NOx emissions from coal combustion, IEACR/36

Author(s): LL Sloss

Ref: IEACR/36
ISBN: 92-9029-189-3
Published Date: 01/03/1991
No. of Tables: 12
No. of Figures: 17
No. of Pages: 62

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The two most important oxides of nitrogen with regard to air pollution are nitric oxide (NO) and nitrogen oxide (NO2), jointly referred to as NOx in the context of the environment. Global emissions of NOx and of another oxide of nitrogen, nitrous oxide (N20), are increasing. These gases play important roles in the environment through acidification, forest damage, smog formation direct and indirect damage to human health, depletion of the stratospheric ozone layer and the greenhouse effect. Although NOx arise from natural sources, the majority of emissions are due to combustion and fossil fuels. Combustion of coal, oil, gas and related fuels in both stationary and mobile sources accounts for around 42% of total global NOx emissions. Power stations are likely to account for 25% of emissions due to human activities, of which only part is due to coal. Emissions of N20 are primarily from natural sources but the increase in emissions in the last century is due to human activities. By far the largest source of NOx in most IEA countries is oil, and particular the transport sector which alone accounts for at least 50% of the emissions arising from human activities. Stationary combustion sources, including power stations firing coal, are often the second largest sources of NOx emissions in these countries. Actual emission values vary between countries due to the difference in type and quantity of fuel burned. Emissions of NOx from all combustion sources, both stationary and mobile, are increasing at a faster rate than the overall economies of nations. As a consequence of increasing emissions, especially those from vehicular sources, ground level concentrations of NOx in major cities are also increasing. Emissions from power stations are normally released from high stacks outside densely populated areas where dispersal of pollutants is optimal. Following recent research into environmental damage and possible future trends, most countries recognise the importance of the reduction in the emission of pollutants such as NOx. The UNECE international agreement requires that all members freeze total NOx emissions at 1987 levels by 1994. Member countries are aiming to achieve this freeze by either adopting the standards laid down in the EC directive or introducing more stringent national limits. Several countries including the FRG, Japan and the USA, introduced restrictions on NOx emissions a number of years ago and these countries are already reporting a reduction in emissions in some areas. Other countries have been slow to follow and we can only speculate as to whether the legislation being introduced is sufficient to reduce total emissions of NOx and whether this will result in any reduction in environmental damage.

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