Adaptive control system for a sulfur recovery process

For a sulfur recovery plant, comprising a furnace (3), first conduit (1) for passing a first feed stream of acid gas containing hydrogen sulfide H2S 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).