Results
summary |
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Lowest
tonnage input and biogas yield estimate, Middle tonnage and biogas yield
estimate, Highest tonnage and biogas yield estimate |
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The Lowest,
middle and high values are defined by the entries on the FeedStockProperties
sheet |
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Input feed properties |
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Estimates |
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Lowest |
Middle |
Highest |
(Biomass) |
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Lorry loads of delivery
each day |
5.0 |
6.6 |
9.3 |
lorries/day |
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from FeedTransportCosts sheet |
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Total
tonnes per day |
1.4 |
1.9 |
2.7 |
tonnes/day |
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from InputFeedMix sheet |
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Dry
solids content range of feed |
5.2% |
6.8% |
9.7% |
% |
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from InputFeedMix sheet. This should be
between 6-15%. If too low, remove water or add dryer feed. If too high, add
water. |
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Total
dry solids per day |
0.07 |
0.13 |
0.26 |
tonnes/day |
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from InputFeedMix sheet |
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VS
content of dry solids |
77.2% |
77.3% |
76.2% |
% |
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from InputFeedMix sheet |
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Total
volatile solids per day |
0.06 |
0.10 |
0.20 |
tonnes/day |
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from InputFeedMix sheet |
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Volatile
solids loading rate |
1.98 |
2.58 |
3.65 |
kg/m^3/day |
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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 |
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Carbon:Nitrogen
ratio |
17.3 |
17.7 |
17.0 |
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from CarbonNitrogen sheet. This should be
between 20 and 30, optimum 25. Add Paper/sawdust to increase, blood or slurry
to decrease |
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If Carbon/Nitrogen ratio is not in the 20-30
target range, biogas yields will be reduced |
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HRT and SRT |
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Two stage
process ? |
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NO |
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from BiogasYields sheet |
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HRT, 1st
phase |
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20 |
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from ParametersPlant sheet |
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HRT, 2nd
phase |
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NA |
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from ParametersPlant sheet |
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SRT,
1st phase |
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20 |
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from BiogasYields sheet |
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SRT,
2nd phase |
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NA |
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from BiogasYields sheet |
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SRT
ratio 2nd phase/1st phase |
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NA |
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5-15 for a two-stage process |
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Digester properties |
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Input buffer diameter |
1.92 |
2.10 |
2.35 |
m |
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from DigesterSizing sheet |
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Input
buffer height |
1.92 |
2.10 |
2.35 |
m |
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from DigesterSizing sheet |
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Pasteuriser
diameter (each) |
0.35 |
0.39 |
0.43 |
m |
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from DigesterSizing sheet |
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Pasteuriser
height (each) |
0.35 |
0.39 |
0.43 |
m |
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from DigesterSizing sheet |
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1st
stage diameter (each) |
3.34 |
3.65 |
4.09 |
m |
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from DigesterSizing sheet |
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1st
stage height (each) |
3.34 |
3.65 |
4.09 |
m |
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from DigesterSizing sheet |
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2nd
stage diameter (each) |
NA |
NA |
NA |
m |
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from DigesterSizing sheet |
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2nd
stage height (each) |
NA |
NA |
NA |
m |
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from DigesterSizing sheet |
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Digestate
buffer diameter |
3.27 |
3.56 |
3.97 |
m |
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from DigesterSizing sheet |
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Digestate
buffer height |
3.27 |
3.56 |
3.97 |
m |
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from DigesterSizing sheet |
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Temperatures |
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Pasteuriser |
70.0 |
70.4 |
70.5 |
C |
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from ThermalBalance sheet |
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1st
stage digester |
36.0 |
38.0 |
38.0 |
C |
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from ThermalBalance sheet |
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2nd
stage digester |
NA |
NA |
NA |
C |
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from ThermalBalance sheet |
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Process problems
affecting biogas yields |
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Approximate biogas yield
(relative to baseline) due to inadequate SRT |
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93% |
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from BiogasYields sheet |
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Approximate
biogas yield (relative to baseline) due to imperfect C:N ratio |
126% |
128% |
124% |
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from BiogasYields sheet |
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Approximate biogas yield
(relative to baseline) due to temperature excursions |
96% |
100% |
100% |
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from BiogasYields sheet |
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Approximate biogas yield
(relative to baseline) due to all above factors |
112% |
119% |
115% |
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Biogas/methane power
outputs |
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Total biogas per day |
29.26 |
60.79 |
122.52 |
m^3 |
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from BiogasYields sheet |
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Average biogas per tonne
feed input (including water) |
20.3 |
32.3 |
46.1 |
m^3/tonne |
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from BiogasYields sheet |
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Average
biogas per tonne feed input (excluding water) |
20.3 |
32.3 |
46.1 |
m^3/tonne |
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from BiogasYields sheet |
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Methane
content range of biogas |
54% |
60% |
66% |
% |
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from BiogasYields sheet |
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Total
methane per day |
15.66 |
36.48 |
81.07 |
m^3 |
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from BiogasYields sheet |
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kWh per
day @ 11.04 kWh/m^3 |
172.87 |
402.70 |
895.04 |
kWh/day |
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from BiogasYields sheet |
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kW
average power (methane) |
7.20 |
16.78 |
37.29 |
kW |
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from BiogasYields sheet |
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Energy |
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Total methane energy
yielded, of which |
7.2 |
16.8 |
37.3 |
kW |
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from BiogasYields sheet |
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Engine heat lost |
2.0 |
4.2 |
8.3 |
kW |
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from EngineSize sheet |
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Generator
heat lost |
0.1 |
0.2 |
0.5 |
kW |
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from EngineSize sheet |
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Process heat required |
1.8 |
2.4 |
3.1 |
kW |
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from ThermalBalance sheet |
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Process
electrical required |
0.4 |
0.5 |
0.7 |
kW |
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from ElectricalLoads sheet |
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Surplus
electricity for export (import if negative) |
1.3 |
3.6 |
8.9 |
kW |
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from ElectricalLoads sheet |
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Surplus
heat (available for CHP export) |
1.6 |
5.9 |
15.7 |
kW |
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from ThermalBalance sheet |
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Check energy sum |
7.2 |
16.8 |
37.3 |
kW |
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Sum energy breakdown to check consistency |
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Surplus CHP water
temperature |
44 |
63 |
72 |
C |
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from ThermalBalance sheet |
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Surplus
CHP water at mass flow rate |
0.01 |
0.03 |
0.06 |
kg/s |
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from ThermalBalance sheet |
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Surplus
CHP water must be returned at or above above |
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8 |
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C |
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from ParametersEngine sheet |
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Efficiency of
electrical export, as a proportion of methane energy |
18% |
22% |
24% |
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Potential
total efficiency of electrical plus CHP energy |
40% |
56% |
66% |
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Profitability
index calculation, NPV using primary discount rate figure, for the 10-year
investment |
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Plant capital cost |
£359 |
£407 |
£481 |
£1000s |
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Invested
capital amount (minus grant) |
£251 |
£285 |
£337 |
£1000s |
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Total
net present value of project at primary discount rate |
-£757 |
-£773 |
-£978 |
£1000s |
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Profitability
index (=NPV/Capital investment) |
-3.01 |
-2.71 |
-2.90 |
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Internal
rate of return (IRR) |
31.8% |
33.1% |
32.2% |
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