SULFUR RECOVERY
The sulfur compounds from the feedstock of a gasification-based process are generally removed from the synthesis gas as a concentrated stream of hydrogen sulfide and carbon dioxide known as acid gas. Depending on the design of the upstream AGR unit, the acid gas may contain other sulfur species such as COS as well as ammonia and hydrogen cyanide. It is unacceptable to emit H2S, a highly toxic, foul-smelling gas, to the atmosphere, so it is necessary to fix it in one form or other. There are essentially two alternative products in which one can fix the sulfur, either as liquid or solid elemental sulfur, or as sulfuric acid. The choice of product will depend on the local market. Where there is a strong local phosphate industry, then there will be a good local market for sulfuric acid. If this is not the case, then elemental sulfur will probably be the better choice, since bulk transport of this material is much easier than of the concentrated acid.