PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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The performance of a steam turbine is not significantly affected by ambient temperature or altitude and, therefore, does not require derating [18]. Otherwise, steam turbine performance may be modelled in the same way as an ICE, as described in section 5.2, using percentage part load efficiency values as the measure of performance. Again, as with an ICE, while the efficiency of the steam turbine drops with partial loading, the amount of waste heat produced increases proportionally, increasing the heat to electricity ratio, and keeping the overall efficiency (heat plus electricity) fairly level [18]. As the steam turbine uses an external heat source to produce the steam necessary to turn the turbine, the efficiency of the boiler employed to produce the required heat to raise the necessary steam must be taken into account when calculating the overall fuel requirement. This is done by calculating the fuel consumption figure using Equation 5.33, 5.35 or 5.36 as appropriate, multiplying this by 100 and dividing by the percentage boiler efficiency. Due to the external nature of the heat source, and fairly slow start-up time, the options to follow heat demand, electricity demand or both are not appropriate for steam turbines, and are, therefore, not available. Again, multiple turbine sets may be used, and these are subject to a minimum recommended load. The output from this procedure is a graph of percentage turbine loading, and fuel use is calculated and dealt with as before in section 5.2. An example of the definition window for a steam turbine is given in Appendix 1, Figure A1.35. 5.6 Fuel Cell Model Various models exist to predict the performance of fuel cells [19,20,21], but these rely on large volumes of information that are specific to a particular fuel cell design. To allow development of a generic model that can be easily applied to the different fuel cell types, manufacturers’ performance data will again be used. This will allow the performance of any fuel cell type (e.g. Phosphoric Acid Fuel Cells, Molten Carbonate Fuel Cells) to be simulated under various load conditions, using the same procedure. 150
The performance of a fuel cell is not significantly affected by ambient temperature or altitude and, therefore, does not require derating. Otherwise, the electricity and heat production of a single fuel cell may be modelled in the same way as an ICE (as described in section 5.2), using percentage part load efficiency values as the measure of performance, and the output to the matching stage is also the same. As electricity is generated directly in a fuel cell, the generator efficiency and power factor considered in the ICE model are not required. Fuel cells also have fast response times, which make them ideal for following demand. There are no other factors that significantly affect the performance of a fuel cell at this level of modelling [22]. Examples of the definition window for a fuel cell system are given in Appendix 1, Figures A1.37 and A1.38. There are, however, some specific considerations that need to be taken into account when modelling fuel cells, and these are outlined below. 5.6.1 Operating Temperature The required operating temperature of a fuel cell depends on the type of electrolyte used. The most common types of fuel cell used for stationary applications are the Phosphoric Acid Fuel Cell (PAFC), which operates at around 200°C, and the Alkaline Fuel Cell (AFC), which operates at around 80°C. This operating temperature is reached, initially, with the help of an external heat source, and is then maintained at a reasonably constant level by waste heat from the operation of the fuel cell. For the purposes of this model, it will be assumed that the fuel cell generating system is running fairly continuously, with some degree of loading, and therefore does not require external heating. Typically, several days of standby can be achieved without the need for external heating [22]. 5.6.2 Fuel Cell Efficiency Fuel cell generating systems can run either on pure hydrogen or on hydrogen rich fuels such as biogas or methanol. The latter type requires an internal reformer, which reduces the overall generating efficiency, and this effect is included in their quoted efficiency figures. The efficiency of a fuel cell also 151
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Decision Support for New and Renewa
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Abstract The global requirement for
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CONTENTS 1 ENERGY SYSTEMS FOR SUSTA
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5.5 Steam Turbine Model 149 5.6 Fue
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FIGURES Figure 1.1 Final Energy Con
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Figure 7.30 Following Electricity a
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on the use of fossil fuels, energy
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The general increase in energy cons
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supply is reduced or eliminated, lo
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Figure 1.3 The Electricity Supply G
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on different generation mixes depen
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Various studies have been carried o
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provision for smaller areas, and he
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1.7 References [1] The Internationa
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2 Options for New and Renewable Ene
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the amount of usable heat that is g
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the conversion of petrol cars; howe
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set times, producing a constant ele
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partial load. Fast response and sta
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2.3 The Production and Storage of H
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dedicated boiler, which runs contin
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Figure 2.3 A Typical Hydrogen Filli
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part of the natural carbon cycle (a
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Figure 2.4 Layout of a Gasification
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met by process integration and the
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Figure 2.5 The Inputs and Outputs o
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1. Scale for measuring out lye and
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feedstock being used. Sugary feedst
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carbon dioxide via steam reforming.
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• Where CHP is used, the balance
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[22] Vehicle Certification Agency (
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[55] M. A. Paisley, J. M. Irving, R
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3 Approaches to Renewable Energy Sy
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Because of the intermittent nature
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A renewable energy supply evaluatio
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the system are kept. The output of
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There are various models available
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When the use of climate dependant i
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3.5 References [1] M. Muselli, G. N
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4 A Procedure for Demand and Supply
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pumped storage and flywheels), a ba
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for the agricultural vehicle use re
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Figure 4.4 Combining Demands to Tak
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ates for vehicles, engines and othe
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Figure 4.5 Derived Fuel Production
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together if desired, and taken forw
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profiles are output from this part
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dividing the production rate at eac
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As it would be too confusing to sho
Page 99 and 100: Figure 4.12 Output of the Matching
Page 101 and 102: However, when more than one transpo
Page 103 and 104: considered, this amount is added to
Page 105 and 106: users are alerted if there is not e
Page 107 and 108: at the matching stage, along with t
Page 109 and 110: vehicles if they are increased by 1
Page 111 and 112: If biogas is being considered, the
Page 113 and 114: The number of timesteps per hour wi
Page 115 and 116: After the algorithm has been follow
Page 117 and 118: • Float Charge - once the battery
Page 119 and 120: Discharge No tank = tank fuel used
Page 121 and 122: equired (kW) = maxkWh x bulk% (5.16
Page 123 and 124: An example of the output graph prod
Page 125 and 126: 5.2.1 Required Power Specifically d
Page 127 and 128: 5.2.3 Engine Performance in the Con
Page 129 and 130: used for gas powered ICEs, but the
Page 131 and 132: and five times, depending on the nu
Page 133 and 134: Is PL < Min ? No Is PL = 0 ? No Is
Page 135 and 136: where Max = maximum energy availabl
Page 137 and 138: where Ratiopart = heat to electrici
Page 139 and 140: (including following heat demand wh
Page 141 and 142: where SFC = specific fuel consumpti
Page 143 and 144: engines running respectively). If t
Page 145 and 146: (continued) Is Fuel Available > (4
Page 147 and 148: of the definition window for a Stir
Page 149: and continuous operation. Again, mu
Page 153 and 154: percentage loading, rather than usi
Page 155 and 156: Is Min = 0 ? No Is Min = PC1 ? No I
Page 157 and 158: 5.6.4 If Fuel Availability is Less
Page 159 and 160: 5.7 Electrolyser Model An electroly
Page 161 and 162: original calculation of the amount
Page 163 and 164: 5.8 Regenerative Fuel Cell Model A
Page 165 and 166: following the heat demand. To follo
Page 167 and 168: C:\ My Documents\ Nic\ Thesis\ Old\
Page 169 and 170: As 1 kWh = 3610.3 kJ, and using lit
Page 171 and 172: Add Heat to Water Storage Tank Usin
Page 173 and 174: Use Stored Hot Water to Supply Heat
Page 175 and 176: information is given about the over
Page 177 and 178: [23] K. Foger, B. Godfrey, “Syste
Page 179 and 180: the gasification and pyrolysis defi
Page 181 and 182: eing used each day for a continuous
Page 183 and 184: Where Biogas = Biogas production ra
Page 185 and 186: 6.1.3 Use of Biogas Various options
Page 187 and 188: The amount of hydrogen that can be
Page 189 and 190: direct proportion, and the weight o
Page 191 and 192: produce in total (Nm 3 per tonne fe
Page 193 and 194: Electricity (kW) = Elec x Feed (6.1
Page 195 and 196: 3. Make hydrogen via steam reformin
Page 197 and 198: Where Methane = Methane Production
Page 199 and 200: (continued) Keep as medium heating
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Yes Feed1 = Yield1 x Land1 / No. of
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production and energy use profiles
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If it is the last timestep of the p
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For each process, the process chara
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At the end of the simulation, graph
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As the time required for one batch
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Ethanol = Factor1 x Eth x Timesteps
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6.5 Electrolysis As it is sometimes
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6.7 Landfill Gas Processing As the
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Demand Profile Design & Profile Dat
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Figure 7.2 Degree-Days Versus Month
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Stage 1 - Sustainable Fuel Supply S
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The different profile of use graphs
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Figure 7.3 Fermentation System Inpu
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Figure 7.7 Fermentation System Info
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Figure 7.10 Fermentation System Out
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The output obtained when a second h
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Figure 7.16 Anaerobic Digestion Par
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Figure 7.19 Fermentation System Inp
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clarity. A constant supply rate of
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Figure 7.25 Heat Demand Profile Fig
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Figure 7.28 Effect of Minimum Load
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esidual heat demand as this would r
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Figure 7.35 Second Engine: Followin
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This chapter described how the over
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heat and electricity during the tou
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Figure 8.2: Overall Yearly Heat Dem
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to allow for efficient operation du
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would be incurred, and the scale of
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Figure 8.5: Electricity Supply and
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heat demand or both, or run at cons
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ut with 30% less land being require
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9 Conclusions and Recommendations T
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through these, technically viable p
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considered. The introduction of coo
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When considering larger geographica
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Appendix 1: Program Windows Figure
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Figure A1.5 CreateClimate.exe Figur
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Figure A1.9: Demand Profile Designe
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Figure A1.13: Derived Fuel Supply W
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Figure A1.17: Fermentation System D
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Figure A1.21: PV Electrolysis Syste
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Figure A1.25: Fuel Supply Profile D
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Figure A1.29: Auxilliary Supply Def
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Figure A1.33: Stirling Engine Syste
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Figure A1.37: Fuel Cell System Defi
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Figure A1.41: Electric Vehicle Syst
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Figure A1.45: Vehicle Conversion Fa
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Figure A1.49: Heating System Defini
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Figure A1.53: Pumped Hydro System D
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Figure A1.57: Auto Search Evaluatio
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PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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