A Claus plant converts gaseous sulfur compounds to elemental sulfur,thereby elim

Question

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 gasication of coal, which contains signicant amounts of sulfur that is converted to H2S during gasication.In the Claus process, theH2S-rich product gas recovered from an acid-gas removal system following the gasifer is split,with one-third going to a furnace where the hydrogensulde is burned at 1atm with a stoichiometric amount of air to form SO2. H2S+3/2O2 ----> SO2+H2O

ThehotgasesleavethefurnaceandarecooledpriortobeingmixedwiththeremainderoftheH2S-rich gases. The mixed gas is then fed to a catalytic reactor where hydrogen sulde and SO2 react to form elemental sulfur. 2H2SSO2 !2H2O3S The coal available to the gasication process is 0.6wt% 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) Whiletheremovalofsulfuremissionstotheatmosphereisenvironmentallybenecial,identifyan environmental concern that still must be addressed with the products from the Claus plant.

Explanation / Answer

Basis : 1 kg of coal, It contains 0.6 wt% Sulfur, Sulfur in the coal =1000 gm*0.6/100 = 60 gm

H2+S---> H2S

1 mole of Suflur reacts to give 1 mole of H2S

Mole of S in the coal = 60/32 ( atomic weight of S= 32)=1.875 moles

Moles of H2S formed= 1.875 moles

1/3 of this is sent for SO2 formation , moles of H2S sent for SO2 formation = (1/3)*1.875=0.625 moles

from the reaction H2S+ 1.5O2---> SO2+H2O

1 mole of H2S required 1.5 moles of O2

0.625 moles of H2S requires 0.625*1.5 =0.9375 moles

Molecular weight of Air = 29, mass of air = 0.9375*29 =27,2 gm=27.2/1000 kg of Air=0.0272 kg air per kg coal

The conversion of H2S to S is only 97% leaving unreacted SO2 and H2S

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