The medium combustion plant requirements of the PPC regulations are designed to control emissions of sulphur dioxide (SO2), nitrogen oxides (NOx) and dust into the air from plants with a net rated thermal input of between 1 and 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 to continue using it.
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 process below will help you decide whether you need to apply by 30 June 2023. If you already know you need to apply please check the contents of this page to find information to help you do this.
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, get in touch using our online form to contact us.
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 PPC permit. If not contact us
- 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 – contact us.
3. Does it have a capacity greater than 20MW and less than 50MW?
- Yes – you should already have a PPC permit. If not contact us.
- No – go to step 4.
- I don’t know – contact us.
4. Does it fit one of the exclusions listed in the Directive?
- Yes – this legislation does not apply to you.
- No – continue to step 5.
- Not sure – contact us. Please make it clear your query is about the Medium Combustion Plant Directive.
5. Is your existing medium combustion plant on a PPC permitted Part A or Part B installation?
- Yes – SEPA will send you an information notice requiring you to provide information about the medium combustion plant at your installation. We will then vary your permit to include conditions relevant to the medium combustion plant at your installation. Details of the variation fee will be provided with the information notice. If you have not received an Information Notice from SEPA by 31 May 2023 please contact us.
- No – continue to step 6.
6. You will need to apply to SEPA for a permit to operate your medium combustion plant by 30 June 2023.
- Find out how to apply for a permit for a 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
- How to apply
- Applications deadlines
- Applications charges
- Exclusions and derogations
- Planning requirements for new plant
- Further information
- Frequently asked questions
- Contact us
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).
This page contains a brief overview of the MCPD requirements; please refer to the Directive and regulations for full details. You can also read the Scottish Government’s consultation about the Directive.
The purpose of the MCPD is to improve air quality. All combustion plant between 1 and 50MW (net rated thermal input) will need a permit by 1 January 2029. An impact assessment has 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. Any plant below 1MW is not within the scope of the regulations.
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. Medium combustion plant already permitted by SEPA under PPC Part A or B were assessed at the time of initial application and therefore don’t require further assessment.
If your plant is on a PPC Part A or Part B permitted installation SEPA will serve a Regulation 63(2) information notice to gather information on your plant and will vary your permit to include the relevant conditions. If you have not heard from us by 31 May 2023 please contact us.
Habitat Impact assessment
Applicants of plant not on a PPC Part A or B 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 CEH) screen plant based on emissions of NOx and sulphur.
Links to both these tools are available within the 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.
Further help and guidance
If you are not sure, please get in touch and one of our regulatory officers will respond.
- New plant between 1 and 50MW must have a PPC permit before it is commissioned.
- 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 PPC permit.
Existing plant – put into operation before 20 December 2018
- Existing plant includes standalone plant as well as plant that is located on a permitted PPC Part A or Part B installation.
- 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 Part A or B site
- SEPA will send you an information notice requiring you to confirm information on any medium combustion plant you may have at your installation. We will then vary your permit to include conditions relevant to the medium combustion plant at your installation.
- If you have not received a Regulation 63(2) information notice by 31 May 2023 please contact us.
All existing standalone plants greater than 5 and less than or equal to 20MW:
- 30 June 2023 – must have applied for a permit.
- 1 January 2025 – must comply with the ELVs set out in their permit.
All existing plants greater than 20 and less than 50MW:
- Please use our online form to contact us.
All existing plants equal to or greater than 1 MW and less than or equal to 5 MW:
- 30 June 2028 – must have applied for a permit.
- 1 January 2030 - must comply with the ELVs set out in their permit.
Applicants and operators of existing medium combustion plant where SEPA has not issued a permit or permit variation should refer to SEPA’s Medium Combustion Plant Regulatory Position Statement
New and existing standalone medium combustion plant not on a permitted Part A or Part B installation:
Please download and complete the medium combustion plant application form accompanied by the application fee of £1,565. Please note the permit is also subject to an annual charge of £296.
The regulations allow SEPA four months to process an application. The permit must be in place before any new plant can operate.
The application also includes requirements for additional assessments to be made if your plant is likely to adversely affect sites covered by conservation legislation.
Existing medium combustion plant on a PPC permitted Part A or Part B installation:
The variation application fee is £469.50 (30% of the full fee).
More information on our charges can be found in The Environmental Regulation (Scotland) Charging Scheme Amendment (No1) 2022. Medium combustion plants subject to a bespoke permit are reference number 10460.
All applications and permits will be placed on SEPA’s public register, including online.
There are a number of exclusions detailed in Article 2(3)) of the MCP Directive 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 MCP Directive. Plants subject to these derogations will still need to be permitted but are exempt (sometimes on a time-limited basis) from compliance with 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 Directive to ensure you have checked the full list. If you are still unsure, please use our online form to contact us making it clear your query is about the Medium Combustion Plant Directive.
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 plant equal to or greater than 1 and less than or equal to 5MW will be postponed 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 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.
What an air modelling method statement should include
A method statement should include:
- choice of model to be used;
- pollutants of interest and air quality standards/objectives that model results will be assessed against;
- background concentrations to be used;
- emission parameters, to include
- stack location
- stack height
- stack diameter
- exit temperature
- efflux velocity or flow rate (actual)
- emission concentrations
- calculated emission rate
- meteorology to be used (including years to be modelled, percentage of calm periods in data and where it has been sourced from);
- buildings to be included in model;
- terrain to be included in model;
- grid domain, resolution and locations of sensitive receptors;
- scenarios to be modelled;
- for plants with non-continuous or reduced operation hours, such as short-term operating reserves (STOR), the method statement must include details of any proposed special treatment to account for the reduced operating hours
- model output formats to be presented;
- stack height assessment method.
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 following the links below:
- Directive (EU) 2015/2193 of the European Parliament and of the Council of 25 November 2015 on the limitation of emissions of certain pollutants into the air from medium combustion plants
- The Pollution Prevention and Control (Scotland) Regulations 2017
- Scottish Government’s Consultation on the implementation of the medium combustion plant Directive in Scotland
What is a medium combustion plant?
Combustion plant are defined as any technical apparatus in which fuels are oxidised in order to use the heat.
A medium combustion plant is any plant or equipment used to burn (combust) materials, with a net rated thermal input between 1 and 50MW.
Medium combustion plant are used to generate heat for large buildings (e.g., large office buildings, hotels, hospitals, prisons, shopping centres, etc) and industrial processes, as well as for power generation.
What is the difference between a new and existing medium combustion plant?
A new medium combustion plant is a combustion unit that was first fired on or after 20 December 2018. Any plant in use before 20 December 2018 is an existing plant.
When does an existing medium combustion plant become a new medium combustion plant?
An existing medium combustion plant will become a new medium combustion plant if it is either:
- altered or repaired which results in an increase to pollution levels (note: changing to a cleaner fuel would not be considered a change from new to existing); or
- substantially refurbished and the refurbishment costs are more than 50% of what a new comparable medium combustion plant would cost (taken from the definition in the Energy Efficiency Directive).
What should I do if I have a new medium combustion plant?
You must obtain a PPC permit from SEPA for new plant equal to or greater than 1MW and less than 50MW net rated thermal input, before it is commissioned. The permit will set out emission limit values for sulphur dioxide (SO2), oxides of nitrogen (NOx) and dust based on plant type, fuel type and size.
What should I do if I have an existing medium combustion plant?
All existing medium combustion plant with a net rated thermal input greater than 20 and less than 50MW must already be permitted by SEPA.
Permit applications for existing medium combustion plant with a net rated thermal input greater than 5MW and less than or equal to 20MW must be submitted to SEPA before 30 June 2023.
Permit applications for existing medium combustion plant with a net rated thermal input equal to or greater than 1MW and less than or equal to 5MW must be submitted to SEPA before 30 June 2028.
What should I do if I have an existing medium combustion plant located on an installation already permitted by SEPA under Part A of the Pollution Prevention and Control (Scotland) Regulations 2012 (as amended)?
SEPA will serve a Notice under Regulation 63(2) Pollution Prevention and Control (Scotland) Regulations 2012 requiring operators to gather information on their medium combustion plant. This will be served on all installations with a Part A permit and a selection of installations with a Part B permit. The required information must then be returned to SEPA with the permit variation fee.
SEPA will vary the permit to insert a schedule of conditions relating to medium combustion plant including emission limit values which may on occasions be stricter than those specified in the Medium Combustion Plant Directive depending on the BAT-AELs specified in the relevant BREF if appropriate, and local air quality.
Please contact SEPA if you expected to receive an information notice but have not received one by 31 May 2023.
What should I do if I plan to add a new medium combustion plant to my installation already permitted by SEPA under Part A or B of the Pollution Prevention and Control (Scotland) Regulations 2012 (as amended)?
New medium combustion plant will usually be added to the existing permit by a standard variation.
A permit variation fee of 30% of the ‘Medium Combustion Plant Subject to a bespoke permit’ application charge applies. Full details of the current charges for medium combustion plant can be found on SEPA’s website: Charging schemes and summary charging booklets | Scottish Environment Protection Agency (SEPA).
How do I apply for two or more medium combustion plant located on one site?
You can apply for multiple medium combustion plant located on one site and operated by the same person using one application form provided the total in RTI on the site is less than 50 megawatts.
Only one application fee is payable in these circumstances.
Medium combustion plant discharging their waste gases through a common stack will be considered as a single plant.
What are the monitoring requirements for medium combustion plant?
The first monitoring of emissions must be undertaken within four months of the grant of the permit or the start of the operation of the medium combustion plant, whichever is later. For existing medium combustion plant SEPA will accept the first monitoring up to two years before the permit application.
The permit conditions will specify the requirements and frequencies for the follow up monitoring which will be annually or once every three years depending on the size of the plant.
Are the rules different for standby medium combustion plant?
Permits are required for medium combustion plant operating less than 500 hours per year. The 500 hour limit is based on a rolling average.
There is a five-year rolling average for existing standby plant and three-year rolling average for new standby plant. There is no annual limit, so in theory an existing standby plant could operate for 2,500 hours, and a new standby plant could operate for 1,500 hours in one year before failing to comply with the permit requirements.
Any operator anticipating or planning to exceed the 500-hour limit must apply to vary the permit beforehand. Operators should be aware that an annual limit of 750 hours is imposed for medium combustion plant permitted in England & Wales.
There is a requirement for standby medium combustion plant to be monitored periodically for carbon monoxide and the required intervals will be specified in the permit. The standby plant should not be switched on just for the purposes of monitoring, although regular testing regimes required for generation purposes should allow for this.
What are the correct emission reference levels?
All emission limit values, and monitoring results should be corrected as follows:
(a) at a temperature of 273.15 K,
(b) at a pressure of 101.3 kPa,
(c) for the water vapour content of the waste gases,
(d) at a standardised O2 content of—
(i) 6 % for medium combustion plants using solid fuels,
(ii) 3 % for medium combustion plants, other than engines and gas turbines, using liquid and gaseous fuels,
(iii) 15 % for engines and gas turbines.
What is a habitats impact assessment?
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. Medium combustion plant already permitted by SEPA under Part A or B of the Pollution Prevention and Control (Scotland) Regulations 2012 (as amended) were assessed at the time of initial application and therefore don’t require further assessment.
The applicant must carry out a Habitats Impact Assessment screening assessment using tools that have been specifically developed for this purpose.
I have six existing emergency generators on my site. Each one has a net rated thermal input of 2.1MW. In combination there is a total net rated thermal input of 12.6MW. When do I need to apply for a MCP Permit?
These are considered as individual plant and not as an aggregate.
The operator would therefore need to apply for a permit for these six existing MCP by 30 June 2028 and comply with the emission limit values set out in the permit by 1 January 2030.
You can use one application form for all six plant and only one application charge is payable.
I have eight existing plant with net rated thermal inputs ranging from <1MW to 11.4MW. When do I need to apply for a MCP Permit?
Any plant <1MW is not considered a medium combustion plant and is not regulated by SEPA.
A permit application for the plant with a net rate thermal input greater than 5MW and less than or equal to 20MW is required by 30 June 2023.
A permit application for the plant with a net rated thermal input equal to or greater than 1MW and less than or equal to 5MW is not required until 30 June 2023. However, if the operator wishes to permit these plant at the same time as the plant >5MW, they may be added to the application form. Compliance with the emission limit values for the plant equal to or greater than 1MW and less than or equal to 5MW will be post-dated
Biomass means any of the following:
a) 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;
b) The following waste:
(i) vegetable waste from agriculture and forestry;
(ii) vegetable waste from the food processing industry, if the heat generated is recovered;
(iii) 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;
(iv) cork waste;
(v) 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 Permitting 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.
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.
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).
Dual Fuel Engine
An internal combustion engine which uses compression ignition and operates according to the Diesel cycle when burning liquid fuels and according to the Otto cycle when burning gaseous fuels.
Dual Fuel combustion plant is capable of burning more than one fuel without a significant change to the setup e.g., natural gas and diesel.
There are some emission limit values categories that differ with dual fuel combustion plant.
Any rotating machine which converts thermal energy into mechanical work, consisting mainly of a compressor, a thermal device in which fuel is oxidised in order to heat the working fluid, and a turbine; this includes both open cycle and combined cycle gas turbines, and gas turbines in cogeneration mode; all with or without supplementary firing.
Gas turbines are commonly used in power plant, these are very similar in construction to jet engines, where gas is the fuel. The torque produced is used to run the generator.
Gas turbines are not as efficient as steam or combined cycle but more efficient than combustion engines. The power output can quickly meet changing demands.
An internal combustion engine with a built-in alternator. Fuel is combusted to provide momentum which the alternator then converts to electrical power. Generators are usually diesel but can be converted to other fuel types.
Heavy and liquid fuel oils (HFO/LFO)
(a) any petroleum-derived liquid fuel falling within CN codes 2710 19 51 to 2710 19 68, 2710 20 31, 2710 20 35, or 2710 20 39; or
(b) any petroleum-derived liquid fuel, other than gas oil as defined in point 19, which, by reason of its distillation limits, falls within the category of heavy oils intended for use as fuel and of which less than 65 % by volume (including losses) distils at 250 °C by the ASTM D86 method. If the distillation cannot be determined by the ASTM D86 method, the petroleum product is likewise categorised as a heavy fuel oil.
HFO/LFO are not gas oil and biodiesel is not gas oil.
Where a medium combustion plant simultaneously uses two or more fuels, the emission limit value for each pollutant shall be calculated by:
(a) taking the emission limit value relevant for each individual fuel as set out in Annex II of the MCPD;
(b) determining the fuel-weighted emission limit value, which is obtained by multiplying the individual emission limit value;
(c) by the thermal input delivered by each fuel, and dividing the product of multiplication by the sum of the thermal inputs delivered by all fuels;
(d) aggregating the fuel-weighted emission limit values.
Means naturally occurring methane with no more than 20% (by volume) of inerts and other constituents. Natural gas must contain a minimum of 80% methane. Landfill gas tends to contain 60% methane and 40% CO2 so is not natural gas.
Net rated thermal input
The rate at which fuel can be burned at the maximum continuous rating of the appliance multiplied by the net calorific value of the fuel expressed as megawatts thermal.
A Permitted installation is where one or more regulated activities, and any directly connected activities, are carried out under the conditions imposed by a Pollution Prevention and Control Permit.
Gas heats water in a boiler; the overheated steam runs through turbines and is then cooled. Steam turbines use the same principle as most other thermal power plants (coal, nuclear, geothermal).
Steam turbines are usually large installations and can take a long time to get up to speed (so no rapid response to demand) but are very efficient.
If you need any further help or information about the regulation of medium combustion plant, please use our online form to contact us.