Selective removal of H2 S from gas mixtures containing CO2 and H2 S

Claim 1

A method for selectively removing H 2 S from a gas mixture containing H 2 S and CO 2 in a molar ratio in excess of 4CO 2 :1H 2 S wherein said gas mixture undergoes substantial variation in flow rate comprising the steps of: (a) Countercurrently contacting said gas mixture in an absorption zone with an aqueous scrubbing solution of alkali metal carbonate at an absorption temperature of at least 60° C. and under super-atmospheric pressure thereby absorbing CO 2 and H 2 S in said solution, (b) Regenerating said solution in a regeneration zone at approximately atmospheric pressure by countercurrently steam stripping said solution, (c) Supplying stripping steam to said regeneration zone at a steam/gas ratio selected to reduce the equilibrium partial pressure of H 2 S above said solution at the bottom of the regenerator to a value which will provide the desired partial pressure of H 2 S in the purified gas leaving said absorption zone, (d) Controlling the partial pressure of H 2 S in the purified gas at a substantially constant value by maintaining said selected steam/gas ratio substantially constant as said gas flow varies, (e) Adjusting the solution/gas ratio in said absorption zone to a selected ratio in the vicinity of that at which the partial pressure of H 2 S in the purified gas remains at said desired value and at which the difference between the partial pressure of CO 2 and H 2 S in the purified gas reaches a maximum level, (f) Maintaining said selected solution/gas ratio at a substantially constant value as said gas flow varies, whereby the purified gas is selectively reduced in H 2 S content and whereby the ratio of H 2 S to CO 2 absorbed is rendered substantially independent of variations in gas flow.

Claim 2

A method for selectively removing H 2 S from a gas mixture containing H 2 S and CO 2 in a molar ratio in excess of 4CO 2 :1H 2 S wherein said gas mixture undergoes substantial variation in flow rate comprising the steps of: (a) Countercurrently contacting said gas mixture in an absorption zone with an aqueous scrubbing solution of alkali metal carbonate at an absorption temperature of at least 60° C. and under super-atmospheric pressure thereby absorbing CO 2 and H 2 S in said solution, (b) Regenerating said solution in a regeneration zone at approximately atmospheric pressure by countercurrently steam stripping said solution, (c) Supplying stripping steam to said regeneration zone at a steam/gas ratio selected to reduce the equilibrium partial pressure of H 2 S above said solution at the bottom of the regenerator to a value which will provide the desired partial pressure of H 2 S in the purified gas leaving said absorption zone, (d) Controlling the partial pressure of H 2 S in the purified gas at a substantially constant value by maintaining said selected steam/gas ratio substantially constant as said gas flow varies, (e) Adjusting the solution/gas ratio in said absorption zone to a selected ratio in the vicinity of that at which the partial pressure of H 2 S in the purified gas remains at said desired value and at which the difference between the partial pressure of CO 2 and H 2 S in the purified gas reaches a maximum level, (f) Maintaining said selected solution/gas ratio at a substantially constant value as said gas flow varies, whereby the purified gas is selectively reduced in H 2 S content and whereby the ratio of H 2 S to CO 2 absorbed is rendered substantially independent of variations in gas flow.

Claim 9

A method for selectively removing H 2 S from a gas mixture containing H 2 S and CO 2 in a molar ratio in excess of 4CO 2 :H 2 S wherein said gas mixture undergoes substantial variation in flow rate comprising the steps of: (a) Countercurrently contacting said gas mixture in an absorption zone with an aqueous scrubbing solution of alkali metal carbonate at an absorption temperature of at least 60° C. and under super-atmospheric pressure thereby absorbing CO 2 and H 2 S in said solution, (b) Regenerating said solution in a regeneration zone at approximately atmospheric pressure by countercurrently steam stripping said solution, (c) Restricting the mass transfer capacity of said regeneration zone such that the steam/gas mixture leaving the top of said regenerator is at a higher temperature than the after-flash temperature of the solution at the top of said regenerator, (d) Supplying stripping steam to said regeneration zone at a steam/gas ratio selected to reduce the equilibrium partial pressure of H 2 S above said solution at the bottom of the regenerator to a value which will provide the desired partial pressure of H 2 S in the purified gas leaving said absorption zone, (e) Controlling the partial pressure of H 2 S in the purified gas at a substantially constant value by maintaining said selected steam/gas ratio substantially constant as said gas flow varies, (f) Adjusting the solution/gas ratio in said absorption zone to a selected ratio in the vicinity of that at which the partial pressure of H 2 S in the purified gas remains at said desired value and at which the difference between the partial pressure of CO 2 and H 2 S in the purified gas reaches a maximum level, (g) Maintaining said selected solution/gas ratio at a substantially constant value as said gas flow varies, whereby the purified gas is selectively reduced in H 2 S content and whereby the ratio of H 2 S to CO 2 absorbed is rendered substantially independent of variations in gas flow.

Claim 10

A method for selectively removing H 2 S from a gas mixture containing H 2 S and CO 2 in a molar ratio in excess of 4CO 2 :H 2 S wherein said gas mixture undergoes substantial variation in flow rate comprising the steps of: (a) Countercurrently contacting said gas mixture in an absorption zone with an aqueous scrubbing solution of alkali metal carbonate at an absorption temperature of at least 60° C. and under super-atmospheric pressure thereby absorbing CO 2 and H 2 S in said solution, (b) Regenerating said solution in a regeneration zone at approximately atmospheric pressure by countercurrently steam stripping said solution, (c) Restricting the mass transfer capacity of said regeneration zone such that the steam/gas mixture leaving the top of said regenerator is at a higher temperature than the after-flash temperature of the solution at the top of said regenerator, (d) Supplying stripping steam to said regeneration zone at a steam/gas ratio selected to reduce the equilibrium partial pressure of H 2 S above said solution at the bottom of the regenerator to a value which will provide the desired partial pressure of H 2 S in the purified gas leaving said absorption zone, (e) Controlling the partial pressure of H 2 S in the purified gas at a substantially constant value by maintaining said selected steam/gas ratio substantially constant as said gas flow varies, (f) Adjusting the solution/gas ratio in said absorption zone to a selected ratio in the vicinity of that at which the partial pressure of H 2 S in the purified gas remains at said desired value and at which the difference between the partial pressure of CO 2 and H 2 S in the purified gas reaches a maximum level, (g) Maintaining said selected solution/gas ratio at a substantially constant value as said gas flow varies, whereby the purified gas is selectively reduced in H 2 S content and whereby the ratio of H 2 S to CO 2 absorbed is rendered substantially independent of variations in gas flow.