Combustion plants (e.g. in relation to industrial heat production, district heating or electricity generation, not forgetting the propulsion of ships) are based on the use of fuels such as natural gas, liquefied petroleum gas, biomethane, heating fuel, coal, heavy fuel oil, biomass or biogas.

Some combustion products released to the atmosphere are undesirable and their rate must be restricted (by exhaust gas clean-up), in relation to the environmental and ecological concern for which sensitivity seems to be - and it is fortunate for those concerned with the sustainability of life, not just human, on the planet - growing, at least in Western Europe.

In many countries in the world, and for a long time, limits of emission of atmospheric pollutants exist, the non-respect of which leads to the impossibility of putting into operation installations e.g. of stationary engines for power generation or the prohibition to penetrate in some territorial waters for boats.

In France, Decree No. 2018-704 of August 3, 2018 amending the nomenclature of Establishments Classified for Environmental Protection (ECEP) and some provisions of the Environment Code (e.g. the contents of the application document package for authorization and registration) transposes into French law (EU) Directive No 2015/2193 of 25 November 2015 on the limitation of emissions of certain pollutants into the air from Medium Combustion Plants (MCP).

This applies in particular:

  • to engines: gas, diesel or dual fuel, defined (in the directive) as follows:
    • "'gas engine"': internal combustion engine operating according to the Otto cycle and using spark ignition to burn fuel
    • "'diesel engine": an internal combustion engine operating on the diesel cycle and using compression ignition to burn fuel
    • "'dual fuel engine": an internal combustion engine using compression ignition and operating according to the diesel cycle to burn liquid fuels and according to the Otto cycle to burn gaseous fuels
  • to gas (combustion) turbines defined (in the directive) as follows:
    • any rotating device which converts thermal energy into mechanical work and consists mainly of a compressor, a thermal device for oxidizing the fuel so as to heat the working fluid and a turbine; this definition includes open circuit gas turbines and combined cycle gas turbines, as well as gas turbines in cogeneration mode, whether or not equipped with an additional burner in each case

The following are concerned: new installations with a capacity of more than 1 megawatt (MW) from 20 December 2018, existing installations with a capacity of more than 5 MW from 1 January 2025 and existing installations with a power between 1 and 5 MW from January 1, 2030.

Emission limit values (in mg/Nm3) are now fixed:

  • depending on the fuel
    • solid: biomass or other
    • liquid: diesel fuel or other
    • gaseous: natural gas or other
  • for different pollutants:
    • sulfur dioxide (SO2
    • nitrogen oxides NOx
    • dust

With regard to nitrogen oxides NOx:

  • for existing engines and gas turbines, these limits are (in Table 3 of part 1 of Annex II of Directive (EU) n° 2015/2193 of 25 November 2015) defined as follows: respectively 190 mg/Nm3 except exceptions [1] and 200 mg/Nm3 except exception [2]
  • for new engines and new gas turbines, these limits are (in Table 2 of Part 2 of Annex II of Directive (EU) No 2015/2193 of 25 November 2015) defined as follows: respectively 190 mg/Nm3 with exceptions [3] and 75 mg/Nm3 except exceptions [4]

Combined or not with silencers designed to reduce noise, Selective Catalytic Reduction SCR devices (catalytic converters) marketed by ITS are able to limit the air pollutants contained in the exhaust gases of heat engines, to prevent the pollution of air. They allow Medium Combustion plants (MCP) to comply with regulation, as in France, transposing a European directive, a decree has been limiting pollutant (e.g. NOx) emissions into the atmosphere since 2018.

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Selective Catalytic Reduction Device SCR - catalytic converter

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[1] 250 mg/Nm3 to 1850 mg/Nm3 depending on the considered combination of variables which are the type of engine (and its fuel), its thermal power, its date of construction
[2] 150 mg/Nm3 if the fuel is natural gas
[3] 225 mg/Nm3 to 1850 mg/Nm3 depending on the considered combination of variables which are the type of engine (and its fuel), its thermal power, its number of hours of use
[4] 50 mg/Nm3 if the fuel is natural gas, 550 mg/Nm3 (until January 1, 2025) for facilties that are part of isolated small networks or micro-grids within the meaning of Article 2 of Directive 2009/72/EC of the European Parliament and of the Council
[5] the emission limit values are valid for a temperature of 273.15 K, a pressure of 101.3 kPa and after correction according to the water vapor content of the waste gases, and for a standardized content of O2 (15% in the case of gas engines and turbines)