Biodigester BS1

The technology provider

We chose Biogas Nord of Germany because they were selling a new technology. Traditionally the digester is fed with a dry based system, a hopper and a series of augers. The disadvantage of which is the introduction of air into the substrate. The oxygen in the air helps to create a thermophilic reaction which can increase the temperature in the digesters, especially during the summer creating significant biological issues. Typically this type of feeding system produces a methane content of 47-52%. Biogas Nord’s new system utilises a hydrolisation process in a separate tank enabling the methane content to be approximately in a 54-57% range. This significantly increases the engine performance as less biogas is required. Since we have added our gas clean-up plant the higher CH4 values have considerably added to the output.

Construction

The bulldozers broke ground on the 8th November 2011, we were generating around the clock at 50% power on the 10th October 2012. Most of the construction was carried out by British sub contractors, this ranged from the ground works through to the building of the tanks, field wiring and most of the pipe work. During the excavation more than 80,000 cubic metres of chalk and earth were moved and displaced in a cut and fill operation to create a yard out of a slope. The reason for positioning the site was to create a natural extension to our farmyard, enabling us to connect cheaply to the grid as we already had an 11KV line for powering our grain dryer. It also has enabled us to recover some of the waste heat from the engine to provide heat for the farmhouse.

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Commissioning

This process was achieved by purchasing digestate from two biogas plants and the required amount of water, in the form of final effluent, from Southern Water. We slowly brought the biodigester tank up to 40 degrees over the course of a 2 week period whilst commencing a very gentle feeding programme. We were very quickly producing electricity around the clock. The plant has been running consistently at 499 kilowatts per hour since Christmas Eve 2012 (the average electrical requirements of 1250 people).