Patent ID: 8527071

Claim:
For a sulfur recovery plant, comprising a furnace ( 3 ), first conduit ( 1 ) for passing a first feed stream of acid gas containing hydrogen sulfide H 2 S into said furnace, second conduit ( 5 ) for passing a second feed stream of air into said furnace to convert part of the H2S contained in the first feed stream to sulfur dioxide SO2, third conduit ( 8 ) for withdrawing the resulting gaseous reaction mixture, containing free sulfur and unreacted H2S and SO2 gases, from said furnace, a catalytic sulfur converter means ( 9 ) to convert a portion of the unreacted H2S and SO2 gases contained in said gaseous reaction mixture to free sulfur, a sulfur removal apparatus to remove the free sulfur from the resulting gaseous reaction mixture produced in said catalytic sulfur converter thereby producing a tail gas stream containing unreacted H2S and SO2; an apparatus comprising a first flow sensor ( 13 ) for establishing a first signal representative ( 15 ) of an actual flow rate of said first feed stream flowing through said first conduit; a second flow sensor system, which is comprised of two flow sensors ( 16 ), ( 19 ), for establishing a second signal representative of an actual flow rate of said second feed stream flowing through said second conduit; a first analyzer ( 22 ) for establishing a third signal representative ( 23 ) of the H2S concentration in said tail gas stream; a second analyzer ( 24 ) for establishing a fourth signal representative ( 25 ) of the SO2 concentration in said tail gas stream; a set point entry module for establishing a fifth signal representative ( 26 ) of a required ratio of H2S concentration in said tail gas stream to SO2 concentration in said tail gas stream through operator entry or programming a default value of 2; a first computation module for establishing a sixth signal representative ( 43 ) through multiplication of said third signal representative by said fifth signal representative and subtracting from this product said fourth signal representative; a second computation module for establishing a principal air flow demand signal ( 49 ); a third computation module for establishing a supplemental air flow demand signal ( 45 ), where supplemental air flow demand can be positive, zero or negative quantity; a fourth computation module for establishing a total air flow demand signal ( 51 ) through summation of said principal air flow demand signal ( 49 ) and said supplemental air flow demand signal ( 45 ); and valve system for manipulating the flow rate of said second feed stream of air in response to said total air flow demand signal ( 51 ).