This page will present a brief description of the combustion process and its emissions.
Definition of Large Combustion Plants (LCPs)
In the EU’s Industrial Emissions Directive (IED) (art. 3, sub (25)) combustion plants are described as:
Under the scope of the IED (Chapter III) large combustion plants are:
Under the scope of the IED (Chapter III) combustion plants are not:
- plants in which the products of combustion are used for the direct heating, drying, or any other treatment of objects or materials;
- post-combustion plants designed to purify the waste gases by combustion which are not operated as independent combustion plants;
- facilities for the regeneration of catalytic cracking catalysts;
- facilities for the conversion of hydrogen sulphide into sulphur;
- reactors used in the chemical industry;
- coke battery furnaces;
- cowpers (i.e. a hot blast stove using coke oven gas);
- any technical apparatus used in the propulsion of a vehicle, ship or aircraft;
- gas turbines and gas engines used on offshore platforms;
- plants which use any solid or liquid waste as a fuel (i.e. incinerators) other than waste biomass.
The EU’s Large Combustion Plant Directive (2001/80/EC) was previously in the process of full incorporation into the IED (2010/75/EU). Since January 2016 the IED applies to all large combustion plants.
Combustion process
Combustion is a fast chemical reaction of oxygen with flammable elements of the fuel. The two relevant chemical elements are carbon and hydrogen and sulphur at a smaller quantity. A good combustion aims to create the maximum possible amount of heat while minimizing losses due to the combustion reaction of fuel with oxygen.
Combustion processes using solid fuels are usually performed at atmospheric pressure or high pressure achieving that all of the energy of the solid fuel is converted into heat and then transferred into steam to produce energy. Steam generators (or boilers) that are used in this process may be of natural forced circulation and of circulation formed in a single step. Boilers are composed of a combination of an economizer, an evaporator, and a super-heater (or re-heater).
The steam turbine consists of a rotary engine using the calorific value of the steam to produce mechanical energy from the expansion of the high pressure steam from the boiler. The combustion technology is determined by the type of solid fuel and by the pollution abatement techniques that will be used.
Electrostatic Precipitators (ESPs) and fabric filters (FF) are particulate collection devices removing particles from flowing gases. Flue Gas Desulphurisation (FDG) plants are a set of technologies used to remove sulphur dioxide (SO2) from exhaust flue gases of fossil-fuel power plants, and from the emissions of other sulphur oxide emitting processes. Control of nitrogen oxides (NOx) emissions is achieved through the application of DENOx systems.
The capacitor is the part of the installation that allows for cooling and condensing the low pressure residual steam coming from the turbine. Depending on the environmental impact that is caused by the water intake and the final discharge, cooling systems of power plants can operate as an open or a closed circuit. Cooling towers use the evaporation of water and cool the working fluid to near the wet-bulb air temperature. In the case of closed circuit dry cooling towers, they rely solely on air to cool the working fluid to near the dry-bulb air temperature.
Normally, large combustion plants operate a considerable number of ancillary systems to the main process of energy production, all with their own environmental impacts.
