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The Medium Combustion Plant Directive - MCPD

On the 25th of November 2015, the Directive 2015/2193 was published “on the limitation of emissions of certain pollutants into the air from medium combustion plants.” It will pass into UK Law on the 19th of December 2017. Referred to as The Medium Combustion Plant Directive or MCPD it plugs the gap between the Industrial Emissions Directive 2010/75/EU (the IED) and the “Eco-Design” Directive 2009/125/EC.

It will apply to all operators and owners of combustion plant rated between 1 MW and 50 MW thermal input.

A “combustion plant” is “…any technical apparatus in which fuels are oxidised in order to use the heat thus generated” so it will cover boilers, turbines, and engines.  The rules are intended to apply to both new and existing equipment.”

The Directive places limits on the concentration levels of sulphur dioxide (SO2), oxides of nitrogen (NOX), and particulates in exhaust gases from affected plant.  These Emissions Limit Values (ELV’s) vary according to the type of plant and the fuel used but the general aim is to reduce the background levels of these harmful substances.  Furthermore, it will be necessary to monitor (but not limit) carbon monoxide (CO). 

Please see below for our FAQ’s on the Medium Combustion Plant Directive.

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Will I be affected?

The Directive applies to any combustion plant with a nett rated thermal input of between 1 MW and 50 MW that doesn’t already fall into Chapter III or IV of the IED (essentially, installations over 50MW or those involved in the incineration of waste). There is a list of other exemptions in Q6.

“combustion plant” is “…any technical apparatus in which fuels are oxidised in order to use the heat thus generated” so it will cover boilers, turbines, and engines.  The rules are intended to apply to both new and existing equipment.  for comparison, 1MW thermal input would capture any steam boiler rated at 1,400 kg/hr (3,000 lb/hr)

I have several appliances that are individually less than 50 MW but the combined input is more than 50 MW. Will MCPD apply to me?

No, you have a Chapter III installation under IED (also referred to as a Part A1 installation in UK pollution permitting and control legislation).

The Large Combustion Plant Directive aggregates all combustion units on a single site including those as low as 15MW nett thermal input; if the total thermal input is >50MW you have an LCP installation.  You should already be working towards an EA permit.

I have several appliances that are individually less than 1 MW but the combined input is more than 1 MW. Will MCPD apply to me?

The UK implementation intends to include all diesel powered generator installations, even if individual units are smaller than 1MW.  Other appliances individually under 1MW will not be covered (even if they add up to an installation of 1MW or more) as they already covered by the “Eco Design” Directive.

I have a mixture of plant, some above 1MW and some below, how will MCPD apply to me?

Assuming that the aggregated total is less than 50 MW, MCPD would apply to apparatus over 1 MW (and all diesel powered generators irrespective of output) while the “Eco Design” Directive would apply to those below. As an example, an installation consists of a 2 MW engine, a 5 MW steam boiler, and two 500 kW hot water boilers. The hot water boilers fall outside MCPD (they are “Eco-Design” Directive) both the engine and the boiler are within the scope of MCPD and need to meet the individual ELV’s for that type of plant.  Generators, irrespective of size, will be regulated under MCPD in the UK.

What is “aggregation”?

Several Directives lump together all of the combustion plant on a site that already share the same stack (or could reasonably do so) into one total input figure (so two 2 MW input appliances would make a 4 MW installation). This is used in part to decide if you are a Large Combustion Plant under IED and will also determine the monitoring interval for your site under MCPD.

MCPD is slightly more complicated in that only plant supplied after 20th December 2018 will be subject to aggregation.  Multi plant sites will need to look closely as they replace an individual piece of plant to see how the MCPD will affect them after the change.  One thing to note is that aggregated plant 20MW and below is subject to triennial testing while aggregated plant over 20MW will be subject to annual testing.

It would be “reasonable” to discharge through a single stack any plant within the same plant room so using separate stacks for plant will not be an effective means of avoiding the aggregation rule.

So what will the new rules be?

All newly registered plant will require a permit from the 20th of December 2018 in order to operate.  It is proposed that installations between 1 MW and 20 MW will be inspected every 3 years to ensure compliance with the ELV’s while installations over 20 MW will be tested annually.  Additionally the carbon monoxide emissions will be recorded for all installations but currently, no limit has been proposed.

Plant registered before 20th December 2017 and operational before 20th December 2018 will have less stringent ELV’s and have longer to meet them.  January 2024 if it is over 5MW (2029 for smaller plant) with emissions limits applying from January 2025 (2030 for smaller plant)

There is some debate about the difficulties of a 3 year (as opposed to annual) testing regime so this may yet change.

How will the law be implemented in the UK?

The implementation will be via amendments to the existing permitting laws;

  • Environmental Permitting (England and Wales) Regulations
  • Pollution Prevention and Control (Scotland) Regulations
  • Pollution Prevention Control (Industrial Emissions) Regulations (Northern Ireland)

These already place emissions limits on installations in the region of 20 MW to 50 MW falling outside of IED (what are known as Part B or Part C installations).  We anticipate that where there is a conflict between the MCPD ELV’s and existing ELV’s that the lower value will apply.

If you are currently outside the scope of these regulations then the MCPD ELV’s will apply.

The Clean Air Act will be amended to avoid double regulation.

Emissions of SO2 are already limited through The Sulphur Content of Liquid Fuels Regulations (SCoLF) and it was thought that these would need to be updated to reflect a necessary drop in the S content of heavy fuel oil, instead DEFRA are relying on a clause inserted in 2014 that gives precedence to any permit setting SO2 limits at least as stringent as those laid out in Annex V of the Industrial Emissions Directive and since MCPD ELV’s are aligned with IED and will require permits to be issued, then there is no need to update the SCoLF Regulations.

Biomass boilers installed under the Renewable Heat Incentive since 2013 already have ELV’s in place for particulates and NOX.  The proposed MCPD limits are tighter and also include SO2 which was not included in the RHI ELV’s.

Who will issue the permits?

This has been a particularly hot potato, but we seem to have finally settled on the following;

England:  The Environment Agency
Northern Ireland: Northern Ireland Environment Agency
Scotland:  SEPA
Wales:  Natural Resources Wales

Local Authorities will be consulted by the appropriate Permitting Authority whenever the plant is considered high risk (e.g., burning non-standard fuels) and whenever a plant falls within an Air Quality Management Area.  To find out if you’re in an AQMA (and a high proportion of plant will be), you can use the interactive map here:

Plant falling within an AQMA may well have stricter ELV’s imposed than those featuring in the tables above.

It is envisaged that the application will be managed through a regional web portal.

Permits are currently predicted to cost between £90 and £310 per year for most applicants with the highest risk plants paying up to £800 per year.  There will also be a one off registration fee around £200 for low-risk plants, and up to £1600 for the highest risk plants.  A more detailed fee structure is not currently available.

Who will do the sampling?

The details are yet to be established but the Environment Agency is eager to see “low risk” plants (which we take to mean those burning standard fuels complying with a recognised standard such as natural gas, LPG, or light oils to BS 2869) receive a “light touch” approach.

Higher risk plant (those burning “dirtier” or non-standard fuels) and plant over 20MW are now looking likely to require an MCERTS approved testing house.  The testing regime will form part of the permit and may in some cases require Continuous Emissions Monitoring

There are two proposed testing regimes;

random testing which would require the end user to arrange testing and retain records which are made available to the authorities on request or;

scheduled testing where the testing is performed either in front of the Regulator or reports are passed to the Regulator at specified times.

The preference appears to be for the former which, as well as being the lower cost option, is also the most likely to maximise compliance.


How do I know if my existing boiler meets the new regulations?

If you operate a Part B or C installation or have a biomass plant registered after September of 2013 you will already have emissions reporting from an MCERTS approved lab so you should only need to compare your most recent test against the MCPD ELV’s.

Everyone else can get an idea of where they stand from recent service reports which should show NOX and, where relevant, SO2.  While these are not a substitute for an MCERTS approved testing house, it will serve as an indication as to whether or not you may have a problem to address in the coming years.

If you’re firing a gaseous fuel from a mainstream source such as natural gas or LPG you will probably already comply with the proposed limits for NOX for existing plant.

Rules controlling the amount of sulphur in liquid fuels will mean that diesel fired plant will automatically meet the proposed ELV’s.

HFO fired plant will not to meet the ELV’s for SO2 or particulates without abatement.

What do I do if my existing boiler doesn’t meet the new regulations?

Existing plant over 5MW will need to comply by the 1st of January 2025 while plant in the 1 to 5MW range will need to comply by 1st of January 2030 so you have a bit of time to bring your plant into compliance. Depending on where you are non-compliant, there are a number of things that can be done; the costs will vary and it will obviously be an economic decision if you replace or modify the plant. Note that if you replace the equipment, it must be put into operation before the 20th of December 2018 to be considered “existing plant”. Plant registered or put into service after these dates will need to comply with the stricter “new equipment” ELV’s

The following is quick overview of techniques available to you to help in reducing your emissions;


NOX is produced primarily from the heat of the flame reacting with nitrogen in the air.  Liquid and solid fuels generally also contain an amount of nitrogen in the chemical structure which add to the NOX level when burned although this difference is already reflected in the different proposed levels.

In order of increasing cost, NOX can be controlled by:

  • careful commissioning of the burner,
  • careful matching of a boiler and a burner
  • the design of the burner itself (multi-nozzle heads, premix heads, water injection) and
  • abatement techniques such as flue gas recirculation (FGR) or by chemical treatment in the flue


SO2 emissions are entirely related to the amount of sulphur present in the fuel to begin with.  To reduce the level of SO2 in the flue gas you have only three options;

  • Specify a low sulphur version of your existing fuel (if one is available)
  • Switch to a different grade of fuel (such as switching from heavy fuel oil to diesel or LPG)
  • Apply abatement techniques post-boiler

Your service provider will advise on the impact of changing fuel grade or sulphur level which could be anything from a simple recommissioning of the existing plant through to infrastructure changes (as would be the case of someone switching to LPG).

Anyone considering LPG or LNG may find that the fuel supplier is prepared to cover the capital costs of converting existing equipment in return for a longer terms supply agreement.


Particulates are caused partly through incombustibles in the fuel (ash) and partly by incomplete combustion of the fuel itself (soot).

  • The combustion of solid fuels and heavy fuel oil will unavoidably require filtration of the flue gas in order to meet the emissions targets
  • “other” liquid fuels meeting BS 2869 should be acceptable so long as the combustion equipment is modern and well looked after

Emission limit values for existing medium combustion plants

Table 1 (below): Emission limit values (mg/Nm3) for existing medium combustion plants with a rated thermal input equal to or greater than 1 MW and less than or equal to 5 MW

Pollutant Solid biomass Other solid fuels Gas oil Liquid fuels other than gas oil Natural gas Gaseous fuels other than natural gas
SO2 200 1 100 350 200
NOx 650 650 200 650 250 250
Dust 50 50 50

Table 2 (below)
: Emission limit values (mg/Nm3) for existing medium combustion plants with a rated thermal input greater than 5 MW

Pollutant Solid biomass Other solid fuels Gas oil Liquid fuels other than gas oil Natural gas Gaseous fuels other than natural gas
SO2 200 400 350 35
NOX 650 650 200 650 200 250
Dust 30 (10) 30 (10) 30

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