A method for removing sulfur dioxide from combustion stack gas. A slurry of finely ground alkaline material such as calcium carbonate is sprayed into the effluent gases before it enters the smokestack. The material reacts chemically with sulfur dioxide to produce a non-hazardous solid product, such as calcium sulfate, that can then be collected by filters or other mechanical means. The technique is called dry injection because the amount of water in the slurry is adjusted so that all moisture evaporates while the chemical reactions are taking place and a dry precipitate results. The use of dry alkali injection can result in a 90% reduction in the emission of sulfur dioxide from a stack. It is more expensive than wet alkali injection or simply adding crushed limestone to the fuel, but it is more effective than these techniques and results in a waste product that is relatively easy to dispose of.

See Also

Air Pollution Control