Wastewater treatment method

Abstract

The invention relates to the technical field of wastewater treatment, and discloses a wastewater treatment method which comprises the following steps: preheating to-be-treated wastewater, introducing the wastewater into an oxidation tower, leading out part of wastewater from a side line of the oxidation tower through a reflux pipeline, refluxing, mixing the wastewater with the preheated wastewater in a mixer, and introducing the mixture into the oxidation tower for oxidation reaction, the treated wastewater is led out from a water outlet in the top of the oxidation tower; the preheating mode is as follows: performing heat exchange on the wastewater to be treated and outlet water at the top of the oxidation tower so as to increase the temperature of the wastewater to be treated; and the temperature of the refluxed wastewater mixed with the preheated wastewater reaches the temperature of the oxidation reaction. The method provided by the invention solves the problems of coking, scaling and blockage of the pipe walls of the heater and the heat exchanger during wet oxidation treatment of high-concentration organic wastewater, improves the heat exchange efficiency and heat utilization rate of the device, and also improves the oxidation efficiency of wastewater treatment.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a wastewater treatment method. Background Art

[0002] The organic pollutants in industrial wastewater are of high concentration, stable structure, strong toxicity, and contain a large number of difficult-to-biodegrade organic matter, which will cause serious pollution to the water body, thus causing the deterioration of the ecological environment and threatening human health. However, the use of conventional physical, chemical and biological treatment technologies cannot completely remove the toxicity of industrial wastewater and reduce the concentration of organic pollutants, and may even lead to the transfer of pollutants and secondary pollution. Therefore, the use of traditional methods to treat industrial wastewater can no longer meet the requirements of the industry, and the efficient treatment technology of difficult-to-biodegrade high-concentration industrial wastewater has become a problem that needs to be solved urgently.

[0003] Wet oxidation is a common technical method for treating high-concentration wastewater. Its working principle is a chemical process that uses oxygen in the air or pure oxygen as an oxidant to oxidize organic pollutants in the liquid phase into small molecular organic matter such as CO2 and water under high temperature and high pressure conditions. Compared with conventional treatment methods, wet oxidation has the characteristics of wide application range, high treatment efficiency, and low secondary pollution. It is a very effective treatment technology, especially for high-concentration toxic and harmful wastewater generated by industries such as dyes, pharmaceuticals, pesticides, and synthetic fibers.

[0004] The wet oxidation processor generally includes a heater (heat exchanger) and an oxidation tower. After the wastewater is heated to the reaction temperature in the heater, it is sent to the oxidation tower and oxygen is introduced for oxidation. However, when using catalytic wet oxidation to treat high-concentration organic wastewater, due to the high organic content in the wastewater, the organic matter is cracked or carbonized or polymerized under high temperature and high pressure environment, forming coking products similar to those attached to the tube wall of the heater / heat exchanger, causing the heater / heat exchanger to scale, resulting in a serious decrease in the heating or heat exchange efficiency of the heater / heat exchanger, or even the inability to exchange heat at all, reducing the life of the equipment, and these coking products are not easy to clean, increasing the cleaning cost. Therefore, it is necessary to deal with the scaling phenomenon of wet oxidation of high-concentration organic wastewater, reduce the occurrence of scaling, and improve the heat exchange efficiency of the equipment.

[0005] CN118005170A discloses a wet oxidation reaction process suitable for wastewater prone to coking, which includes obtaining oxygen-enriched air through a pressure swing adsorption device, and then inputting it into an oxidation unit through an oxygen compressor, and raw water entering a high-pressure diaphragm pump for pressurization, and mixing the outlet with high-pressure oxygen from an air intake unit and circulating wastewater at the outlet of an oxidation reactor, and then transporting it to an oxidation reactor for oxidation reaction. Although the process omits a preheater and uses a steam heat exchanger for circulating heat supplementation to avoid coking of the preheater, there is still the problem of scaling of the steam heat exchanger, and the process requires continuous external heating when the wastewater heat is insufficient, which consumes a large amount of steam energy and has a low heat transfer efficiency; in addition, the heat generated by the oxidation reaction itself is only used to maintain the high temperature of the reaction, resulting in large heat loss and low heat utilization. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems of low oxidation efficiency, heat exchange efficiency and heat utilization rate in the prior art when wet oxidation is used to treat high-concentration wastewater, and to provide a wastewater treatment method, which improves the oxidation efficiency of high-concentration wastewater treated by wet oxidation, and at the same time improves the heat exchange efficiency and heat utilization rate of the reaction equipment.

[0007] In order to achieve the above object, the present invention provides a method for treating wastewater, which comprises: preheating the wastewater to be treated and introducing it into an oxidation tower, drawing out part of the wastewater from the water outlet on the side line of the oxidation tower through a reflux pipeline for reflux and mixing it with the preheated wastewater in a mixer, and then entering the oxidation tower for oxidation reaction, and drawing out the treated wastewater from the water outlet on the top of the oxidation tower;

[0008] The preheating method is as follows: the preheated wastewater to be treated is heat exchanged with the water from the top of the oxidation tower to increase the temperature of the wastewater to be treated; the temperature of the refluxed wastewater is mixed with the preheated wastewater to reach the temperature of the oxidation reaction.

[0009] Through the above technical solution, the present invention has at least the following beneficial effects:

[0010] (1) The method of the present invention has a safer reaction and a higher oxidation efficiency;

[0011] (2) The method of the present invention uses the reaction heat generated during the wet oxidation process to produce by-product steam or remove it through a steam generation system (such as a waste heat boiler), thereby improving the heat utilization rate and broadening the limit of the wet oxidation reaction on the wastewater concentration. The maximum concentration of the wastewater can reach 150,000 mg / L;

[0012] (3) The method of the present invention solves the problem of scaling and clogging of the tube walls of the heater and the heat exchanger during wet oxidation treatment of high-concentration organic wastewater, maintains the long-term stable operation of the wet oxidation processor, avoids frequent shutdown for cleaning, and saves manpower and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The invention provides a wet oxidation reaction device.

[0014] Description of Reference Numerals

[0015] 1 heat exchanger 2 mixer 3 oxidation tower

[0016] 4Steam production system 5External circulation pump 6Heat exchanger DETAILED DESCRIPTION

[0017] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0018] The present invention provides a method for treating wastewater, the method comprising:

[0019] The wastewater to be treated is preheated and introduced into the oxidation tower, part of the wastewater is led out from the outlet on the side line of the oxidation tower through the reflux pipeline for reflux and mixed with the preheated wastewater in the mixer before entering the oxidation tower for oxidation reaction, and the treated wastewater is led out from the outlet on the top of the oxidation tower;

[0020] The preheating method is as follows: the preheated wastewater to be treated is heat exchanged with the water from the top of the oxidation tower to increase the temperature of the wastewater to be treated; the temperature of the refluxed wastewater is mixed with the preheated wastewater to reach the temperature of the oxidation reaction.

[0021] In the present invention, a part of the wastewater treated by the oxidation reaction will be circulated through the reflux pipe of the oxidation tower side line, and mixed with the preheated wastewater in the mixer for mass transfer, so that the temperature of the preheated wastewater quickly reaches the oxidation reaction starting temperature (above 210°C); the other part of the wastewater treated by the oxidation reaction is discharged from the water outlet at the top of the oxidation tower, and its heat is used for by-product steam through the steam production system.

[0022] In order to ensure the cleanliness of the treated wastewater discharged from the side line of the oxidation tower, preferably, the vertical distance between the outlet on the side line of the oxidation tower and the outlet on the top of the tower accounts for 1 / 5-2 / 5 of the height of the oxidation tower.

[0023] Preferably, the temperature of the wastewater to be treated after preheating is 120-150°C.

[0024] Preferably, a heater is provided on the reflux line to heat the refluxed wastewater before it enters the mixer. In the present invention, when the temperature of the wastewater entering the oxidation tower after the preheated wastewater is mixed with the wastewater refluxed from the oxidation tower sideline reflux pipe (high-temperature clean material after oxidation reaction) does not reach the high temperature required for the oxidation reaction, heat is supplemented by the heater on the reflux line to make the temperature of the wastewater reach the oxidation reaction temperature. On the contrary, if the temperature of the refluxed wastewater is enough to make the temperature of the wastewater entering the oxidation tower reach the oxidation reaction temperature, the heater does not need to be started.

[0025] More preferably, the heating conditions of the heater are such that the temperature of the wastewater returning before entering the mixer is ≥250°C, preferably 260-270°C.

[0026] In the present invention, before the preheated wastewater is introduced into the oxidation tower for oxidation reaction, a small amount of wastewater is first introduced into the oxidation tower (the wastewater is heated by a heater and the temperature reaches the temperature of the oxidation reaction). During the flow of the wastewater along the oxidation tower, an oxidation reaction occurs (the oxidation reaction releases a large amount of heat, which makes the temperature of the wastewater higher). The pollutants in the wastewater are decomposed into harmless substances such as CO2, water and N2, so that the wastewater becomes clean, that is, the high-temperature clean material after the oxidation reaction. Part of the high-temperature clean material is drawn out from the side reflux pipe of the oxidation tower and mixed with the preheated wastewater to increase the temperature of the preheated wastewater.

[0027] According to some embodiments of the present invention, the heat exchange is carried out in a heat exchanger, and the heat exchange method is: recovering the heat of the treated wastewater through a steam production system, and inputting the wastewater with recovered heat into the heat exchanger for heat exchange with the wastewater to be treated.

[0028] According to some embodiments of the present invention, the water outlet of the heat exchanger is connected to the water inlet of the mixer; the water inlet at the bottom of the oxidation tower is connected to the water outlet of the mixer; the water inlet of the steam production system is connected to the water outlet at the top of the oxidation tower, and the water outlet of the steam production system is connected to the heat exchanger; and the water outlet of the heater is connected to the water inlet of the mixer.

[0029] In the present invention, the water outlet of the heat exchanger and the water outlet of the heater are connected to the mixer, so that the wastewater to be treated and the refluxed wastewater that are heated after heat exchange enter the mixer, and after mixing, the temperature is raised to the oxidation temperature, which significantly broadens the wastewater concentration that can be treated by wet oxidation technology.

[0030] In the present invention, the mixer may be a common mixer in the art, such as a pipeline mixer.

[0031] According to some embodiments of the present invention, an air inlet is provided on a bottom side wall of the oxidation tower for providing an oxygen source from an external source.

[0032] In the present invention, an air inlet is opened at the bottom of the oxidation tower.

[0033] According to some embodiments of the present invention, the water inlet of the heat exchanger is connected to a source of wastewater to be treated.

[0034] According to some embodiments of the present invention, in order to facilitate reflux, an external circulation pump is provided on the reflux pipeline of the oxidation tower side line; the water inlet of the external circulation pump is connected to the water outlet on the oxidation tower side line, and the water outlet is connected to the inlet of the heater.

[0035] According to some embodiments of the present invention, the steam production system is a waste heat boiler.

[0036] In the present invention, the steam production system (waste heat boiler) can timely remove part of the heat of the water discharged from the oxidation tower and produce water vapor as a by-product, thereby improving the heat utilization rate.

[0037] In the present invention, the temperature of the preheated wastewater discharged from the outlet of the heat exchanger is controlled by the cold water flow in the cold water pipe of the preheating boiler, and the cold water flow in the cold water pipe of the waste heat boiler is related to the COD value of the wastewater to be treated, and the cold water flow can be adjusted according to the COD value of the wastewater to be treated. For example, if the COD value of the wastewater to be treated is high, the heat released by the reaction in the oxidation tower is large, the heat to be removed is large, and the cold water flow is large; if the COD value of the wastewater to be treated is low, the heat released by the reaction in the oxidation tower is small, the heat to be removed is small, and the cold water flow is small.

[0038] In the present invention, the reflux ratio allows the temperature of the wastewater in the mixer to reach the temperature of the oxidation reaction (such as 210-290° C.). According to some embodiments of the present invention, the reflux ratio of the oxidation tower is 2-5.

[0039] In the present invention, controlling the reflux ratio of the oxidation tower within the above-mentioned preferred range is more conducive to heat recovery and simultaneously quickly increases the temperature of the preheated wastewater.

[0040] According to some embodiments of the present invention, the oxidation reaction method comprises: introducing wastewater into the oxidation tower to carry out an oxidation reaction in the presence of an oxygen source and a catalyst.

[0041] Preferably, the oxygen source comprises air and / or oxygen.

[0042] Preferably, the catalyst is selected from homogeneous catalysts and / or heterogeneous catalysts.

[0043] In the present invention, preferably, the homogeneous catalyst is selected from at least one of copper salts, iron salts, zinc salts, nickel salts, cobalt salts and manganese salts.

[0044] In the present invention, preferably, the heterogeneous catalyst is selected from noble metal catalysts and / or non-noble metal catalysts.

[0045] In the present invention, preferably, the catalyst is a homogeneous catalyst, and the amount of the catalyst used is 50-2000 mg / L based on the metal ions in the homogeneous catalyst.

[0046] In the present invention, preferably, the catalyst is a heterogeneous catalyst, and the loading amount of the catalyst is 0.5-3 times the flow rate of the wastewater.

[0047] In the present invention, the wastewater flow rate is related to the COD value of the wastewater to be treated, and the wastewater flow rate can be adjusted according to the COD value of the wastewater to be treated.

[0048] In the present invention, the flow rate of the oxygen source is related to the COD value of the wastewater to be treated, and the flow rate of the oxygen source can be adjusted according to the COD value of the wastewater to be treated.

[0049] According to some embodiments of the present invention, the conditions of the oxidation reaction include: temperature of 210-290° C., preferably 220-270° C.; pressure of 2-9 MPa, preferably 4-7 MPa; residence time of 1-5 h, preferably 2-4 h.

[0050] Preferably, the COD value of the wastewater to be treated is 30,000-150,000 mg / L.

[0051] In the present invention, the pH value of the wastewater to be treated is not particularly limited, and both acidic and alkaline wastewater can be treated by the method of the present invention. In order to improve the efficiency of the oxidation reaction, the pH of the wastewater to be treated needs to be adjusted before entering the system, and preferably, the pH of the wastewater to be treated after adjustment is 3-4.

[0052] The method of the present invention can be carried out in a wet oxidation reaction device. According to a preferred embodiment provided by the present invention, Figure 1The wet oxidation reaction device of the present invention is described in detail. The device includes a heat exchanger 1, a mixer 2, an oxidation tower 3, a steam production system 4, an external circulation pump 5 and a heater 6, wherein the water inlet of the heat exchanger 1 is connected to the wastewater source, and the water outlet of the heat exchanger 1 is connected to one water inlet of the mixer 2; the water inlet at the bottom of the oxidation tower 3 is connected to the water outlet of the mixer 2, and an air inlet is provided at the bottom of the oxidation tower 3 for providing an oxygen source from an external source; the water inlet of the steam production system 4 is connected to the water outlet at the top of the oxidation tower 3, and the water outlet of the steam production system 4 (waste heat boiler) is connected to the heat exchanger 1; an external circulation pump 5 and a heater 6 are arranged on the reflux line of the side line of the oxidation tower 3 (the heater 6 heats the refluxed wastewater before entering the mixer 2), the water inlet of the external circulation pump 5 is connected to the water outlet on the side line of the oxidation tower 3, the water outlet of the external circulation pump 5 is connected to the inlet of the heater 6, and the outlet of the heater 6 is connected to another inlet of the mixer 2.

[0053] According to one embodiment of the present invention, the working principle of the wet oxidation reaction device is as follows: the wastewater to be treated is heat exchanged in the heat exchanger 1, and the cold water flow of the steam production system 4 (waste heat boiler) is adjusted at the same time, so that the wastewater temperature at the outlet of the heat exchanger 1 is relatively low; the circulating water (clean material after high-temperature reaction) from the middle and upper part of the oxidation tower 3 is sent to the bottom of the oxidation tower 3 through the side line of the oxidation tower 3 and the external circulation pump 5, and in the mixer 2, the circulating water (clean material after high-temperature reaction) is mixed with the preheated wastewater for mass transfer, thereby quickly raising the temperature of the wastewater to the temperature required for the oxidation reaction; in addition, an air inlet is opened from the bottom of the oxidation tower 3, and an oxygen source (air or oxygen) is introduced into the oxidation tower from the air inlet, and after mixing with the heated wastewater, an oxidation reaction is carried out in the oxidation tower 3.

[0054] According to one embodiment of the present invention, when the wastewater concentration is high, the reaction in the oxidation tower 3 is violent, and the released heat is large, a part of the heat is used for wastewater preheating in the heat exchanger 1, and the excess heat is recovered through the steam production system 4 (waste heat boiler), and water vapor is produced as a by-product, and the heat can be used for other processes; when the wastewater concentration is low and the oxidation reaction in the oxidation tower 3 releases insufficient heat to maintain its own heat balance, heat is supplemented by the heater 6 arranged on the reflux line of the side line of the oxidation tower 3.

[0055] According to a particularly preferred embodiment of the present invention, a method for treating wastewater is provided, the method comprising:

[0056] (1) exchanging heat between the wastewater and the water discharged from the top of the oxidation tower in a heat exchanger to obtain preheated wastewater, so that the temperature of the preheated wastewater flowing out of the outlet of the heat exchanger is 120-150° C.;

[0057] (2) The clean material (circulating water with a temperature of 260-270°C) after the high-temperature reaction from the middle and upper part of the oxidation tower is led out from the side line through an external circulation pump and refluxed to the bottom of the oxidation tower. In the pipeline mixer, the circulating water is mixed with the preheated wastewater for mass transfer, thereby rapidly raising the temperature of the wastewater. The heated wastewater enters the oxidation tower from the bottom of the oxidation tower;

[0058] Among them, the vertical distance between the water outlet on the side line of the oxidation tower and the water outlet on the top of the tower accounts for 1 / 5-2 / 5 of the height of the oxidation tower 3;

[0059] Among them, the reflux ratio of the oxidation tower is 2-5;

[0060] (3) Oxygen is introduced from the air inlet opened at the bottom of the oxidation tower. In the presence of a catalyst, the heated wastewater undergoes a wet oxidation reaction in the oxidation tower 3. The temperature of the wet oxidation reaction is 240-270°C, the pressure is 4-7MPa, and the residence time is 2-3h. The treated wastewater is discharged from the top of the oxidation tower. A portion of the heat generated by the oxidation reaction is recovered by the steam production system and then enters a heat exchanger for preheating the wastewater. The excess heat is recovered by the steam production system, and water vapor is produced as a by-product. After the reaction is completed, treated purified water is obtained.

[0061] The present invention will be described in detail below through examples.

[0062] In the following embodiments and comparative examples, the steam generating system is a waste heat boiler.

[0063] The clean material after high-temperature reaction in the following embodiments and comparative examples refers to the preheated wastewater. Before it is introduced into the oxidation tower for oxidation reaction, a small amount of wastewater is first introduced into the oxidation tower (the wastewater is heated by a heater and the temperature reaches the temperature of the oxidation reaction). An oxidation reaction occurs in the process of the wastewater flowing along the oxidation tower (the oxidation reaction releases a large amount of heat, which makes the temperature of the wastewater higher). The pollutants in the wastewater are decomposed into harmless substances such as CO2, water and N2, making the wastewater clean, that is, the high-temperature clean material after the oxidation reaction.

[0064] The COD value in wastewater (or purified water) is determined by the potassium dichromate method.

[0065] The catalyst selected is a heterogeneous catalyst, specifically a titanium dioxide-supported ruthenium-iridium metal catalyst, and the filling amount of the catalyst is 1.2 times the wastewater flow rate.

[0066] Unless otherwise specified, the materials used were commercially available.

[0067] Example 1

[0068] The wastewater flow rate of a vitamin production is 8t / h, the COD value is 59300mg / L, and the pH is adjusted to 3.5±0.5 with NaOH solution;

[0069] according to Figure 1 The wet reaction device shown in the figure processes organic matter in wastewater, and the specific method includes:

[0070] (1) The wastewater and the water discharged from the top of the oxidation tower 3 are heat exchanged in the heat exchanger 1 to obtain preheated wastewater, so that the temperature of the preheated wastewater flowing out of the outlet of the heat exchanger 1 is 150° C.;

[0071] (2) The clean material (circulating water with a temperature of 260° C.) after the high-temperature reaction from the upper part of the oxidation tower 3 is led out from the side line of the oxidation tower 3 through the external circulation pump 5 and refluxed to the bottom of the oxidation tower 3. In the pipeline mixer 2, the circulating water is mixed with the preheated wastewater for mass transfer, thereby rapidly raising the temperature of the wastewater to 235° C. The heated wastewater enters the oxidation tower 3 from the bottom of the oxidation tower 3;

[0072] Among them, the vertical distance between the water outlet on the side line of oxidation tower 3 and the water outlet on the top of the tower accounts for 1 / 5 of the height of oxidation tower 3;

[0073] Among them, the reflux ratio of oxidation tower 3 is 3.5;

[0074] (3) Oxygen (the oxygen flow rate is 120 L / h) is introduced from the air inlet opened at the bottom of the oxidation tower 3 (the vertical distance between the air inlet and the bottom of the tower is 1 / 5 of the height of the oxidation tower). In the presence of a catalyst, the heated wastewater undergoes a wet oxidation reaction in the oxidation tower 3. The pressure of the oxidation reaction is 7 MPa and the residence time is 1.5 h. After the reaction, the outlet water temperature at the top of the oxidation tower 3 is 265°C. A part of the heat generated by the oxidation reaction is recovered by the steam production system 4 (waste heat boiler) and then enters the heat exchanger 1 for preheating the wastewater. The excess heat is recovered by the steam production system 4 (waste heat boiler) to produce water vapor as a by-product. After the reaction, treated purified water is obtained.

[0075] Example 2

[0076] The wastewater flow rate of a styrene propylene oxide production plant is 13t / h, the COD value is 154200mg / L, and the pH is adjusted to 3.5±0.5 with HCl solution;

[0077] according to Figure 1 The wet reaction device shown in the figure processes organic matter in wastewater, and the specific method includes:

[0078] (1) The wastewater and the water discharged from the top of the oxidation tower 3 are heat exchanged in the heat exchanger 1 to obtain preheated wastewater, so that the temperature of the preheated wastewater flowing out of the outlet of the heat exchanger 1 is 120° C.;

[0079] (2) The clean material (circulating water with a temperature of 270° C.) after the high-temperature reaction from the upper part of the oxidation tower 3 is led out from the side line through the external circulation pump 5 and refluxed to the bottom of the oxidation tower 3. In the pipeline mixer 2, the circulating water is mixed with the preheated wastewater for mass transfer, thereby rapidly raising the temperature of the wastewater by 230° C. The heated wastewater enters the oxidation tower 3 from the bottom of the oxidation tower 3;

[0080] Among them, the vertical distance between the water outlet on the side line of oxidation tower 3 and the water outlet on the top of the tower accounts for 1 / 5 of the height of oxidation tower 3;

[0081] Among them, the reflux ratio of oxidation tower 3 is 2.8;

[0082] (3) Oxygen (the oxygen flow rate is 460 L / h) is introduced from the air inlet opened at the bottom of the oxidation tower 3 (the vertical distance between the air inlet and the bottom of the tower is 1 / 5 of the height of the oxidation tower). In the presence of a catalyst, the heated wastewater undergoes a wet oxidation reaction in the oxidation tower 3. The reaction temperature in the oxidation tower 3 is set to 275°C, the reaction pressure is 9 MPa, and the residence time is 3 hours. After the reaction, the outlet water temperature at the top of the oxidation tower 3 is 275°C. A part of the heat generated by the oxidation reaction is recovered by the steam production system 4 (waste heat boiler) and then enters the heat exchanger 1 for preheating the wastewater. The excess heat is recovered by the steam production system 4 (waste heat boiler) to produce water vapor as a by-product. After the reaction, treated purified water is obtained.

[0083] Example 3

[0084] The wastewater flow rate of a styrene propylene oxide production plant is 10t / h, the COD value is 100600mg / L, and the pH is adjusted to 3.5±0.5 with HCl solution;

[0085] according to Figure 1 The wet reaction device shown in the figure processes organic matter in wastewater, and the specific method includes:

[0086] (1) The wastewater and the water discharged from the top of the oxidation tower 3 are heat exchanged in the heat exchanger 1 to obtain preheated wastewater, so that the temperature of the preheated wastewater flowing out of the outlet of the heat exchanger 1 is 140° C.;

[0087] (2) The clean material (circulating water with a temperature of 265° C.) after the high-temperature reaction from the upper part of the oxidation tower 3 is led out from the side line through the external circulation pump 5 and refluxed to the bottom of the oxidation tower 3. In the pipeline mixer 2, the circulating water is mixed with the preheated wastewater for mass transfer, thereby rapidly raising the temperature of the wastewater by 225° C. The heated wastewater enters the oxidation tower 3 from the bottom of the oxidation tower 3;

[0088] Among them, the vertical distance between the water outlet on the side line of oxidation tower 3 and the water outlet on the top of the tower accounts for 1 / 5 of the height of oxidation tower 3;

[0089] Among them, the reflux ratio of oxidation tower 3 is 2.5;

[0090] (3) Oxygen (the oxygen flow rate is 250 L / h) is introduced from the air inlet opened at the bottom of the oxidation tower 3 (the vertical distance between the air inlet and the bottom of the tower is 1 / 5 of the height of the oxidation tower). In the presence of a catalyst, the heated wastewater undergoes a wet oxidation reaction in the oxidation tower 3. The pressure of the oxidation reaction is 8 MPa and the residence time is 2 h. After the reaction, the outlet water temperature at the top of the oxidation tower 3 is 270°C. A part of the heat generated by the oxidation reaction is recovered by the steam production system 4 (waste heat boiler) and then enters the heat exchanger 1 for preheating the wastewater. The excess heat is recovered by the steam production system 4 (waste heat boiler) to produce water vapor as a by-product. After the reaction, treated purified water is obtained.

[0091] Example 4

[0092] The method of Example 1 is followed, except that the temperature of the preheated wastewater flowing out of the outlet of the heat exchanger 1 is 180° C., and treated purified water is obtained after the reaction is completed.

[0093] Example 5

[0094] The method of Example 1 is followed, except that the reflux ratio of the oxidation tower 3 is 1, and treated purified water is obtained after the reaction is completed.

[0095] Example 6

[0096] The method of Example 1 is different in that the vertical distance between the water outlet on the side line of oxidation tower 3 and the water outlet on the top of the tower accounts for 1 / 2 of the height of oxidation tower 3.

[0097] Comparative Example 1

[0098] The method of Example 1 is different in that the external circulation pump 5 and the steam production system 4 are not provided in the wet oxidation reaction device, and the heater 6 is provided on the pipeline connecting the heat exchanger 1 and the oxidation tower 3. The wastewater and the water outlet from the top of the oxidation tower 3 are heat exchanged in the heat exchanger 1 to obtain preheated wastewater, so that the temperature of the preheated wastewater flowing out of the outlet of the heat exchanger 1 is 140°C. The temperature of the wastewater is quickly raised to 235°C by the heater 6, and the heated wastewater enters the oxidation tower 3 from the bottom of the oxidation tower 3 for wet oxidation reaction. After the reaction, treated purified water is obtained.

[0099] Test Example 1

[0100] After the reaction was completed, the COD values ​​in the purified water of the embodiment and the comparative example were measured, and the COD removal rate and oxidation efficiency were calculated. The results are shown in Table 1.

[0101] COD removal rate (%) = 100% × (COD value in wastewater - COD value in purified water) / COD value in wastewater.

[0102] Oxidation efficiency refers to the amount of organic matter removed from the wastewater to be treated per unit time. Oxidation efficiency (mg / (L·h)) = (COD value in the wastewater to be treated - COD value in the purified water) / residence time.

[0103] Test Example 2

[0104] The amount of steam produced as a byproduct of the steam production system (waste heat boiler) and the heat utilization rate, as well as the amount of coking in the heat exchanger and the heater in the test examples and comparative examples are shown in Table 1.

[0105] Heat utilization rate = preheating boiler output heat / total heat input system.

[0106] The steam volume (kg / h) was measured using a steam flow meter.

[0107] The amount of coking (kg) in the heat exchanger and heater was measured by gravimetric method after the reaction was run for 15 days.

[0108] Table 1

[0109]

[0110] It can be seen from Examples 1-3 that the use of the preferred implementation of the present invention can further improve the oxidation efficiency of wastewater treatment, while improving the heat exchange efficiency and heat utilization rate of the device, and also solves the problem of coking, scaling and clogging of the tube walls of the heater and heat exchanger during wet oxidation treatment of high-concentration organic wastewater.

[0111] Compared with the embodiment, the temperature of the preheated wastewater flowing out of the outlet of the heat exchanger in embodiment 4 is higher, resulting in a decrease in heat utilization and an increase in the amount of coking in the heat exchanger.

[0112] Compared with the examples, the reflux rate of the oxidation tower in Example 5 is relatively low, resulting in a decrease in heat utilization and an increase in the amount of coking in the heater.

[0113] Compared with the examples, the water outlet on the side line of the oxidation tower in Example 6 is arranged in the middle and lower part of the oxidation tower, resulting in a decrease in oxidation efficiency, heat utilization rate and steam volume, and an increase in the coking amount of the heater.

[0114] Compared with the embodiments, the wet oxidation reaction device in Comparative Example 1 is not equipped with an external circulation pump and a steam production system, and the heater is arranged on the pipeline connecting the heat exchanger and the oxidation tower. After the wastewater is heat exchanged in the heat exchanger, it is heated by the heater, resulting in a decrease in the COD removal rate, serious coking of the tube walls of the heater and the heat exchanger, and a decrease in the oxidation efficiency and heat utilization rate of the wastewater treatment.

[0115] In summary, the method of the present invention can improve the oxidation efficiency of wet oxidation treatment of high-concentration wastewater, improve the heat exchange efficiency and heat utilization rate of the reaction equipment, and reduce the amount of scaling in the heater and heat exchanger tube wall.

[0116] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for treating wastewater, characterized in that: The method comprises: preheating the wastewater to be treated and introducing it into an oxidation tower, drawing out part of the wastewater from a water outlet on a side line of the oxidation tower through a reflux pipeline for reflux and mixing it with the preheated wastewater in a mixer before entering the oxidation tower for oxidation reaction, and drawing out the treated wastewater from a water outlet on the top of the oxidation tower; The preheating method is as follows: the wastewater to be treated is heat exchanged with the water from the top of the oxidation tower to increase the temperature of the wastewater to be treated; the temperature of the refluxed wastewater is mixed with the preheated wastewater to reach the temperature of the oxidation reaction.

2. The method according to claim 1, wherein: The vertical distance between the water outlet on the side line of the oxidation tower and the water outlet on the top of the tower accounts for 1 / 5-2 / 5 of the height of the oxidation tower; And / or, the temperature of the wastewater to be treated after preheating is 120-150°C; Preferably, a heater is provided on the return line so that the returned wastewater is heated before entering the mixer; More preferably, the heating conditions of the heater are such that the temperature of the wastewater returning before entering the mixer is ≥250°C, preferably 260-270°C.

3. The method according to claim 1 or 2, wherein: The heat exchange is carried out in a heat exchanger, and the heat exchange method is: recovering the heat of the treated wastewater through a steam production system, and inputting the wastewater with recovered heat into the heat exchanger for heat exchange with the wastewater to be treated.

4. The method according to claim 3, wherein: The water outlet of the heat exchanger is connected to the water inlet of the mixer; the water inlet at the bottom of the oxidation tower is connected to the water outlet of the mixer; the water inlet of the steam production system is connected to the water outlet at the top of the oxidation tower, and the water outlet of the steam production system is connected to the heat exchanger; the water outlet of the heater is connected to the water inlet of the mixer.

5. The method according to claim 3, wherein: The steam production system is a waste heat boiler.

6. The method according to any one of claims 1 to 5, wherein: The reflux ratio of the oxidation tower is 2-5.

7. The method according to any one of claims 1 to 6, wherein: The oxidation reaction method comprises: introducing wastewater into the oxidation tower to carry out oxidation reaction in the presence of an oxygen source and a catalyst; Preferably, the oxygen source comprises air and / or oxygen; Preferably, the catalyst is selected from homogeneous catalysts and / or heterogeneous catalysts.

8. The method according to claim 7, wherein: The catalyst is a homogeneous catalyst, and the amount of the catalyst used is 50-2000 mg / L based on the metal ions in the homogeneous catalyst; Alternatively, the catalyst is a heterogeneous catalyst, and the filling amount of the catalyst is 0.5-3 times the flow rate of the wastewater; And / or, the conditions of the oxidation reaction include: temperature of 210-290°C, preferably 220-270°C; pressure of 2-9MPa, preferably 4-7MPa; residence time of 1-5h, preferably 2-4h; Preferably, the COD value of the wastewater to be treated is 30,000-150,000 mg / L.

9. The method according to claim 2, wherein: An external circulation pump is arranged on the reflux pipeline of the oxidation tower side line; the water inlet of the external circulation pump is connected to the water outlet on the oxidation tower side line, and the water outlet is connected to the inlet of the heater.

10. The method according to claim 3, wherein: An air inlet is provided at the bottom of the oxidation tower for providing an oxygen source from an external source; And / or, the water inlet of the heat exchanger is connected to a source of wastewater to be treated.

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