28th November 2016
One year on and going strong – Blisworth Hill A.D. Plant
It has almost been a year and a half since Blisworth Hill Anaerobic Digestion Plant became operational.
Over the last year the plant has overcome a number of challenges from hydrogen sulfide levels to condensate issues. Through diligent checks and regular maintenance it has become a successful, productive and valuable commodity to the business and to the client.
The purpose behind building the partially buried, 250kW, twin tank, semi-plug flow digester was to help reduce the carbon footprint of the businesses based in Blisworth Hill Properties Business Park, through generating sustainable energy.
From this investment the client has gained a separate, guaranteed revenue stream from exporting the energy to the surrounding business park and the remainder to the grid out of hours; as well as a greater understanding of anaerobic digestion and diversifying with farm crops.
As previously mentioned, these benefits didn’t come without their challenges. As many find using crop based feedstocks, due to the high dry matter content, water needs to be added. Through a water drainage diversion to the digester, there was an improvement in liquid recirculation and it eliminated gas pocket retention within the digestate. With the crop feedstock, especially when the plant was being fed wholecrop wheat, it created high levels of hydrogen sulfide (H2S). This is not only not good for the health of the plant but also can cause damage to the CHP (Combined Heat and Power unit). Installing a carbon scrubber, using air injection and adding Ferric Hydroxide all contributed towards greatly lowering the H2S levels. The levels are less than 50ppm now with the plant being fed maize and grass silage. The condensate issue was resolved through the installation of a chiller. The chiller cools the gas down to 5℃ which rinses the water out of the gas, then it raises the temperature of the gas to 37℃ enabling it to be burnt more efficiently by the CHP; further to this no water is entering the CHP now.
The digester is currently being fed, on average 16.5 tonnes of maize and grass silage a day. Over the last month the plant has been fed 520 tonnes and from that has produced on average 22,000 m³ of biogas per week. The plan is to transition the plant gradually onto wholecrop oat silage as well. Since the plant started running it has generated over 2.6million kW/h of electricity and produced over 1.7million m³ of biogas.
Roy Taylor, the client at Blisworth AD plant, made the following comments:
“The businesses on the farm are all looking to offset their carbon, so it is great for us to be able to offer this facility. Now we are interested in new innovation that we can apply to the plant to maximise it’s potential.”
Kevin Gascoigne, from Blisworth gave the following advice on maintaining a successful AD plant:
“It’s great to swap ideas and get advice from other AD operators but I feel the plant is individual so study, understand it and treat it as such, this will enable you to react sooner and hopefully reduce downtime.”