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

Natural Resources Wales

September 1
11:38 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 its 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 thats 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:

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:

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 fuels thermal input (find the oxygen correction formula in Part 7 of the Industrial Emissions Directive)
  • divide the sum by the MCPs total rated thermal input

Do this calculation for each fuel. Then add together each fuels contribution to get the MCPs 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.

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

MCPD does not include landfill gas as a fuel in a combustion plant. The Environment Agency and NRW will accept the SO2 ELV for biogas.

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.

ELV exemptions

Check if your MCP is:

  • exempt from meeting ELVs
  • required to meet relaxed ELVs or theres 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 averag

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