Methane emissions in biogas production - The Biogas: Science, Production and Applications - page 252

11.2 Methane emissions from a pilot CHP injection as a function of the
methane potential.

2333mg/Nm 3 . Going by these results, a methane slip value of 1.79% could
be considered as representative, since the resulting methane concentration of
1100mg/Nm 3 lies in the middle of the spectrum of the presented values,
which agrees with the results reported by Liebetrau et al. (2011a, 2011b).
Laaber et al. (2007) report that, in biogas CHP, the methane
concentration decreases with increasing methane content in the biogas.
The relationship is shown in Fig. 11.2. Laaber et al. (2007) confirmed the
result of methane emissions from biogas CHP. The methane slip of a
500 kWe CHP with an average concentration of about 55% methane in
clean biogas was 1.79% of the total annual amount of methane.
In a study and follow-ups commissioned by the Dutch government,
KEMA reported the results of measurement programs (Oltuis and Engelen,
2007; Engelen, 2009; Oltuis, 2010) on methane emissions from natural-gas-
fueled gas engines. The studies revealed many measurement uncertainties,
which were attributed to sampling errors and errors related to measurement
methods such as exhaust gas conditioning, accuracy of calibration gases and
specifications of the analysis equipment employed. The methane emissions
ranged from 0.6 to 3.0% of the fuel input. A further study from the
Netherlands by de Zwart et al. (2011) referred to the KEMA measurements
and the uncertainties revealed, and reported on methane emissions from gas
engines in CHPs at horticulture companies in the Netherlands. The article
was not based on new measurements, but explained what and how process
parameters can influence the methane slip.
Finally, a Danish study by Kristensen et al. (date of report unknown)
reported on gas engines between 1992 and 1998, based on around 500 field

￿ ￿ ￿ ￿ ￿ ￿