One of the first projects with a CHP system from Edina to achieve Renewable Heat Incentive (RHI) accreditation is Strathendrick Biogas. This site was developed by Strathendrick’s Director, Robert Kennedy to be as near to “closed loop” as possible. Robert had previously acted as a renewable energy consultant for the farming industry in particular. The plant has feedstock for the AD process on the doorstep from dairy farm cow slurry, distiller’s draff and pot ale syrup from local whisky distilleries and some grass silage. This produces enough biogas to fuel an engine from Edina which has an output of 500 kWe and 500kWth. The electricity powers the farm and plant with surplus exported to the grid, attracting the FIT (Feed in Tariff). The heat from the engine is sufficient to heat the water for the dryer and to warm the tank enabling a more efficient AD process.
The dryer is a NEWtainer from NEWeco-tec GmbH and is multi-purpose, potentially drying grain, wood or other materials but Strathendrick Biogas use it purely for drying digestate. Using all the waste from the farm as feedstock, a proportion of the dry digestate is stored for 6 months following the AD process which means little odour is emitted when it is used as fertiliser. The remainder of the digestate is dried for over 2 hours at temperatures exceeding 70˚C which destroys pathogens. So far it has received a very favourable response from the farmer trialling it as a bedding material, who finds that it is absorbent, minimises odour and is more economic than purchasing and transporting straw. The RHI is paid on this aspect of the operation only.
The equipment was a sizeable investment and proceeding with the digestate drying would have been barely viable at this juncture without the RHI. Users are confident however that once the technology is more widely applied and demonstrably successful, the system will pay regardless of subsidy and over a shorter period of time.
Non Domestic RHI for commercial biomass and for biomethane injection into the grid has been available for several years. However financial support for heat use from a biogas CHP plant (referred to as biogas combustion) above 200kW thermal output has only been available since December 2013. Anaerobic digestion plants commissioned before this date are ineligible. The RHI for biogas CHP is supported in three band rates depending on the total heat recovered from the CHP installation. Below 200kW thermal the rate is 7.5p/kWh, between 200kW and 600kW the rate is 5.9p/kWh, and above 600kW the rate is 2.2p/kWh.
It has prompted the serious consideration and implementation of schemes which give more thought to capturing heat and using it. It has made possible greater advances in the research and development of drying digestate, (following the anaerobic digestion process) which then lends itself to further uses such as animal bedding, or fuel itself as pellet form, as well as reducing volume for land spreading. Another useful application is steam generation for use in maltings, or food processing industries. Also, drying wood and grain is viable and is under final development stages on several sites currently.