< prev - next > Energy Biogas biogas plants in animal husbandry (Printable PDF)
Using the nomogram
1. Quadrant I: Determine the net calorific value under standard conditions as a function of the
CH4-fraction of the biogas
2. Quadrant II: Determine the net calorific value for a given gas temperature
3. Quadrant III: Determine the net calorific value as a function of absolute gas pressure (P)
4. Quadrant IV: Interim calculation for determining the partial water-vapor pressure as a function
of gas temperature and relative dampness. This yields the gas pressure (PF) = absolute
pressure (P) - partial pressure of water vapor (PW); PF = P - PW. The expanded calorific value
determination with account for the moisture content occurs via quadrant III.
Sample calculation
Given:
Biogas
Gas temperature
Gas dampness
Gas pressure
55 vol. % CH4
T = 40 °C
F = 100%
P = 1030 mbar
Results:
Hu, N
Hu,T
Hu,T,P
PF
- f(PW)
= f (CH4-vol. 70)
= 5.5 kWh/m³
= f(T)
= 4.8 kWh/m³
= f(T, P)
= 4.6 kWh/m³
= f(P, T)
Hu, T, PF = 4.3 kWh/m³
Table 10.3: Partial pressure of water vapor, PW, and absolute humidity, GM, at the saturation
point (Source: Recknagel / Sprenger, 1982)
T (°C)
.0
10
20
30
40
50
60
70
80
90
100
PW (mbar)
6.1
12.3
23.4
42.4
73.7
123.3
199.2
311.6
473.6
701.1
1013.3
GM (g/m³)
4.9
9.4
17.3
30.4
51.2
83.0
130.2
198.2
293.3
423.5
597.7
119