A solvent-based carbon dioxide capture process incorporating overhead vapor compression.

Abstract

A process for solvent-based CO2 capture is described. The process incorporates overhead vapor compression to increase the condensation temperature of water in a CO2 stripper, allowing for recovery of the latent heat of the water vapor to be recovered. The process utilizes a CO2 stripping column, a compressor in the column overhead, and a heat exchanger that exchanges heat between the compressed column overhead and a portion of the rich solvent.

Description

[Technical Field]

[0001] (Related Applications) This application claims priority to U.S. Non-Provisional Patent Application No. 18 / 588,217, filed February 27, 2024, which in turn claims priority to U.S. Provisional Patent Application No. 63 / 490,577, filed March 16, 2023, the entireties of which are incorporated herein by reference. [Background technology]

[0002] Environmental concerns have led to efforts to reduce the amount of CO2 emitted from major sources such as power plants, refineries, and other industrial processes. The goal of these processes is to reduce customers' CO2 emissions through carbon capture and utilization or storage (CCUS).

[0003] Among the processes used for post-combustion CO2 capture are solvent-based CO2 absorption processes for removing CO2 from flue gas streams. Various solvent-based absorption processes exist. Generally, flue gas is contacted with a solvent that removes CO2 from the flue gas stream, with the purified flue gas exiting the top of an absorber tower and a CO2-rich solvent stream exiting at or near the bottom of the absorber tower. The rich solvent stream is sent to a stripping tower, where heat is input to remove CO2 from the solvent, forming an overhead CO2 stream and a lean solvent stream. The overhead CO2 stream can be further processed to remove impurities. The overhead CO2 stream can be further compressed to a pressure suitable for injection into a pipeline. The overhead CO2 stream can be compressed and liquefied for transportation or storage.

[0004] A portion of the heat evaporates water from the solvent, and the heat used to evaporate the water is not productive. It is desirable to recover heat from the stripping column overhead stream to reduce column reboiler or other heat duty.

[0005] In a simple stripping tower process, an overhead condenser condenses the evaporated water and returns it to the stripping tower as reflux. This process loses all heat from the evaporated water. Another process involves the use of a flash stripper, as described in U.S. Patent No. 9,956,505 (incorporated herein by reference in its entirety). This process does not use a stripping reboiler. Instead, heat is provided by a heater, such as a convection steam heater, upstream of the stripping tower. The overhead CO2 stream is heat exchanged with a rich solvent stream from the absorber, condensed to remove water, and compressed. A portion of the waste heat (e.g., approximately 40-50% of the latent heat of vaporization of water) is recovered in a CO2 heat exchanger. The remaining heat is lost as the temperature at which heat is available drops below the process pinch point temperature, where it is no longer useful.

[0006] One challenge with both simple stripping and flash stripping processes is that they require process heat in a stripping column reboiler or stripping column steam heater to remove CO2 from the solvent. This process heat is typically provided by steam generated by burning natural gas or coal in a power plant or by burning natural gas in a separate boiler. In the case of a flash stripping process using steam generated by burning natural gas in a separate boiler, 0.15 to 0.2 kg of CO2 is produced per kg of CO2 recovered from the feed. While CO2 from the boiler can be captured during the process, this increases the overall size of the plant and increases transportation and storage costs. Also, in some situations, it may not be desirable to generate additional CO2 in the process of capturing CO2 from the source.

[0007] Another problem involves the large amount of cooling water required for the process. Fresh water is becoming an extremely scarce resource. Cooling water is needed because the required process temperatures are lower than can reasonably be achieved with air cooling. Flash stripping requires large amounts of process cooling (e.g., on the order of 500 MMBTU per hour to capture 1 million MT of CO2 per year from an FCC plant). Providing this amount of cooling water can be difficult in locations with current or potential future limitations on water availability.

[0008] Therefore, there is a need for a carbon dioxide capture process that has lower heat input requirements and / or reduced cooling water requirements. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram of one embodiment of a flash stripping process in accordance with the present invention. [Figure 2] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 3] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 4] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 5] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 6] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 7] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 8] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 9] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 10]FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 11] FIG. 2 is a diagram of another embodiment of a flash stripping process in accordance with the present invention. [Figure 12] 1 is a diagram of a flash stripping process without overhead compression. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention solves this problem by raising the condensation temperature of the water in the CO2 stripper overhead above the process pinch temperature so that more than 90% of the latent heat of steam can be recovered. The recovered heat is used to heat a portion of the feed, reducing the net heater duty of the stripper by 17% compared to advanced flash strippers, from 2.5 GJ per MT of CO2 recovered to 2.07 GJ per MT of CO2 recovered. The net heater duty energy savings are even higher compared to simple strippers. The process pinch temperature is the point of closest temperature approach between the process high temperature composite curve and the process low temperature composite curve.

[0011] The net heater duty of the stripper is an important metric for solvent-based plant technologies for CO2 capture. The proposed invention trades off higher power usage for reduced heat usage. Power is currently easier to decarbonize than heat, so a process with more power and less heat may have a lower global warming potential, which is beneficial when the plant's concern is CO2 capture. This process scheme also has an equivalent work load that is 3% lower than advanced flash strippers.

[0012] One alternative approach is to use lean vapor compression (LVC) of the lean solvent. In this scheme, the lean solvent is flashed to low pressure, releasing CO2 and additional steam, which is then compressed and returned to the CO2 stripper, reducing the net reboiler duty. LVC, like the proposed invention, reduces heat demand at the expense of higher power duty. However, LVC does not reduce the reboiler duty or equivalent work as much as the present invention. For reference, Lin and Rochelle found that for an 8m PZ solvent, LVC reduces the reboiler duty by 8% and the equivalent work by 3% compared to a simple stripper (Lin, YJ; J. Rochelle, GT, “Approaching a Reversible Stripping Process for CO2 Capture,” Chem. Eng. Journal, 2016, 283, 1033-1043).

[0013] The present invention relates to an advanced solvent carbon capture (ASCC) system that offers an alternative to LVC, reducing net reboiler duty for a lower equivalent work cost while maintaining high stripper pressure, a key benefit of the ASCC process.

[0014] The present invention utilizes a CO2 stripping tower, a compressor in the tower overhead, and a heat exchanger that exchanges heat between the compressed overhead and a portion of the rich solvent. The present invention can be practiced with advanced flash strippers.

[0015] Compressing the entire overhead of the stripping column may be undesirable if it would require additional equipment for the compressor. In some embodiments, the present invention allows for the overhead compressor to be combined with a downstream CO2 compressor on a common drive. In some embodiments, multiple overhead compressors are combined with downstream CO2 compressors on a common drive.

[0016] The total overhead temperature of the stripping tower can be greater than 100°C at the suction of the overhead compressor. After compression, the discharge temperature can be greater than 200°C. Dry gas seals have lower leakage rates than other types of seals, which can make them advantageous, but their temperature limitations can make them unsuitable. Other types of seals, such as carbon ring seals, have higher temperature limitations but higher leakage rates. Conventional centrifugal compressors can only use one type of seal within the machine. In some embodiments, the overhead compressor is an integrally geared compressor to better match the compressor seals of each stage of the overhead compressor.

[0017] There may be a difference in volumetric flow rate between the total overhead of the stripping tower and the downstream CO2 compressor, which results in a mismatch in impeller speed and size when using centrifugal compressors with a common drive. In some embodiments, the overhead compressor is an integrally geared compressor to best match the impeller speed and size of each stage of the overhead compressor and CO2 compressor.

[0018] For very high CO2 recovery rates or low stripping column pressures, the overhead vapor volumetric flow rate may be high enough that the overhead compressor requires an undesirably large compressor frame size. In some embodiments, the overhead compressor is a double-flow inlet compressor to reduce frame size.

[0019] The flue gas stream and lean solvent stream are introduced into an absorber tower where the CO2 is absorbed by an absorbent. Any suitable absorbent can be used as known in the art. Suitable absorbents include, but are not limited to, potassium carbonate, monoethanolamine, diethanolamine, methyldiethanolamine, piperazine, 2-methylpiperazine, amino-2-methyl-1-propanol, or combinations thereof.

[0020] Amine solvents have non-zero vapor pressures, which can result in undesirable solvent loss into the flue gas and acid gas streams. Absorber and stripping towers may have a water wash to reduce solvent loss, as is known in the art. The water wash may be located at the top of the tower or may be a separate tower downstream of the absorber or stripping tower. A single water wash may not reduce solvent loss in the flue gas or acid gas to a level sufficient for high vapor pressure amine solvents. Absorber and stripping towers may have a two-stage water wash or acid wash, as is known in the art.

[0021] A cleaned flue gas stream exits the top of the absorber tower, and a rich solvent stream exits the bottom. The "cleaned" flue gas stream has a lower concentration of CO2 than the inlet gas stream. A "rich solvent" stream is any stream that contains more CO2 than the "lean solvent" stream from the stripping tower.

[0022] The heated rich solvent stream is sent to a stripping tower where the CO2 is separated from the solvent. The CO2 exits in an overhead stream and the lean solvent exits at or near the bottom of the stripping tower. The lean solvent stream is returned to the absorption tower.

[0023] More specifically, the compressor is located overhead of the CO2 stripper, and the stripper total overhead is compressed at a pressure ratio P / P of greater than 1.5, or greater than 1.6, or greater than 1.7, or greater than 1.8. Heat is then exchanged in a heat exchanger between the compressed total overhead and a portion of the rich solvent to heat the portion of the rich solvent entering the CO2 stripper. Heat can be exchanged between the compressed total overhead and any portion of the rich solvent stream, including, but not limited to, a rich solvent bypass taken before the lean / rich exchanger, a warm solvent bypass after the lean / rich exchanger (in the case of a simple stripper configuration), a warm solvent bypass after the cold cross exchanger (advanced flash stripper), or a hot rich bypass taken after the hot cross exchanger (advanced flash stripper). A portion of the heated rich solvent relative to the compressed total overhead stream is then fed to a CO2 stripping column at a suitable feed point at the top of the column, the column sump, or mid-column. Mid-column feed locations are preferred, followed by the column sump, and finally the top of the column. In one example of the invention, a once-through convection steam heater is used to provide the remaining heat duty of the column. In another example, a circulating or kettle reboiler is used to provide the remaining heat to the column.

[0024] One aspect of the invention is a process for CO2 recovery from flue gas. In one embodiment, the process includes introducing a flue gas stream and a cooled lean solvent stream into an absorption tower to form a purified flue gas stream and a rich solvent stream containing CO2. The rich solvent stream is directed through at least a low-temperature heat exchanger followed by a high-temperature heat exchanger, and the lean solvent stream from the stripping tower is directed through a high-temperature heat exchanger followed by a low-temperature heat exchanger to form a heated rich solvent stream and a cooled lean solvent stream. All or a portion of the heated rich solvent stream is sent to the stripping tower. The solvent is separated from the CO2 in the stripping tower to form a lean solvent stream and an overhead stream. The overhead stream is compressed to form a compressed overhead stream. A warm rich bypass stream is separated from the rich solvent stream downstream of the low-temperature heat exchanger and upstream of the high-temperature heat exchanger. The compressed overhead stream contacts all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a heated warm rich bypass stream and a cooled compressed overhead stream. The heated warm rich bypass stream is sent to the stripping column.

[0025] A "rich solvent" stream is any solvent stream that contains more CO2 on a per unit mass basis than the "lean solvent" stream from the stripping tower.

[0026] The purified flue gas stream has a reduced concentration of CO2 compared to the incoming flue gas stream. The CO2 in the purified flue gas stream may be reduced by more than 70%, or more than 80%, or more than 85%, or more than 90%, or more than 95% by mass.

[0027] The type of heat exchanger for the compression overhead / rich solvent heat exchange is not limited, and any suitable heat exchanger can be used, including, but not limited to, a TEMA-type shell-and-tube heat exchanger, a gasketed plate-and-frame heat exchanger, or a welded plate-and-frame heat exchanger.

[0028] The type of overhead compressor is not limited, and any suitable compressor can be used. Suitable compressors include, but are not limited to, reciprocating compressors, axial compressors, or centrifugal compressors. The overhead compressor may have a suction drum installed at the inlet to prevent liquid carryover from the column to the compressor in the event of heat loss or process upset. Standard methods are applied to prevent condensation between the suction drum and the compressor inlet.

[0029] The heated cold rich bypass stream and the heated warm rich bypass stream are introduced into the stripping tower, typically at a higher position in the tower than the heated rich solvent stream. The heated cold rich bypass stream is introduced into the stripping tower, typically at a higher position in the tower than the heated warm rich bypass stream. The warm rich bypass stream is introduced into the stripping tower, typically at a higher position in the tower than the heated warm rich bypass stream.

[0030] Two or more of the rich solvent streams may be mixed before being sent to the stripping column, for example, a heated rich solvent stream may be combined with a heated warm rich bypass stream, or a heated cold rich bypass stream may be combined with a warm rich bypass stream, or a heated cold rich bypass stream may be combined with a heated warm rich bypass stream.

[0031] The warm rich bypass stream may be split into a first portion and a second portion, with the second portion of the warm rich bypass stream being directed to a stripping column.

[0032] The cold rich bypass stream may be separated from the rich solvent stream upstream of the cold heat exchanger. The cold rich bypass stream and the cooled compressed overhead stream may be directed through a CO2 heat exchanger to form a heated cold rich bypass stream and a second cooled compressed overhead stream. The heated cold rich bypass stream may be sent to a stripping column. Water may be condensed from the second cooled compressed overhead stream.

[0033] The warm rich bypass stream may be divided into a first portion and a second portion. The second portion of the warm rich bypass stream may be combined with the heated cold rich bypass stream to form a combined stream, and the combined stream may be directed to a stripping column.

[0034] The heated rich solvent may be heated in a steam heater or in an additional heat exchanger downstream of the high temperature heat exchanger before the heated rich solvent stream is sent to the stripping column.

[0035] The various rich solvent streams entering the stripping column may be introduced at different locations within the column, including above a packed bed, between packed beds, or below a packed bed, or at various positions within a tray column as is well known in the art.

[0036] A first overhead heat exchanger may be provided on the heated rich solvent stream downstream of the high-temperature heat exchanger, and a second overhead heat exchanger may be provided on the heated rich solvent stream downstream of the first overhead heat exchanger. The overhead stream may be compressed in a first overhead compressor to form a first compressed overhead stream. The first compressed overhead stream and the first heated rich solvent stream may be directed through a second overhead heat exchanger to form a first cooled overhead stream and a second heated rich solvent stream. The first cooled overhead stream may be compressed in a second overhead compressor to form a second compressed overhead stream. The second compressed overhead stream and the heated rich solvent stream may be directed through the first overhead heat exchanger to form a second cooled overhead stream and a first heated rich solvent stream. Contacting the compressed overhead stream with all or a portion of the warm rich bypass stream in the warm rich bypass overhead heat exchanger may include contacting a second cooled overhead stream with all or a portion of the warm rich bypass stream.

[0037] The second heated rich solvent may be heated in a steam heater or an additional heat exchanger downstream of the second overhead heat exchanger before the second heated rich solvent stream is fed to the stripping column.

[0038] The process may include a heat pump. The heat pump may include an evaporator, a compressor, a condenser, a pressure reduction device, and a working fluid stream. The condenser is a heat exchanger that exchanges heat from the working fluid to a CO2-containing solvent in which CO2 is being released, and the evaporator is a heat exchanger that exchanges heat from a suitable low-temperature heat source to the working fluid. The heat pump may have a cycle that includes heating a working fluid stream in the evaporator, compressing the heated working fluid stream in the compressor, cooling the compressed stream in the condenser, and reducing the pressure of the cooled stream in the pressure reduction device. A process stream having waste heat may be contacted with the working fluid stream in the evaporator to form a cooled process stream and a heated working fluid stream. The heated rich solvent stream may be contacted with the compressed working fluid stream in the condenser of the heat pump to form a second heated rich solvent stream and a cooled working fluid stream. A suitable vapor compression heat pump is described in U.S. Provisional Application No. 63 / 485,683, entitled "Solvent-Based CO2 Capture Process Incorporating a Heat Pump," filed February 17, 2023, which is incorporated herein in its entirety.

[0039] In some embodiments, the low temperature heat source is a process stream from a CO2 capture facility. In some embodiments, the low temperature heat source includes a feed quench cooler stream, an absorber cooler stream, a lean solvent cooler stream, an overhead vapor condenser stream, a CO2 compressor intercooler stream, a flue gas stream from a flue gas economizer, or a combination thereof from a CO2 capture facility. The term flue gas economizer means that the economizer is located in the flue gas stream entering the absorber. Flue gas economizers are also referred to as boiler economizers, feedwater economizers, or exhaust gas economizers by different entities.

[0040] In some embodiments, the heat pump can be a single-stage heat pump or a two-stage heat pump. In some embodiments, single-stage and two-stage heat pumps can include an internal heat exchanger. In some embodiments where a single-stage heat pump with an internal heat exchanger is present, the internal heat exchanger can be located in parallel with the evaporator. In some embodiments, the heat pump can include a two-stage heat pump with a vapor / liquid separator where vapor is mixed with the first-stage compressor effluent and directed to the second-stage compressor suction. In some embodiments, the heat pump can include a two-stage heat pump with a vapor / liquid separator where a portion of the liquid is evaporated in the heat exchanger, combined with vapor from the first-stage compressor effluent, and directed to the second-stage compressor suction.

[0041] In some embodiments, the heat pump (both single-stage and two-stage) also includes an internal heat exchanger that exchanges heat between the evaporator effluent and the condenser effluent. In some embodiments, the internal heat exchanger instead exchanges heat between the evaporator effluent and a stream located immediately after the pressure drop device. In these embodiments, the internal heat exchanger is located in parallel with the evaporator, and the internal heat exchanger effluent and the evaporator effluent are combined before the compressor suction. These embodiments may be required in some cases to prevent two-phase flow within the compressor when the working fluid is classified as a thermodynamic "dry fluid," typically applied to hydrocarbons such as butane and pentane. Two-phase flow within the compressor would destroy the compressor. For fluids classified as "isentropic" or "wet," two-phase flow is difficult to achieve within the compressor, so an internal heat exchanger may not be required for these fluids.

[0042] In some embodiments, the evaporator includes at least two heat exchangers in parallel. The working fluid is split upstream of the evaporator heat exchangers, heated in one or more of the evaporator heat exchangers, and combined downstream to form a single heated working fluid stream. One or more of the evaporator heat exchangers contact a process stream having waste heat with the working fluid stream to form a cooled process stream and a first heated working fluid stream. The final evaporator heat exchanger contacts the working fluid stream with a suitable heating medium to form the first working fluid stream. Suitable heating mediums include steam, thermal oil, an electric heating element, or a process stream having a temperature greater than about 100°C. The working fluid flow through this final evaporator heat exchanger may be continuous or intermittent. The final evaporator heat exchanger provides a way to vaporize the working fluid using a heat source not connected to the rest of the process. This may be useful during start-up to vaporize the feed or during normal operation to provide additional heat to the heat pump system.

[0043] In some embodiments, the working fluid has a critical temperature of 150° C. or greater and a normal boiling point at 100 kPa of 50° C. or less. In some embodiments, the working fluid has a critical temperature of 160° C. or greater and a normal boiling point at 100 kPa of 40° C. or less.

[0044] In some embodiments, the working fluid comprises a chlorofluorocarbon, a hydrochlorofluorocarbon, a hydrofluorocarbon, a hydrofluoroolefin, a hydrochlorofluoroolefin, a hydrocarbon, an oxygenate, or a combination thereof. Suitable working fluids include, but are not limited to, trans-1-chloro-3,3,3-trifluoropropene, cis-1-chloro-3,3,3-trifluoropropene, trans-1-chloro-2,3,3,3-tetrafluoropropene, cis-1,1,1,4,4,4-hexafluoro-2-butene, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclohexane, diethyl ether, methyl formate, ethylamine, a hydrochlorofluoroolefin having 3 carbon atoms, a hydrofluoroolefin having 4 carbon atoms, or a combination thereof.

[0045] The selection of an appropriate working fluid can be made by considering several factors, including but not limited to, COP, toxicity, cost, and flammability. For example, isopentane is inexpensive and less toxic, but has a lower COP than methyl formate. Methyl formate has a higher COP than isopentane, but there are toxicity concerns. C3 hydrochlorofluoroolefins and C4 hydrofluoroolefins are non-toxic, less flammable, and have better performance than hydrocarbons like isopentane, but are more expensive than isopentane or methyl formate.

[0046] In some embodiments, the pressure reduction device is a valve. In other embodiments, the pressure reduction device is a pressure recovery turbine. A pressure recovery turbine adds capital cost but reduces entropy losses when expanding the fluid compared to a valve. A pressure recovery turbine may be desirable for a single-stage system, while a pressure reducing valve may be desirable for a two-stage system.

[0047] In one embodiment, a process stream having waste heat (e.g., a temperature below the process pinch temperature, typically 110°C or less) is contacted with a working fluid stream in an evaporator. The working fluid is heated while the process stream is cooled. In one embodiment, the waste heat temperature is 70°C or less.

[0048] An overhead heat exchanger may be provided on the heated rich solvent stream downstream of the high-temperature heat exchanger. The overhead stream may be compressed in a first overhead compressor to form a first compressed overhead stream, and the first compressed overhead stream and the heated rich solvent stream may be directed through an overhead heat exchanger to form a first cooled overhead stream and a second heated rich solvent stream. The first cooled overhead stream may be compressed in a second overhead compressor to form a second compressed overhead stream. Contacting the compressed overhead stream with all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a heated warm rich bypass stream and a cooled compressed overhead stream may include contacting a second compressed overhead stream with all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a second heated warm rich bypass stream and a second cooled compressed overhead stream, and delivering all or a portion of the heated rich solvent stream to a stripping tower may include delivering all or a portion of the second heated rich solvent stream to a stripping tower.

[0049] An overhead heat exchanger may be provided on the heated rich solvent stream downstream of the high-temperature heat exchanger. The cooled overhead stream may be compressed in a second overhead compressor to form a second compressed overhead stream. The second compressed overhead stream and the heated rich solvent stream may be directed through an overhead heat exchanger to form a second cooled overhead stream and a second heated rich solvent stream. Delivering all or a portion of the heated rich solvent stream to the stripping column may include delivering all or a portion of the second heated rich solvent stream to the stripping column.

[0050] A second warm rich bypass overhead heat exchanger may be provided on the heated warm rich bypass stream from the warm rich bypass heat exchanger. The overhead stream may be compressed in the first overhead compressor to form a first compressed overhead stream, and the first compressed overhead stream and the heated warm rich bypass solvent stream may be directed through a second warm rich bypass overhead heat exchanger to form a first cooled overhead stream and a second heated warm rich bypass solvent stream. The first cooled overhead stream in the second overhead compressor may be compressed to form the second compressed overhead stream. Contacting the compressed overhead stream with all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a heated warm rich bypass stream and a cooled compressed overhead stream may include contacting a second compressed overhead stream with all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a second heated warm rich bypass stream and a second cooled compressed overhead stream. Directing the heated warm rich bypass stream to a stripping column may include directing the second heated warm rich bypass stream to a stripping column.

[0051] The heated warm rich bypass stream and the heated rich solvent stream can be combined, and delivering all or a portion of the heated rich solvent stream to the stripping tower and directing the heated warm rich bypass stream to the stripping tower can include directing the combined stream to the stripping tower.

[0052] The cooled compressed overhead stream can be compressed in a second overhead compressor to form a second compressed overhead stream. The second compressed overhead stream can be contacted with a heated rich solvent stream in an additional heat exchanger on the heated rich solvent stream, the additional heat exchanger being downstream of the high temperature heat exchanger, to form a second heated rich solvent stream and a second cooled compressed overhead stream. Delivering all or a portion of the heated rich solvent stream to the stripping column can include delivering all or a portion of the second heated rich solvent stream to the stripping column.

[0053] Another aspect of the invention is a process for CO2 recovery from flue gas. In one embodiment, the process includes introducing a flue gas stream and a cooled lean solvent stream into an absorption tower to form a purified flue gas stream and a rich solvent stream containing CO2. The rich solvent stream is directed through a low-temperature heat exchanger followed by a high-temperature heat exchanger, and the lean solvent stream is directed from a stripping tower through a high-temperature heat exchanger followed by a low-temperature heat exchanger to form a first heated rich solvent stream and a cooled lean solvent stream. The heated rich solvent stream is delivered to the stripping tower to form an overhead stream containing CO2 and a lean solvent stream. The overhead stream is compressed to form a first compressed overhead stream. A warm rich bypass stream is separated from the rich solvent stream downstream of the low-temperature heat exchanger and upstream of the high-temperature heat exchanger, and the warm rich bypass stream is directed to the stripping tower. The first heated rich solvent stream and the first compressed overhead stream are directed through an overhead heat exchanger to form a first cooled overhead stream and a second heated rich solvent stream, the first overhead heat exchanger being downstream of the high temperature heat exchanger on the first heated rich solvent stream. Delivering the heated rich solvent stream to the stripping column includes delivering the second heated rich solvent stream to the stripping column.

[0054] The cold rich bypass stream may be separated from the rich solvent stream upstream of the cold heat exchanger, and the cold rich bypass stream and the first cooled overhead stream may be directed to a CO2 heat exchanger to form a heated cold rich bypass stream and a second cooled overhead stream. The heated cold rich bypass stream may be sent to a stripping column.

[0055] The warm rich bypass stream and the heated cold rich bypass stream may be combined and the combined stream can be sent to a stripping column.

[0056] The second heated rich solvent may be heated in a steam heater or an additional heat exchanger downstream of the first overhead heat exchanger before the second heated rich solvent stream is delivered to the stripping column.

[0057] A heat pump may be provided, comprising an evaporator, a compressor, a condenser, a pressure reduction device, and a working fluid stream, and may have a cycle including heating the working fluid stream in the evaporator, compressing the heated working fluid stream in the compressor, cooling the compressed stream in the condenser, and reducing the pressure of the cooled stream in the pressure reduction device. A process stream having waste heat may be contacted with the working fluid stream in the evaporator to form a cooled process stream and a heated working fluid stream, and a second heated rich solvent stream may be contacted with the compressed working fluid stream in the condenser of the heat pump to form a third heated rich solvent stream and a cooled working fluid stream.

[0058] Another aspect of the invention is a process for CO2 recovery from flue gas. In one embodiment, the process includes introducing a flue gas stream and a cooled lean solvent stream into an absorption tower to form a purified flue gas stream and a rich solvent stream containing CO2. The rich solvent stream is directed through a low-temperature heat exchanger followed by a high-temperature heat exchanger, and the lean solvent stream is directed from a stripping tower through a high-temperature heat exchanger followed by a low-temperature heat exchanger to form a first heated rich solvent stream and a cooled lean solvent stream. The heated rich solvent stream is sent to the stripping tower to form an overhead stream containing CO2 and a lean solvent stream. The overhead stream is compressed to form a first compressed overhead stream. A warm rich bypass stream is separated from the rich solvent stream downstream of the low-temperature heat exchanger and upstream of the high-temperature heat exchanger, and the warm rich bypass stream is directed to the stripping tower. The first heated rich solvent stream and the second compressed overhead stream are directed through a second overhead heat exchanger to form a second cooled overhead stream and a second heated rich solvent stream. The second overhead heat exchanger is downstream of the high temperature heat exchanger and upstream of the first overhead heat exchanger on the heated rich solvent stream. The second heated rich solvent stream and the first compressed overhead stream are directed through the first overhead heat exchanger to form a first cooled overhead stream and a third heated rich solvent stream. The first cooled overhead stream is compressed to form a second compressed overhead stream. Delivering the heated rich solvent stream to the stripping tower includes delivering the third heated rich solvent stream to the stripping tower.

[0059] A cold rich bypass stream may be separated from the rich solvent stream upstream of the cold heat exchanger. The cold rich bypass stream and the second cooled compressed overhead stream may be sent to a CO2 heat exchanger to form a heated cold rich bypass stream and a third cooled overhead stream, and the heated cold rich bypass stream may be sent to a stripping column.

[0060] The warm rich bypass stream and the heated cold rich bypass stream can be combined and sent to the stripping column.

[0061] The third heated rich solvent may be heated in a steam heater or an additional heat exchanger downstream of the first overhead heat exchanger before the second heated rich solvent stream is fed to the stripping column.

[0062] This process may include a heat pump as described above.

[0063] Another aspect of the present invention includes an apparatus for recovering heat from a stripping tower overhead stream in a CO2 capture process. In one embodiment, the apparatus includes an absorber tower having a flue gas inlet, a flue gas outlet, a lean solvent inlet, and a rich solvent outlet. There is a stripping tower having a first rich solvent inlet, a second rich solvent inlet, an overhead outlet, and a lean solvent outlet. The apparatus includes a low-temperature heat exchanger having a rich solvent inlet, a rich solvent outlet, a lean solvent inlet, and a lean solvent outlet. The rich solvent inlet of the low-temperature heat exchanger is in downstream fluid communication with the rich solvent outlet of the absorber. There is a high-temperature heat exchanger having a rich solvent inlet, a rich solvent outlet, a lean solvent inlet, and a lean solvent outlet. The rich solvent inlet of the high temperature heat exchanger is in downstream fluid communication with the rich solvent outlet of the low temperature heat exchanger, the rich solvent inlet of the stripping column is in downstream fluid communication with the rich solvent outlet of the high temperature heat exchanger, the lean solvent inlet of the high temperature heat exchanger is in downstream fluid communication with the lean solvent outlet of the stripping column, the lean solvent inlet of the low temperature heat exchanger is in downstream fluid communication with the lean solvent outlet of the high temperature heat exchanger, and the lean solvent inlet of the absorber is in downstream fluid communication with the lean solvent outlet of the low temperature heat exchanger. There is a compressor having an inlet and an outlet, the compressor inlet being in fluid communication with the overhead outlet of the stripping column. There is an overhead heat exchanger having an overhead inlet, an overhead outlet, a rich solvent inlet, and a rich solvent outlet. The overhead inlet of the overhead heat exchanger is in downstream fluid communication with the compressor outlet, the rich solvent inlet of the overhead heat exchanger is in downstream fluid communication with the rich solvent outlet of the low temperature heat exchanger, and the second rich solvent inlet of the stripping column is in downstream fluid communication with the rich solvent outlet of the overhead heat exchanger.

[0064] The overhead compressor may be combined with the CO2 product compressor and share a common drive with the CO2 product compressor.

[0065] The overhead compressor may comprise an integrally geared centrifugal compressor.

[0066] The overhead compressor may include a double-flow inlet compressor.

[0067] FIG. 1 shows one embodiment of a CO2 capture process 100 using a flash stripping tower.

[0068] The CO2-containing flue gas stream 105 is sent to an absorber tower 110 where it contacts a lean solvent stream 115. The CO2 is transferred from the flue gas to the lean solvent, forming a purified flue gas stream 120 and a rich solvent stream 125.

[0069] The rich solvent stream 125 exchanges heat with the lean solvent stream 135 in a low temperature heat exchanger 140 and a high temperature heat exchanger 145 to form a heated rich solvent stream 150 and a cooled lean solvent stream 115 .

[0070] A warm rich bypass stream 155 is taken from the partially heated rich solvent stream between the cold heat exchanger 140 and the hot heat exchanger 145 .

[0071] The heated rich solvent stream 150 is introduced into the stripping column 130 at a first point 160 and flashed to separate the CO2 from the solvent to form an overhead stream 165 containing CO2 and a lean solvent stream 135.

[0072] Overhead stream 165 is sent to compressor 170 to form compressed overhead stream 175. Compressed overhead stream 175 contacts warm rich bypass stream 155 in warm rich bypass overhead heat exchanger 180 to form heated warm rich bypass stream 185 and cooled compressed overhead stream 190. Heated warm rich bypass stream 185 is introduced into stripping column 130 at a second point 195.

[0073] 2, a cold rich bypass stream 205 is removed from the rich solvent stream 125 upstream of the cold heat exchanger 140. The cold rich bypass stream 205 is heated in a heater or heat exchanger 210, and the cooled compressed overhead stream 190 forms a heated cold rich bypass stream 215 and a second cooled overhead stream 220. The heated cold rich bypass stream 215 is sent to the stripping column 130 at a third point 225. Water may be condensed from the second cooled overhead stream 220 (not shown).

[0074] The warm rich bypass stream 155 may be split into a first portion 230 and a second portion 235. The first portion 230 may be contacted with the compressed overhead stream 175 in the warm rich bypass overhead heat exchanger 180. The second portion 235 may be combined with the heated cold rich bypass stream 215 to form a combined stream 240 that is sent to the stripping column 130 at a third point 225.

[0075] The heated rich solvent stream 150 can be further heated in a steam heater or heat exchanger 245 and the second heated rich solvent stream 250 can be sent to the stripping column 130 .

[0076] 3, a second warm rich bypass overhead heat exchanger 315 is upstream of the warm rich bypass overhead heat exchanger 180. The overhead stream 165 is compressed in the compressor 170, and the compressed overhead stream 175 is sent to the warm rich bypass overhead heat exchanger 180 to form a heated warm rich bypass stream 185 and a cooled compressed overhead stream 190.

[0077] The cooled compressed overhead stream 190 is sent to a second compressor 305 to form a second compressed overhead stream 310. The second compressed overhead stream 310 contacts the warm rich bypass stream 155 in a second warm rich bypass overhead heat exchanger 315 to form a second heated warm rich bypass stream 320 and a second cooled compressed overhead stream 325. The second heated warm rich bypass stream 320 is sent to a warm rich bypass overhead heat exchanger 180 to contact the compressed overhead stream 175.

[0078] 4 shows an alternative process 400 in which overhead stream 165 is compressed in a first overhead compressor 405. The first compressed overhead stream 410 contacts heated rich solvent stream 150 in an additional heat exchanger 415 to form a second heated rich solvent stream 420 and a first cooled compressed overhead stream 425. The additional heat exchanger 415 is downstream of the high temperature heat exchanger 145.

[0079] The first cooled compressed overhead stream 425 is sent to the second overhead compressor 430, and the second compressed overhead stream 435 is sent to the warm rich bypass overhead heat exchanger 180 to form the heated warm rich bypass stream 185 and the cooled compressed overhead stream 190.

[0080] 5, the cooled compressed overhead stream 190 is compressed in a second overhead compressor 505 to form a second compressed overhead stream 510. The second compressed overhead stream 510 is contacted with the heated rich solvent stream 150 in an additional heat exchanger 515 to form a second heated rich solvent stream 520 and a second cooled compressed overhead stream 525. The additional heat exchanger 515 is on the heated rich solvent stream downstream of the high temperature heat exchanger 145. The second heated rich solvent stream 520 is sent to the stripping column 130.

[0081] 6, a first overhead heat exchanger 605 and a second overhead heat exchanger 610 are present on the heated rich solvent stream 150. The first overhead heat exchanger 605 is downstream of the high temperature heat exchanger 145, and the second overhead heat exchanger 610 is downstream of the first overhead heat exchanger 605.

[0082] The overhead stream 165 is sent to a first overhead compressor 615 to form a first compressed overhead stream 620. The first compressed overhead stream 620 is contacted with a second heated rich solvent stream 625 in a second overhead heat exchanger 610 to form a third heated rich solvent stream 630 and a cooled compressed overhead stream 635. The third heated rich solvent stream 630 is sent to the stripping column 130.

[0083] The cooled compressed overhead stream 635 is sent to a second overhead compressor 640 to form a second compressed overhead stream 645. The second compressed overhead stream 645 contacts the heated rich solvent stream 150 to form a second heated rich solvent stream 625 and a second cooled compressed overhead stream 650.

[0084] The second cooled compressed overhead stream 650 contacts the warm rich bypass stream 155 in the warm rich bypass overhead heat exchanger 180 to form a heated warm rich bypass stream 185 and a cooled compressed overhead stream 190.

[0085] 7, a first additional overhead heat exchanger 705 is present on the heated rich solvent stream 150 downstream of the high temperature heat exchanger 145. The overhead stream 165 is sent to a first overhead compressor 710 to form a first overhead compressed stream 715.

[0086] The first overhead compressed stream 715 contacts the heated rich solvent stream 150 in the first additional overhead heat exchanger 705 to form a second heated rich solvent stream 720 and a cooled compressed overhead stream 725. The second heated rich solvent stream 720 is sent to the stripping column 130.

[0087] In the process 800 shown in FIG. 8, there is a first overhead heat exchanger 805 downstream of the high temperature heat exchanger 145 on the heated rich solvent stream 150, and there is a second overhead heat exchanger 810 downstream of the first overhead heat exchanger 805.

[0088] Overhead stream 165 is compressed in first overhead compressor 815 to form first compressed overhead stream 820. First compressed overhead stream 820 is sent to second overhead heat exchanger 810 and contacted with second heated rich solvent stream 825 to form third heated rich solvent stream 830 and first cooled overhead stream 835. Third heated rich solvent stream 830 is sent to stripping column 130.

[0089] The first cooled overhead stream 835 is sent to a second overhead compressor 840 to form a second compressed overhead stream 845. The second compressed overhead stream 845 contacts the heated rich solvent stream 150 in the first overhead heat exchanger 805 to form a second heated rich solvent stream 825 and a second cooled overhead stream 850.

[0090] As shown in FIG. 9, the process 900 can include a heat pump.

[0091] The CO2-containing flue gas stream 905 is sent to a quench tower 910 where it contacts a quench stream 915 to form a cooled flue gas stream 105 and a heated quench stream 920. The cooled flue gas stream 105 is sent to an absorber tower 110 where it contacts a lean solvent stream 115.

[0092] Heated quench stream 920 contacts working fluid stream 925 in evaporator 930 to form heated working fluid stream 935 and quench stream 915. Heated working fluid stream 935 is compressed in heat pump compressor 940 to form compressed working fluid stream 945. Compressed working fluid stream 945 contacts heated rich solvent stream 150 in condenser 950 to further heat heated rich solvent stream 150 and cool compressed working fluid stream 945. Cooled compressed working fluid stream 955 is expanded in pressure letdown device 960 to form working fluid stream 925.

[0093] The process 1000 of Figure 10 is similar to the process 300 shown in Figure 3, except for the flow of the overhead stream 165. A second warm rich bypass overhead heat exchanger 1035 is downstream of the warm rich bypass overhead heat exchanger 1010. The overhead stream 165 is compressed in a compressor 170. The compressed overhead stream 1005 exchanges heat with the warm rich bypass stream 155 in the warm rich bypass overhead heat exchanger 1010 to form a heated warm rich bypass stream 1015 and a cooled compressed overhead stream 1020.

[0094] The cooled compressed overhead stream 1020 is sent to a second compressor 1025 to form a second compressed overhead stream 1030. The second compressed overhead stream 1030 contacts the heated warm rich bypass stream 1015 in a second warm rich bypass overhead heat exchanger 1035 to form a second heated warm rich bypass stream 1040 and a second cooled compressed overhead stream 1045. The second heated warm rich bypass stream 1040 is sent to stripping column 130.

[0095] The process of Figure 11 is similar to process 800 shown in Figure 8, except for the flow of overhead stream 165. Overhead stream 165 is compressed in first overhead compressor 815 to form first compressed overhead stream 1105. First compressed overhead stream 1105 is sent to first overhead heat exchanger 1110 and contacts heated rich solvent stream 150 to form second heated rich solvent stream 1115 and first cooled overhead stream 1120.

[0096] The first cooled overhead stream 1120 is sent to a second overhead compressor 1125 to form a second compressed overhead stream 1130. The second compressed overhead stream 1130 contacts a second heated rich solvent stream 1115 in a second overhead heat exchanger 1135 to form a third heated rich solvent stream 1140 and a second cooled overhead stream 1145. The third heated rich solvent stream 1140 is sent to the stripping column 130.

[0097] Any of the processes of FIGS. 1-11 can include a cold, rich solvent bypass stream as shown in FIGS.

[0098] Any of the processes of FIGS. 1-11 can include a heat pump such as that shown in FIG.

[0099] FIG. 12 shows, for comparison, a CO2 capture process 1200 using a flash stripping tower without an overhead compressor 170 and heat exchanger 180.

[0100] A flue gas stream 105 containing CO2 is sent to an absorber tower 110 where it contacts a lean solvent stream 115. The CO2 is transferred from the flue gas to the lean solvent, forming a purified flue gas stream 120 and a rich solvent stream 125. The rich solvent stream 125 is sent to a stripping tower 130.

[0101] The cold rich solvent bypass stream 205 of the rich solvent stream 125 is sent to a heat exchanger 210 to exchange heat with the overhead stream 165 from the stripping column 130 to form a heated first portion 215 and a cooled overhead stream 220.

[0102] The remainder of the rich solvent stream 125 exchanges heat with the lean solvent stream 135 in a low temperature heat exchanger 140 to partially heat the rich solvent stream 125 and cool the lean solvent stream 135 .

[0103] A warm rich solvent stream 155 is removed from rich solvent stream 125 after low temperature heat exchanger 140. Warm rich solvent stream 155 is split into a first portion 230 and a second portion 235. First portion 230 is sent to stripping column 130. Second portion 235 is combined with heated first portion 215, and combined stream 240 is sent to stripping column 130.

[0104] The remainder of the rich solvent stream is sent to high temperature heat exchanger 145 to further heat rich solvent stream 125 to form heated stream 150 .

[0105] The heated rich solvent stream 150 is sent to a steam heater 225 for additional heating to form a second heated rich solvent stream 250, which is then introduced into a stripping column 130 where CO2 is stripped from the second heated rich solvent stream 250 to form an overhead stream 165 containing CO2 and a lean solvent stream 135.

[0106] After lean solvent stream 135 passes through high temperature heat exchanger 145 and low temperature heat exchanger 140 , the cooled lean solvent stream 115 is returned to absorber 110 . [Example]

[0107] Comparative Example 1 The CO2 capture process of Figure 12 was simulated using Aspen Plus® process modeling software, using rate-based heat and mass transfer models of the absorber and stripping towers, and proprietary thermodynamic and kinetic models of the amine solvent for CO2 absorption and stripping. The GERG-2008 equation of state was used to model CO2 compression. Table 1 provides the simulated flow characteristics for the stripping tower overhead acid gas stream 165 before and after heat exchange with the cold rich solvent bypass stream in heat exchanger 210. 9.62 MW th of heat is recovered from the stripping tower overhead acid gas stream in heat exchanger 210 to provide base duty in steam heater 245. Residual water in cooled overhead stream 220 is condensed at 40°C and removed before compressing cooled overhead acid gas stream 220 to a pipeline pressure of 150 bar(a). This additional compression provides an additional 9.16 MW e requires a power of

[0108] [Table 1]

[0109] Example 1 The CO2 capture process in Figure 2 was simulated using Aspen Plus® process modeling software, using rate-based heat and mass transfer models of the absorber and stripping towers, and proprietary thermodynamic and kinetic models of the amine solvent for CO2 absorption and stripping. The GERG-2008 equation of state was used to model CO2 compression. The same criteria as in Comparative Example 1 were used to simulate the process, resulting in the same rich solvent stream 125. Table 2 provides simulated flow characteristics for the stripping tower overhead acid gas stream before compression in overhead exchanger 170 (stream 165), after compression (stream 175), after heat exchange in exchanger 180 (stream 190), and after heat exchange in exchanger 210 (stream 220). Compression of acid gas stream 165 in overhead compressor 170 required a 3.44 MW e The required power is 8.72MW. th of heat is recovered from the acid gas stream in exchanger 180, resulting in 9.97 MW th is recovered from the acid gas stream in exchanger 210. The duty in steam heater 245 is increased by 8.69 MW from the baseline in Comparative Example 1 due to the additional heat recovered in the acid gas stream compared to Comparative Example 1. th The remaining water in stream 220 is condensed and knocked out at 40°C, after which the acid gas stream is reduced to 150 bar. a This requires an additional 7.22 MW of e requires a power of

[0110] 150 bar a The total compression power required to compress the gas to the pipeline pressure of 10.66 MW is e This is 1.50MW higher than Comparative Example 1. e The overhead compressor process of Example 1 reduces the steam heater duty by 8.69 MW compared to Comparative Example 1. th while reducing the power consumption by an additional 1.50MW e of power required, an additional 1 MW required compared to Comparative Example 1 e of electricity per 5.8MW thThis results in a coefficient of performance reduction of the thermal duty.

[0111] [Table 2]

[0112] Specific Embodiments While the following will be described in conjunction with specific embodiments, it will be understood that this description is illustrative, but not intended to limit the scope of the preceding description and appended claims.

[0113] A first embodiment of the present invention is a process for CO2 recovery from flue gas, comprising: introducing a flue gas stream and a cooled lean solvent stream into an absorption tower to form a purified flue gas stream and a rich solvent stream comprising CO2; passing the rich solvent stream through at least a low temperature heat exchanger followed by a high temperature heat exchanger, and passing the lean solvent stream from a stripping tower through a high temperature heat exchanger followed by a low temperature heat exchanger to form a heated rich solvent stream and a cooled lean solvent stream; delivering all or a portion of the heated rich solvent stream to the stripping tower and absorbing the lean solvent stream and the overcooled lean solvent stream. forming a head stream; compressing the overhead stream to form a compressed overhead stream; separating a warm rich bypass stream from a rich solvent stream downstream of the low temperature heat exchanger and upstream of the high temperature heat exchanger; contacting the compressed overhead stream with all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a heated warm rich bypass stream and a cooled compressed overhead stream; and directing the heated warm rich bypass stream to a stripping column. One embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, further comprising dividing the warm rich bypass stream into a first portion and a second portion, and directing the second portion of the warm rich bypass stream to a stripping column. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, further comprising: separating a cold rich bypass stream from the rich solvent stream upstream of the cold heat exchanger; passing the cold rich bypass stream and the cooled compressed overhead stream through a CO2 heat exchanger to form a heated cold rich bypass stream and a second cooled overhead stream; and directing the heated cold rich bypass stream to a third point on the stripping column.An embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph through the first embodiment in this paragraph, further comprising: dividing the warm rich bypass stream into a first portion and a second portion; combining the second portion of the warm rich bypass stream with the heated cold rich bypass stream to form a combined stream; and directing the combined stream to a stripping tower. An embodiment of the present invention is one, any, or all of the previous embodiments in this paragraph through the first embodiment in this paragraph, further comprising heating the heated rich solvent in a steam heater or an additional heat exchanger downstream of the high-temperature heat exchanger before the heated rich solvent stream is delivered to the stripping tower. An embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, and further includes providing a heat pump comprising an evaporator, a compressor, a condenser, a pressure reduction device, and a working fluid stream, wherein the heat pump has a cycle comprising heating the working fluid stream in the evaporator, compressing the heated working fluid stream in the compressor, cooling the compressed stream in the condenser, and reducing the pressure of the cooled stream in the pressure reduction device; contacting a process stream having waste heat with the working fluid stream in the evaporator to form a cooled process stream and a heated working fluid stream; and contacting the heated rich solvent stream with the compressed working fluid stream in the condenser of the heat pump to form a second heated rich solvent stream and a cooled working fluid stream.One embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, further comprising providing an overhead heat exchanger on the heated rich solvent stream downstream of the high temperature heat exchanger; compressing the overhead stream in a first overhead compressor to form a first compressed overhead stream; directing the first compressed overhead stream and the heated rich solvent stream through the overhead heat exchanger to form a first cooled overhead stream and a second heated rich solvent stream; and compressing the first cooled overhead stream in a second overhead compressor to form a second compressed overhead stream. contacting the compressed overhead stream with all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a heated warm rich bypass stream and a cooled compressed overhead stream comprises contacting the second compressed overhead stream with all or a portion of the warm rich bypass stream in a warm rich bypass overhead heat exchanger to form a second heated warm rich bypass stream and a second cooled compressed overhead stream, and delivering all or a portion of the heated rich solvent stream to a stripping column comprises delivering all or a portion of the second heated rich solvent stream to a stripping column. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, further including: providing a second warm rich bypass overhead heat exchanger on the heated warm rich bypass stream downstream of the warm rich bypass heat exchanger; compressing the cooled compressed overhead stream in a second overhead compressor to form a second compressed overhead stream; and directing the second compressed overhead stream and the heated warm rich bypass solvent stream through a second warm rich bypass overhead heat exchanger to form a first cooled compressed overhead stream and a second heated warm rich bypass solvent stream, and directing the heated warm rich bypass stream to the stripping column includes directing the second heated warm rich bypass stream to the stripping column.An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, further comprising combining the heated warm rich bypass stream with the heated rich solvent stream to form a combined stream, delivering all or a portion of the heated rich solvent stream to a stripping tower, and directing the heated warm rich bypass stream to the stripping tower comprises directing the combined stream to the stripping tower. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph to the first embodiment of this paragraph, further comprising: compressing the cooled compressed overhead stream in a second overhead compressor to form a second compressed overhead stream; and contacting the second compressed overhead stream with the heated rich solvent stream in an additional heat exchanger on the heated rich solvent stream downstream of the high-temperature heat exchanger to form a second heated rich solvent stream and a second cooled compressed overhead stream, wherein delivering all or a portion of the heated rich solvent stream to the stripping column comprises delivering all or a portion of the second heated rich solvent stream to the stripping column.An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, and further includes providing a first overhead heat exchanger on the heated rich solvent stream downstream of the high temperature heat exchanger and a second overhead heat exchanger on the heated rich solvent stream downstream of the first overhead heat exchanger; compressing the overhead stream in a first overhead compressor to form a first compressed overhead stream; passing the first compressed overhead stream and the first heated rich solvent stream through a second overhead heat exchanger to form a first cooled overhead stream and a second heated rich solvent stream; and directing the second compressed overhead stream and the heated rich solvent stream through a first overhead heat exchanger to form a second cooled overhead stream and a first heated rich solvent stream, wherein contacting the compressed overhead stream with all or a portion of the warm rich bypass stream in the warm rich bypass overhead heat exchanger comprises contacting the second cooled overhead stream with all or a portion of the warm rich bypass stream, and delivering all or a portion of the heated rich solvent stream to the stripping column comprises delivering all or a portion of the second heated rich solvent stream to the stripping column. One embodiment of the present invention is one, any, or all of the previous embodiment to the first embodiment of this paragraph, further comprising heating the second heated rich solvent in a steam heater or an additional heat exchanger downstream of the second overhead heat exchanger before delivering the second heated rich solvent stream to the stripping column.An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, further including: providing an overhead heat exchanger on the heated rich solvent stream downstream of the high-temperature heat exchanger; compressing the cooled overhead stream in a second overhead compressor to form a second compressed overhead stream; and directing the second compressed overhead stream and the heated rich solvent stream through the overhead heat exchanger to form a second cooled overhead stream and a second heated rich solvent stream, wherein delivering all or a portion of the heated rich solvent stream to the stripping column includes delivering all or a portion of the second heated rich solvent stream to the stripping column.

[0114] A second embodiment of the present invention is a process for CO2 recovery from flue gas, comprising: introducing a flue gas stream and a cooled lean solvent stream into an absorption tower to form a purified flue gas stream and a rich solvent stream comprising CO2; directing the rich solvent stream through a low temperature heat exchanger followed by a high temperature heat exchanger; directing the lean solvent stream from a stripping tower through a high temperature heat exchanger followed by a low temperature heat exchanger to form a first heated rich solvent stream and a cooled lean solvent stream; delivering the heated rich solvent stream to the stripping tower to form an overhead stream comprising CO2 and a lean solvent stream; compressing the overhead stream to form a first compressed overhead stream. separating a warm rich bypass stream from the rich solvent stream downstream of the low temperature heat exchanger and upstream of the high temperature heat exchanger; sending the warm rich solvent bypass stream to a stripping column; and directing the first heated rich solvent stream and the first compressed overhead stream through an overhead heat exchanger to form a first cooled overhead stream and a second heated rich solvent stream, the first overhead heat exchanger being downstream of the high temperature heat exchanger; wherein delivering the heated rich solvent stream to the stripping column comprises delivering the second heated rich solvent stream to the stripping column. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the second embodiment of this paragraph, further comprising: separating a cold rich bypass stream from the rich solvent stream upstream of the cold heat exchanger; directing the cold rich bypass stream and the first cooled overhead stream to a CO2 heat exchanger to form a heated cold rich bypass stream and a second cooled overhead stream; and directing the heated cold rich bypass stream to a stripping column.An embodiment of the present invention is one, any, or all of the previous embodiment in this paragraph through the second embodiment in this paragraph, further comprising combining the warm rich bypass stream with the heated cold rich bypass stream; and directing the heated cold rich bypass stream to a stripping tower, wherein directing the warm rich bypass stream to the stripping tower comprises directing the combined stream to the stripping tower. An embodiment of the present invention is one, any, or all of the previous embodiment in this paragraph through the second embodiment in this paragraph, further comprising heating the second heated rich solvent in a steam heater or an additional heat exchanger downstream of the first overhead heat exchanger before the second heated rich solvent stream is delivered to the stripping tower. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph to the second embodiment of this paragraph, and further includes providing a heat pump comprising an evaporator, a compressor, a condenser, a pressure reduction device, and a working fluid stream, wherein the heat pump has a cycle comprising heating the working fluid stream in the evaporator, compressing the heated working fluid stream in the compressor, cooling the compressed stream in the condenser, and reducing the pressure of the cooled stream in the pressure reduction device; contacting a process stream having waste heat with the working fluid stream in the evaporator to form a cooled process stream and a heated working fluid stream; and contacting a second heated rich solvent stream with the compressed working fluid stream in the condenser of the heat pump to form a third heated rich solvent stream and a cooled working fluid stream. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph to the second embodiment of this paragraph, further including: compressing the first cooled compressed overhead stream to form a second compressed overhead stream; and directing the second heated rich solvent stream and the second compressed overhead stream through a second overhead heat exchanger downstream of the overhead heat exchanger to form a second cooled overhead stream and a third heated rich solvent stream, wherein delivering the heated rich solvent stream to the stripping column includes delivering the third heated rich solvent stream to the stripping column.An embodiment of the present invention is one, any, or all of the previous embodiment in this paragraph through the second embodiment in this paragraph, further comprising: separating a cold rich bypass stream from the rich solvent stream upstream of the cold heat exchanger; directing the cold rich bypass stream and the first cooled overhead stream to a CO2 heat exchanger to form a heated cold rich bypass stream and a second cooled overhead stream; and sending the heated cold rich bypass stream to a stripping tower. An embodiment of the present invention is one, any, or all of the previous embodiment in this paragraph through the second embodiment in this paragraph, further comprising: combining the warm rich bypass stream with the heated cold rich bypass stream; and directing the heated cold rich bypass stream to a stripping tower, wherein directing the warm rich bypass stream to the stripping tower comprises directing the combined stream to the stripping tower. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the second embodiment of this paragraph, further comprising heating the second heated rich solvent in a steam heater or an additional heat exchanger downstream of the first overhead heat exchanger before the second heated rich solvent stream is delivered to the stripping column. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph to the second embodiment of this paragraph, and further includes providing a heat pump comprising an evaporator, a compressor, a condenser, a pressure reduction device, and a working fluid stream, wherein the heat pump has a cycle comprising heating the working fluid stream in the evaporator, compressing the heated working fluid stream in the compressor, cooling the compressed stream in the condenser, and reducing the pressure of the cooled stream in the pressure reduction device; contacting a process stream having waste heat with the working fluid stream in the evaporator to form a cooled process stream and a heated working fluid stream; and contacting a second heated rich solvent stream with the compressed working fluid stream in a condenser of the heat pump to form a third heated rich solvent stream and a cooled working fluid stream.

[0115] A third embodiment of the present invention is an apparatus for recovering heat from an overhead stream of a stripping tower in a CO2 capture process, the apparatus comprising: an absorber tower having a flue gas inlet, a lean solvent inlet, and a rich solvent outlet; a stripping tower having a first rich solvent inlet, a second rich solvent inlet, an overhead outlet, and a lean solvent outlet; a low temperature heat exchanger having a rich solvent inlet, a rich solvent outlet, a lean solvent inlet, and a lean solvent outlet, the low temperature heat exchanger's rich solvent inlet being in downstream fluid communication with the absorber's rich solvent outlet; and a high temperature heat exchanger having a rich solvent inlet, a rich solvent outlet, a lean solvent inlet, and a lean solvent outlet, the high temperature heat exchanger's rich solvent inlet being in downstream fluid communication with the low temperature heat exchanger's rich solvent outlet, and the stripping tower's rich solvent inlet being in downstream fluid communication with the high temperature heat exchanger's rich solvent outlet, a high temperature heat exchanger, the high temperature heat exchanger having a lean solvent inlet in downstream fluid communication with the lean solvent outlet of the stripping column, the low temperature heat exchanger having a lean solvent inlet in downstream fluid communication with the lean solvent outlet of the high temperature heat exchanger, and the absorber having a lean solvent inlet in downstream fluid communication with the lean solvent outlet of the low temperature heat exchanger; a compressor having an inlet and an outlet, the compressor inlet in fluid communication with the overhead outlet of the stripping column; and an overhead heat exchanger having an overhead inlet, an overhead outlet, a rich solvent inlet, and a rich solvent outlet, the overhead inlet of the overhead heat exchanger being in downstream fluid communication with the outlet of the compressor, the rich solvent inlet being in downstream fluid communication with the rich solvent outlet of the low temperature heat exchanger, and a second rich solvent inlet of the stripping column being in downstream fluid communication with the rich solvent outlet of the overhead heat exchanger. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the third embodiment of this paragraph, wherein the overhead compressor is combined with the CO2 product compressor and shares a common drive with the CO2 product compressor.An embodiment of the present invention is one, any, or all of the previous embodiments to the third embodiment of this paragraph, wherein the overhead compressor comprises an integrally geared centrifugal compressor.An embodiment of the present invention is one, any, or all of the previous embodiments to the third embodiment of this paragraph, wherein the overhead compressor comprises a double-flow inlet compressor.

[0116] Without further elaboration, it is believed that, using the preceding description, one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of the present invention, and can make various changes and modifications to the present invention to adapt it to various uses and conditions, without departing from the spirit and scope of the present invention. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0117] Above, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. CO from flue gas ２ A process for recovery, comprising: The flue gas stream (105) and the cooled lean solvent stream (115) are introduced into an absorber tower (110) to produce a purified flue gas stream (120) and a CO ２ forming a rich solvent stream (125) comprising: directing said rich solvent stream (125) through at least a low temperature heat exchanger (140) followed by a high temperature heat exchanger (145), and directing a lean solvent stream (135) from a stripping column (130) through said high temperature heat exchanger (145) followed by said low temperature heat exchanger (140) to form a heated rich solvent stream (150) and said cooled lean solvent stream (115); delivering all or a portion of the heated rich solvent stream (150) to the stripping column (130) to form the lean solvent stream (135) and an overhead stream (165); compressing said overhead stream (165) to form a compressed overhead stream (175); separating a warm rich bypass stream (155) from the rich solvent stream downstream of the low temperature heat exchanger (140) and upstream of the high temperature heat exchanger (145); contacting the compressed overhead stream (175) with all or a portion of the warm rich bypass stream (155) in a warm rich bypass overhead heat exchanger (180) to form a heated warm rich bypass stream (185) and a cooled compressed overhead stream (190); directing the heated warm rich bypass stream (185) to the stripping column (130); The process includes:

2. dividing the warm rich solvent stream (155) into a first portion (230) and a second portion (235); directing the second portion (235) of the warm rich bypass stream (155) to the stripping column (130); The process of claim 1 further comprising:

3. separating a low-temperature rich bypass stream (205) from the rich solvent stream (125) upstream of the low-temperature heat exchanger (140); and combining the low-temperature rich bypass stream (205) and the cooled compressed overhead stream (190) with a CO ２ through a heat exchanger (210) to form a heated, low temperature, rich bypass stream (215) and a second cooled overhead stream (220); directing the heated cold rich bypass stream (215) to a third point on the stripping column (130); The process of any one of claims 1 to 2, further comprising:

4. dividing the warm rich solvent stream (155) into a first portion (230) and a second portion (235); combining the second portion (235) of the warm rich bypass stream (155) with the heated cold rich bypass stream (125) to form a combined stream (240); directing the combined stream (240) to the stripping column (130); The process of claim 3 further comprising:

5. providing a heat pump comprising an evaporator (930), a compressor (940), a condenser (950), a pressure reduction device (960), and a working fluid stream (925), the heat pump having a cycle comprising: heating the working fluid stream (125) in the evaporator (930), compressing the heated working fluid stream (935) in the compressor (940), cooling the compressed stream (945) in the condenser (950), and reducing the pressure of the cooled stream (955) in the pressure reduction device (960); contacting a process stream (920) having waste heat with the working fluid stream (925) in the evaporator (930) to form a cooled process stream (915) and a heated working fluid stream (935); contacting the heated rich solvent stream (150) with the compressed working fluid stream (945) in the condenser (950) of the heat pump to form a second heated rich solvent stream and the cooled working fluid stream (955); The process of any one of claims 1 to 2, further comprising:

6. providing an overhead heat exchanger (415) on the heated rich solvent stream (150) downstream of the high temperature heat exchanger (145); compressing said overhead stream (165) in a first overhead compressor (405) to form a first compressed overhead stream (410); passing the first compressed overhead stream (410) and the heated rich solvent stream (150) through the overhead heat exchanger (415) to form a first cooled overhead stream (425) and a second heated rich solvent stream (420); compressing the first cooled overhead stream (425) in a second overhead compressor (430) to form a second compressed overhead stream (435); Further comprising: contacting the compressed overhead stream with all or a portion of the warm rich bypass stream in the warm rich bypass overhead heat exchanger to form the heated warm rich bypass stream and the cooled compressed overhead stream comprises contacting the second compressed overhead stream (435) with all or a portion of the warm rich bypass stream (155) in the warm rich bypass overhead heat exchanger (180) to form the second heated warm rich bypass stream (185) and the second cooled compressed overhead stream (190); 3. The process of claim 1, wherein delivering all or a portion of the heated rich solvent stream to the stripping tower comprises delivering all or a portion of the second heated rich solvent stream to the stripping tower.

7. providing a second warm rich bypass overhead heat exchanger (1035) on the heated warm rich bypass stream (1015) downstream of the warm rich bypass heat exchanger (1010); compressing the cooled compressed overhead stream (1020) in a second overhead compressor (1025) to form a second compressed overhead stream (1030); directing the second compressed overhead stream (1030) and the heated warm rich bypass solvent stream (1015) through the second warm rich bypass overhead heat exchanger (1035) to form a first cooled compressed overhead stream (1045) and a second heated warm rich bypass solvent stream (1040); Further comprising:

3. The process of claim 1, wherein directing the heated warm rich bypass stream to the stripping tower comprises directing the second heated warm rich bypass stream (1040) to the stripping tower (130).

8. further comprising combining the heated warm rich bypass stream (185) with the heated rich solvent stream (150) to form a combined stream; 3. The process of any one of claims 1 to 2, wherein delivering all or a portion of the heated rich solvent stream (150) to the stripping tower (130) and directing the heated warm rich bypass stream (185) to the stripping tower (130) comprises directing the combined stream to the stripping tower (130).

9. compressing the cooled compressed overhead stream (190) in a second overhead compressor (505) to form a second compressed overhead stream (510); contacting the second compressed overhead stream (510) with the heated rich solvent stream (150) in an additional heat exchanger (515) downstream of the high temperature heat exchanger (145) and on the heated rich solvent stream (150) to form a second heated rich solvent stream (520) and a second cooled compressed overhead stream (525); Further comprising:

3. The process of claim 1, wherein delivering all or a portion of the heated rich solvent stream (150) to the stripping tower (130) comprises delivering all or a portion of the second heated rich solvent stream (520) to the stripping tower (130).

10. CO ２ 1. An apparatus for recovering heat from an overhead stream of a stripping column in a recovery process, comprising: an absorber tower (110) having a flue gas inlet, a lean solvent inlet, and a rich solvent outlet; a stripping column (130) having a first rich solvent inlet, a second rich solvent inlet, an overhead outlet, and a lean solvent outlet; a low-temperature heat exchanger (140) having a rich solvent inlet, a rich solvent outlet, a lean solvent inlet, and a lean solvent outlet, the rich solvent inlet of the low-temperature heat exchanger (140) being in downstream fluid communication with the rich solvent outlet of the absorber (110); a high-temperature heat exchanger (145) having a rich solvent inlet, a rich solvent outlet, a lean solvent inlet, and a lean solvent outlet, wherein the rich solvent inlet of the high-temperature heat exchanger (145) is in downstream fluid communication with the rich solvent outlet of the low-temperature heat exchanger (140), and the rich solvent inlet of the stripping column (130) is in downstream fluid communication with the rich solvent outlet of the high-temperature heat exchanger (145); a high-temperature heat exchanger (140), the lean solvent inlet of the low-temperature heat exchanger (140) being in downstream fluid communication with the lean solvent outlet of the stripping tower (130), the lean solvent inlet of the low-temperature heat exchanger (140) being in downstream fluid communication with the lean solvent outlet of the high-temperature heat exchanger (145), and the lean solvent inlet of the absorber tower (110) being in downstream fluid communication with the lean solvent outlet of the low-temperature heat exchanger; a compressor (170) having an inlet and an outlet, the compressor inlet in fluid communication with the overhead outlet of the stripping column (130); an overhead heat exchanger (180) having an overhead inlet, an overhead outlet, a rich solvent inlet, and a rich solvent outlet, wherein the overhead inlet of the overhead heat exchanger (180) is in downstream fluid communication with an outlet of the compressor, the rich solvent inlet is in downstream fluid communication with the rich solvent outlet of the low-temperature heat exchanger (140), and the second rich solvent inlet of the stripping column (130) is in downstream fluid communication with the rich solvent outlet of the overhead heat exchanger (180); An apparatus comprising:

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