Regeneration of ion exchangers that are used for salt removal from acid gas capture plants

In one aspect, the invention relates to a method of regenerating an ion exchanger used to capture a salt from a solution. In another aspect, the invention relates to the integration of an ion exchange step and an acid gas trapping step. In one particularly preferred embodiment, the captured acid gas comprises one or more of sulfur dioxide, hydrogen sulfide and carbon dioxide.

Separation of acid gases such as sulfur dioxide, hydrogen sulfide or carbon dioxide from gas streams such as combustion emissions or hydrocarbon-containing streams by absorption into aqueous amine solvents is well known. Many of these methods, called amine processing equipment steps, are described in "Gas Purification", 5th Edition, Ed. Arthur L. Kohl and Richard B. Nielsen, Gulf Publishing Company, Houston, TX.

The amine treatment equipment step uses a reproducible amine solvent, the acid gas is trapped in the solvent at a certain temperature, and the acid gas is generally deabsorbed or stripped from the solvent at a higher temperature.

The amine solvent for removing a given acid gas component from the feed stream can be selected such that the acid gas can be removed from the solvent by steam stripping. If steam stripping is used, then the acid gas must be volatile while in solution in order to separate the acid gas from the solvent. Preferably, the acid ionization constant (pKa) of the conjugate acid of the amine is about 3 or 4 units higher than the pKa of the acid gas. If this difference in pKa is greater than about 3 or 4 units, the salt formed between the amine and the acid is too stable to actually dissociate by steam stripping.

In commercial operations, the acid gas capture process encounters stronger acid intrusion and / or in-process formation than the acid for which the removal process is designed. These stronger acids, together with the amine solvent, are non-renewable in steam and thus form a thermostable amine salt, or a salt simply referred to as a thermostable salt.

If thermostable salts are capable of accumulating, they will eventually neutralize all amines in the solvent, which will react with the acid gas component as intended and will not be able to be removed. Therefore, the device for accumulating strong acid in the amine solvent needs to be prepared for removing the heat-stable salt.

Various means for removing heat-stable salts from amine solutions for gas treatment are known. These include distilling of free amines from salts at atmospheric pressure or below atmospheric pressure (see, eg, "Gas Purification," p. 255, ff), electrodialysis (see, eg, US Pat. No. 5,292,407). ) And ion exchange (eg, US Pat. No. 4122149, US Pat. No. 4113849, US Pat. No. 4,970344, US Pat. No. 5045291, US Pat. No. 5,292,407, US Pat. No. 5368818, US Pat. No. 5788864 and US Pat. (See No. 6245128).

One problem with the ion exchange method is that the ion exchange medium or resin must be regenerated from time to time. During the stock solution charging step of the ion exchange step, the anion removing capacity is exhausted as the heat stable salt is removed from the amine solvent. When the anion removal capacity of the ion exchange resin is exhausted or reduced by a certain amount, the supply of the heat stable salt concentrated amine solvent to the ion exchange resin is stopped so that the ion exchange resin can be regenerated. .. Since the ion exchange resin regenerant is usually sent to waste water treatment or otherwise discarded, the flow of the resin regenerant to the column is to be recovered in order to recover the dilute amine solvent solution before the ion exchange resin is regenerated. Before starting, the amine solvent in the amine resin bed can be expelled and washed away with a large volume of water. When the dilute amine solvent solution is returned to the acid gas trapping step, thereby avoiding the loss of the amine solvent, which introduces water into the amine solvent during the acid gas trapping step, thereby in the solvent solution in the amine treatment equipment step. Dilute the concentration of the amine solvent in.

The amine treatment equipment process is designed to work at a fixed optimum amine solvent concentration. Therefore, dilution of the amine solvent is not desirable. Therefore, if the diluted amine solution can be returned to the acid gas treatment step or the dilute amine solvent stream can be dumped as waste, water must be removed from the amine solvent, resulting in loss of amine solvent. ..

<p num="0010"> According to one embodiment of the present invention, an improved method for regenerating an ion exchange resin is provided. In particular, the drawback of high volume washing required to efficiently recover amines after the amine dilution and charging steps can be minimized by integrating the operation of the amine treatment equipment and the ion exchange process. It was decided that it could be done.</p><p num="0011"> In operation, the ion exchange medium (hereinafter commonly referred to herein as resin) can be housed, for example, in a packed bed in a tower. The heat-stable salt-rich amine solvent is passed through the column. The thermostable salt is trapped in the ion exchange resin while the amine solvent passes through the column. When it is determined that the ion exchange resin must be regenerated, the flow of the amine absorber through the column is stopped and the regenerant is supplied and passed through the column. Prior to regeneration of the ion exchange medium, it is preferred to remove all or substantially all amine solvents from the column.</p><p num="0012"> The amount of amine dilution caused by the return of the dilute amine solution formed by flushing the amine from the column prior to the ion exchange resin regeneration step uses reflux from the amine processor regeneration column at the end of the exhaustion step. It can be reduced by expelling and flushing the amine from the ion exchange tower. The used amine solvent containing reflux can then be recycled to the amine treatment equipment process. A large volume of reflux can be used to ensure a high degree of amine recovery from the column and can be returned to the amine treatment equipment process, but this is because the wash water is sourced from the treatment solvent itself and therefore. This is because it does not result in dilution of the amine during the process. The ion exchange bed wash water, preferably obtained from the reflux stream of the steam stripper and used to flush the amine absorber from the ion exchange bed, is recycled into the acid gas trapping step without the addition of any make-up water.</p><p num="0013"> Therefore, the source of wash water for removing the amine absorber from the ion exchange bed may be water obtained from most or essentially acid gas capture steps. This offers two advantages. First, the dilution of the amine solvent is reduced or substantially eliminated. In particular, the water used to flush the amine from the ion exchange bed is obtained from the acid gas capture step (ie, reflux stream), unless additional step water is added to the wash water supply stream from an external source of the treatment agent step. Only water. Therefore, no net dilution of the amine absorber occurs. Even if some additional make-up water is required due to the limited availability of reflux, the amount of dilution at that time is significantly reduced compared to the use of external wash water alone. Another advantage is that by recycling the wash water containing the amine absorber into the amine treatment equipment process, the generation of wash drainage streams that must either be disposed of or treated is avoided or at least reduced.</p><p num="0014"> According to another aspect of the invention, preferably the acidic solution obtained from the reflux stream provides wash water for removing the acid gas absorber from the ion exchanger prior to regeneration of the ion exchange resin. Use. The wash water utilized can include all or part of the reflux stream obtained from the steam stripping tower used in the amine treatment equipment process. For example, when treating a feed gas stream containing sulfur dioxide using an amine treatment equipment process, reflux will contain sulfite, a hydrate of sulfur dioxide, in the solution. Alternatively, if an amine treatment apparatus process is used to treat the feed gas stream containing hydrogen sulfide and / or carbon dioxide, then the reflux stream will contain carbonic acid and / or hydrogen sulfide in the solution. Become. Although the reflux stream is acidic, it does not interfere with the regeneration process if the concentration of acid gas dissolved during reflux is less than 5% by weight, more preferably less than 3% by weight, most preferably less than 2% by weight. ..</p><p num="0015"> According to another embodiment of the present invention, the washing water used for removing the amine solvent from the ion exchange bed may release the concentration of water in the treatment agent amine solvent, reflux to the preliminary washing tower, and the like. It will be well understood that it can be obtained from alternative sources if it can be controlled by other means.</p><p num="0016"> In some amine processing equipment steps, the hot feed gas is typically quenched before contacting the feed gas with the aqueous amine solvent to prevent decomposition and dehydration of the amine solvent. The quenching process uses water evaporation to cool and saturate the gas with water. This quenching is often done, for example, in a spray pre-cleaning tower. The water in the pre-cleaning tower is pumped to the spray nozzle. Control the pH, concentration of dissolved solids and levels of suspended solids by releasing some water. Add make-up water, usually deionized water or steam condensate to the pre-scrubber to keep the amount of water retained constant. According to another aspect of the invention, the drainage stream from the ion exchange process is used as make-up water for the pre-scrubber and from the regeneration of the ion exchange resin which must otherwise be treated for disposal. Eliminate or significantly reduce the volume of wastewater provided.</p><p num="0017"> Therefore, according to one embodiment of the present invention, a method for removing an amine-capturable gas from a feed gas stream using an amine solvent. (a) A step of contacting the supply gas stream with a dilute amine solvent to form a concentrated amine solvent, in which a heat-stable salt is present in the concentrated amine solvent. (b) A step of stripping a amine-capturable gas from a concentrated amine solvent to form a dilute amine solvent and an overhead reflux stream. (c) A step of periodically contacting at least a part of one or both of the dilute amine solvent and the concentrated amine solvent with the anion exchange resin to form the first thermostable salt dilute amine solvent. (d) A step of periodically regenerating the anion exchange resin, in which at least a portion of the reflux stream is used to flush the amine solvent from the anion exchange resin during the regeneration of the anion exchange resin for a second thermal stability. Steps to make a salt dilute amine solvent, (e) With the step of recycling at least a portion of the first and second thermostable salt dilute amine solvents for use to capture amine-capturable gases from the feed gas. Methods are provided that include.</p><p num="0018"> In one embodiment, the method SOs a gas that can be captured by amines.₂, H₂S and CO₂Includes additional steps to choose from one or more of.</p><p num="0019"> In another embodiment, the method further comprises selecting a dilute amine solvent as the amine solvent to be contacted with the anion exchange resin.</p><p num="0020"> In another embodiment, during step (d), the anion exchange resin is treated and then the amine solvent is removed before the anion exchange resin is regenerated.</p><p num="0021"> In another embodiment, step (d) (a) Bringing the anion exchange resin into contact with water to wash away the amine solvent from the anion exchange resin, (b) Subsequently, the anion exchange resin was brought into contact with the regenerating agent to obtain the regenerated anion exchange resin and the used regenerating agent solution. (c) Rinse the anion exchange resin with water to remove the regenerating agent from the resin, and obtain the regenerating agent cleaning wastewater. including.</p><p num="0022"> In another embodiment, the method further comprises rinsing the regenerated anion exchange resin with water to remove the regenerating agent from the resin before using the regenerated anion exchange resin in step (c). ..</p><p num="0023"> In another embodiment, the method (a) Steps to pre-clean the supplied gas stream and (b) With the step of using all or part of one or both of the used regenerant solution and the regenerant wash drainage in the pre-cleaning operation. Including further.</p><p num="0024"> In another embodiment, the method further comprises removing the amine solvent from the anion exchange resin before contacting the anion exchange resin with water to wash away the amine solvent from the anion exchange resin.</p><p num="0025"> In another embodiment, the method further comprises the step of preparing an amine solvent having an amine having a pKa in the range of 2.5-6. Preferably, this method is SO as a gas trappable with amines.₂Includes additional steps to select.</p><p num="0026"> In another embodiment, the method further comprises the step of preparing an amine solvent having an amine having a pKa in the range of 7.5-10. Preferably, this method uses an amine-capturable gas.₂S and CO₂Includes additional steps to choose from one or more of.</p><p num="0027"> In another embodiment, the thermostable salt dilute amine is recycled in step (a).</p><p num="0028"> In another embodiment, the thermostable salt dilute amine is recycled in step (b).</p><p num="0029"> In another embodiment, the method SOs as a gas trappable with amines.₂Includes additional steps to select.</p><p num="0030"> In another embodiment, reflux is utilized undiluted to flush the amine solvent from the anion exchange resin.</p><p num="0031"> According to another embodiment of the present invention. (a) A step of obtaining a solvent solution containing a heat-stable salt from an amine treatment apparatus step, and (b) The step of contacting the solvent solution with the anion exchange resin to obtain a heat-stable salt dilute solvent solution, (c) The step of periodically regenerating the anion exchange resin and flushing the anion exchange resin with at least a portion of the reflux stream from the amine treatment apparatus step to produce a thermostable salt dilute amine stream prior to the regeneration of the anion exchange resin. When, (d) Steps to recycle heat-stable salt dilute amines into the amine treatment equipment process A method for regenerating an ion exchange resin, including the above, is provided.</p><p num="0032"> In another embodiment, the amine treatment equipment process processes the supply gas to SO.₂, H₂S and CO₂Remove one or more of.</p><p num="0033"> In another embodiment, during step (c), the anion exchange resin is treated to remove the amine solvent from the resin before the anion exchange resin is regenerated.</p><p num="0034">In another embodiment, step (c) is (a) Bringing the anion exchange resin into contact with water to wash away the amine solvent from the anion exchange resin, (b) Subsequently, the anion exchange resin was brought into contact with the regenerating agent to obtain the regenerated anion exchange resin and the used regenerating agent solution. (c) Rinse the anion exchange resin with water to remove the regenerating agent from the resin, and obtain the regenerating agent cleaning wastewater. including.</p><p num="0035"> In another embodiment, the method further comprises rinsing the regenerated anion exchange resin with water to remove the regenerating agent from the resin before using the regenerated anion exchange resin in step (b). ..</p><p num="0036"> In another embodiment, the method (a) A step of performing a pre-cleaning operation on the supply gas stream supplied to the amine treatment equipment process, and (b) With the step of using all or part of the used regenerant solution and one or both of the regenerant wash drainage in the pre-cleaning operation. Including further.</p><p num="0037"> In another embodiment, the method further comprises removing the amine solvent from the anion exchange resin before contacting the anion exchange resin with water to wash away the amine solvent from the anion exchange resin.</p><p num="0038"> In another embodiment, the thermostable salt dilute amine is recycled into the amine treatment equipment process.</p><p num="0039"> In another embodiment, reflux is utilized undiluted to flush the amine solvent from the anion exchange resin.</p><p num="0040"> These and other advantages of the present invention will be more fully and fully understood by the description of preferred embodiments of the present invention below.</p>

In one aspect, the invention is intended for a regeneration step for an ion exchange device that processes an amine solution, but the present invention is exemplified in combination with an amine treatment device step.

As shown in FIGS. 1 and 2, the ion exchange apparatus (FIG. 2) can be integrated with the amine treatment apparatus step (FIG. 1) to remove the thermostable salt from the amine solvent. It is well understood that any particular design known in the art can be used for amine treatment equipment and ion exchange equipment, and the embodiments shown in FIGS. 1 and 2 are exemplary. Will be. For example, the supply gas can contain either a single target gas (eg, sulfur dioxide) or multiple target gases (eg, sulfur dioxide and carbon dioxide). If multiple gases are targeted for removal from the feed gas, the amine treatment equipment may have multiple absorption zones, each utilizing a different solvent stream, thereby creating multiple solvent streams, which they produce. Can be played individually. For example, the first solvent loop may be provided using the first solvent to remove sulfur dioxide from the acid gas, and the first solvent may be regenerated. The second solvent loop is provided using the second solvent to remove carbon dioxide from the acid gas following sulfur dioxide, and the second solvent may be regenerated. The first ion exchange device may be used to remove the heat-stabilizing salt from the first amine absorber, and the second ion exchange device may be used to remove the heat-stabilizing salt from the second amine absorber. It may be used for. Each ion exchange device may include one or more ion exchange reactors or towers, ensuring continuous supply to the ion exchange towers as is known in the art, and rapid throughout the process. It will also be well understood that supply and storage tanks, such as those used to reduce variability, may be utilized.

Supply gas stream is only one or more acid gases, eg SO₂And / or H₂S and / or CO₂It will be appreciated that the supply gas streams can be sequentially treated at different stages to reduce the concentration of each acid gas below a predetermined level. Therefore, the feed gas stream is brought into contact with the first amine solvent and the first acid gas, eg SO₂The concentration of can be reduced below a predetermined level. This supply gas stream is then contacted with a second amine solvent to bring a second acid gas, eg CO₂And / or H₂S can be selectively captured from the supply gas stream. The feed gas stream is then contacted with a third amine solvent and a third gas, eg NO_xCan be selectively captured from the supply gas stream. Alternatively, two or more gases can be removed in one treatment step. Therefore, one solvent can be used to capture two or more gases from the feed gas stream. The feed gas stream can be captured by the iron (II) EDTA complex NO_xIt will be well understood that it may include. NO from the gas stream_xThe FeEDTA (nitrosyl) salt formed by the absorption of is removed by the ion exchange resin, so that the heat-stable salt is a renewable NO._xIt is preferred to remove it from the absorbent by other means known in the art. Therefore, the ion exchange steps presented herein are a gas trapped in an amine (ie, a gas that can be stripped from a feed gas by an amine solvent, eg, SO.₂, H₂S, CO₂) Is preferably used in combination with the regeneration of the absorbent used in the capture step.

Thermostable salts may accumulate in each solvent. Therefore, at least a part of each solvent may be separately supplied to the ion exchange device to remove the heat-stabilizing salt from the solvent. Therefore, the first solvent may be supplied to the first ion exchange tower and the second solvent may be supplied to the second ion exchange tower. In this way, each solvent can be circulated in separate loops to prevent mixing of different solvent streams. Alternatively, each solvent can be treated separately in one ion exchange device.

The supply gas provided to the amine treatment equipment process may be any gas stream containing at least one acid gas. Preferably the supply gas stream is SO₂, CO₂And H₂Contains at least one of S, more preferably at least SO₂And CO₂Contains. The supply gas may be a process gas stream or a waste gas stream obtained from various sources. For example, the supply gas stream may be: (a) Acidic natural gas containing methane, other hydrocarbons, hydrogen sulfide, carbon dioxide and water, usually at high pressures below 100 bar and medium temperature near ambient temperature. (b) Sulfur-free fossil fuel combustion emissions, nitrogen, oxygen, carbon dioxide and water, close to atmospheric pressure, temperatures up to 200 ° C or higher. (c) Combustion exhaust gas of sulfur-containing fuels containing nitrogen, oxygen, carbon dioxide, sulfur dioxide, sulfur trioxide and water and having a high temperature of 200 ° C or higher at substantially atmospheric pressure. (d) Sulfuric acid plant exhaust gas containing nitrogen, oxygen, sulfur dioxide and sulfur trioxide, close to atmospheric pressure and at slightly higher temperatures below 200 ° C.

Sulfur dioxide dissolves in water and when it reacts with water, sulfurous acid, H₂SO₃Produces carbonic acid, H, which is produced by the hydration of carbon dioxide₂CO₃(pKa1 = 6.4), or an acid (pKa1 = 1.8) that is significantly stronger than hydrogen sulfide (pKa1 = 7.0). If it is desired to capture sulfur dioxide from the feed gas using a renewable amine treatment equipment process, it is preferable to use a reasonably weak amine with a pKa of less than 6. Weak amines have a significant amount of CO₂Cannot be captured, so CO₂Stays in the treated gas. Therefore, such weak amines are SO₂And CO₂SO from the supply gas containing₂Can be used to selectively capture. Sulfate mist (pKa2 = -3) is a renewable SO₂Strong enough to form a thermostable salt with the solvent.

SO₂The alkanolamine solvent used to selectively capture the alkanolamine may be any of those disclosed in US Pat. No. 5,019,361, and the disclosure of this patent is incorporated herein by reference. In particular, this solvent can be represented by the following structural formula.

<chemistry num="1"><img id="000002" he="25" wi="26" file="JP5344934B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry>In the formula, R¹Is an alkylene with two or three carbon atoms, R², R³, R⁴, And R⁵Can be the same or different, hydrogen, alkyl (eg, lower alkyl containing 1 to about 8 carbon atoms, including cycloalkyl), hydroxyalkyl (eg, lower of 2 to about 8 carbon atoms). Hydroxyalkyl), aralkyl (eg, 7 to about 20 carbon atoms), aryl (preferably monocyclic or bicyclic), alkalinel (eg, 7 to about 20 carbon atoms). Well, R², R³, R⁴, And R⁵Can all form a cyclic structure. Diamines are organic compounds containing two nitrogen atoms, which are often preferred because they are commercially available and generally have a lower viscosity. Amines, such as diamines, are preferably tertiary diamines from the standpoint of their stability. However, others can also be used in the presence of weakly oxidative or thermal conditions that minimize the chemical reaction of the solvent. Often, preferred amine salt absorbers have a hydroxyalkyl group as a substituent on the amine group. In some cases, hydroxy substituents are thought to delay the oxidation of sulfites or hydrogen sulfites to sulfates.

To allow a high input of recoverable sulfur dioxide to be absorbed into the absorption medium under atmospheric pressure conditions, the free amine form of the amine absorber has a molecular weight of less than about 300, preferably less than about 250. It is preferable to have. Often the tertiary diamine is of the following equation:

<chemistry num="2"><img id="000003" he="25" wi="25" file="JP5344934B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry>In the formula, R¹Is an alkylene group, preferably containing 2-3 carbon atoms as a straight chain or as a branched chain, and each R²Are the same or different, alkyl groups, preferably methyl or ethyl, or hydroxyalkyl groups, preferably 2-hydroxyethyl. Specifically, preferred compounds are N, N', N'-(trimethyl) -N- (2-hydroxyethyl) -ethylenediamine (pKa = 5.7), N, N, N', N'-tetramethylethylenediamine ( pKa = 6.1), N, N, N', N'-Tetramethyl (2-hydroxyethyl) ethylenediamine (pKa = 4.9), N- (2-hydroxyethyl) ethylenediamine (pKa = 6.8), N, N'-dimethyl Piperazine (pKa = 4.8), N, N, N', N'-tetrakis (2-hydroxyethyl) -1,3-diaminopropane, and N', N'-dimethyl-N, N-bis (2-hydroxy) Ethylenediamine. Among the similarly useful diamines are heterocyclic compounds such as piperazine (pKa = 5.8). The pKa value is related to sorbed nitrogen.

H₂S and / or CO₂If you want to capture a weakly acidic gas such as, it is preferable to use a stronger amine with a pKa&gt; 7.5 such as monoethanolamine, diethanolamine or methyldiethanolamine. H₂Acids that are significantly stronger than S and carbonic acid form thermostable salts. An example is SO₂, Formic acid, acetic acid, hydrochloric acid, sulfuric acid and thiocyanic acid.

The carbon dioxide solvent amine is a primary, secondary or tertiary amine having a pKa in the range of 6.0 to 10, preferably 6.5 to 10, more preferably 6.5 to 9.5. Preferred amines to prevent loss of amines with the gas being treated preferably have a vapor pressure of less than 1 mmHg above the solvent at 50 ° C. Preferred amines include 4- (2-hydroxyethyl) -1-piperazineethanesulfonic acid (pKa = 7.5), morpholinoetansulfonic acid (pKa = 6.1), N- (2-hydroxyethyl) ethylenediamine (pKa1 = 9.5, pKa2 = 6.5), piperazine (pKa1 = 9.8, pKa2 = 5.6), N- (2-hydroxyethyl) piperazine (pKa1 = 9.0, pKa2 = 4.5), benzimidazole (pKa = 5.5), and N, N'-bis Includes (2-hydroxyethyl) piperazine (pKa1 = 7.8, pKa2 = 3.9) and mixtures thereof.

SO₂And CO₂If you want to capture both, CO₂SO in the capture process₂In order to avoid all of the formation of thermostable salts, preferably first SO₂With a suitable solvent. Then in the second step CO₂To remove. Hydrogen sulfide is SO₂Or because it is not thermodynamically stable in the presence of oxygen, SO₂Or O₂It is generally present in the containing stream in very small concentrations.

In a preferred embodiment of FIG. 1, the supply gas stream 12 processed by the amine treatment apparatus 10 is a single target gas that can be captured by an amine, such as SO.₂Contains. As shown in FIG. 1, preferably, the feed gas stream 12 is first pre-washed to remove particulate matter from the feed gas stream 12, and preferably quench to at least near its adiabatic saturation temperature. In some cases, the supply gas temperature can even be lowered by providing a heat exchanger that cools the circulating water. This pretreatment with water can also remove other contaminants such as hydrochloric acid and sulfuric acid from the supply gas. Any pre-cleaning device known in the art can be used. As shown in FIG. 1, the supply gas stream 12 may be supplied to the pre-cleaning device 14, where it may be brought into contact with the pre-cleaning stream 16, preferably water, in a countercurrent manner, where the pre-cleaning liquid is pre-prepared through a suitable nozzle 18. It may be sprayed into the cleaning device 14. The pre-cleaning fluid stream 16 is preferably recirculated. Therefore, the recycle stream 20 can be supplied to the pump 22, from which the return stream 24 is returned to the pre-cleaning device 14. Extraction streams 26 to waste can be used to control the levels of dissolved and suspended solids in recirculated water, and hydration streams 28 can be used to evaporate and release into the feed gas. Can replace the water.

After passing through the optional pre-cleaning device 14, the pretreated supply gas stream may then pass through the absorption zone 30 in the column 32, which zone may be the sulfur dioxide absorption zone. The pre-cleaned gas 34 can flow from the pre-cleaning device 14, for example, through the chimney tray 36 to the absorption tower 32, where the chimney tray passes the gas upwards, but the liquid enters the pre-cleaning device 14. Prevent it from running down.

The dilute (ie, acid gas impurities are dilute) amine solvent is preferably a regenerated solvent and can be introduced into the absorption tower 32 by stream 38, where the pretreated feed gas 34 is preferred. The stream is brought into contact with a countercurrent to produce a concentrated amine solvent stream 40 and a treated supply gas stream 42. Preferably, the dilute amine solvent stream 38 flows downward, eg, through a filler in the absorption zone 32, which facilitates good gas-liquid contact with the upwardly flowing gas. The dilute solvent selectively traps acid gas impurities and leaves the absorption tower as a concentrated solvent stream 40.

The treated supply gas stream 42 is then introduced into one or more additional absorption zones (not shown), released to the atmosphere, sent to additional equipment for further treatment, or recycled in-process. be able to. For example, a second absorption zone can be designed to remove carbon dioxide from the gas stream. NO from the supply gas stream to the third absorption zone_xAnd it can be optionally designed to remove some mercury. It will be well understood that acid gases can be selectively removed from the feed gas in any desired order. For example, carbon dioxide absorption zones are sulfur dioxide and NO_xIt may be upstream or downstream of the absorption zone. But SO₂Is more likely to form thermostable salts in solvents for weaker acids, so SO before other impurity gases₂It is preferable to capture.

The trapped contaminants are removed from the concentrated amine solvent stream by heating the stream to release the trapped contaminants. Preferably, a steam stripping tower is utilized in which the steam provides at least a portion of the heat required to release the trapped contaminants from the solvent. As shown in FIG. 1, the concentrated amine solvent stream 40 and the hot dilute amine solvent stream 46 can be passed through the indirect heat exchanger 44 to generate the hot concentrated amine solvent stream 48, which is steam stripping tower 50. Introduce to.

Like the absorption tower 32, the steam stripping tower 50 may be of any design known in the art and may be either filled or trayed. The hot concentrated amine solvent stream 48 preferably flows downward through, for example, the filling 52 in the regeneration or steam stripping column 50. The hot concentrated amine solvent stream 48 is introduced into the upper part of the column 50 and flows downward through the column 50. If desired, a pump 64 is used to circulate the stream 66 from the bottom of the regeneration tower 50 to the reboiler 54. It will be well understood that the reboiler 54 may be a forced circulation reboiler, a can reboiler or a thermosiphon reboiler. Preferably, a pump for hot dilute amines is provided to push this solvent through a dilute-rich exchanger into a dilute amine surge tank (not shown). The steam generated by boiling the amine solvent in the reboiler 54 enters tower 50 as a stream 60, providing energy and mass transfer facilitation for acid gas stripping from the amine solvent.

The reboiler is heated by any means known in the art. Preferably, the reboiler 54 is heated indirectly by the stream 56 (which may be steam or may be obtained from any source), for example through a heat transfer tube bundle, to produce a steam condensate stream 58, which further produces steam. It may be recycled for use or used elsewhere in the plant. Boiling of the solvent in the reboiler 54 creates a flow of steam and desorbed acid gas 60 into the tower 50. The steam and desorbed acid gases heat the downward stream of the hot concentrated amine solvent stream 48 and carry the gaseous contaminants generated from the solvent upwards through the desorption zone (filling 52) of column 50. Climb upwards. Steam and contaminants (in this case sulfur dioxide) exit tower 50 as stream 62. Preferably, the steam and deabsorbed acid gas leave the tower 50 as a stream 62 after moving upward through the reflux-rectification compartment 68 of the regeneration tower 50.

The stream 62 is cooled in the top condenser 70, which condenses most of this stream to form a two-phase stream 72, which is the top liquid reflux stream 76 and acid gas stream 78 in the reflux reservoir 74. It should be separated into. Acid gas can flow to disposal or further processing. The column top reflux stream 76 is divided into a stream 80 used in the ion exchange process and a stream 82 returning to the regeneration column 50 so as to return to the amine solvent.

The regenerated solvent collects at the bottom of column 50 and is removed from column 50 as stream 66, a portion of which is recycled as regenerated hot dilute amine solvent stream 46. The dilute amine from the bottom of the regeneration tower 50 flows as a stream 46 through the heat exchanger 44 to form a cold dilute amine stream 84.

Thermostable salts tend to accumulate in amine solvents. Therefore, the amine solvent is subjected to an ion exchange step to remove the heat-stabilizing salt. For example, at least a portion of the amine solvent is ion exchanged to remove the thermostable salt from it, preferably only a portion thereof (eg, bleed stream). Preferably, the bleed stream is extracted from the cold dilute amine stream 84. According to such an embodiment, as shown in FIG. 1, the stream 86 sends the concentrated amine solvent of the heat-stable salt to the ion-exchange heat-stable salt removing device 90. The ion exchanger 90 returns a first thermostable salt dilute amine solvent stream 88 with a lower thermostable salt content. Stream 38 sends the dilute amine solvent to absorption tower 32 for acid gas cleaning to complete the circuit.

As is known to those familiar with the art, the details of the amine treatment equipment process can be modified or added without changing the general principles or their suitability for the present invention. For example, various types of devices for providing gas-liquid contact in absorbers and regenerators can be used to achieve absorption and stripping of the same effect. Other flow sheets, such as those with dilute and semi-dilute amine streams, can also be used in the application of the present invention.

FIG. 2 shows an embodiment of an ion exchange device 90 that can be used according to the present invention. As shown herein, the ion exchange device 90 includes an optional surge tank 92 and a single ion exchange tower 94. The ion exchange resin in the ion exchange tower 94 must be regenerated from time to time, but periodically (ie, sometimes as needed) stops the flow of the heat stable salt concentrated dilute amine solvent stream 96 through the ion exchange tower 94. It will be well understood that it enables the regeneration of ion exchange resins. It will be well understood that in one alternative embodiment, a plurality of ion exchange towers 94 may be provided. Thus, the heat-stable salt-rich dilute amine solvent stream 96 can be continuously fed through at least one ion exchange tower 94 to remove the heat-stable salt from this stream, during which one or more replacement towers 94. The ion exchange resin inside is regenerated.

Any structure known in the art for ion exchange reactors can be utilized. Usually, the ion exchange medium is a resin formed as beads. Therefore, the ion exchange tower usually has a support that receives the ion exchange resin beads. Therefore, the ion exchange medium may be polymer beads having functional groups on the polymer. Anion exchange resins generally have a basic functional group as an exchange site. Various ion exchange resins can be used in the method of the present invention. Strongly basic anion exchange resins are usually characterized by having fixed quaternary amine anion exchange sites, which are positively charged at any pH. Weakly basic anion exchange resins have immobilized primary or secondary amine anion exchange sites. These sites are positively charged depending on the pH of the solution. At higher pH these sites are neutral.

The type I strong basic resin contains a tetramethylammonium functional group. Type II strong basic resins generally contain a hydroxyethyltrimethylammonium functionalizer. An example of a strong basic type I anion exchange resin has a quaternary ammonium group attached to the polymer backbone. styrene - divinylbenzene resin, for example Resintech sold by Resintech Company (TM) SBG-1 and Sybron (TM ) ASB-1. Strongly basic type II anion exchange resins include styrene-divinylbenzene resins with quaternary alkanolamine groups attached to the polymer skeleton, such as Resintech SBG-II and Sybron , also available from the Resintech Company. ASB-II is included. Other resins that can be used include Bayer AG's Mobay M500, a type I strong basic anion exchange resin that is a polystyrene resin with a quaternary ammonium group attached to the polymer skeleton; Rohm and Haas Amberlyst A-26, Type I strongly basic anion exchange resin, a styrene-divinylbenzene copolymer with a quaternary ammonium group attached to the polymer backbone; and Rohm and Hass Amberlite IRA-410 , Type II strongly basic amine type anion exchange resin and other materials are included. Also included is a styrene-divinylbenzene strong basic anion exchange resin having a quaternary amine as the Dow functional group. These materials are available under the DOWEX trademark. Weakly basic acrylic gel resins, such as those supplied by Purolite , can also be used. Both gels and macroporous resins can be used.

The aforementioned resins merely exemplify useful ion exchange resins and are not intended to limit the resins that can be used in the practice of the methods of the invention. For the purposes of the present invention, it is intended that any ion exchange resin used for the regeneration of used amine solvents can be regenerated using the methods disclosed herein. These resins can be easily identified by those skilled in the art.

A stream that may simply be an extension of the bleed stream 86 if the heat stable salt concentrated dilute amine solvent stream 96 (which can be obtained from the surge tank 92) or the surge tank 92 is not provided is flowed through the ion exchange tower 94. The first thermostable salt dilute amine solvent stream 88 is produced. This is a step of putting into resin or a step of exhausting resin. During this step, the resin in column 94 interacts with the amine solvent to remove the thermostable salt from the amine solvent. When the ability of the ion exchange resin to remove the thermostable salt from the amine solvent reaches a desired level, or after a predetermined time, the flow of the amine solvent through the column 94 is stopped.

Since ion exchange resins also tend to react with the amine-absorbable gas anions present in the amine solvent, the thermostable anions are amine-absorbable gases with respect to amine-absorbable gases rather than concentrated amine solvents. It is preferable to remove it from the dilute amine solvent. Therefore, by supplying the dilute amine solvent to Tower 94, a larger proportion of the ion exchange resin can be associated with the thermostable salts present in the dilute amine solvent rather than anions such as sulfite roots from a gas that can be absorbed by the amine. Interact. Therefore, a larger amount of thermostable salt per unit volume of the amine solvent passing through the ion exchange tower will be removed from the amine solvent.

As a result of the interaction of the amine solvent with the ion exchange resin, the amine solvent is converted to its free base form. The amine solvent with the reduced concentration of the thermostable salt (ie, the first thermostable salt dilute amine solvent stream 88) is then returned to the amine treatment apparatus 10. The first thermostable salt dilute amine solvent stream 88 can be returned to any desired position in the amine treatment equipment process, preferably downstream of the heat exchanger 44 and in tower 32 as shown in FIG. Introduce upstream.

Some amine treatment equipment steps can work at significant levels of the thermostable salts present (see, eg, US Patent Application No. 10/639678). In such a case, the thermostable salt is only partially reduced, but the ion-exchange resin is still thermally stabilized before the ion-exchange resin is regenerated by passing the column 94 through a sufficient thermostable salt-containing amine solvent. It is desirable to completely saturate with the sex anion. This maximizes the efficiency of the ion exchange process with respect to the loss of amine per unit amount of anion removed as well as the amount of regenerant and rinse required.

Following this exhaustion step, preferably the ion exchange resin is treated to remove the amine solvent from the resin before initiating the regeneration step. Therefore, according to the present invention, preferably the ion exchange resin is brought into contact with a wash stream which may be acidic to remove the amine solvent from the column 94.

Reflux after passing through column 94 produces a second thermostable salt dilute amine solvent stream 98 by adding water into the portion fed to column 94 of the reflux stream 80. The concentration of amines in stream 98 is low compared to the amines circulating in the amine treatment apparatus 10. However, by recycling the stream 98 to the amine treatment device 10, all the water and amines that are essentially directed to the ion exchange device 90 are returned to the amine treatment device 10, thereby essentially imbalance the mass balance of the amine treatment device 10. Maintain and thus prevent the dilution of amines in the amine treatment equipment 10 that occurs when fresh water is used for the washing step instead of reflux 80.

It will be well understood that in an alternative embodiment, some make-up water can be added to the reflux stream 80 if desired. The amount of reflux produced is small due to the low amount of steam required for regeneration, but additional wash water is required if the rate of accumulation of heat stable salts is high and high availability of the IX exchanger is required. The need may arise. Up to 3 parts of water can be added to 1 part of reflux, but it is preferable to add as little as possible.

The stream 98 can be returned to the continuous amine loop in the amine processor 10 downstream of heat exchanger 44 and upstream of tower 32 (similar to stream 88). Alternatively, the stream 98 can be returned to the steam stripping portion of the amine processing equipment process (may be added to one or both of the streams 82 and 48). Such an alternative route is that the gas that can be absorbed by amine is SO.₂Can be used when.

A further advantage of utilizing reflux to flush the amine from column 94 is the metal cation precipitated from the amine (eg Fe).³⁺) Or the metal cations (eg, calcium carbonate) deposited in the ion exchange tower from the solid suspended in the amine are likely to be resolubilized. If these metal cations are not resolubilized, they can impede the flow of liquid through the ion exchange tower or interfere with the transport of anions in and out of the resin.

Preferably, the ion exchange resin is washed with deionized water or steam condensate at the end of the washing step and before the regeneration step. This water can be supplied by stream 100. This wash water is supplied from the tower 94 to remove reflux. The wash water 100 that has passed through the tower 94 becomes the wash drain stream 102 and can be put into the storage tank 104 for reuse.

Subsequently, the ion exchange resin is regenerated using a regenerating agent. For example, the regenerant may be a caustic solution (eg, a 4% sodium hydroxide solution) and is supplied by stream 106. The regenerant converts the ion exchange resin into its original form. Therefore, when the ion exchange resin is an anion exchange resin and the regenerating agent is caustic alkali, the caustic alkali uses the ion exchange resin in its basic form (for example, in the case of a weak basic resin, it is a free amine, and in the case of a strongly basic resin. Is converted to the hydroxide form). As a result of the regeneration step, a used regeneration agent solution 108 is produced. The stream 108 may be fed to the pre-cleaning tower 14 (which forms part or all of the stream 28). Therefore, the water in stream 108 can be used to quench the supply gas. In addition, all unreacted caustic alkali can be utilized to neutralize strong acids such as sulfuric acid present in the pre-scrubber water stream 20.

Following the regeneration step, the ion exchange resin is washed again to remove the caustic alkali from the resin. Therefore, fresh water and / or water from the tank 104 can be supplied to the ion exchange tower 94 by the stream 110. Expulsion of the caustic alkali regenerant from the ion exchange bed avoids contamination of the amine solvent with caustic alkali or sodium salts during the next charging step. Used wash water containing some caustic alkali may also be sent to the pre-wash tower by stream 28.

Preferably, the final ion exchange resin wash is performed with deionized water or steam condensate supplied by Stream 100 to remove additional amounts of caustic alkali and salt from the ion exchange resin. Since this used wash water has a relatively low dissolved caustic solvent (concentration), the wash water can be sent to tank 104 by stream 102 for reuse. After the final cleaning step, the next resin charging step can be started.

Removal of the heat-stable salt from both the strong amine solvent and the weak amine solvent can be carried out by essentially the same method, depending on the type of resin, the type and amount of regenerant, and the specific amine solvent and heat-stable salt of each. It has been found that only optional adjustments can be made to the rinse volume required to optimize for the type of solvent.

It will be well understood that various modifications and modifications can be made and that all of these modifications and modifications are within the scope of the ancillary claims. For example, which SO known in the art₂, CO₂And H₂It can also be used in S solvent. These solvents can be regenerated and recycled, in which case they can be regenerated and recycled by any means known in the art. Surge tanks and storage tanks can be used in ion exchange equipment to store various streams used in or produced by ion exchange equipment. Any ion exchange resin or series of resins known in the art can be used. It will also be well understood that this step can be done in various combinations or even partial combinations.

The operation of the present invention is exemplified by the following typical examples. As will be apparent to those skilled in the art of ion exchange, many details of the examples can be modified while still practicing the inventions described herein.

The operation of the present invention was tested in a pilot plant. Diamine SO with 26.9% amine, 12.5% sulfate and 1.8% sulfite₂Experiments were conducted on the removal of thermostable salts from the absorbent (Cansolv Absorbent DM). The concentration of the thermostable salt (sulfate) in this amine solvent was 1.36 mol / molamine. A 6 inch diameter ion exchange tower was filled with Purolite A-830 weakly basic resin up to a height of 21.3 inches, equivalent to a 10 liter resin floor volume (BV). The liquid from the heating tank was supplied to the ion exchange tower by a centrifugal pump. Appropriate valves, pressure gauges, thermometers and rotor meters were installed for the safe and easy-to-use operation of the device. All fluids were heated to 50 ° C. SO₂A synthetic reflux solution was prepared by bubbling the gas into water until it reached a nominal concentration of 1.5% (pH = 1.5).

The analysis of amines and anions was performed by ion chromatography, and low concentrations of sodium ions were quantified using a calibration curve by conductivity measurement. Low concentrations of amines in the aqueous matrix were quantified by gas chromatography. The operation cycle of the process consisted of the following sequence. The thermostable anion is charged into the resin by passing it through a tower in a 1.4 BV amine solvent. 2. Extrude the amine solvent from the resin with a 25.25 BV reflux solution to wash away the amine. Replace the reflux fluid with 3.0.5 BV of deionized water. The resin is regenerated and regenerated by passing it through a column of 4.4 BV of 4% sodium hydroxide. Final wash with water left from the end of the final wash of the 5.1.5 BV preceding batch, and then with 4.5 BV deionized water. 6. The following input steps were performed.

The experimental sequences averaged over a number of cycles with the following results: 1. 100 grams of SO per liter of resin₄^2-Was obtained. 2. The amine loss was removed from the amine solution, mainly due to incomplete removal of the amine from the column by reflux washing.₄^2-It was 21 grams per kilogram. 3. During one cycle, about 0.4% of the amines returned to the treatment agent step (eg amine 26,) due to water contamination in the amines at the interface between the final wash of the preceding cycle and the amines of the next cycle. 9% to 26.8%) diluted. If the amine wash water was from an external source, the dilution would have been 34% (26.9% to 17.8%). This final concentration of amine is calculated as the sum of the interfacial mixing of 4 BV amine solvent (0.2 BV water) and the dilution of 2.25 BV wash water.

<figref num="1">It is a process flow diagram which becomes an example of an amine processing apparatus process, and shows the stream which connects it to the ion exchange process by one Embodiment of this invention.</figref><figref num="2">FIG. 5 is a diagram of an embodiment as an example of a process flow chart of an ion exchange process that can be used together with the amine treatment apparatus process of FIG. 1, and shows a stream connecting the same to the amine treatment apparatus process according to the embodiment of the present invention. There is.</figref><figref num="3">It is a preferable sequence diagram of the operation of one cycle from the exhaustion of the resin of the ion exchange tower operation to the final washing with water after regeneration.</figref>