Guidance to inform operators of anaerobic digestion (AD) plants of the legal, technical and regulatory requirements of injecting biogas into Britain's gas grid has been published by the Department of Energy and Climate Change (DECC).

The DECC guidance is expected to benefit AD operators across the country. Pictured: the BiogenGreenfinch AD plant at Ludlow in Shropshire

The document, entitled ‘Biomethane into the Gas Network: A Guide for Producers' has been developed following a Government commitment in the Renewable Energy Strategy in July to explain the gas regulatory system.

DECC claims that it will help producers of biogas, who may not have considered injecting it into the gas grid, to make an informed choice between the various marketing options.

Biogas is a gas manufactured from organic matter, as opposed to the natural gas which is produced from geological strata underground. It is a term used to refer to a combustible gas created by anaerobic digestion (AD) of organic material, and composed of approximately 60% methane, 40% carbon dioxide, and other trace levels of contaminants.

This can be used to produce biomethane, which has similar thermal characteristics to natural gas and can be injected into the natural gas network and used in existing gas appliances, subject to meeting quality requirements. It is expected that such biomethane injection might contribute towards meeting the UK's 2020 renewable energy targets.

DECC's report explains that to convert biogas to biomethane, the main requirement is to remove the majority of the carbon dioxide, as well as some of the trace impurities.

DECC's report notes that there are a number of commercial technologies to perform this "clean up", including water scrubbing, selexol absorption, cryogenic separation, membrane separation, and pressure swing adsorption processes.

Permission

The guidance was prepared by DECC, with the assistance of a working group comprising representatives from industry, renewables trade associations, the Health and Safety Executive and Ofgem.

DECC explains that biomethane produced from the treatment of waste can only be injected into the gas network with the permission of whoever is responsible for the network - i.e. the regional gas distribution network (DN)

It claims that it is up to the DN to decide whether the gas would need to be cleaned up and treated to an appropriate agreed standard.

In terms of regulatory implications arising from the biomethane being produced from waste, the report advises that the issue is currently being considered with the competent authorities responsible for implementing the EU Waste Framework Directive. These include the Environment Agency and Scottish Environment Protection Agency.

Information

Some of the information set out in the report includes:

• Technical information;
• Explanation of who is who in the gas market;
• How a biomethane producer can connect to the gas grid - including licensing arrangements and contractual agreements;
• What equipment is needed.

It also explains that all gas conveyed into a Gas Transporter pipe-line must comply with gas quality requirements set out in the Gas Safety (management) Regulations 1996 and must also meet any additional requirements specified in the relevant Network Entry Agreement (NEA).

According to DECC, the NEA additional requirements may include limits on calorific value, temperature and radioactivity.

Other information provided in the report includes advice on why AD operators should inject their biogas into the grid, rather than utilising it on-site in combined heat and power (CHP) units.

Efficient 

DECC claims that upgrading the biogas to biomethane and sending it to the grid would be more energy efficient, as using the gas on-site for electricity-only applications would harness only 30-35% of the energy in the gas.

This compares to using more than 90% of the energy in the gas in an efficient modern domestic boiler, having transported it through the gas pipe-line system.

It also adds that injecting biomethane into the grid would provide a higher delivery of renewable heat to be transported to more than 80% of homes in Great Britain.