PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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Larger scale biodiesel production can take place through a continuous process that goes through the same stages as the batch process and is, therefore, not easily stopped and started [72]. The energy required for either process is around 2% of the electricity and 3% of the heat that would be obtained from a typical suitable CHP plant using the fuel produced [73]. A substantial amount of alcohol is required for this process, and methanol is the easier alcohol to use, though it is more difficult to make in a sustainable manner. Suitable processes are beginning to be developed using ethanol, which can be made by fermentation, as described in the next section. The batch transesterification process can be time consuming, and safety precautions must be taken at all stages due to the chemicals being used and the reactions taking place. 2.5.4 Fermentation Fermentation is the biological conversion of sugar, starch or cellulose, to ethanol and carbon dioxide, through anaerobic respiration by yeast or other organisms. Roughly half of the weight of sugars is converted to ethanol, and half to carbon dioxide, and the ethanol produced has roughly 90% of the energy content of the sugars used, or roughly 96% of the heat of combustion of the cellulose used. The carbon dioxide produced is pure, and can be sold to industry [17]. Possible feedstocks for fermentation include sugar cane, sugar beet, fruit waste, wheat, cereals, potatoes, wood, newspapers, and municipal waste. Of these feedstocks, grains can be stored without degradation, but tubers, fruits and beet crops rot rapidly once harvested, and should be used as soon as possible. Any crop residues remaining after the harvest of energy crops, can be burned directly to produce heat and/or electricity, or put into an anaerobic digester or gasifier, depending on the residue type, and energy needs [74]. Pre-treatment of the feedstock is required to produce simple, fermentable sugars (glucose and fructose), and the type of pre-treatment required depends on the 54
feedstock being used. Sugary feedstocks (such as sugar beet or fruit waste) require crushing and mixing with water in order to release these sugars. Starchy feedstocks may require grinding or milling to free the starchy material, and cooking in water to dissolve and gelatinise the starch. Cellulosic materials may require chipping or similar pre-processing. Hydrolysis of starchy and cellulosic feedstocks is then necessary, where enzymes are added to break down the starch and cellulose to glucose and fructose. The exothermic fermentation process may then take place where the produced sugars are diluted in water, and yeast or other organisms are added to break down the sugars and convert them to ethanol in solution with water (roughly 10% ethanol by volume). Distillation then takes place to remove the water and other wastes, to produce 95% ethanol by volume [68,75]. An overview of the general ethanol production process is given in Figure 2.7. Various residues are produced by this process. The non-soluble component separated before fermentation, and the solids separated after fermentation, are known as stillage. This can be used as an animal feed or fertiliser, sent to an anaerobic digester, or dried and used directly as a fuel in boilers, engines or turbines. The liquid remaining after distillation is known as vinasse, and this may be sent to an anaerobic digester, or used as an animal feed or fertiliser [17]. Again, small-scale production of ethanol by fermentation is batch-wise, and various larger scale commercial continuous processes also exist [76-78]. The time for one batch can be between two to four days, but a few fermenters can be run simultaneously to allow a daily production. Batch production processes can take up to two tonnes of feedstock per batch, and continuous ethanol production plants can process from 15 kg/hr upwards. The amount of ethanol and carbon dioxide produced, and the amount of electricity and heat required vary with the feedstock and process being used. A substantial use is often made of crop residues and stillage to provide some or all of the process energy requirements [79-81]. A large amount of water is required for this process, which makes it unsuitable for some areas. 55
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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 and 36: set times, producing a constant ele
Page 37 and 38: partial load. Fast response and sta
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: 1. Scale for measuring out lye and
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
Page 87 and 88: ates for vehicles, engines and othe
Page 89 and 90: Figure 4.5 Derived Fuel Production
Page 91 and 92: together if desired, and taken forw
Page 93 and 94: profiles are output from this part
Page 95 and 96: dividing the production rate at eac
Page 97 and 98: 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
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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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