Methane emissions in biogas production - The Biogas: Science, Production and Applications - page 251

Table 11.3 Results of methane slip measurements in gas engines

CH 4
concentration
in biogas
(mg/Nm 3 )

CH 4
concentration
in flue gas
(mg/Nm 3 )

Electric
power (We) Source Remarks

Germany 30-340 55 290 Refers to C n H m

emissions, which are
approximately
equivalent to the CH 4
concentration for
combustion of biogas

Denmark — 65 880-920 2200-2300 for natural

gas with a conversion
factor for biogas of 0.4

Austria
(4 different
biogas
-CHP plants)

348
249
130
130

64
61
60
60

861
2333
280
293

Laaber et al . 500 55 1100 The value stated was

1.79% of the CH 4 input
(assumption of 5%
oxygen concentration in
the CHP flue gas)

(2007)

employed, emissions are much lower because their permeability is only 10%
of the permeability of EPDM membranes. In newer plants, the application
of double membranes is considered to be 'state of the art'.

11.3 Methane emissions in biogas utilization, biogas
upgrading and digestate storage

11.3.1 Biogas utilization and upgrading

￿ ￿ ￿ ￿ ￿ ￿

Combined heat and power

Liebetrau et al. (2011a, 2011b) concluded that biogas utilization in a gas
engine was the second major source of methane emissions. Methane slip
measurements for eight combined heat and power (CHP) systems with
different capacities showed emissions ranging from 0.44 to 2.43% of the
utilized methane.
Work by Woess-Gallasch et al. (2007a, 2007b) gives an overview of results
provided in the literature for emissions as a result of methane slip in CHP
engines, together with results of methane concentration measurements in
flue gases of biogas-powered CHP plants in Austria, Denmark and
Germany (see Table 11.3). The measured values are between 280 and