WO2000030738A1

WO2000030738A1 - Split flow process and apparatus

Info

Publication number: WO2000030738A1
Application number: PCT/US1999/027714
Authority: WO
Inventors: Ray Won; Peter Condorelli; Jeff Scherffius; Carl Mariz
Original assignee: Fluor Corporation
Priority date: 1998-11-23
Filing date: 1999-11-22
Publication date: 2000-06-02
Also published as: AU1742900A; JP4566405B2; AU758934B2; CA2351436A1; EP1152815A1; DE69940612D1; EP1152815A4; ES2322305T3; CA2351436C; JP2002530187A; ATE425806T1; DK1152815T3; EP1152815B1; ZA200104095B; US6645446B1

Abstract

A recovery plant for recovery of a gaseous component, such as carbon dioxide, from a process gas, such as the exhaust from a combustion turbine, has an absorber (110) employing a lean solvent (126) in an upper section of the absorber and a semi-lean solvent (172) in a lower section of the absorber. A regenerator (120) extracts the gaseous component from the rich solvent (117) thereby producing a regenerated lean solvent (126) and a semi-lean solvent (127). A solvent flow control element (170) combines at least a part of the semi-rich solvent (118) from the upper section of the absorber with the semi-lean solvent (127) from the regenerator to form a mixed solvent (171), and a cooler (112) cools the mixed solvent that is subsequently fed into the lower section of the absorber (110). By cooling the mixed solvent prior to entry into the absorber, the thermal energy required to remove the carbon dioxide from the exhaust gas can be reduced.

Description

SPLIT-FLOW PROCESS AND APPARATUS

This application claims the benefit of U S provisional application number 60/109.613 incorporated herein by reference in its entirety

Field of The Invention

The field of the invention is removal of a gaseous component from a process gas

Background of The Invention

Various methods are known in the art to

e a gaseous component from a stream of a process gas. including a wide range of distillation-, adsorption- and absorption processes, and one relatn eh common process involves regenerator-absorber systems

In a typical regenerator-absorber system, gas is introduced in the absorber where the gas contacts a lean solvent traλ eling down the column The gaseous component is at least partialh absorbed by the lean solvent, and the purified process gas leaves the absorber for further processing or discharge The lean solvent containing the gaseous component (l e the rich solvent) flows through a cross heat exchanger thereb> increasing its temperature The heated rich soh ent is then stripped at low pressure in a regenerator The stripped solvent (1 e lean solvent) is sent back through the cross heat exchanger to reduce the temperature in the lean soh ent before completing the loop back to the absorber The regenerator-absorber system process

picalh allow s continuous operation of removal of a gaseous compound from a process gas at relatn eh low cost However, the efficiency of removal of the gaseous component is not alwa\ s satisfactory, and especially when the gaseous component is carbon dioxide, stringent emission standards can often not be achieved with a standard regenerator-absorber system To o\ ercome problems with low efficiency the temperature or pressure m the regenerator may be increased However, corrosivity and solvent degradation generally limit the degree of optimization for this process

An improved regenerator-absorber system is shown by Shoeld in U S Pat No 1.971.798 that comprises a split-loop absorption cycle, in which the bulk of the solvent is renxn ed from an intermediate stage of the regenerator column and recycled to an intermediate stage of the absorber In this arrangement onh a small portion of the solvent is stripped to the lowest concentration, and a high vapor to liquid ratio for stripping is achieved in the bottom tra\ s of the absorber, resulting in somewhat lower energs use at low outlet concentrations Howeλ er. the reduction in energy use is relatively low due to thermodynamic inefficiencies in stripping, mainh because of variations m the solvent composition as it circulates within the split loop

To circumvent at least some of the problems with the split loop process. \ aπous ιmpro\e- ments have been made For example, one improvement to the split-loop process is to more accurate!} control the concentration of solvents To more accurateb control the solvent concentrations, two modifications are generalh necessary The first modification comprises an intermediate reboiler. which is installed to a main regenerator to boil off w ater from the semi-lean soh ent to adjust the concentration of the semi-lean soh ent stream to the concentration of the lean soh ent The second modification comprises a side-regenerator to regenerate condensate from the main regenerator The condensate from the main regenerator is sent to the top section of the main regenerator, where it undergoes partial stripping, and is then further stripped to a \ en low concentration of dissolved gas in the side-regenerator, before being returned to the bottom reboiler of the main regenerator

Since only a relatively small portion of the total soh ent (typicalh ~ 20%) is stripped to the ultra-low concentration, the process allow s achieving relatπ eh low outlet concentrations with comparably low energy use Furthermore, when metfr, 1 diethanolamine (MDEA) is employed as a solvent in the improved split-loop process, the liquid circulation can be reduced b> about 20% Howe\ er. the modifications to improλ e energy use and lower soh ent circulation generalh require a substantial modification in the configuration of the main regenerator, and the installation of a side-regenerator, both of which may result in substantial costs and significant down-time of an existing absorber-regenerator system

Another improvement to the split-loop process is described b\ Shethna and Towler [^""Gas Sweetening to Ultra-low Concentrations using Alkanolammes Absorption^". Paper 46f. AlChE Spring Meeting. New Orleans 1996]. in which two regenerator columns are utilized A pπmaiy regenerator produces a semi-lean solvent, and a secondary regenerator produces an ultra-lean solvent A small portion of the purified process gas leaving the absorber is expanded to a lower pressure level thereby producing a cooled purified process gas The heated ultra-lean solvent stream leaving the secondary regenerator is cooled by the cooled purified process gas thereb> producing a heated purified process gas. which is subsequently fed into the secondars regenerator. The recycled gas is then recovered from the secondary regenerator and reintroduced into the feed gas stream at the absorber.

The use of a substitute vapor instead of a reboiled solvent at the secondary regenerator advantageously lowers the partial pressure of the solvent vapor in the secondary regenerator, and allows the secondary regenerator to operate a lower temperature than the primary regenerator column Operating the secondary regenerator at a reduced temperature typically results in a reduced corrosivity of the solvent, which in turn may allow for the use of cheaper materials such as carbon steel in place of the conventional stainless steel. Furthermore, a split-loop process using vapor substitution may be combined with fixed-bed irreversible absorption technology, e.g. to remove H₂S and or COS from the recycle gas in a bed of solid sorbent. thereby ensuring a relatively long bed life of the absorber. However, the split-loop process using vapor substitution requires the use of least two regenerator columns, and it may further be necessary to re-tray the top stages of an existing absorber to accommodate for the needs of this particular process. Moreover, due to the recycle gas and the use of a secondary regenerator column, retrofitting of existing absorber-regenerator combinations may be relatively expensive and time consuming.

Although various improvements to the general layout of a absorber-regenerator process have been known in the art, all or almost all of them suffer from one or more than one disadvantage. Therefore, there is a need to provide improved methods and apparatus for the removal of a gaseous component from process gases.

Summary of the Invention

The present invention is directed to a recovers' plant to recover a gaseous component from a process gas. having an absorber that employs a lean solvent and a semi-lean solvent which absorb the gaseous component from the process gas. thereby producing a rich solvent, a semi-rich solvent, and a lean process gas. A regenerator is coupled to the absorber, wherein the regenerator extracts the gaseous component from the rich solvent, thereby regenerating the lean solvent and the semi-lean solvent. A solvent flow control element is coupled to the absorber and combines at least part of the semi-rich solvent with at least part of the semi-lean solvent to form a mixed solvent A cooler is coupled to the absorber that cools the mixed solvent, and the cooled mixed solvent is subsequently fed into the absorber via a connecting element

In one aspect of the inventive subject matter, the process gas is a flue gas from a combustion turbine, having a pressure of less than 20psιa when fed into the absorber, and wherein the gaseous component is carbon dioxide The concentration of carbon dioxide is preferabh greater than 2 mole%. more preferably greater than 5 mole%. and most preferabh greater than 10 mole%

In another aspect of the inventive subject matter, the soh ent comprises a chemical solvent, preferabh selected from the group consisting of monoethanolamine. diethanolamine. diglycolamme. and methyldiethanolamine It is also preferred that appropriate so ents have a concave equilibrium curve

In a further aspect of the inventive subject matter, a method of removing a gaseous component from a process gas has a first step in which a stream of lean solvent and a stream of semi-lean solvent is provided In a second step, the process gas is contacted with the stream of lean solvent and semi-lean solvent in an absorber to produce a stream of semi-rich soh ent and a stream of rich soh ent In a further step, at least part of the semi-rich soh ent and at least part of the semi-lean soh ent are combmed to form a mixed soh ent stream, in a still further step the mixed solvent stream is cooled and the cooled mixed solvent stream is introduced to the absorber to absorb the gaseous component

Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawmgs in which like numerals represent like components

Brief Description of The Drawings Fig 1 is a schematic of an improved C0₂ removal plant accordmg to the inventive subject matter

Fig 2 is a flow diagram of an improΛ ed process for C0₂ removal from a flue gas accordmg to the mventive subject matter Detailed Description

As used herein, the term "absorber" refers to an apparatus in which significant amounts of at least one gaseous compound are removed from a mixture of gaseous compounds, and that contains, when in operation, a solvent that is substantially selective towards the compound. The term "'substantially selective^" means that the solvent absorbs the compound to a significant higher degree (i. e.. >20%) than the other compounds present in the mixture of gaseous compounds The solvent with the highest concentration of the absorbed gaseous compound leaving the absorber is termed ""rich solvent^", while the solvent with the lowest concentration of the absorbed gaseous compound leaving the regenerator is termed ^""lean solvent^". The term ^"'semi-lean solvent^" refers to the solvent leaving the regenerator, which has a higher concentration of the absorbed gaseous compound than the lean solvent. The solvent that leaves the absorber having a lower concentration of the absorbed compound than the rich solvent is termed "semi-rich solvent^".

As also used herein, the term '"regenerator^" refers to an apparatus in which an absorbed gaseous compound is at least partially removed from a rich solvent under elev ated temperatures of about 110°C to about 130°C.

In Figure 1. a recovery plant 100 has an absorber 110 and a regenerator 120. A stream of process gas 160 comprising a gaseous component enters the absorber, and a stream of rich solvent 117 leaves the absorber via rich solvent pump 1 1 1. The stream of rich solvent is heated in the cross heat exchanger 130 and enters the regenerator 120. The gaseous component is carbon dioxide and is removed from the rich solvent in two different locations, whereby a semi-lean solvent stream 127 is generated at a position higher that a lean solvent stream 126. Part of the lean solvent stream 126 is redirected via the lean solvent pump 121 to the bottom reboiler 122. and enters again the regenerator 120. The gaseous compound leaves the regenerator in a stream of gaseous compound 150. while carried over solvent is recovered and recycled from the stream of gaseous compound via condenser 123 and condenser pump 125. Both the lean solvent stream and the semi-lean solvent stream are cooled in the cross heat exchanger 130. and the lean solvent stream 126 is further cooled via additional cooler 114 before entering the absorber 1 10. The semi-lean solvent stream 127 is mixed in the solvent flow control element 170 with semi-rich solvent stream 118. which is delivered from the absorber 110 via semi-rich solvent stream pump 113 A mixed solvent stream 171 is further cooled via cooler 112. and cooled mixed solv ent stream 172 enters the absorber via the connecting element 173 at a lower position than the lean so ent stream A stream of lean process gas 140 leaves the absorber 1 10 via the condenser 1 16. and a condenser pump 115 pumps the condensate liquid back to the absorber

In a preferred embodiment, the absorber 110 m carbon dioxide removal plant 100 is a random packed-bed absorber with a diameter of about 20ft and a height of approximate 70ft. configured to process about 30 million standard cubic feet process gas per hour The regenerator 120 is a standard regenerator with a diameter of about 1 ft. and a height of approximately 5 Oft. generating a stream of carbon dioxide 150 Process gas 160 is flue gas from a combustion turb e with a carbon dioxide content of about 13 mole% hav mg a pressure of about 2 psig w hen fed mto the absorber, and the lean process gas 140 has a carbon dioxide content of about 3 mole% The solv ent m all solv ent streams is monoethanolamme. which absorbs the gaseous component carbon dioxide The lean so ent stream 126 has a carbon dioxide loading of less than 0 25 while the carbon dioxide loading m the semi-lean solvent stream 127 is approximateh 0 4 The rich solvent stream 117 has a carbon dioxide loadmg of about 0 5. and the semi-rich solvent stream 1 18 has a carbon dioxide loading of greater than 0 3 The rich solvent stream 1 17 is heated in a standard cross heat exchanger 130 before entermg the regenerator, and both the lean solvent stream and the semi-lean solvent stream are cooled m the cross heat exchanger The solvent flow control element 170 is a static mixer ith two inlet ports, and one outlet port through which the mixed solv ent stream 171 exits the solv ent flow control element Cooler 1 12 and 1 14 are standard side coolers with water as a coolant or air coolers Cooled mixed solvent stream 172 is approximateh 20°C cooler than the mixed soh ent stream 171. and is fed into the absorber via a lme 173 The steam operated reboiler 122 reheats a portion of the lean solvent stream 121 before recirculating the lean solvent stream mto the regenerator The pumps 111. 113. 115. 121. and 125. condenseis 116 and 123. and all lines are standard elements in plant for treatment of mdustnal gases, and well known to the art

In alternative aspects of the inventive subject matter, the absorber need not be limited to a random packed-bed absorber with a diameter of about 20ft and a height of approximateh 70ft. configured to process about 30 million standard cubic feet per hour, but may mclude various alternative types, sizes, and capacities For example, where reduced cost of material is desirable. contemplated absorbers mav include structured packed-bed absorbers, while m applications that mclude crude process gases, or gases with a relatively high degree of impurities, a trayed-type absorber may be employed Similarlv . where relatively large capacities of process gas are to be purified, multiple absorbers with same or different capacitv may be utilized Contemplated process gas capacities mclude flow rates of between 1-50 million standard cubic feet per hour (MMSCF/hr). however larger flow rates between 50 -100 MMSCF hr are also contemplated Where smaller quantities of process gas are to be purified, flow rates of between 0 1 -50 MMSCF hr and less are contemplated Consequently, the size of appropriate absorbers may \ arv from 1 to 30 ft m diameter, and the height mav v arv between 50 and 100ft

With respect to the process gas 160. it is contemplated that various gases other than a flue gas from a combustion turbine with a carbon dioxide content of about 13 mole% are also appropriate For example, depending on the fuel source and combustion process, the carbon dioxide content may vary between less than 3 mole% and more than 20 mole% Therefore, the carbon dioxide content may be greater than 2 mole%. greater than 5 mole%. and greater than 10 mole% It should further be appreciated that gases other than flue gases from a combustion turbme are also contemplated, including natural gas. various refiners gases, or steam reformer gases, all of which may or may not be pretreated Contemplated pretreatment mav therebv mclude fractionation. filtration, scrubbing, and combmation or dilution with other gases It is further contemplated that the pressure of the process gas need not be limited to 2psιg when fed mto the absorber, but may exhibit higher pressures Contemplated higher pressures mclude pressures of less than about 20psιa. less than 50psιa. less than 150psιa. and less than 300psιa

It is also contemplated that the solvent in all of the solvent streams need not be limited to monoethanolamine (MEA). but mav comprise various alternative solvents, including physical and chemical solvents, and any reasonable combmation thereof For example, physical solvents mclude Selexol and methanol. while chemical solvents mclude organic amines and mixed amines Especially contemplated chemical solvents are MEA. diethanolamine. diglycolamme. and methyldiethanolamine It should further be appreciated that co-solvents m combmation with contemplated solvent are also appropriate Furthermore, contemplated solvents may further comprise additives, including anti-oxidants. corrosion inhibitors, and anti-foam agents With respect to the carbon dioxide loadmg of the various solvents it should be appreciated that the carbon dioxide loading may vary in the various solvents predominantly dependmg on the carbon dioxide content of the process gas Therefore, the data given for the lean solvent stream, the semi-lean solvent stream, the semi-rich solvent stream, and the rich solvent stream are not mtended to be limitin ^xtg>

Furthermore, dependmg on the nature of the process gas and the physico-chemical properties of the solvent, the stream of the gaseous compound 150 is not limited to carbon dioxide, but may include hydrogen sulfide. nitrogen, oxygen, hydrogen, helium, etc

In further alternative aspects of the inventive subject matter, the regenerator may mclude various regenerators other than a standard regenerator with a diameter of about 1 Oft. and a height of approximately 50ft For example, where relativ ely low amounts of process gas are purified, smaller regenerators mav be sufficient, whereas for the purification of relati ely high amounts of process gas a single larger regenerator or multiple regenerators are contemplated In general, the regenerator is not limited in size or number so long as appropriate regenerators regenerate sufficient amounts of lean and semi-lean solvent streams, and liberate the gaseous compound Likewise, the reboiler 122 is not restricted to a steam operated reboiler but mav also be alternative reboilers. mcludmg oil-heated, or flame heated, or electrically heated reboilers

With respect to the heating of the rich solvent stream 1 17 and coolmg of the lean solvent stream 126 and semi-lean so ent stream 127 it is contemplated that v arious de ices other than a cross heat exchanger are also appropriate For example, the rich so ent stream 1 17 may be heated utilizing residual heat from the steam reboiler. or from heat sources other than a heat exchanger, including hot fluids, hot gases, and electricity It is especially contemplated that the heated rich solvent stream is fed to the top of the regenerator m a smgle solvent stream, however. alternative configurations are also contemplated Appropriate configurations include feedmg the heated rich solvent at one or more than one point at the side of the regenerator

Similarly, the cooling of the lean solvent stream 126 and semi-lean solvent stream 127 may be performed with a single, or two independent coolmg devices that employ water, air. or other refrigerants as coolants The cooling devices may thereby be energetically coupled or independent from the gas purification process Although the coolers 1 12 and 1 14 are preferabh side coolers coupled to the absorber, various alternative configurations are also contemplated. mcludmg multiple side coolers or a single side cooler with two mdependent channels for the two solvent streams In general, the size, nature of coolant, and coolmg capacity are not limiting to the coolers, so long as the cooled mixed solvent stream is cooler than the mixed so ent stream and so long as the cooled lean solvent stream is cooler than the lean solvent stream Contemplated coolers preferabh reduce the temperature of the lean soh ent stream and the mixed solvent stream more than 10°C. more preferably more than 25°C. and most preferabh more than 50°C It is further contemplated that the connecting element 173 need not be limited to a line, but mav hav e various sizes, shapes, or forms so long as the connecting element feeds the cooled mixed so ent mto the absorber For example, contemplated connectmg elements include a simple openmg. a smgle. or multiple pipes or lmes vvich mav or may not be flexible, or a flange or other mounting means

In still further alternativ e aspects of the mv entπ e subject matter, the semi-rich solvent stream need not be limited to a single semi-rich solvent stream with a carbon dioxide loading of greater than 0 3. but may include multiple semi-rich soh ent streams with identical or different carbon dioxide loading, so long as at least part of the semi-rich solvent stream is mixed with at least part of the semi-lean solvent stream For example, appropriate semi-rich soh ent streams mav be drawn off the absorber at different positions that mav or ma not have the same v ertical distance from the top of the absorber

With respect to the soh ent flow control element 170 it is contemplated that v arious alternative devices other than a static mixer with two inlet ports and one outlet port are also appropriate, so long as at least part of the semi-lean soh ent stream is mixed with at least part of the semi-rich solvent stream For example, one or more than one simple T- or Y-shaped pipe connectors may already be sufficient, especially where portions of the cooler 1 12 mav help m mixing the two solvent streams Where it is desirable to control the ratio of the mixture of the two solvent streams, additional elements, mcludmg a flow control valve is contemplated It should be especially appreciated that a configuration where a semi-lean so ent stream is mixed with a semi-rich solvent stream to form a mixed solvent stream, and where the mixed soh ent stream is cooled before entermg an absorber reduces the thermal energy required to remov e carbon dioxide from a flue gas Further advantages of this design mclude an increase in solvent capacity, and a reduction of the solvent circulation rate In Figure 2. a flow diagram 200 depicts a method of removing a gaseous component from a process gas. wherem m the first step 210 a stream of lean solvent and a stream of semi- lean solvent are provided In a second step 220. the process gas is contacted m an absorber with the stream of lean solvent and the stream of semi-lean solvent to produce a stream of semi-rich solvent and a stream of rich solvent, and a subsequent step 230 at least part of the stream of se i- πch solvent and at least part of the stream of semi-lean solvent are combmed to form a mixed solvent stream In a further step 240 the mixed solvent stream is cooled and the cooled mixed solvent stream is introduced into the absorber to absorb the gaseous component

In a preferred embodiment the stream of lean solvent and the stream of semi-lean solv ent both comprise MEA as a soh ent. and are both produced bv a regenerator The process gas is a low-pressure flue gas from a combustion turbine with a pressure of less than 20 psia hen fed mto the absorber, and the gaseous component m the flue gas is carbon dioxide at a concentration of typically less than 20 mole%. and more t pically less than 10 mole% The low pressure flue gas (1 e less than lOOpsia when fed mto the absorber) is contacted m an absorber with a counter current stream of lean solvent having a carbon dioxide loadmg of about 0 2. and a stream of semi- lean solvent having a carbon dioxide loadmg of about 0 4. to produce a stream of semi-rich solvent havmg a carbon dioxide loadmg of more than 0 3 and a stream of rich soh ent hav ing a carbon dioxide loading of about 0 5 Subsequently , the stream of semi-rich solvent and the stream of semi-lean solvent are combmed in a static mixer to form a mixed so ent stream Next, the mixed solvent stream is cooled by a side cooler to form a cooled mixed solvent stream and the cooled mixed solvent stream is then fed into the absorber

With respect to identical components between the preferred method of Figure 2 and preferred components of Figure 1. the same considerations as previously discussed applv

Thus, specific embodiments and applications of improved methods and apparatus for the removal of a gaseous component from a process gas have been disclosed It should be apparent however, to those skilled m the art that many more modifications besides those alreadv described are possible without departing from the inventive concepts herein The mventiv e subject matter therefore, is not to be restricted except in the spirit of the appended claims Moreov er. in interpreting both the specification and the claims, all terms should be mterpreted m the broadest possible manner consistent with the context In particulai. the terms ' comprises^" and "comprising^" should be interpreted as referring to elements, components, or steps m a nonexclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.

Claims

CLAIMS What is claimed is: 1 A recovery plant that recovers a gaseous component from a process gas. comprising. an absorber employing a lean solvent and a semi-lean solvent that absorb the gaseous component from the process gas. thereby producmg a rich solvent, a semi-rich solvent, and a lean process gas: a regenerator fluidly coupled to the absorber, wherein the regenerator extracts the gaseous component from the rich solvent, thereby regenerating the lean solvent and the semi-lean solvent; a solvent flow control element, fluidly coupled to the absorber, that combmes at least part of the semi-rich solvent with al least part of the semi-lean solvent to form a mixed solvent; a cooler fluidly coupled to the absorber, the cooler cooling the mixed solvent; and a connecting element that feeds the cooled mixed solvent into the absorber. 2. The recovers' plant of claim 1 herem the process gas comprises a flue gas from a combustion turbine. 3. The recovery plant of claim 1 wherein the process gas has a pressure of less than 20 psia when fed into the absorber. 4. The recovery plant of claim 1 wherein the process gas has a pressure of less than 300 psia when fed into the absorber. 5. The recovery plant of claim 1 wherein the gaseous component is carbon dioxide. 6. The recovery plant of claim 5 wherein the carbon dioxide in the process gas has a concentration of greater than 10 mole %. 7. The recover^' plant of claim 5 wherein the carbon dioxide in the process gas has a concentration of greater than 5 mole %. The recovery plant of claim 5 wherem the carbon dioxide m the process gas has a concentration of g &reater than 2 mole % The recovery plant of claim 1 wherem the solvent comprises a chemical soh ent The recovery plant of claim 9 wherem the chemical solvent comprises at least one of an organic amine and a mixed amine The recovers' plant of claim 9 wherem the chemical soh ent is selected from the group consistmg of monoethanolamine. diethanolamine. diglycolamme. and methv ldiethanol- amme The recovery plant of claim 9 wherem the chemical soh ent is monoethanolamine The recovery plant of claim 1 wherem the rich solvent is fed to the top of the regeneratoi m a smgle rich solvent stream The recovery plant of claim 1 wherem the cooler reduces the temperature of the mixed solvent more than 50 °C The recov ery plant of claim 1 wherem the cooler reduces the temperature of the mixed solv ent more than 10°C A method of removing a gaseous component from a process gas. comprising providing a lean solvent stream and a semi-lean solvent stream. contacting the process gas m an absorber with the lean solvent stream and the semi-lean solvent stream to produce a semi-rich solvent stream and a rich solvent stream. combining at least part of the semi-rich solvent stream and at least part of the semi-lean solvent stream to form a mixed solvent stream, and coolmg the mixed solvent stream, and mtroducmg the cooled mixed solvent stream mto the absorber to absorb the gaseous component The method of claim 16 wherem the process gas comprises a flue gas The method of claim 16 wherem the process gas comprises a low pressure gas when fed mto the absorber The method of claim 18 wherem the low-pressure gas has a pressure of less than 20 psia when fed mto the absorber The method of claim 16 wherem the gaseous component is carbon dioxide The method of claim 20 wherem the carbon dioxide is present m the process gas at a concentration of less than 10 mole% The method of claim 20 wherem the carbon dioxide is present m the process gas at a concentration of less than 20 mole% The method of claim 16 wherem the lean solvent comprises monoethanolamine AMENDED CLAIMS [received by the International Bureau on 30 March 2000 (30.03.00); original claims 1 and 16 amended; remaining claims unchanged (3 pages)]

1. A recovery plant that recovers a gaseous component from a process gas, comprising:

an absorber employing a lean solvent and a semi-lean solvent that absorb the gaseous component from the process gas, thereby producing a rich solvent, a semi-rich solvent, and a lean process gas;

a regenerator fluidly coupled to the absorber, wherein the regenerator receives at least part of the rich solvent and extracts the gaseous component from the rich solvent, thereby regenerating the lean solvent and the semi-lean solvent;

a solvent flow control element, fluidly coupled to the absorber, that combines at least part of the semi-rich solvent with at least part of the semi-lean solvent to form a mixed solvent;

a cooler fluidly coupled to the absorber, the cooler cooling the mixed solvent; and

a connecting element that feeds the cooled mixed solvent into the absorber.

2. The recovery plant of claim 1 wherein the process gas comprises a flue gas from a combustion turbine.

3. The recovery plant of claim 1 wherein the process gas has a pressure of less than 20 psia when fed into the absorber.

4. The recovery plant of claim 1 wherein the process gas has a pressure of less than 300 psia when fed into the absorber.

5. The recovery plant of claim 1 wherein the gaseous component is carbon dioxide.

6. The recovery plant of claim 5 wherein the carbon dioxide in the process gas has a concentration of greater than 10 mole %.

7. The recovery plant of claim 5 wherein the carbon dioxide in the process gas has a concentration of greater than 5 mole %.

8. The recovery plant of claim 5 wherein the carbon dioxide in the process gas has a concentration of greater than 2 mole %.

9. The recovery plant of claim 1 wherein the solvent comprises a chemical solvent.

10. The recovery plant of claim 9 wherein the chemical solvent comprises at least one of an organic amine and a mixed amine.

11. The recovery plant of claim 9 wherein the chemical solvent is selected from the group consisting of monoethanolamine, diethanolamine, diglycolamme, and methyldiethanolamine.

12. The recovery plant of claim 9 wherein the chemical solvent is monoethanolamine.

13. The recovery plant of claim 1 wherein the rich solvent is fed to the top of the regenerator in a single rich solvent stream.

14. The recovery plant of claim 1 wherein the cooler reduces the temperature of the mixed solvent more than 50 °C.

1 . The recovery plant of claim 1 wherein the cooler reduces the temperature of the mixed solvent more than 10°C.

16. A method of removing a gaseous component from a process gas, comprising:

providing a lean solvent stream and a semi-lean solvent stream;

contacting the process gas in an absorber with the lean solvent stream and the semi-lean solvent stream to produce a semi-rich solvent stream and a rich solvent stream;

combining at least part of the semi-rich solvent stream and at least part of the semi-lean solvent stream to form a mixed solvent stream, wherein at least part of the semi-lean solvent stream is produced by a regenerator; and

cooling the mixed solvent stream, and introducing the cooled mixed solvent stream into the absorber to absorb the gaseous component.

17. The method of claim 16 wherein the process gas comprises a flue gas.

18. The method of claim 16 wherein the process gas comprises a low pressure gas when fed into the absorber.

19. The method of claim 18 wherein the low-pressure gas has a pressure of less than 20 psia when fed into the absorber.

20. The method of claim 16 wherein the gaseous component is carbon dioxide.

21. The method of claim 20 wherein the carbon dioxide is present in the process gas at a concentration of less than 10 mole%.

22. The method of claim 20 wherem the carbon dioxide is present in the process gas at a concentration of less than 20 mole%.

23. The method of claim 16 wherein the lean solvent comprises monoethanolamine.