where:
D = density of biogas (g/l)
DN = density under s.t.p. conditions (0 °C, 1013 mbar)
V = volume of biogas (m³)
VN = volume of biogas under s.t.p. conditions
P = absolute pressure of biogas (mbar)
PN = pressure under s.t.p. conditions (1013 mbar)
T = absolute temperature of biogas (measured in ºKelvin = ºC + 273)
TN= temperature under s.t.p. conditions (0 0ºC = 273 °K)
Table 10.2: Atmospheric pressure as a function of elevation (Source: Recknagel/Sprenger,
1982)
Elevation (km)
0 0.5 1.0 2 3 4 6 8
Atm.pressure (mbar) 1013
955
899
795
701
616
472
365
Determining the calorific value
Fig. 10.9: Nomogram for
correcting gas
pressures/temperatures
(Source: OEKOTOP)
Fig. 10.10: Nomogram for finding the net calorific
value of biogas as a function of temperature,
pressure and moisture content. T gas temperature
(°C), F relative dampness of biogas (%), Hu, N net
calorific value (n.c.v.) of biogas under s.t.p.
conditions (0 °C, 1013 mbar), Hu, T net calorific
value (n.c.v.) at gas temperature, P gas pressure
(mbar), Hu, T, P net calorific value (n.c.v.) at gas
temperature and pressure, PW partial pressure of
water vapor, Hu, T, PF net calorific value (n.c.v.) of
biogas at gas temperature, corrected to reflect the
water-vapor fraction (Source: OEKOTOP)
118