A salt-containing wastewater treatment system based on the hot and cold ends of a heat pump

Abstract

This application belongs to the field of wastewater treatment, and specifically relates to a saline wastewater treatment system based on the hot and cold ends of a heat pump. This application has a raw liquid circulation system and a refrigerant circulation system. The raw liquid circulation system can form ice crystals and concentrated liquid through an ice crystal production device, and then use a solid-liquid separation device to separate the two. After separation, the raw liquid circulation system is divided into an ice crystal circulation system and a concentrated liquid circulation system. The ice crystal circulation system melts the ice crystals into water, and the concentrated liquid circulation system performs evaporation crystallization for wastewater treatment, and the heat of the refrigerant realizes a closed-loop flow. This application can make full use of environmental heat energy, significantly reduce energy consumption, and improve the efficiency of wastewater treatment.

Description

Technical Field

[0001] This application belongs to the technical field of wastewater treatment, and particularly relates to a salt-containing wastewater treatment system based on the hot and cold ends of a heat pump. Background Art

[0002] At present, the full-quantification treatment of salt-containing wastewater mainly adopts the drying combination process of "MVR evaporation + evaporation kettle". This process has high chemical consumption, is prone to scaling, and has high operation and maintenance costs.

[0003] Chinese Utility Model Patent No. 2023201755130 discloses a wastewater treatment system coupling freezing concentration and negative-pressure vacuum evaporation crystallization. This system uses the cold source of the heat pump for pre-concentration during the ice-making process and uses the heat source to evaporate and crystallize the concentrated mother liquor. However, in the above system, the ice crystals produced by ice-making and the unfrozen original liquid flow back to the original storage tank through the ice-making circulation pump. The original liquid in the above system reaches the eutectic point in a gradually enriched form, which results in a decrease in the output of the ice-making unit as the salinity of the raw water increases. The increase in the salt content of the ice crystals will also cause a decrease in the water quality compliance rate of the ice-melting unit, a low output of compliant water, and a large volume of the required treatment system. In addition, in the above system, the mother liquor that reaches the eutectic point or the mother liquor after sufficient concentration of the original liquid is sent to the mother liquor storage tank. Since the mother liquor needs to go through multiple ice-making reciprocating cycles, there will be no mother liquor to evaporate during multiple cycles. Therefore, the time when freezing and evaporation can play their roles simultaneously is seriously mismatched, and it is difficult for the system to effectively utilize the coupled heat. In addition, the cold energy and heat energy in the wastewater treatment process are not effectively recovered, resulting in continuous cycling of ice melting and ice making for some solutions, causing excessive energy loss and significantly increasing the overall energy consumption. Summary of the Invention

[0004] This application provides a salt-containing wastewater treatment system based on the hot and cold ends of a heat pump, which can make full use of environmental heat energy and significantly reduce energy consumption.

[0005] The technical solution of this application is as follows:

[0006] A salt-containing wastewater treatment system based on the hot and cold ends of a heat pump includes a raw liquid circulation system and a refrigerant circulation system;

[0007] The raw liquid circulation system sequentially includes a raw liquid inlet, a low-temperature heat exchanger A, an ice crystal production device, and a solid-liquid separation device according to the flow direction of the raw liquid. The low-temperature heat exchanger A is a place for low-temperature heat exchange of the raw liquid. The ice crystal production device crystallizes and concentrates the raw liquid that has undergone low-temperature heat exchange into a mixture of ice crystals and concentrated liquid and inputs it into the solid-liquid separation device. The solid-liquid separation device is used to separate ice crystals and concentrated liquid;

[0008] The raw liquid circulation system branches into an ice crystal circulation system and a concentrated liquid circulation system at the solid-liquid separation device;

[0009] The ice crystal circulation system includes:

[0010] A low-temperature heat exchanger B, which is a place where ice crystals melt. After the ice crystals melt into water, the water flows into the low-temperature heat exchanger A to exchange heat with the stock solution at a low temperature;

[0011] The concentrated liquid circulation system sequentially includes, according to the concentrated liquid circulation flow direction:

[0012] An evaporation heat exchanger E, which is a place for the concentrated liquid to exchange heat and increase in temperature;

[0013] An evaporation crystallization device, which is a place for the concentrated liquid to evaporate and crystallize. The evaporation crystallization device has a reaction cavity, a steam outlet and a residue discharge port; the reaction cavity includes a heating layer in area A and a heating layer in area B. The heating layer in area A has a steam inlet and a condensate outlet, and the condensate outlet is communicated with the evaporation heat exchanger E; the heating layer in area B has a refrigerant inlet and a refrigerant outlet. The heating layer is an independent space in the reaction cavity for heating the concentrated liquid in the reaction cavity. The heat source of the heating layer in area A is steam, and the heating layer in area B is a refrigerant. After the steam in the heating layer in area A releases heat, it flows into the condensate outlet and will not flow into the reaction cavity.

[0014] An evaporation heat exchanger C, which is a place for heat exchange of the steam generated during the evaporation crystallization process; an inlet steam pipe and an exhaust steam pipe are respectively provided between the evaporation heat exchanger C and the steam inlet and the steam outlet;

[0015] The refrigerant circulation system is a closed-loop structure. The refrigerant circulates through a heat pump compressor, an evaporation heat exchanger C, a refrigerant inlet, a heating layer in area B, a refrigerant outlet, an evaporation heat exchanger D, and a low-temperature heat exchanger B, an expansion valve, and an ice crystal production device; the evaporation heat exchanger D is connected to a cooling tower to restore the refrigerant to the ambient temperature.

[0016] Further, a storage tank for storing the concentrated liquid is provided between the solid-liquid separation device and the evaporation heat exchanger E,

[0017] Further, the steam in the inlet steam pipe flows from the evaporation heat exchanger C to the steam inlet, and the steam in the exhaust steam pipe flows from the steam outlet to the evaporation heat exchanger C.

[0018] Further, a vacuum pump is provided on the inlet steam pipe to keep the evaporation heat exchanger C and the evaporation crystallization device in a negative pressure state.

[0019] Further, the vacuum pressure range of the evaporation crystallization device is 9.106 kPa to 19.918 kPa.

[0020] Further, a screw pump is provided between the solid-liquid separation device and the low-temperature heat exchanger B.

[0021] Further, a circulation pump is provided between the cooling tower and the low-temperature heat exchanger B.

[0022] Due to the adoption of the above technical solution, the beneficial effects of the present application are as follows:

[0023] 1. The present application has a raw liquid circulation and a refrigerant circulation. In the raw liquid circulation, the ice crystals and the concentrated liquid are further divided into two sub-circulations. At the cold end of the present application, that is, the end connected to the ice crystal production device, the refrigerant has the ability to absorb heat after expansion. In the ice crystal production device, it absorbs the heat of the wastewater to promote the crystallization of the wastewater. Subsequently, after being compressed by the heat pump compressor, it obtains the ability to release heat. At the hot end, that is, in the evaporation crystallization device, after entering the B area, it releases heat to promote the evaporation and drying of the concentrated liquid. Finally, after returning to the ambient temperature through the cooling tower, it releases heat again in the low-temperature heat exchanger B to melt the ice crystals. During the circulation process of the refrigerant, its heat absorption ability and heat release ability are fully utilized, significantly reducing energy consumption.

[0024] 2. The solid-liquid separation device of the present application is the starting point of the differentiation, which can immediately separate the ice crystals, thereby timely separating the salts and organic matters intercepted in the ice crystals, and further contributing to obtaining ice crystals with higher cleanliness and a more concentrated concentrated liquid. Ice crystals with higher cleanliness can simplify the subsequent purification process and increase the production of up-to-standard water; a more concentrated concentrated liquid can improve the evaporation crystallization efficiency, improve the wastewater treatment efficiency, and significantly reduce energy consumption.

[0025] 3. In the evaporation crystallization device of the present application, there is an evaporation zone. The heating layer in the A area uses steam as the heating medium, with a temperature of 40 - 50 degrees; the heating layer in the B area uses the refrigerant as the heating medium, with a temperature of 60 - 90 degrees. Thus, an evaporation gradient is formed during the evaporation crystallization process, which can fully utilize the latent heat of evaporation, make up for the heat energy gap of the heat pump, and ensure the evaporation output under the condition of heat energy shortage.

[0026] 4. In a preferred embodiment of the present application, the vacuum pump converts the evaporation heat exchanger C and the evaporation crystallization device into a negative pressure environment, which can evaporate the condensed water in the steam into gas in a negative pressure and high-temperature environment. This not only helps the recycling of steam but also can fully utilize the latent heat of vaporization of the gas for evaporation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments and descriptions thereof of the present application are used to explain the present application and do not constitute an improper limitation to the present application.

[0028] Figure 1 It is a flowchart of a salt-containing wastewater treatment system based on the hot and cold ends of a heat pump provided by the present application.

[0029] In the drawings:

[0030] 110. Low-temperature heat exchanger A; 120. Ice crystal production device; 130. Solid-liquid separation device; 140. Low-temperature heat exchanger B; 150. Screw pump; 210. Vacuum pump; 220. Evaporation heat exchanger C; 230. Evaporation heat exchanger D; 240. Cooling tower; 250. Circulation pump; 260. Evaporation heat exchanger E; 310. Evaporation crystallization device; 320. Storage tank; 410. Heat pump compressor; 420. Expansion valve; 510. Temperature sensor; 520. Residue discharge port. Detailed implementation mode

[0031] Based on the background technology described above, the existing salt-containing wastewater treatment system cannot achieve reasonable and effective utilization of heat. Therefore, the present application provides a salt-containing wastewater treatment system based on the hot and cold ends of a heat pump. Refer to the attached Figure 1 , the salt-containing wastewater treatment system includes a raw liquid circulation system and a refrigerant circulation system.

[0032] The raw liquid circulation system sequentially includes a raw liquid inlet, a low-temperature heat exchanger A 110, an ice crystal production device 120, and a solid-liquid separation device 130 according to the flow direction of the raw liquid. The low-temperature heat exchanger A 110 is a place for low-temperature heat exchange of the raw liquid. The ice crystal production device 120 crystallizes and concentrates the raw liquid after low-temperature heat exchange into a mixture of ice crystals and concentrated liquid and inputs it into the solid-liquid separation device 130. The solid-liquid separation device 130 is used to separate ice crystals and concentrated liquid.

[0033] The low-temperature concentration method utilizes the principle that water molecules repel foreign impurities during the crystallization process to obtain relatively pure ice and concentrated liquid. The lower the freezing temperature, the faster the freezing rate, and the faster the crystal branches grow. At this time, the content difference of water molecules between the liquid phase and the solid / liquid two-phase interface increases, thereby accelerating the migration of water molecules from the liquid phase to the solid / liquid two-phase interface. When this rate exceeds the rate of salt and organic matter migrating from the solid / liquid two-phase interface to the liquid phase, salt and organic matter molecules will be wrapped in ice crystals in the form of extremely small liquid beads. Therefore, to obtain ice crystals with high purity, the freezing speed should be as slow as possible, but this will greatly reduce the production efficiency. Reducing the refrigeration temperature and increasing the freezing speed will reduce the pass rate of ice crystals, and the existing process cannot effectively solve this problem.

[0034] In the technical solution of the present application, the raw liquid circulation system is divided into an ice crystal circulation system and a concentrated liquid circulation system at the solid-liquid separation device 130. The ice crystal circulation is used to melt ice crystals to produce melted water, and the concentrated liquid circulation evaporates and crystallizes the concentrated liquid and then discharges the waste residue, and the heated steam is converted into condensed water when it is cooled.

[0035] The ice crystal circulation system includes: a low-temperature heat exchanger B140, which is a place for ice crystal melting. After the ice crystals melt into water, they flow into the low-temperature heat exchanger A110 to exchange heat with the original liquid at a low temperature. The heat source required for ice crystal melting is the heat possessed by the refrigerant after returning to room temperature in the refrigerant circulation through the cooling tower 240. In a preferred embodiment of the present application, a screw pump 150 is provided between the solid-liquid separation device 130 and the low-temperature heat exchanger B140, and the screw pump 150 is used to transfer the ice crystals into the low-temperature heat exchanger B140.

[0036] The concentrated liquid circulation system sequentially includes, according to the concentrated liquid circulation flow direction: an evaporation heat exchanger E260, which is a place for the concentrated liquid to exchange heat and increase in temperature. It should be noted that the salt content rate of the concentrated liquid in the present application should preferably reach twice or more of the initial solution or a solution close to saturation. In specific implementation, the temperature of the condensed water is controlled at about 40°C. The temperature of the concentrated liquid is relatively low or even negative after solid-liquid separation. Therefore, the temperature of the concentrated liquid will increase after heat exchange with the condensed water.

[0037] An evaporation crystallization device 310, which is a place for the concentrated liquid to evaporate and crystallize. The evaporation crystallization device 310 has a reaction cavity, a steam outlet, and a residue discharge port 520; a scraper is equipped in the evaporation crystallization device 310, which can discharge the salt and residues inside into the residue discharge port 520. The reaction cavity includes a heating layer in area A and a heating layer in area B. The heating layer in area A has a steam inlet and a condensed water outlet, and the condensed water outlet is communicated with the evaporation heat exchanger E260; the heating layer in area B has a refrigerant inlet and a refrigerant outlet; the heating layer in area A and the heating layer in area B are located in one cavity, and they have an evaporation sequence, that is, after the concentrated liquid enters the reaction cavity, it is first initially evaporated by the heating layer in area A, and then secondarily evaporated by the heating layer in area B. The heat source for evaporation in area A is the heat carried by the steam in the evaporation heat exchanger C220, and the heat source for evaporation and drying in area B is the heat release of the refrigerant. Based on the above settings, due to the different heat sources of the heating layers in area A and area B, an evaporation gradient is formed, thereby improving the evaporation efficiency and the evaporation amount.

[0038] The evaporation heat exchanger C220 serves as the heat exchange site for the steam generated during the evaporation crystallization process. An inlet steam pipe and an exhaust steam pipe are respectively provided between the evaporation heat exchanger C220 and the steam inlet and the steam outlet. A refrigerant pipe is provided between the evaporation heat exchanger C220 and the refrigerant inlet. In a preferred embodiment of the present application, the steam in the inlet steam pipe flows from the evaporation heat exchanger C220 to the steam inlet, and the steam in the exhaust steam pipe flows from the steam outlet to the evaporation heat exchanger C220. In a specific embodiment of the above embodiment, a vacuum pump 210 is provided in the inlet steam pipe to keep the evaporation heat exchanger C220 and the evaporation crystallization device 310 in a negative pressure state. In a preferred embodiment of the above embodiment, the degree of vacuum in the evaporation crystallization device 310 is set within the range of 9.106 kPa to 19.918 kPa of the vacuum pressure.

[0039] The refrigerant circulation system is a closed-loop structure. The refrigerant circulates through the expansion valve 420, the ice crystal production device 120, the heat pump compressor 410, the evaporation heat exchanger C220, the refrigerant inlet, the heating layer in area B, the refrigerant outlet, the evaporation heat exchanger D230, and the low-temperature heat exchanger B140. The evaporation heat exchanger D230 is connected to the cooling tower 240 to restore the refrigerant to the ambient temperature. The expansion valve 420 is arranged between the low-temperature heat exchanger B140 and the ice crystal production device 120. After the refrigerant expands, it has the ability to absorb heat. In the ice crystal production device 120, the refrigerant absorbs heat from the wastewater to promote the formation of ice crystals. The heat pump compressor 410 is the place where the refrigerant is heated. The heat pump compressor 410 transports the heated refrigerant to the evaporation heat exchanger C220, and the refrigerant exchanges heat with the steam in the evaporation heat exchanger C220 and then releases heat in the heating layer of area B. After being pressurized by the heat pump compressor 410, the refrigerant becomes a high-temperature and high-pressure gas and sequentially passes through the evaporation heat exchanger C220, the heating layer in area B, and the evaporation heat exchanger D230, and then continuously releases heat at the low-temperature heat exchanger B140 and becomes a high-temperature and high-pressure liquid. The liquid passes through the expansion valve 420 and becomes a low-temperature and low-pressure gas-liquid mixture state, and then enters the ice crystal production device 120 to absorb heat and turn into a gas, and then returns to the heat pump compressor 410 to complete a cycle.

[0040] In the present application, the refrigerant can adopt environmentally friendly mixed refrigerants such as R404a, R507, and R449A, and preferably R404a.

[0041] As a preferred embodiment of the present application, a storage tank 320 for storing the concentrated liquid is provided between the solid-liquid separation device 130 and the evaporation heat exchanger E260.

[0042] As a preferred embodiment of the present application, a circulation pump 250 is provided between the cooling tower 240 and the low-temperature heat exchanger B140.

[0043] In this application, several temperature sensors 510 are provided between the pipelines of the system to monitor the internal temperature of the pipelines.

[0044] What is not described in this application can be implemented by adopting or referring to the existing technologies.

[0045] The above are only the embodiments of this application and are not used to limit this application. For those skilled in the art, this application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the scope of the claims of this application.

Claims

1. A salt-containing wastewater treatment system based on the hot and cold ends of a heat pump, characterized in that it includes a raw liquid circulation system and a refrigerant circulation system; The raw liquid circulation system sequentially includes a raw liquid inlet, a low-temperature heat exchanger A, an ice crystal production device, and a solid-liquid separation device according to the raw liquid flow direction. The low-temperature heat exchanger A is a place for low-temperature heat exchange of the raw liquid. The ice crystal production device crystallizes and concentrates the raw liquid after low-temperature heat exchange into a mixture of ice crystals and concentrated liquid and inputs it into the solid-liquid separation device. The solid-liquid separation device is used to separate ice crystals and concentrated liquid; The raw liquid circulation system branches into an ice crystal circulation system and a concentrated liquid circulation system at the solid-liquid separation device; The ice crystal circulation system includes: A low-temperature heat exchanger B, which is a place for ice crystal melting. After the ice crystals melt into water, they flow into the low-temperature heat exchanger A for low-temperature heat exchange with the raw liquid; The concentrated liquid circulation system sequentially includes according to the concentrated liquid circulation flow direction: An evaporation heat exchanger E, which is a place for heating and heat exchange of the concentrated liquid; An evaporation crystallization device, which is a place for evaporation and crystallization of the concentrated liquid. The evaporation crystallization device has a reaction cavity, a steam outlet, and a residue discharge port. The reaction cavity includes a heating layer in area A and a heating layer in area B. The heating layer in area A has a steam inlet and a condensate outlet, and the condensate outlet is communicated with the evaporation heat exchanger E. The heating layer in area B has a refrigerant inlet and a refrigerant outlet; An evaporation heat exchanger C, which is a place for heat exchange of the steam generated during the evaporation crystallization process. An inlet steam pipe and an exhaust steam pipe are respectively provided between the evaporation heat exchanger C and the steam inlet and the steam outlet; The refrigerant circulation system is a closed-loop structure. The refrigerant circulates through a heat pump compressor, an evaporation heat exchanger C, a refrigerant inlet, a heating layer in area B, a refrigerant outlet, an evaporation heat exchanger D, and a low-temperature heat exchanger B, an expansion valve, and an ice crystal production device. The evaporation heat exchanger D is connected to a cooling tower to restore the refrigerant to the ambient temperature.

2. The salt-containing wastewater treatment system based on the hot and cold ends of a heat pump according to claim 1, characterized in that A storage tank for storing concentrated liquid is provided between the solid-liquid separation device and the evaporation heat exchanger E.

3. The salt-containing wastewater treatment system based on the hot and cold ends of a heat pump according to claim 1, characterized in that The steam in the inlet steam pipe flows from the evaporation heat exchanger C to the steam inlet, and the steam in the exhaust steam pipe flows from the steam outlet to the evaporation heat exchanger C.

4. The salt-containing wastewater treatment system based on the hot and cold ends of a heat pump according to claim 3, characterized in that A vacuum pump is provided on the inlet steam pipe to keep the evaporation heat exchanger C and the evaporation crystallization device in a negative pressure state.

5. The salt-containing wastewater treatment system based on the hot and cold ends of a heat pump according to claim 4, characterized in that The vacuum pressure range of the evaporation crystallization device is 9.106 kPa to 19.918 kPa.

6. The salt-containing wastewater treatment system based on the hot and cold ends of a heat pump according to claim 5, characterized in that A screw pump is provided between the solid-liquid separation device and the low-temperature heat exchanger B.

7. The salt-containing wastewater treatment system based on the hot and cold ends of a heat pump according to claim 1, characterized in that A circulation pump is provided between the cooling tower and the low-temperature heat exchanger B.

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