Medium combustion plant (MCP): comply with emission limit values (2022)

If you need a permit, before you apply you must check what ELV your MCP must meet.

This guidance explains:

  • the ELV the MCP must meet, based on its type, such as if it’s new or existing, the fuel it burns and technology it uses
  • if the MCP is exempt from meeting ELVs

It also explains when the MCP may need to meet a stricter ELV, such as when the MCP, including a mobile MCP deployment, is located within:

  • a local authority Air Quality Management Area (AQMA) air quality zone
  • the minimum distance to a habitats site

If your MCP is also a specified generator see the ELVs and controls that apply to specified generators.

If you have a MCP that’s already permitted as part of a Part A1 Industrial Emissions Directive (IED) activity you will need to check which ELVs you must meet by what date.

You will need to do monitoring to demonstrate you can meet the ELVs set in your permit conditions. See the:

  • deadlines for meeting ELVs
  • guidance on how to comply with your MCPD permit

Minimum ELVs your MCP must comply with

A new MCP must meet ELVs from 20 December 2018 or before you commission your new MCP.

MCPD sets the minimum ELVs your MCP must comply with. See the MCPD Annex 2 tables. For:

  • a new MCP that is not an engine or gas turbine (GT) the ELVs are listed in part 2, table 1
  • a new MCP that is an engine or GT the ELVs are listed in part 2, table 2
  • an existing MCP that is not an engine or GT between more than 5 and less than 50MWth the ELVs are listed in part 1, table 2 – it must meet these by 1 January 2025
  • an existing MCP that is not an engine or GT between greater than or equal to 1 and less than 5MWth the ELVs are listed in part 1, table 1 – it must meet these by 1 January 2030
  • an existing MCP between 1 and 50MWth which is an engine or GT the ELVS are listed in part 1, table 3 – it will depend on its capacity as to what deadline applies

You must refer to the notes with the tables.

ELV to use for MCP using 2 or more fuels

How to calculate ELVs for this type of MCP.

Co-fired and multi-fuelled MCPs

To calculate the ELV for one MCP which uses 2 or more fuels at the same time, you will first need to determine the:

  • MCP’s total rated input (net calorific value) using Regulatory Guidance Note (RGN) 2
  • fuel consumption for the monitoring period

You then need to determine the fuel weighted ELV based on the:

  • Annex 2 ELV for each fuel
  • thermal input delivered by each fuel

For fuel 1:

  • multiply the relevant Annex 2 ELV, corrected to the same common oxygen concentration where necessary, by the fuel’s thermal input (find the oxygen correction formula in Part 7 of the Industrial Emissions Directive)
  • divide the sum by the MCP’s total rated thermal input

Do this calculation for each fuel. Then add together each fuel’s contribution to get the MCP’s aggregated ELV.

If one of the fuels is a gas or liquid there may not be an ELV for some pollutants. For example, there will be negligible SO2 and particulate emissions from natural gas, therefore the ELV contribution from that fuel is zero.

(Video) Flexitricity's Medium Combustion Plant Directive Webinar

You normally need to apply for a bespoke MCPD permit for this type of MCP.

Dual fuel MCPs

Two different ELVs apply where different fuels are fired on the same MCP separately. For example, where liquid fuel is used as a backup fuel if the natural gas supply is interrupted.

You normally need to apply for a bespoke MCPD permit for this type of MCP.

GT with supplementary firing

Two different ELVs apply where a GT has a supplementary fired waste heat recovery boiler (WHRB) – one for the GT and one for the boiler.

Where both the GT and boiler are being fired, or the GT alone, the GT ELV applies at 15% O2.

Where the WHRB is being fired alone (auxiliary mode), the boiler ELV applies at 3% O2.

ELV to use for landfill gas engines

The Environment Agency and Natural Resources Wales (NRW) do not consider landfill gas to be biogas so you cannot use the higher SO2 ELV.

New engines must have a permit by 20 December 2018 or before you commission a new MCP. You must meet ELV monitoring requirements within 4 months.

Existing engines less than 5MWth must have a permit by 1 January 2029 and comply with the ELV by 1 January 2030.

The ELV for:

  • NOx is 190mg/m3
  • SO2 is 15mg/m3 at 15% O2

ELV exemptions

Check if your MCP is:

  • exempt from meeting ELVs
  • required to meet relaxed ELVs or there’s a delay to meeting them

Less than 500 operating hours per year exemption

Existing MCPs operating less than 500 hours per year as a 5 year rolling average are exempt from meeting MCPD ELVs.

New MCPs operating less than 500 hours per year as a 3 year rolling average are exempt from meeting MCPD ELVs.

If a dual fuel MCP uses its backup fuel for less than 500 hours per year (over the rolling average) the MCP is exempt from meeting the ELVs that apply to the backup fuel.

A MCP that is also a Part B activity must comply with MCPD ELVs even if the MCP operates for less than 500 hours per year on a:

  • 5 year rolling average – existing
  • 3 year rolling average – new

However you do not need to monitor every year. Instead you must monitor every 500 operating hours or every 5 years, whichever comes first.

(Video) Gas Monitoring for New Medium Combustion Plant Directive - MCPD

Extension to 1,000 hours

You can extend the 500 operating hours per year to 1,000 operating hours per year when you use an emergency or standby MCP:

  • for backup power generation in islands when the power supply is interrupted
  • to supply heat in exceptionally cold weather – the Department for Environment, Food and Rural Affairs (Defra) or Welsh Government will advise the Environment Agency or NRW when they class cold weather as exceptional

For dust the ELV of 200mg/Nm3 applies for plants firing solid fuel.

How to calculate operating hours

Operating hours start from when the MCP is operating and discharging emissions to air. The clock starts ticking at the end of start up (SU) and stops at the beginning of shut down (SD).

The regulators have adopted the IED rule on SU and SD. This defines a minimum start up load and a minimum shut down load for stable generation. Below this the combustion unit cannot deliver:

  • its output to the national grid (NG) safely and reliably
  • useful heat or electricity to an industrial or commercial site

See the detail in the Joint Environmental Programme (JEP) guide: IED compliance protocol for utility boilers and GTs.

For each MCP you must record its SU and SD value. This means one of the following:

  • the SU and SD thresholds as a fixed percentage of rated output
  • another separate criterion, for example a physical state of the MCP such as a valve opening which indicates stable operation

You must keep SU and SD periods as short as possible.

Manufacturers usually recommend a minimum percent load for their engines depending on the fuel. For example, typically 30% for diesel engines. The regulators will accept this where the value is not determined.

If the MCP has multiple flues, the start time begins once the first flue passes its SU threshold.

For GTs, ELVs apply above 70% full load, so the SU and SD value is 70% full load.

The first 12 month period starts on the day the permit is issued. You need to add up the operating hours of the first 5 or 3 year period and take the average. Thereafter the following 12 month period is added and the first 12 month period dropped off and you calculate a new average.

If your MCP qualifies for a 500 hour exemption it can run for more than 500 hours per 12 month period but it must not exceed:

  • 2,500 over 5 years
  • 1,500 over 3 years

The maximum number of operational hours allowed in a single 12 month period is 750:

  • before the MCP’s 5 or 3 year rolling operational period starts
  • if the MCP closes before the 5 or 3 year operational period ends

You must keep records of each 12 month period of operational hours for each MCP for 6 years.

You must tell the Environment Agency or NRW if any MCP exceeds the 500 hour annual operational limit in one 12 month period. You must prove that you have not exceeded the 500 hours rolling average over 5 or 3 years.

Gas compressor stations

GTs more than 5MWth used to drive gas compressor stations on the gas national transmission system are exempt from meeting ELVs until 1 January 2030.

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The compressor must be for natural gas on the NG and their operation must be essential to the safety and security of national gas supply.

Fuel supply interruption

When there’s a shortage of fuel supply or it’s stopped or interrupted, the regulator can suspend you from ELV compliance. If you normally operate your MCP with:

  • low sulphur fuel and cannot because of an interruption to fuel supply – you can get a suspension for up to 6 months
  • natural gas and you need to fire on standby liquid fuels (which would need secondary abatement to meet MCPD ELVs) – you can get a suspension for up to 10 days or longer

You must write to the Environment Agency or NRW to:

  • tell them why you need a suspension and the likely length required
  • provide evidence of fuel interruption and why you must maintain energy supplies

The Environment Agency or NRW:

  • will confirm acceptance in writing
  • must immediately inform Defra or Welsh Government

MCP located within an AQMA

If your MCP generates electricity you also need to review the specified generator permit conditions.

If your MCP is not a generator, for example it’s a boiler you must find out if your MCP is located within a local authority AQMA. You need to tell us this in your application. The regulator will consult the local authority to check if your MCP is identified in the associated Air Quality Management Plan.

If it is, your MCP emissions may be identified as adversely impacting air quality in the area. The local authority, in its plan, will identify how much stricter the ELV needs to be to deliver a noticeable improvement to air quality.

The regulator will include the agreed stricter ELV in your permit conditions.

MCP located near a habitats site

A habitats site can be a:

  • Special Area of Conservation
  • Special Protection Area
  • Ramsar site
  • Site of Special Scientific Interest

If your MCP is of low risk to air quality and can meet the rules in a standard rule permit, it sets the minimum requirements for the:

  • distance from the habitats site
  • stack height

The limits that apply to your MCP will depend on the fuel it uses and its technology.

If your MCP is of higher risk to air quality you may need to do an air emissions risk assessment of impacts to nature conservation sites. You will need to apply for a bespoke permit and submit your risk assessment with your application.

Read the guidance on how to do air emissions risk assessment.

Dark smoke

The MCP must not persistently emit dark smoke. See the guidance on how to identify dark smoke.

Monitoring requirements

For a new MCP you must start monitoring its emissions within 4 months of the permit being issued or the start of operation, whichever is the latest.

For an existing MCP you must start monitoring within 4 months of permit issue, you must have your permit issued by:

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  • 1 January 2024 – for an existing MCP between 5MWth and 50MWth
  • 1 January 2029 – for an existing MCP between 1MWth and less than 5MWth

You are required to do periodic monitoring at least every:

  • 3 years for a MCP less than or equal to 20MWth
  • year for a MCP greater than 20MWth

Apply for a MCPD environmental permit

You cannot apply for a permit until you can meet the required ELVs. You will need to fit secondary abatement ahead of applying for your permit if it’s needed to meet ELVs. Improvement conditions are not available for MCPD permits.

You need to:

  • select the correct permit to apply for
  • complete and submit the correct form, the fee and required information

See the guidance on Medium combustion plant: apply for an environmental permit.


Contact the Environment Agency

General enquiries

National Customer Contact Centre
PO Box 544
S60 1BY


Telephone 03708 506 506

Telephone from outside the UK (Monday to Friday, 8am to 6pm GMT) +44 (0) 114 282 5312

Monday to Friday, 8am to 6pm.

The impact of COVID-19 means you may experience some delays in responses.


Contact NRW.

(Video) (Webinar Recording) Ecodesign Webinar


What is medium combustion plant? ›

A medium combustion plant ( MCP ) includes all the following: a combustion unit, such as an engine, boiler or turbine. any abatement. the attached stack or flue.

Are generators classed as plant? ›

A generator is a combustion plant that generates electricity. The specified generator regulations apply to generators with a capacity up to 50MWth burning any fuel. Generators are classed as Tranche A or Tranche B.

What is a tranche a generator? ›

A generator with a rated thermal input of less than 1MWth is classed as Tranche A if it meets any of these conditions: its under a capacity agreement from the 2014, 2015 or 2016 capacity auctions (regardless of when the generator came into operation)

Do I need planning permission to install a generator? ›

Standby Diesel generators, especially those in inner-city or urban areas, can often require planning permission. With stricter guidelines around air quality and environmental health, planning for generators is a complex topic.

Can you run a house on a generator? ›

Small generators can power an appliance or two, while a whole-home generator (sometimes called a home standby generator) can power an entire house. The size of the generator that you purchase will depend on how you plan to use it.

Do generators need to be tested? ›

NFPA 101(12), Sec. 7.9. 2.4 requires that emergency generators providing power to emergency lighting systems be installed, tested and maintained in accordance with NFPA 110, Standard for Emergency and Standby Power Systems.

What is the noise level of diesel generator? ›

The maximum permissible sound pressure level for new diesel generator (DG) sets with rated capacity up to 1000 KVA, manufactured on or after the 2[1st January, 2005] shall be 75 dB(A) at 1 metre from the enclosure surface. Second Amendment Rules, 2002 notified vide Notification G.S.R. 371(E), dated 17.5.

What size generator do I need to run my house UK? ›

What size generator do I Need to Run the Whole House? Most essential house appliances, such as lighting and freezers, can be run from a generator with a 5,000 to 7,500-watt rating. A portable generator rated at the higher end of this scale can run most of your appliances at once.

What is the difference between plant and generator? ›

A Power Plant is built from a blueprint and a Generator is created in the upgraded Factory.

Is a power plant the same as a generator? ›

A portable generator is a machine the converts different types of energies into electric energy, while a portable power station is a rechargeable battery-driven source of power that is big enough to power your house or a campsite.

Which generator is used in power plant? ›

Other types of generators
GeneratorPlant typeMain fuel/energy source
Combustion gas turbineSingle cycleNatural gas2
Wind turbineAll typesWind
Hydroelectric turbineConventionalWater
PhotovoltaicAll typesSolar
11 more rows
1 Nov 2021


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