PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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ut only fuelled Stirling engines will be considered here. This type of engine has many advantages over other engines and turbines as it allows the use of fuels that are hard to process, and it has a fairly simple design, which makes it suitable for small-scale applications, gives the plant a lower capital cost and reduces maintenance costs. Theoretical efficiency is also greater than steam turbines (discussed later), which can also use the same types of fuel, and Stirling engines are particularly suited to CHP production due to the large amount of heat that is passed through the engine cooler [25]. Interest in Stirling engines is beginning to re-emerge due to increased interest in biofuel use; however, they are not yet commonly used. Currently available Stirling engine generating set outputs vary from 1 kWe to 200kWe, although larger engines are feasible. Electrical efficiencies can vary from 15 to 35%, and heat to electricity ratios can be from 1.5:1 to 5:1, again, varying with partial load [27,6]. Stirling engines are better suited to constant loads at specified times of the day and year or continuous operation, rather than load following, due to their fairly slow response times. They are generally run constantly, and sized to provide for the heat demand, with hot water storage smoothing out the peaks and troughs, and electricity production sent to the grid [28,29]. Engines may be run on any number of combustible fuels, including biodiesel, biogas, straw and wood, with varying efficiencies depending on the plant and fuel used [30,31]. 2.2.3 Gas Turbines Another common type of plant used for electricity and heat generation is the gas turbine. Gas turbines may be run on biogas, and are available with rated outputs of between 3 and 50MWe [32]. Their operation is based on the Brayton Cycle, where incoming air is compressed to a high pressure, fuel added to the air is burned to increase the gas temperature and pressure, and the resulting gases are expanded across the turbine blades, giving rotational movement [25]. Coupled to a generator, this provides electricity generation, and waste heat may also be recovered for use. Heat to electricity ratios are typically in the order of 2:1, and electrical efficiencies at full load are around 25 to 30%, again varying with 36
partial load. Fast response and start-up times make gas turbines suitable for load following applications. 2.2.4 Steam Turbines For larger applications (between 1 and 1000 MW), steam turbines may be used. These use an external boiler to raise steam, which may be fuelled by any type of solid, liquid or gaseous fuel desired. This steam is then expanded across turbine blades to produce rotary motion, and, when coupled with a generator, electricity [25,30,31]. Again, waste heat may be recovered for use. Electrical efficiencies at full load can range from 15 to 50%, depending on the complexity of design. This means that heat to electricity ratios can vary from 1:1 to 5:1, and it is common practice to use a simple, electrically inefficient and relatively inexpensive turbine when there is a useful outlet for large quantities of waste heat. This generation method is particularly suited to the use of large quantities of solid waste or biomass, provided suitable boilers are used, though start-up times are slow. The efficiency of a steam turbine decreases, and the heat to electricity ratio increases at lower loads. 2.2.5 Fuel Cells The principle of the fuel cell was discovered over 150 years ago, but was not significantly developed until NASA started to investigate their emission free operation for use in spacecraft. Over the past two decades, further investigation has also been carried out into their use in vehicles, and in stationary and portable applications. As a result of this increased interest, stationary power plants from 200W to 2 MW are now commercially available, with efficiencies ranging from 30 to 50% and heat to electricity ratios from 0.5:1 to 2:1 [33-35]. As the efficiency of a fuel cell typically increases at lower loadings, the opposite situation to all the other plant being considered here, fuel cells are more suited for low load factor applications, and this, coupled with their fast response, make them well suited to load following and transport applications. 37
Page 1 and 2: Decision Support for New and Renewa
Page 3 and 4: Abstract The global requirement for
Page 5 and 6: CONTENTS 1 ENERGY SYSTEMS FOR SUSTA
Page 7 and 8: 5.5 Steam Turbine Model 149 5.6 Fue
Page 9 and 10: FIGURES Figure 1.1 Final Energy Con
Page 11 and 12: Figure 7.30 Following Electricity a
Page 13 and 14: on the use of fossil fuels, energy
Page 15 and 16: The general increase in energy cons
Page 17 and 18: supply is reduced or eliminated, lo
Page 19 and 20: Figure 1.3 The Electricity Supply G
Page 21 and 22: on different generation mixes depen
Page 23 and 24: Various studies have been carried o
Page 25 and 26: provision for smaller areas, and he
Page 27 and 28: 1.7 References [1] The Internationa
Page 29 and 30: 2 Options for New and Renewable Ene
Page 31 and 32: the amount of usable heat that is g
Page 33 and 34: the conversion of petrol cars; howe
Page 35: set times, producing a constant ele
Page 39 and 40: 2.3 The Production and Storage of H
Page 41 and 42: dedicated boiler, which runs contin
Page 43 and 44: Figure 2.3 A Typical Hydrogen Filli
Page 45 and 46: part of the natural carbon cycle (a
Page 47 and 48: Figure 2.4 Layout of a Gasification
Page 49 and 50: met by process integration and the
Page 51 and 52: Figure 2.5 The Inputs and Outputs o
Page 53 and 54: 1. Scale for measuring out lye and
Page 55 and 56: feedstock being used. Sugary feedst
Page 57 and 58: carbon dioxide via steam reforming.
Page 59 and 60: • Where CHP is used, the balance
Page 61 and 62: [22] Vehicle Certification Agency (
Page 63 and 64: [55] M. A. Paisley, J. M. Irving, R
Page 65 and 66: 3 Approaches to Renewable Energy Sy
Page 67 and 68: Because of the intermittent nature
Page 69 and 70: A renewable energy supply evaluatio
Page 71 and 72: the system are kept. The output of
Page 73 and 74: There are various models available
Page 75 and 76: When the use of climate dependant i
Page 77 and 78: 3.5 References [1] M. Muselli, G. N
Page 79 and 80: 4 A Procedure for Demand and Supply
Page 81 and 82: pumped storage and flywheels), a ba
Page 83 and 84: for the agricultural vehicle use re
Page 85 and 86: 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
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Figure 4.12 Output of the Matching
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However, when more than one transpo
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considered, this amount is added to
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users are alerted if there is not e
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at the matching stage, along with t
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vehicles if they are increased by 1
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If biogas is being considered, the
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The number of timesteps per hour wi
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After the algorithm has been follow
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• Float Charge - once the battery
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Discharge No tank = tank fuel used
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equired (kW) = maxkWh x bulk% (5.16
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An example of the output graph prod
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5.2.1 Required Power Specifically d
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5.2.3 Engine Performance in the Con
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used for gas powered ICEs, but the
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and five times, depending on the nu
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Is PL < Min ? No Is PL = 0 ? No Is
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where Max = maximum energy availabl
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where Ratiopart = heat to electrici
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(including following heat demand wh
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where SFC = specific fuel consumpti
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engines running respectively). If t
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(continued) Is Fuel Available > (4
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of the definition window for a Stir
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and continuous operation. Again, mu
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The performance of a fuel cell is n
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percentage loading, rather than usi
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Is Min = 0 ? No Is Min = PC1 ? No I
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5.6.4 If Fuel Availability is Less
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5.7 Electrolyser Model An electroly
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original calculation of the amount
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5.8 Regenerative Fuel Cell Model A
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following the heat demand. To follo
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C:\ My Documents\ Nic\ Thesis\ Old\
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As 1 kWh = 3610.3 kJ, and using lit
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Add Heat to Water Storage Tank Usin
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Use Stored Hot Water to Supply Heat
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information is given about the over
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[23] K. Foger, B. Godfrey, “Syste
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the gasification and pyrolysis defi
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eing used each day for a continuous
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Where Biogas = Biogas production ra
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6.1.3 Use of Biogas Various options
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The amount of hydrogen that can be
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direct proportion, and the weight o
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produce in total (Nm 3 per tonne fe
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Electricity (kW) = Elec x Feed (6.1
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3. Make hydrogen via steam reformin
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Where Methane = Methane Production
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(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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