Environmental Engineering Reference
In-Depth Information
Table 11.4
Fugitive emissions as a percentage of seasonal biogas production
rates
Winter
a
Spring
b
Summer
c
Autumn
Average
Normal (%)
2.9
2.7
5.2
1.7
3.1
Flaring (%)
20
25
—
13
19
Maintenance (%)
0.5
—
1.8
—
1.2
a
No maintenance during winter measurements.
b
No flaring during the spring measurement; also low biogas production due to
non-ideal feedstock material.
c
No maintenance during summer measurements.
were measured during autumn, winter, spring and summer seasonal
campaigns, with each campaign lasting 6-7 days. Three operation periods
were identified - high emissions during biogas flaring low emissions during
plant maintenance and emissions during normal operation. The seasonal
fugitive emissions as a percentage of methane production rates are shown in
Table 11.4. The results show that during normal operations, the emissions
ranged from 1.7% in the summer to 5.2% in the spring. Over all four
seasons, the average was 3.1% of gas production. The emission rate over
any prolonged period will ultimately depend on the frequency of flaring and
maintenance. During normal operations,
the feedstock hopper was
identified as the main source of emissions.
In a report for Avfall Sverige (a Swedish waste management company),
Rylander and Wiqvist (2007a, 2007b) elaborate on how to measure
emissions in biogas plants, but do not include any measured result. The
report is based on Swedish installations. The authors describe the voluntary
agreement for biogas plants, introduced in 2007 by Avfall Sverige, whereby
the owners of biogas plant commit themselves to identify and reduce their
emissions systematically. Their report explains how the system is built,
including a systematic method for leak detection and emission measure-
ments, reporting and methods for reducing emissions. The system boundary
is defined as only those items owned by the owner of the plant and the items
that the owner may influence. Therefore, items related to the compression of
biogas, propane dosing for injection into the net, gas storage and filling
stations fall outside the system boundary. In addition, the system covers
only the parts that are related to the production, purification and upgrading
of biogas. Emissions associated with the use of gas (CHP), manure and
digestate and the emissions associated with transport of substrates,
fertilizers and gas are not included in the system. Of the greenhouse gases
in a biogas system, only methane is considered to be in the system.
The most critical points in a biogas plant are the parts that are not
coupled to the gas system of the plant, but still may have emissions of
methane. According to Rylander and Wiqvist, the main emission points in a
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