Sample calculations
Energy demand (D)
Basic data
8-person family, 2 meals per day. Present rate of energy consumption: 1.8 1 kerosene per day for cooking and fueling 1 lamp (0.6 1 kerosene = 1 m³ biogas).
Desired degree of coverage with biogas
Cooking: all
Lighting: 2 lamps, 3 hours each
Cooling: 60 I refrigerator
Daily gas demand (D)
Cooking
1. Present fuel demand for cooking:
1.21 kerosene = 2 m³ gas
2. Gas demand per person and meal:
0.15 m³ biogas
Gas demand per meal: 1.2 m³ biogas
Cooking-energy demand: 2.4 m³ biogas
3. Consumption rate of gas burner:
175 l/h per flame (2-flame cooker)
Operating time: 2 x 3 h + 1 h for tea
Biogas demand: 7 h x 3501 = 2.5 m³
Defined cooking-energy demand:
2.5 m³ biogas/d
Lighting
Gas consumption of lamp: 120 1/h
Operating time: 2 x 3 h = 6 h
Biogas demand: 0.7 m³/day
Cooling (60 l refrigerator)
Specific gas demand: 30 1/h
Biogas demand: 0.7 m³/day
Total biogas demand: 3.9 m³/d
Biomass supply/Biogas production (P)
Basic data
9 head of cattle, 230 kg each, 24-h stabling,
green matter from garden as supplement.
Daily biomass incidence
Animal dung, calculated as % liveweight (as per 1.) or as daily yield per head (as per 2.) as listed in pertinent literature..
1. Dung as % liveweight
Daily yield per head of cattle: 10% of
230 kg = 23 kg/d
Volatile solids/d: 1.8 kg VS per day and animal
Total yield: 207 kg/d (16 kg VS/d)
2. Manure yield on per-head basis
Dung yield per head of cattle: 15 kg/d
Urine: 9 1/d
Volatile solids: 9% = 2.1 kg VS/d
Total yield: 216 kg/d (19 kg VS/d)
Useful percentage: 75%
The lowest values are used as the basis of calculation.
Green matter: 20 kg agricultural waste with 30% VS.
Total biomass incidence 170 kg/d (18 kg VS/d)
Category 1: cattle 150 kg (12 kg)
Category 2: green matter 20 kg ( 6 kg)
Sizing the plant
Basic data (calculation for category 1)
Daily biomass: 150 kg/d
VS: 12kg/d
TS-content: 12%
Soil temperature: max 31 °C, min. 22 °C, average 25 °C
Digester volume (Vd)
Retention time (chosen): RT = 60 d (at
25 °C, i.e. f = 1.0)
Substrate input: Sd = biomass + water
Digester TS-content: = 7% (chosen)
Daily water input: Wd = 100 kg
Sd= 100+ 150=250 l
Digester volume: Vd = 250 1 x 60 d = 15 000 = 15 m³
Daily biogas yield
G = kg/d VS x Gy,vs .
= 12 kg/d x 0.25 = 3.0 m³/d
G = kgid biomass x Gy (moist)
= 150 x 0.02 = 3.0 m³/d
G = number of animals x Gy per animal x d
= 9 x 0.35 = 3.2 m³/d
Anticipated daily biogas yield = 3.0 m³/d
Balancing the biogas production and demand
Demand: 3.9 m³/d
Production: 3.0 m³/d
Changes/accommodations
On the demand side: 1 less lamp, reducing the demand to 3.55 m³
Production side: increasing the digester volume to 18 m³, resulting in a retention time of 75 days (f = 1.2) and a daily gas yield of 3.6 m³
Plant parameters
Digester volume: Vd = 18m³
Daily gas production: G = 3.6 m³
Daily substrate input: Sd = 2501
Specific gas production:
Gp = G : Vd
Gp = 3.6 (m³/d): 18 m³ = 0.2 m³/m³ Vd x d
Digester loading:
Ld = TS/VS-input: Vd
Ld = 18: 18 = 1.0 kgTS/m³ Vd
Ld = 12: 18 = 0.7 kg VS/m³ Vd
Gasholder volume:
Vg = 1.6 m³, as calculated on the basis of:
consumption volume:
Vg1 = 0.175 m³/h x 2 flames x 3 h = 1.05 m3
Storage volume:
Vg2 = 10 h x 0.15 m³ gas/h = 1.5 m³
Vd:Vg=18: 1.6=11 :1
Basic data
8-person family, 2 meals per day. Present rate of energy consumption: 1.8 1 kerosene per day for cooking and fueling 1 lamp (0.6 1 kerosene = 1 m³ biogas).
Desired degree of coverage with biogas
Cooking: all
Lighting: 2 lamps, 3 hours each
Cooling: 60 I refrigerator
Daily gas demand (D)
Cooking
1. Present fuel demand for cooking:
1.21 kerosene = 2 m³ gas
2. Gas demand per person and meal:
0.15 m³ biogas
Gas demand per meal: 1.2 m³ biogas
Cooking-energy demand: 2.4 m³ biogas
3. Consumption rate of gas burner:
175 l/h per flame (2-flame cooker)
Operating time: 2 x 3 h + 1 h for tea
Biogas demand: 7 h x 3501 = 2.5 m³
Defined cooking-energy demand:
2.5 m³ biogas/d
Lighting
Gas consumption of lamp: 120 1/h
Operating time: 2 x 3 h = 6 h
Biogas demand: 0.7 m³/day
Cooling (60 l refrigerator)
Specific gas demand: 30 1/h
Biogas demand: 0.7 m³/day
Total biogas demand: 3.9 m³/d
| 1st priority: cooking | 2.5 m³ |
| 2nd priority: 1 lamp | 0.35 m³ |
| 3rd priority: 1 lamp/refigerator | 1.05 m³ |
Basic data
9 head of cattle, 230 kg each, 24-h stabling,
green matter from garden as supplement.
Daily biomass incidence
Animal dung, calculated as % liveweight (as per 1.) or as daily yield per head (as per 2.) as listed in pertinent literature..
1. Dung as % liveweight
Daily yield per head of cattle: 10% of
230 kg = 23 kg/d
Volatile solids/d: 1.8 kg VS per day and animal
Total yield: 207 kg/d (16 kg VS/d)
2. Manure yield on per-head basis
Dung yield per head of cattle: 15 kg/d
Urine: 9 1/d
Volatile solids: 9% = 2.1 kg VS/d
Total yield: 216 kg/d (19 kg VS/d)
Useful percentage: 75%
The lowest values are used as the basis of calculation.
Green matter: 20 kg agricultural waste with 30% VS.
Total biomass incidence 170 kg/d (18 kg VS/d)
Category 1: cattle 150 kg (12 kg)
Category 2: green matter 20 kg ( 6 kg)
Sizing the plant
Basic data (calculation for category 1)
Daily biomass: 150 kg/d
VS: 12kg/d
TS-content: 12%
Soil temperature: max 31 °C, min. 22 °C, average 25 °C
Digester volume (Vd)
Retention time (chosen): RT = 60 d (at
25 °C, i.e. f = 1.0)
Substrate input: Sd = biomass + water
Digester TS-content: = 7% (chosen)
Daily water input: Wd = 100 kg
Sd= 100+ 150=250 l
Digester volume: Vd = 250 1 x 60 d = 15 000 = 15 m³
Daily biogas yield
G = kg/d VS x Gy,vs .
= 12 kg/d x 0.25 = 3.0 m³/d
G = kgid biomass x Gy (moist)
= 150 x 0.02 = 3.0 m³/d
G = number of animals x Gy per animal x d
= 9 x 0.35 = 3.2 m³/d
Anticipated daily biogas yield = 3.0 m³/d
Balancing the biogas production and demand
Demand: 3.9 m³/d
Production: 3.0 m³/d
Changes/accommodations
On the demand side: 1 less lamp, reducing the demand to 3.55 m³
Production side: increasing the digester volume to 18 m³, resulting in a retention time of 75 days (f = 1.2) and a daily gas yield of 3.6 m³
Plant parameters
Digester volume: Vd = 18m³
Daily gas production: G = 3.6 m³
Daily substrate input: Sd = 2501
Specific gas production:
Gp = G : Vd
Gp = 3.6 (m³/d): 18 m³ = 0.2 m³/m³ Vd x d
Digester loading:
Ld = TS/VS-input: Vd
Ld = 18: 18 = 1.0 kgTS/m³ Vd
Ld = 12: 18 = 0.7 kg VS/m³ Vd
Gasholder volume:
Vg = 1.6 m³, as calculated on the basis of:
consumption volume:
Vg1 = 0.175 m³/h x 2 flames x 3 h = 1.05 m3
Storage volume:
Vg2 = 10 h x 0.15 m³ gas/h = 1.5 m³
Vd:Vg=18: 1.6=11 :1
