Results summary
Lowest tonnage input and biogas yield estimate, Middle tonnage and biogas yield estimate, Highest tonnage and biogas yield estimate
The Lowest, middle and high values are defined by the entries on the FeedStockProperties sheet
Input feed properties
    Estimates    
  Lowest Middle Highest (Biomass)
Lorry loads of delivery each day 6.5 9.1 19.8 lorries/day from FeedTransportCosts sheet
Total tonnes per day 292.4 330.4 482.4 tonnes/day from InputFeedMix sheet
Dry solids content range of feed 9.1% 11.4% 12.7% % from InputFeedMix sheet. This should be between 6-15%. If too low, remove water or add dryer feed. If too high, add water.
Total dry solids per day 26.74 37.56 61.03 tonnes/day from InputFeedMix sheet
VS content of dry solids 86.8% 87.3% 87.5% % from InputFeedMix sheet
Total volatile solids per day 23.21 32.78 53.42 tonnes/day from InputFeedMix sheet
Volatile solids loading rate 3.92 4.90 5.47 kg/m^3/day from InputFeedMix sheet. This can be up to about 6-7 for a single stage, and 25-50 for a two-stage acidogenesis+methanogenesis system
Carbon:Nitrogen ratio 40.4 37.7 36.6 from CarbonNitrogen sheet. This should be between 20 and 30, optimum 25. Add Paper/sawdust to increase, blood or slurry to decrease
If Carbon/Nitrogen ratio is not in the 20-30 target range, biogas yields will be reduced
HRT and SRT        
Two stage process ?   NO     from BiogasYields sheet
HRT, 1st phase   20     from ParametersPlant sheet
HRT, 2nd phase   NA     from ParametersPlant sheet
SRT, 1st phase   20     from BiogasYields sheet
SRT, 2nd phase   NA     from BiogasYields sheet
SRT ratio 2nd phase/1st phase   NA     5-15 for a two-stage process
Digester properties
Input buffer diameter 11.27 11.74 13.32 m from DigesterSizing sheet
Input buffer height 11.27 11.74 13.32 m from DigesterSizing sheet
Pasteuriser diameter (each) 2.08 2.17 2.46 m from DigesterSizing sheet
Pasteuriser height (each) 2.08 2.17 2.46 m from DigesterSizing sheet
1st stage diameter (each) 15.56 16.21 18.39 m from DigesterSizing sheet
1st stage height (each) 15.56 16.21 18.39 m from DigesterSizing sheet
2nd stage diameter (each) NA NA NA m from DigesterSizing sheet
2nd stage height (each) NA NA NA m from DigesterSizing sheet
Digestate buffer diameter 19.04 19.73 22.33 m from DigesterSizing sheet
Digestate buffer height 19.04 19.73 22.33 m from DigesterSizing sheet
Temperatures
Pasteuriser 70.0 70.9 70.9 C from ThermalBalance sheet
1st stage digester 38.0 38.0 38.5 C from ThermalBalance sheet
2nd stage digester NA NA NA C from ThermalBalance sheet
Process problems affecting biogas yields
Approximate biogas yield (relative to baseline) due to inadequate SRT   93%     from BiogasYields sheet
Approximate biogas yield (relative to baseline) due to imperfect C:N ratio 35% 55% 66%   from BiogasYields sheet
Approximate biogas yield (relative to baseline) due to temperature excursions 100% 100% 99%   from BiogasYields sheet
Approximate biogas yield (relative to baseline) due to all above factors 32% 51% 60%  
Biogas/methane power outputs
Total biogas per day 2773.39 10472.94 28795.91 m^3 from BiogasYields sheet
Average biogas per tonne feed input (including water) 9.5 31.7 59.7 m^3/tonne from BiogasYields sheet
Average biogas per tonne feed input (excluding water) 30.0 80.3 102.0 m^3/tonne from BiogasYields sheet
Methane content range of biogas 50% 60% 65% % from BiogasYields sheet
Total methane per day 1386.70 6283.76 18717.34 m^3 from BiogasYields sheet
kWh per day @ 11.04 kWh/m^3 15309.13 69372.74 206639.42 kWh/day from BiogasYields sheet
kW average power (methane) 637.88 2890.53 8609.98 kW from BiogasYields sheet
Energy
Total methane energy yielded, of which 637.9 2890.5 8610.0 kW from BiogasYields sheet
Engine heat lost 74.8 260.1 774.9 kW from EngineSize sheet
Generator heat lost 10.4 49.1 146.4 kW from EngineSize sheet
Process heat required 110.9 204.6 292.6 kW from ThermalBalance sheet
Process electrical required 145.3 88.5 140.3 kW from ElectricalLoads sheet
Surplus electricity for export (import if negative) 52.1 845.2 2640.7 kW from ElectricalLoads sheet
Surplus heat (available for CHP export) 244.4 1443.0 4615.1 kW from ThermalBalance sheet
Check energy sum 637.9 2890.5 8610.0 kW Sum energy breakdown to check consistency
Surplus CHP water temperature 61 75 80 C from ThermalBalance sheet
Surplus CHP water at mass flow rate 1.11 5.13 15.28 kg/s from ThermalBalance sheet
Surplus CHP water must be returned at or above above   8   C from ParametersEngine sheet
Efficiency of electrical export, as a proportion of methane energy 8% 29% 31%  
Potential total efficiency of electrical plus CHP energy 46% 79% 84%  
Profitability index calculation, NPV using primary discount rate figure, for the 10-year investment
Plant capital cost 6,392 7,149 9,494 1000s
Invested capital amount (minus grant) 6,392 7,149 9,494 1000s
Total net present value of project at primary discount rate -1,843 5,498 34,950 1000s
Profitability index (=NPV/Capital investment) -0.29 0.77 3.68  
Internal rate of return (IRR) 1.6% 14.9% 20.5%