In order to minimise pollutants produced by industrial combustion processes such as energy from waste plants lime is used to ‘scrub’ acid pollutants such as HCL and SO2 from the exhaust gases.
Flue gases produced when burning fossil fuels that contain sulphur result in emissions to the atmospheres that are the principal cause of acid rain. Acid gases containing oxides of sulphur can be treated by introducing limestone, chalk, quicklime or hydrated lime as a powder or slurry, promoting a reaction to form insoluble calcium sulphate or gypsum which can then be collected. If carried out under the correct conditions this process can produce a saleable gypsum co-product.
Energy from Waste
In recent years there has been an increase in the number of energy from waste plants all of which could be sources of acid rain whether they burn municipal or industrial waste, clinical waste, animal carcasses or natural fuels. Almost all incinerators around the world have utilised lime as a means of removing harmful gases for many years and proved lime to be cost effective, efficient and sustainable.
Lime is sprayed into the flue gas stream in the form of a dry powder or as a suspension in water. It then reacts with the pollutants to form an insoluble salt which is easy to dispose of. In the case of desulphurisation it is possible to produce quality gypsum (calcium sulphate) which can be used as a raw material in plaster or plasterboard.
Flue Gas Treatment
Lime, being the most cost effective alkali, is widely used in the removal of acidic gases emitted by power stations.
Lime based techniques for the abatement of acidic gases can be divided into 5 groups:
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