Biogas-to-biomethane upgrading plant

Chesterfield BioGas (CBG) supplied the UK’s first biogas upgrading plant to produce clean biomethane for direct injection into the national gas grid for use by all consumers. The project was successfully completed and gas injected into the national grid at the wastewater treatment site of Thames Water site at Didcot, Oxfordshire in October 2010.

This achievement was a benchmark moment for use of ‘green’ energy in the UK and the progress of the project has been monitored closely by the renewable energy industry.

The gas injected into the grid is produced from raw biogas generated naturally during the wastewater treatment process at Didcot. It is subsequently processed through anaerobic digestion and linked to the upgrading unit supplied and installed by CBG. There the gas is upgraded to 98% pure methane (biomethane).

The gas produced is being injected into the grid owned by Scotia Gas Networks, and purchased by British Gas for sale to its domestic users.

The Manuka+ upgrading unit at Didcot is of modular design and has the capacity to process up to 130 Nm3/hr of raw biogas using an oil-free compressor system. It is one of a range of water-scrubbing upgrading units available from CBG, as exclusive UK manufacturers, under licence from Greenlane Biogas Ltd. The process is well proven, with over 60 sites operational around the world, but the Didcot project was the first of its kind to be completed in the UK.

The process achieves the upgrade in a single pass, utilising specially developed media within the scrubbing tower. Almost all siloxanes are removed and hydrogen sulphide carryover is only 0.1ppm. The water used in the process is cleaned and recycled within the unit.

CBG engineers worked closely with the partnership to integrate the upgrading unit into the overall system that also included propane mixing, odour injection, metering and monitoring systems and grid connection.

This ‘closed loop’ production process for biomethane is environmentally sustainable. From this project, the enthusiasm for injection of biomethane into the gas grid across the UK has now taken hold, with a number of new projects going forward. These include Chesterfield’s second project in Stockport which will be taking the feedstock of food waste and producing biogas in a similar, but somewhat larger, upgrading unit.

Much of the critical information that has helped the gas industry develop new regulations and specifications to help utilise biomethane has come from the Didcot project, with the design of lower-cost monitoring equipment just one of the benefits. Without this first project reaching fruition, the industry would have had much less information to study and act upon.

Research published by National Grid shows that, if all potential sources of biogas were collected and processed using anaerobic digestion and biogas upgrading, it could fulfil almost 50% of the UK’s domestic gas requirement. This would contribute significantly to a reduction in greenhouse gases and help ensure security of supply by reducing the volume of imported gas usage.

The UK Government’s Renewable Heat Incentive (RHI) sets feed-in tariffs which reward generators of renewable energy from a variety of sources and further improves the viability of installing this type of plant.

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