International Review of Waste Management Policy - Department of ...

If the biogas is cleaned of impurities it can be subsequently used as a vehicle fuel,
displacing the use of diesel. Our assumptions for modelling this option assume the
fuel to be used within a fleet of vehicles, re-fuelled from a central point, as is the
practice in Scandinavia and France. Some modification to the vehicle will be required
to allow it to run on gas as opposed to diesel. Assumptions used to model this option
are summarised in Table 63-30.
Table 63-30: Emissions from the Use of Biogas in a Vehicle
Parameter Parameter
Assumption
Assumption
Energy used during upgrade process 0.2 kWh / Nm 3 biogas
Process losses for CH4 (from upgrade process) 2%
Fuel consumption of CBG bus 23.4 MJ / km
Emissions avoided by diesel production 13.63 g CO2 equ / MJ
Emissions from diesel bus 1,226 g CO2 equ / km
Sources: W. Urban (2008) Methods and costs of the generation of natural gas substitutes from
biomass – presentation of results of latest field research, 17 th Annual Convention of Fachverband
Biogas e.V, 15 th -17 th January 2008, Nuremberg; N. Nylund, K. Erkkilä, M. Lappi, and M. Ikonen (2004)
Transit Bus Emission Study: Comparison of Emissions from Diesel and Natural Gas Buses, VTT
Processes, October 2004; Bio-NETT (2008) Bio-methane in Lille: A Case Study
63.9.2 Air Quality Impacts
63.9.2.1 Combustion of the Biogas in a Gas Engine
Where biogas is used to generate energy using a gas engine, emissions are
associated with the combustion process. The most significant air quality impacts
resulting from the combustion of biogas relate to emissions of SOx and NOx.
SOx emissions are generally a matter for process management. To the extent that
they stem from the H2S in raw gas, the emissions are related to the use of, for
example, precipitation salts which seek to precipitate out the sulphur emitted from
the degradation of proteins as iron sulphide.
NOx emissions result from high temperature reactions occurring between
atmospheric nitrogen, and trace elements such as NH3 and H2S contained within the
biogas. 1272 These emissions can be significantly reduced using Selective Catalytic
Reduction (SCR) techniques. Use of this technique was cited as the Best Available
Technique (BAT) in the Reference Document for the Waste Treatment Industries for
MBT systems using AD. However, although this equipment is widely used to reduce
NOx emissions from waste incineration facilities across Europe, use of SCR within AD
1272 V. Aschmann, R Kissel and A Gronauer (2008) Efficiency and Environmental Compatibility of
Biogas Fired Cogeneration Plants in Practical Service, 17 th Annual Convention of Fachverband Biogas
e.V, 15 th -17 th January 2008, Nuremberg
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International Review of Waste Policy: Annexes