4. Problems derived from the combustion of heavy liquid fuels
The use of heavy oils has several handicaps under practical conditions. Most of them stem from the chemical composition of the fuel. For instance, emissions of NOX and SOX, which lead to air pollution, smog, acid rain, etc., can arise from the nitrogen and sulphur contained in the fuel. Particulates, which originate from the heavier fractions of the fuels, cause severe environmental pollution and intense public health concern. Moreover, they also inflict severe economic losses on operators as unburned fuel and deposits in combustion facilities.
In addition, expensive fines are imposed if the legislated emission limits are exceeded.
A clear understanding of the processes whereby these species are formed and emitted can facilitate the formulation of practical strategies aimed at their reduction.
Nitrogen present in the combustion system, provided either in the combustion air or the fuel, reacts during combustion to form NO and NOX, and also NXO in fairly minor amounts. It is generally understood that the oxides of nitrogen (NOX) consist of nitric oxide (NO) and nitrogen dioxide (NOX). Normally NO is formed in much larger amounts than NO2, and the latter is thought to be formed by further reaction of NO. Hence, NO formation determines the total amount of NOX emitted.
Nitrogen oxides are atmospheric pollutants. They contribute to the ozone-depletion cycles in the stratosphere and to photochemical smog, and they constitute the most important emission from combustion devices. Motor vehicles, electric power plants and industrial boilers account for most of the emissions of NOX.
However, the most noxious effect are caused by NOX, by reacting with hydrocarbons, ozone and light to produce smog. In addition, NOX reacts with water to produce acid which causes corrosion problems and acid rain.
The maximum NOX emissions from liquid fuels permitted in Europe by EU Directive 88/609 are 450 mg/Nm3 (EEC: Council Directive of 24 November 1988) .
Pollutant formation and interaction in the combustion of heavy liquid fuels
Luis Javier Molero de Blas, PhD thesis, University of London, 1998
© Luis Javier Molero de Blas
