System and method for separation and recovery of acid gas

Abstract

Disclosed is a system and method of separating and collecting acid gas such as carbon dioxide in which the energy consumption in a stripping column for regenerating an absorbent may be reduced. In the system and method, the energy consumption may be reduced using heat generated during the acidic gas separation and collection processes. In the system and method, a low-temperature condensate from a condenser may be preheated by heat exchange with a high-temperature processed gas, and then supplied into the stripping column, thereby to reduce the heat duty of a reboiler and the energy consumption in the condenser for cooling. A partial flow of a carbon diode-absorbed absorbent from an absorber column may be preheated by heat exchange with high-temperature processed gas from an upper portion of the stripping column, and then supplied into the stripping column, thereby to further reduce the heat duty of the reboiler.

Claims

1. A system for separating and collecting acidic gas, the system comprising an absorber column and a stripping column, wherein the absorber column is configured to process the acidic gas using an absorbent contained therein, wherein the stripping column is configured to separate the acidic gas from the absorbent which is transferred from the absorber column to the stripping column, the system further comprising: first to sixth heat exchangers; a branched absorbent supply line comprising a first absorbent supply line and a second absorbent supply line, wherein the first absorbent supply line configured to transfer a first portion of the absorbent with the acidic gas to the stripping column via the fifth heat exchanger, the first heat exchanger and the sixth heat exchanger, wherein the second absorbent supply line is configured to transfer a second portion of the absorbent with the acidic gas to the stripping column via the second heat exchanger, a processed gas transfer line configured to transfer processed gas discharged from the stripping column to a condenser via the second heat exchanger, the fourth heat exchanger, and then the third heat exchanger; a reboiler configured to heat a recycle absorbent supplied from the stripping column; a reboiler's condensate discharge line configured to transfer a first condensate discharged from the reboiler to the sixth heat exchanger; a recycle absorbent transfer line configured to transfer heated recycle absorbent discharged from the reboiler to the absorber column via the first heat exchanger; and a condensate supply line configured to transfer a second condensate for recycling from the condenser to the absorber column via the fourth heat exchanger and the fifth heat exchanger, wherein the second absorbent supply line and the processed gas transfer line are configured to heat-exchange with each other in the second heat exchanger, wherein the processed gas transfer line and the condensate supply line are configured to heat-exchange with each other in the fourth heat exchanger, wherein the condensate supply line and the first absorbent supply line are configured to heat-exchange with each other in the fifth heat exchanger, and wherein the reboiler's condensate discharge line and the first absorbent supply line are configured to heat-exchange with each other in the sixth heat exchanger.

2. The system of claim 1, wherein an operating temperature of the condenser is in a range of about 30° C. to about 40° C.

3. The system of claim 1, wherein the acidic gas comprises carbon dioxide (CO2), methane (CH4), hydrogen sulfide (H2S), carbonyl sulfide (COS), or mercaptan (RSH, where R is a hydrocarbon).

4. The system of claim l, wherein the first absorbent supply line and the recycle absorbent transfer line are configured to heat-exchange with each other in the first heat exchanger.

5. A method of separating and collecting acidic gas, the method comprising: supplying an exhaust gas that includes an acidic gas to an absorber column to absorb the acidic gas into an absorbent, thereby to obtain an acidic gas-absorbed absorbent; supplying a first portion of the acidic gas-absorbed absorbent discharged from the absorber column to a stripping column through a first absorbent line, and a second portion of the acidic gas-absorbed absorbent to the stripping column through a second absorbent line; processing, at the stripping column, the acidic gas-absorbed absorbent received through the first and second absorbent lines to separate processed gas and a recycle absorbent for discharging the processed gas toward a condenser and the recycle absorbent toward a reboiler; processing, at a condenser, the processed gas to separate condensed water and acidic gas; heating the second portion of the acidic gas-absorbed absorbent, which comprises heat-exchanging the second portion of the acidic gas-absorbed absorbent with the processed gas discharged out of the stripping column; heating the condensed water, which comprises heat-exchanging the condensed water from the condenser with the processed gas; and heating the first portion of the acidic gas absorbed absorbent, which comprises heat-exchanging the first portion of the acidic gas-absorbed absorbent with the condensed water that was heat-exchanged with the processed gas.

6. The method of claim 5, wherein an operating temperature of the condenser is in a range of about 30° C. to about 40° C.

7. The method of claim 5, wherein the acidic gas comprises carbon dioxide (CO2), methane (CH4), hydrogen sulfide (H2S), carbonyl sulfide (COS), or mercaptan (RSH, where R is a hydrocarbon).

8. The method of claim 5, further comprising heating the first portion of the acidic gas-absorbed absorbent, wherein heating comprises heat-exchanging the first portion of the acidic gas-absorbed absorbent with the recycle absorbent discharged from the reboiler that is connected to a lower portion of the stripping column.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a conventional system of separating and collecting acidic gas; and

(2) FIG. 2 illustrates a system of separating and collecting acidic gas, according to an embodiment of the present disclosure.

EMBODIMENTS

(3) One or more embodiments of a system and method of separating and collecting acidic gas now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. However, this invention should not be construed as limited to the embodiments set forth herein, and may be embodied in many different forms without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

(4) In the drawings illustrating embodiments of the present invention, like numbers refer to like elements throughout, and detailed description of the same or like elements are not repeated.

(5) Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

(6) Absorbent, processed gas, or condensate transfer lines that may exchange heat with one another are described herein as “intersecting with each other” in a heat exchanger for heat exchanging. In other words, two of these fluid transfer lines may intersect with each other in a heat exchanger to exchange heat with each other.

(7) FIG. 1 illustrates a conventional system for separating and collecting acidic gas. In the conventional system of FIG. 1, an exhaust gas that contains an acidic gas such as carbon dioxide is supplied into an absorber column 1 that is filled with filling matter having a large surface area to facilitate contact between gas and liquid, and thereby to contact the exhaust gas with an absorbent solution that is sprayed above the absorber column 1 under an atmospheric condition. The contact is performed at a temperature of about 40° C. to about 50° C. to absorb the acidic gas such as carbon dioxide present in the exhaust gas into the absorbent solution.

(8) The absorbent solution discharged from the absorber column 1, i.e., the absorbent in which the acidic gas such as acidic gas is absorbed, is transferred to a stripping column 2, and then thermally treated at a temperature of about 120° C. to obtain a processed gas that is free of the absorbent. Then, the processed gas free of the absorbent is discharged through an upper portion of the stripping column 2, while the recycle absorbent free of the processed gas is recycled by being supplied back to the absorber column 1 via a reboiler 80. The processed gas discharged out of the stripping column 2 is supplied to a condenser 70 through a processed gas discharge line 300. The condenser 70 condenses part of steam into water so that the steam remaining uncondensed and acidic gas such as carbon dioxide are obtained as final products. The condensate is supplied back into the stripping column 2 through a condensate supply line 400 for recycling. The recycling of the condensate may improve the separation efficiency of the stripping column 2 but may also increase the heat duty of the reboiler 80 due to the inflow of the low-temperature condensate. The recycle absorbent is transferred through a recycle absorbent supply line 500 to preheat the acidic gas-absorbed absorbent that is to be supplied into the stripping column 2 through the first heat exchanger 10, and to be supplied back to absorber column 1 in order to absorb newly supplied acidic gas. The recycle absorbent supply line 500 and an absorbent supply line 700 for supplying the acidic gas-absorbed absorbent from the absorber column 1 to the stripping column 2 intersect with each other in the first heat exchanger 10.

(9) FIG. 2 illustrates a system for separating and collecting acidic gas according to an embodiment of the present disclosure. The system of FIG. 2 includes an absorber column 1 that absorbs acidic gas into an absorbent to obtain an acidic gas-absorbed absorbent, and a stripping column 2 that separates the absorbent as a recycle absorbent from a processed gas, The system of FIG. 2 includes; a branched absorbent supply line 700 including a first absorbent supply line 100 that may supply the acidic gas-absorbed absorbent from the absorber column 1 to the stripping column 2 via a fifth heat exchanger 50, a first heat exchanger 10, and a sixth heat exchanger 60; and a second absorbent supply line 200 that may supply the acidic gas-absorbed absorbent to the stripping column 2 via a second heat exchanger 20; a processed gas transfer line 300 that may supply the processed gas discharged from the stripping column 2 to a condenser 70 via the second heat exchanger, a fourth heat exchanger, then a third heat exchanger; a reboiler 80 that may heat the recycle absorbent having low temperature supplied from the stripping column 2; a reboiler's condensate discharge line 650 that may supply a condensate discharged from the reboiler 80 to the sixth heat exchanger 60; a recycle absorbent transfer line 550 that may supply a high-temperature recycle absorbent discharged from the reboiler 80 to the absorber column 1 via the first heat exchanger 10; and a condensate supply line 450 that may supply the condensate for recycling from the condenser 70 to the absorber column 1 via the fourth heat exchanger 45 and then the fifth heat exchanger 50.

(10) In the system of FIG. 2, the second absorbent supply line 200 and a portion of the processed gas transfer line 300 that passes through the stripping column 2 intersect with each other in the second heat exchanger 20, a portion of the processed gas transfer line 300 that passes through the second heat exchanger 20, and the condensate supply line 450 intersect with each other in the fourth heat exchanger 45, a portion of) the condensate supply line 450 that passes through the fourth heat exchanger 45, and the first absorbent supply line 100 intersect with each other in the fifth heat exchanger 50, and the reboiler's condensate discharge line 650 and a portion of the first absorbent supply line 100 that passes through the fifth heat exchanger 50 and the first heat exchanger 10 intersect with each other in the sixth heat exchanger 60.

(11) In the conventional system of FIG. 1, the operating pressure and temperature of the reboiler 80 may be about 2 bar and about 120° C., respectively. However, in the system of FIG. 2, a thermal medium for heating an absorbent solution in the reboiler 80 may be steam having a temperature of about 135° C. or higher. The steam may provide latent heat to heat the absorbent solution in the reboiler 80, and may be discharged out of the system as condensate via condensation.

(12) The temperature of the condensate may be about 130° C. or higher that is high enough for heat recovery. This high-temperature condensate may be used to heat the absorbent solution that passed through the fifth heat exchanger 50 and the first heat exchanger 10 before the absorbent solution is supplied into the stripping column 2, so that the heat duty of the reboiler 80 may be reduced.

(13) A flow of the processed gas that passes through the upper portion of the stripping column 2 may include a considerable amount of high-temperature steam. Accordingly, the heat energy consumption may be reduced by recovering heat from the high-temperature processed gas. In some embodiments, in the process system of FIG. 2 the second heat exchanger 20 may be disposed above the upper portion of the stripping column 2 to allow thermal exchange between the high-temperature processed gas and a flow of the absorbent in which acidic gas such as carbon dioxide is absorbed, from the absorber column 1 through the second absorbent supply line 200 of the branched absorbent supply line 700, thereby further heating the flow of the acidic gas-absorbed absorbent that is to be supplied into the stripping column 2. Accordingly, the heat duty of the reboiler 80 may be reduced.

(14) In some embodiments, the operating temperature of the condenser 70 may be in is a range of about 30° C. to about 40° C. In some embodiments, the acidic gas may be selected from carbon dioxide (CO.sub.2), methane (CH.sub.4), hydrogen sulfide (H.sub.2S), carbonyl sulfide (COS), or mercaptane (RSH, where R is a hydrocarbon), but is not limited thereto. In some embodiments, the first absorbent supply line 100 and the absorbent transfer line 650 that transfers the recycle absorbent from the stripping column 2 to the absorption column 1 via the reboiler 80 connected to a lower portion of the stripping column 2 may intersect with each other in the first heat exchanger 10, so that the absorbent transferred through the first absorbent supply line 100 may be preheated in the first heat exchanger 10.

(15) According to another aspect of the present disclosure, a method of separating and collecting acidic gas includes: supplying an exhaust gas that includes an acidic gas to an absorber column to absorb the acidic gas into an absorbent; supplying a first portion of the acidic gas-absorbed absorbent discharged from the absorber column to a stripping column, and supplying a second portion of the acidic gas-absorbed absorbent to the stripping column after preheating through thermal exchange with a processed gas discharged out of the stripping column, thereby to separate the acidic gas-absorbed absorbent into the absorbent and the acidic gas in the stripping column; preheating the processed gas that underwent heat exchange with the second portion of the acidic gas-absorbed absorbent after discharged out of the stripping column, by thermal exchange with a condensate produced in a condenser by cold condensation before the processed gas is supplied into the condenser for cold condensation, and then preheating the first portion of the acidic gas-absorbed absorbent; supplying the processed gas discharged from the stripping column to a condenser after heat exchange with a condensate previously discharged from the condenser and then with the second portion of the acidic gas-absorbed absorbent; preheating the condensate that underwent the heat exchange with the second portion of the acidic gas-absorbed absorbent, by heat exchange with the first portion of the acidic gas-absorbed absorbent; and preheating the preheated first portion of the acidic gas-absorbed absorbent by thermal exchange with a condensate produced in a reboiler that is connected to the stripping column.

LIST OF REFERENCE NUMERALS

(16) 1: absorber column

(17) 2: stripping column

(18) 10: first heat exchanger

(19) 20: second heat exchanger

(20) 30: third heat exchanger

(21) 45: fourth heat exchanger

(22) 50: fifth heat exchanger

(23) 60: sixth heat exchanger

(24) 70: condenser

(25) 100: first absorbent supply line

(26) 200: second absorbent supply line

(27) 300: processed gas discharge line

(28) 400: condensate supply line

(29) 500: recycle absorbent transfer line

(30) 650: reboiler's condensate discharge line