Modelling a demand driven biogas system for production of electricity at peak demand and for production of biomethane at other times

Four feedstocks were assessed for use in a demand driven biogas system. Biomethane potential (BMP) assays were conducted for grass silage, food waste, Laminaria digitata and dairy cow slurry. Semi-continuous trials were undertaken for all feedstocks, assessing biogas and biomethane production. Three kinetic models of the semi-continuous trials were compared. A first order model most accurately correlated with gas production in the pulse fed semi-continuous system. This model was developed for production of electricity on demand, and biomethane upgrading. The model examined a theoretical grass silage digester that would produce 435 kW_e in a continuous fed system. Adaptation to demand driven biogas required 187 min to produce sufficient methane to run a 2 MW_e combined heat and power (CHP) unit for 60 min. The upgrading system was dispatched 71 min following CHP shutdown. Of the biogas produced 21% was used in the CHP and 79% was used in the upgrading system.