EA and NRW set out medium combustion plant guidance

The Environment Agency and Natural Resources Wales have published detailed guidance on how they will regulate combustion plants with a thermal input of less than 50 megawatts.

The guidance completes the implementation of the Medium Combustion Plant Directive in England and Wales, legislation that filled an unregulated gap between simple ecodesign requirements at the small scale and the complexities of the Industrial Emissions Directive at the larger end. It sets well-defined limits on emissions of sulphur dioxide, nitrogen oxides and dust alone.

As has been established already, the agencies have adopted three different approaches to regulating medium combustion plants (MCPs), depending on their risk. The simplest are covered by standard rules permits, less straightforward ones by simple or complex bespoke permits, depending on whether air dispersion modelling is needed or not. That can be related to their scale, presence within an air quality management area and other factors.

These permits apply to some installations such as backup diesel generators, or smaller ones used on construction sites that have a thermal input of less than one megawatt. The directive itself applies only above 1 MW but certain smaller with a grid balancing or capacity agreement were included in its transposition in England, Wales and Northern Ireland due to concerns about their impact on urban air pollution.

Operators of such ‘specified generators’ were supposed to have a permit in place by 1 January this year, or face potential prosecution. However, due to the number of applications received and the time needed to process them, the Welsh deadline was extended to 30 June, with the EA giving itself until 31 August.


The guidance lays out simple instructions for applying for a permit, such as providing the net rated thermal input of the plant, its location (if stationary), fuel and type, start of operation and expected operating annual hours.

Plants running for less than 500 hours per year, as a rolling average over five years, are excluded from meeting the directive’s emission limit values. If an operator wishes to take advantage of this, a signed declaration must be provided with the application, stating that the plant will not exceed the permitted hours.

Application charges have not been amended.

Applicants must also demonstrate their competence to be operators. Details of any relevant offences, and bankruptcy and insolvency proceedings must be provided. In addition, operators must confirm that they have a written management system.

MCPs with a thermal rating of 20MW or more, schedule 24 of the Environmental Permitting Regulations applies. This implements the requirements of the EU Energy Efficiency Directive, specifying that a cost-benefit assessment for operating as a high-efficiency cogeneration, district heating or district cooling plant may need to be conducted.

Further rules apply for MCPs within an air quality management area (AQMA). In this case, applicants for a stationary unit (such as a boiler) must supply the details of the AQMA and the plant’s emissions. For mobile MCPs, a generic assessment of its impact on a location with high background air pollution needs to be conducted to provide evidence that there will be no harm to local air quality. If necessary, an emissions limit value stricter than that specified in the directive will be set, following discussions with the local authority.

An air emissions risk assessment may also be needed if an MCP is near a conservation area – within 2km for sites of special scientific interest or local nature sites, or 10km for special protection areas,   special areas of conservation or protected wetlands.

Lastly, the MCP Directive requires operators to monitor emissions. Permit applicants must describe what secondary abatement they use, how and if continuous emissions monitors will be employed and stack and sample point configurations.

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