Medium combustion plant

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.

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. 

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. 

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). 

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. 

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.

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.

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). 

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.  

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. 

For medium combustion plant that have a separate backup fuel, such as gas oil, monitoring of emissions must also be undertaken on the backup fuel to demonstrate compliance with the backup fuel emission limit values. Where the backup fuel emission limit values cannot be met, SEPA will allow up to 50 hours of testing per year and during this period the emissions are exempt from complying with the backup fuel emission limits. Medium combustion plant must not run on the backup fuel for more than 50 hours per year unless the operator can demonstrate compliance with the appropriate emission limit values.

Medium combustion plant running on natural gas or liquefied petroleum gas (LPG) that experience a sudden interruption in the gas supply, can continue to run on liquid fuel. Operators must apply for an exemption from meeting the emission limit values for up to 10 days, by notifying SEPA.

Backup medium combustion plant that operate less than 500 hours per year may be exempt from emission limit values but are still required to carry out emissions monitoring for carbon monoxide.

There are some other cases where exemptions from meeting the emission limit values may apply, and these are outlines in the PPC 2012 Regulations and in Article 6 of the Medium Combustion Plant Directive.

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. 

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.

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. 

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.  

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 2028. 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. 

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). 

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.

(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.  

See Article 6(13) of the MCPD. 

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.  

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.