Acid gas recovery apparatus and method

Abstract

To provide an acidic gas recovery apparatus and an acidic gas recovery method which remove an impurity-containing substance from an absorption liquid without requiring high temperature and pressure reduction.SOLUTION: An acidic gas recovery apparatus includes: an acidic gas absorption part for absorbing at least a part of acidic gas in treated gas containing acidic gas in an absorption liquid containing an amine-based compound, and discharging the treated gas as acidic gas removal gas; a regeneration part for emitting the acidic gas from the absorption liquid absorbing the acidic gas in the acidic gas absorption part; and a separation part for generating a mixed liquid in which at least a part of the absorption liquid and an organic solvent supplied from the outside are mixed, and separating the impurity-containing substance from the mixed liquid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE An embodiment of the present invention relates to an acid gas recovery apparatus and an acid gas recovery method. [Background technology]

[0002] In thermal power plants and steelworks that use large amounts of fossil fuels, the combustion exhaust gas generated by burning fossil fuels in boilers, coal gasification gas (gasification gas) produced by gasifying coal, and natural gas, for example, emit carbon dioxide (CO 2 ), sulfur oxides (SOx), nitrogen oxides (NOx), hydrogen sulfide (H 2 It contains acidic gas components such as S.

[0003] In order to prevent the release of acidic gas components contained in combustion exhaust gases into the atmosphere, the main 2 Carbon dioxide Capture and Storage (CCS) equipment, consisting of an absorption tower and a regeneration tower, is one type of equipment for recovering CO. In this CCS equipment, gas containing acidic gas components is brought into gas-liquid contact with an absorbing solution containing an amino group-containing compound (amine) in the absorption tower, and the acidic gas components are absorbed into the absorbing solution, removing the acidic gas components from the treated gas and reducing the amount of CO 2 In the regeneration tower, the absorbing liquid that has absorbed the acidic gas components is heated to remove the acidic gas components, and the absorbing liquid is regenerated so that it can be reused.

[0004] However, during operation of the CCS unit, the CO in the flue gas 2 When absorbing CO2, in addition to SOx and NOx, carbonyl sulfide, hydrogen cyanide, thiocyanic acid, thiosulfuric acid, and other inorganic acids react with the amines in the absorbing solution to generate impurities called heat stable salts (HSS). HSS is also generated when the amines decompose due to reaction with heat or oxygen in the gas when the absorbing solution is heated for regeneration.

[0005] HSS accumulates in the absorbing solution because it is not decomposed or separated by heating when the absorbing solution is regenerated in the regeneration tower of the CCS unit. When HSS accumulates, it not only reduces the acid gas absorption efficiency of the absorbing solution, but also causes corrosion of the CCS unit, so it is desirable to remove HSS from the absorbing solution. In addition, amines generate impurities other than HSS, and impurities such as exhaust gas-derived components such as soot and metal components from plant piping also accumulate.

[0006] Distillation is known as a method for removing impurities such as HSS from the absorbent. Distillation can separate the amine that evaporates from the residue, which is HSS and other impurities that do not evaporate. However, distillation requires high temperatures when the boiling point of the amine is high, which can cause thermal degradation of the amine or cause losses of amine that does not evaporate remaining in the residue. For this reason, vacuum distillation, which lowers the temperature under reduced pressure, is also performed, but this requires pumps and energy for the reduction in pressure, and the equipment is complicated. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-76810 A Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide an acid gas recovery apparatus and method for removing impurities from an absorbing liquid without requiring high temperatures or reduced pressure. [Means for solving the problem]

[0009] In order to solve the above problems, the acidic gas recovery apparatus of the embodiment has an acidic gas absorption section that absorbs at least a portion of the acidic gas in a treated gas containing acidic gas into an absorption liquid containing an amine compound and discharges the treated gas as an acidic gas removal gas, a regeneration section that releases the acidic gas from the absorption liquid that has absorbed the acidic gas in the acidic gas absorption section, and a separation section that generates a mixed liquid by mixing at least a portion of the absorption liquid with an organic solvent supplied from the outside and separates impurities from the mixed liquid. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing a configuration example of an acid gas recovery apparatus according to a first embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing a configuration example of an acid gas recovery apparatus according to a second embodiment. [Diagram 3] FIG. 13 is a schematic diagram showing a configuration example of an acid gas recovery apparatus according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment for carrying out the invention will be described.

[0012] (First embodiment) FIG. 1 is a schematic diagram showing a configuration example of an acidic gas recovery apparatus according to a first embodiment. In this embodiment, the acidic gas recovery apparatus uses carbon dioxide (CO 2 ) will be used as an example for explanation. However, the present invention is not limited to CCS devices. In the acid gas recovery system shown in Figure 1, CO 2 CO in the treated gas (exhaust gas) 101 containing 2 The absorbing liquid that absorbs the CO circulates between the absorber 1 and the regenerator 2 (hereinafter referred to as "within the system"). 2 The absorbent 1 is supplied with a rich absorbent 111 that has absorbed CO. The rich absorbent 111 is then fed to the absorber 1 from the regenerator 2. 2The absorbing solution (lean absorbing solution) 110a from which the acid gases have been removed and which has been regenerated is supplied.

[0013] The absorbing liquid is preferably an amine-based aqueous solution containing an amino group-containing compound (amine) and water. Preferred amines include, for example, primary amines such as monoethanolamine and 2-amino-2-methyl-1-propanol, secondary amines such as diethanolamine and 2-methylaminoethanol, tertiary amines such as triethanolamine and N-methyldiethanolamine, polyethylene polyamines such as ethylenediamine, triethylenediamine, and diethylenetriamine, cyclic amines such as piperazines, piperidines, and pyrrolidines, polyamines such as xylylenediamine, and amino acids such as methylaminocarboxylic acid, and these can be used alone or in combination of two or more.

[0014] The absorption liquid is usually used as an aqueous solution containing 10 to 70% by weight of these amines. In addition, the absorption liquid may contain a reaction accelerator, CO 2 Other compounds, such as nitrogen-containing compounds that improve the absorption performance of acidic gases, anticorrosive agents for preventing corrosion of plant equipment, antifoaming agents for preventing foaming, antioxidants for preventing deterioration of the absorption liquid, and pH adjusters, can be appropriately contained in any ratio within the range that does not impair the effect of the absorption liquid.

[0015] A typical example of the gas to be treated 101 is CO 2 The exhaust gas contains, for example, combustion exhaust gas discharged from a boiler or gas turbine of a thermal power plant, process exhaust gas generated in a steel mill, etc. The gas to be treated 101 is preferably pressurized by a blower or the like, cooled by a cooler, and then supplied to the inside of the absorber 1 from the lower part through the gas to be treated supply line L1.

[0016] The absorber 1 shown in FIG. 2an acid gas absorption section 1a for absorbing the acid gas (acid gas) into a lean absorption liquid 110a supplied to the absorber 1 via a line L14; 2 and a gas scrubbing section 3 for scrubbing the gas to be treated 101 (acid-gas-free gas) from which the acid gas has been removed with a scrubbing liquid 121a and recovering the absorbing liquid accompanying the acid-gas-free gas.

[0017] Here, the acidic gas absorption section 1a is preferably formed of a packing material to increase the gas-liquid contact efficiency. A liquid distributor (not shown) can be provided above the acidic gas absorption section 1a, and the lean absorbing liquid 110a supplied to the absorber 1 is dispersed and falls toward the acidic gas absorption section 1a by the liquid distributor. The treated gas 101 fed into the absorber 1 flows from the lower part of the absorber 1 toward the tower top (upper part). In the acidic gas absorption section 1a, when the treated gas 101 ascending inside the absorber comes into countercurrent contact with the lean absorbing liquid 110a, reactions such as those shown in the following formulas (1) and (2) occur, for example, to convert a thermally decomposable salt (R 3 NH 2 CO 3 ) and heat stable salts (HSS, R 3 NHX) is formed, and CO 2 is absorbed in the lean absorbing liquid 110a and removed from the gas 101 to be treated.

[0018] The lean absorbing solution 110a absorbs CO 2 The rich absorbent 111 absorbs the oxygen contained in the gas 101 to be treated and becomes a rich absorbent 111, which is stored in the lower portion. The rich absorbent 111 accumulates HSS generated by absorbing organic acids generated by reaction with oxygen contained in the gas 101 to be treated, SOx, NOx, carbonyl sulfide, hydrogen cyanide, thiocyanic acid, thiosulfuric acid, and other inorganic acids contained in the gas 101 to be treated. Here, R represents hydrogen, or a substituted or unsubstituted alkyl group (which may form a heterocycle). R 3 N+CO 2 +H 2 O → R 3 NH 2 CO 3 (1) R 3 N+HX → R 3 NHX ···(2)

[0019] The acid-gas-removed gas that has passed through the acid gas absorption section 1a rises inside the absorber 1 and is supplied to the gas cleansing section 3. The acid-gas-removed gas is purified in the gas cleansing section 3 and then discharged to the outside as treated flue gas 102 from a treated flue gas discharge line L2 provided at the top of the absorber 1.

[0020] On the other hand, the rich absorbing solution 111 stored in the lower part of the absorber 1 is discharged from the lower part of the absorber 1, passes through the rich absorbing solution supply line L3, is pressurized by a pump (not shown) provided in the rich absorbing solution supply line L3, and is heat exchanged with the lean absorbing solution 110a regenerated in the regenerator 2 in the heat exchanger 9, and is then supplied to the regenerator 2. In the heat exchanger 9, the rich absorbing solution 111 is heat exchanged with the lean absorbing solution 110a, so that the lean absorbing solution 110a serves as a heat source to heat the rich absorbing solution 111. Conversely, the rich absorbing solution 111 serves as a cooling source to cool the lean absorbing solution 110a. As the heat exchanger 9, a known heat exchanger such as a plate heat exchanger or a shell and tube heat exchanger can be used.

[0021] The regenerator 2 converts the rich absorbent 111 into CO 2 The rich absorbing solution 111 is supplied to the regenerator 2 and heated by steam in the reboiler 8 to release CO 2 is desorbed, and some or almost all of the CO contained in the rich absorption liquid 111 is 2 The lean absorbent 110a is obtained by removing the

[0022] At this time, the lean absorbing solution 110a generates water vapor and also releases the remaining CO 2 CO 2 It is released as a gas: CO 2The gas is discharged from the top of the regenerator 2 into a line L5 together with the water vapor that simultaneously evaporates from the lean absorbing liquid 110a. 2 The regenerator outlet gas 118 containing gas and water vapor is cooled by cooling water in the cooler 6, and the water vapor is condensed to water. Then, this condensed water and CO 2 The regenerator outlet gas 119 containing gas is supplied to the gas-liquid separator 7, and CO 2 Gas 103 is separated from the condensed water 120a and CO 2 The gas 103 is discharged to the outside through a line L6. Condensed water 120a is extracted from the lower part of the gas-liquid separator 7 and supplied to the upper part of the regenerator 2 through a line L7.

[0023] The lean absorbing solution 110a stored in the lower part of the regenerator 2 is discharged from the lower part of the regenerator 2 through the lean absorbing solution discharge line L4, and is cooled by heat exchange with the rich absorbing solution 111 in the heat exchanger 9. Thereafter, the lean absorbing solution 110a is cooled in the cooler 5 and then supplied to the absorber 1 through the line L14.

[0024] An absorbing liquid extraction line L8 is provided which branches off from the lean absorbing liquid discharge line L4 and is connected to the separator 4, and the lean absorbing liquid 105 is extracted from the absorbing liquid 105. An organic solvent 104 is supplied to the separator 4 from an organic solvent supply line L9. Preferred organic solvents include, for example, acetonitrile, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and other solvents which dissolve in water and have a boiling point not higher than that of the amine used in the absorbing liquid, and these can be used alone or in combination of two or more kinds.

[0025] Since the polarity of the organic solvent is lower than that of water, the solubility of impurities such as HSS is different. Therefore, the mixture of the organic solvent 104 and the lean absorption liquid 105 undergoes phase separation in the separator 4, and the impurity-containing material 107 such as HSS precipitates. The impurity-containing material 107 may be in a liquid phase rather than a solid phase.

[0026] In the separator 4, a mixing means such as a stirrer may be installed to uniformly mix the lean absorption liquid 105 and the organic solvent 104. The lean absorption liquid 105 and the organic solvent 104 may be continuously or intermittently supplied to the separator 4, but since the impurity-containing material 107 is more easily separated by being left to stand after mixing, it is preferable to supply them intermittently and allow time for them to stand. It is also possible to remove the impurity-containing material 107 by providing a filter (not shown) and passing the mixed liquid of the organic solvent 104 and the lean absorption liquid 105 through this filter.

[0027] The mixed liquid 106 from which the impurity-containing substances 107 have been removed is sent to the first evaporator 10 through a line L11. In the first evaporator 10, the mixed liquid 106 is heated to a temperature equal to or higher than the boiling point of the organic solvent 104 by steam, an electric heater, or the like, to remove the steam 108 containing the organic solvent 104 from the mixed liquid 106, thereby obtaining a lean absorbing liquid 109. The lean absorbing liquid 109 is sent to a line L14 through a line L13, merges with the lean absorbing liquid 110a discharged from the regenerator 2, and is sent to the absorber 1.

[0028] For example, acetonitrile that can be used as the organic solvent 104 has a boiling point of 82° C., and by heating to a temperature above the boiling point, it is possible to efficiently remove only the acetonitrile.

[0029] The mixing ratio of the lean absorption liquid 105 and the organic solvent 104 in the separator 4 can be set arbitrarily, but the mixing ratio of the lean absorption liquid 105 and the organic solvent 104 is preferably 1:1 to 1:5. The larger the mixing amount of the organic solvent 104, the larger the amount of the organic solvent 104 evaporated in the first evaporator 10, and the larger the energy required for separation.

[0030] The boiling points of the amines used as the absorbing liquid are all high, for example, monoethanolamine, which is a primary amine, is 170° C., diethanolamine, which is a secondary amine, is 269° C., and N-methyldiethanolamine, which is a tertiary amine, is 247° C. By mixing with an organic solvent 104 having a lower boiling point, distillation at a lower temperature compared to the distillation of the amine is possible.

[0031] The absorbing liquid and the organic solvent 104 may be other than those described as examples. The absorbing liquid withdrawal line L8 may be provided anywhere in the system, for example, it may be provided in the line L3 that discharges the rich absorbing liquid 111 from the absorber 1. The lean absorbing liquid 109 from the line L13 may be sent anywhere in the system, for example, it may be sent to the line L3 that discharges the rich absorbing liquid 111 from the absorber 1.

[0032] Furthermore, a neutralizing agent may be added to the lean absorption liquid 105. By adding the neutralizing agent, the HSS formed by the amine reacts with the neutralizing agent to liberate the amine. This can improve the recovery rate of the amine. Examples of the neutralizing agent include sodium hydroxide, sodium carbonate, and potassium hydroxide, and they may be used as an aqueous solution.

[0033] As described above, according to this embodiment, by mixing the organic solvent 104 with the lean absorbing liquid 105, the impurity-containing substance 107 can be separated and removed from the lean absorbing liquid 105 without applying high temperature or reduced pressure. Furthermore, it becomes possible to distill the mixed liquid 106 at about the boiling point of the organic solvent 104, and the organic solvent 104 can be removed from the mixed liquid 106 without applying high temperature or reduced pressure to obtain the lean absorbing liquid 109.

[0034] Second Embodiment 2 is a schematic diagram showing a configuration example of an acidic gas recovery apparatus according to a second embodiment. Note that the same parts as those in the first embodiment are given the same reference numerals and detailed description thereof will be omitted.

[0035] In the second embodiment, the vapor 108 containing the organic solvent 104 discharged from the first evaporator 10 is cooled in the cooler 12 via line L12 to become a liquid containing the organic solvent 104, and is sent to line L9 and used as the organic solvent 104 in the separator 4. This makes it possible to reduce the amount of the organic solvent 104 used.

[0036] In addition, the liquid containing the organic solvent 104 may be temporarily stored in a tank and then sent to the separator 4 in accordance with the operation of the separator 4.

[0037] Thus, according to this embodiment, by mixing the organic solvent 104 with the lean absorbing liquid 105, the impurity-containing substance 107 can be separated and removed from the lean absorbing liquid 105 without high temperature or reduced pressure. Furthermore, it is possible to distill the mixed liquid 106 at approximately the boiling point of the organic solvent 104, and the organic solvent 104 can be removed from the mixed liquid 106 without high temperature or reduced pressure to obtain the lean absorbing liquid 109. In addition, the vapor 108 containing the organic solvent 104 discharged from the first evaporator 10 is cooled to become a liquid, and the liquid is used as the organic solvent 104 in the separator 4, thereby reducing the amount of the organic solvent 104 used.

[0038] (Third embodiment) 3 is a schematic diagram showing a configuration example of an acidic gas recovery apparatus according to the third embodiment. Note that the same parts as those in the first and second embodiments are given the same reference numerals and detailed description thereof will be omitted.

[0039] In the third embodiment, an absorbing solution extraction line L8 is provided which is branched from the lean absorbing solution discharge line L4 and connected to the separator 4, and the extracted lean absorbing solution 105 is supplied to the second evaporator 11. In the second evaporator 11, the temperature is preferably set to about 100°C to 140°C, so that water 112 is removed from the lean absorbing solution 105 through a line L15. The water 112 may be sent to the absorbing solution in the system through the line.

[0040] The lean absorption solution 113 from which the water 112 has been removed is sent to the separator 4 through the line L16 and mixed with the organic solvent 104. Since the water 112 has been removed from the lean absorption solution 113, impurities are less likely to dissolve therein, and even if the amount of the organic solvent 104 mixed is small, the mixture of the organic solvent 104 and the lean absorption solution 113 is more likely to undergo phase separation in the separator 4, which is preferable.

[0041] Furthermore, the mixed liquid 106 from which the impurity-containing substances 107 have been removed is sent to the first evaporator 10. In the first evaporator 10, the mixed liquid 106 is heated to a temperature equal to or higher than the boiling point of the organic solvent 104 by steam, an electric heater, or the like, so that the steam 108 containing the organic solvent 104 is removed from the mixed liquid 106, and a lean absorption liquid 109 is obtained.

[0042] Thus, according to this embodiment, by mixing the organic solvent 104 with the lean absorbing liquid 105, the impurity-containing material 107 can be separated and removed from the lean absorbing liquid 105 without high temperature or reduced pressure. Furthermore, it is possible to distill the mixed liquid 106 at about the boiling point of the organic solvent 104, and the organic solvent 104 can be removed from the mixed liquid 106 without high temperature or reduced pressure to obtain the lean absorbing liquid 109. In addition, the amount of the organic solvent 104 used can be reduced by cooling the steam 108 containing the organic solvent 104 discharged from the first evaporator 10 to a liquid and using it as the organic solvent 104 in the separator 4. Then, the amount of the organic solvent 104 used can be reduced by supplying the lean absorbing liquid 113 obtained by removing the water 112 from the lean absorbing liquid 105 to the separator 4.

[0043] According to at least one embodiment of the acidic gas recovery apparatus and the acidic gas recovery method described above, by mixing at least a part of the absorbing liquid with an organic solvent, it is possible to separate and remove impurities without applying high temperatures or reduced pressure. Furthermore, by distilling the organic solvent from the mixed liquid from which the impurities have been removed, it is possible to remove the organic solvent from the mixed liquid without applying high temperatures or reduced pressure, thereby making it possible to reuse the absorbing liquid.

[0044] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0045] 1: Absorber 2:Regenerator 4: Separator 10: First evaporator 11: Second evaporator 104: Organic solvents 106: Mixed liquid 107: Impurity-containing substances 108: Vapor containing organic solvent 104

Claims

1. an acid gas absorption section that absorbs at least a part of the acid gas in a gas to be treated that contains an acid gas into an absorption liquid containing an amine compound, and discharges the gas to be treated as an acid gas-removed gas; a regeneration section that releases the acidic gas from the absorbing solution that has absorbed the acidic gas in the acidic gas absorption section; a separation unit that generates a mixed liquid by mixing at least a part of the absorption liquid with an organic solvent supplied from an outside, and separates impurities from the mixed liquid; a first distillation section for distilling the organic solvent from the mixed liquid from which the impurity-containing substance has been separated; having The organic solvent is at least one of acetonitrile, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol.

2. 2. The apparatus for recovering acidic gas according to claim 1, wherein the organic solvent distilled in the first distillation section is supplied to the separation section.

3. 3. The acid gas recovery system according to claim 1, further comprising a second distillation section for distilling water from the absorption liquid supplied to the separation section.

4. The separation section generates a mixed liquid by mixing at least a portion of the lean absorption liquid from which the acidic gas has been released from the rich absorption liquid that has absorbed the acidic gas in the regeneration section with the organic solvent supplied from the outside, and separates impurities from the mixed liquid. The acidic gas recovery apparatus according to any one of claims 1 to 3.

5. an acid gas absorption step of absorbing at least a part of the acid gas in a gas to be treated containing the acid gas into an absorbing solution containing an amine compound, and discharging the gas to be treated as an acid gas-removed gas; a regeneration step of releasing the acidic gas from the absorption liquid having absorbed the acidic gas in the acidic gas absorption step; a separation step of generating a mixed liquid by mixing at least a part of the absorption liquid with an organic solvent supplied from an outside, and separating an impurity-containing substance from the mixed liquid; a first distillation step of distilling the organic solvent from the mixture from which the impurity-containing substance has been separated; having The method for recovering an acidic gas, wherein the organic solvent is at least one of acetonitrile, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol.

6. The method for recovering acidic gas according to claim 5, wherein the organic solvent distilled in the first distillation step is supplied to the separation step.

7. 7. The method for recovering acidic gas according to claim 5, further comprising a second distillation step of distilling water from the absorption liquid to be supplied to the separation step.

8. The separation step comprises generating a mixed liquid by mixing at least a portion of the lean absorption liquid from which the acidic gas has been released from the rich absorption liquid that has absorbed the acidic gas in the regeneration step with the organic solvent supplied from the outside, and separating impurities from the mixed liquid. The acidic gas recovery method according to any one of claims 5 to 7.

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