Abstract
The present invention provides a gas pressurized separation system to strip a product gas from a liquid stream and yield a high pressure gaseous effluent containing the product gas. The system comprises a gas pressurized stripping apparatus, such as a 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 containing the product gas; and two or more heat supplying apparatuses provided at different locations along the column. Processes for separating a product gas from a gaseous mixture to yield a high pressure gaseous effluent containing the product gas, utilize the gas pressurized separation system described above.
Claims
1. A gas pressurized separation system to strip a product gas from a liquid stream to yield a gaseous effluent that contains the product gas, the system comprising: (a) a gas pressurized stripping apparatus with at least one liquid inlet allowing flow of one or more liquid streams into the apparatus and at least one stripping gas inlet allowing flow of one or more stripping gas streams into the apparatus, wherein each stripping gas stream is separate and independent from the liquid streams and separate and independent from by-products of the liquid streams, and wherein the stripping gas streams are configured to strip the product gas into the stripping gas streams and yield through at least one outlet a gaseous effluent that contains the product gas; and (b) heat supply apparatuses allowing for independent control of temperature along the gas pressurized stripping apparatus at locations between the at least one liquid inlet allowing flow of one or more liquid streams into the apparatus and the at least one stripping gas inlet allowing flow of one or more gas streams into the apparatus.
2. The gas pressurized separation system of claim 1, wherein the heat supplying apparatuses provide heat at two or more different locations along the gas pressurized stripping apparatus and are connected to each other.
3. The gas pressurized separation system of claim 1, wherein the heat supplying apparatuses provide heat at two or more different locations along the gas pressurized stripping apparatus and are separate from each other.
4. The gas pressurized separation system of claim 1, wherein the heat supplying apparatuses provide heat at two or more different locations along the column and are internal to the gas pressurized stripping apparatus.
5. The gas pressurized separation system of claim 1, wherein the heat supplying apparatuses provide heat at two or more different locations along the column and are external to the gas pressurized stripping apparatus.
6. The gas pressurized separation system of claim 1, wherein heat is provided through the high pressure stripping gas streams and wherein the stripping gas inlet allows for flow of one or more stripping gas streams at a pressure of at least 4 atm.
7. A gas pressurized separation system to strip a product gas from a liquid stream to yield a high pressure gaseous effluent that contains the product gas, the system comprising: (a) a gas pressurized stripping apparatus with a liquid stream inlet and a high pressure gas stream inlet, wherein the high pressure gas stream entering at the high pressure gas stream inlet is separate and independent from the liquid stream entering at the liquid stream inlet and separate and independent from by-products of the liquid stream, and wherein the high pressure gas stream is configured to strip the product gas into the high pressure gas stream and yield a high pressure gaseous effluent that contains the product gas at an outlet; and (b) heat supply apparatuses allowing for independent control of temperature along the gas pressurized stripping apparatus at locations between the high pressure gas stream inlet and the liquid stream inlet.
8. The gas pressurized separation system of claim 7, wherein the heat supplying apparatuses provide heat at two or more different locations along the gas pressurized stripping apparatus and are connected to each other.
9. The gas pressurized separation system of claim 7, wherein the heat supplying apparatuses provide heat at two or more different locations along the gas pressurized stripping apparatus and are separate from each other.
10. The gas pressurized separation system of claim 7, wherein the heat supplying apparatuses provide heat at two or more different locations along the column and are internal to the gas pressurized stripping apparatus.
11. The gas pressurized separation system of claim 7, wherein the heat supplying apparatuses provide heat at two or more different locations along the column and are external to the gas pressurized stripping apparatus.
12. The gas pressurized separation system of claim 7, wherein the high pressure gas stream inlet allows for flow of the high pressure gas stream at a pressure of at least 4 atm.
13. A gas pressurized separation system to strip a product gas from a liquid stream to yield a high pressure gaseous effluent that contains the product gas, the system comprising: (a) a gas pressurized stripping apparatus with at least one liquid stream inlet allowing flow of one or more liquid streams into the apparatus and at least one high pressure gas stream inlet allowing flow of one or more high pressure gas streams into the apparatus at a pressure of at least 4 atm, wherein each high pressure gas stream is separate and independent from the liquid streams and by-products of the liquid streams, and wherein each high pressure gas stream is configured to strip the product gas into the high pressure gas stream and yield a high pressure gaseous effluent that contains the product gas through at least one outlet; and (b) heat supply apparatuses allowing for independent control of temperature along the gas pressurized stripping apparatus at locations between the liquid stream inlet allowing flow of one or more liquid streams into the apparatus and the at least one high pressure gas stream inlet allowing flow of one or more high pressure gas streams into the apparatus.
14. The gas pressurized separation system of claim 13, wherein the heat supplying apparatuses provide heat at two or more different locations along the gas pressurized stripping apparatus and are connected to each other.
15. The gas pressurized separation system of claim 13, wherein the heat supplying apparatuses provide heat at two or more different locations along the gas pressurized stripping apparatus and are separate from each other.
16. The gas pressurized separation system of claim 13, wherein the heat supplying apparatuses provide heat at two or more different locations along the column and are internal to the gas pressurized stripping apparatus.
17. The gas pressurized separation system of claim 13, wherein the heat supplying apparatuses provide heat at two or more different locations along the column and are external to the gas pressurized stripping apparatus.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a schematic diagram of a conventional prior art absorption process for CO.sub.2 separation.
(2) FIG. 2 illustrates a tray-type gas pressurized column in accordance with one aspect of the present invention;
(3) FIG. 3 illustrates a packed gas pressurized column in accordance with one aspect of the present invention;
(4) FIG. 4 is a schematic diagram of one embodiment of the process of the present invention;
(5) FIG. 5 is an exemplary schematic diagram of a separation process of one embodiment of the present invention using heptane as a high pressure gas stream to separate carbon dioxide from a liquid followed by condensation as a final separation process;
(6) FIG. 6 is an exemplary schematic diagram of a separation process of one embodiment of the present invention using neopentane as a high pressure gas stream to separate carbon dioxide from a liquid followed by a combination of condensation and distillation as a final separation process;
(7) FIG. 7 is an exemplary schematic diagram of a separation process of one embodiment of the present invention using neopentane as a high pressure gas stream to separate carbon dioxide from a liquid followed by distillation as a final separation process;
(8) FIG. 8 is an exemplary schematic diagram of a separation process of one embodiment of the present invention using helium as a high pressure gas stream to separate carbon dioxide from a liquid followed by cryogenic condensation as a final separation process;
(9) FIG. 9 is an exemplary schematic diagram of an alternative embodiment of the invention using multiple absorption steps integrated with a stripping step in a gas pressurized column;
(10) FIG. 10 is an exemplary schematic diagram of an alternative embodiment of the invention using repeated absorption and stripping steps; and
(11) FIG. 11 is a schematic diagram of one embodiment of the process of the present invention using dual solvents.
DETAILED DESCRIPTION OF THE INVENTION
(12) A gas pressurized separation system of the present invention comprises 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. The directions of each stream within the column may be the same as or different from each other, and may change with respect to each other. For example, they may be co-current (in the same direction) or counter-current (opposite directions) to each other, or anywhere between these two extremes; for example, perpendicular to each other. Also, contact between the streams may include intimate and/or turbulent mixing of the streams.
(13) The separation column may further comprise two or more heat supplying apparatus, such as heat exchangers or heating coils, positioned in different locations along the column. The heat supplying apparatuses may be connected to each other, such as in a coil arrangement wherein heat is supplied in theoretically up to infinite different locations along the length of the column. Alternatively, the heat supplying apparatuses may be separate from each other with means for independent control of the temperature along the stripping column. Whether connected or not, within the meaning of this application the heat supplying apparatuses are considered or counted via the distinct locations (where the liquid has different product gas loadings) at which heat is supplied. Thus a single continuous heating unit that supplies heat at a plurality of different locations is a plurality of heating sources within this application. The heat supplying apparatuses may be internal to or external to the column and may be spaced evenly or otherwise spaced along the column. The heat supplying apparatuses may be integral to trays in a tray-type column or integral to packing in a packed column.
(14) The second inlet in the gas pressurized separation system of the present invention is designed to accommodate one or more high pressure gas streams, with pressures of at least 4 atm, alternatively at least 10 atm, often at least 30 atm, 50 atm and even at least 100 atm. The high pressure gas stream may be a single pure gas, or may comprise a mixture of different gases. It may also contain a portion of the desired product gas. In certain select applications for specific products the second inlet need not be at high pressures at all, although as discussed herein there are advantages with such high pressure applications.
(15) FIG. 2 depicts a tray-type separation column 100 or 120, while FIG. 3 illustrates a packed column 130 or 140. In the operation of the separation column of the present invention, a liquid containing a desired product gas is introduced as a first stream into the column from one end, e.g., the top, through a first inlet and flows in a first direction, typically downward. A high pressure stripping gas stream is introduced to the column, for example, from the bottom, through a second inlet and flows countercurrent to the first stream. The use of a high pressure gas stream allows for stripping and recovery of the desired product gas from the first stream in a high pressure output stream comprising a gaseous effluent.
(16) The columns depicted in FIGS. 2 and 3 have only one feed stream inlet 28 and one high pressure stripping gas stream inlet 108, as shown. In principle, however, multiple feed streams or multiple stripping gas streams are possible. Additionally, one or more side products (either gas phase product or liquid phase products) may be extracted if desired.
(17) In the tray type column 100 of FIG. 2, the rich solution enters column 100 at line 28, with the stripping column 100 having multiple trays 102 each having a heating coil 104 associated with a steam line 106. Lean solution exits at the bottom of the stripping column 100 at line 32. High pressure stripping gas is supplied to the bottom of the stripping column 100 at line 108 and the product gas exits the top of the stripping column at 110.
(18) In the tray type column 120 of FIG. 2, the rich solution enters column 120 at line 28, with the stripping column 120 having multiple trays 102 each having an external heating apparatus 124 associated with a steam line 106 and with a liquid recirculation line 122 drawing liquid from the column 120 at the tray 102. Lean solution exits at the bottom of the stripping column 120 at line 32. High pressure stripping gas is supplied to the bottom of the stripping column 120 at line 108 and the product gas exits the top of the stripping column 120 at 110.
(19) In the packed type column 130 of FIG. 3, the rich solution enters column 130 at line 28, with the stripping column 130 having an internal steam circuit with entrance 132 near the top of the stripping column 130 and an exit 134 near the bottom of the stripping column, and with spaced heating coils 104 positioned along the steam circuit. Lean solution exits at the bottom of the stripping column 130 at line 32. High pressure stripping gas is supplied to the bottom of the stripping column 130 at line 108 and the product gas exits the top of the stripping column 130 at 110.
(20) In the packed type column 140 of FIG. 3, the rich solution enters column 140 at line 28 at the top. The stripping column 140 has multiple liquid collector sites 142 each having an external heating apparatus 124 associated with a steam line 106 and with a liquid recirculation line 122 drawing liquid from the column 140 at the associated collector 142. Lean solution exits at the bottom of the stripping column 140 at line 32. High pressure stripping gas is supplied to the bottom of the stripping column 140 at line 108 and the product gas exits the top of the stripping column 140 at 110.
(21) The two pairs of columns 100/120 and 130/140 in the respective FIGS. 2 and 3 display examples of two different heat supply configurations. In the left columns 100 and 130, heat is supplied through multiple heat supplying apparatuses such as coils 104 residing inside the respective column 100 and 130 on each tray 102 in column 100 or at certain intermittent heights of packing in column 130. In the right column 120 and 140, heat is supplied by multiple external heat supplying apparatuses 124 such as steam from line 106 passing through external heat exchangers forming the heating apparatus 124, heating liquid diverted from the column 120 or 140 at intermittent levels in associated lines 122. The use of multiple heat supplying apparatuses 104 or 124 further enables the columns to yield a high pressure output stream at line 110 using less energy than conventional separation columns.
(22) Varieties of heat supplying apparatuses are suitable for the gas pressurized column of the present invention. FIGS. 2 and 3 are only two typical examples for both tray and packed columns. Other mechanisms are also possible. For example, heat exchanging means may be incorporated into structured packing or a series of heating tubes may be inserted into packing vertically. For tray columns, heat may be supplied through integrated heating elements in the column as well.
(23) In still another example, heat may be provided through the high pressure stripping gases. Either the sensible heat of the high pressure gas or the latent heat of some gas components such as water vapor in the high pressure gas stream can be used.
(24) The number of heat supply apparatuses for the column is flexible, provided there are at least two. The greater the number of the heat supplying apparatuses in the column, the better the potential thermodynamic efficiency of the separation process.
(25) Also provided by the present invention is 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 one or more liquid flowing in an absorption apparatus, to absorb the product gas into the liquid and yield one or more 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 one or more 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 in the gaseous mixture; (c) recovering heat from the product-lean liquid; and (d) recycling at least a portion of the product-lean liquid to step (a).
(26) Many variations on the process are possible. One or more absorption columns and one or more gas pressurized columns may be arranged in various combinations. For example, the gas pressurized column may be divided into a series of columns that are sequentially connected or a series of gas pressurized columns and conventional stripping columns consecutively connected. Each of the columns may operate at different pressure and temperature. In an extreme case, a gas pressurized column (tray or packed) may be divided into a series of conventional columns connected serially, thus each column will have one heat supplying source. In an even more extreme case, some of the conventional stripping columns may not have any heat supplying source at all. Some of the variations mentioned above may improve the thermodynamic efficiency of the stripping process, but may make the process unnecessarily complicated and capital intensive.
(27) Also, at least a portion of the product-enriched liquid from the absorption column may be introduced into one or more additional absorption columns and contacted with a gas stream that comprises some or all of the gaseous effluent from the gas pressurized column, to absorb more of the product gas into the product-enriched liquid.
(28) Additionally, after step (a) and before step (b), the process may further comprise introducing some or all of the product-enriched liquid from the first absorption column and/or from any additional absorption columns into at least one flasher to remove product gas prior to introduction of the product-enriched liquid into the gas pressurized column. In this embodiment, a plurality of flashers may be used in parallel and the product-enriched liquid from the absorption column is split into several streams for passage through the flashers.
(29) In an additional particular embodiment, the process further comprises after step (a) and before step (b), (i) introducing at least a portion of the product-enriched liquid from the absorption apparatus in step (a) into at least one additional absorption apparatus and into contact with a gas stream that comprises at least a portion of the gaseous effluent from the gas pressurized column in step (b), to absorb the product gas into the product-enriched liquid and yield a further product-enriched liquid; and (ii) subsequently introducing the further product-enriched liquid from the additional absorption apparatus into at least one flasher to recover a portion of the product gas prior to introduction of the product-enriched liquid into the gas pressurized column in step (b). Often more than one additional absorption apparatus is used and they are arranged in series, with the product-enriched liquid leaving each absorber being introduced into the subsequent absorber.
(30) The process of the present invention will be described below using carbon dioxide as the desired product gas. Often carbon dioxide is present in combustion flue gas from a carbonaceous fuel burning facility. This is for illustrative purposes only and is in no way intended to limit the invention.
(31) In a preferred embodiment, the process steps are arranged as follows: absorption/absorption/stripping (flashers)/high pressure gas stripping. This process sequence provides a significant energy savings over conventional separation processes of alternating absorption/stripping/absorption/stripping sequences. In this preferred process, for example, CO.sub.2-rich solution (product-enriched liquid) from a first absorption column goes to a second absorption column to absorb CO.sub.2 from the gaseous effluent coming from the GPS column. The CO.sub.2-rich solution leaving the second absorption column goes through a series of flashers (depending the needs) to produce high pressure, pure CO.sub.2. The new product-enriched liquid (a semi-rich solution,) after passing through the flashers, then enters the GPS column to strip out the remaining CO.sub.2. In the GPS column a high pressure gas stream is introduced from the bottom to strip the CO.sub.2 from the semi-rich solution. The high pressure gas could be any pure gas or mixtures of any gases. Along with the high pressure stripping gas (or gas mixture), multiple 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 mixture of CO.sub.2 and the high pressure stripping gas, which is recycled to the second absorption column as noted above to have CO.sub.2 removed.
(32) The high pressure stripping gas stream may be any gases that are not harmful to solvents in the liquid and will not interfere with the stripping system. Inorganic gases such as He, Ar, O.sub.2, N.sub.2, air, and their mixtures or organic gases such as CH.sub.4, C.sub.2H.sub.6, C.sub.3H.sub.8, C.sub.2H.sub.4 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. 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 pressure and the amount of the selected stripping gas are flexible. The pressure is selected based on (and always higher than) the equilibrium partial pressure of CO.sub.2 in the rich solution entering the GPS column at stripping conditions. The amount of stripping gas introduced to the GPS column is determined by the desired CO.sub.2 loading in the lean solution leaving the GPS column.
(33) The gaseous effluent exiting from the GPS column is a mixture of CO.sub.2 (product gas) and the stripping gas. If the stripping gas is nitrogen (which is actually preferred due to its availability, low cost, inertia and negligible solubility in solvent) then the situation will be similar to the separation of the flue gas except that CO.sub.2 partial pressure in the gas product is much higher. Obviously, if absorption is the best option for separating CO.sub.2 from nitrogen, then the same absorption process can be repeated to separate CO.sub.2 from the stripping gas. In some applications, the high pressure gaseous effluents with the product gas therein maybe used in the combined state as a product gas without further separation.
(34) FIG. 4 is a schematic diagram for one system 150 of the process sequences absorption/absorption/stripping (flashers)/high pressure gas stripping. Raw flue gas 14 enters the bottom of the absorption column 12 and clean flue gas 16 exits the top while a CO.sub.2-lean solution 18 enters into the absorption column 12 from the top and flows downward producing a CO.sub.2-rich solution exiting at 20. The CO.sub.2-rich solution goes through pump 22 and in line 24 the rich solution (product-enriched liquid) from the bottom of the first absorption column 12 enters the second absorption column 152 from top to absorb CO.sub.2 contained in the gaseous effluent flowing upward, which comes from the top of a conventional stripping column or a GPS column 192 through line 196, through heat exchanger 162 and line 158 to bottom of column 152. Gas exiting the column 152 at line 160 is directed through heat exchanger 162 and through line 198 to bottom of column 192. The CO.sub.2 loaded rich solution (product-enriched liquid) from the bottom of the second absorber 152 is directed through line 154 through heat exchanger 156 and enters a flasher 166 (or a series of flashers) through line 164 to flash high pressure CO.sub.2 out. CO.sub.2 in line 170 from the flasher 166 is cooled in cooling unit 172 and supplied by line 174 to liquid gas separator 176 with liquid or water exiting at line 178 and gas exiting at line 180. The gas in line 180 is compressed in compressor 182 to sequestration-ready pressure for the gas at line 184 and the condensed water from the system 150 is removed via line 178. Multi-stage compression with inter-stage cooling can be used if required. The semi-rich solution (product-enriched liquid) from the bottom of the flasher 166 (or last flasher if there are more than one flasher) is directed through line 168 to a combined stream in line 190 then enters the GPS column 192 from the top. The high pressure stripping gas stream in line 198 enters the bottom of the GPS column 192 and strips the CO.sub.2 from product-enriched liquid flowing countercurrent. After exchanging heat with gas exiting the second absorption column from line 160 in the heat exchanger 162, the gaseous effluent from the GPS column 192 enters the second absorption column 152 in line 154 as noted. In the second absorption column, the gaseous effluent from the GPS column 192 flows countercurrent to the product-enriched liquid from the first absorption column 12. After CO.sub.2 is removed from the gaseous effluent by liquid in the second absorption column 152, the now CO.sub.2-lean gaseous effluent passes back through the heat exchanger 162 and is recycled back to the GPS column 192 as the high pressure gas stream.
(35) In the specification the term GPS column references a column 100, 120, 130, 140 or modifications thereof within the present invention. Column 192 is preferably a GPS column as noted but a conventional column could also be utilized in this system, however preferential results are believed to be achieved with the GPS column 100, 120, 130, 140 or minor variations thereof.
(36) The CO.sub.2-lean solution is directed via line 194 from the column 192 to heat exchanger 156 to line 200 wherein make-up solvent (amine) may be added through line 42 into the lean solution before it enters the absorber in line 18 and the cycle repeats.
(37) As noted above, a portion of the product-enriched liquid exiting from the first absorption column may be introduced into one or more additional absorption columns and contacted with a gas stream that comprises some or all of the gaseous effluent from the GPS column, to absorb more of the product gas into the product-enriched liquid. The product-enriched liquid exiting from the first absorption column 12 may be split into multiple streams via control valve 186 and line 188 combining with line 168 from the flasher 166 to form combined stream at line 190. CO.sub.2 partial pressure (e.g. 5 atm) in the gaseous effluent from the GPS column 192 is much higher than that in the original gaseous mixture (e.g., flue gas 0.15 atm). Thus the working capacity of the liquid in the second absorption column 152 will be much higher than that of the liquid in the first absorption column 12. It is possible to use only a fraction product-enriched liquid exiting from the first absorption column 12 to absorb CO.sub.2 contained in the gaseous effluent from the GPS column 192. The rest of the product-enriched liquid exiting from the first absorption column 12 can directly go to the GPS column 192 via line 188 or certain flasher if a series of flashers are used. As a result, the final loading of the product-enriched liquid exiting from the second absorption column 152 could be several times higher than that of the product-enriched liquid exiting from the first absorption column 12. A higher CO.sub.2 loading in the liquid translates to a higher equilibrium CO.sub.2 pressure in the stripper (flashers).
(38) FIG. 4 is an example embodiment of the process of the present invention using repeated absorption/stripping steps. In this example, product-enriched liquid from the first absorption column is divided into two streams. Of course the split of rich solution is not necessary. FIG. 4 only displays two consecutive absorption columns. However, if necessary, multiple (more than two) consecutive absorption and stripping configurations are also possible. In this case the arrangement will be as follows: absorption/ . . . /absorption/absorption/stripping (flashing)/stripping/ . . . /stripping.
(39) In certain embodiments of the present invention, the process further comprises after step (b) subjecting the high pressure gaseous effluent from the gas pressurized column to at least one final separation process to purify the product gas. In principle, many separation methods could be used to separate the product gas from the gaseous effluent. For example, the final separation process may comprise one or more condensation, cryogenic condensation, and distillation, absorption, and/or adsorption steps or combined, in series or parallel.
(40) When the stripping gases used in the high pressure gas stream entering the GPS column have much higher boiling point than the product gas, such stripping gas or gases and the product gas can be easily separated through condensation. FIG. 5 is an example of many possible flow diagrams. In the embodiment with system 210 illustrated in FIG. 5, heptane vapor is used as the stripping gas in the high pressure gas stream.
(41) In FIG. 5 rich solution enters column 100 at the top in line 28 and lean solution exits the bottom in line 32 as noted above. Further column 100 is illustrated, but any column 120, 130, 140 or variations thereof can be used. Stripping gas enters column 100 at 108 and exits in line 110 at the top of column 100. Line 110 leads to a first phase separator 216 through unit 212 and line 214. Water is drawn off of the separator 216 in line 222 and gas exits in line 218 to a compressor 224 to be directed in line 226 to a subsequent phase separator 228. Line 220 is directed from the separator 216 through an expander 240 to a phase separator 244 through line 242. Water is drawn off of the separator 228 in line 230 and gas exits in line 234 to a compressor 224 to be directed in line 226 to a subsequent phase separator 228. Line 232 is directed from the separator 228 through an expander 240 to a phase separator 244 through line 242. Additional or fewer phase separators 228 can be incorporated into the system 210 as dictated by desired operational parameters. The final separator 228 has line 264 providing the high pressure CO.sub.2. The separator 244 has an exit line 246 extending to a compressor 250 to a line 252 combining with the line 218 from the first separator in the series, however it could be alternatively be directed to be combined with subsequent lines 234 as well. The separator 244 includes an outlet line 248 leading through unit 252 to line 254 to heating source 260, which is shown as a heat exchanger with steam line 256. The high pressure line 108 comes from the heating source 260.
(42) When the volatility difference between stripping gases and the product gas are not significant enough, simple condensation may not be sufficient and a distillation column may be required to obtain pure product gas. FIG. 6 is an example of a system 270, where pure neo-pentane is used as the stripping gas. Neo-pentane has higher normal boiling point (30 C.) than CO.sub.2 and can be separated relatively easily with CO.sub.2.
(43) In FIG. 6, as above rich solution enters column 100 at the top in line 28 and lean solution exits the bottom in line 32. Further, again column 100 is illustrated, but any column 120, 130, 140 or variations thereof can be used. Stripping gas enters column 100 at 108 and exits in line 110 at the top of column 100. Line 110 leads to a first phase separator 216 through unit 212 and line 214. Water is drawn off of the separator 216 in line 222 and gas exits in line 218. Line 220 is directed from the separator 216 through an expander 240 to a phase separator 272 through line 242. Water is drawn off of the separator 272 in line 276 and gas exits in line 274. Line 278 is directed from the separator 272 through an expander 280 to a phase separator 282. Water is drawn off of the separator 282 in line 284 and gas exits in line 288. The separator 282 includes an outlet line 286 leading through unit 290 to line 292 to heating source 260, which is shown as a heat exchanger with steam line 256. The high pressure line 108 comes from the heating source 260. Gas line 288 leads to compressor 294 to line 296 that combines with line 274 forming line 298 leading to compressor 300. Outlet of the compressor 300 in line 302 is combined with line 218 to form line 304 leading to compressor 306 having outlet 308 leading to distillation column 310. The outlet 312 at the bottom of column 310 can be combined with line 110 in part and recycled to the column 310 through a heating unit 314, which may be a heat exchanger with a steam line 318. The outlet 320 of column 310 provides the high pressure CO.sub.2 from the system with unit 322 have a recirculation line 324 extending to the column 310. Three phase separators 216, 272 and 282 are shown but more or even less, separators could be incorporated into the system 270 effectively as shown depending upon the operational parameters desired.
(44) In FIG. 6, the product gas coming from top of the GPS column 100 is cooled and neo-pentane and water are condensed out. Due to the immiscibility of water and neo-pentane they can be separated by a decanter. The condensed neo-pentane liquid may still contain considerable amount of CO.sub.2. Since the liquid is under pressure it is therefore expanded through an expander and its pressure and temperature are reduced. After the expansion, the stream will contain a gas phase concentrated with CO.sub.2 and a liquid phase concentrated with neo-pentane. A series of such condensers and expanders as shown can be used to achieve high neo-pentane purity. The gas phase concentrated in CO.sub.2 is also under higher pressure and contains some neo-pentane. To achieve high purity CO.sub.2, and reduce neo-pentane loss, a distillation column 310, or a series of columns 310, may be desired.
(45) When boiling point of the stripping gas is close to that of the product gas (low relative volatility coefficient), the separation processes may not be sufficient and a series of distillation columns may be required. FIG. 7 is an example of a system 350, where three distillation columns were used to obtain pure CO.sub.2 and neo-pentane. In system 350 the details of the absorption column 12 and GPS column 130 are described above. Column 130 is illustrated, but any column 100, 120, 140 or variations thereof can be used. Stripping gas enters column 130 at 108 and exits in line 110 at the top of column 130, which can also be analogized to line 52 described above. Line 110 goes through cooling unit 56, which may have a return (not shown here) to the GPS column 130, to the first distillation column 354 in line 352. Gas exits column 354 at line 356 and unit 358 may have a return to the column 354. The line 356 combines with gas exiting in line 380 from the third distillation column 378 in line 360 to enter the second distillation column 362. High pressure CO.sub.2 exits the second distillation column 362 with unit 366 providing a return line 368 to the column 362. Liquid in line 355 from the first column 354 may be re-circulated to the column 354 through unit 357 or combined with the outlet 370 from the second distillation column 362 to be directed in line 376 to the third distillation column 378. Similarly, liquid in line 370 from the second column 362 may be re-circulated to the column 362 through unit 372 and line 374 or combined with the outlet 355 from the first distillation column 354 to be directed in line 376 to the third distillation column 378. The gas outlet 380 of the third column 378 may be returned through unit 382 to the column 378 or combined with outlet 356 to form line 360 as noted above. The liquid outlet 384 of the third distillation column 378 may be, in part, re-circulated to the column 378 through a heating source 386 such as a heat exchanger 386 with steam line 388, and in part directed through pump 390 through line 392 to heat source 394 in the form of a heat exchanger with steam line 396, wherein line 108 exits from the heat source 394.
(46) FIG. 7 illustrates only one of the many possible distillation sequences. Other different sequences are possible. In principle, one column will be enough to separate CO.sub.2 and neo-pentane (or any two component mixture) as long as they do not form an azeotrope. However, thermodynamic efficiency of these distillation sequences will be different.
(47) The previous three embodiments are for stripping gases that are less volatile than the product gas. Gases such as He, Ar, N.sub.2, O.sub.2 or their mixture or air have lower boiling points than CO.sub.2. When they are used as the stripping gas, CO.sub.2 will be condensed out first if the stripping gas product is cooled. CO.sub.2 will be condensed out as liquid if its partial pressure in the product gas is higher than the vapor pressure of CO.sub.2 at triple point (5.1 atm). When its partial pressure is below vapor pressure at triple point it will be condensed out as solid (dry ice). System 400 of FIG. 8 is an example of CO.sub.2 separation from stripping gas product when He is used as the stripping gas. In this process, the stripping product gas is cooled and the moisture in the product stripping gas is removed. It is then further cooled to remove some of the CO.sub.2 as liquid if initial partial pressure is >5.1 atm. If the partial pressure of CO.sub.2 in the product gas is <5.1 atm then all CO.sub.2 will be condensed out as a solid (called frosting or anti-sublimation). In this example, only simple condensation steps were used. If simple condensation is not sufficient a cryogenic distillation process may be used to obtain pure CO.sub.2.
(48) FIG. 8 does not depict any refrigeration systems that are required for cryogenic separation process. However, such a design is evident to one skilled in the art. Specifically in FIG. 8, as above rich solution enters column 100 at the top in line 28 and lean solution exits the bottom in line 32. Further, again column 100 is illustrated, but any column 120, 130, 140 or variations thereof can be used. Stripping gas enters column 100 at 108 and exits in line 110 at the top of column 100. Line 110 leads to a heat exchanger 402 to a first phase separator or cooling unit 408 through line 406. Water is drawn off of the separator 408 in line 410 and gas exits in line 412. Line 412 leads to a heat exchanger 414 to a second phase separator or cooling unit 418 through line 416. Here liquid CO.sub.2 is drawn off of the separator 418 in line 420 and gas exits in line 422. Line 422 leads to a heat exchanger 424 to a third phase separator or cooling unit 428 through line 426. Here liquid/solid CO.sub.2 is drawn off of the separator 428 in line 432 and gas exits in line 430. Line 430 extends to heat exchanger 424, to line 434, to exchanger 414 to line 436 to exchanger 438 and finally to heat source 260. Heat source 260 is in the form of a heat exchanger with steam line 256 with line 108 coming from the heat source 260.
(49) FIG. 9 is the schematic diagram of an example when both the repeated absorption/stripping process and GPS column are used to recover carbon dioxide as a product gas from a gaseous mixture. However, here the entire product-enriched liquid from the first absorption column is introduced into the second absorption column. The product-enriched liquid exiting from the second absorption column has high loading and will be able to produce a high pressure pure product gas stream through a series of flashers (FIG. 9 showed three flashers). After the flashers, the CO.sub.2 loading in the solution will be reduced. The less rich solution is then introduced into the GPS column to produce a mixture of stripping gas and CO.sub.2. The product gas mixture is recycled to the second absorption column after exchanging heat with the CO.sub.2 free (may contain small amount of CO.sub.2). After the GPS process, the lean solution from the stripper is recycled to the first absorber after exchanging heat with the rich solution and a new cycle begins.
(50) Specifically in the system 450 of FIG. 9, as with the above systems, raw flue gas 14 enters the bottom of the absorption column 12 and clean flue gas 16 exits the top while a CO.sub.2-lean solution 18 enters into the absorption column 12 from the top and flows downward producing a CO.sub.2-rich solution exiting at 20. The CO.sub.2-rich solution goes through pump 22 and, in line 24, the rich solution (product-enriched liquid) from the bottom of the first absorption column 12 enters the second absorption column 152 from top to absorb CO.sub.2 contained in the gaseous effluent flowing upward, which comes from the top of a conventional stripping column or a GPS column 192 through line 196, through heat exchanger 162 and line 158 to bottom of column 152. Gas exiting the column 152 at line 160 is directed through heat exchanger 162 and through line 198 to bottom of column 192. The CO.sub.2 loaded rich solution (product-enriched liquid) from the bottom of the second absorber 152 is directed through line 154 through heat exchanger 156 and enters a first flasher 166 of, here, a series of flashers 166, through line 164 to flash high pressure CO.sub.2 out. CO.sub.2 in line 170 from the flasher 166 is cooled in cooling unit 172 and supplied by line 174 to liquid gas separator 176 with liquid or water exiting at line 178 and gas exiting at line 180. The gas in line 180 is compressed in compressor 182 to sequestration-ready pressure for the gas at line 184 and the condensed water from the system 150 is removed via line 178. The exit line 168 from the first flasher 166 enters a second of the series of flashers 166. CO.sub.2 in line 170 from the second and subsequent flashers 166 is cooled in a respective cooling unit 172 and supplied by line 174 to liquid gas separator 176 with liquid or water exiting at line 178 and gas exiting at line 180, wherein the gas in line 180 is compressed in compressor 182 then combined with the outlet 170 of the upstream flasher 160 as shown. Thus multi-stage compression with inter-stage cooling is used from the downstream flashers 166. The semi-rich solution (product-enriched liquid) from the bottom of the last flasher 166 is directed to the GPS column 192 from the top. The high pressure stripping gas stream in line 198 enters the bottom of the GPS column 192 and strips the CO.sub.2 from product-enriched liquid flowing countercurrent. After exchanging heat with gas exiting the second absorption column from line 160 in the heat exchanger 162, the gaseous effluent from the GPS column 192 enters the second absorption column 152 in line 154 as noted. In the second absorption column, the gaseous effluent from the GPS column 192 flows countercurrent to the product-enriched liquid from the first absorption column 12. After CO.sub.2 is removed from the gaseous effluent by liquid in the second absorption column 152, the now CO.sub.2-lean gaseous effluent passes back through the heat exchanger 162 and is recycled back to the GPS column 192 as the high pressure gas stream. The CO.sub.2-lean solution is directed via line 194 from the column 192 to heat exchanger 156 to line 200 through cooling unit 400 wherein make-up solvent (amine) may be added through line 42 into the lean solution before it enters the absorber in line 18 and the cycle repeats.
(51) System 500 of FIG. 10 is another embodiment, where both a GPS column and the repeated absorption/stripping are used. In this configuration, however, only a fraction of the product-enriched liquid from the first absorber 12 is introduced to the second absorption column 152. The rest of it may be further divided and directly goes to the flashers or the GPS column depending on the loading. Ideally the product gas loading in the product-enriched liquid is higher than the product gas loading in the flasher entering, but lower than the upstream neighboring flasher. Essentially the system 500 is similar to system 450 described above except that line 24 included valve 186 for directing a substantial portion through line 188 through heat exchanger 502 to line 504. Line 504 is coupled through control valves 506 and lines 508 to the input lines 168 of the subsequent flashers 166, and through valve 510 and line 512 to the input line 168 of the GPS column 192. Outlet 194 includes control valve 516 and line 526 leading to heat exchanger 502 with line 528 leading from heat exchanger 502 to combine with line 200 from heat exchanger 156. Outlet 194 also leads to line 520 leading to heat exchanger 156. These additions provide for greater control possibilities for the system 500 over the system 450.
(52) FIG. 11 illustrates a system 600 utilizing two independent absorption solvents. This system 600 allows greater flexibility by allowing the two separate solvents to be optimized for their particular operating environments. In such an embodiment the process of the present invention further comprises the additional steps of introducing the gas effluent from the GPS column into a second absorption apparatus and into contact with one or more second liquids/absorption solvents, which may be different from those used in the first absorption column. The product gas is absorbed into the second liquid to yield a product-enriched second solution. This second solution may be subsequently introduced into at least one flasher to recover a product gas stream. Specifically in the system 600 of FIG. 11, as with the above systems, raw flue gas 14 enters the bottom of the absorption column 12 and clean flue gas 16 exits the top while a CO.sub.2-lean solution 18 enters into the absorption column 12 from the top and flows downward producing a CO.sub.2-rich solution exiting at 20. The CO.sub.2-rich solution goes through pump 22 and, in line 24, the rich solution (product-enriched liquid) from the bottom of the first absorption column 12. In FIG. 6 rich solution enters column 100 at the top in line 28 and lean solution exits the bottom in line 32 as noted in greater detail above. Further column 100 is illustrated, but any column 120, 130, 140 or variations thereof can be used. The unique features of the system 600 include the use of a second absorption column subsequent to the GPS column using an independent absorption solvent. Specifically rich stripping gas exits the GPS column 100 at line 602 and passes through heat exchanger 604 and is directed via line 606 to pump 608 and enters the second absorption column 620 at line 610. Lean stripping gas exits the second absorption column 620 at line 622 through heat exchanger 604 and through line 624 to pump 626 and enters the GPS column via line 628. The CO.sub.2 loaded rich solution (product-enriched liquid) from the bottom of the second absorber 620 is directed through line 630, pump 632, line 634 through heat exchanger 156 and enters through line 164 a flasher 166 to flash high pressure CO.sub.2 out. CO.sub.2 in line 170 from the flasher 166 is cooled in cooling unit 172 and supplied by line 174 to liquid gas separator 176 with liquid or water exiting at line 178 and gas exiting at line 180. The gas in line 180 is compressed in compressor 182 to sequestration-ready pressure for the gas at line 184 and the condensed water from the system 150 is removed via line 178. The exit line 636 from the flasher 166 goes through pump 638 through line 640 to heat exchanger 156 then through line 644 and cooled in exchanger 646 and enters the second absorption column 620 through line 648. Additional solvent, as needed, can be added at line 650.
(53) In the representative FIGS. 1-11 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 there presence in an operational system. Additionally no 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.
(54) Computer simulations were conducted for the process of the present invention wherein five representative processes were simulated. Computer simulations were all limited to equilibrium calculations. No kinetic simulations (or called rate based) were performed. The first two processes are both conventional absorption/stripping processes, one uses MEA (methyl ethanolamine, 30 wt. %) and the other uses MDEA (methyl dimethanolamine, 50 wt. %). The third process uses 30% MEA solution as solvent and neo-pentane as stripping gas. Condensation/distillation combined separation method (embodiment two) was used to separate neo-pentane and CO.sub.2. The fourth and the last one both use GPS/repeated absorption process. The fourth uses MEA as solvent and the last one uses MDEA/MEA (40%/10%) mixture as solvent. In these simulations all the embodiments of the process of the present invention demonstrated improved energy performance compared to the conventional processes. MDEA/MEA mixed solvent with GPS/Absorption demonstrated the best energy performance in these simulations. This is expected since MDEA has smaller heat of absorption and larger absorption capacity. Under simulated process conditions (not optimized), the invented process is able to reduce the heat consumption by about 30% compared to the current MEA-based CO.sub.2 capture system and reduce the compression work by about 90%. Comparing each component, it is clear that the invented GPS/repeated absorption process can almost reduce the stripping heat by 78%.
(55) 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. For example the high pressure gaseous effluents with the product gas therein maybe used in the combined state as a product gas without further separation. The scope of the present invention is defined by the appended claims and equivalents thereto.
