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Limitation of sulphur content in fuels
In the past, Hong Kong was suffering from serious air pollution caused by sulphur dioxide emission from factories and power plants burning sulphur-containing fossil fuels. Starting from 1990, the sulphur content in liquid fuel (e.g. diesel, kerosene etc.) is limited to 0.5% by weight and that of solid fuel (e.g. coal, coke, charcoal etc) to 1% by weight. To further reduce the amount of sulphur dioxide in air, diesel-driven vehicles are required to use fuel with sulphur content not more than 0.2% by weight starting from April 1995. Desulphurization of flue gas
Sulphur dioxide, a major air pollutant, is released during the combustion of coal which contains sulphur. By using low sulphur content coal, the quantity of sulphur dioxide released from combustion is much reduced. To further reduce sulphur dioxide emission, the generating unit of the coal-fired plant in Lamma Island is equipped with flue gas desulphurization (FGD) system. The FGD system utilizes a scrubbing process which is capable of removing 90% of the sulphur dioxide emitted from the boiler plant when burning coals with a wide range of sulphur contents. Flue gas from the boiler is directed to the absorber which contains a recycled slurry of limestone for the removal of sulphur dioxide. The treated flue gas leaving the absorber is then directed to the chimney for dispersal into the atmosphere.
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A
flue gas desulphurization plant in the United States
The flue gas cooler (a) upstream of the flue gas desulphurization
plant (FGD) transfers heat from the flue gas side to the air side by a
heat transfer circuit (b) and an air preheater (c). Therefore the main
air preheater (d) requires only approx. 75% of the flue gases leaving
the boiler. The remaining 25% are used to heat the feedwater