Purification method for efficiently removing desulfurization amine liquid degradation product

Abstract

The invention relates to an efficient purification method of a flue gas desulfurization amine liquid, which comprises the following steps: adding a composite purifying agent into a regeneration lean agent to be purified, simultaneously continuously introducing nitrogen for steam stripping, and after the composite purifying agent is completely added, continuously introducing nitrogen for steam stripping for at least 3 minutes; and after steam stripping is finished, cooling the obtained mixed solution to 20-45 DEG C, standing, layering and separating to obtain a free amine solution on the upper layer and a saline solution containing sulfate radicals and degradation products on the lower layer. According to the purification method, a steam stripping coupling salting-out mode is utilized, organic amine degradation products and sulfate radicals can be synchronously and efficiently removed, the removal rate of one-time purification is high, and the device is easy and convenient to operate, low in energy consumption, small in amine loss and small in amine-containing wastewater discharge and meets the new requirement for clean production of the dual-carbon target.

Description

Technical Field

[0001] The invention relates to the energy-saving and environmental protection industry, belongs to the field of waste gas separation and treatment, specifically to the technical field of improving the service life of flue gas desulfurization agents, and particularly to a purification method for efficiently removing degradation products of desulfurization amine liquid. Background Art

[0002] In recent years, organic amines have been widely used in the industry for flue gas desulfurization. During use, the problem of decreased desulfurization performance of the system amine liquid has become increasingly prominent due to the accumulation of heat-stable salts, degradation products, corrosion products, etc.

[0003] At present, there are many studies on the purification methods of flue gas desulfurization agent amine liquid, such as ion exchange amine liquid purification method. Such studies include: Patent CN 111701397A discloses a process for removing sulfate ions and chloride ions from organic amine desulfurization solution and reducing the loss of organic amine solution, using ion exchange to remove sulfate; Patent CN211999296 U discloses a method for removing sulfate from flue gas desulfurization agent amine liquid by connecting an ion exchange resin bed and freezing crystallization in series, which requires deep cooling to 0-2°C. Such methods usually have problems such as high waste liquid generation and still large amine loss, and the industrial application value is not high.

[0004] Patent CN 102858430 A discloses a method for removing sulfate from an absorbent by a phase separation method, wherein an acidic gas absorbent is mixed with an alkaline solution to form a mixture with a pH value higher than the pH equivalent point of the amine; the mixture is cooled to a temperature below 50°C, and the regenerated acidic gas absorbent is separated. Although this method avoids waste liquid caused by ion exchange and reduces amine loss to a certain extent, there are still many unresolved problems in this method, including the problem of selecting the appropriate solubility of the amine type, long standing separation time, large amine loss, etc., resulting in its purification efficiency is still low and no industrial application has been seen.

[0005] The above patented technology mainly focuses on the removal of heat-stable sulfate in organic amine solution of flue gas desulfurizer, but practice has proved that starting from this perspective cannot solve the problem of purification of organic amine solution of flue gas desulfurizer well, and the purification effect is not ideal. For industrial devices using organic amine flue gas desulfurization, most of the devices still encounter the following confusion while adopting the above-mentioned measures to remove heat-stable salts: the initial operation is good, and the desulfurization effect and various indicators are all normal; but after long-term operation, the effect gradually deteriorates, and some enterprises even have the phenomenon of all amine liquid failure. The main manifestations are: ① The amine concentration and pH value are both within the normal range, and the purification unit for removing heat-stable salt also operates normally, but the desulfurization ability of the solvent deteriorates; ② The amount of solvent regeneration steam is much higher than the design value, but the sulfite content in the lean agent is still high, and the desulfurization is unqualified; ③ Even if the resin in the heat-stable salt purification unit is newly replaced, the sulfate content in the solvent is still high, and the desulfurization effect has not improved much; ④ The amine concentration and pH value are both within the normal range, but the desulfurization effect deteriorates, and it can only rely on large amounts of alkali injection to control emissions to meet standards, resulting in large amounts of alkali waste and slag discharge, and serious deterioration in economic efficiency.

[0006] In order to find out the reason why "the amine concentration and pH value are both within the normal range, but the desulfurization effect is poor", the inventors conducted a lot of experimental research. During the experiment, it was first found that there was a large amount of NH4 + , through ion chromatography analysis, it was further found that there were other unknown peaks in the desulfurization solvent. After chemical purification and comparison with chromatograph and mass spectrometer standards, it was confirmed that the unknown peak was MEA. In the actual flue gas desulfurization process, the organic amine desulfurizer is in an oxygen-containing, low pH operating environment. Theoretically, it is inferred that NH4 + Both NH4 and MEA are produced by the degradation of desulfurizers. Therefore, a degradation experiment was conducted on the new desulfurizer under simulated production conditions, and NH4 was indeed found in the experimental products. + and MEA chromatographic peaks (see chromatograms before and after degradation Figure 1 ), and finally determined that NH4 + Both MEA and desulfurizer are produced by degradation of desulfurizer.

[0007] The inventors further discovered that the degradation product NH4 + The presence of NH4 and MEA seriously affects the correct judgment of the effective amine concentration of the system based on the titration method and the half-acidification ratio of the amine based on the pH value, and is also the fundamental reason why sulfate ions are difficult to remove. +and MEA exist in the form of ammonium sulfate and sulfate of MEA. After analyzing the amine concentration by acid-base titration, it was found that the sulfate of ammonium sulfate and MEA would consume alkali, making the effective amine concentration analysis too high, resulting in a misjudgment of the effective amine concentration. In addition, the pH value of ammonium sulfate and sulfate of MEA is between 5-6, which will also have a certain buffering effect on the pH of the amine solution that generates heat-stable salts; when the heat-stable salts in the system increase, the pH value of the lean agent should be lower than the normal operating value of pH 5.5-6.0; if the desulfurized amine solution is completely bound and turned into heat-stable salts, the pH value should be around 3. However, due to the buffering effect of the sulfate of ammonium sulfate and MEA, the actual measured pH value is still between 5-6, resulting in a misjudgment of the semi-acidified state of the amine solution. These two misjudgments have led to blind operation in actual production.

[0008] In order to solve the above problems in production practice, it is necessary to remove the degradation product NH4 in the desulfurization amine solution in a targeted manner. + and MEA. However, in the prior art, the ion exchange resin method cannot remove the sulfate of ammonium sulfate and MEA. In order to ensure the regeneration performance, the resin used in the ion exchange resin method is weakly alkaline, and the alkalinity of the resin is weaker than that of sodium hydroxide, ammonia water and MEA, so the sulfate of the organic amine heat-stable salt can be removed by anion exchange resin, but the sulfate of the degradation product cannot be removed. Moreover, the degradation product sulfate will cause pH interference, resulting in misjudgment of the purification degree of the effective amine heat-stable salt, and ultimately causing over-purification. The result of over-purification is that all the sulfates bound to the dinitrogen organic amine are removed, and both nitrogen atoms will be bound to sulfites, which eventually leads to the problem of difficulty in regenerating sulfites. Therefore, in practice, this situation occurs: the amount of solvent regeneration steam is much higher than the design value, but the sulfite content in the lean agent is still high, and the desulfurization is unqualified. In addition, since the sulfate solubility of ammonium sulfate and MEA is large and the content does not reach the saturation amount, the existing freezing desalination method can only remove sodium sulfate salts, and cannot remove the sulfates of ammonium sulfate and MEA. The method disclosed in CN 102858430A for removing sulfate from the absorbent by phase separation does not remove the degradation product NH4 + The problem of selecting suitable amine solubility is solved from the perspective of MEA. Therefore, although a lot of time is spent on adding materials and stratification, the purification efficiency of degradation products is actually very low. The accumulation of degradation products in the system after long-term online purification will still cause people to misjudge the amine concentration in the device and the semi-acidified state of the ionic liquid.

[0009] It can be seen that the degradation product NH4 in the desulfurization amine solution + MEA and its sulfate interfere with or destroy the normal operation of the amine desulfurization process. It is difficult to overcome or eliminate this problem using existing purification methods. It is necessary to develop targeted removal methods to solve the above problems in production practice. Summary of the invention

[0010] In view of the fact that the inventors found that the degradation product NH4 + and MEA are the fundamental reasons that affect the normal operation of the device. The purpose of the present invention is to provide a method for efficiently removing the degradation product NH4 in the desulfurization amine solution. + The method of using MEA can achieve good removal capacity with simple operation method, ensuring the long-term stable operation of the desulfurizer.

[0011] In order to achieve the above object, the present invention provides the following technical solutions:

[0012] A method for efficiently removing NH4, a degradation product of flue gas desulfurization amine liquid + A method for purifying MEA comprises the following steps:

[0013] 1) Add the composite purifier to the regenerated lean agent to be purified, and continuously introduce nitrogen for stripping. After the purifier is added, continue to introduce nitrogen for stripping for at least 3 minutes.

[0014] 2) After the stripping described in 1) is completed, the obtained mixed solution is cooled to 25-45° C., allowed to stand for stratification and separation, and the upper layer is a purified free amine liquid layer, and the lower layer is a brine layer containing sulfate and degradation products.

[0015] The regenerated lean agent to be purified in the present invention is an organic amine salt solution with a pH of 4.0 to 6.0 from a flue gas desulfurization device in a refinery or metallurgical plant, which contains a salted organic amine desulfurizer, an indefinite amount of sulfate and a degradation product NH4 + and MEA, etc. The main organic amine component is an organic amine molecule containing two or more nitrogen atoms, preferably N-hydroxyethylpiperazine, N-ethylpiperazine, N,N'-bis(2-hydroxyethyl)piperazine, dihydroxypropylpiperazine, hydroxyethyl-propylpiperazine, hydroxyethylhexahydro-s-triazine, 3-pyridinecarboxamide, 4,4'-(1,2-ethylidene)bismorpholine or 4,4'-(oxybis(methylene))dimorpholine, or a mixture of two or more thereof, and further preferably 4,4'-(1,2-ethylidene)bismorpholine or 4,4'-(oxybis(methylene))dimorpholine, or a mixture of two or more thereof; the mass fraction of the main component in the desulfurization amine solution is 10-40%.

[0016] In the preferred embodiment of the present invention, the composite purifier described in 1) mainly comprises three components: sodium hydroxide, salt water layer stratification promoter A and free amine layer stratification promoter B. Sodium hydroxide can be solid alkali or liquid alkali, and its main function is to undergo a replacement reaction with the salted organic amine to form free amine and sodium sulfate; the salt water layer stratification promoter A is at least one of sodium sulfate and sodium hydroxide, and its main function is to adjust the brine ratio of the salt water layer, increase the density of the salt water, and reduce the solubility of the salt water layer to the free amine; the free amine layer stratification promoter B is at least one of organic solvents containing nitrogen or (and) oxygen or (and) sulfur, such as hexanol, octanol, methylcyclohexanol, tripentylamine, trioctylamine, ethyl sulfone, etc., and its main function is to promote the condensation of free amine, accelerate the salting-out stratification speed, and shorten the standing time.

[0017] In the preferred embodiment of the present invention, in the composite purifier described in 1), the amount of sodium hydroxide and the salt water layer stratification promoter A added is determined according to the sulfate content in the lean agent to be regenerated, and the sodium hydroxide is added in a molar ratio of sodium hydroxide to sulfate (n(NaOH: SO4 2- )) is configured to be 2.0-2.5; the salt water layer stratification promoter A is configured to make the sodium sulfate in the salt water layer reach 70%-90% of the solubility, preferably 70%-80%; the free amine layer stratification promoter B takes the effective amine concentration in the salt water layer (controlling amine loss) as an indicator. When the organic amine in the lean agent to be regenerated is an amine type with strong water solubility (the hydrophobic parameter (logP) of the amine is ≤-0.5, such as a piperazine-based organic amine desulfurizer), a relatively large amount of the free amine layer stratification promoter B needs to be added. At this time, the amount of the free amine layer stratification promoter B is generally configured according to 10%-25% of the mass of the regenerated lean agent to be purified, preferably 10%-20%; when the organic amine in the lean agent to be regenerated is an amine type with weak water solubility (the hydrophobic parameter (logP) of the amine is >-0.5, such as a morpholine-based organic amine desulfurizer), a small amount of B may be added or even no B may be added.

[0018] In the scheme described in the present invention, the introduction of nitrogen for stripping in 1) has two main purposes: ① After the regenerated lean agent to be purified is added to the composite purifier, heat is released simultaneously under the action of dilution and acid-base neutralization reaction, so that the temperature of the mixed liquid increases; at this time, the degradation product NH4 + In an alkaline environment, it is restored to the form of ammonia water, and nitrogen is introduced to remove ammonia by nitrogen vaporization to achieve the removal of NH4 + Purpose. ② To stir the mixed liquid evenly and cool it down.

[0019] In the scheme described in the present invention, the greater the amount of nitrogen used in the stripping described in 1), the more conducive it is to the removal of ammonium ions. However, the removal efficiency will reach a balance at a certain amount of nitrogen used. Therefore, in the preferred scheme of the present invention, the amount of nitrogen used in 1) is 1% to 7% v of the regenerated lean agent, more preferably 2% to 5% v of the regenerated lean agent, and more preferably 3% to 5% of the regenerated lean agent.

[0020] In the scheme described in the present invention, the principle of mixed liquid stratification described in 2) is that the sodium hydroxide in the composite purifier converts the salted amine into free amine, and at the same time, the two stratification promoters fully increase the density difference between the free amine layer and the salt water layer, reduce the solubility of the free amine in the salt water layer, and form a two-phase with a large density difference and low mutual solubility of the solutes between the upper and lower layers, and the salting out stratification phenomenon occurs. The degradation product MEA is highly water-soluble, and part of it will be distributed in the lower layer, and separated with the salt water layer, so as to achieve the purpose of removing the degradation product MEA. Therefore, the three components in the composite purifier in the present invention play a full synergistic role, which plays a vital role in improving the static stratification speed of the mixed solution.

[0021] In the scheme described in the present invention, the purpose of cooling the obtained mixed solution to 25-45°C described in 2) is to promote the occurrence of salting out and stratification. The lower the temperature, the more conducive it is to the occurrence of salting out and stratification; but the temperature still needs to be controlled within an appropriate range. If the temperature is too low, the lower salt water layer will form a supersaturated solution and solids will precipitate; if the temperature is too high, the solubility of the upper and lower solvent layers will be enhanced, and the organic amine desulfurizer and degradation products will be redistributed in the two phases, and the degradation products cannot be effectively removed, and the amine loss will increase. Therefore, in the preferred scheme of the present invention, the mixed solution described in 2) is cooled to 25-35°C.

[0022] The purification method of the present invention is to degrade the NH4 + The process flow of steam stripping coupled with salting out specially developed for the removal of MEA solves the problems existing in industrial practical applications with a simple method. After the composite purifier is added to the regenerated lean agent to be purified, the degradation product NH4 + Exists in the form of ammonia, and MEA sulfate exists in the form of MEA. NH4 can be removed once by stripping + , through continuous salting out, the amount of MEA can be controlled to a lower level, eliminating the problem of continuous accumulation. In addition, surprisingly, it was found that this method can remove more than 96% of sulfate, eliminating the need for ion exchange resin and freezing desalination.

[0023] Compared with the prior art, the beneficial effects of the purification method of the present invention are mainly reflected in the following aspects:

[0024] 1. The method of the present invention can effectively remove the degradation product NH4 by steam stripping coupled with salting-out technology +and MEA. The inventors have found that NH4 + MEA and are degradation products of organic amine desulfurizers in flue gas desulfurization industrial devices. Their presence interferes with the system's use of pH value as the basis for determining effective amine concentration, and is also the main reason for people to misjudge the amine concentration in the device and the semi-acidification state of the ionic liquid. Based on the above findings, the present invention adds a composite purifier to the regenerated lean agent while introducing nitrogen stripping to remove NH4 + It is removed in the form of ammonia to achieve efficient purification of degradation products. During the salting-out process, the distribution coefficient of MEA between the upper and lower layers is about 1. After one salting-out separation, about 50% of MEA will be removed. After long-term online purification, the degradation substance MEA in the system will tend to be trace.

[0025] 2. The method of the present invention is simple to operate, has a high one-time removal rate of degradation products, is stable in removal, and has low amine loss. At the same time, it is surprisingly found that this technology can effectively remove sulfate, and can replace ion exchange resin or freeze desalination method to remove sulfate, as a means of controlling the half-acidification level of sulfuric acid in desulfurizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The upper and lower parts of the figure are the chromatograms of the desulfurizer before and after degradation. Since the molecular weight of the amine solution is too large and the retention time in the ion chromatogram is too long, the amine solution peak is not shown in this figure.

[0027] Figure 2 It is a purification flow chart in a specific implementation manner of the present invention.

[0028] Description of reference numerals:

[0029] V101-purifier storage tank; V102-mixing tank; V103-sedimentation tank; V104-purification solvent tank. DETAILED DESCRIPTION

[0030] The present invention is a method for efficiently removing degradation products from desulfurization amine solution, and its process mainly comprises steam stripping coupled with salting-out technology. Figure 2 As shown, the method specifically includes the following process:

[0031] 1) The lean agent to be purified from the system (amine liquid from the system) is filtered through a filter and introduced into the stirring tank V102. The composite purifier in the storage tank V101 is filtered through a filter and added into the stirring tank V102 in batches while being added. Heat is released during the mixing process of the lean agent to be purified and the composite purifier, so that the temperature of the mixed liquid in the stirring tank V102 increases.

[0032] 2) While adding the composite purifier in step 1), nitrogen stripping is introduced into the bottom of the stirred tank V102. After all the composite purifiers are added, the bottom of the stirred tank V102 is continuously stripped with nitrogen for 5 minutes. After the composite purifier is added, the ammonium sulfate in the lean agent gradually exists in the form of ammonia under strong alkaline conditions, and is gradually discharged from the top of the stirred tank V102 in the form of ammonia during the exothermic heating and stripping process, and enters the tail gas treatment process.

[0033] 3) After the stripping is completed, the mixed liquid in the stirred tank V102 is introduced into the settling tank V103 from the bottom of the tank, cooled to 25-45°C, preferably to 25-35°C, and the mixed liquid is allowed to stand for stratification separation; the upper layer is the purified free amine liquid layer, and the lower layer is the brine layer containing sulfate and degradation products.

[0034] 4) The free amine liquid layer on the upper layer of the settling tank V103 is introduced into the purification solvent tank V104, and after being mixed and diluted with the desalted water from outside the system, it can be circulated back to the flue gas desulfurization system for use; the salt water solution in the lower layer of the settling tank V103 is discharged from the bottom and circulated to the flue gas pre-washing tower.

[0035] Based on the above Figure 2 The method shown in the following is a detailed description of a method for efficiently removing degradation products in desulfurization amine solution provided by the present invention in combination with the embodiments. The following embodiments are merely illustrative and can further illustrate the present invention, and they cannot be understood as limiting the scope of protection of the present invention.

[0036] Example 1-Example 3 and Comparative Example 1

[0037] The desulfurization amine liquid of a flue gas desulfurization unit of a petrochemical company was used as the lean agent to be purified, marked as 1# amine liquid. The main components of the desulfurization agent were 80% 4,4'-(1,2-ethylenediamine)bismorpholine and 20% N,N'-bis(2-hydroxyethyl)piperazine, calculated by mass percentage. The amine liquid was divided into 5 equal parts, 100g each, and a composite purifier was added to each amine liquid. In the composite purifier, sodium hydroxide was added according to the molar ratio of sodium hydroxide to sulfate (n(NaOH: SO4 2- )) is configured as 2.5, the salt water layer stratification promoter A sodium sulfate is configured according to 60%, 80%, 90%, and 100% of the solubility of the salt water layer sodium sulfate, and the free amine layer stratification promoter B trioctylamine is configured according to 15% of the mass of the lean agent to be purified. The composite purifier is added in batches, and nitrogen is stripped at the same time, and the nitrogen dosage is 3%v. After all the composite purifiers are added to the stirring tank, continue stripping for 5 minutes. The mixed liquid is introduced into the sedimentation tank and cooled to 35°C. It is allowed to stand for 30 minutes to observe the stratification effect and analyze the amine loss. The performance of the desulfurization amine liquid is shown in Table 1, and the purification result data is shown in Table 2.

[0038] Table 1 1# amine solution test data table

[0039]

[0040] Table 2 Salting-out results of different addition amounts of brine layer stratification promoter A

[0041]

[0042]

[0043] The data in Table 2 show that as the percentage of sodium sulfate in the brine layer reaches solubility increases, the amine loss gradually decreases. When too much stratification accelerator A is added, the amine loss no longer changes. The greater the amount of stratification accelerator A added, the closer the brine layer is to saturation, resulting in an increasing density of the brine layer, and the solubility of free amines in the brine layer is decreasing, which promotes the stratification effect and reduces the amine loss. However, the amount added should not exceed the saturated solubility. Considering the effect of the amount added and the cost, the optimal amount of stratification accelerator A in the brine layer is 80% of the solubility of sodium sulfate in the brine layer.

[0044] Example 4-Example 6 and Comparative Example 2-Comparative Example 3

[0045] Referring to the method of Example 2, the free amine layer stratification promoter B trioctylamine is 5%, 10%, 15%, 20%, 25% of the mass of the lean agent to be purified, and the sodium hydroxide, salt water layer stratification promoter A, the amount of stripping nitrogen, the salting temperature, the standing time and other process conditions are the same as those in Example 2. The purification result data is shown in Table 3.

[0046] Table 3 Salting out results of free amine layer stratification accelerator B with different addition amounts

[0047]

[0048]

[0049] The data in Table 3 show that the more free amine layer stratification promoter B is added, the smaller the amine loss is. If too much stratification promoter B is added, the amine loss will no longer change. During the purification process, stratification promoter B has a certain stripping effect on the lost amine in the lower salt solution, reducing the amine loss; at the same time, it promotes the condensation of free amine in the upper layer, accelerates the salting out stratification speed, and shortens the standing time. However, in Experiment 5 disclosed in CN102858430 A (Comparative Example 3), the amine loss is still large after standing for 2 hours. The economic addition amount of free amine layer stratification promoter B is recommended to account for 10% to 20% of the mass fraction of the lean agent to be purified.

[0050] Example 7-Example 8 and Comparative Example 4-Comparative Example 5

[0051] Referring to the method of Example 2, the amounts of stripping nitrogen were 0%, 1%, 3%, 5%, and 7%, respectively, and the composite purifier, salting-out temperature, standing time, and other process conditions were the same as those of Example 2. The purification result data are shown in Table 4.

[0052] Table 4 Effect of different nitrogen amounts in stripping on removal of ammonium ions

[0053]

[0054]

[0055] The data in Table 4 show that the greater the amount of nitrogen stripping, the more conducive it is to the removal of ammonium ions. When the amount reaches 5%, it is basically in a balanced state. The preferred amount of stripping nitrogen is 3%v~5%v.

[0056] Example 9-Example 11 and Comparative Example 6-Comparative Example 7

[0057] Three desulfurizers with different main components from 1# amine solution were prepared, the main components of which were 4,4'-(1,2-ethylenediamine)bismorpholine, N-hydroxyethylpiperazine, and N,N'-bis(2-hydroxyethyl)piperazine. The three desulfurizers were purified according to the process conditions of Example 2. The purification results are shown in Table 5.

[0058] Table 5 Effect of main components of different desulfurizers on salting out

[0059]

[0060]

[0061] The data in Table 5 show that the morpholine desulfurizer has better salting-out and stratification effect than the piperazine desulfurizer, and the method is more applicable. From the structural point of view, there are essential differences between the two. 4,4'-(1,2-ethylidene)bismorpholine has no hydrogen bond donor, and the hydrophobic parameter (logP) is -0.4; the piperazine desulfurizer has two hydrogen bond donors, and the hydrophobic parameters (logP) of N,N'-bis-(2-hydroxyethyl)piperazine and N-hydroxyethylpiperazine are -1.3 and -1.1 respectively, and the morpholine desulfurizer is more hydrophobic. Due to the strong hydrophobicity of morpholine desulfurizers, salting-out and stratification are conducive to the occurrence of amine loss, and the amine loss is small. Piperazine has hydrogen bond donors, strong hydrogen bonding with water molecules, and relatively poor salting-out effect. Without adding stratification promoter, the removal rate of degradation products is poor and the amine loss is high; after adding free amine layer and salt water layer salting-out promoter, under the bidirectional action, the removal rate of degradation products is improved and the amine loss is relatively reduced. Considering the removal effect of amine loss and degradation products, the desulfurizer is preferably an organic amine with a hydrophobic parameter (logP) greater than -0.5.

[0062] Example 12-Example 13 and Comparative Example 8-Comparative Example 9

[0063] The method of reference example 2, wherein the salting-out temperatures are 5°C, 15°C, 25°C, 30°C, 45°C, respectively, and the composite purifier, the amount of stripping nitrogen, the salting-out temperature, the standing time and other process conditions are the same as those of example 2. The purification result data are shown in Table 6.

[0064] Table 6 Analysis results of different salting-out temperatures

[0065]

[0066]

[0067] The data in Table 6 show that the lower the temperature, the more conducive it is to salting out and stratification. Because the lower the temperature, the lower the solubility of the solute in the salt water layer, and the easier it is to reach saturation. If the temperature is too low, a supersaturated solution will be formed, and solids will precipitate; if the temperature is too high, the solubility of the upper and lower phase solvents will be enhanced, and the desulfurizer will be redistributed in the two phases. The desulfurizer originally gathered in the upper layer will be partially redistributed to the lower layer; the degradation products in the lower layer will also be redistributed to the upper layer, which will not achieve the effect of removing the degradation products, and at the same time increase the amine loss. Therefore, the salting out temperature is preferably 25℃-35℃.

[0068] Industrial implementation cases

[0069] Taking the flue gas desulfurization device of a petrochemical company as an industrial experimental base, an amine liquid was drawn out from the regeneration tower as the lean agent to be purified, and the method of Example 2 of the present invention was used for purification. The quality data of the lean amine liquid before and after purification are shown in Table 8. The resin bed was operated for 350 days, 12 times a day, and the designed capacity of desulfurization was 84kg / time. The economic comparison of the ion exchange resin purification method and the purification method of the present invention is shown in Table 7:

[0070] Table 7 Quality data of lean amine liquid before and after purification

[0071]

[0072] In the actual purification process, as the purification continued, the pH of the system slowly increased from 5.6 at the beginning to 6.2, indicating that the heat-stable salt of the system was constantly decreasing. On the second day after the purification started, the alkali injection was gradually reduced from 3t / h to stopped, and the tail gas could still be discharged normally. After stopping the alkali injection, the SO2 content of the exhaust gas dropped to 25mg / m 3 .

[0073] Table 8 Comparison of costs between traditional purification method and purification method of the present invention

[0074]

[0075] As can be seen from Table 8, the alkaline agent consumption, wastewater discharge, steam consumption, etc. of the salting-out purification method of the present invention are all lower than those of ion exchange resins, and the total cost of the purification unit can be reduced by about 6.5 million yuan per year.

Claims

1. A method for efficiently purifying flue gas desulfurization amine liquid, comprising the following steps: Adding a composite purifier to the regenerated lean agent to be purified, and continuously introducing nitrogen for stripping, and after the composite purifier is added, continuing to introduce nitrogen for stripping for at least 3 minutes; after the stripping is completed, cooling the obtained mixed solution to 20-45° C., standing to separate the layers and separating, obtaining a free amine solution in the upper layer and a brine solution containing sulfate and degradation products in the lower layer; The regeneration lean agent to be purified is an aqueous solution of an organic amine salt with a pH of 4.0 to 6.0 from a flue gas desulfurization device in a refinery or metallurgical plant, which contains salted organic amines, sulfate, NH4 + and MEA; The composite purifier is composed of sodium hydroxide, a salt water layer stratification promoter and a free amine layer stratification promoter; the salt water layer stratification promoter is sodium sulfate and / or sodium hydroxide, and the free amine layer stratification promoter is selected from any one of hexyl alcohol, octanol, methylcyclohexanol, tripentylamine, trioctylamine or ethyl sulfolane, or a mixture of two or more thereof; The amount of the composite purifier added is controlled according to the following standards: the molar ratio of sodium hydroxide to sulfate is 2.0-2.5; the salt water layer stratification promoter can make the sodium sulfate in the salt water layer reach 70%-90% of the solubility; the free amine layer stratification promoter is not higher than 25% of the mass of the regenerated lean agent to be purified.

2. The purification method according to claim 1, characterized in that: In the regenerated lean agent to be purified, the salified organic amine is a salified organic amine containing two or more nitrogen atoms, preferably one of N-hydroxyethylpiperazine, N-ethylpiperazine, N,N'-bis(2-hydroxyethyl)piperazine, dihydroxypropylpiperazine, hydroxyethyl-propylpiperazine, hydroxyethylhexahydro-s-triazine, 3-pyridinecarboxamide, 4,4'-(1,2-ethylene)bismorpholine or 4,4'-(oxybis(methylene))dimorpholine, or a mixture of two or more thereof.

3. The purification method according to claim 1, characterized in that: In the regenerated lean agent to be purified, the salified organic amine is an organic amine with a salified hydrophobic parameter (logP) > -0.5; and the free amine layer stratification promoter in the composite purifier is 0% to 10% of the mass of the regenerated lean agent to be purified; preferably 0% to 5%.

4. The purification method according to claim 3, characterized in that: The organic amine with a hydrophobic parameter (logP)>-0.5 is a morpholine organic amine containing two or more nitrogen atoms, preferably one of 4,4'-(1,2-ethylidene)bismorpholine and 4,4'-(oxybis(methylene))dimorpholine or a mixture of two or more thereof.

5. The purification method according to claim 1, characterized in that: In the regenerated lean agent to be purified, the salified organic amine is an organic amine with a salified hydrophobic parameter (logP) ≤ -0.5; and the free amine layer stratification promoter in the composite purifier is 10% to 25% of the mass of the regenerated lean agent to be purified; preferably 15% to 20%.

6. The purification method according to claim 5, characterized in that: The organic amine with a hydrophobic parameter (logP) ≤ -0.5 is a piperazine organic amine containing two or more nitrogen atoms, preferably any one of N-hydroxyethyl piperazine, N-ethyl piperazine, N,N'-bis(2-hydroxyethyl) piperazine, dihydroxypropyl piperazine, hydroxyethyl-propyl piperazine, and hydroxyethyl hexahydro-s-triazine, or a mixture of two or more thereof.

7. The purification method according to claim 1, characterized in that: The nitrogen usage is 1% v / v to 7% v / v of the regenerated lean agent to be purified.

8. The purification method according to claim 1, characterized in that: The nitrogen dosage is 2% v / v to 5% v / v of the regenerated lean agent to be purified.

9. The purification method according to claim 1, characterized in that: The mixed solution is cooled to 25-45°C.

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