PROCESS FOR SEPARATING A PRODUCT GAS FROM A GASEOUS MIXTURE UTILIZING A GAS PRESSURIZED SEPARATION COLUMN AND A SYSTEM TO PERFORM THE SAME

Abstract

A gas pressurized separation system strips a product gas from a stream yielding a high pressure gaseous effluent containing the product gas such as may be used to capture CO.sub.2 from coal fired post combustion flue gas capture and to purify natural gas, syngas and EOR recycle gas. The system comprises a gas pressurized stripping column allowing flow of one or more raw streams in a first direction and allowing flow of one or more high pressure gas streams in a second direction, to strip the product gas into the high pressure gas stream and yield a high pressure gaseous effluent that contains the product gas. The process can further comprise a final separation process to further purify the product gas from the GPS column. For CO.sub.2 product, a preferred energy efficient final separation process, compound compression and refrigeration process, is also introduced.

Claims

1. A process for separating a product gas from a gaseous mixture to yield a high pressure gaseous effluent in which the product gas has a partial pressure at least 4 times higher than in the gaseous mixture, comprising: (a) introducing the gaseous mixture into contact with at least one liquid in an absorption apparatus, to absorb the product gas into the liquid and yield at least one product-enriched liquid; (b) introducing the product-enriched liquid into at least one inlet of a gas pressurized column and into contact with at least one high pressure gas streams to strip the product gas into the high pressure gas stream and to yield at least one product-lean liquid and at least one high pressure gaseous effluents enriched with the product gas; (c) introducing the product-enriched liquid into at least one flasher between steps (a) and (b), wherein each flasher produces a stream enriched with the product gas prior to introducing the product-enriched liquid into the gas pressurized stripping column in step (b); (d) recovering heat from the product-lean liquid; and (e) recycling at least a portion of the product-lean liquid to the absorption apparatus at step (a).

2. The process of claim 1, wherein the product gas comprises carbon dioxide.

3. The process of claim 1, wherein the high pressure stripping gas stream comprises a single pure gas selected from the group of He, Ar, O2, N2, CH4, C2H6, C3H8, C2H4, C4H10, and C5H12.

4. The process of claim 1, wherein the high pressure gas stream comprises a mixture of different gases selected from a mixture of gas selected from the group of He, Ar, O2, N2, air, CH4, C2H6, C3H8, C2H4 C4H10, and C5H12.

5. The process of claim 1, wherein the high pressure gas stream contains carbon dioxide.

6. The process of claim 1, wherein the high pressure gas stream is selected from the group of nitrogen, methane, ethane, propane, purified syngas, natural gas, and CO.sub.2 EOR recycled gas.

7. The process of claim 1, wherein the product gas is CO.sub.2, wherein the gaseous mixture is coal fired postcombustion flue gas, and wherein the operating pressure in the gas pressurized stripping column is at least 4 atm.

8. The process of claim 1, wherein the gaseous mixture is a raw gas under pressure, and wherein the operating pressure in the gas pressurized stripping column is similar to the operating pressure in absorption column.

9. The process of claim 8 wherein the liquid is an aqueous alkanolamine.

10. The process of claim 8 wherein the raw gas is syngas.

11. The process of claim 1 further comprising after step (b) the step of subjecting the high pressure gaseous effluent from the gas pressurized stripping column to a compound compression and refrigeration process.

12. The process of claim 1, wherein the gaseous mixture is natural gas.

13. The process of claim 12, wherein the product gas comprises carbon dioxide.

14. The process of claim 13, wherein the high pressure gas stream is at least 60 Bar within the high pressure stripping column.

15. The process of claim 1, wherein the gaseous mixture is syngas.

16. The process of claim 15, wherein the product gas comprises carbon dioxide.

17. The process of claim 16, wherein the high pressure gas stream is at least 75 Bar within the high pressure stripping column.

18. The process of claim 1, wherein the gaseous mixture is CO.sub.2 EOR recycled gas.

19. The process of claim 18, wherein the product gas comprises carbon dioxide, and wherein the high pressure gas stream is at least 30 Bar within the high pressure stripping column.

20. A gas pressurized stripping system that comprises: (i) a gas pressurized stripping column with at least one first inlet allowing flow of one or more liquid streams in a first direction and at least one second inlet allowing flow of one or more high pressure gas streams in a second direction, to strip the product gas into the high pressure gas stream and yield through at least one outlet a high pressure gaseous effluent that contains the product gas; (ii) heat is provided through heat supply apparatuses from one or more different locations along the column allowing for independent control of the temperature along the stripping column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a schematic diagram of a conventional prior art absorption process for CO.sub.2 separation;

[0044] FIG. 2 is a schematic diagram of one embodiment of the process of the present invention using aqueous amine as solvent to separate a product gas from a gas mixture;

[0045] FIG. 3 is an exemplary schematic diagram of a separation process of one embodiment of the present invention using physical solvent to separate product gas from high pressure raw gas;

[0046] FIG. 4 is an exemplary schematic diagram of a separation process of one embodiment of the present invention using nitrogen as a high pressure gas stream and aqueous amine as solvent to separate carbon dioxide from post-combustion flue gas followed by compression-refrigeration process as a final separation process; and

[0047] FIG. 5 is an exemplary schematic diagram of a compound compression refrigeration separation process.

DETAILED DESCRIPTION OF THE INVENTION

[0048] A gas pressurized separation (GPS) system and associated processes to strip a product gas from a liquid stream and yield a high pressure gaseous effluent containing the product gas are disclosed in related U.S. Patent Publication 2014-0017622, WO 2012-006610 and U.S. Pat. No. 8,425,655, which are incorporated herein by reference. The GPS system in the previously related invention is always a core component in any application introduced in the improved invention. The modification in the present embodiment to the setting of original GPS system includes the number of the heat supplying apparatus necessary to be integrated to the GPS system. The greater the number of the heat supplying apparatuses in the column is; the better the potential thermodynamic efficiency of the separation process will be. However, the complexity of the GPS column and thus the capital costs of the column as well as the operating cost of the GPS system increases with the number of heat supply apparatus. Therefore, instead of using at least two heat supplying apparatus, the simplified processes of the present invention provide one or more heat supplying apparatus can be positioned in one or different location(s) along the column. The modified setting is applicable to either tray-type separation column or packed-type separation column and to either internal heating or external heating apparatus to the column.

[0049] The previously related invention disclosed an application/process which uses an additional absorption apparatus to absorb the product gas from at least a portion of the gaseous effluent from the gas pressurized column with at least a portion of the product-enriched liquid from the absorption apparatus to yield a further product-enriched liquid. Moreover, at least one flasher is used to recover a portion of the high pressure product gas from the further product-enriched liquid prior to introduction of the product-enriched liquid into the gas pressurized column. For the present invention embodiments, however, the additional absorption apparatus need not be employed anymore in any applications of GPS system for separating a product gas from a gas mixture to simplify the process and reduce capital cost.

[0050] A process in the present invention for separating a product gas from a gaseous mixture to yield a high pressure gaseous effluent in which the product gas has a partial pressure generally at least 4 times higher than in the gaseous mixture comprises: (a) introducing the gaseous mixture into contact with a liquid flowing in an absorption apparatus, to absorb the product gas into the liquid and yield a product-enriched liquid; (b) introducing the product-enriched liquid into at least one inlet of a gas pressurized stripping (GPS) column and into contact with one or more high pressure gas streams to strip the product gas into the high pressure gas stream and to yield a product-lean liquid and one or more high pressure gaseous effluents enriched with the product gas, wherein the product gas has a partial pressure higher than that in the gaseous mixture; (c) introducing the product-enriched liquid into at least one high pressure flasher between (a) and (b) wherein each flasher produces a stream enriched with the product gas prior to introducing the product-enriched liquid into the gas pressurized stripping column; (d) recovering heat from the product-lean liquid; and (e) recycling at least a portion of the product-lean liquid to step (a).

[0051] The process of the improved invention will be described below using carbon dioxide as the desired product gas. Often carbon dioxide is present in natural gas, syngas or combustion flue gases from a carbonaceous fuel burning facility. This is for illustrative purposes only and is in no way intended to limit the invention.

[0052] In a preferred embodiment, the primary separation steps are arranged as follows: absorption/flasher(s)/gas pressurized stripping. This process sequence provides a significant energy savings over conventional separation processes. In this preferred process, for example, the CO2-rich solution leaving the absorption column can go through one or more flashers (depending the CO2 loading in the rich solutions) to produce high pressure pure CO2. The new product-enriched liquid (a semi-rich solution) after passing through the flashers, then enters the GPS column to strip out the remaining CO2 to restore the specific lean CO2 concentration for absorption after being recycled to the absorber. In the GPS column a pressurized gas stream is introduced from the bottom to strip the CO2 out from the semi-rich solution. The pressurized gas could be any pure gas or mixtures of any gases as long as it is not harmful and will not condense in the system. Along with the high pressure stripping gas (or gas mixture), one or more heat supplying apparatuses are also provided to the GPS column to deliver heat needed for the stripping process. The gaseous effluent from top of the GPS column is a CO2-riched product gas containing small amount of stripping gas. Depending on the requirement of the product gas, the CO2-riched product gas containing small amount of stripping gas could be directly used as product or it can be further condensed, compressed and dehydrated to form final CO.sub.2 product as specified. This process can separates at least 90% mol of CO.sub.2 from the raw gas depending on the applications and the CO.sub.2 purity in the final product can vary depending on the subsequent applications of the CO.sub.2 product. Depending on the operating conditions, 99% mol (dry base) purity can be achieved.

[0053] The stripping gas stream may be any gases that are not harmful to system/solvents in the liquid, will not condense and will not interfere with the stripping system. Inorganic gases such as He, Ar, O2, N2, air, and their mixtures or organic gases such as CH4, C2H6, C3H8, C2H4 and their mixtures or any mixtures of organic and inorganic gases can all be used as stripping gas. In some applications the combination of methane, ethane, propane, butane, pentane and mixtures thereof represent an effective class of available stripping gasses. The high pressure stripping gas stream may comprise a single pure gas selected from the group of He, Ar, O2, N2, CH4, C2H6, C3H8, C2H4, C4H10, and C5H12. Alternatively the high pressure gas stream may comprise a mixture of different gases selected from a mixture of gas selected from the group of He, Ar, O2, N2, air, CH4, C2H6, C3H8, C2H4 C4H10, and C5H12. The high pressure gas stream may contain carbon dioxide and may be selected from the group of nitrogen, methane, ethane, propane, purified syngas, natural gas, and CO.sub.2 EOR recycled gas. There are virtually unlimited options for the stripping gases. The stripping gases are usually introduced into the GPS column from the bottom and may contain a small amount of carbon dioxide as well. The usage of the selected stripping gas is determined by purity requirement of CO.sub.2 product. The pressure of the selected stripping gas is determined by the desired CO2 loading in the lean solution leaving the GPS column.

[0054] FIG. 2 is a schematic diagram for one system implementing the process sequences absorption/flasher(s)/pressurized gas stripping. Raw gas 14 enters the bottom of the absorption column 12 and clean gas 16 exits the top of the column 12 while a CO2-lean solution 18 enters into the absorption column 12 from the top and flows downward producing a CO2-rich solution exiting at the bottom in line 20.

[0055] The CO2-rich solution is directed through pump 22, line 24, heat exchanger 26 and heater 30, and enters a high pressure flasher 34 (or a series of flashers with pressure from high to low) to flash high pressure CO2 out through line 42. The semi-rich solution (product-enriched liquid) from the bottom of the flasher 34 (or the last flasher if there is more than one flasher) is directed through line 38 and then enters the GPS column 70 from the top. The high pressure stripping gas stream in line 50 enters the bottom of the GPS column 70 and strips the CO2 from the semi-rich solution (product-enriched liquid) flowing countercurrent.

[0056] The CO2-lean solution is directed via line 72 from the column 70 through pump 74 to heat exchanger 26 to cooler 80 and to line 82 wherein make-up solvent (amine and water) may be added through line 86 into the lean solution through a mixer 84 before it enters the absorber in line 18 and the cycle repeats. The gaseous effluent 52 from the GPS column 70 mixes with gaseous effluent in line 42 from the last flasher through mixer 54 and then is cooled in cooling unit 58 and supplied by line 60 to liquid gas separator 62 with liquid or water exiting at line 46 used as makeup solvent and gas exiting at line 64. The gas in line 64 is compressed in compressor 66 to a specific pressure for the product gas at line 68. Multi-stage high pressure flashers can be used for the high product-enriched solution with the gaseous effluent 42 combining with the corresponding pressure product rich gas from line 68 and repeating the cooling 58, gas-liquid separation 62 and compression 66 process.

[0057] Multi-stage compression with inter-stage cooling can be used for the product gas wherever required. For better mass transfer efficiency, one or more heat supplying apparatus can be installed to GPS column 70 as side heating devices. Similarly, one or more cooling apparatus can be installed associated with the absorption column 12.

[0058] The process depicted in FIG. 2 can be used for purifying various raw gas under various pressure. Minor modification can be applied to the process to optimize for different raw gas streams. For example, the process may be used to capture CO.sub.2 from post combustion flue gas. Flue gas emits from fossil fuel combustion as exhaust gases from furnaces, boilers or steam generators. Flue gas composition depends on what is being burned but it usually consists of mostly nitrogen derived from the combustion air, carbon dioxide and water vapor as well as excess oxygen after pollution control. Minimal or even no flashers may be required in the process owing to the rich CO.sub.2 loading is not sufficiently high. Instead, with no flashers as shown in FIG. 4, the rich solution is directed to the GPS column 70 from the heat exchanger 26. Moreover, the operating pressure in the GPS column is possibly much higher (e.g. at least 4 atm) than that in the absorption column (atmospheric pressure). The process depicted in FIG. 4 can separate at least 90% of CO.sub.2 from the raw gas at a desired CO.sub.2 purity in the final product and depending on the operating conditions a 99% purity can be achieved, if required. Table 1 illustrates an example when the process of FIG. 2 with the flashers omitted is applied for CO.sub.2 capture from flue gas which includes flows, conditions, energy requirements and composition of flue gas, clean flue gas, stripping gas and CO.sub.2 product streams.

TABLE-US-00001 TABLE 1 An example of the invention application to CO.sub.2 capture from flue gas Raw Clean flue flue Stripping CO.sub.2 Parameters gas gas gas product Flow rate, kmol/hr 109,300 81,930 395 13457 Pressure, bar 1.03 1.01 6 153 Compositions, mol % CO.sub.2 13.26 1.73 0 96.86 N.sub.2 67.71 90.35 100 2.89 H.sub.2O 16.68 4.77 0 0.25 O.sub.2 2.35 3.14 0 0 Energy demand, MW Heat 306 Power 41 Number of flashers 0

[0059] The process depicted in FIG. 2 can be used to purify raw gas mixture under pressure (2 atm and above), which includes but not limits to natural gas, syngas and CO.sub.2 enhanced oil recovery (EOR) recycle gases. The operating configuration of the process can be adjusted to accommodate the condition of raw gas (i.e. raw gas pressure and CO.sub.2 content) for better energy performance. For example, the operating pressure for both absorption and GPS column are preferred to set to be the same or close each other to reduce the power consumption in pumping the circulation solvent when the raw gas pressure is high, such as 4 atm and above; one or more flashers are preferred in the process to obtain the high pressure CO.sub.2 product to reduce subsequent compression power. Moreover, the process depicted in FIG. 2 can separate at least 90% mol of CO.sub.2 from the raw gas at a desired CO.sub.2 purity in the final product (depending on the operating conditions a 99% purity (dry base) can be achieved if required.

[0060] Natural gas is a hydrocarbon gas mixture consisting primarily of methane, but commonly includes varying amounts of other higher alkanes and even a lesser percentage of carbon dioxide, nitrogen, and hydrogen sulfide. Natural gas is an energy source often used for heating, cooking, and electricity generation. It is also used as fuel for vehicles and as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals. Table 2 illustrates an example when the process of FIG. 2 with only a single flasher is applied for natural gas purification which includes flowrates, conditions, energy requirements and composition of flue gas, purified natural gas, stripping gas and CO.sub.2 product streams.

TABLE-US-00002 TABLE 2 An example of the invention application to natural gas purification Raw Clean natural natural Stripping CO.sub.2 Parameters gas gas gas product Flow rate, kmol/hr 4,823 3,795 57 1,093 Pressure, bar 63 63 63 153 Compositions, mol % CO.sub.2 23.69 2.84 2.84 95.13 N.sub.2 3.03 3.85 3.85 0.20 H.sub.2O 0.03 0.10 0.10 0.18 CH.sub.4 71.99 91.61 91.61 4.42 C.sub.2H.sub.6 1.07 1.36 1.36 0.06 C.sub.3H.sub.8+ 0.19 0.24 0.24 0.01 Energy demand, MW Heat 19.1 Power 0.7 Number of flashers 1

[0061] Syngas is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and carbon dioxide. Syngas is usually a product of fossil fuel gasification and the main application is electricity generation. Syngas is also used as intermediates in creating synthetic natural gas and for producing ammonia or methanol. Syngas is combustible and often used as a fuel of internal combustion engines. Table 3 illustrates an example when the process of FIG. 2 with only a single flasher is applied for syngas purification which includes flowrates, conditions, energy requirements and composition of flue gas, purified syngas, stripping gas and CO.sub.2 product streams.

TABLE-US-00003 TABLE 3 An example of the invention application to syngas purification Raw Clean Stripping CO.sub.2 Parameters syngas syngas gas product Flow rate, kmol/hr 4,823 3,320 75 1,579 Pressure, bar 75 75 75 153 Compositions, mol % CO.sub.2 33.15 2.78 0 95.06 N.sub.2 0.38 0.70 100 4.43 H.sub.2O 0.00 0.09 0 0.19 CH.sub.4 0.44 0.64 0 0.00 H.sub.2 64.53 93.62 0 0.32 CO 1.5 2.18 0 0.01 Energy demand, MW Heat 25.4 Power 0.7 Number of flashers 1

[0062] Enhanced Oil Recovery, EOR, is a technique for increasing the amount of crude oil that can be extracted from an oil field. CO.sub.2 injection is presently the most commonly used EOR approach. Gaseous stream in crude oil, mostly CO.sub.2 and small percentage of natural gas, is CO.sub.2 EOR recycle gas, which is usually separated to recover natural gas and produce CO.sub.2 for recycling back to the EOR process. Table 4 illustrates an example when the process of FIG. 2 (with three flashers in series) is applied for CO.sub.2 EOR recycle gas separation. Table 4 includes flowrates, conditions, energy requirements and composition of CO.sub.2 EOR recycle gas, recovered natural gas, stripping gas and CO.sub.2 product streams.

TABLE-US-00004 TABLE 4 An example of the invention application to CO.sub.2 EOR recycle gas separation Raw Recovered Stripping CO.sub.2 Parameters gas gas gas product Flow rate, kmol/hr 5,787 583 275 5,464 Pressure, bar 14.8 14.8 30 153 Compositions, mol % CO.sub.2 91.87 22.67 0 95.17 N.sub.2 0.88 8.74 0 0.00 H.sub.2O 0.00 0 0.20 H.sub.2S 0.91 0.00 0 0.17 CH.sub.4 1.51 20.29 100 4.46 C.sub.2H.sub.6 1.35 13.40 0 0.00 C.sub.3H.sub.8 1.60 15.88 0 0.00 C.sub.4H.sub.10+ 1.88 19.02 0 0.00 Energy demand, MW Heat 86.18 Power 8.73 Number of flashers 3

[0063] FIG. 2 is illustrated for an aqueous alkanolamines solvent system. However, the GPS technology can be also applicable to physical solvent. FIG. 3 is an example of a system using physical solvent to purify a raw syngas. In system the details of the absorption column 12 and GPS column 70 are described above. The primary differences from the process depicted in FIG. 2 are: 1) the gaseous effluent from the first high pressure flasher after heat exchanger 26 is returned back to combine with raw syngas to enter the absorption column to reduce the loss of hydrogen product; 2) a low pressure flasher is applied to the lean solution exited from bottom of the GPS column 70 to restore CO.sub.2 content in the lean solvent to specified concentration; 3) the operating pressure in the GPS column is much lower than that in the absorption column. The process depicted in FIG. 3 separates at least 90% mol of CO.sub.2 from the raw gas with the CO.sub.2 purity in the final product is at least 95% mol (dry base).

[0064] Unlike amine based acid gas removal solvents that rely on a chemical reaction with the acid gases, physical solvent absorb acid gas without chemical reaction involved. As a result, physical solvent usually requires less energy than the amine based processes. However, physical solvent only applies to high pressure feed gas because its working capacity is reduced when the feed gas pressures is below about 300 psia (20.7 bar). Physical solvent is made up of dimethyl ethers of polyethylene glycol. Physical solvent is commercially available such as DMPEG/Selexol, Purisol or Rectisol. Table 5 illustrates an example when the process of FIG. 3 is applied for syngas purification. Table 5 includes flowrates, conditions, energy requirements and composition of syngas, Purified syngas, stripping gas and CO.sub.2 product streams.

TABLE-US-00005 TABLE 5 An example of the invention application to syngas purification with physical solvent Raw Clean Stripping CO.sub.2 Parameters syngas syngas gas product Flow rate, kmol/hr 4,823 3,321 75 1,570 Pressure, bar 75 75 83 153 Compositions, mol % CO.sub.2 33.15 2.75 0 95.05 N.sub.2 0.38 1.09 100 4.15 H.sub.2O 0.00 0.00 0 0.00 CH.sub.4 0.44 0.62 0 0.03 H.sub.2 64.53 93.39 0 0.72 CO 1.50 2.15 0 0.05 Energy demand, MW Heat 18.55 Power 4.86 Number of flashers 3

[0065] In certain embodiments of the improved invention, the process further comprises after step (b) subjecting the high pressure gaseous effluent from the gas pressurized column to a final separation process to further purify the product gas. In principle, many separation methods could be used to separate the product gas from the gaseous effluent. For CO.sub.2 product, for example, a preferred energy efficient final separation process is compound compression and refrigeration process which illustrated in FIG. 4. The primary advantage of the compression/refrigeration process is elevating the pressure of gas effluent from the GPS column to reduce compression work and stripping heat. Moreover, this process produces high purity CO.sub.2 product (its purity is at least 99% mol).

[0066] FIG. 4 does not depict any refrigeration systems that are required for this compound separation process. However, such a design is evident to one skilled in the art. Specifically in FIG. 4, as the CO.sub.2 rich solution enters column 70 at the top in line 28 and lean solution exits the bottom in line 72. Stripping gas, N2, enters column 70 at 50 and exits in line 52 at the top of column 70. The high-pressure CO.sub.2 and N2 mixture from the GPS column is further separated and compressed with a compound compression and refrigeration process, as shown in FIG. 4. Line 52 first leads to cooling unit and a first phase separator 54. Liquid is returned to the GPS column from the separator 54 in line 34 and gaseous stream exits in line 56. The Gaseous stream in line 56 is then compressed to about 20 bar through low pressure compressors and then goes through a CO.sub.2 dryer and purification unit 62.

[0067] FIG. 5 further exhibits the compound compression-refrigeration process represented unit 62 in FIG. 4. The purification unit 62 mainly comprises of a CO.sub.2 dehydration and two-stage compound compression-cooling-refrigeration process: 20 to 40 bar and 40 to 80 bar or variations thereof can be used. The compressed gaseous stream 60 is cooled at cooler 200 to 35° C. and then goes through a liquid-gas separator 204 to remove condensed water through stream 46.

[0068] The gaseous stream 206 from separator 204 enters the bottom of a dehydrator 208 and contact with desiccant to further remove water in the gaseous stream. The dehydrated gaseous stream 210 is then compressed to 40 bar at the first stage compression 212. The compressed gaseous stream 214 is cooled to 35° C. first at cooler 200 and further cooled by the liquefied CO.sub.2 product through a cross heat exchanger 218.

[0069] Next, the gaseous stream 220 is further cooled to −5° C. by refrigeration 222 to liquefy the majority of CO.sub.2 from the stream 220. The liquefied CO.sub.2 in stream 224 is separated by a gas-liquid separator 226 through stream 250. The gaseous stream 228 from separator 226 is further compressed to 80 bar through the second stage compression 212. The further compressed gaseous stream 212 is cooled to 35° C. first at cooler 200 and then is further cooled up to −20° C. by refrigeration 222 to further liquefy CO.sub.2. The liquefied CO.sub.2 in stream 224 is removed by a gas-liquid separator 226 through stream 256. The N2 concentration in remaining gaseous stream 228 is sufficiently high to meet stripping gas specifications.

[0070] The remaining gaseous stream 228 enters three stages of expansion 234 with inter-stage heating 230 to recover power in the high pressure gaseous stream 228. The expansion cycles used were 80-40 bar, 40-20 bar, and 20-10 or 8 bar. Finally, the remaining gas stream 40 (at 8-10 bar) is recycled to the GPS column for use as a stripping gas after mixed with make-up stripping gas stream 32. The liquefied CO.sub.2 stream 250 is pumped to 80 bar and then merged with liquefied CO.sub.2 stream 256 to for CO.sub.2 product stream 260 with CO.sub.2 purity over 99.5%. The refrigeration heat in the liquefied CO.sub.2 product is recovered through heat exchangers 218 to 30° C.

[0071] The refrigeration heat is provided by any refrigeration process. For example, ammonia can be used in a compression-expansion circulation. Refrigeration heat is generated by expanding high-pressure ammonia gas to low-pressure to obtain a low-temperature gas-liquid mixture. The temperature of the mixture can be controlled by adjusting the expander outlet pressure.

[0072] In the representative FIGS. 1-5 of this application not all blowers or pumps or valves are illustrated as the use of these are well known to those of ordinary skill in the art. Only a representative sample of these elements are specifically illustrated in the figures to evidence their presence in an operational system. Additionally not shown are the controllers and system sensors used for operating similar systems, but these are also known to those of ordinary skill in the art.

[0073] The process of the present invention has numerous applications, as discussed above, such as where the product gas is CO.sub.2 and where the gaseous mixture is coal fired post-combustion flue gas, and in which, typically, the operating pressure in the gas pressurized stripping column will be at least 4 atm. Alternatively, the process of invention may be utilized where the gaseous mixture is a raw gas, such as syngas or natural gas, under pressure, and where the operating pressure in the gas pressurized stripping column is similar to the operating pressure in absorption column, wherein the liquid is an aqueous alkanolamine.

[0074] The process of the present invention has numerous applications with distinct operating parameters, as discussed above, such as, where the gaseous mixture is natural gas and the product gas comprises carbon dioxide, the high pressure gas stream is at least 60 Bar within the high pressure stripping column. Alternatively, where the gaseous mixture is syngas and the product gas comprises carbon dioxide, the high pressure gas stream is at least 75 Bar within the high pressure stripping column. Further, where the gaseous mixture is CO.sub.2 EOR recycled gas, and the product gas comprises carbon dioxide, the high pressure gas stream is at least 30 Bar within the high pressure stripping column.

[0075] The above description and associated figures are intended to be illustrative of the present invention and not be restrictive thereof. A number of variations may be made to the present invention without departing from the spirit and scope thereof. The scope of the present invention is defined by the appended claims and equivalents thereto.