Biogas can be upgraded to biomethane and injected into a gas grid. This can be the national high pressure gas transmission grid or a local low pressure gas distribution network. To be used in the gas grid in the UK biogas needs to cleaned of impurities, dried and upgraded to a higher methane content (> 95%) so that it resembles the qualities of natural gas. This approach is already being used in many countries including Germany, France, Austria and the USA.
A report by National Grid suggested that, with the right support and incentives, renewable gas could meet a significant proportion of UK residential gas demand. This included both gas produced by AD and by the thermochemical gasification of waste. A paper by National Grid also highlights the opportunities for renewable heat from the gas grid with biogas and gasification of organic waste.
DECC have produced a guide to biomethane production and injection into the gas network that outlines the major legal, technical and regulatory requirements. In addition, OFGEM have produced a factsheet providing basic information on how to get connected and issues arising from biomethane injection.
A summary of the connection process and a detailed procedure for biomethane injection enquiries, including a useful process flow diagram, can be found on the Northern Gas Networks website.
Injecting biomethane into the grid has several advantages:
- biomethane injection is supported under the Renewable Heat Incentive (RHI)
- provides a far more flexible fuel than biogas
- biomethane has a higher energy density than biogas
- ensures energy that is captured in the biogas is used efficiently
- can be cheaper for the AD plant operator to install a gas grid connection than an electricity connection.
However, there are currently many barriers to grid injection, both practical and financial:
no specific UK standard for biomethane
upgrading adds substantially to the cost and energy requirement
upgrading can reduce carbon savings
- no incentive for grid operators to accept biomethane
AD plants may be some distance from the gas distribution network.
These issues are the focus of the Energy Market Issues from Biomethane (EMIB) working group. Check the latest meeting reports for up to date status and progress towards resolution.
To read more about the strengths and weaknesses of upgrading biogas, as well as how to meet UK gas grid quality standards, see this report from BIS.
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