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  • Medium combustion plant guidance

Medium combustion plant guidance

Medium combustion plant

The medium combustion plant requirements of the Environmental Authorisations (Scotland) Regulations (EASR) are designed to control emissions of sulphur dioxide (SO2), nitrogen oxides (NOx) and dust into the air from plants with a rated thermal input equal to or more than 1 megawatt and less than 50 megawatts (MW), contributing to better air quality and reducing the potential risks to human health and the environment.

If you operate your own boiler, engine or generator (including back-up/stand by) for the production of heat or power you may be running a medium combustion plant (MCP), and it is likely you will have to apply for a permit from SEPA.

This page is designed to help you understand if the legislation is relevant to you and, if it is, what you have to do, when you have to do it by and how we can help you.

The Pollution Prevention and Control (Scotland) Regulations 2012 (PPC) were superseded by EASR in 2025. If you already have a permit issued under PPC, it is still current and you must continue to adhere to the conditions. Please contact SEPA if you have any queries about EASR and/or permit compliance.

Do I need to register my boiler, generator or engine?

  1. Do you have a boiler, generator or engine burning any fuel which was put into operation before 20 Dec 2018?
    • Yes – go to step 2.
    • No – if your plant was put into operation after 20 December 2018, it should already have a medium combustion plant permit. If you do not, please contact SEPA.
  2. Does it have a capacity of greater than 5 megawatts (MW) net rated thermal input but less than 50MW?
    • Yes – go to step 3.
    • The input is higher – you should already have a permit (this may have been issued under PPC which was superseded by EASR; these PPC permits are still current as they are ‘deemed’ into the regulations). If you do not already have a permit please contact SEPA.
    • The input is lower – if your plant is between 1 and 5MW you may need to register with SEPA in the future. You have until 30 June 2028 to do this.
    • I don’t know – please contact SEPA.
  3. Does it have a capacity greater than 20MW and less than 50MW?
    • Yes – you should already have a PPC/EASR permit. If not please contact SEPA.
    • No – go to step 4.
    • I don’t know – please contact SEPA.
  4. Does it fit one of the exclusions listed in MCPD? These are discussed further below
    • Yes – this legislation does not apply to you.
    • No – continue to step 5.
    • Not sure – please contact SEPA. Please make it clear your query is about medium combustion plant
  5. Was your existing medium combustion plant on a PPC permitted Part A or Part B installation prior to 2024?
    • Yes – Your permit should have been varied to include conditions relevant to the medium combustion plant at your installation. If your permit was not varied to include medium combustion plant, please contact SEPA.
    • No – continue to step 6.
  6. You will need to apply to SEPA for a permit to operate your medium combustion plant.
    • If you have more than one medium combustion plant on your site:
    • When we speak about medium combustion plant we mean an individual boiler, generator or engine. If you have more than one plant on your site you need to think of them individually for the purposes of this flowchart/process.
    • You can apply for all the medium combustion plant for your site on one application form if you operate them all - as long as the total capacity for the site is less than 50MW. Please use our online form to contact us if you are unsure.

The legislation

The Pollution Prevention and Control (Scotland) Regulations 2012 (known as PPC) were amended in December 2017 to transpose the requirements of the Medium Combustion Plant Directive (MCPD – Directive (EU) 2015/2193 of 25 November 2015 on the limitation of emissions of certain pollutants into the air from medium combustion plant). PPC was superseded by the Environmental Authorisations (Scotland) Regulations (EASR) in 2025. If you already have a permit issued under PPC, it is still current and you must continue to adhere to the conditions. Please contact SEPA if you have any queries about EASR and/or permit compliance. The technical requirements relating to medium combustion plant are described in schedule 27 of EASR

This page contains a brief overview of the schedule 27 requirements; please refer to MCPD for full details. You can also read the Scottish Government’s EAS consultation about MCPD.

This page contains a brief overview of MCPD requirements; please refer to MCPD and EASR for full details. You can also read the Scottish Government’s consultation about implementing MCPD.

The purpose of MCPD is to improve air quality. All combustion plant with rated thermal input equal to or more than 1 MW and less than 5 MW will need a permit by 1 January 2029. An impact assessment estimated that between 30,000 and 35,000 of these plants are operating in the UK, with approximately 7.5% being located in Scotland, which is around 2,000 plant. Additional requirements for one or more electricity generators with combined input more than 1 MW will be introduced from 1 January 2029.

You can find out more information about this activity on the SEPA website.

Before an application is granted the effect of the emissions from medium combustion plant on sensitive designated habitats must be assessed against The Conservation (Natural Habitats, &c.) Regulations 1994.

Habitat impact assessment

Operators of plant not on a PPC/EASR Industrial Activity-regulated site must carry out a Habitats Impact Assessment screening assessment using tools that have been specifically developed for this purpose.

  • The Proximity Screening tool (hosted on the APIS website) screens for sensitive protected habitats and species in statutory nature conservation sites based on fuel type, thermal capacity and distance between ecological receptor and the emission source.
  • The SCAIL Combustion tool (developed by Centre for Ecology and Hydrology) screen plant based on emissions of NOx and sulphur.

Links to both these tools are available within the mcp application form.

Simple, user-friendly instructions on the use of these tools are provided within the application form and on the hosts’ websites.

Please submit the output of the screening assessment with the application. Should both screening assessments “fail” then additional modelling will be required. In some circumstances a change in the operation which may include a reduction in operating hours or an increase in stack height may be required.

Application deadlines

New plant - put into operation after 20 December 2018

  • New plant with a rated thermal input equal to or more than 1 MW and less than 50 MW must have an EASR permit before it is put into operation.
  • Emission Limit Values (ELVs) for sulphur dioxide (SO2), oxides of nitrogen (NOx) and dust are set out in the permit and are based on plant, fuel type and engine size.
  • If your plant is up and running but was put into operation after 20 December 2018, you must contact SEPA now, as you should already have a permit.

Existing plant – put into operation before 20 December 2018

  • Existing plant with a rated thermal input equal to or more than 1 MW and less than 50 MW includes standalone plant as well as plant that is located on a permitted PPC installation or at an EASR Schedule 20 and/or Schedule 26 authorised place.
  • ELVs for sulphur dioxide (SO2), oxides of nitrogen (NOx) and dust will be set out in the permit and based on plant, fuel type and engine size.

Existing plant on a PPC site

If you have not received a regulation 63(2) information notice please contact us.

All existing standalone plants greater than 5 and less than or equal to 20MW

  • 1 January 2024 – must have a permit.
  • 1 January 2025 – must comply with the ELVs set out in their permit.

Exclusions and derogations

There are a number of exclusions detailed in Article 2(3)) of the MCPD including:

  • combustion plant used to propel a vehicle, ship or aircraft
  • turbines and engines used on offshore platforms;
  • some driers
  • thermal oxidisers

There are a number of derogations listed in Article 6 of the MCPD. Plants subject to these derogations will still need to be permitted but are exempt (sometimes on a time-limited basis) from compliance with some ELVs.These include:

  • plant operating under a certain number of hours
  • use of biomass
  • plant serving a public District Heating Network

All exclusions and derogations have been adopted in the Scottish regulations. Please use the links to the detail in the MCPD to ensure you have checked the full list. If you are still unsure, please use our online form to contact SEPA making it clear your query is about medium combustion plant.

Monitoring

The operator must carry out monitoring of emissions to demonstrate compliance with the ELVs within four months of a permit being granted, and then at the following frequency:

  • Greater than 20MW - less than 50MW must monitor annually:
  • Equal to or greater than 1MW - less than or equal to 20MW must report every three years.

Plants must monitor for sulphur dioxide (SO2), nitrogen oxides (NOx), dust and carbon monoxide.

There is more information on Emission Limit Values in tables in the Medium Combustion Plant Directive (Annex II) and these will also be detailed in your permit.

The emissions monitoring requirements for existing plant equal to or greater than 1 and less than or equal to 5MW is not required until 2029 however SEPA would recommend that monitoring is carried out before this date to ensure the emissions comply with the ELVs and to allow time to upgrade if required.

A reduced frequency is allowed for plant operating under the limited hours exemption, but monitoring (for carbon monoxide only) will be required no less than once every five years.

Planning requirements for new plant

Planning approval may be required for new development and requirements should be discussed with the local planning authority. Depending on the size, scale and location of the medium combustion plant, an air quality impact assessment (AQIA) may be required to protect local air quality. We recommend pre-application consultation with the planning authority to determine if an AQIA is required as part of the planning application.

We strongly recommend that an air modelling method statement is submitted to the local planning authority and SEPA in advance of any modelling work being carried out as part of an AQIA to support a planning application. This has the advantage of agreeing the methods and input parameters in advance, saving time and money.

Further information

We will update the information about medium combustion plant on our website on a regular basis. You can also find more information on medium combustion plant by searching the documents and regulations below.

Biomass

Biomass means any of the following:

  • products consisting of any vegetable matter from agriculture or forestry which can be used as a fuel for the purpose of recovering its energy content;
  • The following waste:
  • vegetable waste from agriculture and forestry;
  • vegetable waste from the food processing industry, if the heat generated is recovered;
  • fibrous vegetable waste from virgin pulp production and from production of paper from pulp, if it is co-incinerated at the place of production and the heat generated is recovered;
  • cork waste;
  • wood waste with the exception of wood waste which may contain halogenated organic compounds or heavy metals as a result of treatment with wood preservatives or coating and which includes, in particular, such wood waste originating from construction and demolition waste.
  • SEPA’s Authorisation Guidance for Biomass Combustion provides guidance on when biomass is considered a fuel and when it is considered waste and therefore which permit is required.

Boiler

Large vessel containing water that is heated by a burner (gas, oil, etc.) which then can be used to provide steam, or for other industrial purposes. Furnaces would usually be considered a boiler.

Combined cycle gas turbine (CCGT)

The exhaust from a gas turbine is used to turn water into steam and run a steam turbine. A CCGT has good efficiency and can provide a rapid response. CCGT can be expensive to construct, but the lower running costs may offset the construction costs.

Combustion engine

An internal combustion engine (ICE) like in a car, with pistons which move in cycles. It is inefficient but can be easily scaled down to very small sizes.

Combustion engines are usually used as a backup in industrial settings.

Combustion engines lose efficiency due to heat loss and to the number of moving parts (in different directions).