A printing and dyeing wastewater waste heat recovery process

Abstract

The application provides a printing and dyeing wastewater waste heat recovery process, and belongs to the technical field of waste heat recovery.The process comprises the following steps: S1, partition collection; according to the different temperature intervals of printing and dyeing hot wastewater, the wastewater is collected and transported respectively; S2, pretreatment; the hot wastewater is subjected to catalytic degradation and coagulation and sedimentation double treatment to obtain up-to-standard wastewater; the reagent for catalytic degradation comprises persulfate and a CNTs-Co-ACFs catalyst; the CNTs-Co-ACFs catalyst is a three-dimensional cage structure catalyst of carbon fiber and carbon nanotube composite loaded cobalt; S3, waste heat recovery; the up-to-standard wastewater is introduced into a sewage source heat pump; the wastewater recovered through heat is discharged from the heat medium output end of the sewage source heat pump and is further subjected to water quality treatment to be discharged; clean softened water is heated through the sewage source heat pump to form high-temperature hot water which enters a high-temperature hot water use equipment.The application improves the removal rate of organic matters in the printing and dyeing hot wastewater before a heat exchanger, improves the waste heat recovery efficiency, and effectively avoids the blockage, pollution and corrosion of the heat exchanger or the sewage source heat pump.

Description

Technical Field

[0001] This invention belongs to the field of waste heat recovery technology, specifically relating to a waste heat recovery process for dyeing and printing wastewater. Background Technology

[0002] The dyeing and printing industry is a high-energy-consuming industry, which consumes a large amount of steam and discharges wastewater containing a large amount of heat into the environment. On average, 3.5-5.5 tons of wastewater at different temperatures are generated for every 100m³ of product processed. Dyeing and printing wastewater is characterized by large volume and high content of organic pollutants, complex composition, deep color, and large variation in water quality, making it difficult to treat industrial wastewater.

[0003] Currently, dyeing and printing enterprises either directly discharge their hot wastewater into wastewater treatment systems, causing the wastewater temperature in these systems to reach around 50°C. This not only inhibits the efficiency of biochemical treatment but also results in a serious waste of waste heat resources. Alternatively, they directly pass the hot wastewater into heat exchangers or wastewater source heat pumps for heat exchange, achieving both waste heat recovery and cooling of the hot wastewater. However, because the hot wastewater contains a large number of colloidal particles and impurities, these particles and impurities are prone to adsorption, leading to a decrease in the efficiency of heat exchangers or wastewater source heat pumps. This can even cause blockages, contamination, and corrosion of the heat exchangers or wastewater source heat pumps, affecting heat exchange efficiency and potentially requiring frequent cleaning and maintenance, increasing process costs and time.

[0004] The colloidal particles and impurities in dyeing and printing wastewater mainly include dyes, sizing agents, dyeing auxiliaries, fiber impurities, oils, acids, alkalis, and inorganic salts. Among these, colloidal particles primarily consist of organic colloidal particles, various oily impurities appearing as emulsions, and fine fibers and cilia from hydrophobic synthetic fibers. Furthermore, due to the thermal motion and collision forces between water molecules, these colloidal and fine suspended matter undergo random Brownian motion and are affected by electrostatic repulsion. Effective treatment of these substances typically requires electrocoagulation technology or the use of coagulants, such as inorganic salts like aluminum sulfate, alum, and ferric chloride, and polymeric coagulants like basic aluminum chloride and polyacrylic acid (PAM). However, relying on these common coagulants is not ideal for removing organic matter from dyeing and printing wastewater; the organic matter removal rate is low, affecting the efficiency of subsequent waste heat recovery from the wastewater. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides a waste heat recovery process for dyeing and printing wastewater, which improves the removal rate of organic matter in dyeing and printing wastewater before the heat exchanger, enhances the waste heat recovery efficiency of dyeing and printing wastewater, and effectively avoids blockage, pollution and corrosion of heat exchangers or sewage source heat pumps.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A process for recovering waste heat from dyeing and printing wastewater includes the following steps:

[0008] S1. Zoned collection: The hot wastewater generated by the dyeing and printing equipment is collected and transported separately according to different temperature ranges.

[0009] S2. Pretreatment; simultaneously, the hot wastewater is subjected to dual treatment of catalytic degradation and coagulation sedimentation to obtain wastewater that meets the standards; wherein, the catalytic degradation agents include persulfate and CNTs-Co-ACFs catalyst, and the CNTs-Co-ACFs catalyst is a three-dimensional cage-like structure catalyst with cobalt supported by carbon fiber and carbon nanotube composite.

[0010] S3, Waste heat recovery; The qualified wastewater obtained from S2 is fed into the sewage source heat pump. The wastewater that has undergone heat recovery flows out from the heating medium output end of the sewage source heat pump and undergoes further biochemical treatment before being discharged; The clean and softened water is heated by the sewage source heat pump to form high-temperature hot water, which then enters the high-temperature hot water usage equipment.

[0011] Furthermore, the preparation method of the CNTs-Co-ACFs catalyst is as follows:

[0012] A1. First, soak the carbon fiber in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 65-75% strong acid solution and soak it at room temperature for 4-5 hours. Filter it out and dry it naturally to obtain acid-washed carbon fiber.

[0013] A2. The acid-washed carbon fiber is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the carbon fiber is cooled to room temperature under the protection of high-purity nitrogen to obtain air-blown carbon fiber.

[0014] A3. Immerse the air-blown carbon fiber in a 0.02-0.05 mol / L cobalt nitrate solution, add 60% strong acid solution dropwise, the volume ratio of strong acid solution to cobalt nitrate solution is 0.03-0.05:1, immerse for 4-5 hours, filter out, and dry naturally to obtain the CNTs-Co-ACFs catalyst.

[0015] Furthermore, the strong acid is any one of hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid.

[0016] Furthermore, in A3, the volume ratio of the strong acid solution to the cobalt nitrate solution is 0.04:1.

[0017] Furthermore, in S1, the temperature of the hot wastewater generated by the dyeing and printing equipment is divided into three intervals: the first interval, with a temperature below 60℃; the second interval, with a temperature between 60℃ and 80℃; and the third interval, with a temperature above 80℃.

[0018] Further, the specific operating steps of S2 are as follows: Hot wastewater is introduced into a pretreatment tank, sodium persulfate is added to the hot wastewater at a mass ratio of 0.8‰-2‰, and coagulant is added to the hot wastewater at a mass ratio of 0.2‰-0.4‰; the pretreatment tank is equipped with a filter box for holding CNTs-Co-ACFs catalyst, and an ultrasonic oscillator is provided in the pretreatment tank. Ultrasonic stimulation synergistically degrades organic matter in the hot wastewater by CNTs-Co-ACFs catalyst and persulfate; simultaneously, the coagulant causes colloidal particles in the hot wastewater to coagulate and flocculate, thus separating them; filtration yields the qualified wastewater.

[0019] Furthermore, in S2, the coagulant used for coagulation and sedimentation is one or more of aluminum sulfate, alum, and ferric chloride.

[0020] Furthermore, in S3, the water biochemical treatment includes anaerobic treatment, anoxic treatment, aerobic treatment, and sedimentation treatment.

[0021] Furthermore, in S3, the high-temperature hot water usage equipment includes a flash evaporation device and a steam compressor, which further flash evaporates and compresses the high-temperature hot water to prepare high-temperature steam, which is used to supplement the high-temperature steam required for production in the dyeing and printing enterprise workshop.

[0022] This part of the process equipment includes a wastewater source heat pump, a flash tank, a steam compressor, and a buffer tank connected by pipelines. The flash tank is used to collect high-temperature hot water formed by heating clean softened water from the wastewater source heat pump; the flash tank is connected to the wastewater source heat pump through a first pipeline, on which a steam trap is installed; the flash tank is also connected to the steam compressor, which is connected to the wastewater source heat pump through the buffer tank.

[0023] This application has the following beneficial effects:

[0024] 1. This invention employs a dual treatment process of catalytic degradation and coagulation sedimentation for dyeing and printing wastewater. After obtaining wastewater that meets standards, heat exchange is then performed. Before heat exchange, the removal rate of organic matter in the dyeing and printing wastewater is improved, thereby enhancing the subsequent waste heat recovery efficiency and effectively preventing blockage, contamination, and corrosion of the heat exchanger or wastewater source heat pump. The catalytic degradation agents include persulfate and CNTs-Co-ACFs catalysts. The CNTs-Co-ACFs catalyst is a three-dimensional cage-like catalyst composed of carbon fiber and carbon nanotubes loaded with cobalt, which can efficiently activate persulfate, rapidly and efficiently generating strong oxidizing free radicals, and rapidly and efficiently degrading organic matter. Simultaneously, synergistic coagulation sedimentation further improves the organic matter removal rate.

[0025] 2. A composite catalyst with a three-dimensional cage structure formed by immobilizing a cobalt-supported cobalt catalyst on a carbon-based support (carbon fiber (ACFs)-derived carbon nanotubes (CNTs)) activates persulfate. Ultrasound intensifies the stretching and rotational vibrations of molecules, enhances the probability of intermolecular collisions, and the ultrasound can travel through the three-dimensional cage structure. With the support of intense heat energy, it generates highly oxidizing free radicals more efficiently.

[0026] 3. The wastewater inlet of the hot wastewater collection device of the present invention is equipped with a fine screen to intercept substances such as yarn and particulate matter in the wastewater; the outer wall of the device is equipped with an insulation layer for heat preservation, thereby minimizing heat loss from the hot wastewater; the bottom of the side wall of the device is equipped with a scraper and a drain outlet with an opening and closing door, and the bottom surface of the device is inclined to facilitate timely discharge of deposited pollutants at the bottom of the hot wastewater collection device; in addition, the hot wastewater collection device is symmetrically equipped with a flow-pushing agitator to ensure that hot wastewater of different temperatures within the same temperature range can be mixed evenly, ensuring the stable operation of the waste heat recovery system for dyeing and printing hot wastewater. Attached Figure Description

[0027] Figure 1 This is a flow chart of the waste heat recovery process for dyeing and printing wastewater according to the present invention.

[0028] Figure 2 This is a schematic diagram illustrating the principle of the cobalt catalyst catalyzing the degradation of organic matter in thermal wastewater by persulfate.

[0029] Figure 3 This is a schematic diagram illustrating the principle of ultrasonic synergistic CNTs-Co-ACFs catalytic degradation of organic matter in thermal wastewater by persulfate in this invention;

[0030] Figure 4 The COD of the compliant wastewater and effluent in Examples 1-6 of this invention cr Removal rate and BOD5 removal rate trend chart;

[0031] Figure 5 The COD of the compliant wastewater and effluent in Examples 2 and Comparative Examples 1-10 of this invention is shown. cr Removal rate and BOD5 removal rate trend chart;

[0032] Figure 6 The COD of the compliant wastewater and effluent in Examples 2 and Comparative Examples 1-5 of this invention is shown. cr Removal rate and BOD5 removal rate trend chart;

[0033] Figure 7 The COD of the compliant wastewater and effluent in Examples 2 and Comparative Examples 6-10 of this invention is shown. cr Removal rate and BOD5 removal rate trend chart. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the embodiments.

[0035] The time taken for the same processing steps in each embodiment and comparative example is basically the same, and will not be described in detail here.

[0036] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0037] Example 1

[0038] A process for recovering waste heat from dyeing and printing wastewater includes the following steps:

[0039] S1. Zoned collection: The hot wastewater generated by the dyeing and printing equipment is collected and transported separately according to different temperature ranges.

[0040] Specifically, based on the different temperatures of the hot wastewater generated by the dyeing and printing equipment, it is divided into three zones: the first zone, with a temperature below 60℃; the second zone, with a temperature between 60℃ and 80℃; and the third zone, with a temperature above 80℃. The hot wastewater from each of the three zones is collected, transported, and treated separately.

[0041] The wastewater inlet of the hot wastewater collection device is equipped with a fine screen to intercept substances such as wool and particulate matter in the wastewater. The outer wall of the device is equipped with an insulation layer to keep it warm and minimize heat loss from the hot wastewater. The bottom of the side wall of the device is equipped with a scraper and a drain outlet with an opening and closing door, and the bottom surface of the device is sloped to facilitate the timely discharge of pollutants deposited at the bottom of the hot wastewater collection device. In addition, the hot wastewater collection device is symmetrically equipped with a flow agitator to ensure that hot wastewater of different temperatures within the same temperature range can be mixed evenly, ensuring the continuous and stable operation of the dyeing and printing hot wastewater waste heat recovery system.

[0042] S2. Pretreatment; simultaneously, the hot wastewater undergoes dual treatment of catalytic degradation and coagulation sedimentation to obtain compliant wastewater; wherein, the catalytic degradation uses persulfate and CNTs-Co-ACFs catalyst, and the CNTs-Co-ACFs catalyst is a three-dimensional cage-like structure catalyst with cobalt supported by carbon fiber and carbon nanotube composite.

[0043] Specifically, hot wastewater is fed into a pretreatment tank, and sodium persulfate is added to the hot wastewater at a mass ratio of 0.8‰, while coagulant is added at a mass ratio of 0.2‰. The pretreatment tank is equipped with a filter box for holding CNTs-Co-ACFs catalyst and an ultrasonic vibrator. Ultrasonic stimulation synergizes with CNTs-Co-ACFs to catalyze the degradation of organic matter in the hot wastewater by persulfate. At the same time, the coagulant causes colloidal particles in the hot wastewater to coagulate and flocculate, thus separating them. After filtration, the qualified wastewater is obtained.

[0044] The coagulant is aluminum sulfate.

[0045] The preparation method of the CNTs-Co-ACFs catalyst is as follows:

[0046] A1. First, soak the carbon fiber in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 68% strong acid solution and soak it at room temperature for 4 hours. Filter it out and dry it naturally to obtain acid-washed carbon fiber.

[0047] A2. The acid-washed carbon fiber is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the carbon fiber is cooled to room temperature under the protection of high-purity nitrogen to obtain air-blown carbon fiber.

[0048] A3. Immerse the air-blown carbon fibers in a 0.03 mol / L cobalt nitrate solution, then add a 60% strong acid solution (volume ratio of strong acid solution to cobalt nitrate solution is 0.04:1). Immerse for 4 hours, filter, and air dry to obtain the CNTs-Co-ACFs catalyst. The strong acid is nitric acid.

[0049] S3. Waste heat recovery: The qualified wastewater obtained from S2 is fed into a sewage source heat pump. The wastewater that has undergone heat recovery flows out from the heating medium output end of the sewage source heat pump for further biological treatment. The biological treatment includes anaerobic treatment, anoxic treatment, aerobic treatment and sedimentation treatment. The dyeing and printing wastewater that has undergone waste heat recovery can be further treated until the water quality meets the requirements of relevant standards and specifications before being discharged, thereby further reducing pollution.

[0050] Clean and softened water is heated by a wastewater source heat pump to form high-temperature hot water, which then enters high-temperature hot water usage equipment, including boilers and dyeing equipment.

[0051] High-temperature hot water can also be sequentially introduced into flash evaporation equipment and steam compressor for further flash evaporation and compression to prepare high-temperature steam, which can be used to supplement the high-temperature steam required for production in the dyeing and printing workshop.

[0052] Specifically, this part of the process equipment includes a wastewater source heat pump, a flash tank, a steam compressor, and a buffer tank connected by pipelines. The flash tank is used to collect high-temperature hot water formed by heating clean softened water from the wastewater source heat pump; the flash tank is connected to the wastewater source heat pump through a first pipeline, on which a steam trap is installed; the flash tank is also connected to the steam compressor, which is connected to the wastewater source heat pump via the buffer tank.

[0053] During use, high-temperature hot water from the wastewater source heat pump flows into the flash tank for flash evaporation. The flash steam then enters the steam compressor for compression. The compressed flash steam then enters the buffer tank, and the steam pressure can be adjusted as needed to supply the production sections required by the dyeing and printing enterprise workshop.

[0054] The buffer tank is also equipped with a minimum pressure steam valve and a buffer tank pressure sensor. The buffer tank pressure sensor has a preset pressure value for the buffer tank. When the pressure inside the buffer tank is lower than the preset pressure value, the minimum pressure steam valve remains closed; when the pressure inside the buffer tank is higher than the preset pressure value, the minimum pressure steam valve opens. This is used to automatically regulate the minimum steam pressure to ensure sufficient pressure is supplied smoothly to the production stages required by the dyeing and printing enterprise workshop.

[0055] Example 2

[0056] The only difference between this embodiment and embodiment 1 is that in S2, hot wastewater is introduced into the pretreatment tank, sodium persulfate is added to the hot wastewater at a mass ratio of 1.5‰, and coagulant is added to the hot wastewater at a mass ratio of 0.3‰.

[0057] Specifically as follows:

[0058] S2. Pretreatment: Hot wastewater is fed into a pretreatment tank. Sodium persulfate is added to the hot wastewater at a mass ratio of 1.5‰, and a coagulant is added at a mass ratio of 0.3‰. The pretreatment tank is equipped with a filter box for holding the CNTs-Co-ACFs catalyst. The filter box contains the CNTs-Co-ACFs catalyst. The pretreatment tank is also equipped with an ultrasonic vibrator. Ultrasonic stimulation synergistically degrades organic matter in the hot wastewater by CNTs-Co-ACFs with the degradation of persulfate. Simultaneously, the coagulant causes colloidal particles in the hot wastewater to coagulate and flocculate, thus separating them. After filtration, the treated wastewater meets the standards. The coagulant is alum.

[0059] Example 3

[0060] The only difference between this embodiment and embodiment 1 is that in S2, hot wastewater is introduced into the pretreatment tank, sodium persulfate is added to the hot wastewater at a mass ratio of 2‰, and coagulant is added to the hot wastewater at a mass ratio of 0.4‰.

[0061] Specifically as follows:

[0062] S2. Pretreatment: Hot wastewater is fed into a pretreatment tank. Sodium persulfate is added to the hot wastewater at a mass ratio of 2‰, and coagulant is added at a mass ratio of 0.4‰. The pretreatment tank is equipped with a filter box for holding the CNTs-Co-ACFs catalyst. The filter box contains the CNTs-Co-ACFs catalyst. The pretreatment tank is also equipped with an ultrasonic vibrator. Ultrasonic stimulation synergistically degrades organic matter in the hot wastewater by CNTs-Co-ACFs with the degradation of persulfate. Simultaneously, the coagulant causes colloidal particles in the hot wastewater to coagulate and flocculate, thus separating them. After filtration, the qualified wastewater is obtained. The coagulant is a mixture of equal parts aluminum sulfate and alum.

[0063] Example 4

[0064] The only difference between this embodiment and embodiment 1 is that in S2, hot wastewater is introduced into the pretreatment tank, sodium persulfate is added to the hot wastewater at a mass ratio of 1.85‰, and coagulant is added to the hot wastewater at a mass ratio of 0.25‰.

[0065] Specifically as follows:

[0066] S2. Pretreatment: Hot wastewater is introduced into a pretreatment tank. Sodium persulfate is added to the hot wastewater at a mass ratio of 1.85‰, and a coagulant is added at a mass ratio of 0.25‰. The pretreatment tank is equipped with a filter box for holding the CNTs-Co-ACFs catalyst. The filter box contains the CNTs-Co-ACFs catalyst. The pretreatment tank is also equipped with an ultrasonic vibrator. Ultrasonic stimulation synergistically degrades organic matter in the hot wastewater by CNTs-Co-ACFs with the degradation of persulfate. Simultaneously, the coagulant causes colloidal particles in the hot wastewater to coagulate and flocculate, thus separating them. After filtration, the treated wastewater meets the standards. The coagulant is ferric chloride.

[0067] Example 5

[0068] The only difference between this embodiment and Example 1 is that in the preparation method of the CNTs-Co-ACFs catalyst, in step A3, the volume ratio of the strong acid solution to the cobalt nitrate solution is 0.03:1.

[0069] Specifically, the preparation method of CNTs-Co-ACFs catalyst is as follows:

[0070] A1. First, soak the carbon fiber in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 68% strong acid solution and soak it at room temperature for 4 hours. Filter it out and dry it naturally to obtain acid-washed carbon fiber.

[0071] A2. The acid-washed carbon fiber is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the carbon fiber is cooled to room temperature under the protection of high-purity nitrogen to obtain air-blown carbon fiber.

[0072] A3. Immerse the air-blown carbon fibers in a 0.04 mol / L cobalt nitrate solution, then add a 60% strong acid solution (volume ratio of strong acid solution to cobalt nitrate solution is 0.03:1). Immerse for 4 hours, filter, and air dry to obtain the CNTs-Co-ACFs catalyst. The strong acid is nitric acid.

[0073] Example 6

[0074] The difference between this embodiment and Example 1 is that in the preparation method of CNTs-Co-ACFs catalyst, in step A3, the volume ratio of strong acid solution to cobalt nitrate solution is 0.05:1.

[0075] Specifically, the preparation method of CNTs-Co-ACFs catalyst is as follows:

[0076] A1. First, soak the carbon fiber in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 74% strong acid solution and soak it at room temperature for 4 hours. Filter it out and dry it naturally to obtain acid-washed carbon fiber.

[0077] A2. The acid-washed carbon fiber is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the carbon fiber is cooled to room temperature under the protection of high-purity nitrogen to obtain air-blown carbon fiber.

[0078] A3. Immerse the air-blown carbon fibers in a 0.05 mol / L cobalt nitrate solution, then add a 60% strong acid solution dropwise. The volume ratio of the strong acid solution to the cobalt nitrate solution is 0.05:1. Immerse for 4 hours, filter, and air dry to obtain the CNTs-Co-ACFs catalyst. The strong acid is nitric acid.

[0079] Comparative Example 1

[0080] The only difference between this comparative example and Example 2 is that in the S2 pretreatment, the hot wastewater is only subjected to coagulation and sedimentation treatment and filtration to obtain qualified wastewater. The coagulant is the same as in Example 2, which is alum.

[0081] Comparative Example 2

[0082] The only difference between this comparative example and Example 2 is that in the S2 pretreatment, the hot wastewater is only subjected to catalytic degradation treatment to obtain wastewater that meets the standards.

[0083] Comparative Example 3

[0084] The only difference between this comparative example and Example 2 is that, in the S2 pretreatment, catalytic degradation and coagulation sedimentation treatment are not performed simultaneously. Specifically:

[0085] S2. Pretreatment: The hot wastewater is first subjected to catalytic degradation treatment, and then subjected to coagulation and sedimentation treatment to obtain wastewater that meets the standards; wherein, the catalytic degradation agents include persulfate and CNTs-Co-ACFs catalyst, and the CNTs-Co-ACFs catalyst is a three-dimensional cage-like structure catalyst with cobalt supported by carbon fiber and carbon nanotube composite.

[0086] Specifically, hot wastewater is fed into a pretreatment tank, where sodium persulfate is added at a mass ratio of 0.8‰. The pretreatment tank is equipped with a filter box for holding CNTs-Co-ACFs catalyst and an ultrasonic oscillator. Ultrasonic stimulation synergistically degrades organic matter in the hot wastewater using CNTs-Co-ACFs catalyst. Then, the hot wastewater from the pretreatment tank flows into a second pretreatment tank, where a coagulant is added at a mass ratio of 0.2‰. The coagulant causes colloidal particles in the hot wastewater to coagulate and flocculate, separating them. After filtration, the treated wastewater meets the standards.

[0087] Comparative Example 4

[0088] The only difference between this comparative example and Example 2 is that, in the S2 pretreatment, an ultrasonic oscillator is not installed in the pretreatment pool.

[0089] Comparative Example 5

[0090] The only difference between this comparative example and Example 2 is that in the S2 pretreatment, the coagulant is polydimethyldiallylammonium chloride.

[0091] Comparative Example 6

[0092] The only difference between this comparative example and Example 2 is that the preparation method of the CNTs-Co-ACFs catalyst does not include the A1 and A2 treatment steps. Specifically:

[0093] The preparation method of CNTs-Co-ACFs catalyst is as follows: carbon fibers are soaked in a 0.03 mol / L cobalt nitrate solution, and a 60% strong acid solution is added dropwise. The volume ratio of the strong acid solution to the cobalt nitrate solution is 0.04:1. After soaking for 4 hours, the solution is filtered out and naturally dried to obtain the CNTs-Co-ACFs catalyst. The strong acid is nitric acid.

[0094] Comparative Example 7

[0095] The only difference between this comparative example and Example 2 is that the preparation method of the CNTs-Co-ACFs catalyst does not include the A2 treatment step. Specifically:

[0096] The preparation method of CNTs-Co-ACFs catalyst is as follows: first, carbon fiber is soaked in distilled water and anhydrous ethanol respectively and ultrasonically cleaned for 30 min, then immersed in 68% strong acid solution and soaked at room temperature for 4 hours, filtered out, and naturally dried to obtain acid-washed carbon fiber.

[0097] The acid-washed carbon fibers were immersed in a 0.03 mol / L cobalt nitrate solution, and a 60% strong acid solution was added dropwise. The volume ratio of the strong acid solution to the cobalt nitrate solution was 0.04:1. After immersion for 4 hours, the solution was filtered out and naturally dried to obtain the CNTs-Co-ACFs catalyst. The strong acid was nitric acid.

[0098] Comparative Example 8

[0099] The only difference between this comparative example and Example 2 is that in the preparation method of the CNTs-Co-ACFs catalyst, in the A3 treatment step, a strong acid solution is not added dropwise to the cobalt nitrate solution. Specifically:

[0100] The preparation method of CNTs-Co-ACFs catalyst is as follows:

[0101] A1. First, soak the carbon fiber in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 68% strong acid solution and soak it at room temperature for 4 hours. Filter it out and dry it naturally to obtain acid-washed carbon fiber. The strong acid is nitric acid.

[0102] A2. The acid-washed carbon fiber is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the carbon fiber is cooled to room temperature under the protection of high-purity nitrogen to obtain air-blown carbon fiber.

[0103] A3. Immerse the air-blown carbon fiber in a 0.03 mol / L cobalt nitrate solution for 4 hours, filter it out, and dry it naturally to obtain the CNTs-Co-ACFs catalyst.

[0104] Comparative Example 9

[0105] The only difference between this comparative example and Example 2 is that in the preparation method of the Co metal catalyst (CNTs-Co-ACFs catalyst), graphene is used as the Co support. Specifically:

[0106] The preparation method of Co metal catalyst is as follows:

[0107] A1. First, soak the graphene in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 68% strong acid solution and soak it at room temperature for 4 hours. Filter it out and dry it naturally to obtain acid-washed graphene.

[0108] A2. The acid-washed graphene is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the graphene is cooled to room temperature under the protection of high-purity nitrogen to obtain gas-blown graphene.

[0109] A3. Immerse the air-blown graphene in a 0.03 mol / L cobalt nitrate solution, then add a 60% strong acid solution dropwise. The volume ratio of the strong acid solution to the cobalt nitrate solution is 0.04:1. Immerse for 4 hours, filter, and allow to air dry to obtain the Co metal catalyst. The strong acid is nitric acid.

[0110] Comparative Example 10

[0111] The only difference between this comparative example and Example 2 is that in the preparation method of the Co metal catalyst (CNTs-Co-ACFs catalyst), graphene oxide is used as the Co support. Specifically:

[0112] The preparation method of Co metal catalyst is as follows:

[0113] A1. First, soak the graphene oxide in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 68% strong acid solution and soak it at room temperature for 4 hours. Filter it out and dry it naturally to obtain acid-washed graphene oxide.

[0114] A2. The acid-washed graphene oxide is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the mixture is cooled to room temperature under the protection of high-purity nitrogen to obtain gas-blown graphene oxide.

[0115] A3. Immerse the air-blown graphene oxide in a 0.03 mol / L cobalt nitrate solution, then add a 60% strong acid solution (volume ratio of strong acid solution to cobalt nitrate solution is 0.04:1). Immerse for 4 hours, filter, and allow to air dry to obtain the Co metal catalyst. The strong acid is nitric acid.

[0116] Experimental Example 1

[0117] Existing wastewater treatment technologies include Fenton oxidation, Fe-C treatment, and ozone oxidation.

[0118] Table 1 shows a comparison of the parameters of the Co catalytic oxidation method selected in this invention with the three existing technologies mentioned above.

[0119] Table 1

[0120]

[0121] As can be seen from the comparison of statistical parameters in Table 1, the Co catalytic oxidation method selected in this invention has obvious advantages in terms of the removal rate of organic matter in wastewater treatment. Therefore, this invention preferably uses the Co catalytic oxidation method as the basis for pretreatment of dyeing and printing heat wastewater before preheating and recovery.

[0122] Experimental Example 2

[0123] Testing standard: GB / T4287-2012 "Water Pollutant Discharge Standard for Textile Dyeing and Finishing Industry";

[0124] Test objects: Select the same batch of dyeing and printing wastewater and treat it using the methods of Examples 1-6 and Comparative Examples 1-10. The qualified wastewater after S2 treatment and the effluent after S3 treatment in Examples 1-6 and Comparative Examples 1-10 are tested.

[0125] Test items:

[0126] 1. COD of compliant wastewater cr Removal rate and BOD5 removal rate are as follows:

[0127]

[0128]

[0129] 2. COD of the discharged water cr Removal rate and BOD5 removal rate are as follows:

[0130]

[0131]

[0132] Among them, dyeing and printing wastewater refers to wastewater before pretreatment; qualified wastewater refers to wastewater after pretreatment; and effluent refers to wastewater that has undergone biochemical treatment before being discharged.

[0133] Test results: See Table 2.

[0134] Table 2. Test data of qualified wastewater and effluent from Examples 1-6 and Comparative Examples 1-10

[0135]

[0136] Results Analysis

[0137] Analyze Examples 1-6 and Table 2, and combine them with Figure 4 It can be seen that after pretreatment, the COD of the compliant wastewater... cr The removal rate is consistently above 85%, and then heat exchange (waste heat recovery) is carried out, which can significantly improve the waste heat recovery efficiency and effectively avoid the heat exchanger or sewage source heat pump being blocked, contaminated and corroded; among them, Example 2 is the best example.

[0138] Analyze Example 2 and Comparative Examples 1-5 and Table 2, and combine them with... Figure 5 and Figure 6 It can be seen that the simultaneous catalytic degradation and coagulation treatment processes have a synergistic effect on the removal of organic matter, and the removal effect is significantly better than that of sequential processing. This can shorten the working time, improve work efficiency, and enhance the work effect. Furthermore, the ultrasonic environment enhances the work effect during the dual treatment process. The coagulant used in conjunction with the CNTs-Co-ACFs catalyst of this invention is preferably an inorganic salt coagulant.

[0139] Analyze Example 2 and Comparative Examples 6-10 and Table 2, and combine them with... Figure 5 and Figure 7 It can be seen that acid washing and gas blowing pretreatment are indispensable in the preparation of CNTs-Co-ACFs catalysts; otherwise, the catalyst's performance in the dual treatment processes of catalytic degradation and coagulation will be directly affected. Furthermore, during the reaction of cobalt salt with the support solution, acid adjustment of the environment is required; otherwise, the performance will also be directly affected. Carbon fiber is the preferred raw material support and cannot be simply replaced with graphene and graphene oxide, which have similar properties; otherwise, the performance will also be directly affected.

[0140] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0141] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A process for recovering waste heat from dyeing and printing wastewater, characterized in that, Includes the following steps: S1. Zoned collection: The hot wastewater generated by the dyeing and printing equipment is collected and transported separately according to different temperature ranges. S2. Pretreatment; simultaneously, the hot wastewater is subjected to dual treatment of catalytic degradation and coagulation sedimentation to obtain wastewater that meets the standards; wherein, the catalytic degradation agents include persulfate and CNTs-Co-ACFs catalyst, and the CNTs-Co-ACFs catalyst is a three-dimensional cage-like structure catalyst with cobalt supported by carbon fiber and carbon nanotube composite. S3, Waste heat recovery; The qualified wastewater obtained from S2 is fed into the sewage source heat pump. The wastewater that has undergone heat recovery flows out from the heating medium output end of the sewage source heat pump and undergoes further biochemical treatment before being discharged; The clean and softened water is heated by the sewage source heat pump to form high-temperature hot water, which then enters the high-temperature hot water usage equipment. The preparation method of the CNTs-Co-ACFs catalyst is as follows: A1. First, soak the carbon fiber in distilled water and anhydrous ethanol respectively and ultrasonically clean it for 30 minutes. Then, immerse it in a 65-75% strong acid solution and soak it at room temperature for 4-5 hours. Filter it out and dry it naturally to obtain acid-washed carbon fiber. A2. The acid-washed carbon fiber is fed into a vapor deposition furnace and heated to 720°C within 3 hours under the protection of high-purity nitrogen. Then, acetylene gas is introduced and maintained at 720°C for 40 minutes. After that, the acetylene is turned off and the carbon fiber is cooled to room temperature under the protection of high-purity nitrogen to obtain air-blown carbon fiber. A3. Immerse the air-blown carbon fiber in a 0.02-0.05 mol / L cobalt nitrate solution, add a 60% strong acid solution with a volume ratio of 0.04:1 between the strong acid solution and the cobalt nitrate solution, soak for 4-5 hours, filter out, and air dry to obtain the CNTs-Co-ACFs catalyst. The strong acid is nitric acid.

2. The waste heat recovery process for dyeing and printing wastewater according to claim 1, characterized in that, In S1, the temperature of the hot wastewater generated by the dyeing and printing equipment is divided into three zones: the first zone, with a temperature below 60℃; the second zone, with a temperature between 60℃ and 80℃; and the third zone, with a temperature above 80℃.

3. The waste heat recovery process for dyeing and printing wastewater according to claim 1, characterized in that, The specific operating steps of S2 are as follows: Hot wastewater is introduced into a pretreatment tank. Sodium persulfate is added to the hot wastewater at a mass ratio of 0.8‰-2‰, and coagulant is added to the hot wastewater at a mass ratio of 0.2‰-0.4‰. The pretreatment tank is equipped with a filter box for holding CNTs-Co-ACFs catalyst and an ultrasonic vibrator. Ultrasonic stimulation synergistically degrades organic matter in the hot wastewater by CNTs-Co-ACFs catalyst and persulfate. Simultaneously, the coagulant causes colloidal particles in the hot wastewater to coagulate and flocculate, thus separating them. Filtration yields the qualified wastewater.

4. The waste heat recovery process for dyeing and printing wastewater according to claim 1, characterized in that, In S2, the coagulant used for coagulation and sedimentation is one or more of aluminum sulfate, alum, and ferric chloride.

5. The waste heat recovery process for dyeing and printing wastewater according to claim 1, characterized in that, In S3, the water biochemical treatment includes anaerobic treatment, anoxic treatment, aerobic treatment, and sedimentation treatment.

6. The waste heat recovery process for dyeing and printing wastewater according to claim 1, characterized in that, In S3, the high-temperature hot water usage equipment includes a flash evaporation device and a steam compressor, which further flash evaporates and compresses the high-temperature hot water to prepare high-temperature steam, which is used to supplement the high-temperature steam required for production in the dyeing and printing enterprise workshop.

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