Acid gas enrichment method and system

Abstract

A process for treating an H.sub.2S- and CO.sub.2-comprising fluid stream, in which a) the fluid stream is treated in a first absorber at a pressure of 10 to 150 bar with a first substream of a regenerated H.sub.2S-selective absorbent to obtain a treated fluid stream and an H.sub.2S-laden absorbent; b) the H.sub.2S-laden absorbent is heated by indirect heat exchange with regenerated H.sub.2S-selective absorbent; c) the heated H.sub.2S-laden absorbent is decompressed to a pressure of 1.2 to 10 bar in a low-pressure decompression vessel to obtain a first CO.sub.2-rich offgas and a partly regenerated absorbent; d) the partly regenerated absorbent is regenerated in a desorption column to obtain an H.sub.2S-rich offgas and regenerated absorbent; e) the H.sub.2S-rich offgas is fed to a Claus unit and the offgas from the Claus unit is fed to a hydrogenation unit to obtain hydrogenated Claus tail gas; f) the hydrogenated Claus tail gas and the first CO.sub.2-rich offgas are treated in a second absorber at a pressure of 1 to 4 bar with a second substream of the regenerated H.sub.2S-selective absorbent to obtain a second CO.sub.2-rich offgas and a second H.sub.2S-laden absorbent; and g) the second H.sub.2S-laden absorbent is guided into the first absorber. Also described is a plant suitable for performance of the process. The process is notable for a low energy requirement.

Claims

1. A process for treating an H.sub.2S- and CO.sub.2-comprising hydrocarbonaceous fluid stream, in which a) the fluid stream is treated in a first absorber at a pressure of 10 to 150 bar with a first substream of a regenerated H.sub.2S-selective absorbent to obtain a treated fluid stream and H.sub.2S-laden absorbent; b) the H.sub.2S-laden absorbent is heated by indirect heat exchange with regenerated H.sub.2S-selective absorbent; c) the heated H.sub.2S-laden absorbent is decompressed to a pressure of 1.2 to 10 bar in a low-pressure decompression vessel to obtain a first CO.sub.2-rich offgas and a partly regenerated absorbent; d) the partly regenerated absorbent is regenerated in a desorption column to obtain an H.sub.2S-rich offgas and regenerated absorbent; e) the H.sub.2S-rich offgas is fed to a Claus unit and the offgas from the Claus unit is fed to a hydrogenation unit to obtain hydrogenated Claus tail gas; f) the hydrogenated Claus tail gas and the first CO.sub.2-rich ragas are treated in a second absorber at a pressure of 1 to 4 bar with a second substream of the regenerated H.sub.2S-selective absorbent to obtain a second CO.sub.2-rich offgas and a second H.sub.2S-laden absorbent; and g) the second H.sub.2S-laden absorbent is guided into the first absorber.

2. The process according to claim 1, wherein the H.sub.2S-laden absorbent is decompressed in a high-pressure decompression vessel to a pressure of 5 to 20 bar after leaving the first absorber and before the decompression in the low-pressure decompression vessel.

3. The process according to claim 1, wherein the partly regenerated absorbent is heated by indirect heat exchange with regenerated H.sub.2S-selective absorbent and a partly cooled regenerated absorbent is obtained and the partly cooled regenerated absorbent is used to heat the H.sub.2S-laden absorbent by indirect heat exchange.

4. The process according to claim 1, wherein the first CO.sub.2-rich tags and the hydrogenated Claus tail gas are cooled individually or in combination before the treatment in the second absorber.

5. The process according to claim 1, wherein the second H.sub.2S-laden absorbent is guided into the first absorber below the feed point for the first substream of the regenerated H.sub.2S-selective absorbent.

6. The process according to claim 1, in which the H.sub.2S-selective absorbent comprises an aqueous solution of at least one amine selected from the group consisting of tertiary amines and sterically hindered amines.

7. The process according to claim 6, in which the H.sub.2S-selective absorbent comprises an aqueous solution of methyldiethanolamine.

8. The process according to claim 6, wherein the absorbent comprises an acid.

9. The process according to claim 1, wherein there is a partial H.sub.2S pressure of at least 0.1 bar and a partial CO.sub.2 pressure of at least 0.2 bar in the fluid stream.

10. The process according to claim 1, wherein the hydrogenated Claus tail gas comprises 0.5% to 5% by volume of H.sub.2S.

11. A plant for conducting the process of claim 1, comprising a) a first absorber connected via a first heat exchanger in a fluid-conducting manner to a desorption column, in order to accept a first substream of a regenerated H.sub.2S-selective absorbent from the desorption column, the first absorber being designed to promote the absorption of H.sub.2S and CO.sub.2 from the fluid stream into the first substream of the regenerated H.sub.2S-selective absorbent at a pressure of 10 to 150 bar to obtain a treated fluid stream and an H.sub.2S-laden absorbent; and the first heat exchanger being designed to heat the H.sub.2S-laden absorbent by indirect heat exchange with regenerated H.sub.2S-selective absorbent from the desorption column; b) a low-pressure decompression vessel which is connected in a fluid-conducting manner to the first heat exchanger and is designed to decompress the heated H.sub.2S-laden absorbent at a pressure of 1.2 to 10 bar to obtain a first CO.sub.2-rich offgas and a partly regenerated absorbent; c) a line which guides the partly regenerated absorbent into the desorption column to obtain an H.sub.2S-rich offgas and regenerated absorbent; d) a Claus unit which accepts the H.sub.2S-rich offgas, and a hydrogenation unit which accepts the offgas from the Claus unit to obtain hydrogenated Claus tail gas; e) a second absorber which is connected in a fluid-conducting manner to the desorption column and is designed to promote the absorption of H.sub.2S from the hydrogenated Claus tail gas and the first CO.sub.2-rich offgas into a second substream of the regenerated H.sub.2S-selective absorbent at a pressure of 1 to 4 bar to obtain a second CO.sub.2-rich offgas and a second H.sub.2S-laden absorbent; and f) a line which guides the second H.sub.2S-laden absorbent into the first absorber.

12. The plant according to claim 11, further comprising a high-pressure decompression vessel which is designed to decompress the H.sub.2S-laden absorbent from the first absorber.

13. The plant according to claim 11, further comprising a cooler designed to cool the regenerated H.sub.2S-selective absorbent coming from the first heat exchanger.

14. The plant according to claim 11, wherein the low-pressure decompression vessel is connected via a second heat exchanger in a fluid-conducting manner to the desorption column, and the second heat exchanger is designed to beat the partly regenerated absorbent by indirect heat exchange with the regenerated H.sub.2S-selective absorbent.

Description

(1) The invention is illustrated in detail by the appended drawings and the examples which follow. FIGS. 1 to 4 use the same reference symbols for elements of the same function. Plant components not required for understanding, such as pumps, are not shown in the figures for the sake of clarity. In general, the person skilled in the art would provide pump internals in lines 3.01, 3.02 and 3.15, and 4.01, 4.02 and 4.18.

(2) FIG. 1 is a schematic diagram of a plant suitable for treatment of an H.sub.2S- and CO.sub.2-comprising fluid stream.

(3) FIG. 2 is a schematic diagram of a further plant suitable for treatment of an H.sub.2S- and CO.sub.2-comprising fluid stream.

(4) FIG. 3 is a schematic diagram of a plant suitable for performing the process of the invention.

(5) FIG. 4 is a schematic diagram of a further plant suitable for performing the process of the invention.

(6) According to FIG. 1, via the inlet Z, a suitably pretreated gas comprising hydrogen sulfide and carbon dioxide is contacted in countercurrent, in an absorber A1, with regenerated absorbent fed in in the upper region via the absorbent line 1.01 and the partly laden absorbent fed in in the middle region via the absorbent line 1.28. The absorbent removes hydrogen sulfide and carbon dioxide from the gas by absorption; this affords a hydrogen sulfide- and carbon dioxide-depleted, treated fluid stream via the offgas line 1.02.

(7) Via an absorbent line 1.03, the CO.sub.2- and H.sub.2S-laden absorbent is passed into a high-pressure decompression vessel HPF and decompressed (for example from about 70 bar to from 5 to 20 bar), the temperature being essentially equal to the temperature of the laden absorbent. Typically, the temperature differential is less than 10 C., preferably less than 5 C. Under these conditions, essentially the hydrocarbons present in the laden absorbent are released as gas and can be discharged via line 1.04.

(8) Via an absorbent line 1.05, a heat exchanger 1.06 in which the CO.sub.2- and H.sub.2S-laden absorbent is heated up with the heat from the regenerated absorbent conducted through the absorbent line 1.07, and the absorbent line 1.08, the CO.sub.2- and H.sub.2S-laden absorbent is fed to a desorption column D and regenerated.

(9) From the lower portion of the desorption column D, a substream of the regenerated absorbent conducted via the absorbent line 1.07 is conducted via the absorbent line 1.09 into the oiler 1.10, where it is heated and recycled at least partly as vapor into the desorption column D, in the present case via the absorbent line 1.11.

(10) A further substream of the regenerated absorbent conducted via the absorbent line 1.07 is conducted onward via the heat exchanger 1.06, in which the regenerated absorbent heats up the CO.sub.2- and H.sub.2S-laden absorbent and is itself cooled down in the process, the absorbent line 1.12, the cooler 1.13 and the absorbent line 1.14, and divided into the substreams 1.01 and 1.15.

(11) The substream 1.01 is fed to the absorber A1. The substream 1.15 is in turn divided into substreams 1.16 and 1.17.

(12) The CO.sub.2- and H.sub.2S-containing gas released in the desorption column D leaves the desorption column D via the offgas line 1.18. It is conducted via a cooler 1.19 into a condenser with integrated phase separation 1.20, where it is separated from entrained absorbent vapor. Subsequently, a liquid consisting mainly of water is conducted through the absorbent line 1.21 into the upper region of the desorption column D, and a CO.sub.2- and H.sub.2S-containing gas is conducted onward via the gas line 1.22. The gas stream 1.22 is divided into substreams 1.23 and 1.24.

(13) The substream 1.23 is conducted into an absorber A2 and contacted in countercurrent therein with regenerated absorbent which is supplied via the absorbent line 1.16. The absorbent removes hydrogen sulfide from the gas by absorption; this affords essentially pure carbon dioxide via the offgas line 1.25. Via the absorbent line 1.26, an H.sub.2S-laden absorbent is guided into the absorbent line 1.05 and fed via the heat exchanger 1.06 and the absorbent line 1.08 to the desorption column D and regenerated.

(14) The CO.sub.2- and H.sub.2S-containing gas stream 1.24 is fed to a Claus plant CL, the offgas from which comprises mainly N.sub.2, CO.sub.2, SO.sub.2, COS, CS.sub.2, H.sub.2S, H.sub.2O and sulfur. The offgas is hydrogenated in the hydrogenation plant HY. The hydrogenated Claus tail gas comprising essentially H.sub.2, N.sub.2, CO.sub.2, H.sub.2O and H.sub.2S is conducted through a quench cooler Q and cooled. The quench fluid in the quench cooler Q is essentially water.

(15) The cooled hydrogenated Claus tail gas is fed via the gas line 1.27 into the tail gas absorber TGA, where it is contacted in countercurrent with the regenerated absorbent fed in via the absorbent line 1.17. Via the absorbent line 1.28, a partly H.sub.2S-laden absorbent from the tail gas absorber TGA is fed into the middle section of the absorber A1. Via a gas line 1.29, the H.sub.2S-depleted gas is removed from the tail gas absorber TGA and discharged from the process.

(16) According to FIG. 2, via the inlet Z, a suitably pretreated gas comprising hydrogen sulfide and carbon dioxide is contacted in countercurrent, in an absorber A1, with regenerated absorbent fed in in the upper region via the absorbent line 2.01 and the partly laden absorbent fed in in the middle region via the absorbent line 2.28. The absorbent removes hydrogen sulfide and carbon dioxide from the gas by absorption; this affords a hydrogen sulfide- and carbon dioxide-depleted, treated fluid stream via the offgas line 2.02.

(17) Via an absorbent line 2.03, the CO.sub.2- and H.sub.2S-laden absorbent is passed into a high-pressure decompression vessel HPF and decompressed (for example from about 70 bar to from 5 to 20 bar), the temperature being essentially equal to the temperature of the laden absorbent. Typically, the temperature differential is less than 10 C., for example less than 5 C. Under these conditions, essentially all the hydrocarbons present in the laden absorbent are released as gas and can be discharged via line 2.04.

(18) Via an absorbent line 2.05, a heat exchanger 2.06 in which the CO.sub.2- and H.sub.2S-laden absorbent is heated up with the heat from the regenerated absorbent conducted through the absorbent line 2.07, and the absorbent line 2.08, the CO.sub.2- and H.sub.2S-laden absorbent is guided into a low-pressure decompression vessel LPF and decompressed (for example to a pressure of 1.2 to 10 bar, for example 1.2 to 3 bar). Under these conditions, significant portions of the carbon dioxide present in the laden absorbent are released as gas and can be conducted onward via the gas line 2.09 to obtain a partly regenerated absorbent.

(19) The CO.sub.2 gas is conducted via a cooler 2.10 into a condenser with integrated phase separation 2.11, where it is separated from entrained absorbent vapor. Subsequently, a liquid consisting mainly of water is conducted via the absorbent line 2.12 into the upper region of the low-pressure decompression vessel LPF. The CO.sub.2 gas comprises considerable amounts of H.sub.2S, which has to be removed before the CO.sub.2 can be discharged. For this purpose, the gas is fed via the gas line 2.13 into the absorber A2, where it is contacted in countercurrent with the regenerated absorbent fed in via the absorbent line 2.14. The absorbent removes hydrogen sulfide by absorption from the gas; this affords essentially pure carbon dioxide which is conducted out of the plant via a gas line 2.15.

(20) The partly regenerated absorbent discharged via the absorbent line 2.16 from the lower region of the low-pressure decompression vessel LPF and the H.sub.2S-laden absorbent discharged via the absorbent line 2.17 from the lower region of the absorber A2 are fed via the absorbent lines 2.18 into the upper region of the desorption column D and regenerated.

(21) From the lower portion of the desorption column D, a substream of the regenerated absorbent conducted via the absorbent line 2.07 is conducted via the absorbent line 2.19 into the boiler 2.20, where it is heated and recycled at least partly as vapor into the desorption column D, in the present case via the absorbent line 2.21.

(22) A further substream of the regenerated absorbent conducted via the absorbent line 2.07 is conducted onward via the heat exchanger 2.06, in which the regenerated absorbent heats up the CO.sub.2- and H.sub.2S-laden absorbent and is itself cooled down in the process, the absorbent line 2.22, the cooler 2.23 and the absorbent line 2.24, and divided into the substreams 2.01 and 2.25. The substream 2.01 is fed to the absorber A1. The substream 2.25 is in turn divided into the substreams 2.14 and 2.26.

(23) The CO.sub.2- and H.sub.2S-containing gas released in the desorption column D leaves the desorption column D via the offgas line 2.27. It is conducted via a cooler 2.29 into a condenser with integrated phase separation 2.30, where it is separated from entrained absorbent vapor. Subsequently, a liquid consisting mainly of water is conducted through the absorbent line 2.31 into the upper region of the desorption column D, and a CO.sub.2- and H.sub.2S-containing gas is conducted onward via the gas line 2.32.

(24) The CO.sub.2- and H.sub.2S-containing gas stream 2.32 is fed to a Claus plant CL, the offgas from which comprises mainly N.sub.2, CO.sub.2, SO.sub.2, COS, CS.sub.2, H.sub.2S, H.sub.2O and sulfur. The offgas is hydrogenated in the hydrogenation plant HY. The hydrogenated Claus tail gas comprising essentially H.sub.2, N.sub.2, CO.sub.2, H.sub.2O and H.sub.2S is conducted through a quench cooler Q and cooled. The quench fluid in the quench cooler Q is essentially water.

(25) The cooled hydrogenated Claus tail gas is fed via the gas line 2.33 into the tail gas absorber TGA, where it is contacted in countercurrent with the regenerated absorbent fed in via the absorbent line 2.26. Via the absorbent line 2.28, a partly H.sub.2S-laden absorbent from the tail gas absorber TGA is fed into the middle section of the absorber A1. Via a gas line 2.34, the H.sub.2S-depleted gas is removed from the tail gas absorber TGA and discharged from the process.

(26) According to FIG. 3, via the inlet Z, a suitably pretreated gas comprising hydrogen sulfide and carbon dioxide is contacted in countercurrent, in an absorber A1, with regenerated absorbent fed in in the upper region via the absorbent line 3.01 and the partly laden absorbent fed in in the middle region via the absorbent line 3.02. The absorbent removes hydrogen sulfide and carbon dioxide from the gas by absorption; this affords a hydrogen sulfide- and carbon dioxide-depleted, treated fluid stream via the offgas line 3.03.

(27) Via an absorbent line 3.04, the CO.sub.2- and H.sub.2S-laden absorbent is passed into a high-pressure decompression vessel HPF and decompressed (for example from about 70 bar to from 5 to 20 bar), the temperature being essentially equal to the temperature of the laden absorbent. Typically, the temperature differential is less than 10 C., preferably less than 5 C. Under these conditions, essentially the hydrocarbons present in the laden absorbent are released as gas and can be discharged via line 3.05.

(28) Via an absorbent line 3.06, a heat exchanger 3.07 in which the CO.sub.2- and H.sub.2S-laden absorbent is heated up with the heat from the regenerated absorbent conducted through the absorbent line 3.08, and the absorbent line 3.09, the CO.sub.2- and H.sub.2S-laden absorbent is guided into a low-pressure decompression vessel LPF and decompressed to a pressure of 1.2 to 10 bar, preferably 1.2 to 3 bar. Under these conditions, significant portions of the carbon dioxide present in the laden absorbent are released as gas and can be conducted onward as the first CO.sub.2-rich offgas via the gas line 3.10 to obtain a partly regenerated absorbent.

(29) The partly regenerated absorbent discharged via the absorbent line 3.11 from the lower region of the low-pressure decompression vessel LPF is fed into the upper region of the desorption column D and regenerated. From the lower portion of the desorption column D, a substream of the regenerated absorbent conducted via the absorbent line 3.08 is conducted via the absorbent line 3.12 into the boiler 3.13, where it is heated and recycled at least partly as vapor into the desorption column D, in the present case via the absorbent line 3.14.

(30) Instead of the boiler shown, it is also possible to use other heat exchanger types to raise the stripping vapor, such as a natural circulation evaporator, forced circulation evaporator or forced circulation flash evaporator. In the case of these evaporator types, a mixed-phase stream of regenerated absorbent and stripping vapor is retumed to the bottom of the desorption column, where the phase separation between the vapor and the absorbent takes place.

(31) A further substream of the regenerated absorbent conducted via the absorbent line 3.08 is conducted onward via the heat exchanger 3.07, in which the regenerated absorbent heats up the CO.sub.2- and H.sub.2S-laden absorbent and is itself cooled down in the process, the absorbent line 3.15, the cooler 3.16 and the absorbent line 3.17, and divided into the substreams 3.01 and 3.18. The substream 3.01 is fed to the upper region of the absorber A1. The substream 3.18 is fed into the upper region of a tail gas absorber TGA.

(32) The H.sub.2S-rich offgas released in the desorption column D leaves the desorption column D via the offgas line 3.19. It is conducted via a cooler 3.20 into a condenser with integrated phase separation 3.21, where it is separated from entrained absorbent vapor. In this and all the other plants suitable for performance of the process of the invention, condensation and phase separation may also be present separately from one another. Subsequently, a liquid consisting mainly of water is conducted through the absorbent line 3.22 into the upper region of the desorption column D, and the H.sub.2S-rich offgas is conducted onward via the gas line 3.23.

(33) The H.sub.2S-rich offgas is fed via the gas line 3.23 to a Claus plant CL, the offgas from which comprises mainly N.sub.2, CO.sub.2, SO.sub.2, COS, CS.sub.2, H.sub.2S, H.sub.2O and sulfur. The offgas is hydrogenated in the hydrogenation plant HY to obtain hydrogenated Claus tail gas. The hydrogenated Claus tail gas comprising essentially H.sub.2, N.sub.2, CO.sub.2, H.sub.2O and H.sub.2S, just like the first CO.sub.2-rich offgas of gas line 3.10, is conducted through a quench cooler Q and cooled. The quench fluid in the quench cooler Q is essentially water.

(34) The hydrogenated Claus tail gas and the first CO.sub.2-rich offgas are combined and fed via the gas line 3.24 into the tail gas absorber TGA, where the gas is contacted in countercurrent with the regenerated absorbent fed in via the absorbent line 3.18. Via the absorbent line 3.02, a second H.sub.2S-laden absorbent from the tail gas absorber TGA is fed into the middle section of the absorber A1. The remaining absorption capacity of the second H.sub.2S-laden absorbent from the tail gas absorber TGA can thus be utilized. Via a gas line 3.25, a second CO.sub.2-rich offgas is removed from the tail gas absorber TGA and discharged from the process.

(35) According to FIG. 4, via the inlet Z, a suitably pretreated gas comprising hydrogen sulfide and carbon dioxide is contacted in countercurrent, in an absorber A1, with regenerated absorbent fed in in the upper region via the absorbent line 4.01 and the partly laden absorbent fed in in the middle region via the absorbent line 4.02. The absorbent removes hydrogen sulfide and carbon dioxide from the gas by absorption; this affords a hydrogen sulfide- and carbon dioxide-depleted, treated fluid stream via the offgas line 4.03.

(36) Via an absorbent line 4.04, the CO.sub.2- and H.sub.2S-laden absorbent is passed into a high-pressure decompression vessel HPF and decompressed (for example from about 70 bar to from 5 to 20 bar), the temperature being essentially equal to the temperature of the laden absorbent. Typically, the temperature differential is less than 10 C., preferably less than 5 C. Under these conditions, essentially all the hydrocarbons present in the laden absorbent are released as gas and can be discharged via line 4.05.

(37) Via an absorbent line 4.06, a heat exchanger 4.07 in which the CO.sub.2- and H.sub.2S-laden absorbent is heated up with the heat from the regenerated absorbent conducted through the absorbent line 4.08, the heat exchanger 4.09 and the absorbent line 4.10, and the absorbent line 4.11, the CO.sub.2- and H.sub.2S-laden absorbent is guided into a low-pressure decompression vessel LPF and decompressed to a pressure of 1.2 to 10 bar, preferably 1.2 to 3 bar. Under these conditions, significant portions of the carbon dioxide present in the laden absorbent are released as gas and can be conducted onward as the first CO.sub.2-rich offgas via the gas line 4.12 to obtain a partly regenerated absorbent.

(38) The partly regenerated absorbent discharged via the absorbent line 4.13 from the lower region of the low-pressure decompression vessel LPF is fed via the heat exchanger 4.09, in which the partly regenerated absorbent is heated up with the heat from the regenerated absorbent conducted through the absorbent line 4.08, and the absorbent line 4.14, into the upper region of a desorption column D and regenerated. From the lower portion of the desorption column D, a substream of the regenerated absorbent conducted via the absorbent line 4.08 is conducted via the absorbent line 4.15 into the boiler 4.16, where it is heated and recycled at least partly as vapor into the desorption column D, in the present case via the absorbent line 4.17.

(39) Instead of the boiler shown, it is also possible to use other heat exchanger types to raise the stripping vapor, such as a natural circulation evaporator, forced circulation evaporator or forced circulation flash evaporator. In the case of these evaporator types, a mixed-phase stream of regenerated absorbent and stripping vapor is returned to the bottom of the desorption column, where the phase separation between the vapor and the absorbent takes place.

(40) A further substream of the regenerated absorbent conducted via the absorbent line 4.08 is conducted onward via the heat exchanger 4.09, in which the regenerated absorbent heats up the partly regenerated absorbent and is itself cooled down in the process, the absorbent line 4.10 in which the regenerated absorbent heats up the CO.sub.2- and H.sub.2S-laden absorbent and is itself cooled down in the process, the absorbent line 4.18, the cooler 4.19 and the absorbent line 4.20, and divided into the substreams 4.01 and 4.21. The substream 4.01 is fed to the upper region of the absorber A1. The substream 4.21 is fed into the upper region of a tail gas absorber TGA.

(41) The H.sub.2S-rich offgas released in the desorption column D leaves the desorption column D via the offgas line 4.22. It is conducted via a cooler 4.23 into a condenser with integrated phase separation 4.24, where it is separated from entrained absorbent vapor. In this and all the other plants suitable for performance of the process of the invention, condensation and phase separation may also be present separately from one another. Subsequently, a liquid consisting mainly of water is conducted through the absorbent line 4.25 into the upper region of the desorption column D, and the H.sub.2S-rich offgas is conducted onward via the gas line 4.26.

(42) The H.sub.2S-rich offgas is fed via the gas line 4.26 to a Claus plant CL, the offgas from which comprises mainly N.sub.2, CO.sub.2, SO.sub.2, COS, CS.sub.2, H.sub.2S, H.sub.2O and sulfur. The offgas is hydrogenated in the hydrogenation plant HY to obtain hydrogenated Claus tail gas. The hydrogenated Claus tail gas comprising essentially H.sub.2, N.sub.2, CO.sub.2, H.sub.2O and H.sub.2S, just like the first CO.sub.2-rich offgas of gas line 4.12, is conducted through a quench cooler Q and cooled. The quench fluid in the quench cooler Q is essentially water.

(43) The hydrogenated Claus tail gas and the first CO.sub.2-rich offgas are combined and fed via the gas line 4.27 into the tail gas absorber TGA, where the gas is contacted in countercurrent with the regenerated absorbent fed in via the absorbent line 4.21. Via the absorbent line 4.02, a second H.sub.2S-laden absorbent from the tail gas absorber TGA is fed into the middle section of the absorber A1. The remaining absorption capacity of the second H.sub.2S-laden absorbent from the tail gas absorber TGA can thus be utilized. Via a gas line 4.28, a second CO.sub.2-rich offgas is removed from the tail gas absorber TGA and discharged from the process.

EXAMPLES

(44) A simulation model was used for the performance of the examples. The phase equilibria were described using a model by Pitzer (K. S. Pitzer, Activity Coefficients in Electrolyte Solutions 2nd ed., CRC Press, 1991, Chapter 3, Ion Interaction Approach: Theory). The model parameters were fitted to gas solubility measurements of carbon dioxide, hydrogen sulfide and hydrocarbons in aqueous MDEA solutions. The reaction kinetics of CO.sub.2 with MDEA were determined by experiments in a twin stirred cell and incorporated into the simulation model.

(45) For all examples, an aqueous absorbent comprising 45% by weight of MDEA and 0.5% by weight of phosphoric acid was assumed. The composition of the fluid stream to be treated was fixed as 10.06% by volume of CO.sub.2, 2.01% by volume of H.sub.2S, 82.90% by volume of methane and 5.03% by volume of ethane (323 786 m.sup.3 (STP)/h, 40.0 C., 61.0 bar). This composition is based on the fluid stream excluding the water content (1876 m.sup.3 (STP)/h), i.e. the dry fluid stream. The separation task was to lower the H.sub.2S content to less than 5 ppm by volume and the CO.sub.2 content to less than 2.3% by volume. In addition, the H.sub.2S content of the treated gases which are discharged from the absorbers connected downstream of the first absorber was to be less than 100 ppm by volume in each case.

(46) In the absorber A1, the internals used were random packings (IMTP40). The packing height in the absorber A1 was 16 m; the design of the column diameter was based on 80% of the flood limit.

(47) In the absorber A2, the internals used were random packings (IMTP40). The packing height in the absorber A2 was 6 m; the design of the column diameter was based on 80% of the flood limit.

(48) In the absorber TGA, the internals used were random packings (IMTP40). The packing height in the absorber TGA was 6 m; the design of the column diameter was based on 80% of the flood limit.

(49) In the desorption column D, the internals used were Pall rings (size: 50 mm). The packing height of the desorption column was 10 m; the design of the column diameter was based on 65% of the flood limit.

Example 1 (Comparative Example)

(50) By means of the simulation model, a process for treatment of an H.sub.2S- and CO.sub.2-comprising fluid stream using the above-described absorbent was examined. The pilot plant corresponded to FIG. 1. The following table states the compositions of various dry fluid streams:

(51) TABLE-US-00001 V T p CO.sub.2 H.sub.2S CH.sub.4 C.sub.2H.sub.6 N.sub.2 H.sub.2 # [m.sup.3 (STP)/h] [ C.] [bar] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] Z 323 786 40.0 61.0 10.06 2.01 82.90 5.03 0.00 0.00 1.02 290 474 45.9 60.9 2.21 0.0* 92.20 5.59 0.00 0.00 1.04 804 69.0 8.0 24.36 2.70 68.87 4.07 0.00 0.00 1.18 42 128 98.1 2.1 69.84 30.02 0.14 0.01 0.00 0.00 1.23 19 440 45.0 2.0 69.86 30.00 0.14 0.01 0.00 0.00 1.24 22 630 45.0 2.0 69.86 30.00 0.14 0.01 0.00 0.00 1.25 11 379 45.7 1.8 99.74 0.01 0.23 0.02 0.00 0.00 1.27 29 313 40.0 1.4 54.04 0.93 0.00 0.00 42.98 45.24 1.29 27 844 45.6 1.3 52.58 0.01 0.00 0.00 45.24 2.16 *3 ppm by vol.

Example 2 (Comparative Example)

(52) By means of the simulation model, a process for treatment of an H.sub.2S- and CO.sub.2-comprising fluid stream using the above-described absorbent was examined. The pilot plant corresponded to FIG. 2. The following table states the compositions of various dry fluid streams:

(53) TABLE-US-00002 V T p CO.sub.2 H.sub.2S CH.sub.4 C.sub.2H.sub.6 N.sub.2 H.sub.2 # [m.sup.3 (STP)/h] [ C.] [bar] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] Z 323 786 40.0 61.0 10.06 2.01 82.90 5.03 0.00 0.00 2.02 290 482 45.8 60.9 2.21 0.00* 92.20 5.59 0.00 0.00 2.04 795 69.0 8.0 24.47 2.74 68.74 4.06 0.00 0.00 2.09 19 967 97.2 2.5 87.91 11.79 0.28 0.02 0.00 0.00 2.13 19 947 40.0 2.4 87.92 11.78 0.28 0.02 0.00 0.00 2.15 15 177 46.1 2.3 98.80 0.01 0.37 0.03 0.00 0.00 2.27 18 472 93.7 2.1 63.27 36.73 0.00 0.00 0.00 0.00 2.32 18 453 45.0 2.0 63.28 36.72 0.00 0.00 0.00 0.00 2.33 24 766 40.0 1.4 47.14 1.09 0.00 0.00 49.71 2.05 2.34 23 663 45.6 1.3 45.82 0.01 0.00 0.00 52.02 2.15 *2 ppm by vol.

Example 3

(54) By means of the simulation model, a process for treatment of an H.sub.2S- and CO.sub.2-comprising fluid stream using the above-described absorbent was examined. The pilot plant corresponded to FIG. 3. The following table states the compositions of various dry fluid streams:

(55) TABLE-US-00003 V T p CO.sub.2 H.sub.2S CH.sub.4 C.sub.2H.sub.6 N.sub.2 H.sub.2 # [m.sup.3 (STP)/h] [ C.] [bar] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] Z 323 786 40.0 61.0 10.06 2.01 82.90 5.03 0.00 0.00 3.03 290 452 46.3 60.9 2.21 0.00* 92.20 5.59 0.00 0.00 3.05 870 69.7 8.0 26.07 4.05 66.03 3.85 0.00 0.00 3.10 22 233 95.6 2.5 83.73 15.99 0.26 0.02 0.00 0.00 3.19 16 880 96.6 2.1 59.79 40.21 0.00 0.00 0.00 0.00 3.23 16 857 45.0 2.0 59.82 40.18 0.00 0.00 0.00 0.00 3.24 45 361 40.0 1.4 63.25 8.43 0.13 0.01 27.14 1.05 3.25 38 772 45.4 1.3 66.86 0.01 0.15 0.01 31.74 1.22 *4 ppm by vol.

Example 4

(56) By means of the simulation model, a process for treatment of an H.sub.2S- and CO.sub.2-comprising fluid stream using the above-described absorbent was examined. The pilot plant corresponded to FIG. 4. The following table states the compositions of various dry fluid streams:

(57) TABLE-US-00004 V T p CO.sub.2 H.sub.2S CH.sub.4 C.sub.2H.sub.6 N.sub.2 H.sub.2 # [m.sup.3 (STP)/h] [ C.] [bar] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] [% by vol.] Z 323 786 40.0 61.0 10.06 2.01 82.90 5.03 0.00 0.00 4.03 290 452 46.2 60.9 2.21 0.00* 92.20 5.59 0.00 0.00 4.05 849 69.3 8.0 25.24 3.29 67.50 3.96 0.00 0.00 4.12 14 484 86.1 2.5 87.65 11.91 0.41 0.03 0.00 0.00 4.22 22 625 97.0 2.1 69.98 30.02 0.00 0.00 0.00 0.00 4.26 22 596 45.0 2.0 70.00 30.00 0.00 0.00 0.00 0.00 4.27 43 480 40.0 1.4 65.56 4.59 0.14 0.01 28.33 1.37 4.28 38 915 45.5 1.3 66.65 0.01 0.15 0.01 31.65 1.53 *3 ppm by vol.

(58) For the examples, the relative regeneration energy was determined on the basis of the power of the boiler of the desorption column and the relative total circulation rate of the scrubbing agent. The total circulation rate of the scrubbing agent is understood to mean the respective mass flow of streams 1.12, 2.22, 3.15 and 4.15.

(59) TABLE-US-00005 Relative Relative total circulation rate Example regeneration energy** Absorbent** 1* 100% 100% 2* 101% 92.3% 3 87.5% 85.6% 4 83.2% 83.4% *comparative example **relative to example 1

(60) It is clear that the processes of examples 3 and 4 require a lower regeneration energy and a lower total circulation rate of the absorbent than the processes of examples 1 and 2.