Wastewater treatment system and treatment method for crude phenol extraction process

Abstract

The present invention provides a wastewater treatment system and a treatment method for a crude phenol extraction process. The wastewater treatment system includes a causticizing reactor, a filtering device, an evaporating device, and a regenerative calcining furnace. The sodium carbonate wastewater generated by the crude phenol extraction process is subjected to a causticizing reactor to obtain a mixed solution containing calcium carbonate and sodium hydroxide; the mixed solution is filtered through a filtering device to obtain a dilute alkali solution and a precipitate containing calcium carbonate; the dilute alkali solution is concentrated through an evaporating device to obtain a concentrated alkali solution to be circulated for fraction washing; the precipitate containing calcium carbonate enters a regenerative calcining furnace for calcination and decomposition to obtain calcium oxide and carbon dioxide, the calcium oxide is circulated for causticizing reaction, and the carbon dioxide is circulated for decomposition of sodium phenolate. The wastewater treatment system and the treatment method can effectively realize the recycling of resources and have good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, and in particular to a wastewater treatment system and a treatment method for a crude phenol extraction process. Background Art

[0002] The phenol in coal tar is mainly concentrated in phenol oil and naphthalene oil, accounting for 35.1% and 38.6% of the total phenol content in tar, respectively, followed by wash oil, accounting for 13%. Therefore, the raw material oil for extracting crude phenol is mainly phenol oil and naphthalene oil or a three-mixed fraction including phenol oil, naphthalene oil and wash oil. In order to increase the concentration of phenol in the raw material, the raw material for crude phenol extraction generally selects phenol, naphthalene and wash three-mixed fractions. At this time, the phenol concentration can reach more than 86%. The method of crude phenol extraction is fraction washing and sodium phenolate decomposition.

[0003] In the fraction washing process, phenolic compounds have phenolic hydroxyl groups and are weakly acidic, and can react with alkali to form sodium phenol salts. Therefore, the industrial extraction of crude phenol uses sodium hydroxide aqueous solution to wash the tar three-mixed fraction to obtain sodium phenol salts.

[0004] After washing the fraction, sodium phenolate is decomposed. Since sodium phenolate is a strong base and weak acid salt, it can be decomposed to obtain crude phenol by using an acid stronger than phenol acid. In industry, sodium phenolate is generally decomposed by sulfuric acid decomposition or carbon dioxide decomposition. Among them, the process line of sulfuric acid decomposition is relatively short, and most domestic enterprises originally chose sulfuric acid decomposition. However, the corrosion of equipment and pipelines of sulfuric acid decomposition is serious, and the treatment of sodium sulfate wastewater is difficult, so it has been gradually eliminated. Compared with sulfuric acid decomposition, the process line of carbon dioxide decomposition is longer, but the carbon dioxide decomposition method can completely solve the problems of equipment corrosion and waste liquid treatment.

[0005] The carbon dioxide decomposition method requires a reliable and stable source of carbon dioxide. The carbon dioxide decomposition gas source can be liquid carbon dioxide vaporization, coke oven flue gas, fertilizer plant carbon dioxide waste gas and tubular furnace tail gas. To ensure the decomposition effect, the carbon dioxide content of the flue gas is required to be no less than 15% to 17%.

[0006] Carbon dioxide decomposes phenol sodium salt to obtain crude phenol and produces sodium carbonate solution. As wastewater, if the sodium carbonate solution is not recycled, it will be sent to the sewage treatment plant for treatment. If equipped with causticizing equipment, the causticizing reaction of sodium carbonate solution and lime can be used to produce sodium hydroxide solution and precipitate containing calcium carbonate. The sodium hydroxide solution can be concentrated to a concentration of 12% to 14% by evaporation and sent to the fraction washing unit for use. However, calcium carbonate can only be treated as hazardous solid waste and entrusted to a qualified solid waste treatment unit because it contains a small amount of organic matter.

[0007] Therefore, how to turn waste into profit in the crude phenol extraction process, recycle the reaction raw materials and products, and achieve better economic, environmental and social benefits is a technical problem that needs to be solved urgently in this field.

[0008] It should be noted that the information disclosed in the aforementioned background technology section is only used to enhance the background understanding of the present disclosure, and therefore it may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0009] A main purpose of the present invention is to overcome at least one defect of the above-mentioned prior art and to provide a wastewater treatment system and a treatment method for a crude phenol extraction process so as to solve the problems of improper treatment of sodium carbonate wastewater generated in the existing crude phenol extraction process, resulting in high treatment costs, waste of resources and environmental pollution.

[0010] In order to achieve the above objectives, the present disclosure adopts the following technical solutions:

[0011] The present invention provides a wastewater treatment system for a crude phenol extraction process. The crude phenol extraction process comprises washing a crude oil fraction to obtain sodium phenol salt, and the sodium phenol salt enters a decomposition tower and is decomposed by carbon dioxide to obtain crude phenol and wastewater containing sodium carbonate. The wastewater treatment system comprises: a causticizing reactor, a filtering device, an evaporating device and a regenerative calcining furnace, wherein the liquid inlet of the causticizing reactor is connected to the wastewater outlet of the decomposition tower for causticizing sodium carbonate to obtain a mixed solution containing calcium carbonate and sodium hydroxide; the liquid inlet of the filtering device is connected to the liquid outlet of the causticizing reactor for filtering the mixed solution. A dilute alkali solution and a precipitate containing calcium carbonate are obtained; the liquid inlet of the evaporator is connected to the liquid outlet of the filter device to concentrate the dilute alkali solution to obtain a concentrated alkali solution for circulation for fraction washing; the feed inlet of the regenerative calciner is connected to the discharge port of the filter device, the discharge port of the regenerative calciner is connected to the discharge port of the causticizing reactor, and the gas outlet of the regenerative calciner is connected to the gas inlet of the decomposition tower; wherein the precipitate containing calcium carbonate enters the regenerative calciner for calcination and decomposition to obtain calcium oxide and carbon dioxide, the calcium oxide is circulated for causticizing reaction, and the carbon dioxide is circulated for decomposition of sodium phenolate.

[0012] According to one embodiment of the present disclosure, the evaporation device includes a primary evaporator and a secondary evaporator connected in sequence.

[0013] According to one embodiment of the present disclosure, the air inlet of the primary evaporator is connected to the air outlet of the regenerative calcining furnace, and the air outlet of the primary evaporator is connected to the air inlet of the decomposition tower. The flue gas generated by the calcination and decomposition enters the decomposition tower after heat exchange through the primary evaporator.

[0014] According to one embodiment of the present disclosure, a heat supply pipe is provided between the regenerative calcining furnace and the secondary evaporator, and the heat released by cooling the calcium oxide obtained by calcination and decomposition is used as a heat source for the secondary evaporator through the heat supply pipe.

[0015] According to one embodiment of the present disclosure, the regenerative calcining furnace is further provided with a dust collector.

[0016] The present disclosure also provides a method for treating wastewater in a crude phenol extraction process, which is carried out using the above-mentioned wastewater treatment system, and comprises: wastewater containing sodium carbonate enters a causticizing reactor for causticizing reaction to obtain a mixed solution containing calcium carbonate and sodium hydroxide; the mixed solution is filtered through a filtering device to obtain a precipitate containing calcium carbonate and a dilute alkali solution; the dilute alkali solution is concentrated through an evaporating device to obtain a concentrated alkali solution, and the concentrated alkali solution is circulated for fraction washing; and the precipitate containing calcium carbonate is calcined and decomposed through a regenerative calcining furnace to obtain calcium oxide and carbon dioxide, the calcium oxide is circulated for causticizing reaction, and the carbon dioxide is circulated for decomposition of sodium phenolate.

[0017] According to one embodiment of the present disclosure, the mass percentage concentration of sodium hydroxide in the dilute alkali solution does not exceed 11%, and the mass percentage concentration of sodium hydroxide in the concentrated alkali solution is 12% to 14%.

[0018] According to one embodiment of the present disclosure, the precipitate containing calcium carbonate also includes organic matter; the mass percentage concentration of carbon dioxide in the flue gas generated by calcination and decomposition is above 20%, wherein the carbon dioxide in the flue gas includes carbon dioxide generated by calcination and decomposition of organic matter and carbon dioxide generated by calcination and decomposition of calcium carbonate.

[0019] According to one embodiment of the present disclosure, the evaporation device includes a primary evaporator and a secondary evaporator connected in sequence, and the dilute alkali solution is concentrated in the primary evaporator and the secondary evaporator in sequence.

[0020] According to one embodiment of the present disclosure, the flue gas generated by calcination and decomposition also includes water vapor, and the water vapor is condensed by a flue gas condenser in the evaporation device to generate condensed water for recycling.

[0021] It can be seen from the above technical solution that the beneficial effects of the present disclosure are:

[0022] The present invention provides a new wastewater treatment system for crude phenol extraction process. The wastewater treatment system is used to treat sodium carbonate wastewater generated in the crude phenol extraction process. On the one hand, a high-concentration sodium hydroxide solution can be obtained, which is then sent to a fraction washing unit for repeated recycling. On the other hand, a regenerative calciner is used to heat and decompose calcium carbonate generated by the causticization reaction into calcium oxide and carbon dioxide. A small amount of organic matter attached to the calcium carbonate is volatilized and the decomposed carbon dioxide is burned and consumed in the calciner furnace. The calciner flue gas rich in carbon dioxide is cooled to decompose sodium phenol salt, and calcium oxide participates in the causticization reaction, thereby truly turning waste into resources and recycling. Good economic benefits, environmental benefits and social benefits can be achieved after wastewater treatment is implemented using the wastewater treatment system of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the embodiments of the present disclosure easier to understand, the following is a detailed description with reference to the accompanying drawings. It should be noted that according to standard examples in the industry, the various components are not necessarily drawn to scale and are only used for illustration purposes. In fact, in order to make the discussion clear and understandable, the size of the various components can be arbitrarily enlarged or reduced.

[0024] Figure 1 It is a schematic diagram of the structure of a wastewater treatment system of a crude phenol extraction process according to an embodiment of the present disclosure;

[0025] Figure 2 The present invention is a process flow chart of a wastewater treatment method of a crude phenol extraction process according to an embodiment of the present invention.

[0026] The reference numerals are described as follows:

[0027] 100: Causticizing Reactor

[0028] 200: Filter device

[0029] 301: Primary evaporator

[0030] 302: Secondary evaporator

[0031] 3011, 3021: Flue gas condenser

[0032] 400: Regenerative calcining furnace

[0033] 401: Dust Collector

[0034] A: Distillate washing unit

[0035] B: Decomposition Tower

[0036] C: Exhaust gas purification tower

[0037] I: Heating pipes DETAILED DESCRIPTION

[0038] Typical embodiments that embody the features and advantages of the present disclosure will be described in detail in the following description. It should be understood that the present disclosure can have various changes in different embodiments without departing from the scope of the present disclosure, and the descriptions and drawings therein are essentially for illustrative purposes rather than for limiting the present disclosure.

[0039] In the following description of different exemplary embodiments of the present disclosure, reference is made to the accompanying drawings, which form a part of the present disclosure and in which different exemplary structures, systems and steps that can implement multiple aspects of the present disclosure are shown by way of example. It should be understood that other specific schemes of components, structures, exemplary devices, systems and steps can be used, and structural and functional modifications can be made without departing from the scope of the present disclosure. Moreover, although the terms "above", "between", "within", etc. may be used in this specification to describe different exemplary features and elements of the present disclosure, these terms are used herein only for convenience, such as according to the direction of the examples described in the accompanying drawings. Nothing in this specification should be construed as requiring a specific three-dimensional orientation of the structure to fall within the scope of the present disclosure.

[0040] See also Figure 1 , which representatively shows a schematic diagram of the structure of a wastewater treatment system for a crude phenol extraction process according to an exemplary embodiment of the present disclosure. The wastewater treatment system proposed in the present disclosure is described by taking the application to the crude phenol extraction process as an example. It is easy for those skilled in the art to understand that in order to apply the relevant designs of the present disclosure to other types of process wastewater treatment, various modifications, additions, substitutions, deletions or other changes are made to the specific embodiments described below, and these changes are still within the scope of the principles of the wastewater treatment system proposed in the present disclosure.

[0041] like Figure 1 As shown, in this embodiment, the wastewater treatment system of the crude phenol extraction process proposed in the present disclosure mainly includes a causticizing reactor 100, a filtering device 200, an evaporation device and a regenerative calcining furnace 400, wherein the evaporation device may include a primary evaporator 301 and a secondary evaporator 302 connected in sequence. It should be noted that Figure 1 This is only a partial schematic diagram of the wastewater treatment system, and does not show structures such as circulation pumps and distributors. Figure 2 , Figure 2 The process flow chart of the wastewater treatment method of the crude phenol extraction process according to one embodiment of the present disclosure is as follows. In conjunction with the above-mentioned figures, the structure, connection mode and functional relationship of each main component of an exemplary embodiment of the wastewater treatment system of the crude phenol extraction process proposed in the present disclosure are described in detail.

[0042] According to the present disclosure, the crude phenol extraction process mainly includes fraction washing and sodium phenolate decomposition. Figure 1As shown, the raw oil fraction, such as phenol, naphthalene, and washing mixed fraction of coal tar, enters the fraction washing unit A for fraction washing to obtain sodium phenolate, and the obtained sodium phenolate enters the decomposition tower B for decomposition by carbon dioxide to obtain crude phenol and waste water containing sodium carbonate. In the prior art, if the waste water is not recycled, it is sent to the sewage treatment device for treatment. If equipped with causticizing equipment, the causticizing reaction of sodium carbonate solution and lime can be used to produce sodium hydroxide solution and precipitate containing calcium carbonate. The sodium hydroxide solution can be sent to the fraction washing unit for use after evaporation and concentration to a concentration of 12% to 14%. However, calcium carbonate can only be treated as hazardous solid waste and entrusted to a qualified solid waste treatment unit for treatment because it contains a small amount of organic matter. In order to solve the problem of recycling waste water and waste residue in the decomposition process of sodium phenolate, the inventor of the present disclosure adopts a new wastewater treatment system.

[0043] Combination Figure 1 and Figure 2 As shown, the wastewater treatment system of the crude phenol extraction process includes a causticizing reactor 100, a filtering device 200, an evaporating device and a regenerative calcining furnace 400, wherein the evaporating device may include a primary evaporator 301 and a secondary evaporator 302 connected in sequence. The liquid inlet of the causticizing reactor 100 is connected to the wastewater outlet of the decomposition tower B, the liquid inlet of the filtering device 200 is connected to the liquid outlet of the causticizing reactor 100, the liquid inlet of the primary evaporator 301 is connected to the liquid outlet of the filtering device 200, and the liquid outlet of the primary evaporator 301 is connected to the liquid inlet of the secondary evaporator 302; the feed inlet of the regenerative calcining furnace 400 is connected to the discharge port of the filtering device 200, the discharge port of the regenerative calcining furnace 400 is connected to the discharge port of the causticizing reactor 100, and the gas outlet of the regenerative calcining furnace 400 is connected to the gas inlet of the decomposition tower B. In some embodiments, the regenerative calcining furnace 400 is also provided with a dust collector 401.

[0044] The following specifically describes the process of treating wastewater using the wastewater treatment system of the crude phenol extraction process in combination with the structure and connection relationship of the wastewater treatment system.

[0045] First, when the sodium phenol salt enters the decomposition tower B and is decomposed by carbon dioxide to obtain crude phenol and wastewater containing sodium carbonate, the wastewater containing sodium carbonate enters the causticizing reactor 100 through the wastewater outlet of the decomposition tower B, and undergoes a causticizing reaction with the lime in the causticizing reactor 100 to obtain a mixed solution containing calcium carbonate (CaCO3) and sodium hydroxide (NaOH).

[0046] Next, the mixed liquid enters the filter device 200 through the liquid outlet of the causticizing reactor 100 for filtration. The filter device 200 may be a closed fully automatic filter, or a filter unit consisting of multiple filters, but the present disclosure is not limited thereto. After the mixed liquid is filtered through the filter device 200, a dilute alkali solution and a precipitate containing calcium carbonate are obtained.

[0047] The diluted alkali solution is a sodium hydroxide solution with a mass percentage concentration of sodium hydroxide not exceeding 11%. The diluted alkali solution obtained after filtration is collected by a sodium hydroxide solution receiving tank and sent to the primary evaporator 301 and the secondary evaporator 302 for concentration treatment via a sodium hydroxide solution pump. Figure 1 As shown, the primary evaporator 301 and the secondary evaporator 302 are connected in sequence, and the dilute alkali solution is concentrated by the primary evaporator 301 and the secondary evaporator 302 to obtain a concentrated alkali solution. The mass percentage concentration of sodium hydroxide in the concentrated alkali solution is 12% to 14%, and the concentrated alkali solution can be directly recycled for fraction washing and dephenolization.

[0048] The calcium carbonate-containing precipitate is filtered by the filter device 200 and enters the filter cake hopper, i.e., the feed port, of the regenerative calcining furnace 400 in the form of a calcium carbonate precipitate filter cake. The fuel of the regenerative calcining furnace is generally natural gas or coal gas, but the present disclosure is not limited thereto. The regenerative calcining furnace includes a preheating section, a calcining section, and a cooling section, and the calcining temperature is generally 800° C. to 1300° C. Energy can be recovered significantly through the regenerative chamber.

[0049] Calcium carbonate is decomposed into calcium oxide (CaO) and carbon dioxide (CO2) in the regenerative calciner 400. CaO can release a large amount of heat after cooling. In some embodiments, a heat supply pipe I is provided between the regenerative calciner 400 and the secondary evaporator 302. The heat released by CaO after cooling enters the secondary evaporator 302 as a heat source through the heat supply pipe I, so that this part of energy is fully utilized. The cooled CaO can continue to enter the causticizing reactor 100 for recycling as a reaction raw material.

[0050] The calcium carbonate-containing precipitate obtained after filtration generally also contains a small amount of water and organic matter such as phenol. In the regenerative calcining furnace 400, a small amount of organic vapor, water vapor and carbon dioxide decomposed by calcium carbonate are removed from the furnace top and enter the dust collector 401 for dust removal, and then enter the furnace of the regenerative calcining furnace 400 for incineration. The carbon dioxide generated by the combustion of a small amount of organic matter is mixed into the flue gas of the regenerative calcining furnace 400, which increases the carbon dioxide content in the flue gas to more than 20%, so that the flue gas at this CO2 concentration can enter the decomposition tower B for recycling.

[0051] like Figure 1As shown, in some embodiments, the flue gas generated by the regenerative calcining furnace 400 passes through the primary evaporator 301 for heat exchange before entering the decomposition tower B. Specifically, the air inlet of the primary evaporator 301 is connected to the air outlet of the regenerative calcining furnace 400, and the air outlet of the primary evaporator 301 is connected to the air inlet of the decomposition tower B. The flue gas generated by calcination and decomposition is cooled to about 130°C by the regenerator of the regenerative calcining furnace 400 and enters the primary evaporator 301 as the heat source of the primary evaporator. At the same time, the flue gas is sent to the decomposition tower B for recycling after heat exchange from the primary evaporator 301, as the carbon dioxide gas source of the decomposition tower. The primary evaporator 301 and the secondary evaporator 302 are also respectively provided with flue gas condensers 3011 and 3021 (also heaters). After the water vapor in the flue gas is condensed in the flue gas condensers 3011 and 3021, it can be used as condensed water for circulating water replenishment.

[0052] In summary, through the treatment of the wastewater treatment system, the dilute alkali solution and calcium carbonate generated by the sodium carbonate-containing wastewater after treatment in the causticizing reactor are effectively recycled.

[0053] The obtained dilute alkali solution can be concentrated by evaporation to obtain a sodium hydroxide solution with a concentration of 12% to 14%, which is then sent to the fraction washing unit for repeated use. Furthermore, the neutral sodium phenolate washed with the sodium hydroxide solution fraction is blown to remove oil impurities before decomposition to make it pure sodium phenolate. The neutral sodium phenolate in the neutral sodium phenolate tank is sent to the sodium phenolate heat exchanger by the sodium phenolate distillation pump, and heats with the gas discharged from the distillation kettle, and then enters the distillation column of the phenolate distillation kettle. The distillation kettle uses heat transfer oil to heat the sodium phenolate solution to generate steam, and distills and blows steam to replace direct steam to reduce the amount of waste water. The pure sodium phenolate of water and neutral oil is blown out, cooled by the pure sodium phenol cooler, and then flows into the pure sodium phenolate tank. After the gas at the top of the distillation column exchanges heat with the neutral sodium phenolate in the sodium phenolate heat exchanger, it is cooled to 50°C with circulating water, and then enters the oil-water separator, the separated water flows into the phenol water tank of the tar distillation device, and the neutral oil flows into the phenol oil tank.

[0054] Next, phenolate decomposition is performed. The flue gas generated by the regenerative calciner 400 is sent to the decomposition tower B for recycling, wherein the decomposition tower B includes a primary decomposition tower and a secondary decomposition tower (not shown). Specifically, the flue gas generated by the regenerative calciner 400 is sent to the upper and lower sections of the primary decomposition tower and the upper and lower sections of the secondary decomposition tower by a Roots blower after cooling. The clean sodium phenolate is pumped into the upper section of the primary decomposition tower by the primary decomposition pump to countercurrently contact with the rising flue gas, and then flows into the lower section of the decomposition tower, and is countercurrently contacted with the flue gas again for decomposition, and the crude phenol and sodium carbonate mixed liquid flows into the separator at the bottom of the tower, and the crude phenol is discharged from the upper part to the primary decomposition intermediate tank, and the sodium carbonate is discharged from the bottom to the sodium carbonate tank. The crude phenol primary product of the primary decomposition intermediate tank contains a small amount of undecomposed sodium phenolate, which is then sent to the top of the secondary decomposition tower for decomposition. Similarly, after secondary decomposition in the upper and lower sections, it is separated at the bottom of the tower, and the decomposed crude phenol flows to the crude phenol tank by gravity, and the sodium carbonate solution is discharged from the bottom to the sodium carbonate tank. The waste gas from the primary decomposition tower and the secondary decomposition tower enters the tail gas purification tower C, is purified by sodium phenol salt, and then washed and purified by the water washing tower, and then discharged to the factory tail gas system and enters the tubular furnace for combustion.

[0055] It has been verified that, on the one hand, the wastewater treatment system disclosed in the present invention can obtain about 8000t of sodium hydroxide solution with a byproduct concentration of about 14%, and this part of the sodium hydroxide solution can be directly used for fraction washing and dephenolization, which greatly improves the recycling rate and saves costs; on the other hand, calcium carbonate is heated and decomposed into calcium oxide and carbon dioxide by a regenerative calcining furnace, and calcium oxide participates in the causticization reaction. Carbon dioxide decomposed by calcium carbonate and a small amount of organic matter attached to calcium carbonate are volatilized and burned to produce carbon dioxide, which can make the carbon dioxide concentration in the flue gas of the calcining furnace reach more than 20%, so that this part of the flue gas can enter the decomposition tower for recycling, ensuring that the decomposition rate of sodium phenol reaches more than 99%, and the water content of the obtained crude phenol is less than 10%. The various indicators of crude phenol meet the requirements of YB / T5079-2012.

[0056] The wastewater treatment system disclosed in the present invention can save 900 tons of carbon dioxide, 1,200 tons of calcium oxide with a purity of more than 98% on a dry basis, and reduce the discharge of 2,100 tons of solid calcium carbonate per year. In addition, the regenerative calcining furnace disclosed in the present invention adopts a regenerative high-temperature low-oxygen combustion method. The high-temperature low-oxygen combustion has the advantages of greatly saving energy and greatly reducing nitrogen oxide emissions. Therefore, the regenerative calcining furnace is not only energy-saving, but also can achieve ultra-low emissions of nitrogen oxides. In short, the wastewater treatment system and wastewater treatment method of the crude phenol extraction process disclosed in the present invention fully reflect the requirements of the circular economy, and are energy-saving, safe, and environmentally friendly, realizing the true transformation of waste into resources and recycling.

[0057] It should be noted by those skilled in the art that the embodiments described in the present disclosure are merely exemplary, and various other substitutions, changes and improvements may be made within the scope of the present disclosure. Therefore, the present disclosure is not limited to the above embodiments, but is only limited by the claims.

Claims

1. A wastewater treatment system for a crude phenol extraction process, wherein the crude phenol extraction process comprises washing a crude oil fraction to obtain sodium phenol salt, wherein the sodium phenol salt enters a decomposition tower and is decomposed by carbon dioxide to obtain crude phenol and wastewater containing sodium carbonate, wherein: The wastewater treatment system comprises: A causticizing reactor, wherein the liquid inlet of the causticizing reactor is connected to the wastewater outlet of the decomposition tower, and is used for performing a causticizing reaction of sodium carbonate to obtain a mixed solution containing calcium carbonate and sodium hydroxide; A filtering device, wherein the liquid inlet of the filtering device is connected to the liquid outlet of the causticizing reactor, and is used to filter the mixed liquid to obtain a dilute alkali solution and a precipitate containing calcium carbonate; an evaporation device, wherein the liquid inlet of the evaporation device is connected to the liquid outlet of the filtering device, and is used to concentrate the dilute alkali solution to obtain a concentrated alkali solution for recycling for washing the fraction; the evaporation device comprises a primary evaporator and a secondary evaporator connected in sequence; and A regenerative calciner, wherein the feed port of the regenerative calciner is connected to the discharge port of the filtering device, the discharge port of the regenerative calciner is connected to the discharge port of the causticizing reactor, and the air outlet of the regenerative calciner is connected to the air inlet of the decomposition tower; wherein the precipitate containing calcium carbonate enters the regenerative calciner for calcination and decomposition to obtain calcium oxide and carbon dioxide, the calcium oxide is circulated for the causticizing reaction, and the carbon dioxide is circulated for the decomposition of the sodium phenolate; the regenerative calciner is also provided with a dust collector.

2. The wastewater treatment system according to claim 1, characterized in that: The air inlet of the primary evaporator is connected to the air outlet of the regenerative calcining furnace, and the air outlet of the primary evaporator is connected to the air inlet of the decomposition tower. The flue gas generated by the calcination and decomposition enters the decomposition tower after heat exchange through the primary evaporator.

3. The wastewater treatment system according to claim 1, characterized in that: A heat supply pipeline is provided between the regenerative calcining furnace and the secondary evaporator, and the heat released by cooling the calcium oxide obtained by calcination and decomposition is used as a heat source for the secondary evaporator through the heat supply pipeline.

4. A method for treating wastewater from a crude phenol extraction process, using the wastewater treatment system according to any one of claims 1 to 3, characterized in that: include: The wastewater containing sodium carbonate enters the causticizing reactor for causticizing reaction to obtain a mixed solution containing calcium carbonate and sodium hydroxide; The mixed solution is filtered through the filtering device to obtain a precipitate containing calcium carbonate and a dilute alkali solution; The dilute alkali solution is concentrated by the evaporation device to obtain a concentrated alkali solution, and the concentrated alkali solution is circulated for washing the fraction; and The calcium carbonate-containing precipitate is calcined and decomposed in the regenerative calcining furnace to obtain calcium oxide and carbon dioxide. The calcium oxide is circulated for the causticizing reaction, and the carbon dioxide is circulated for the decomposition of the sodium phenolate.

5. The wastewater treatment method according to claim 4, characterized in that: The mass percentage concentration of sodium hydroxide in the dilute alkali solution does not exceed 11%, and the mass percentage concentration of sodium hydroxide in the concentrated alkali solution is 12% to 14%.

6. The wastewater treatment method according to claim 5, characterized in that: The calcium carbonate-containing precipitate also includes organic matter; the mass percentage concentration of carbon dioxide in the flue gas generated by calcination and decomposition is above 20%, wherein the carbon dioxide in the flue gas includes carbon dioxide generated by calcination and decomposition of the organic matter and carbon dioxide generated by calcination and decomposition of calcium carbonate.

7. The wastewater treatment method according to claim 5, characterized in that: The evaporation device comprises a primary evaporator and a secondary evaporator which are connected in sequence, and the dilute alkali solution is concentrated in the primary evaporator and the secondary evaporator in sequence.

8. The wastewater treatment method according to claim 5, characterized in that: The flue gas generated by the calcination and decomposition also includes water vapor, and the water vapor is condensed by the flue gas condenser in the evaporation device to generate condensed water for recycling.

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