Chemical Engineering question. An analysis of the waste solvent vapors from a pl

Question

Chemical Engineering question.

An analysis of the waste solvent vapors from a plant showed that the gas contained 20 mol% CH4, 20 mol% CS2, 10 mol% SO2 and 50 mol% H2O. It has been proposed that the gas be combusted with excess air and then emitted to the air. Air pollution regulations limit the concentration of SO2 in the stack gases to below 2 mol% on a dry basis. Using a sutiable basis for it.

1)Calculate the minimum percent excess air assuming complete combustion, that must be used to meet this requirement.

2) What is the composition of the stack gases on a wet basis?

Explanation / Answer

CH4 + 2O2 ----->CO2 + 2H2O

20 mol% CH4 means

20 mol% CO2 and 40 mol% H2O

CS2 + 3O2 ----> CO2 + 2SO2

20 mol% CS2 means 20 mol% CO2 and 40 mol% SO2

SO2 + H2O ---->H2SO3

SO 40 mol% SO2 and 40 mol% H2O will combine to give 40 mol% H2SO3

10 mol% SO2 in the original will combine with 10 mol% H2O to give 10 mol% H2SO3

1) Oxygen required is 100 mol% with respect to the flue gas because 40mol% is required for CH4 and 60 mol% is required for CS2.

2) The output gas is 40mol% CO2 + 40 mol% H2O so in the total

So finally we have 50 mol% CO2 and 50mol% H2O

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