Reclaiming device, method, and recovery unit of CO2, H2S, or both of CO2 and H2S

Abstract

Provided are a reclaimer 51 that introduces, through a branch line L.sub.11, and stores a part 17a of an absorbent 17 regenerated in a regenerator of a recovery unit that recovers CO.sub.2 or H.sub.2S in a gas, a first alkaline agent supply section 53A that supplies an alkaline agent 52 to the reclaimer 51, a heating section 54 that heats the absorbent 17 stored in the reclaimer 51 and to which the alkaline agent 52 has been mixed to obtain recovered vapor 61, a first vapor cooler 55A that cools the recovered vapor 61 discharged from the reclaimer 51 through a vapor line L.sub.12, a first gas-liquid separator 56A that separates a coexisting substance 62 entrained in the cooled recovered vapor 61 into a recovered absorption agent vapor (gas) 17b and the liquid coexisting substance 62 by gas-liquid separation, and an introduction line L.sub.13 that introduces the recovered absorption agent vapor 17b separated in the first gas-liquid separator 56A into a regenerator 20.

Claims

1. A reclaiming device comprising: a reclaimer configured to introduce and store a part of an absorbent regenerated in an absorbent regenerator of a recovery unit that recovers CO.sub.2 or H.sub.2S in a gas; a first alkaline agent supply section configured to supply an alkaline agent to the reclaimer; a heating section configured to heat the absorbent stored in the reclaimer and to which the alkaline agent has been mixed to obtain recovered vapor; a second vapor cooler configured to cool the recovered vapor discharged from the reclaimer through a vapor line; a first gas-liquid separator configured to separate a coexisting substance entrained in the cooled recovered vapor into recovered absorption agent vapor and a liquid coexisting substance by gas-liquid separation; a cooler configured to cool the separated recovered absorption agent vapor; a second gas-liquid separator configured to separate the recovered absorption agent vapor after cooling into a low-boiling point substance flue gas and a recovered absorbent by gas-liquid separation; a heat exchanger configured to perform heat exchange of the liquid coexisting substance separated in the first gas-liquid separator with vapor condensed water from vapor supplied to the reclaimer to increase a temperature; a CO.sub.2 absorber configured to bring the liquid coexisting substance after increase in the temperature and a CO.sub.2 gas in contact; a second alkaline agent supply section configured to supply the alkaline agent to the liquid coexisting substance after absorption of CO.sub.2; and a distiller configured to distill the liquid coexisting substance to which the alkaline agent has been supplied while introducing the CO.sub.2 gas thereinto.

2. The reclaiming device according to claim 1, wherein the second vapor cooler includes a first cooler configured to perform cooling with the liquid coexisting substance separated from the recovered vapor in the first gas-liquid separator by gas-liquid separation, a second cooler configured to perform cooling with reflux water from the absorbent regenerator, and a third cooler provided at a downstream side of a rich/lean solution heat exchanger disposed in a lean solution supply line, and configured to cool, with a rich solution, the recovered vapor after cooling with the second cooler.

3. The reclaiming device according to claim 1, comprising: a CO.sub.2 gas introduction line configured to introduce the CO.sub.2 gas discharged from the CO.sub.2 absorber into the distiller; and a nitrogen supply section configured to introduce a nitrogen gas into the CO.sub.2 gas introduction line.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of a CO.sub.2 recovery unit according to a first embodiment.

(2) FIG. 2 is a schematic diagram of a reclaiming device according to the first embodiment.

(3) FIG. 3 is a schematic diagram of another reclaiming device according to the first embodiment.

(4) FIG. 4 is a schematic diagram of a reclaiming device according to a second embodiment.

(5) FIG. 5 is a schematic diagram of another reclaiming device according to the second embodiment.

(6) FIG. 6 is a schematic diagram of a reclaiming device according to a third embodiment.

(7) FIG. 7 is a diagram illustrating selective removal ratios in recovered vapor in a conventional example and the first embodiment.

(8) FIG. 8 is a diagram illustrating selective removal ratios in recovered vapor in a conventional example and the second embodiment.

(9) FIG. 9 is a diagram illustrating recovery ratios of an absorption agent in the first embodiment and the second embodiment.

(10) FIG. 10 is a diagram illustrating selective removal ratios in recovered vapor in a conventional example and the third embodiment.

(11) FIG. 11 is a diagram illustrating recovery ratios of an absorption agent in the first embodiment and the third embodiment.

DESCRIPTION OF EMBODIMENTS

(12) Hereinafter, favorable embodiments of the present invention will be described in detail with reference to the appended drawings. Note that the present invention is not limited by the embodiments, and when there is a plurality of embodiments, the present invention includes those obtained by combining the embodiments.

First Embodiment

(13) While an employable process to remove CO.sub.2, H.sub.2S, or both of them in a gas of the present invention is not especially limited, an example of a removing device that removes CO.sub.2 will be described with reference to FIG. 1.

(14) Examples of gases to be treated by the present invention include a coal gasifier gas, a synthesis gas, a coke oven gas, a petroleum gas, a natural gas, and a combustion flue gas. However, the gases are not limited to these examples, and any gas can be employed as long as the gas contains an acid gas such as CO.sub.2 or H.sub.2S.

(15) In the following embodiment, a flue gas containing CO.sub.2 as the acid gas will be described.

(16) FIG. 1 is a schematic diagram illustrating a configuration of a CO.sub.2 recovery unit according to the first embodiment. As illustrated in FIG. 1, a CO.sub.2 recovery unit 12 according to the first embodiment includes a flue gas cooling device 16 that cools a flue gas 14 containing CO.sub.2 and CO.sub.2 discharged from an industrial combustion facility 13 such as a boiler or a gas turbine with cooling water 15, a CO.sub.2 absorber (hereinafter, also referred to as absorber) 18 including a CO.sub.2 recovery section 18A that brings the cooled flue gas 14 containing CO.sub.2 and a CO.sub.2 absorbent (hereinafter, also referred to as absorbent) 17 that absorbs CO.sub.2 in contact to remove CO.sub.2 from the flue gas 14, and an absorbent regenerator (hereinafter, also referred to as regenerator) 20 that desorbs CO.sub.2 from a CO.sub.2 absorbent (hereinafter, also referred to as rich solution) 19 that has absorbed CO.sub.2 to regenerate a CO.sub.2 absorbent. Then, in the CO.sub.2 recovery unit 12, the regenerated CO.sub.2 absorbent (hereinafter, also referred to as lean solution) 17 from which CO.sub.2 has been removed in the absorbent regenerator 20 is reused in the CO.sub.2 absorber 18 as the CO.sub.2 absorbent.

(17) Note that, in FIG. 1, the reference sign 13a is a flue gas duct, 13b is a stack, 27a is steam condensed water. There are two cases for the CO.sub.2 recovery unit 12, which includes a case of providing the CO.sub.2 recovery unit later to recover CO.sub.2 from an already provided flue gas source, and a case of placing the CO.sub.2 recovery unit along with a newly provided flue gas source at the same time. An openable/closable damper is installed to the stack 13b, and is closed at the time of an operation of the CO.sub.2 recovery unit 12. Further, the damper is set to open when the operation of the CO.sub.2 recovery unit 12 is stopped although the flue gas source is operated.

(18) In a method of recovering CO.sub.2 using the CO.sub.2 recovery unit 12, first, a pressure of the flue gas 14 containing CO.sub.2 from the industrial combustion facility 13 such as a boiler or a gas turbine is increased by a flue gas blower 22, and the flue gas 14 is then sent to the flue gas cooling device 16, cooled with the cooling water 15, and sent to the CO.sub.2 absorber 18.

(19) In the CO.sub.2 absorber 18, the flue gas 14 is brought in countercurrent contact with the CO.sub.2 absorbent 17 that is an amine absorbent according to the present embodiment, and CO.sub.2 in the flue gas 14 is absorbed in the CO.sub.2 absorbent 17 by a chemical reaction.

(20) The CO.sub.2-removed flue gas from which CO.sub.2 has been removed in the CO.sub.2 recovery section 18A is brought, in gas-liquid contact with circulating rinse water 21 containing the CO.sub.2 absorbent supplied through a nozzle in a water cleaning section 18B of the CO.sub.2 absorber 18, the CO.sub.2 absorbent 17 entrained in the CO.sub.2-removed flue gas is recovered, and then a flue gas 23 from which CO.sub.2 has been removed is discharged outside the system.

(21) Further, a pressure of the rich solution that is the CO.sub.2-absorbed CO.sub.2 absorbent 19 is increased by a rich solution pump 24, heated with the lean solution that, is the CO.sub.2 absorbent 17 regenerated in the absorbent regenerator 20, in a rich/lean solution heat exchanger 25 disposed on a rich solution supply line L.sub.1, and supplied to the absorbent regenerator 20.

(22) The rich solution 19 discharged from an upper portion to an inside of the absorbent regenerator 20 causes an endothermic reaction by water vapor supplied from a bottom portion, and desorbs most of CO.sub.2. The CO.sub.2 absorbent that has desorbed a part or most of CO.sub.2 in the absorbent regenerator 20 is called semi-lean solution. This semi-lean solution becomes the CO.sub.2 absorbent (lean solution) 17 from which nearly all of CO.sub.2 has been removed, when the semi-lean solution is about to reach the bottom portion of the absorbent regenerator 20. A part of the lean solution 17 is heated with water vapor 27 in a regenerating heater 26, and supplies water vapor to the inside of the absorbent regenerator 20.

(23) Meanwhile, a CO.sub.2-entrained gas 28 accompanied by the water vapor discharged from the rich solution 19 and the semi-lean solution in the regenerator is led from a top of the absorbent regenerator 20, the water vapor is condensed by a condenser 29, water is separated in a separation drum 30, and a CO.sub.2 gas 40 is discharged outside the system and is separately compressed by a compressor 41 and recovered. This compressed/recovered CO.sub.2 gas 42 is pressed into an oil field using an enhanced oil recovery method (EOR) or stored in an aquifer after through a separation drum 43 to achieve measurements against the global warming.

(24) Reflux water 31 separated/refluxed from the CO.sub.2-entrained gas 28 accompanied by the water vapor in the separation drum 30 is supplied to the upper portion of the absorbent regenerator 20 and the rinse water 21 side with a reflux water circulation pump 35.

(25) The regenerated CO.sub.2 absorbent (lean solution) 17 is cooled with the rich solution 19 in the rich/lean solution heat exchanger 25 disposed on an intersection of the rich solution supply line L.sub.1 and a lean solution supply line L.sub.2, then a pressure is increased by a lean solution pump 32, and the CO.sub.2 absorbent (lean solution) 17 is cooled in a lean solution cooler 33 and is then supplied to the CO.sub.2 absorber 18. Note that, in this embodiment, an outline has been merely described. Description is given omitting a part of devices that come with the CO.sub.2 recovery unit.

(26) A part of the CO.sub.2 absorbent 17 regenerated in the absorbent regenerator 20 is branched at a branch line L.sub.11 from the lean solution supply line L.sub.2 and introduced into a reclaimer 51, and the water vapor 27 is supplied to indirectly heat the absorbent, so that a coexisting substance is separated.

(27) FIG. 2 is a schematic diagram of a reclaiming device according to the first embodiment.

(28) As illustrated in FIG. 2, a reclaiming device according to the present embodiment includes the reclaimer 51 that introduces, through a branch line L.sub.11, and stores a part 17a of the absorbent 17 regenerated in the regenerator of the recovery unit that recovers CO.sub.2 or H.sub.2S in a gas, a first alkaline agent supply section 53A that supplies an alkaline agent 52 to the reclaimer 51, a heating section 54 that heats the absorbent 17 stored in the reclaimer 51 and to which the alkaline agent 52 has been mixed to obtain recovered vapor 61, a first vapor cooler 55A that cools the recovered vapor 61 discharged from the reclaimer 51 through a vapor line L.sub.12, a first gas-liquid separator 56A that separates a coexisting substance 62 entrained in the cooled recovered vapor 61 into recovered absorption agent vapor (gas) 17b and a liquid coexisting substance 62 by gas-liquid separation, and an introduction line L.sub.13 that introduces the recovered absorption agent vapor 17b separated in the first gas-liquid separator 56A into the regenerator 20.

(29) Note that, the reference sign 57 in the drawing illustrates a coexisting substance cooler that cools the coexisting substance (liquid) 62 after the gas-liquid separation, and the reference sign 58 illustrates a reclaimer residue.

(30) The temperature of the recovered vapor 61 discharged from the reclaimer 51 is decreased by the first vapor cooler 55A by about 6 to 7 C.

(31) In the reclaimer 51, the coexisting substance 62 having a vapor pressure is entrained in the recovered vapor 61. Therefore, the entrained coexisting substance 62 can be separated and removed by performing separation using the first gas-liquid separator 56A as in the present embodiment.

(32) That, is, the coexisting substance 62 having a higher boiling point than amines in a free state of the absorbent is cooled in the first vapor cooler 55A, and the temperature is decreased by about 6 to 7 C., so that the coexisting substance 62 is liquefied and separated in the first gas-liquid separator 56A. When a temperature (T.sub.1) of the recovered vapor 61 is 130 C., the recovered vapor 61 is cooled in the first vapor cooler 55A, and a temperature (T.sub.2) of the recovered vapor 61 after cooling is made to 123 C., so that the coexisting substance (liquid) 62 can be separated.

(33) An effect of the present embodiment will be described with reference to FIG. 7.

(34) FIG. 7 is a diagram illustrating selective removal ratios in recovered vapor in a conventional example and the first embodiment (where the conventional example is a reference (1)). The conventional technology is a case of recovering the recovered vapor 61 from the reclaimer 51 as it is without providing the gas-liquid separator as in the present embodiment.

(35) The selection removal ratio of the coexisting substance 62 from the recovered vapor 61 in the present embodiment is 40, and the coexisting substance can be substantially removed, where the conventional example is the reference (1).

(36) Further, in the present embodiment, as illustrated in FIG. 3, a first cooler 55A-1 that performs cooling using the reflux water 31 from the regenerator 20 of the CO.sub.2 recovery unit 12, and a second cooler 55A-2 provided at a downstream side of a rich/lean solution heat exchanger 25 disposed at an intersection of the rich solution supply line L.sub.1 and the lean solution supply line L.sub.2, and which cools the recovered vapor 61 with the rich solution 19 are included as the first vapor cooler 55A.

(37) Accordingly, when the temperature (T.sub.1) of the recovered vapor 61 is 130 C., the recovered vapor is cooled to the temperature (T.sub.2=125 C.) by the first cooler 55A-1, and then cooled to a temperature (T.sub.3=123 C.) by the second cooler 55A-2.

(38) Here, the reflux water 31 is brought to pass through a coexisting substance cooler 57 for cooling the coexisting substance (liquid) 62 separated in the first gas-liquid separator 56A, and is then introduced into the first cooler 55A-1 through a cooling water line L.sub.14.

(39) The first cooler 55A-1 is provided at an intersection of the vapor line L.sub.12 and the cooling water line L.sub.14 and the second cooler 55A-2 is provided at an intersection of the vapor line L.sub.12 and the rich solution supply line L.sub.1, and thus cooling is possible with heat in the system of the CO.sub.2 recovery unit 12.

Second Embodiment

(40) A reclaiming device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic diagram of a reclaiming device according to a second embodiment. FIG. 5 is a schematic diagram of another reclaiming device according to the second embodiment. Note that the same member as the first embodiment is denoted with the same reference sign, and description thereof is omitted.

(41) As illustrated in FIG. 4, a reclaiming device according to the present embodiment includes a reclaimer 51 that introduces, through a branch line L.sub.11, and stores a part 17a of an absorbent 17 regenerated in a regenerator of a recovery unit that recovers CO.sub.2 or H.sub.2S in a gas, a first alkaline agent supply section 53A that supplies an alkaline agent 52 to the reclaimer 51, a heating section 54 that heats the absorbent 17 stored in the reclaimer 51 and to which the alkaline agent 52 has been mixed to obtain recovered vapor 61, a second vapor cooler 55B that cools recovered vapor 61 discharged from the reclaimer 51 through a vapor line L.sub.12, a first gas-liquid separator 56A that separates a coexisting substance 62 entrained in the cooled recovered vapor 61 into recovered absorption agent vapor (gas) 17b and a liquid coexisting substance 62 by gas-liquid separation, a fourth cooler 71 that cools the separated recovered absorption agent vapor 17b, a second gas-liquid separator 56B that separates the recovered absorption agent vapor 17b after cooling into a low-boiling point substance flue gas 72 and a recovered absorbent 17c by gas-liquid separation, a heat exchanger 63 that performs heat exchange of the liquid coexisting substance 62 separated in the first gas-liquid separator 56A with vapor condensed water 27a from vapor 27 supplied to the reclaimer 51 to increase the temperature, a CO.sub.2 absorber 64 that brings the liquid coexisting substance 62 after increase in the temperature, and a CO.sub.2 gas (recovered CO.sub.2) 40 in contact, a second alkaline agent supply section 53B that supplies an alkaline agent 52 to a liquid coexisting substance 62A after absorption of CO.sub.2, and a distiller 68 that distills a liquid coexisting substance 62B to which the alkaline agent 52 has been supplied while introducing the CO.sub.2 gas (recovered CO.sub.2) 40 thereto. Further, a coexisting substance (liquid) 63A is discharged from the distiller 68. Further, CO.sub.2 discharged from the CO.sub.2 absorber 64 is introduced into the distiller 68 through a CO.sub.2 gas introduction line L.sub.21.

(42) In the present embodiment, the recovered vapor 61 is cooled in the second vapor cooler 55B, and then separated into recovered absorption agent vapor (gas) 17b and the liquid coexisting substance 62 by gas-liquid separation in the first gas-liquid separator 56A.

(43) A volatile low-boiling point substance such as ammonia is entrained in this recovered adsorbent vapor (gas) 17b. Therefore, the recovered adsorbent vapor (gas) 17 is cooled in a fourth cooler 71 and is introduced into the second gas-liquid separator 56B, and the low-boiling point substance flue gas 72 is separated. This separated low-boiling point substance flue gas 72 is introduced into a top of the absorber 18. Reflux water 31 from a CO.sub.2 recovery unit 12 is introduced into the fourth cooler 71 to perform cooling.

(44) Further, the temperature of the separated liquid coexisting substance 62 is increased in the heat exchanger 63 by subjecting to heat exchange with the vapor condensed water 27a from the vapor 27 supplied to the reclaimer 51, and the liquid coexisting substance 62 after increase in the temperature is introduced into the CO.sub.2 absorber 64 into which a CO.sub.2 gas 40 is introduced. In the CO.sub.2 absorber 64, the liquid coexisting substance 62 is brought into countercurrent contact, with the recovered CO.sub.2 gas 40 to react with CO.sub.2. As the CO.sub.2 gas 40, the CO.sub.2 gas 40 recovered in the CO.sub.2 recovery unit 12 is used.

(45) Following that, amines of the absorption agent are made into amines in a free state by supplying the alkaline agent 52 from the second alkaline agent supply section 53B to the liquid coexisting substance 62A, and making a pH of the liquid coexisting substance 62A high (for example, by about 0.3 to 0.5).

(46) Following that, the liquid coexisting substance 62B to which the alkaline agent 52 has been added is introduced into the distiller 68, and in performing distillation here, the coexisting substance 62B absorbs the introduced CO.sub.2 gas 40 and is on a liquid side. Therefore, the coexisting substance 62B loses a vapor pressure.

(47) The absorption agent is in a vapor state with a high pH by release of a release valve 67. Therefore, the absorption agent, does not react with the CO.sub.2 gas 40 and is separated as vapor by the distillation in the distiller 68.

(48) Here, the CO.sub.2 gas 40 introduced into the distiller 68 is CO.sub.2 discharged from the CO.sub.2 absorber 64 and introduced through the CO.sub.2 gas introduction line L.sub.21.

(49) The coexisting substance (liquid) 63A separated in the distiller 68 is cooled in a coexisting substance cooler 57. Note that, as a refrigerant used in the coexisting substance cooler 57, the reflux water 31 from the CO.sub.2 recovery unit 12 is introduced to perform cooling in the present embodiment. Then, the cooled reflux water 31 is introduced into the fourth cooler 71 through a cooling water line L.sub.14, and then introduced into the reclaimer 51.

(50) An effect of the present embodiment will be described with reference to FIG. 8.

(51) FIG. 8 is a diagram illustrating selective removal ratios in recovered vapor in a conventional example and the second embodiment (where the conventional example is a reference (1)). The conventional technology is a case of recovering the recovered vapor 61 from the reclaimer 51 as it is without providing the first gas-liquid separator 56A and the second gas-liquid separator 56B as in the present embodiment.

(52) The selection removal ratio of the coexisting substance 62 from the recovered vapor 61 in the present embodiment is 30, and the coexisting substance can be substantially removed, where the conventional example is the reference (1).

(53) FIG. 9 is a diagram illustrating recovery ratios of the absorption agent in the first embodiment and the second embodiment (where the first embodiment is a reference (1)).

(54) In a case of providing the first gas-liquid separator 56A, the second gas-liquid separator 56B, the CO.sub.2 absorber 64, and the distiller 68 as in the second embodiment, the recovery of the absorption agent from the recovered vapor 61 is improved by about 1.3 times.

(55) Next, another reclaiming device according to the second embodiment will be described.

(56) FIG. 5 is a schematic diagram of another reclaiming device according to the second embodiment.

(57) In the present embodiment, as illustrated in FIG. 5, a first cooler 55B-1 that performs cooling with the coexisting substance 62 separated from the recovered vapor 61 in the first gas-liquid separator 56A, a second cooler 55B-2 that performs cooling using the reflux water 31 from a regenerator 20 of the CO.sub.2 recovery unit 12, and a third cooler 55B-3 provided at a downstream side of a rich/lean solution heat exchanger 25 disposed in a lean solution supply line L.sub.1, and which cools the recovered vapor 61 with a rich solution 19 are included as the second vapor cooler 55B.

(58) Accordingly, when a temperature (T.sub.1) of the recovered vapor 61 is 130 C., the recovered vapor is cooled to a temperature (T.sub.2=128 C.) by the first cooler 55B-1, then cooled to a temperature (T.sub.3=125 C.) by the second cooler 55B-2, and then cooled to a temperature (T.sub.4=123 C.) by the third cooler 55B-3.

(59) Here, after the reflux water 31 performs cooling in the fourth cooler 71 for cooling that cools the recovered absorption agent vapor (gas) 17b separated in the first gas-liquid separator 56A, the reflux water 31 is introduced into the second cooler 55B-2 through the cooling water line L.sub.14, and further performs cooling.

(60) Note that the first cooler 55B-1 is provided at an intersection of the vapor line L.sub.12 and a liquid coexisting substance discharge line L.sub.16, the second cooler 55B-2 is provided at an intersection of the vapor line L.sub.12 and the cooling water line L.sub.14, and the third cooler 55B-3 is provided at an intersection of the vapor line L.sub.12 and a rich solution line L.sub.1, and thus cooling is possible with heat in the system of the CO.sub.2 recovery unit 12.

Third Embodiment

(61) A reclaiming device according to an embodiment of the present invention will be described with reference to the drawing. FIG. 6 is a schematic diagram of a reclaiming device according to a third embodiment. Note that the same member as the first and second embodiments is denoted with the same reference sign, and description thereof is omitted.

(62) As illustrated in FIG. 6, the reclaiming device according to the present embodiment further includes a CO.sub.2 gas introduction line L.sub.21 through which a CO.sub.2 gas 40 discharged from a CO.sub.2 absorber 64 is introduced into a distiller 68, and a nitrogen supply section 69 that introduces a nitrogen (N.sub.2) gas into the CO.sub.2 gas introduction line L.sub.21, in the reclaiming device of the second embodiment.

(63) Since the N.sub.2 gas is added to the CO.sub.2 gas 40 from the nitrogen supply section 69, a CO.sub.2 partial pressure in the distiller 68 can be decreased. In this case, since N.sub.2 is mixed in a recovered absorption agent (gas body), it is desirable to supply the N.sub.2 gas to a bottom of an absorber 18 in a case of recovering CO.sub.2 as a product. When there is no problem with the purity of the CO.sub.2 product, the CO.sub.2 may be put back to a regenerator 20, as illustrated in FIG. 6.

(64) An effect of the present embodiment will be described with reference to FIG. 10.

(65) FIG. 10 is a diagram illustrating selective removal ratios in recovered vapor in a conventional example and the third embodiment (where the conventional example is a reference (1)). The conventional technology is a case of recovering the recovered vapor 61 from a reclaimer 51 as it is without providing a first gas-liquid separator 56A, a second gas-liquid separator 56B, a CO.sub.2 absorber 64, and the distiller 68 as in the present embodiment.

(66) The selection removal ratio of a coexisting substance 62 from recovered vapor 61 in the present embodiment is 35, and the coexisting substance can be substantially removed, where the conventional example is the reference (1).

(67) FIG. 11 is a diagram illustrating recovery ratios of the absorption agent in the first embodiment and the third embodiment (where the first embodiment is the reference (1)).

(68) By introduction of nitrogen as in the third embodiment, the CO.sub.2 partial pressure is decreased, addition of an alkaline agent 52 can be decreased, and the recovery ratio of the absorption agent from the recovered vapor 61 is improved by about 1.3 times.

REFERENCE SIGNS LIST

(69) 12 CO.sub.2 recovery unit 13 Industrial combustion facility 14 Flue gas 16 Flue gas cooling device 17 CO.sub.2 absorbent (lean solution) 18 CO.sub.2 absorber 19 CO.sub.2-absorbed CO.sub.2 absorbent (rich solution) 20 Absorbent regenerator 21 Rinse water 51 Reclaimer 52 Alkaline agent 55A First vapor cooler 55B Second vapor cooler 56A First gas-liquid separator 56B Second gas-liquid separator 61 Recovered vapor 62 Coexisting substance