. Maar ook zijn familie en secretaresse (Julia !) ben ik erkentelijk voor de enerverende en zeer leerzameperiode die ik de afgelopen tijd heb beleefd. Dank ben ik ook verschuldigd aan A. de Groot, B. de Melker en N. Woudstra van de TU Delft en aan M. Verschoor van TNO Apeldoorn wellce alien o.a. betrokken zijn bij de ontvvilckeling van Cycle-Tempo, de software v,aarmeealle simulaties hebben plaatsgevonden. Zij zijn zecr behulpzaam gewcest bij het onder de lcnie krijgen van verscheident problemendie zich voordeden tijdens het modelleren.
J.T. Drenth augustus'95
FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 2
TABLE OF CONTENTS
EXECUTIVE SUMMARYINTRODUCTION 11
NOMENCLATURE 13
BACKGROUND OF THE PROJECT 15
1.1 INTRODUCTION 15
1.2 WHY CHOOSE A COMBINATION OF GAS TURBINES AND FUEL CELLS 15
1.3 THE JOULE-I1 PROGRAMME 15
1.4 PROJECT PARTNERS AND PARTNER'S ROLE IN PROJECT 16
1.4.1 EUROPEAN GAS TURBINES LTD./GEC ALSTHOM 16
1.4.2 NATIONAL POWER PLC 16
1.4.3 ELENCO NV 16
1.4.4 BLOMENCO BV 17
1.4.5 CONTRANS 17
1.5 AIMS AND DESIGN PHILOSOPHY 18
GAS TURBINES
2.1 INTRODUCTION
2.2 HISTORY 20
2.3 THERMODYNAMICS 21
2.3.1 A PRACTICAL GAS TURBINE CYCLE 21
2.3.2 USE OF A POWER TURBINE 22
2.3.3 INTERCOOLING 23
2.3.4 REHEAT 24
2.3.5 RECUPERATION 25
2.3.6 EFFECT OF PRESSURE LOSSES 26
2.3.7 PERFORMANCE CHARACTERISTICS
/6
2.4 SELECTION OF GAS TURBINES FORJOULE2-PROJECT 28
FUEL CELLS 29 3.1 INTRODUCTION 19 3.2 HISTORY 3.3 OPERATING PRINCIPLES -W 3.4 THERMODYNAMICS` 3.4.1 REVERSIBLE THERMODYNAMICS 33 3.4.2 IRREVERSIBLE THERMODYNAMICS 35 3.4.3 CELL EFFICIENCY 37
3.5 SELECTED FUEL CELL TYPES 38
3.5.1 ALKALINE FUEL CELL 38
3.5.2 SOLID POLYMER FUEL CELL 40
3.5.4 MOLTEN CARBONATE FUEL CELL 44
3.5.5 SOLID OXIDE FUEL CELL 46
FUEL CELL SYSTEMS 48
4.1 INTRODUCTION 48 4.2 FUEL PROCESSING 49 4.2.1 DESULFURISATION 49 4.2.2 STEAM REFORMING 50 4.2.3 SHIFT CONVERSION 56 4.3 POWER CONDITIONING 56 4.3.1 INVERTER 56
4.3.2 POWER CONTROL SYSTEM 56
4.4 HEAT AND POWER RECOVERY SYSTEM 57
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5.1 INTRODUCTION 59
5.2 GAS TURBINE-REFORMER COMBINATIONS 59
5.3 GAS TURBINE-FUEL CELL COMBINATIONS 60
SOFTWARE SELECTION 61
6.1 INTRODUCTION 61
6.2 OPTIONS 61
6.3 SELECTED SOFTWARE: CYCLE-TEMPO 62
6.4 MODELLING PROBLEMS AND SOLUTIONS 62
6.4.1 BLADE COOLING 63
6.4.2 DEFINITION OF FUEL UTILISATION 65
DEFINITION BASIS OF DESIGN 66
7.1 INTRODUCTION 66
7.2 BASIS OF DESIGN 66
8 DESIGN MATRIX #1 68
8.1 INTRODUCTION 68
8.2 INITIAL DESIGN MATRIX 68
8.3 CODING SYSTEM 70
GAS TURBINE SIMULATIONS 71
9.1 INTRODUCTION 71
9.2 DESIGN H-SEL: HERON TURBINE 71
9.2.1 GENERAL DESCRIPTION 71
9.2.2 CYCLE-TEMPO INPUT DESCRIPTION 71
9.2.3 CYCLE-TEMPO OUTPUT DESCRIPTION 72
9.3 DESIGN T-SEL: RUSTON TYPHOON TURBINE 74
9.3.1 GENERAL DESCRIPTION 74
9.3.2 CYCLE-TEMPO INPUT DESCRIPTION 74
9.3.3 CYCLE-TEMPO OUTPUT DESCRIPTION 75
9.4 DESIGN L-SEL: RLM1600 TURBINE 75
9.4.1 GENERAL DESCRIPTION 75
9.4.2 CYCLE-TEMPO INPUT DESCRIPTION 76
9.4.3 CYCLE-TEMPO OUTPUT DESCRIPTION 76
9.5 DISCUSSION 77
HERON-REFORMER SIMULATIONS 78
10.1 INTRODUCTION 78
10.2 (POTENTIAL) REFORMER POSITIONS INHERON-CYCLE 78
10.3 POSITION #1: DESIGN 2HRF10 79
10.3.1 CYCLE-TEMPO INPUT DESCRIPTION 79
10.3.2 CYCLE-TEMPO OUTPUT DESCRIPTION 79
10.4 POSITION #1: DESIGN 3HRF10 81
10.4.1 CYCLE-TEMPO INPUT DESCRIPTION 81
10.4.2 CYCLE-TEMPO OUTPUT DESCRIPTION 81
10.5 POSITION #2: DESIGN 2HRF13 82
10.5.1 CYCLE-TEMPO INPUT DESCRIPTION 82
10.5.2 CYCLE-TEMPO OUTPUT DESCRIPTION 82
10.6 DISCUSSION 83
TYPHOON-REFORMER SIMULATIONS 84
11.1 INTRODUCTION 84
11.2 (POTENTIAL) REFORMER POSITIONS INTYPHOON-CYCLE 84
11.3 POSITION #1: DESIGN TRFII 85
11.3.1 CYCLE-TEMPO INPUT DESCRIPTION 85
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11.3.2 CYCLE-TEMPO OUTPUTDESCRIPTION 85
11.4 POSITION #2: DESIGN TRHRF11 86
11.4.1 CYCLE-TEMPO INPUT DESCRIPTION 86
11.4.2 CYCLE-TEMPO OUTPUTDESCRIPTION 87
111
14.5 POSITION #3: DESIGN TRHRF2I 88
11.5.1 CYCLE-TEMPO INPUT DESCRIPTION 88
11.5.2 CYCLE-TEMPO OUTPUTDESCRIPTION 1
88
11.6 DISCUSSION 89
LM1600-REFORMER SIMULATIONS 91
12.1 INTRODUCTION
91
12.2 (POTENTIAL) REFORMERPOSITIONS IN LM1600-CYCLE 91
12.3 POSITION #1: DESIGN LRF13 92
12.3.1 CYCLE-TEMPO INPUT DESCRIPTION 92
12.3.2 CYCLE-TEMPO OUTPUTDESCRIPTION 92
12.4 POSITION 42: DESIGN LRHRF13 93
12.4.1 CYCLE-TEMPO INPUTDESCRIPTION 93
12.4.2 CYCLE-TEMPO OUTPUT DESCRIPTION 93
112.5 POSITION #3: DESIGN LRHRFI7 94
12.5.1 CYCLE-TEMPO INPUTDESCRIPTION
112:6 DISCUSSION
95
DESIGN ISSUES (THEORETICAL) 97
13.1 INTRODUCTION 97 13.2 INTERCOOLING 97 13.3 REHEAT 98 13.4 REHEAT TURBINE 99 13.5 RECUPERATION 99 13.6 REGENERATIVE REFORMER 100
13.7 COMBUSTION OF LOWHEATING VALUE FUELS
,
100.13.8 MISMATCHES IN POWER OUTPUT 101
14. DESIGN ISSUES (PRACTICAL) 102
14.1 INTRODUCTION 102
14.2 SIMILARITY THEORY 101
14.3 APPLICATION OF SIMILARITYTHEORY TO CYCLE-TEMPO MODELS 104
14.4 REVIEW 105
14.5 CONSIDERATIONS ONMODELLING OF ROTATING ELEMENTS '107
14.6 CONCLUSION 107
THEORETICAL INTEGRATION OPTIONS OF GAS TURBINES& FUEL CELLS 108
15.1 INTRODUCTION 108
15.2 NATURAL GAS INTEGRATION 108
15.3 AIR INTEGRATION 109
15.4 OPTIMISATION REFLECTIONS 110
GAS TURBINE - AFC SIMULATIONS 11L,
16.1 INTRODUCTION
16.2 CO2 REMOVAL TECHNIQUES 114
16.3 OPTIONS FOR INTEGRATION 112
16.4 SYSTEM DESCRIPTION. TYPHOON-AFC (TAF62) 113
16.4.1 CYCLE-TEMPO INPUT DESCRIPTION 113
16.4.2 CYCLE-TEMPO OUTPUT DESCRIPTION 114
46.4.3 DISCUSSION 116
GAS TURBINE - SPFC SIMULATIONS 117
17.1 INTRODUCTION- 117
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20.1 CYCLE-TEMPO ANALYSES: BEST CASE' CYCLESWITH INTERNALLY
REFORMED SOFC150 17.2 WATER BALANCE
117
17.3 OPTIONS FORINTEGRATION 117
17.4 SYSTEM DESCRIPTION #1: HERON-SPEC (HSP62)
119 17.4.1 CYCLE-TEMPO INPUT DESCRIPTION
119
17.4.2 CYCLE-TEMPO OUTPUT DESCRIPTION
120 17.4.3 DISCUSSION
)21
17.5 SYSTEM DESCRIPTION#2: TYPHOON-SPFC (TSP82)
121
17.5.1 CYCLE-TEMPO INPUT DESCRIPTION
121
17.5.2 CYCLE-TEMPO OUTPUT DESCRIPTION
122
17.5.3 DISCUSSION
123
18. GAS TURBINE - PAFC 'SIMULATIONS
124
18.1 INTRODUCTION
124
18.2 PAEC-COOLING
124
18.3 OPTIONS FOR INTEGRATION
125
48.4 SYSTEM DESCRIPTION#1: HERON-PAFC (HPA65),
126
18.4.1 FINCH TECHNOLOGY ANALYSIS
'126
18.4.2 CYCLE-TEMPO INPUT DESCRIPTION
129 18.4.3 CYCLE-TEMPO OUTPUT DESCRIPTION
130
18.4.4 DISCUSSION
130
18.5 SYSTEM DESCRIPTION#2: TYPHOON-pAFC (TPA82)
131
18.5.1 CYCLE-TEMPO INPUT DESCRIPTION
131
18.5.2 CYCLE-TEMPOOUTPUT DESCRIPTION
132
18.5.3 DISCUSSION
132 18.6 SYSTEM DESCRIPTION#3: LM1600-PAFCi(LPA66)
133
18.6.1 CYCLE-TEMPO INPUT DESCRIPTION
133
18.6.2 CYCLE-TEMPO OUTPUT DESCRIPTION
135
18.6.3 DISCUSSION
136
19. GAS TURBINE,- MCFC SIMULATIONS
137
19.1 INTRODUCTION
137'
19.2 DESIGN PRINCIPLESFOR CYCLE COMBINATIONS
137
19.3 SELECTED CYCLE DESIGN
137
19.4 CYCLE-TEMPO MODELLING OF THE POWERCYCLE
140 19.5 RESULTS
144
19.6 DISCUSSION
149
20.. GAS TURBINE-SOFC SIMULATIONS
150
20.1.1 HERON - 'BEST CASE'CYCLE WITH IR SOFC 150
20.1.2 TYPHOON - 'BESTCASE' CYCLE WITH ER SOFC
150 20.1.3 FtLM1600 - 'BEST CASE' CYCLE WITH ER SOFC
150 20.2 BASIC CASE GAS TURBINE CYCLES WITHREFORMING
151
20.3 TURBINE PLUSEXTERNALLY REFORMED SOFC
151
20.4 SOFC AS THECOMBUSTOR IN A GAS TURBINE CYCLE
1511 20.5 DISCUSSION 151 21. DESIGN MATRIX #2 153 21.1 INTRODUCTION 153
21.2 FINAL DESIGN MATRIX
153
22. SYSTEMATIC COST & ECONOMIC ANALYSES'
155
22.1 INTRODUCTION
155
22.2 ECONOMIC ASSUMPTIONS
155 22.3 GAS TURBINE AFCCOMBINATION
157 22.3.1 TYPHOON-AFCCOMBINATION
157
22.4 GAS TURBINE SPEC COMBINATIONS
159
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22.4.1 HERON-SPFC: HSP62
159
22.4.2 TYPHOON-SPFC: TSP8,
22.5 GAS TURBINE-PAFC COMBINATIONS
160 162 22.5.1 HERON-PAFC: HPA65 162 22.5.2 TYPHOON-PAFC: TPA82 163 22.5.3 LM1600-PAFC: LPA66 165
22.6 GAS TURBINE-SOFC COMBINATIONS
167 22.6.1 HERON-IR SOFC: HS00150I
167
22.6.2 TYPHOON - EXTERNALREFORMING - SOFC COMBINATION
168
22.6.3 TYPHOON - INTERNAL REFORMING - SOFC COMBINATION 169
22.6.3 LM1600 - INTERNALREFORMING - SOFC COMBINATION
170
22.7 ECONOMIC COMPARISON
172
23. POSSIBILITIES FOR FURTHER WORK. CONCLUSIONS 175 REFERENCES 178 ADDENDA 182 .... 173
EXECUTIVE SUMMARY
Within the EC Joule-II programme which covers the field of non-nuclear research a joined research project has been carried out aimed to arrive at an objective, systematic system analysis of combinations of gas turbines and fuel cells for the generation of electric power. Knowing that pres-surised fuel cell systems are more efficient than unprespres-surised versions, but have suffered overall due to poor performance and/or unreliability of the system rotating components or other peripherals, the basic idea behind the combination systems proposed here is that the proven gas turbine components should ensure reliable pressurised fuel cell operation.
Five different parties participated, all having different backgrounds:
El European Gas Turbines Ltd./GEC Alsthom, a manufacturer of aero- and industrial gas turbines
from 1.5 to 230 MW. The Mechanical Engineering Centre (MEC) has expertise in all the basic gas turbine technologies. Also in the fuel cell technology MEC has expertise in the modelling of solid oxide fuel cell (SOFC) stacks and the design, build and testing of low temperature fuel cells in specialist battlefield and sub-sea applications.
"). National Power PLC, the largest of the privatised UK electric utilities. National Power Research
and Technology has been involved in cycle thermodynamic and economic analyses. Many of the
studies have involved gas turbines in combination with other types of plant such as
thermo-chemical reformers and gasifiers.
Elenco N.V., based in Belgium, is specialised in the research, development and demonstration as well as (pre-) production of alkaline fuel cells (AFC). The technology includes electrodes, stacks, system engineering, prototype construction and testing.
Blomenco By., a small Dutch company specialised
inconsulting and contracting of
(management of) research, development, demonstration and commercialisation of energy tech-nologies. Blomenco B.V. is also involved in the Heron turbine commercialisation, one of the se-lected gas turbines for this project.Contrans, based in Czechia, is specialised in thermodynamic and component analysis of gas tur-bine engines and facilities, gas calculations and system studies, as well as aerodynamics.
The analyses involved three different natural gas fired gas turbines: the 1.4 MW intercooled. recuperated, reheat Heron turbine, the 3.56 MW heavy duty Ruston Typhoon and the 13.35 MW aero-derivative LM1600. These were combined with the five most well-known fuel cell types: Alka-line Fuel Cell (AFC), Solid Polymer Fuel Cell (SPFC), Phosphoric Acid Fuel Cell (PAFC), Molten Carbonate Fuel Cell (MCFC) and the Solid Oxide Fuel Cell (SOFC). The design philosophy has been to maximise the efficiency of electricity generation, without introducing too much complexity into the circuit arrangement since complexity increases the cost.
Before the real work could start, basic assumptions had to be done on environmental condi-tions, incoming streams and outgoing streams from any system used. Furthermore the detailed data on the different gas turbines had to be gathered as well as the data on the different fuel cell types and the economic assumptions. All these were listed in a so-called Basis-of Design.
In order to be able to work out all the selected options objectively, and obviously for time rea-sons, it was decided to use standard software. A choice was made for Cycle-Tempo which has been co-developed by the Delft University of Technology and the TNO Institute of Environmental and Energy Technology in Apeldoorn, the Netherlands. One of the reasons to choose this software was the fact that the Cycle-Tempo modelling package has the advantage of including standard modules for fuel cells and other components used during these cycle investigations. It turned out. however, that there are a number of points in the pre-commercial version of Cycle-Tempo supplied to us that
require attention (i.e. graphical user interface, low temperature fuel cell models). Many of these
points will be met by the upcoming upgrade of Cycle-Tempo. In addition further improvements are considered by the Delft University of Technology and by TNO to put the software more firmly in an engineering context.
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FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 8
Following the definition of the Basis of Design, selection, modification and testing of the soft-ware, a design matrix was developed containing the gas turbine-fuel cell combinations the parties were planning to analyse as well a manageable coding system for those designs
Simulations started with the modelling of the three gas turbines according to the Basis of De-sign data. Unfortunately, not all relevant data were known and some turned out to be inaccurate. Matching the energy input, by adjusting the inlet temperature of the high pressure turbine, with the Basis of Design values resulted in three designs staying behind somewhat in both power output and electrical efficiency. The most likely reason for this seemed the fact that the Basis of Design manu-facturer's performance data was not derived for the specific natural gas composition used in Cycle-Tempo. Nevertheless, it was believed that the models were sufficiently accurate and realistic for the purpose of supplying data on the typical characteristics of any rotating plant items used in gas tur-bine/(reformer)/fuel cell combinations.
Fuel cells operate on hydrogen (rich) gas which can be converted from a mixture of steam and natural gas in a so-called reformer. This reaction, often termed -steam reforming", is widely used in the chemical process industry for production of hydrogen-rich gases. The overall reforming reaction is highly endothermic and enhances the heating value of the fuel. When applied to gas turbines, the efficiency of a gas turbine cycle can be improved by using exhaust heat to drive the endothermic chemical reaction involving the fuel. The energy recovered from the exhaust returns to the combustor in the form of added chemical energy in the fuel. In the combustor, this chemical energy is converted wholly to sensible energy in the resulting gas mixture. Therefore we first developed several gas tur-bine-reformer models, out of which we intended to choose one model per turbine ready for expansion with a fuel cell later on.
Starting with the Heron turbine the three most promising Heron-reformer combinations were worked out using Cycle-Tempo. A reformer positioned between the power turbine and the recupera-tor resulted in the most efficient Heron-reformer combination. It was thought, however, that the final
result was limited by the extremely good integration of the standard Heron cycle: the final exhaust
gas temperature is a mere 228 °C which makes it impossible to generate large amounts of
super-heated steam. Consequently the hydrogen yield of the reformer and thus the cycle efficiency increase (from 42.3% to 45.4%) is rather small.
Next, three different Typhoon-reformer combinations were developed, two of which involveda reheated Typhoon gas turbine, Adding reheat, sometimes in combination with intercooling and/or recuperation, in some cases turned out to be beneficial for the resulting electrical efficiency since it
increased the energy content of the exhaust gases. Compared to the standard Typhoon cycle, the
relative efficiency gain resulting from adding a reformer was almost 25% (from 30.2% to 39.7%) ! Finally, the aero-derivative LM1600 cycle was equipped with a reformer. Again, three inter-esting options were investigated, including two reheat cycles. The most efficient design showed an efficiency increase from 34.1% to 43.5%.
Once that the turbine-reformer combinations had been developed, the real work could start. The first gas turbine combination system worked out is a Typhoon-AFC combination. The integra-tion opintegra-tions are limited by the AFC's low operating temperature of 80 °C. Therefore the AFC can only be integrated downstream the power turbine, i.e. also downstream the gas turbine combustor. As a result, the AFC entering gas stream will have a high CO: content which presents large problems since alkaline electrolytes do not reject CO:. Therefore the incoming CO: must be removed from the AFC inlet streams. The selection of a CO2-removal process depends on the specific conditions of the process in question. Here, the Cycle-Tempo separator model is used. The physical meaning of this model is that of a separator of solid particles; physically this resembles separation by membranes as far as gases are concerned. On the fuel side we have had to make a similar assumption since the only fuel AFC's can currently operate on is (pure) H2. The net electrical efficiency of theresulting design, which also included a small steam cycle, showed a remarkable dependence upon the operating cell
voltage. Varying this from 0.69 to 0.83, which seem realistic values for year 1994 and 2005. raises the electrical efficiency from 42.6% to 49.7%. It would turn out later that all other designs show a similar dependency.
The second fuel cell type to be analysed was the SPFC. Like the AFC. this fuel cell currently
also only operates on (pure) ft as a fuel. Also the CO content of the oxidant must be very low.
Again, this was achieved using the Cycle-Tempo separator model. Present SPFC's do not use any electrolyte other than a hydrated membrane. The membrane operates most efficiently and offers a low resistance to current flow in a fully saturated state. This makes the water balance in SPFC's a very important factor. Like with the AFC, the SPFC's low operating temperature limits the number of integration options. However, it was found that within the Heron cycle, the SPFC could be incor-porated downstream the intercooler. This resulted in pressurised fuel cell operation and consequently a higher operating cell voltage. Again, the impact of the operating cell voltage upon the final result is enormous. Operation on the higher cell voltage resulted in a design which was 51.4% efficient. It must be kept in mind that this requires operation on low current densities which will therefore result in a large fuel cell area and consequently higher fuel cell cost. The economic analysis at the end of the study had to prove whether such a highly efficient, small, only 3.3 MW (!), power plant is also economically attractive.
A reheated Typhoon reformer-SPFC combination was also worked out. In this configuration the SPFC operated at atmospheric pressure which until now has not been realised in practice (however. it is said that the first atmospheric SPFC will not be long). Again, a small steam cycle was incorpo-rated using the high temperature heat of the reformer outlet. The atmospheric cell operation, how-ever, reduced the operating cell voltage and thus the electrical efficiency was found to be 46.6 %.
Compared to the state-of-the-art SPFC systems, a net electrical efficiency of over 46% or even over 51% for a natural gas based SPFC systemis very good.
Of all fuel cell types, the PAFC is currently closest to commercialisation. Although the PAFC operating conditions are less severe than for the AFC and for the SPFC.. the danger of catalytic poi-soning still exists. Of particular concern is the CO contaminant level. Normally a so-called shift re-actor will satisfy the CO demand. In such a rere-actor, the incoming CO and steam are converted to H2 and CO2.
In PAFC stacks, provisions must be included to remove the heat generated during cell opera-tion. In this study the boiling water-cooling is preferred. Not only because the power consumption is less than for air-cooling or dielectric-cooling, but also because the steam generated in this way can be used in the reformer reactions.
The Heron turbine is equipped with an atmospheric PAFC. Of all cycles investigated here, this cycle requires only,' very few modificatiorfs to the turbine part (only the combustors need adaptations to burn the low calorific fuel), whereas the fuel cell part should be commercially available shortly. The net electrical efficiency of the resulting 5.6 MW combination is already more than 52 % !
The only option seen to combine a (reheat) Typhoon turbine with a PAFC resulted in an at-mospheric fuel cell. Again a small steam cycle was incorporated to employ some leftover high tem-perature heat in a useful way. The calculated efficiency was 52%.
The last PAFC gas turbine cycle is also the most extensive cycle developed. It is an
inter-cooled, recuperated LM 1600 equipped with supplementary firing and a PAFC operating at 4 bar. The PAFC cathode was incorporated after the first compression step. The cathode outlet was first passed through an intercooler to reduce the compression cost of the high pressure compressor. Con-sequently, the lower outlet temperature of the compressed air made it possible to incorporate recu-perative heating. Although the final gas turbine part bears little relation to a standard LM 1600. the turbine component in the model (like in all models) has been given the characteristics of. in this par-ticular case, the turbine in an LM 1600. Although it must be acknowledged that the resulting cycle is complex, its electrical efficiency of 53.9% achieved with data on current turbine inlet temperatures certainly looks interesting.
FINAL, REPORT-: JOU-2-CT93-0287 (DG 12 WSME) 10
'Concerning MCFC-gas turbine cycle, two different variants which use gas turbine compo-nents similar to those used in the Ruston Typhoon and the RLM1600 have been worked out. Both cycles use a low pressure internal reforming fuel cell. In order to reduce the complexity (exhaust gas .recirculation !) and improve the ease with which changes could be made to various cycle variables, each cycle has been modelled in two separate parts dealing with the fuel cell part of the cycle and the gas turbine part respectively. The characteristics of the flows which pass from one part of the cycle to the other are consistent (pressures, temperatures, chemical composition, etc.). The efficiencies calculated are 59,1% for the Typhoon cycle and 60.2% for the LM1600 cycle. This is higher than the highest efficiency of a currently operation plant using combined cycle gas turbine technology, i.e. 55%.
The Cycle-Tempo SOFC-gas turbine analyses can be split in cycles with internally reformed ,SOFC and with externally reformed SOFC. It turned out that gas turbine plus SOFC cycles with external reforming are rather inefficient by comparison with internally reformed cycles. The inter-nally reformed SOFC plus gas turbine cycles have been shown to have electrical efficiencies
ap-proaching 60%.Furthermore an analysis was undertaken to investigate the potential of a simple gas turbine cycle having the SOFC as a combustor with the cathode air and the anode fuel being preheated by the turbine exhaust. Rotating components were defined assuming state-of-the-art efficiencies and appropriate to a SOFC operating pressure of 3 bar. With a total output of only 1.46 MW, 1.0 MW from the cell and 0.46 MW from the turbine, the (net) electrical efficiency is 69.7%!
Although this study has come up with several new designs in which the advantages of combin-ing existcombin-ing (reliable) proven rotatcombin-ing equipment components with fuel cells have resulted in promis-ing potential system designs, there are several interestpromis-ing and/or promispromis-ing aspects of gas turbine-fuel cell combined cycles which it has not been possible during the course of this study, and which would therefore be appropriate topics for a follow-on study. Examples are the environmental emis-sions of these new combination systems part load conditions and the definition of a genericgas
tur-bine.
One of the most important conclusions may be that the efficiencies of total systems are not Just a function of the type of fuel cell, but are mainly dependent upon the fuel and system design
cho-sen
When optimising the cycles, several parameters turned out to be critical including the turbine inlet temperatures vs. the steam reforming temperature for hydrogen production, as well as several gas specification options in the cycle. The, fuel cell's operating cell voltage turned out to be the most critical parameter for the net electrical efficiency. It is therefore believed that the very good results of gas turbine-fuel cell combinations presented here are certainly not the end of the line since fuel cell-cell voltages are certain to increase in the near future as fuel cell-cell development matures. The positive outcome of this study should therefore much more be considered as a crude indicator of the potential of gas turbine-fuel cell combinations !'
INTRODUCTION
Fuel cells are electrochemical devices which generate electrical energy by electrochemical
conversion of a fuel and an oxidant, thereby releasing water and heat. Fuel cell systems can be di-vided into unpressurised. and pressurised systems. Early generation, unpressurised systems yield only marginally interesting efficiencies: e.g. PAFC (Phosphoric Acid Fuel Cell) on the basis of
natu-ral gas fuel can reach 37% (lower heating value based) net electrical efficiency, MCFC (Molten
Carbonate Fuel Cell) 48%; on coal gas these values are relatively 10-20% lower. This fact was
realised early in the development and demonstration stages of fuel cells, and therefore all fuel cell system developers tended to design pressurised systems. It is well known that in a pressurised system (with any fuel cell type) the fuel cell itself produces higher voltage, at a given current density, but also the other system components generally operate better and at lower losses, provided the process of pressurisation itself does not cause appreciable losses. This requires high performance rotating equipment, specifically designed for the job.
In practice. most fuel cell demonstration programs performed to date showed that the rotating equipment was one of the, perhaps even the, weakest link in the chain: performance of most of all, over 100, demonstrations. has so far been:
satisfactory with regard to the fuel cell stacks,
relatively weak with regards to the rotating components
relatively weak with regards to the peripheral systems (control system, valves, water cooling systems, steam system, start-up systems, etc.)
Of the statistically analysed projects, the majority of outages/faults could be attributed to ro-tating equipment and 'peripherals'.
The problem of rotating equipment development (which is expensive) for fuel cell systems is
aggravated by the fact that one needs compression of both the
cathode (air-rich) and anode(hydrogen-rich) inlet - streams. and in order to recover part of the compression energy this also
usually requires expansion in one, or often two, turbine(s). This implies three or four specially de-signed rotating components, which arc being developed by some large fuel cellmanufacturing firms.
It is therefore quite logical to use gas turbines, as an alternative to these"dedicated" rotating components, with existing and proven rotating components in the fuel cell system, and therewith to simplify the system by replacing the weaker and less reliable components in the fuel cell flowsheets by the existing gas turbine parts.
This principle was applied by Heron Turbines BV and KTI/Mannesmann, when they devel-oped a series of fuel cell/gas turbine combinations (ref 1,2.), both with and without steamreforming. It was also developed (but restricted to high temperature fuel cells) in a parallel running research program by other European firms (e.g. Donnerwith their SOFC/gas turbine combination).
However, until now these combination systems have never been analysed systematically taking into account each of the five most well-known fuel cell types and a variety of gas turbines. There-fore, the initiator of this project. Blomenco BV. contacted a number of organisations which are di-rectly involved in the production and/or use ofgas turbines and/or fuel cell systems. The fact that a
number of completely independent organisations decided to participate, each with own-and-complimentary experience and expertise, should ensure the objective value of the results of this
study.
This report first describes the different components to arrive at an overview of the theoretical background. Next, the performed simulations are explained. starting with the gas turbine simulations and the gas turbine reformer simulations. The most important part of the report are the chapters de-scribing the simulations of the different gas turbines-fuel cell combination systems which are opti-mised for maximum electrical efficiency using natural gas as a fuel. Several of the heat exchanger networks ("HEN-) were optimised using a HEN-optimiser technique called pinch technology.
7111
FINAL REPORT JOU-2-CT93=0287 (DG 12WS ME), 12
natty, an 'economic study was performed which involved cost estimates for initial units, first series
and for low volume production, using standard industrial methods for the prediction of learning
curve and production costreduction.
NOMENCLATURE
The most widely used abbreviations and the symbols for components and streams in this report are introduced here.
Abbreviations
AFC Alkaline Fuel Cell
B.O.D. Basis Of Design
CRGT Chemically Recuperated Gas Turbine
RR. External Reforming
F.O.A.K. First Of A Kind
F.S. First Series
Hl-IV Higher Heating Value
I.R. Internal Reforming
Kelvin
LHV Lower Heating Value
LVP Low Volume Production
MCFC Molten Carbonate Fuel Cell
PAFC Phosphoric Acid Fuel Cell
PEM (=SPFC) Proton Exchange Membrane
specific entropy
S/C Steam-to-Carbon ratio
S/F Steam-to-Fuel ratio
SOFC Solid Oxide Fuel Cell
SPFC Solid Polymer Fuel Cell
ST1G Steam Injected Gas Turbine
Symbols for components & streams in Cycle-Tempo figures:
Throughout this report the following standard symbols have been used for all pipes and components in the gas turbine flowsheets (chapter 9), the gas turbine-reformer flowsheets (chapters 10, II & 12) and the gas turbine-low temperature fuel cell combination flowsheets (chapters 16, 17 & 18).
Water Steam
Flue gas Air Gas
Standard (DIN) pipe symbols
Library ofsystem elements
TYPE 1. TYPE 3: TURBINE
lit TYPE 2. REHEATER I TYPE 4 CONDENSER BOILER 1 --1-7-
-4--&--TYPE 5: F.W. HEATER TYPE 6112 HEATEX- TYPE7: DEAERATOR TYPE 8. PUMPCHANGER
C4 41
TYPE 9/11: JUNCTION/ TYPE 10: SINK/SOURCE TYPE 13: COMBUSTOR
TYPE 14: VALVE/ SPLITTER
SPLITTER
1
TYPE 15: DRUM TYPE 17: ABSORBER TYPE 18: REGENERATOR TYPE 20 REFORMER
--7- 0
TYPE 21: FUELCELL TYPE 22: MOIST SEP./ TYPE 23: GASIFIER TYPE 25 SCRUBBER FLUE GAS CONDENSER
--4b.
7----,..0.--,_
-
,---17
TYPE 26. SEPARATOR TYPE 27: REACTOR TYPE 28: SATURATOR
TYPE 29 COMPRESSOR
mis-2028 doc 14-08-95
FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 14
I
I
---r
IL
BACKGROUND OF THE PROJECT
1.1
INTRODUCTION
This introductory chapter starts with a paragraph explaining the logic of combining gas tur-bines and fuel cells. This is followed by a short description of the Joule research programme under the terms of which this project takes place. The five parties involved are introduced mentioning their
specific backgrounds and role in the project. Finally the aims and design philosophy are set out. 1.2
WHY CHOOSE A COMBINATION OF GAS TURBINES AND FUEL
CELLS?
It has been outlined in the Introduction paragraph most fuel cell developers tended to design pressurised systems because, with any fuel cell type, an increase in operating pressure has several
beneficial effects on the fuel cell performance: the higher reactant partial pressure. higher mass
transfer rates and a better gas solubility result in a higher cell voltage at a given current density. This will result will in a higher net electrical efficiency for a complete fuel cell power plant provided the process of pressurisation does not cause appreciable losses. Pressurisation requires high performance rotating equipment, specifically designed for the job.
The problem of rotating equipment development (which is expensive) for fuel cell systems is aggra-vated by the fact that one needs to compress both the cathode (air-rich) and the anode (hydrogen-rich) inlet-streams, and in order to recover part of the compression energy, this also requires expan-sion in one, or often two, turbine(s). This implies three or four specially designed rotating compo-nents, which are being developed by some large fuel cell manufacturing firm.
Knowing that:
the majority of outages/faults of the analysed projects could be attributed to the rotating equip-ment and 'peripherals'
in a gas turbine a large air stream is available from which the air may be utilised in a fuel cell first, and in designing fuel cell power plants, streams with excess oxygen are available, as well as unutilised fuel which can be burnt, the following question arises.
Why not replace the weaker and less reliable components in the fuel cell flowshe,ets with the existing and proven rotating parts of a gas turbine? This is the basic question which led to the
pres-dent project.
THE JOULE-II PROGRAMME
1)In 1983 the European Community started co-ordinating her Research and Technology Devel-opment (RTD) activities in long-term framework programmes. These framework programmes con-sist of specific RTD-programmes on clear-cut research areas like environment or healthcare.
In 1990 a Third Framework programme was approved. This 5 year lasting (1990-1994) Framework programme was allocated 5.7 billion ECU and covered some 15 specific RTD
pro-grammes in different domains.
Joule-II is the specific RTD programme in the field of non-nuclear energy. The Joule-II
pro-gramme is a further development and extension of the Joule-I propro-gramme: Non-Nuclear Energy
Sources and Rational Use of Energy (1989-1992). The general objective of Joule-II is to contribute to the development of:
New energy-options which are both economically feasible and safer for the environment Energy saving technologies
FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 16
A detailed proposal aiming to arrive at an objective. systematic system analysis of combina-tions of gas turbine cycles and fuel cells of all main types for the generation of electric power was sent in in June 1993. In December the co-ordinator/proposer of the study, Blomenco BV, received confirmation that the Commission had selected the above mentioned proposal.
1.4
PROJECT PARTNERS AND PARTNER'S ROLE IN
PROJECT
Five parties with different backgrounds participated in this joint research project. All organi-sations are directly involved in the production and/or use of gas turbines and/or fuel cell systems and therefore directly strategically involved with the combination systems proposed here. First some
specific details of the experience of each organisation will be given. Then the project control diagram will be presented and the relative role of each participant on all taskswill be outlined.
The five project partners are:
1.4.1 EUROPEAN GAS TURBINES LTD./GEC ALSTHOM
EGT Ltd is a manufacturer of aero- and industrial gas turbines from 1.5 MW to 230 MW. Gas turbines are applied in stand alone mode, in combined heat and power plants and in combined cycle plants (Steam And Gas Turbine, STAG). The company's technology covers natural gas. oil
and coal derived low calorific value gas fuels.
The Mechanical Engineering Centre (MEC) has expertise in allthe basic gas turbine
tech-nologies: materials, structures. aerodynamics, thermal analysis, combustion. tribology. system op-timisation, control and instrumentation.
Also, in fuel cell technology MEC has expertise in the modelling of solid oxide fuel cell
(SOFC) stacks and the design. build and testing of low temperature fuel cells in specialist battlefield and sub-sea applications. MEC has worked with partners on projects within the CEC MAST pro-gramme and the UK DTI Wealth from theOceans programme.
MEC had the expertise to assist this project in the provision of gas turbine/steam turbine
combined cycle data and the system optimisation of fuel cells using a variety of fuels in complex cy-cles with gas and steam turbines. (Refs. 2-6).
1.4 .2 NATIONAL POWER PLC
National Power is the largest of the privatised UK electric utilities. National Power Research and Technology has been involved in cycle thermodynamic and economic analyses for a number of years (Refs. 7-10). This work is the responsibility of the Future Plant Group, which, at the start of this project, had a staff of ten professional scientists and engineers.
The cycle analysis work has involved a wide variety of plants including various novel and un-usual cycles in addition to conventional plant. Many of the studies have involved gas turbines in combination with other types of plant such as recuperative heat exchangers. intercoolers. thermo-chemical reformers and gasifiers. The studies have included co-generation and energy storage in addition to straightforward power generation. There is emphasis on process integration methods to achieve the optimum configuration.
Theoretical and experimental studies are also being undertaken by the group as well as par-ticipation in an international programme on Phosphoric Acid Fuel Cells (PAFC).
1.4.3 ELENCO NV
The Belgium-based company Elenco NV has been involved in the development of fuel cells since January 1976, when the company was formed with that specific purpose. Main activities have included research, development and demonstration as well as (pre-) production of alkaline fuel cells (Refs. 11-14). The technology includes electrodes, stacks, system engineering. prototype construc-tion and testing.
Highlight projects include the EUREKA city bus demonstration project, now in execution, and work for the HERMES space plane (1985-1992). Elenco has a semi-industrial automated electrode manufacturing pilot plant. Very recently, however, freezing of the HERMES program caused severe financial problems for Elenco.
1.4.4 BLOMENCO BV
Blomenco BV is a small Dutch company specialised in consulting and contracting
of (management of) research, development, demonstration and commercialisation ofenergy technolo-gies. The co-ordinater of this project has founded the company based on a I3-year experience in in-ternational R&D management, formerly as Group Vice President for R&D in the KTI Group, a 200 million ECU/yr. turnover contractor of chemical plants.He was among others responsible for the design, initiation and construction of the first three Europe-based fuel cell power plants, all with imported Japanese PAFC stacks, but with KTI designs of all other components and of the system integration (Ref. 15).
Besides the management of over 60 R&D projects, he wrote and edited two books. hold pat-ents and is the author of approximately 100 papers and publications (e.g. Refs. 16-18)
Blomenco BV is also involved in the Heron turbine commercialisation, one of the selected turbines for this project.
1.4.5 CONTRANS
Being a subcontractor to Blomenco. the Czech company Contrails advises on the gas turbine technology and cycle calculations. This company is specialised in thermodynamic and component analysis of gas turbine engines and facilities, gas calculations and system studies, as well as aerody-namics.
The main officer of Contrans is Dr. Karel Celikovky, who has some 30 years of experience in R&D ofthe Czech aero industry, and is the author of several publications on turbomachinery (e.g. Refs. 19-22).
The Figure below gives a project control diagram of the companies involved.
Co-ordinator/proposer Assoc. contractor Elenco N.V. Blomenco B.V. Contractor Assoc. contractor National Power
Project control diagram
Assoc. contractor European Gas Turbines Ltd. (EGT) Con trans Sub-contractor mis-2028.doc 14-08-95 Fig.
It may be clear from the above that the partners cover the necessary know-how for all fuel cell types and for the gas turbines. From this a task distribution was defined, which is shown in table 1.1.
Table 1.1 Task distribution
LTfc Low Temperature fuel cell HTfc High Temperature fuel cell gt gas turbine
* incl. CONTRANS as subcontractor
The relative role of each participant has been adjusted to each partners' specific background. Table 1.2 on page 19 lists the role for each activity per partner, and total, in man-hours.
The table includes a detailed allocation of hours to be spent on the different activities per par-ticipant as agreed upon between the parties involved before the actual start of the project. It would turn out however that, for reasons described later in this report, EGT, National Power and Blomenco exceeded this planned time allocation.
1.5
AIMS AND DESIGN PHILOSOPHY
The aim of this joint research project is to arrive at an objective, systematic system analysis of
combinations of natural gas fired gas turbine cycles and fuel cells for the generation of electric
power. A variety of gas turbine types (i.e. industrial, aero-derivative) and a variety of the main fuel cell types (Alkaline Fuel Cell, Solid Polymer Fuel Cell, Phosphoric Acid Fuel Cell. Molten Carbon-ate Fuel Cell and Solid Oxide Fuel Cell) have been taken into account.
The general design philosophy is to maximise the efficiency of electricity generation, without introducing too much complexity into the circuit arrangement. since complexity increases the cost. Where possible heat has been used internally within the system in order to achieve maximum effi-ciency. The alternative possibility of using heat for co-generation has been noted where appropriate, but detailed co-generation scenario's are outside the scope of this project.
mis-2028.doc 14-08-95
PARTNER
Elenco input Low-Temp. fuel cells + software assistance
National Power flowsheet simulations High Temp. fc/gas turbine combinations EGT input 2 gas turbines and HT-fc + simulations HTfc/gt's
Blomenco* simulations LTfc's/ges + software LTfc's + economics + co-ordination + reporting
inch. CONTRANS subcontract (1200 hours)
The 400 "co-ordination, miscellaneous" hours are 'for extra
activities during the course of the
study and some co-ordination tasks. This row in the table shows
an approximate distribution of
those hours. They are budgeted in the Blomenco budget (the
main proposer of the study)
and will be distributed for those tasks once assigned.
Table 1.2 Relative role of each participant (number of hours)
rms-2028 doc 14-08-95 Not.Power Blomenco 1 input t.c. parameters 40 40 40 120 input optim.optiOns I 15 20 20 40 95 3 software input 20 20 ! 20 /I . 60 1 4 - input QT. parameters 100 - 40 , 140
I 5 definition basis of design 5
10 TO I 20 45
- I approval by all parties 5 5 15 30
7 software adopt. i AFC .
1
40 1
100 140
8 I software adopt.1 ft t SPE()FC 1 40
1
-I
-100 140
i 9 software adapt.PAFC
I' 100 100
10 software adapt.MCFC
100, 100
I I'll software adopt SOFC
II 140 __. 140 12 AFC-GTcombination I 20 i280 300 1 13 I SP(E)FC-GTcombination 20 I - -280 300 14 PAFC-GTcombination Il -- 300 300 I 15 MCFC-GTcombination __ ii 160 160 1 10 330 1 16 SOFC-GTcombination . 160 160 15 ' 335
17 design cross checks
5 45 i ' 15 50 J 1[15 i 1 18 (re-) optimisation - 40 1 - I 80 120. 19 11
11 system. cost & econ.
analyses - 50 200 250 20 : sensitivity analyses l'20 I 120 21 final report 10 10 10 90 ' 120 Subtotal I, 200 800 400 2000-I 3400 Co-ordination, miscellaneous" ' 50" U, 50" i_ I50" 250" fi 400" iTotal I I 1
_
i L 3800 -2 5-FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME)
2.
GAS TURBINES
2.1
INTRODUCTION
After a historical review of gas turbine technology, the basic thermodynamics of various parts of a practical gas turbine cycle will be considered in more detail. A short paragraph on gas turbine performance is also included picturing the theoretical correlation of important gas turbine
parame-ters. The last section describes the gas turbine selection process for this project. 2.2 HISTORY(REK 1)
The gas turbine, the name is used for the gas turbine engine and for the gas turbine expander, has had a long successful history. In the beginning, however, problems occurred due to thermody-namic reasons, These can be explained best by comparing gas turbine engines with steam engines and internal combustion piston engines.
Steam engines were relatively easy to design and build so that they would at least run: Very little work is required to force water into a boiler, little sophistication is required to boil water and when steam is formed at high pressure and led to either a piston engine or a turbine it will produce more power than required by the feed pump.
Developers of internal-combustion piston engines also got them to function fairly easily be-cause, although relatively much more work is required to compress air than is needed to get water into a boiler, the combustion temperatures are so high (several thousand degrees C) that the piston expansion work is much greater than the piston compression work, even if the compression and ex-pansion processes themselves involve considerable flow losses.
Gas turbine engines could not use such high temperatures at the start of expansion. and there-fore the compression and expansion losses must be low to make sure that net positive work is pro-duced. For many decades, the losses during compression, in particular, were too high for positive work to be given at the temperatures the materials of the day could withstand. Accordingly, many inventors produced machines that never achieved even the ability to run without an external power output.
The earliest patent for a gas turbine engine was John Barber's of 1791, but nothing resulted
from this. In the first two decades of this century many abortive attempts were made to produce
working gas turbine engines. Some of the very few successful designs will be mentioned in the fol-lowing.
The first gas turbine activity to result in a working engine was started in France by Charles Lemale. who was granted a patent for a constant-pressure (BraTton or Joule) cycle in 1901. He de-signed a 25-stage centrifugal compressor in three casings on one shaft running at 4000 rpm and ab-sorbing 245 kW, giving a pressure ratio of three to one. This was made by Brown Seven.. and it achieved an isentropic efficiency of 65-70%. Normally this would not be enough to allow a gas tur-bine engine to produce net power, but an astonishingly high combustion temperature of 1800 °C was reportedly attained in a carborundum-lined combustor. and the two stage turbine was water-cooled. The steam raised in the cooling circuit was led to nozzles and passed throughthe same turbine wheel. This ambitious engine produced positive power, albeit at only 3.5% thermal efficiency - the first
constant pressure gas turbine engine to "work".
The second engine to achieve partial success was proposed by Hans Holzwarth in 1906-1908. and constructed in 1908-1913 by Brown Boveri. This was an explosion or constant-volumecycle, in which the potentially high temperatures of combustion obtained in a periodic-firing system. as in an engine cylinder, can compensate for poor compression and expansion efficiencies. Holtzwarth's 735 kW (1000 hp) design produced only 147 kW (200 hp). and both its size and efficiency were less fa-vourable than then-available reciprocating engines.
mis-2028.doc 14-08-95
The various efforts which led to the modem successful gasturbine engine can be said to have started in the years 1927 to 1936 by different people. The first of these, who has had a major impact. was Aurel Stodola, a professor at theZurich Polytechnic. He was involved in testing a
Holtzvvarth engine at the Thyssen steel works, and noted the high heat transfer in the water jacket around the turbine. By using the waste heat in a steam generator.the so-called Velox boiler was
developed from 1933-1936. This had an axial compressor "supercharging" a boiler in which gas or liquid fuel was burned, with the hot gases subsequently being expandedthrough a gas turbine that drove the com-pressor. During shop tests of the turbomachinery,a high intensity combustor was substituted
for the boiler in 1936, and net power was produced at a reasonable thermal efficiency. Thus the first suc-cessful industrial gas turbine engine was arrived at "by chance".
In the same decade that saw the shaft-power gas turbineengine reach successful operation, the turbojet was independently developed by people in Britainand in Germany of which Whittle and Von Ohain were the most important.
Frank Whittle, a Royal Air Force cadet, was firstwith his invention. 1929, and patent, 1930. although he was not first atsuccessful running or in the first flight. His patent was for an axial-plus-centrifugal compressor and a two-stage turbine. Thedesign included free-vortex-twist turbine blades
and incorporation ofblade-angle variations, which allowed for radial
flow equilibrium, and gave British engines a higher efficiency than their Germanopponents. Whittle had two principal problems: to make a combustor with about 10 times theprevious maximum combustion
intensity for liquid-fuel combustion, and to overcome the mechanical failuresthat plagued his turbines.
Whittle's counterpart in Germany was Hans vonOhain who started later but achieved his first engine running and his first flight sooner. This waspartly due to better backing: Heinkel wanted to build the world's fastest plane; partly to excellent assistance: Heinkel also hired Max Hahn to help Von °bairn and partly to wise tactical decisions. Von Ohain knew that to get continued support from
Heinkel he had to demonstrate quickly something that showed promise. The configuration
he chose was a centrifugal compressor plus a radial-inflow turbine, made mostly of mild steel,
and he avoided the liquid-fuel-combustion problem by using hydrogenfor his first run in 1937. With greater support forthcoming subsequently, he was able to solve the combustion problem ahead of Whittle. andthe first flight of a jet aircraft, the Heinkel 178, was onAugust 27, 1939, with anengine weighing 361 kg giving 4890 N thrust at 13000 rpm.
In the 50 years since the end of the second WorldWar, gas turbine engines, including turbo-jets, have developed rapidly. Much of the developmentcan be attributed to one overriding factor, the
increase in turbine-inlet temperatures.
2.3
THERM
ODYNAMICS(RE' 2)This paragraph tends to clarify the basic gas turbinethermodynamics. Starting with a simple practical gas turbine cycle the thermodynamic consequencesare shown when additional components
arc added.
2.3.1 A PRACTICAL GAS TURBINE CYCLE
The most basic gas turbineis one operating in an open cycle in which a rotary compressor and a turbine are mounted on a common shaft. as shown diagrammatically in Fig. 2.1.
Air is drawn into the compressor. C. and after compression passes into a combustion cham-ber, CC. Energy is supplied in the combustionchamber by spraying fuel into the airstream. and the resulting hot gases expand through the turbine. T. to the atmosphere. In order tovachieve net work output from the unit, the turbine must develop more gross work output than is required to drive the compressor and to overcomemechanical losses in the drive.
mis-2028.doc
FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 22
Air inlet
Fig. 2.1 Open-cycle gas turbine unit
The open-cycle gas turbine cannot be compared directly with the ideal constant pressurecycle. During combustion there is no energy exchange with the surroundings, the effect being a gradual decrease in chemical energy with a corresponding increase in enthalpy of the working fluid. The combustion reaction will not be considered in detail here, and a simplification will be made by as-suming that the chemical energy released on combustion is equivalent to a transfer of heat at con-stant pressure to a working fluid of concon-stant mean specific heat. This simplified approach allows the actual process to be compared with the ideal and to be represented in a temperature-specific entropy
(T-s) diagram.
Neglecting the pressure loss in the combustion chamber the cycle may be drawn in a T-s dia-gram as shown in Fig. 2.2. Line 1-2 represents irreversible adiabatic compression; line 2-3 repre-sents constant pressure heat supply in the combustion chamber; line 3-4 reprerepre-sents irreversible adia-batic expansion. The process 1-2s represents the ideal isentropic process between the same pressures P i and p- ). Similarly,the process 3-4s represents the ideal isentropic expansion process between the pressures p2 and pi.
Fuel
Fig. 2.2 Gas turbine cycle in a T-s diagram
2.3.2 USE OF A POWER TURBINE
It is sometimes more convenient to have two separate turbines instead of one turbine, one of which drives the compressor, while the other provides the power output. The first, or high-pressure (HP) turbine, is then known as the compressor turbine, and the second, or low-pressure (LP) turbine,
Exhaust Net work
output
5
is called the power turbine. The arrangement is shown in Fig. 2.3(a). Assuming that each turbine has its own isentropic efficiency, the cycle is as shown in a T-s diagram in Fig. 2.3(b). The numbers in
Fig. 2.3(b) correspond to those of Fig. 2.3(a).
The work ratio is the ratio of work output and work input. These will be derived in the follow-ing sections from each Figure.. It is important to have as high a work ratio as possible (see also sec-tion 2.3.7: Performance characteristics), and methods of increasing the work ratio are intercooling between compressor stages, and reheating between turbine stages. lntercooling and reheating, while increasing the work ratio, can cause a decrease in the cycle efficiency, but when they are used in conjunction with a heat exchanger, then intercooling and reheating increase both the work ratio and the cycle efficiency.
mis=2028 doc Air inlet I n'tercooler (a) Net power output 6 Exhaust (b) (b)
Fig. 2.3 Gas turbine unit with separate power turbine (a) and the cycle in a T-s diagram (h)
2.3.3 INTERCOOLING
When the compression is performed in two stages with an intercoolcr between the stages, then the work input for a given pressure ratio and mass flow is reduced. Consider a system as shown in Fig. 2.4(a); the T-s diagram for the unit is shown in Fig. 2.4(b). The actual cycle processes are 1-2 in the LP compressor, 2-3 in the intercooler, 3-4 in the HP compressor, 4-5 in the combustion cham-ber, and 5-6 in the turbine. The ideal cycle for this arrangement is 1-2s-3-4s-5-6s: the compression process without intercooling is shown as 1-A in the actual case, and 1-As in the idealisentropic case.
Fig. 2.4 Gas turbine unit with intercooling (a) and the cycle in a T-s diagram (h)
FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 24
The work input with intercooling is given by
Work input (with intercooling) = cp(T2- T1) + cp(T4- 7'3)
(21)
The work input with no intercooling is given byWork input (no intercooling) = cp(TA-TO
= c p(T 2 - T + c p(T A - T2) (2.2) Comparing this last equation with equation (2.1), it can be seen that the work input with inter-cooling is less than the work input with no interinter-cooling, if cp(T4 - T3) is less than cp(TA - T2). This is so if it is assumed that the isentropic efficiencies of the two compressors. operating separately, are each equal to the isentropic efficiency of the single compressor which would be required if no inter-cooling were used. Then (T4 - 7'3) < (TA - 2) since the pressure lines diverge from left to right in the T-s diagram.
2.3.4 REHEAT
As stated earlier, the expansion process is very frequently performed in two separate turbine stages, the HP turbine driving the compressor, the LP turbine providing the useful power output. The work output of the LP turbine can be increased by raising the temperature at inlet to this stage. This can be done by placing a second combustion chamber between the two turbine stages in order to heat the gases leaving the HP turbine. The system is shown diagrammatically in Fig. 2.5(a), and the cycle is represented in a T-s diagram in Fig. 2.5(b). The line 4-A represents the expansion in the LP tur-bine if reheating is not used.
As before, the work output of the HP turbine must be exactly equal to the work input required for the compressor (neglecting mechanical losses), i.e.
cpa(T2-TO=cpg(T3 - T4) (2.3)
mis-2028.doc
I a
(b)
Fig. 2.5 Gas turbine unit with reheating (a) and the cycle in a T-s diagram (h) The net work output. which is the work output of the LP turbine, is given by
If reheating is not used, then the work of the LP turbine is given by
14-08-95
Since pressure lines diverge to the right in the T-s diagram, it can be seen that the temperature difference (Ts - T6) is always greater than (T4 - TA), so that reheating increases the net work out-put.
2.3.5 RECUPERATION
The inefficiencies in the compression and expansion processes become greater for smaller
stand-alone gas turbine units and therefore a heat exchanger, also known as recuperator, is some-times used in order to improve the cycle efficiency.
The exhaust gases leaving the turbine at the end of expansion are still at a high temperature. and therefore at high enthalpy. If these gases are allowed to pass into the atmosphere, then this rep-resents an irreversible loss of available energy. Some of this energy can be recovered by passing the gases from the turbine through a heat exchanger, where the heat transferred from the eases is used to
heat the air leaving the compressor. This simple unit with a heat exchanger added is shown
dia-grammatically in Fig. 2.6(a), and the cycle is represented in a T-s diagram in Fig. 2.6(b). Heat exchanger Exhaust Air Inlet Net power Output T2 = 6 Available temperature difference 3
Fig. 2.6 Gas turbine unit with heat exchanger (a) and the cycle bra T-s diagram (h)
In the ideal heat exchanger the air would be heated from T2 to T3= 7'5, and the gases would be cooled from T5 to T6 = T2. This ideal case is shown in Fig. 2.6(b). In practice this is impossible, since a finite temperature difference is required at all points in the heat exchanger in order to over-come the resistance to the heat transfer.
Fig. 2.7 T-s diagram for a gas turbine unit with a heat exchanger showing
temperature difference for heat transfer
mis-2028.doe 14-08-95
Net work output (no reheat) = cpg(7.4 - TA) (2.5)
(a) (b)
FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 26
Referring to Fig. 2.7, the required temperature difference between the gases and the air enter-ing the heat exchanger is (T6 - T2), and the required temperature difference between the gases and the air leaving the heat exchanger is (T5 - T3).
If no heat is lost from the heat exchanger to the atmosphere, the heat given up by the gases must be exactly equal to the heat taken by the air, i.e.
macpa(T3 - T2) = mgcpg(T5 - T6) (2.6)
The assumption that no heat is lost from the heat exchanger is sufficiently accurate in most practical cases. This equation is therefore true whatever the temperatures 7.3 and T6 may be.
When a recuperator heat exchanger is used, then the heat to be supplied in the combustion
chamber is reduced, assuming that the maximum cycle temperature is unchanged. The net work out-put is unchanged and hence the cycle efficiency is increased. However, there is a major objection to
incorporate recuperators in big units. The large gas flows, one of which at high temperature and
pressure (compressed air), the other at even higher temperature and atmospheric pressure (power
turbine flue gases) result in large size and heavy equipment. Therefore, recuperators seem to be
practical for modest capacities only.
2.3.6 EFFECT OF PRESSURE LOSSES
So far, all pressure losses were neglected. In an actual gas turbine unit there arc pressure
losses due to friction and turbulence in the intercooler, in the air side of the heat exchanger, in both combustion chambers, and in the gas side of the heat exchanger, and in the exhaust duct. The high heat transfer rate in a combustion chamber leading to an appreciable velocity increase in a duct of approximately constant cross-sectional area causes a further pressure loss in addition to that due to friction and turbulence.
3
P.
Fig. 2.8 T-8 diagram showing pressure losses
2.3.7 PERFORMANCE CHARACTERISTICS(REF 3)
The theoretical correlation of pressure ratio, temperature, specific power (horizontal axis) and efficiency (vertical axis) is shown in Figure 2.9, having taken into account the individual component efficiencies. 10 P I 0 = mis-2028.doc 14-08-95 7 Pe,/ 8 PH 9s P7 7s /73
mis-2028.doc
2 3
SPEC. GASVERMOGEN
x-axis Spec. gasvermogen = Specific power y-axis Thermisch rendement = Thermal efficiency
T3t/T0 Turbine inlet temperature / Compressor exit temperature 133/130 Compressor outlet pressure / Atmospheric pressure
Fig. 2.9 Theoretical correlation between pressure ratio, temperature, specific power and thermal efficiency
Without paying attention to the exact values, it can be seen that when the pressure ratio is kept at a constant level, an increasing turbine inlet-temperature will result in an increase of power output, leaving the efficiency more or less unaffected. Increasing the pressure ratio while maintaining the turbine inlet-temperature a constant will result in a permanent increase of efficiency, whereas the power output will show a maximum value.
The specific power is defined as the power per kg air consumption per unit of time and by that it measures the gas turbine size. Therefore, when a higher specific power output is needed, first the highest permissible turbine inlet-temperature should be determined, after which the pressure ratio corresponding with the highest specific power output can be chosen. This is the general design route
for aircraft engines. All the time the criterion will be the technologically allowable turbine
inlet-temperature.
The very high temperatures are being made possible by the availability of high temperature
materials based on nickel or cobalt. These materials, however, give extreme manufacturing and
modelling problems caused by their tenacity.
The required pressure-ratio in rotating compressors is achieved by increasing the kinetic energy of
the air which is then converted into pressure. This diffusion process reduces the airspeed therewith causing aerodynamical problems.
14-08-95 60 50 40 cr 30 20 (0 -it
FINAL REPORT - JOU-2-CT93-0287 (DG 12 WSME) 28
2.4
SELECTION OF GAS TURBINES FOR JOULE2-PROJECT
At the first meeting held in Amsterdam on February 7th 1994 it was agreed that the selection of the gas turbines should be according to the following principles:
3 different gas turbines would be included in the study
One of the three gas turbines would be the Heron turbine. because 1) this is a good example of an intercooled-recuperatecl-reheat turbine. 2) it has the highest electrical efficiency reported for single-cycle gas turbines and 3) Heron has the first patents on gas turbine / fuel cell combina-tions
Of the two other gas turbines, one would be a state-of-the-art industrial gas turbine and the other would be a state-of-the-art aero-derivative
Before making a final choice, a few additional principles and preferences for selection of the other two gas turbines were defined.
It is not the purpose of the study to identify which particular manufacturer makes the most suitable gas turbine for use with fuel cells, but rather to explore the fuel cell/gas turbine cycles with representative state-of-the-art gas turbines, which can bring out the advantages and disadvantages of using each generic gas turbine type in this kind of cycle.
The gas turbines selected should be of modest size in order that they be potentially suitable for use in combination with a fuel cell. It is preferred that there should be a spread of gas turbine sizes in order to bring out cost and performance features associated with different sizes of plant as well as those associated with different pressures, temperatures and thermal efficiencies.
There would be an advantage in selecting one or both gas turbines which are manufactured byEGT or by General Electric, since this should make it easier to obtain additional information beyond that which is normally included in gas turbine specialised databases such as GTPRO.
Instead of specifying an existing state-of-the-art gas turbine, an alternative approach might be to specify gas turbines which are expected to be in the market place by the time that the fuel cell/gas turbine system could be commercialised. However, we wanted to use the same three gas turbines for all the fuel cell types considered in the study because we wished to know how much differenceit
makes to use one fuel cell type rather than another in an integrated cycle. Also each fuel cell type has a different time scale for commercialisation. Apart from the different time scales, the specification of a gas turbine which is not commercially available would involve further speculation. It could be ar-gued that near-term gas turbine developments are likely to produce only incremental changes to the specifications currently available and that therefore the outcome of the study is unlikely to be signifi-cantly affected.
Bearing in mind the above mentioned reflections the following gas turbines were selected: The 1.4 MW Heron turbine
The 4.55 MW Ruston Typhoon industrial gas turbine The 13.43 MW RLM1600 aero-derivative gas turbine
By selecting these three turbines there resulted not only a variation in pressure ratio, turbine inlet temperature and simple cycle efficiency, but also a considerable variation in gas turbine output. This can be seen as an advantage because it highlights cost and performance factors associated with economy of scale as well as with other factors.
A more detailed description of each selected gas turbine as well as the results of the software simulations of these three cycles will be presented in Chapter 9.
