Dilute sulfuric acid wastewater treatment system and treatment method

Abstract

The present invention relates to a dilute sulfuric acid wastewater treatment system and a treatment method. The dilute sulfuric acid wastewater treatment system comprises: a preheating device, a pre-concentration device, an evaporation crystallizer, a condensation device and a vacuum device. Among them, the evaporation crystallizer includes at least two independently working heaters, which ensures the long-term stable operation of the system. The preheating device makes full use of the heat energy generated in the dilute sulfuric acid wastewater treatment system, greatly saving the energy consumption of the system operation. The equipment through which the dilute sulfuric acid wastewater passes adopts zirconium and graphite materials, which reduces the corrosion of the acid waste liquid to the system equipment. The dilute sulfuric acid wastewater treatment method concentrates the dilute sulfuric acid wastewater at a temperature not exceeding 70°C, avoids the corrosion of the equipment by the sulfuric acid waste liquid at high temperature, and is conducive to long-term stable operation.

Description

Technical Field

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

[0002] There are three main methods for treating waste sulfuric acid with traditional technology: one is to directly discharge waste sulfuric acid and wastewater into the surrounding environment, causing serious pollution; the second is to use simple neutralization treatment, but due to the large amount of waste residue and the difficulty in dehydration, it is very easy to cause secondary pollution, and the operating cost is too high; the third is to use the traditional ion exchange method, but it is easy to produce wastewater during the regeneration process, and the operating cost is high, which is difficult to promote and apply on a large scale. In the process of industrial wastewater production, the cost of treating these sulfuric acid waste liquids is high and the effect is poor. Summary of the invention

[0003] Based on this, it is necessary to provide a dilute sulfuric acid wastewater treatment system and method with stable operation and energy saving.

[0004] In one aspect, the present invention provides a dilute sulfuric acid wastewater treatment system, comprising:

[0005] A preheating device, used to preheat the raw solution of dilute sulfuric acid wastewater;

[0006] A pre-concentration device, comprising an evaporation device and a first steam compressor, wherein the first liquid inlet of the evaporation device is connected to the first liquid outlet of the preheating device, and is used to evaporate and concentrate the preheated dilute sulfuric acid wastewater to obtain a first concentrated liquid and a first steam; one end of the first steam compressor is connected to the first air outlet of the evaporation device, and the other end is connected to the air inlet of the evaporation device, so that the first steam can be used as an evaporation heat source for the evaporation device after the first steam compressor increases the temperature and pressure; and

[0007] The evaporation crystallizer comprises a separator, at least two heaters and a second steam compressor; the first liquid inlet of the separator is connected to the concentrated liquid outlet of the evaporation device, and each of the heaters is independently connected to the separator to form a supernatant circulation channel, so that the supernatant in the separator enters the heater for heating and then returns to the separator for flash separation to obtain a second steam, a supernatant and a second concentrated liquid containing crystals; one end of the second steam compressor is connected to the air outlet of the separator, and the other end is connected to the air inlet of each of the heaters, so that the second steam can be used as a heating source for the heater after the second steam compressor is heated and pressurized.

[0008] In some embodiments, the dilute sulfuric acid wastewater treatment system further comprises:

[0009] a first condensing device, the first condensing device being communicated with the second gas outlet of the evaporating device, so that the first steam after heat exchange in the evaporating device forms condensed water and non-condensable gas in the first condensing device; and

[0010] The second condensing device is connected to the gas outlet of each of the heaters, so that the second steam after heat exchange in the heater forms condensed water and non-condensable gas in the second condensing device.

[0011] In some embodiments, the dilute sulfuric acid wastewater treatment system further comprises:

[0012] a first vacuum device, wherein an air inlet of the first vacuum device is connected to an air outlet of the first condensing device, and is used to control the vacuum degree of the evaporating device; and the air outlet of the first vacuum device is used to discharge non-condensable gas of the first condensing device; and

[0013] A second vacuum device, the air inlet of the second vacuum device is connected to the air outlet of the second condensing device, and is used to control the vacuum degree of the separator and each of the heaters; the air outlet of the second vacuum device is used to discharge the non-condensable gas of the second condensing device.

[0014] In some embodiments, the condensed water outlet of the evaporation device is connected to the preheating device, so that the condensed water after the steam in the evaporation device is condensed returns to the preheating device and provides the heat required for the preheating; and / or

[0015] The condensate outlet of each heater is connected to the preheating device, so that the condensate after the steam in each heater is condensed returns to the preheating device and provides the heat required for the preheating; and / or

[0016] The concentrated liquid outlet of the separator is communicated with the preheating device, so that the second concentrated liquid produced in the separator returns to the preheating device and provides the heat required for the preheating.

[0017] In some embodiments, the preheating device includes a first heat exchanger, a second heat exchanger and a third heat exchanger; the concentrated liquid outlet of the separator is connected to the first heat exchanger; the condensed water outlet of the evaporation device is connected to the second heat exchanger; and the condensed water outlet of each of the heaters is connected to the third heat exchanger.

[0018] In some embodiments, the pipe between the first liquid outlet of the evaporation device and the first liquid inlet of the separator is made of graphite; and / or

[0019] The separator, each of the heaters and the first heat exchanger are made of graphite; and / or

[0020] The pipe between the separator and the heater is made of graphite; and / or

[0021] The pipe between the separator and the first heat exchanger is made of graphite.

[0022] In some embodiments, the dilute sulfuric acid wastewater treatment system further comprises a raw liquid pool, and the pipe material between the raw liquid pool and the first liquid inlet of the preheating device is zirconium; and / or

[0023] The material of the pipe between the first liquid outlet of the preheating device and the first liquid inlet of the evaporation device is zirconium; and / or

[0024] The evaporation device is made of zirconium.

[0025] In some embodiments, the dilute sulfuric acid wastewater treatment system also includes a fresh steam source; the fresh steam source is connected to the first steam compressor for providing an evaporation heat source to the evaporation device; the fresh steam source is connected to the separator for providing an evaporation heat source to the separator.

[0026] In some of the embodiments, the dilute sulfuric acid wastewater treatment system further includes a fully automatic CIP cleaning device, and the fully automatic CIP cleaning device is used to automatically clean each of the heaters.

[0027] In some of the embodiments, the dilute sulfuric acid wastewater treatment system includes a demister, which is disposed above the separator; wherein the demister is a combination of a folded plate demister and a wire mesh demister stacked together.

[0028] In some of the embodiments, a forced circulation pump is provided between each of the heaters independently and the supernatant circulation channel formed by the separator; the dilute sulfuric acid wastewater treatment system also includes a PLC control device, and the PLC control device and each of the forced circulation pumps are used to control the operation of each of the forced circulation pumps.

[0029] In the above-mentioned dilute sulfuric acid wastewater treatment system, at least two heaters are arranged in the evaporation crystallizer, each heater is independently connected to the separator and forms a supernatant circulation channel. When a heater has problems such as scaling and clogging during operation, the heater can be isolated and cleaned separately without shutting down the whole machine, which has low maintenance costs and is conducive to the long-term stable operation of the dilute sulfuric acid wastewater treatment system. At the same time, the steam generated by the wastewater during the evaporation process is heated and pressurized as an evaporation heat source, which makes full use of the heat energy generated by the steam during the evaporation process, which is conducive to reducing energy consumption.

[0030] By setting up a preheating device, the raw dilute sulfuric acid wastewater is heat-exchanged with the second concentrated liquid, the evaporation device and the condensed water in the heater. In this way, the raw dilute sulfuric acid wastewater is preheated by the high-temperature second concentrated liquid and the condensed water that have been evaporated and concentrated, and a large amount of heat from the second concentrated liquid and the condensed water is recovered. At the same time, the temperature of the concentrated liquid and the condensed water that need to be discharged from the system is also reduced, thereby improving the heat recovery rate of the system and reducing energy consumption.

[0031] The equipment and pipelines through which the raw dilute sulfuric acid wastewater passes are made of zirconium, and the equipment and pipelines through which the first concentrated liquid and the second concentrated liquid pass are made of graphite, thereby avoiding the corrosion of the equipment by the high-temperature sulfuric acid wastewater and ensuring the safe operation of the equipment. At the same time, the vacuum device provides a high vacuum environment, which reduces the boiling temperature of the dilute sulfuric acid wastewater, thereby avoiding increasing the corrosion rate of the equipment under high temperature conditions.

[0032] Another aspect of the present invention provides a method for treating dilute sulfuric acid wastewater, comprising the following steps:

[0033] Preheating the dilute sulfuric acid wastewater stock solution;

[0034] The preheated dilute sulfuric acid wastewater raw liquid is evaporated and concentrated to obtain a first concentrated liquid and a first steam; the first steam is compressed, heated and pressurized, and then returned to the evaporation and concentration step to provide an evaporation heat source; and

[0035] The first concentrated liquid is evaporated and crystallized to obtain a second vapor, a supernatant and a second concentrated liquid containing crystals; the supernatant is divided into at least two flow paths for heating and evaporation respectively, and then independently returned to the evaporation and crystallization step; the second vapor is compressed, heated and pressurized, and then returned to the heating step of the supernatant to provide an evaporation heat source.

[0036] In some embodiments, the dilute sulfuric acid wastewater treatment method further comprises:

[0037] The vacuum degree of the step of evaporating and concentrating the preheated dilute sulfuric acid wastewater stock solution and the step of evaporating and crystallizing the first concentrated solution is controlled so that the step of evaporating and concentrating the preheated dilute sulfuric acid wastewater stock solution and the step of evaporating and crystallizing the first concentrated solution are performed at a temperature not higher than 70°C.

[0038] In the above-mentioned dilute sulfuric acid wastewater treatment method, the supernatant is divided into at least two flow paths for heating and evaporation respectively. When a device on a certain flow path fails during operation, the device can be isolated and maintained separately without shutting down the entire machine, which is conducive to the long-term stable operation of the dilute sulfuric acid wastewater treatment system. At the same time, the steam generated by the wastewater during the evaporation process is heated and pressurized as an evaporation heat source, which fully utilizes the thermal energy of the steam generated during the evaporation process, which is conducive to reducing energy consumption.

[0039] Providing a vacuum environment in the evaporation step reduces the boiling temperature of the dilute sulfuric acid wastewater, thereby avoiding increasing the corrosion rate of the equipment under high temperature conditions. Evaporation concentration and flash evaporation are carried out at a temperature not higher than 70°C, which is less corrosive to the equipment. The scaling rate of calcium sulfate and magnesium sulfate decreases at low temperatures, which is conducive to long-term treatment of dilute sulfuric acid wastewater.

[0040] By setting up a preheating device, the raw dilute sulfuric acid wastewater is heat-exchanged with the second concentrated liquid and condensed water. In this way, the raw dilute sulfuric acid wastewater is preheated by the second concentrated liquid and distilled water that have undergone evaporation concentration and flash evaporation, and a large amount of heat from the second concentrated liquid and condensed water is recovered. At the same time, the temperature of the second concentrated liquid and condensed water that need to be discharged from the system is also reduced, thereby improving the heat recovery rate of the system and further reducing the energy consumption of the treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of a dilute sulfuric acid wastewater treatment system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0044] See also Figure 1 Some embodiments of the present invention provide a dilute sulfuric acid wastewater treatment system, including: a preheating device 100, a pre-concentration device 200, and an evaporation crystallizer 300.

[0045] The preheating device 100 is used to preheat the dilute sulfuric acid wastewater raw liquid.

[0046] The pre-concentration device 200 includes a first evaporation device 210, a second evaporation device 220 and a first steam compressor 230. The first liquid inlet of the first evaporation device 210 is connected to the first liquid outlet of the preheating device 100, and the first liquid inlet of the second evaporation device 220 is connected to the first liquid outlet of the first evaporation device 210. The first evaporation device 210 and the second evaporation device 220 are used to evaporate and concentrate the preheated dilute sulfuric acid wastewater to obtain a first concentrated liquid and a first steam. One end of the first steam compressor 230 is connected to the first air outlet of the first evaporation device 210, and the other end is connected to the air inlet of the second evaporation device 220, so that the first steam is used as an evaporation heat source for the second evaporation device 220 after the first steam compressor 230 increases the temperature and pressure. The air outlet of the second evaporation device 220 is connected to the air inlet of the first evaporation device, so that the dilute sulfuric acid wastewater evaporates and concentrates in the second evaporation device 220 to generate the first steam, which returns to the first evaporation device 210 as an evaporation heat source. The condensed water generated by the evaporation heat source condensing in the second evaporation device 220 passes through the first evaporation device 210 and is discharged from the pre-concentration system together with the condensed water generated by the evaporation heat source condensing in the first evaporation device 210 .

[0047] In this embodiment, the first evaporation device 210 and the second evaporation device 220 are both horizontal tube spray evaporation devices, which are currently the most energy-saving evaporation devices.

[0048] The pre-concentration device 200 is provided with a first evaporation device 210 and a second evaporation device 220 to grade and concentrate the preheated dilute sulfuric acid wastewater raw liquid. When the amount of dilute sulfuric acid wastewater is large, the pre-concentration multiple can be achieved. It can be understood that the number of evaporation devices in the pre-concentration device 200 is not limited to the number specified in this embodiment. In other embodiments, according to the amount of wastewater to be treated, the number of evaporation devices in the pre-concentration device 200 can be one, two or more.

[0049] Specifically, when there is only one evaporation device in the pre-concentration device 200, the first liquid inlet of the first evaporation device 210 is connected to the first liquid outlet of the preheating device 100, one end of the first steam compressor 230 is connected to the first gas outlet of the first evaporation device 210, and the other end is connected to the gas inlet of the first evaporation device 210, so that the first steam returns to the first evaporation device 210 as an evaporation heat source after the first steam compressor 230 increases the temperature and pressure. The first concentrated liquid obtained by evaporation and concentration in the first evaporation device 210 is discharged from the pre-concentration device 200 through the first liquid outlet of the first evaporation device 210.

[0050] The evaporation crystallizer 300 includes a separator 310, at least two heaters 320 and a second steam compressor 330; the first liquid inlet of the separator 310 is connected to the concentrated liquid outlet of the second evaporation device 220, and each heater 320 is independently connected to the separator 310 to form a supernatant circulation channel, so that the supernatant in the separator 310 enters the heater 320 for heating and then returns to the separator 310 for flash separation to obtain a second steam, a supernatant and a second concentrated liquid containing crystals; one end of the second steam compressor 330 is connected to the air outlet of the separator 310, and the other end is connected to the air inlet of each heater 320, so that the second steam can be used as an evaporation heat source for the heater 320 after the second steam compressor 330 heats up and increases the pressure.

[0051] Specifically, when in use, the first concentrated liquid evaporated and concentrated by the pre-concentration device 200 enters the separator 310, is mixed with the supernatant liquid in the suspension chamber below the separator 310, enters each heater 320 for heating, and then returns to the separation chamber above the separator 310 to be evaporated and concentrated to precipitate crystals. After passing through the suspension chamber, the supernatant liquid continues the above-mentioned evaporation and concentration, and the second concentrated liquid containing the crystals is discharged from the evaporation crystallizer 300 through the concentrated liquid outlet of the separator 310.

[0052] In some embodiments, the dilute sulfuric acid wastewater treatment system further includes a first condensing device 410 and a second condensing device 420 .

[0053] The first condensing device 410 is communicated with the second gas outlet of the first evaporating device 210 , so that the first steam after heat exchange in the first evaporating device 210 and the second evaporating device 220 forms condensed water and non-condensable gas in the first condensing device 410 .

[0054] The second condensing device 420 is communicated with the gas outlet of each heater 320 , so that the second steam after heat exchange in the heater 320 forms condensed water and non-condensable gas in the second condensing device 420 .

[0055] In some embodiments, the dilute sulfuric acid wastewater treatment system further includes a first vacuum device 510 and a second vacuum device 520 .

[0056] The air inlet of the first vacuum device 510 is connected to the air outlet of the first condensing device 410 to control the vacuum degree of the first evaporating device 210 and the second evaporating device 220. The air outlet of the first vacuum device 510 is used to discharge the non-condensable gas of the first condensing device 410.

[0057] The air inlet of the second vacuum device 520 is connected to the air outlet of the second condensing device 420 to control the vacuum degree of the separator 310 and each heater 320. The air outlet of the second vacuum device 520 is used to discharge the non-condensable gas of the second condensing device 420.

[0058] Specifically, the first vacuum device 510 and the second vacuum device 520 control the vacuum degree in the first evaporation device 210, the second evaporation device 220, and the separator 310 according to the concentration of the dilute sulfuric acid wastewater to reduce the boiling temperature of the wastewater. During operation, the evaporation concentration and flash evaporation of the dilute sulfuric acid wastewater are performed at a temperature not higher than 70°C. Preferably, the temperature of the evaporation concentration and flash evaporation is between 60°C and 70°C.

[0059] The vacuum degree of the first evaporation device 210 and the second evaporation device 220 is controlled by the first vacuum device 510, and the vacuum degree of the separator 310 and each heater 320 is controlled by the second vacuum device 520, so that the dilute sulfuric acid wastewater can be concentrated at a lower temperature, thereby avoiding the corrosion of the equipment by the sulfuric acid wastewater at high temperature. In addition, at low temperatures, calcium sulfate and magnesium sulfate are not easy to scale, thereby ensuring the safe and continuous operation of the equipment.

[0060] In some embodiments, the condensed water outlet of the first evaporation device 210 is connected to the preheating device 100, so that the condensed water after the steam in the first evaporation device 210 and the second evaporation device 220 is condensed back to the preheating device 100 and provides the heat required for preheating. In some embodiments, the condensed water outlet of each heater 320 is connected to the preheating device 100, so that the condensed water after the steam in each heater 320 is condensed back to the preheating device 100 and provides the heat required for preheating. In some embodiments, the concentrated liquid outlet of the separator 310 is connected to the preheating device 100, so that the second concentrated liquid produced in the separator 310 is returned to the preheating device 100 and provides the heat required for preheating.

[0061] In some embodiments, the preheating device 100 includes a first heat exchanger 110, a second heat exchanger 120, and a third heat exchanger 130. The concentrated liquid outlet of the separator 310 is connected to the first heat exchanger 110; the condensed water outlet of the first evaporation device 210 is connected to the second heat exchanger 120; and the condensed water outlet of each heater 320 is connected to the third heat exchanger 130.

[0062] In some embodiments, the dilute sulfuric acid wastewater treatment system further includes a first condensed water tank 610 and a second condensed water tank 620 .

[0063] One end of the first condensed water tank 610 is connected to the condensed water outlet of the first evaporation device 210 and the condensed water outlet of the first condensation device 410, and the other end is connected to the condensed water inlet of the preheating device 100, and is used to receive the condensed water generated in the first evaporation device 210, the second evaporation device 220 and the first condensation device 410. The condensed water is discharged from the system after heat exchange with the dilute sulfuric acid wastewater stock solution through the preheating device 100. The first condensed water tank 610 is also provided with an outlet connected to the first evaporation device 210 to fully utilize the small amount of steam generated by the heat of the condensed water as an evaporation heat source.

[0064] One end of the second condensed water tank 620 is connected to the condensed water outlet of each heater 320 and the second condensing device 420, and the other end is connected to the condensed water inlet of the preheating device 100, which is used to receive the condensed water generated by the condensation of the steam heat source in the heater 320 and the condensed water generated by the second steam after heat exchange in the second condensing device 420. The condensed water is discharged from the system after heat exchange with the dilute sulfuric acid wastewater stock solution through the preheating device 100. The second condensed water tank 620 is also provided with an outlet connected to the separator 310 to make full use of the small amount of steam generated by the heat of the condensed water as an evaporation heat source.

[0065] In some embodiments, the pipe between the first liquid outlet of the second evaporation device 220 and the first liquid inlet of the separator 310 is made of graphite; and / or

[0066] The separator 310, each heater 320 and the first heat exchanger 110 are made of graphite; and / or

[0067] The pipe between the separator 310 and the heater 320 is made of graphite; and / or

[0068] The material of the pipeline between the separator 310 and the first heat exchanger 110 is graphite.

[0069] In some embodiments, the dilute sulfuric acid wastewater treatment system further includes a raw liquid pool, and the pipe material between the raw liquid pool and the first liquid inlet of the preheating device 100 is zirconium; and / or

[0070] The material of the pipe between the first liquid outlet of the preheating device 100 and the first liquid inlet of the first evaporation device 210 is zirconium; and / or

[0071] The first evaporation device 210 and the second evaporation device 220 are made of zirconium.

[0072] For sulfuric acid wastewater of different concentrations, equipment and pipelines made of zirconium and graphite are used respectively, which can effectively reduce the corrosion of sulfuric acid to equipment and pipelines, thereby ensuring the safe operation of the equipment.

[0073] In some of the embodiments, a liquid delivery pump is provided between the raw liquid pool and the preheating device 100; the dilute sulfuric acid wastewater treatment system further includes a frequency converter; and the frequency converter is used to control the liquid delivery pump.

[0074] The characteristic of using a frequency converter to control the liquid delivery pump is that it saves energy. The difference from the traditional control by a regulating valve is that the pump does not need to run at full frequency and full load, which reduces the wear and tear of the pump, reduces the replacement cost of the equipment, and flexibly adapts to the wastewater delivery control under different densities. Specifically, when the system is running, the liquid delivery pump automatically adjusts the frequency in the range of 0~50Hz through the frequency converter control.

[0075] In some of the embodiments, the dilute sulfuric acid wastewater treatment system also includes a fresh steam source; the fresh steam source is connected to the first steam compressor 230, and is used to provide an evaporation heat source to the second evaporation device 220; the fresh steam source is connected to the separator 310, and is used to provide an evaporation heat source to the separator 310.

[0076] In some of the embodiments, the dilute sulfuric acid wastewater treatment system further includes a fully automatic CIP cleaning device, which is used to automatically clean each heater 320 .

[0077] When scaling, fouling, blockage, etc. occur in one of the heaters during operation, the heat exchanger can be immediately and automatically isolated and cleaned separately without shutting down the machine. This fully considers the convenience of the owner's operation, inspection and maintenance, improves the continuous operation operability and flexibility of the evaporation system, and is conducive to the long-term stable operation of the forced circulation evaporation system.

[0078] In some of the embodiments, the dilute sulfuric acid wastewater treatment system includes a demister, which is disposed above the separator 310; wherein the demister is a combination of a folded plate demister and a wire mesh demister stacked together.

[0079] In some of the embodiments, a forced circulation pump is provided between each heater and the supernatant circulation channel formed independently by the separator; the dilute sulfuric acid wastewater treatment system also includes a PLC control device, and the PLC control device and each forced circulation pump are used to control the operation of each forced circulation pump.

[0080] Specifically, the frequency load of each forced circulation pump is controlled by the PLC control device, and the frequency of the forced circulation pump can be adjusted according to the actual amount of wastewater to be treated, so as to achieve efficient wastewater treatment. At the same time, the frequency of each forced circulation pump is controlled by the PLC control device, and the water volume of different flow paths can be adjusted. When the heater of a certain flow path needs to be isolated for maintenance, the forced circulation pump on the flow path is controlled by the PLC control device to be in a closed state to isolate the heater.

[0081] In the above-mentioned dilute sulfuric acid wastewater treatment system, at least two heaters are arranged in the evaporation crystallizer, each heater is connected with the separator to form a supernatant circulation channel, when a heater has structural or blockage problems during operation, the heater can be isolated and cleaned separately without shutting down the whole machine, the maintenance cost is low, and it is conducive to the long-term stable operation of the dilute sulfuric acid wastewater treatment system. At the same time, the steam generated by the wastewater during the evaporation process is heated and pressurized as an evaporation heat source, which makes full use of the heat energy of the steam generated by the evaporation process, which is conducive to reducing energy consumption.

[0082] By setting up a preheating device, the raw dilute sulfuric acid wastewater is heat-exchanged with the concentrated liquid and the condensed liquid. In this way, the raw dilute sulfuric acid wastewater is preheated by the high-temperature second concentrated liquid and the condensed water after evaporation and concentration, and a large amount of heat of the second concentrated liquid and the condensed water is recovered. At the same time, the temperature of the concentrated liquid and the condensed water that need to be discharged from the system is also reduced, thereby improving the heat recovery rate of the system and reducing energy consumption.

[0083] The equipment and pipelines through which the raw dilute sulfuric acid wastewater passes are made of zirconium, and the equipment and pipelines through which the first concentrated liquid and the second concentrated liquid pass are made of graphite, thereby avoiding the corrosion of the equipment by the high-temperature sulfuric acid wastewater and ensuring the safe operation of the equipment. At the same time, the vacuum system provides a high vacuum environment, which reduces the boiling temperature of the dilute sulfuric acid wastewater, thereby avoiding increasing the corrosion rate of the equipment under high temperature conditions.

[0084] Another aspect of the present invention provides a method for treating dilute sulfuric acid wastewater, which can be carried out using the above-mentioned dilute sulfuric acid wastewater treatment system. The method for treating dilute sulfuric acid wastewater includes the following steps S10 to S30.

[0085] S10: preheating the dilute sulfuric acid wastewater stock solution.

[0086] S20: Evaporating and concentrating the preheated dilute sulfuric acid wastewater to obtain a first concentrated solution and a first steam; and returning the first steam to the evaporation and concentration step after being compressed, heated and pressurized to provide an evaporation heat source.

[0087] S30: Evaporating and crystallizing the first concentrated liquid to obtain a second vapor, a supernatant, and a second concentrated liquid containing crystals, dividing the supernatant into at least two flow paths for heating and evaporation respectively, and then independently returning to the evaporation and crystallization step, and returning the second vapor to the supernatant heating step after compressing, increasing temperature and pressure to provide an evaporation heat source. In some embodiments, the steps of the dilute sulfuric acid wastewater treatment method also include:

[0088] The vacuum degree of the step of evaporating and concentrating the preheated dilute sulfuric acid wastewater stock solution and the step of evaporating and crystallizing the first concentrated solution is controlled so that the step of evaporating and concentrating the preheated dilute sulfuric acid wastewater stock solution and the step of evaporating and crystallizing the first concentrated solution are performed at a temperature not higher than 70°C.

[0089] In the above-mentioned dilute sulfuric acid wastewater treatment method, the supernatant is divided into at least two flow paths for heating and evaporation respectively. When a device on a certain flow path fails during operation, the device can be isolated and maintained separately without shutting down, which is conducive to the long-term stable operation of the dilute sulfuric acid wastewater treatment system. At the same time, the steam generated by the wastewater during the evaporation process is heated and pressurized as an evaporation heat source, which fully utilizes the thermal energy of the steam generated during the evaporation process, which is conducive to reducing energy consumption.

[0090] Providing a vacuum environment in the evaporation step reduces the boiling temperature of the dilute sulfuric acid wastewater, thereby avoiding increasing the corrosion rate of the equipment under high temperature conditions. Evaporation concentration and flash evaporation are carried out at a temperature not higher than 70°C, which is less corrosive to the equipment. The scaling rate of calcium sulfate and magnesium sulfate decreases at low temperatures, which is conducive to long-term treatment of dilute sulfuric acid wastewater.

[0091] By setting up a preheating device, the raw dilute sulfuric acid wastewater is heat-exchanged with the second concentrated liquid and the condensed water. In this way, the raw dilute sulfuric acid wastewater is preheated by the second concentrated liquid and the condensed water after evaporation concentration and flash evaporation, and a large amount of heat of the second concentrated liquid and the condensed water is recovered. At the same time, the temperature of the second concentrated liquid and the condensed water that need to be discharged from the system is also reduced, the heat recovery rate of the system is improved, and the energy consumption of the treatment is further reduced.

[0092] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A dilute sulfuric acid wastewater treatment system, characterized in that: include: A preheating device, used to preheat the raw solution of dilute sulfuric acid wastewater; A pre-concentration device, comprising an evaporation device and a first steam compressor, wherein the first liquid inlet of the evaporation device is connected to the first liquid outlet of the preheating device, and is used to evaporate and concentrate the preheated dilute sulfuric acid wastewater to obtain a first concentrated liquid and a first steam; one end of the first steam compressor is connected to the first air outlet of the evaporation device, and the other end is connected to the air inlet of the evaporation device, so that the first steam can be used as an evaporation heat source for the evaporation device after the first steam compressor increases the temperature and pressure; and An evaporation crystallizer, comprising a separator, a second steam compressor and at least two heaters; a first liquid inlet of the separator is connected to a concentrated liquid outlet of the evaporation device, each of the heaters is independently connected to the separator and forms a supernatant circulation channel, so that the supernatant in the separator enters the heater for heating and then returns to the separator for flash separation, and obtains a second steam, a supernatant and a second concentrated liquid containing crystals; one end of the second steam compressor is connected to the air outlet of the separator, and the other end is connected to the air inlet of each of the heaters, so that the second steam is used as a heating source for each of the heaters after the second steam compressor is heated and pressurized; The concentrated liquid outlet of the separator is communicated with the preheating device, so that the second concentrated liquid produced in the separator returns to the preheating device and provides the heat required for the preheating; the preheating device includes a first heat exchanger, and the concentrated liquid outlet of the separator is communicated with the first heat exchanger; A suspension chamber is provided above the separator, and a separation chamber is provided below the separator. The first concentrated liquid evaporated and concentrated by the pre-concentration device enters the separator, is mixed with the supernatant in the suspension chamber below the separator, enters each of the heaters for heating, and then returns to the separation chamber above the separator.

2. The dilute sulfuric acid wastewater treatment system according to claim 1, characterized in that: The dilute sulfuric acid wastewater treatment system also includes: a first condensing device, the first condensing device being communicated with the second gas outlet of the evaporating device, so that the first steam after heat exchange in the evaporating device forms condensed water and non-condensable gas in the first condensing device; and The second condensing device is connected to the gas outlet of each of the heaters, so that the second steam after heat exchange in the heater forms condensed water and non-condensable gas in the second condensing device.

3. The dilute sulfuric acid wastewater treatment system according to claim 2, characterized in that: The dilute sulfuric acid wastewater treatment system also includes: a first vacuum device, wherein an air inlet of the first vacuum device is connected to an air outlet of the first condensing device, and is used to control the vacuum degree of the evaporating device; and the air outlet of the first vacuum device is used to discharge non-condensable gas of the first condensing device; and A second vacuum device, the air inlet of the second vacuum device is connected to the air outlet of the second condensing device, and is used to control the vacuum degree of the separator and each of the heaters; the air outlet of the second vacuum device is used to discharge the non-condensable gas of the second condensing device.

4. The dilute sulfuric acid wastewater treatment system according to claim 1, characterized in that: The condensed water outlet of the evaporation device is connected to the preheating device, so that the condensed water after the steam in the evaporation device is condensed returns to the preheating device and provides the heat required for the preheating; and / or The condensed water outlet of each of the heaters is connected to the preheating device, so that the condensed water after the steam in each of the heaters is condensed returns to the preheating device and provides the heat required for the preheating.

5. The dilute sulfuric acid wastewater treatment system according to claim 4, characterized in that: The preheating device includes a second heat exchanger and a third heat exchanger; the condensed water outlet of the evaporating device is connected to the second heat exchanger; and the condensed water outlet of each of the heaters is connected to the third heat exchanger.

6. The dilute sulfuric acid wastewater treatment system according to claim 5, characterized in that: The pipe between the first liquid outlet of the evaporator and the first liquid inlet of the separator is made of graphite; and / or The separator, each of the heaters and the first heat exchanger are made of graphite; and / or The pipe between the separator and the heater is made of graphite; and / or The pipe between the separator and the first heat exchanger is made of graphite.

7. The dilute sulfuric acid wastewater treatment system according to claim 1, characterized in that: The dilute sulfuric acid wastewater treatment system further comprises a raw liquid pool, and the pipe material between the raw liquid pool and the first liquid inlet of the preheating device is zirconium; and / or The material of the pipe between the first liquid outlet of the preheating device and the first liquid inlet of the evaporation device is zirconium; and / or The evaporation device is made of zirconium.

8. The dilute sulfuric acid wastewater treatment system according to claim 1, characterized in that: The dilute sulfuric acid wastewater treatment system also includes a fresh steam source; the fresh steam source is connected to the first steam compressor and is used to provide an evaporation heat source to the evaporation device; the fresh steam source is connected to the separator and is used to provide an evaporation heat source to the separator.

9. The dilute sulfuric acid wastewater treatment system according to claim 1, characterized in that: The dilute sulfuric acid wastewater treatment system also includes a fully automatic CIP cleaning device, which is used to automatically clean each of the heaters.

10. The dilute sulfuric acid wastewater treatment system according to claim 1, characterized in that: The dilute sulfuric acid wastewater treatment system comprises a demister, which is arranged above the separator; wherein the demister comprises a folded plate demister and a wire mesh demister which are stacked.

11. The dilute sulfuric acid wastewater treatment system according to claim 1, characterized in that: A forced circulation pump is provided on the supernatant circulation channel independently formed by each of the heaters and the separator; the dilute sulfuric acid wastewater treatment system also includes a PLC control device, which is used to control the operation of each of the forced circulation pumps.

12. A method for treating dilute sulfuric acid wastewater, characterized in that: The dilute sulfuric acid wastewater treatment system according to any one of claims 1 to 11 is used, and the dilute sulfuric acid wastewater treatment method comprises the following steps: Preheating the dilute sulfuric acid wastewater stock solution; The preheated dilute sulfuric acid wastewater raw liquid is evaporated and concentrated to obtain a first concentrated liquid and a first steam; the first steam is compressed, heated and pressurized, and then returned to the evaporation and concentration step to provide an evaporation heat source; and The first concentrated liquid is evaporated and crystallized to obtain a second vapor, a supernatant and a second concentrated liquid containing crystals; the supernatant is divided into at least two flow paths for heating and evaporation respectively, and then returned to the evaporation and crystallization step; the second vapor is compressed, heated and pressurized, and then returned to the heating step of the supernatant to provide an evaporation heat source.

13. The method for treating dilute sulfuric acid wastewater according to claim 12, characterized in that: The steps of the dilute sulfuric acid wastewater treatment method also include: The vacuum degree of the step of evaporating and concentrating the preheated dilute sulfuric acid wastewater stock solution and the step of evaporating and crystallizing the first concentrated solution is controlled so that the step of evaporating and concentrating the preheated dilute sulfuric acid wastewater stock solution and the step of evaporating and crystallizing the first concentrated solution are performed at a temperature not higher than 70°C.

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