For bioenergy installations producing heat, the minimum required GHG savings will be 85% from 2026. This is significant and a considerable challenge for biogas systems. This paper investigates use of biogas from pig farms at a nearby milk processing facility, a large energy user. The paper examines minimisation of greenhouse gas (GHG) associated with plant layout and in particular in transporting slurry by road to a large centralised anaerobic digestion (CAD) facility or transporting biogas by low pressure pipe from decentralised anaerobic digestion (DAD) at the pig farms.
In detail four scenarios were assessed: "CAD1" road transport of slurry to a CAD located at the biogas end user (milk processing. facility); "CAD2" transport of biogas by pipeline from an optimally located CAD located a distance from the biogas end user; "DAD1" DAD with biogas transportation in a biogas pipe network; and "DAD2" DAD with biogas transportation via a biogas pipe network of minimum length to reduce cost.
Scenario CAD2 (transporting biogas by pipe from optimally located CAD) reduced CO(2)eq emissions associated with the road haulage of pig slurry by 51% compared to CAD1 (transporting slurry by road to a CAD at the milk processing facility) and 7% overall. Scenario DAD1 (distributed biogas production in DAD and transportation of the biogas by pipe) was shown to be the best scenario with CO(2)eq emissions reduction of 19% compared to Scenario CAD1 (road transport of slurry with CAD at the biogas user). Scenario DAD2 (distributed biogas production in DAD while minimising length of the biogas network) reduced CO(2)eq emissions by 18% relative to scenario CAD1, reduced the network length by 34% compared to scenario DAD1 but increasing total CO(2)eq emissions by 1% compared to Scenario DAD1.