A Claus plant converts gaseous sulfur compounds to elemental sulfur, thereby eliminating emission of sulfur into the atmosphere. The process can be especially important in the gasification of coal, which contains significant amounts of sulfur that is converted to H2S during gasification. In the Claus process, the H2S-rich product gas recovered from an acid-gas removal system following the gasifier is split, with one-third going to a furnace where the hydrogen sulfide is burned at 1 atm with a stoichiometric amount of air to form SO2.

The hot gases leave the furnace and are cooled prior to being mixed with the remainder of the H2S-rich gases. The mixed gas is then fed to a catalytic reactor where hydrogen sulfide and SO2 react to form elemental sulfur.
2H2S + SO2 ( 2H2O + 3S
The coal available to the gasification process is 0.6 wt% sulfur, and you may assume that all of the sulfur is converted to H2S, which is then fed to the Claus plant.
(a) Estimate the feed rate of air to the Claus plant in kg/kg coal.
(b) While the removal of sulfur emissions to the atmosphere is environmentally beneficial, identify an environmental concern that still must be addressed with the products from the Claus plant.

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H2S +O2 → SO +H2O|