Multi-stage dew point evaporation concentration system and method

Abstract

The present invention discloses a multi-stage dew point evaporation concentration system and method, comprising a dust collector, a fan, an evaporation device, a regenerator, a preheater, a raw material liquid tank, a feed liquid pump, a mixing tank, a circulation pump, a heater, a first-stage concentrated liquid pump, a concentrated liquid tank, a crystallizer feed pump, a crystallizer and a centrifuge; the present invention provides multiple evaporators and regenerators in the system, and adjusts the liquid flow in evaporators and regenerators of different stages by solution diversion, so that the liquid-gas mass flow ratio in the second-stage evaporator and the second-stage regenerator is higher than the liquid-gas mass flow in the first-stage evaporator and the first-stage regenerator, so as to reduce the temperature and humidity difference in gas-liquid heat and mass transfer and the system entropy increase, improve thermal efficiency, and thus improve the performance of the dew point evaporation system.

Description

Technical Field

[0001] The present invention relates to the technical field of evaporation and concentration, in particular to a multi-stage dew point evaporation and concentration system and method. Background Art

[0002] Evaporation and concentration are common unit operations in process industries, with widespread applications in petrochemicals, food, pharmaceuticals, wastewater treatment, and desalination. However, the evaporation and concentration process consumes significant amounts of energy. Traditional evaporation and concentration technologies, such as mechanical vapor recompression and multi-effect evaporation, are primarily powered by fossil fuels, consuming significant amounts of fossil energy while also generating significant carbon emissions. Furthermore, these two evaporation and concentration technologies suffer from drawbacks such as large footprints, high investment costs, difficult maintenance, and susceptibility to corrosion and scaling. Consequently, a new evaporation technology is urgently needed.

[0003] Dew-point evaporation is a novel evaporation technology that simulates the natural rainwater cycle and utilizes the moisture-carrying capacity of air to achieve evaporation and water production. Dew-point evaporation achieves evaporation at atmospheric pressure and low temperature, requiring a low-quality heat source and efficiently utilizing low-grade thermal energy and renewable energy. Furthermore, its atmospheric pressure and low-temperature evaporation characteristics allow the use of low-cost, corrosion-resistant materials such as polypropylene, resulting in low manufacturing costs and easy maintenance. However, conventional dew-point evaporation technology is relatively inefficient compared to multi-effect evaporation and mechanical vapor recompression technologies. Improving the efficiency of dew-point evaporation is key to its further promotion and application. Summary of the Invention

[0004] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0005] The technical problem to be solved by the present invention is the low efficiency of dew point evaporation technology.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: a multi-stage dew point evaporation and concentration system, comprising a dust collector, a fan, an evaporation device, a heat recovery device, a preheater, a raw material liquid tank, a liquid pump, a mixing tank, a circulation pump, a heater, a first-stage concentrated liquid pump, a concentrated liquid tank, a crystallizer feed pump, a crystallizer, and a centrifuge;

[0007] The dust collector, fan, evaporation device and heat recovery device are connected in sequence through pipelines, the preheater is connected to the heat recovery device through a pipeline, the raw liquid tank is connected to the preheater through a liquid pump, the mixing tank is connected to the heat recovery device through a circulation pump, the solution outlet of the preheater is divided into two branches, one branch is connected to the raw liquid tank, and the other branch is connected to the mixing tank. The heater is connected between the evaporation device and the heat recovery device through a pipeline, the evaporation device is connected to the concentrated liquid tank through a concentrated liquid inlet pipe via a first-level concentrated liquid pump, the concentrated liquid tank is connected to the crystallizer feed pump, and the crystallizer feed pump, crystallizer and centrifuge are connected in sequence through pipelines.

[0008] As a preferred embodiment of the multi-stage dew point evaporation and concentration system of the present invention, the evaporation device includes a primary evaporator and a secondary evaporator, the air inlet of the primary evaporator is connected to the fan, the air inlet of the secondary evaporator is connected to the air outlet of the primary evaporator, the air outlet of the secondary evaporator is connected to the heat recovery device, and the liquid inlet of the secondary evaporator is connected to the heater.

[0009] As a preferred embodiment of the multi-stage dew point evaporation and concentration system of the present invention, the heat recovery device includes a secondary heat regenerator and a primary heat regenerator, the air inlet of the secondary heat regenerator is connected to the air outlet of the secondary evaporator, the air outlet of the secondary heat regenerator is connected to the air inlet of the primary heat regenerator, the air outlet of the primary heat regenerator is connected to the air inlet of the preheater, the liquid inlet of the primary heat regenerator is connected to the circulation pump, the liquid outlet of the primary heat regenerator is connected to the liquid inlet of the secondary heat regenerator, and the liquid outlet of the secondary heat regenerator is connected to the heater.

[0010] As a preferred embodiment of the multi-stage dew-point evaporation and concentration system of the present invention, the system further includes a secondary concentrate pump, a primary circulation valve, and a secondary circulation valve. The liquid outlet of the secondary evaporator is divided into two branches via the secondary concentrate pump. One branch is connected to the liquid inlet of the primary evaporator via the primary circulation valve, and the other branch is connected to the solution connecting pipes of the primary and secondary regenerators via the secondary circulation valve. This ensures that the liquid-gas mass flow ratio in the secondary evaporator and the secondary regenerator is higher than the liquid-gas mass flow rate in the primary evaporator and the primary regenerator.

[0011] As a preferred embodiment of the multi-stage dew point evaporation and concentration system of the present invention, it further includes an air return valve and an air exhaust valve. Two pipes are provided at the air outlet of the preheater, one of which is connected to the fan through the air return valve, and the other is connected to the outside of the system through the air exhaust valve, thereby improving the overall evaporation rate of the system.

[0012] As a preferred embodiment of the multi-stage dew-point evaporation and concentration system of the present invention, a crystallization liquid circulation pipe is provided at the bottom of the concentrate tank and is connected to the crystallizer feed pump, so that the crystal particles accumulated at the bottom of the concentrate tank remain in a flowing state, thereby preventing a large amount of crystal particles from settling and causing the crystallizer feed pump to malfunction.

[0013] As a preferred solution of the multi-stage dew point evaporation and concentration system of the present invention, it further includes a mother liquid pump, and the liquid outlet of the centrifuge is connected to the mixing tank via the mother liquid pump, thereby realizing the recycling of the solution.

[0014] The evaporation and concentration method using the multi-stage dew point evaporation and concentration system comprises the following steps:

[0015] 1) External air enters the system from the air intake, and after passing through the dust collector to remove solid particle pollutants in the air, it is first transported into the system by the fan. Then the raw material solution flows into the raw material liquid tank, and is transported to the preheater by the liquid pump to exchange heat with the wet air. Part of the heated raw material liquid flows back to the raw material liquid tank, and the other part flows into the mixing tank;

[0016] 2) The solution in the mixing tank flows into the primary regenerator through a circulation pump to recover part of the heat of the humid air. The heated solution is mixed with the concentrated liquid at the outlet of the secondary evaporator from the secondary circulation valve branch and flows into the secondary regenerator. It then flows into the heater and is heated to the specified temperature.

[0017] 3) The heated high-temperature solution first flows into the secondary evaporator, where it undergoes heat and mass transfer with the air, causing the solution temperature to drop. Part of the water evaporates and is carried away by the air, resulting in evaporation and concentration of the solution. A portion of the solution flowing out of the secondary evaporator flows into the primary evaporator through the primary circulation valve, where it again comes into contact with the air for heat and mass transfer, further evaporating and concentrating the solution. The remaining portion of the solution flows through the secondary circulation valve and mixes with the solution flowing out of the primary regenerator.

[0018] 4) The concentrated liquid from the first-stage evaporator is transported to the concentrated liquid tank through the first-stage concentrated liquid pump;

[0019] If the evaporated solution requires further crystallization, the concentrated solution containing crystal particles flows from the crystallization liquid outlet pipe through the crystallizer feed pump into the crystallizer for further crystallization. The mixed solution containing the crystal particles then enters the centrifuge for separation. The separated salt is discharged from the system, and the mother liquor is returned to the mixing tank via the mother liquor pump, repeating the above cycle.

[0020] b. If the solution to be evaporated does not need to be crystallized, the concentrated liquid in the concentrate tank will be directly discharged from the system through the crystallizer feed pump via the crystallizer liquid outlet pipe.

[0021] The beneficial effects of the present invention are:

[0022] 1. Set up multiple evaporators and regenerators in the system, and adjust the liquid flow in evaporators and regenerators of different stages by solution diversion, so that the liquid-gas mass flow ratio in the secondary evaporator and secondary regenerator is higher than the liquid-gas mass flow in the primary evaporator and primary regenerator, so as to reduce the temperature and humidity difference and system entropy increase in the gas-liquid heat and mass transfer process, and improve the thermal efficiency of the system;

[0023] 2. Preheat the raw material liquid by setting a preheater in the system to recover the waste heat in the wet air. The heat and mass transfer performance of the preheater is improved by circulating the raw material liquid at a large flow rate, thereby completely recovering the heat of the wet air.

[0024] 3. By setting up an air return valve and an air exhaust valve in the system, different air circulation forms (open or closed) can be selected according to different operating conditions and the actual thermal state of the air at the preheater outlet, thereby targetedly enhancing different types of system performance under different operating conditions and selectively enhancing the system's evaporation performance or thermal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0026] Figure 1 This is a schematic diagram of the system process flow of a multi-stage dew point evaporation and concentration system.

[0027] Figure 2 This is the temperature-enthalpy operating diagram of a conventional single-stage dew point evaporation concentration system.

[0028] Figure 3 This is the temperature-enthalpy operating line diagram of the multi-stage dew point evaporation concentration system.

[0029] Figure 4 This is a comparison chart of system thermal efficiency.

[0030] Figure 5 is the temperature enthalpy curve of saturated moist air.

[0031] In the figure: 1. Dust collector; 2. Fan; 3. Primary evaporator; 4. Secondary evaporator; 41. Primary circulation valve; 42. Secondary circulation valve; 5. Secondary regenerator; 6. Primary regenerator; 7. Preheater; 71. Air return valve; 72. Air exhaust valve; 8. Raw liquid tank; 9. Liquid pump; 10. Mixing tank; 11. Circulation pump; 12. Heater; 13. Secondary concentrate pump; 14. Primary concentrate pump; 15. Concentrate tank; 151. Crystallization liquid outlet pipe; 152. Crystallization liquid circulation pipe; 153. Concentrate inlet pipe; 16. Crystallizer feed pump; 17. Crystallizer; 18. Centrifuge; 19. Mother liquor pump; 21. Fresh water storage tank. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0034] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0035] Example 1

[0036] Reference 1 is a first embodiment of the present invention, which provides a multi-stage dew point evaporation concentration system.

[0037] Dust collector 1, fan 2, evaporation device, heat recovery device, preheater 7, raw material liquid tank 8, liquid pump 9, mixing tank 10, circulation pump 11, heater 12, first-stage concentrated liquid pump 14, concentrated liquid tank 15, crystallizer feed pump 16, crystallizer 17 and centrifuge 18; dust collector 1, fan 2, evaporation device and heat recovery device are connected in sequence through pipelines, preheater 7 is connected to heat recovery device through pipelines, raw material liquid tank 8 is connected to preheater 7 through liquid pump 9, mixing tank 10 is connected to preheater 7 through circulation pump 11 is connected to the heat recovery device, the solution outlet of the preheater 7 is divided into two branches, one branch is connected to the raw material liquid tank 8, and the other branch is connected to the mixing tank 10. The heater 12 is connected between the evaporation device and the heat recovery device through a pipeline. The evaporation device is connected to the concentrated liquid tank 15 through the concentrated liquid inlet pipe 153151 via the first-level concentrated liquid pump 14. The concentrated liquid tank 15 is connected to the crystallizer feed pump 16. The crystallizer feed pump 16, the crystallizer 17 and the centrifuge 18 are connected in sequence through pipelines.

[0038] After the external air enters from the air intake, the solid particle pollutants in the air are removed by the dust collector 1, and the air is transported to the evaporation device by the fan 2, and then flows into the heat recovery device, and flows into the preheater 7 from the heat recovery device, and finally discharged from the system from the preheater 7; in this process, the raw material solution first flows into the raw material liquid tank 8, and is transported to the preheater 7 through the liquid pump 9 to exchange heat with the wet air, recovering part of the waste heat of the wet air. The solution outlet of the preheater 7 is divided into two branches, the first branch is connected to the raw material liquid tank 8, and the second branch is connected to the mixing tank 10, so that part of the heated raw material liquid flows back to the raw material liquid tank 8. The raw material liquid circulates continuously between the preheater 7 and the raw material liquid tank 8, thereby increasing the amount of waste heat recovered from the wet air and improving the efficiency of the system;

[0039] Another part of the raw material liquid flows into the mixing tank 10, and the solution in the mixing tank 10 flows into the heat recovery device through the circulation pump 11 to recover part of the heat of the wet air, and then flows into the heater 12 to be heated to a specified temperature. The heat required in the heater 12 comes from low-grade waste heat, thereby reducing fossil energy consumption and reducing carbon emissions; the heated high-temperature solution flows into the evaporation device to transfer heat and mass with the air, the solution temperature decreases, and part of the water evaporates and is carried away by the air to achieve evaporation and concentration; the concentrated liquid in the evaporation device is transported to the concentrated liquid tank 15 by the first-level concentrated liquid pump 14, and then transported into the crystallizer 17 through the crystallizer feed pump 16 for crystallization, and then the mixed liquid containing the crystals enters the centrifuge 18 for separation, and the separated salt is discharged from the system.

[0040] The evaporation device includes a primary evaporator 3 and a secondary evaporator 4, the air inlet of the primary evaporator 3 is connected to the fan 2, the air inlet of the secondary evaporator 4 is connected to the air outlet of the primary evaporator 3, the air outlet of the secondary evaporator 4 is connected to the heat recovery device, and the liquid inlet of the secondary evaporator 4 is connected to the heater 12;

[0041] The reheating device includes a secondary reheater 5 and a primary reheater 6, the air inlet of the secondary reheater 5 is connected to the air outlet of the secondary evaporator 4, the air outlet of the secondary reheater 5 is connected to the air inlet of the primary reheater 6, the air outlet of the primary reheater 6 is connected to the air inlet of the preheater 7, the liquid inlet of the primary reheater 6 is connected to the circulation pump 11, the liquid outlet of the primary reheater 6 is connected to the liquid inlet of the secondary reheater 5, and the liquid outlet of the secondary reheater 5 is connected to the heater 12;

[0042] It also includes a secondary concentrated liquid pump 13, a primary circulation valve 41 and a secondary circulation valve 42. The liquid outlet of the secondary evaporator 4 is divided into two branches through the secondary concentrated liquid pump 13. One branch is connected to the liquid inlet of the primary evaporator 3 through the primary circulation valve 41, and the other branch is connected to the solution connecting pipes of the primary regenerator 6 and the secondary regenerator 5 through the secondary circulation valve 42.

[0043] like Figure 2As shown in the figure, in a conventional single-stage dew point evaporation and concentration system, the saturated vapor pressure of water vapor increases exponentially with temperature. Therefore, the temperature enthalpy operating line of wet air is an exponential curve, while the temperature enthalpy operating line of liquid is approximately a straight line. The line shapes of the gas-liquid operating lines do not match and the difference is large. Due to the significant difference in line shape, the gas-liquid operating lines cannot be completely close. Even if the pinch point temperature difference in the evaporator and the regenerator is reduced by enhancing the heat and mass transfer performance of the evaporator and the regenerator, there is still a relatively significant average heat transfer temperature difference and mass transfer concentration difference between the gas and the liquid, which will lead to a large increase in system entropy, thereby limiting the improvement of the system thermal efficiency.

[0044] Therefore, in this embodiment, the evaporation device consists of a primary evaporator 3 and a secondary evaporator 4, and the heat recovery device consists of a secondary heat recovery device 5 and a primary heat recovery device 6. The solution in the mixing tank 10 flows into the primary heat recovery device 6 through the circulation pump 11 to recover part of the heat of the humid air. The heated solution is mixed with the concentrated liquid at the outlet of the secondary evaporator 4 from the branch of the secondary circulation valve 42 and flows into the secondary heat recovery device 5 to further recover the waste heat of the air.

[0045] Then it flows into the heater 12 and is heated to a specified temperature. The heated high-temperature solution flows into the secondary evaporator 4 and undergoes heat and mass transfer with the air. The temperature of the solution decreases, part of the water evaporates and is carried away by the air, and the solution is evaporated and concentrated. A part of the solution flowing out of the secondary evaporator 4 flows into the primary evaporator 3 through the primary circulation valve 41 by the secondary concentrate pump 13, and comes into contact with the air again to undergo heat and mass transfer, and the solution is further evaporated and concentrated; the other part is mixed with the outlet solution of the primary regenerator 6 through the secondary circulation valve 42 and flows into the secondary regenerator 5; the diversion of the outlet solution of the secondary evaporator 4 makes the liquid flow in the primary evaporator 3 and the primary regenerator 6 always smaller than the liquid flow in the secondary evaporator 4 and the secondary regenerator 5, that is, the liquid-gas mass flow ratio in the primary evaporator 3 and the primary regenerator 6 is smaller than the liquid flow in the secondary evaporator 4 and the secondary regenerator 5, thereby increasing the matching degree of the gas-liquid temperature enthalpy operating line, reducing the entropy increase of the system, and improving the thermal efficiency of the system.

[0046] This embodiment is provided with at least two evaporators and regenerators, such as Figure 3 As shown in FIG, by adjusting the liquid flow in evaporators and regenerators of different stages through solution diversion, the liquid-gas mass flow ratio in the secondary evaporator 4 and the secondary regenerator 5 is made higher than the liquid-gas mass flow in the primary evaporator 3 and the primary regenerator 6, thereby achieving a liquid operating line that is closer to the saturated air curve and reducing the mismatch between the gas-liquid temperature enthalpy operating line; Figure 4 As shown in the figure, by reducing the temperature and humidity difference and system entropy increase in the gas-liquid heat and mass transfer process, the thermal efficiency of the system can be improved. The maximum thermal efficiency of the two-stage system can be increased by about 40% compared with the conventional system.

[0047] Example 2

[0048] Reference Figure 1 and Figure 5 , which is the second embodiment of the present invention, and is based on the previous embodiment.

[0049] It also includes an air return valve 71 and an air exhaust valve 72. Two pipes are provided at the air outlet of the preheater 7. One pipe is connected to the fan 2 through the air return valve 71, and the other pipe is connected to the outside of the system through the air exhaust valve 72.

[0050] The air circulation of conventional dew point evaporation system is a separate open or closed system, such as Figure 5 As shown in the figure, the saturated vapor pressure of water vapor increases exponentially with temperature, so the enthalpy value contained in saturated moist air also increases exponentially with temperature; when the temperature is lower than 40℃, the growth rate of the enthalpy of saturated moist air is slower, while when the temperature exceeds 40℃, the growth rate of the enthalpy of saturated moist air is faster, and the latent heat contained in saturated moist air is larger.

[0051] Therefore, in this embodiment, external air is transported to the first-level evaporator 3 by the fan 2, and the air is in direct contact with the solution in the first-level evaporator 3 to transfer heat and mass. The air heats up and absorbs moisture, taking away part of the moisture in the solution. The air after heating and absorbing moisture then continues to flow into the second-level evaporator 4, and again directly contacts the high-temperature solution in the second-level evaporator 4, its temperature and moisture content are further increased, and part of the moisture in the solution is taken away; the high-temperature and high-humidity air then flows into the second-level regenerator 5 to exchange heat with the incoming cold solution, recovering part of the waste heat of the wet air, and at the same time, some condensed water is precipitated; the cooled wet air enters the first-level regenerator 6 to preheat the incoming cold solution, further recovering the waste heat of the wet air; the air continues to flow into the preheater 7, exchanges heat with the circulating raw material liquid, the air temperature further drops, and at the same time, some condensed water is precipitated; the condensed water generated by the first-level regenerator 6, the second-level regenerator 5 and the preheater 7 flows to the fresh water storage tank 21 under the action of gravity for recycling.

[0052] After the air flows into the preheater 7 and exchanges heat with the circulating raw material liquid, if the temperature of the air flowing out of the preheater 7 is greater than 40°C, the moisture content of the air is still high and contains a large amount of latent heat. At this time, the air return valve 71 is opened and the air exhaust valve 72 is closed. The air adopts a closed cycle and the air re-enters the system for circulation to avoid heat loss caused by direct exhaust of wet air, thereby improving the thermal efficiency of the system; if the temperature of the air flowing out of the preheater 7 is less than 40°C, the air moisture content is small and the latent heat contained is relatively low. At this time, the air return valve 71 is closed and the air exhaust valve 72 is opened. The air adopts an open cycle and the air is directly exhausted. The fan 2 directly inhales fresh air with a lower moisture content from the outside, thereby improving the evaporation rate of the system.

[0053] A crystallization liquid circulation pipe 152 is provided at the bottom of the concentrated liquid tank 15 and is connected to the crystallizer feed pump 16 .

[0054] By installing a crystallization liquid circulation pipe 152 at the bottom of the concentrated liquid tank 15, the other end of the crystallization liquid circulation pipe 152 is connected to the liquid outlet end of the crystallizer feed pump 16. During the process of the concentrated liquid in the concentrated liquid tank 15 being transported by the crystallizer feed pump 16, a part of the concentrated liquid returns to the concentrated liquid tank 15, impacting the crystal particles accumulated at the bottom of the concentrated liquid tank 15 to keep them in a flowing state, thereby preventing a large amount of crystal particles from being deposited and causing the crystallizer feed pump 16 to fail to work normally.

[0055] A mother liquid pump 19 is also included, and the liquid outlet of the centrifuge 18 is connected to the mixing tank 10 via the mother liquid pump 19.

[0056] By arranging a mother liquid pump 19 between the centrifuge 18 and the mixing tank 10, the solution can be recycled to improve the overall evaporation and concentration rate of the system.

[0057] Example 3

[0058] Reference Figure 1 This embodiment is based on the previous two embodiments and uses the evaporation and concentration method of the multi-stage dew point evaporation and concentration system, including the following steps:

[0059] 1) External air enters the system from the air intake, passes through the dust collector 1 to remove solid particulate pollutants in the air, and is first transported into the system by the fan 2. Then the raw material solution flows into the raw material liquid tank 8, and is transported to the preheater 7 by the liquid pump 9 to exchange heat with the wet air. Part of the heated raw material liquid flows back to the raw material liquid tank 8, and the other part flows into the mixing tank 10;

[0060] 2) The solution in the mixing tank 10 flows into the primary regenerator 6 via the circulation pump 11 to recover some of the heat from the humid air. The heated solution is mixed with the concentrated liquid at the outlet of the secondary evaporator 4 from the branch of the secondary circulation valve 42 and flows into the secondary regenerator 5 to further recover the waste heat from the air. The solution then flows into the heater 12 to be heated to the specified temperature.

[0061] 3) The heated high-temperature solution first flows into the secondary evaporator 4, where heat and mass transfer occurs with the air, causing the solution temperature to drop. Part of the water evaporates and is carried away by the air, resulting in evaporation and concentration of the solution. A portion of the solution flowing out of the secondary evaporator 4 flows into the primary evaporator 3 through the primary circulation valve 41, where it again comes into contact with the air to cause heat and mass transfer, further evaporating and concentrating the solution. The other portion of the solution flows through the secondary circulation valve 42 and mixes with the solution flowing out of the primary regenerator 6, so that the liquid flow rate in the primary evaporator 3 and the regenerator is always smaller than the liquid flow rate in the secondary evaporator 4 and the regenerator. That is, the liquid-to-gas mass flow rate ratio in the primary evaporator 3 and the regenerator is smaller than the liquid flow rate in the secondary evaporator 4 and the regenerator, thereby increasing the matching degree of the gas-liquid temperature enthalpy operating line, reducing the entropy increase of the system, and improving the thermal efficiency of the system.

[0062] 4) The concentrated liquid from the primary evaporator 3 is transported to the concentrated liquid tank 15 via the primary concentrated liquid pump 14;

[0063] Application Example 1

[0064] This system is used in scenarios such as saline wastewater treatment and salt production that require concentration and crystallization. The evaporated solution in the system needs to be further crystallized. The concentrated liquid containing crystal particles flows from the crystallization liquid outlet pipe 151 through the crystallizer feed pump 16 into the crystallizer 17 for further crystallization. Then the mixed liquid containing the crystal particles enters the centrifuge 18 for separation. The separated salt is discharged from the system, and the mother liquor flows back to the mixing tank 10 through the mother liquor pump 19, repeating the above cycle.

[0065] Application Example 2

[0066] This system is used in scenarios where evaporation is required, such as seawater desalination. The evaporated solution in the system does not need to be crystallized, and the concentrated solution in the concentrated solution tank 15 is directly discharged from the system through the crystallizer feed pump 16 via the crystallizer liquid outlet pipe 151.

[0067] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A multi-stage dew point evaporation and concentration system, characterized by: include, Dust collector, fan, evaporation device, heat recovery device, preheater, raw material liquid tank, liquid pump, mixing tank, circulation pump, heater, first-stage concentrate pump, concentrate tank, crystallizer feed pump, crystallizer and centrifuge; The dust collector, the fan, the evaporation device and the heat recovery device are connected in sequence through pipelines, the preheater is connected to the heat recovery device through a pipeline, the raw liquid tank is connected to the preheater through a liquid pump, the mixing tank is connected to the heat recovery device through a circulation pump, the solution outlet of the preheater is divided into two branches, one branch is connected to the raw liquid tank, and the other branch is connected to the mixing tank, the heater is connected between the evaporation device and the heat recovery device through a pipeline, the evaporation device is connected to the concentrated liquid tank through a concentrated liquid inlet pipe via a primary concentrated liquid pump, the concentrated liquid tank is connected to the crystallizer feed pump, and the crystallizer feed pump, the crystallizer and the centrifuge are connected in sequence through pipelines; The evaporation device includes a primary evaporator and a secondary evaporator, the air inlet of the primary evaporator is connected to the fan, the air inlet of the secondary evaporator is connected to the air outlet of the primary evaporator, the air outlet of the secondary evaporator is connected to the heat recovery device, and the liquid inlet of the secondary evaporator is connected to the heater; The heat recovery device includes a secondary heat recovery device and a primary heat recovery device, the air inlet of the secondary heat recovery device is connected to the air outlet of the secondary evaporator, the air outlet of the secondary heat recovery device is connected to the air inlet of the primary heat recovery device, the air outlet of the primary heat recovery device is connected to the air inlet of the preheater, the liquid inlet of the primary heat recovery device is connected to the circulation pump, the liquid outlet of the primary heat recovery device is connected to the liquid inlet of the secondary heat recovery device, and the liquid outlet of the secondary heat recovery device is connected to the heater; It also includes a secondary concentrated liquid pump, a primary circulation valve and a secondary circulation valve. The liquid outlet of the secondary evaporator is divided into two branches through the secondary concentrated liquid pump. One branch is connected to the liquid inlet of the primary evaporator through the primary circulation valve, and the other branch is connected to the solution connecting pipe of the primary regenerator and the secondary regenerator through the secondary circulation valve.

2. The multi-stage dew point evaporation concentration system according to claim 1, characterized in that: It also includes an air return valve and an air exhaust valve. Two pipes are set at the air outlet of the preheater, one is connected to the fan through the air return valve, and the other is connected to the outside of the system through the air exhaust valve.

3. The multi-stage dew point evaporation concentration system according to claim 1, characterized in that: A crystallization liquid circulation pipe is provided at the bottom of the concentrate tank and is connected to the crystallizer feed pump.

4. The multi-stage dew point evaporation concentration system according to claim 1, characterized in that: The centrifuge also includes a mother liquid pump, and the liquid outlet of the centrifuge is connected to the mixing tank via the mother liquid pump.

5. The evaporation concentration method using the multi-stage dew point evaporation concentration system according to any one of claims 1 to 4, characterized in that: The steps include: 1) External air enters the system from the air intake, passes through the dust collector to remove solid particle pollutants in the air, and is first transported into the system by the fan. Then the raw material solution flows into the raw material liquid tank, and is transported to the preheater by the liquid pump to exchange heat with the wet air. Part of the heated raw material liquid flows back to the raw material liquid tank, and the other part flows into the mixing tank; 2) The solution in the mixing tank flows into the primary regenerator through a circulation pump to recover part of the heat of the humid air. The heated solution is mixed with the concentrated liquid at the outlet of the secondary evaporator from the secondary circulation valve branch and flows into the secondary regenerator. It then flows into the heater and is heated to the specified temperature. 3) The heated high-temperature solution first flows into the secondary evaporator, where it undergoes heat and mass transfer with the air. The solution temperature drops, and part of the water evaporates and is carried away by the air, achieving evaporation and concentration. Part of the solution flowing out of the secondary evaporator flows into the primary evaporator through the primary circulation valve, where it comes into contact with the air again to undergo heat and mass transfer, further evaporating and concentrating the solution. The remaining part flows through the secondary circulation valve and mixes with the solution flowing out of the primary regenerator. 4) The concentrated liquid from the first-stage evaporator is transported to the concentrated liquid tank through the first-stage concentrated liquid pump; If the evaporated solution requires further crystallization, the concentrated solution containing crystal particles flows from the crystallization liquid outlet pipe through the crystallizer feed pump into the crystallizer for further crystallization. The mixed solution containing the crystal particles then enters the centrifuge for separation. The separated salt is discharged from the system, and the mother liquor is returned to the mixing tank via the mother liquor pump, repeating the above cycle. b. If the solution to be evaporated does not need to be crystallized, the concentrated liquid in the concentrate tank will be directly discharged from the system through the crystallizer feed pump via the crystallizer liquid outlet pipe.

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