An energy and greenhouse gas comparison of centralised biogas production with road haulage of pig slurry, and decentralised biogas production with biogas transportation in a low-pressure pipe network.

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. [ABSTRACT FROM AUTHOR]