< prev - next > Energy Biogas biogas plants in animal husbandry (Printable PDF)
Overnight stabling
- dung only (10%
losses)
- dung and
urine,concrete
floor
1 kg/d moist dung
1 l/d manure
1 kg/d manure
1 kg TS/d
5-8
11-16
~200
180-
270
220-
320
~35
~20
~22
~240
1 kg VS/d
~250 ~300
220-310
260-380
8-10
16-20
240-
300
260-
330
~40 ~34
~25 ~20
~27 ~22
~200 ~240
~250 ~300
2290-
360
330-
410
-
-
-
-
~40 -
~24 ~50
~26 -
~227 ~340
0
~335 ~430
0
-
-
-
~60
-
Sizing the gasholder
The size of the gasholder, i.e. the gasholder volume (Vg), depends on the relative rates of gas
generation and gas consumption. The gasholder must be designed to:
- cover the peak consumption rate (Vg 1) and
- hold the gas produced during the longest zero-consumption period (Vg 2).
Vg1 = gc, max x tc, max = vc, max
Vg2 = G x tz, max
gc, max = maximum hourly gas consumption (m³/h)
tc, max = time of maximum consumption (h)
vc, max = maximum gas consumption (m³)
G = gas production (m³/h)
tz, max = maximum zero-consumption time (h)
The larger Vg-value (Vgl or Vg2) determines the size of the gasholder. A safety margin of 10-20%
should be added. Practical experience shows that 40-60% of the daily gas production normally has
to be stored. Digester volume vs. gasholder volume. (Vd: Vg) The ratio
Vd : Vg
is a major factor with regard to the basic design of the biogas plant. For a typical agricultural biogas
plant, the Vd/Vg-ratio amounts to somewhere between 3: 1 and 10: 1, with 5: 1 - 6: 1 occurring most
frequently.
4.4 Balancing the gas production and gas demand by iteration
As described in subsection 4.1, the biogas/ energy production (P) must be greater than the energy
demand (D).
P>D
This central requirement of biogas utilization frequently leads to problems, because small farms with
only a few head of livestock usually suffer from a shortage of biomass. In case of a negative
balance, the planner must check both sides - production and demand - against the following criteria:
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