A design method of low-energy-consumption MVR waste liquid treatment evaporator structure

Abstract

This invention discloses a design method for a low-energy MVR waste liquid treatment evaporator structure, relating to the field of solvent distillation and recovery technology. The method includes: matching and designing the heat exchange structure of the MVR system and establishing an initial model of the heat exchange structure; using the sum of equipment investment cost and operating cost as the total cost of the heat exchange structure, and outputting it as the objective function of the heat exchange structure model; using a genetic algorithm to optimize the structure of the initial heat exchange structure model; establishing a design model of the distillation unit, and calculating the distillation unit structural parameters matching the MVR system based on the process parameters in the heat exchange structure optimization model; using a Roots compressor to compress the steam generated by the distillation unit; using mechanical vapor recompression technology to recover and utilize the potential energy of the discharged secondary steam; and summarizing and integrating the MVR waste liquid treatment evaporator structure. By forming a closed-loop thermal energy circulation system, energy consumption is significantly reduced, and efficient utilization of thermal energy is achieved.

Description

Technical Field

[0001] This invention relates to the field of solvent distillation and recovery technology, specifically to a design method for a low-energy MVR waste liquid treatment evaporator structure. Background Technology

[0002] MVR stands for Mechanical Vapor Recompression. MVR is an energy-saving technology that reuses the energy of the secondary steam it generates, thereby reducing the need for external energy sources. As early as the 1960s, this technology was used in chemical, food, paper, pharmaceutical, seawater desalination, and wastewater treatment industries. The evaporator's operation involves compressing low-temperature steam through a compressor, increasing its temperature, pressure, and enthalpy, before it enters a heat exchanger for condensation, fully utilizing the steam's latent heat. Except for start-up, no live steam is required during the entire evaporation process.

[0003] Large quantities of high-concentration saline wastewater are generated during the production processes of dyeing, printing, chemicals, papermaking, pharmaceuticals, and pesticides. Some of this wastewater contains inorganic salts that have recycling value; direct discharge leads to water pollution and resource waste. Conventional multi-effect evaporation can treat and recycle this type of wastewater, but it suffers from high energy consumption, numerous supporting equipment, and high operating costs. Therefore, researching a wastewater treatment method that is energy-efficient, has low operating costs, and a compact structure is of practical significance. Summary of the Invention

[0004] To address the aforementioned technical problems, a design method for a low-energy MVR waste liquid treatment evaporator structure is provided. This technical solution resolves the issues raised in the background section.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A design method for a low-energy MVR waste liquid treatment evaporator structure includes:

[0007] Using the heat transfer effectiveness-number of heat transfer units theory of heat exchangers, the relevant structural parameters of the heat exchange structure are calculated, the heat exchange structure of the MVR system is matched and designed, and an initial model of the heat exchange structure is established.

[0008] The total cost of the heat exchange structure is the sum of the equipment investment cost and the operating cost, and this sum is output as the objective function of the heat exchange structure model.

[0009] Based on the objective function of the heat transfer structure model, a genetic algorithm is used to realize the structural optimization process of the initial heat transfer structure model, resulting in an optimized heat transfer structure model.

[0010] Based on the design principles of separators, a design model of the distillation unit is established. Based on the process parameters in the heat exchange structure optimization model, the structural parameters of the distillation unit that match the MVR system are calculated, and a structural model of the distillation unit is constructed.

[0011] A Roots compressor is used to compress the steam generated by the distillation unit, and the structure of the Roots compressor is analyzed.

[0012] Mechanical vapor recompression technology is used to recover and utilize the potential energy of the discharged secondary steam as heating steam to provide a heat source for the MVR system;

[0013] The structure of the MVR waste liquid treatment evaporator was summarized and integrated, and an overall process integration diagram of the MVR system was drawn.

[0014] Preferably, the step of using the heat transfer effectiveness-number of heat transfer units theory of heat exchangers to calculate the relevant structural parameters of the heat exchange structure, matching and designing the heat exchange structure of the MVR system, and establishing an initial model of the heat exchange structure specifically includes:

[0015] The steam in the heat exchange structure consists of two parts: steam cooling and steam condensation. The heat exchange structure is set as a cooling sensible heat section and a condensation latent heat section.

[0016] The heat transfer effectiveness of the two heat exchange structures is calculated based on the heat transfer effectiveness-number of heat transfer units theory.

[0017] Calculate the number of heat transfer units in the heat exchange structure;

[0018] Obtain the empirical range of the overall heat transfer coefficient, and preset the overall heat transfer coefficient of the heat exchange structure based on this empirical range;

[0019] Calculate the initial heat transfer area using the heat transfer area formula;

[0020] The inner diameter of the pipe in the pre-designed heat exchange structure;

[0021] Determine the flow area of ​​the tube;

[0022] Calculate the number of heat exchange tubes and the length of each heat exchange tube;

[0023] The heat transfer effectiveness-number of heat transfer units theory is as follows:

[0024]

[0025] In the formula, ε is the heat transfer efficiency, and t si t is the inlet temperature of the hot end. ti The inlet temperature is Δt. s The temperature difference between the inlet and outlet of the hot end, Δt t The temperature difference between the inlet and outlet of the cold end;

[0026] The number of heat transfer units is:

[0027]

[0028] In the formula, N is the number of heat transfer units, and f is the function relating heat transfer effectiveness to the number of heat transfer units in the pre-defined non-mixed countercurrent heat exchange structure.

[0029] The formula for the heat exchange area is:

[0030]

[0031] In the formula, k is the overall heat transfer coefficient, A is the initial heat transfer area, and W min The minimum heat capacity of the waste liquid; the flow area of ​​the tube side is:

[0032]

[0033] In the formula, S is the tube-side flow area, F is the steam flow rate, v is the tube-side velocity, and ρ is the steam density; the number of heat exchange tubes is:

[0034]

[0035] In the formula, n is the number of heat exchange tubes, and r is the preset inner diameter of the heat exchange tubes;

[0036] The length of each heat exchange tube is:

[0037]

[0038] In the formula, L is the length of each heat exchange tube.

[0039] Preferably, the step of using the sum of equipment investment cost and operating cost as the total cost of the heat exchange structure and outputting it as the objective function of the heat exchange structure model specifically includes:

[0040] The total cost of a heat exchange structure includes equipment investment costs and operating costs;

[0041] The equipment investment cost is the investment cost of the heat exchange area;

[0042] Operating costs are the energy costs incurred by the pump to overcome pressure drop;

[0043] Obtain the heat transfer area parameters of the material selected for the heat exchange structure, namely the heat transfer area parameters of stainless steel;

[0044] Based on the heat exchange area parameters of stainless steel, the equipment investment cost is calculated using the investment cost formula.

[0045] Calculate operating costs using the energy cost formula;

[0046] The sum of the investment cost and operating cost of the output equipment is the objective function of the heat exchange structure model;

[0047] The investment cost formula is as follows:

[0048]

[0049] In the formula, C1 is the equipment investment cost, and a1, a2, and a3 are the first, second, and third heat exchange area parameters of stainless steel, respectively.

[0050] The energy cost formula is as follows:

[0051]

[0052] In the formula, C2 represents the operating cost, η represents the pump efficiency, and ΔP t , △P s These are the pressure losses on the tube side and the shell side, respectively.

[0053] Preferably, the objective function based on the heat transfer structure model, and the structural optimization process of the initial heat transfer structure model using a genetic algorithm to obtain the optimized heat transfer structure model, specifically include:

[0054] S101: Randomly generate a heat exchanger structure model and combine it with the initial heat exchanger structure model as the initial population;

[0055] S102: Evaluate all individuals in the population based on the objective function of the heat exchange structure model to obtain the fitness value of each individual;

[0056] S103: Select superior individuals as parents based on fitness values;

[0057] S104: Perform non-equipotential exchange operations between parent individuals to exchange the position and content of heat transfer structure model parameters and generate new offspring individuals;

[0058] S105: Perform random mutation operations on offspring individuals to introduce new parameter values ​​as genetic genes;

[0059] S106: Replace the non-superior individuals in the population with newly generated offspring individuals;

[0060] S107: Determine whether the preset maximum number of iterations has been reached. If yes, end the iteration and output the current population as the heat exchange structure optimization model. If no, return to step S102.

[0061] Preferably, the step of establishing a design model for the distillation unit based on the separator design principle, and calculating the distillation unit structural parameters matching the MVR system based on the process parameters in the heat exchange structure optimization model, specifically includes:

[0062] The main distillation unit consists of a cylinder, feed pipe, heat exchanger tube, concentrated liquid outlet, demister and steam outlet;

[0063] Obtain distillation parameters, waste liquid density, and vapor density;

[0064] Calculate the maximum permissible steam velocity using the critical velocity formula;

[0065] The diameter of the distillation main cylinder is calculated based on the maximum allowable steam velocity.

[0066] The height of the distillation main body is set to twice the diameter of the distillation main body.

[0067] Set the diameter of each interface to the inner diameter of the heat exchange tube;

[0068] A wire mesh demister is used to eliminate liquid droplets entrained in the steam;

[0069] The formula for the critical velocity is:

[0070]

[0071] In the formula, v max The maximum allowable velocity of steam is given by m, which is a distillation parameter, and ρ1 and ρ2 are the density of the waste liquid and the density of the steam, respectively.

[0072] The diameter of the distillation main unit cylinder is:

[0073]

[0074] In the formula, D is the diameter of the distillation main body cylinder, and F' is the steam flow rate inside the distillation main body.

[0075] Preferably, the step of using a Roots compressor to compress the steam generated by the distillation unit, and the analysis of the structure of the Roots compressor specifically includes:

[0076] A Roots compressor is a positive displacement compressor with two rotors whose axes are parallel to each other;

[0077] The rotor is composed of a shaft and impellers, and there are pre-set gaps between the impellers and between the impellers and the casing and baffles;

[0078] The two rotors are driven by a pair of meshing synchronous gears and rotate in opposite directions at the same angular velocity;

[0079] The compressor's inlet and outlet are not directly connected, and the volume of the basic unit of the enclosed space formed by the impeller, casing, and baffles remains constant during rotation.

[0080] When the basic volume is connected to the exhaust port, the high-pressure gas flows back to the basic volume to equalize the pressure, thereby compressing the steam generated by the distillation unit.

[0081] Preferably, the method of using mechanical vapor recompression technology to recover and utilize the potential energy of the discharged secondary steam as heating steam to provide a heat source for the MVR system specifically includes:

[0082] In the distillation unit, a collector is used to collect the secondary steam generated by the heating and evaporation of the concentrated liquid;

[0083] The collected secondary steam is fed into a Roots compressor for compression. During the compression process, the pressure and temperature of the steam increase.

[0084] The compressed steam is sent back to the heat exchange structure to provide a heat source for the MVR system.

[0085] Preferably, the process of summarizing and integrating the structures of the MVR waste liquid treatment evaporator and drawing an overall process integration diagram of the MVR system specifically includes:

[0086] Waste liquid is fed into the inlet of the MVR waste liquid treatment evaporator;

[0087] Waste liquid is fed into the distillation unit;

[0088] The waste liquid undergoes heat exchange through a heat exchange structure;

[0089] The distillation unit outputs steam and concentrated liquid;

[0090] Steam is fed into a Roots compressor for compression to produce distilled water.

[0091] The secondary steam generated by the heating and evaporation of the concentrated liquid is collected and fed into a Roots compressor for compression. The compressed steam is then sent back to the heat exchange structure.

[0092] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0093] During the evaporation process, the heat released by the secondary steam generated by the heating and evaporation of the concentrated liquid is recovered and input into the heat exchange structure. This efficient heat recovery and utilization technology not only improves energy utilization efficiency but also reduces production costs. The modular design makes the structure compact, occupies a small area, and is easy to install and transport. At the same time, its integrated design tightly combines the various components, improving the overall performance and stability of the equipment. Attached Figure Description

[0094] Figure 1 This is a flowchart illustrating the design method of the low-energy MVR waste liquid treatment evaporator structure of the present invention.

[0095] Figure 2 This is a flowchart of the method for establishing an initial model of the heat exchange structure according to the present invention;

[0096] Figure 3The flowchart of the method of the present invention is as follows: taking the sum of equipment investment cost and operation cost as the total cost of heat exchange structure, and outputting it as the objective function of heat exchange structure model;

[0097] Figure 4 This is a flowchart of the structural optimization process of the initial model of the heat exchange structure using a genetic algorithm, as described in this invention.

[0098] Figure 5 This is a flowchart of the method for constructing a distillation main unit structural model according to the present invention;

[0099] Figure 6 This is a flowchart of the method for analyzing the structure of a Roots compressor according to the present invention;

[0100] Figure 7 This is a flowchart of the method for recovering and utilizing the potential energy of discharged secondary steam using mechanical steam recompression technology according to the present invention.

[0101] Figure 8 This is an integrated flowchart of the MVR system of the present invention. Detailed Implementation

[0102] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0103] Reference Figure 1 As shown, a design method for a low-energy MVR waste liquid treatment evaporator structure includes:

[0104] Using the heat transfer effectiveness-number of heat transfer units theory of heat exchangers, the relevant structural parameters of the heat exchange structure are calculated, the heat exchange structure of the MVR system is matched and designed, and an initial model of the heat exchange structure is established.

[0105] The total cost of the heat exchange structure is the sum of the equipment investment cost and the operating cost, and this sum is output as the objective function of the heat exchange structure model.

[0106] Based on the objective function of the heat transfer structure model, a genetic algorithm is used to optimize the initial heat transfer structure model, resulting in an optimized heat transfer structure model.

[0107] Based on the design principles of separators, a design model of the distillation unit is established. Based on the process parameters in the heat exchange structure optimization model, the structural parameters of the distillation unit that match the MVR system are calculated, and a structural model of the distillation unit is constructed.

[0108] A Roots compressor is used to compress the steam generated by the distillation unit, and the structure of the Roots compressor is analyzed.

[0109] Mechanical vapor recompression technology is used to recover and utilize the potential energy of the discharged secondary steam as heating steam to provide a heat source for the MVR system;

[0110] The structure of the MVR waste liquid treatment evaporator was summarized and integrated, and an overall process integration diagram of the MVR system was drawn.

[0111] Reference Figure 2 As shown, using the heat transfer effectiveness-number of heat transfer units theory of heat exchangers, the relevant structural parameters of the heat exchange structure are calculated, the heat exchange structure of the MVR system is matched and designed, and the initial model of the heat exchange structure is established, specifically including:

[0112] The steam in the heat exchange structure consists of two parts: steam cooling and steam condensation. The heat exchange structure is set as a cooling sensible heat section and a condensation latent heat section.

[0113] The heat transfer effectiveness of the two heat exchange structures is calculated based on the heat transfer effectiveness-number of heat transfer units theory.

[0114] Calculate the number of heat transfer units in the heat exchange structure;

[0115] Obtain the empirical range of the overall heat transfer coefficient, and preset the overall heat transfer coefficient of the heat exchange structure based on this empirical range;

[0116] Calculate the initial heat transfer area using the heat transfer area formula;

[0117] The inner diameter of the pipe in the pre-designed heat exchange structure;

[0118] Determine the flow area of ​​the tube;

[0119] Calculate the number of heat exchange tubes and the length of each heat exchange tube;

[0120] The heat transfer effectiveness-number of heat transfer units theory is as follows:

[0121]

[0122] In the formula, ε is the heat transfer efficiency, and t si t is the inlet temperature of the hot end. ti The inlet temperature is Δt. s The temperature difference between the inlet and outlet of the hot end, Δt t The temperature difference between the inlet and outlet of the cold end;

[0123] The number of heat transfer units is:

[0124]

[0125] In the formula, N is the number of heat transfer units, and f is the function relating heat transfer effectiveness to the number of heat transfer units in the pre-defined non-mixed countercurrent heat exchange structure.

[0126] The formula for the heat exchange area is:

[0127]

[0128] In the formula, k is the overall heat transfer coefficient, A is the initial heat transfer area, and W min The minimum heat capacity of the waste liquid; the flow area of ​​the tube side is:

[0129]

[0130] In the formula, S is the tube-side flow area, F is the steam flow rate, v is the tube-side velocity, and ρ is the steam density; the number of heat exchange tubes is:

[0131]

[0132] In the formula, n is the number of heat exchange tubes, and r is the preset inner diameter of the heat exchange tubes;

[0133] The length of each heat exchange tube is:

[0134]

[0135] In the formula, L is the length of each heat exchange tube.

[0136] The number of heat transfer units (NTU) is a parameter that reflects the ease of heat exchange between hot and cold fluids and is also a parameter that measures the heat transfer capacity of a heat exchange structure. When using the number of heat transfer units method to calculate the heat exchange process, the concept of heat transfer efficiency must also be introduced. The heat transfer efficiency within a heat exchange structure refers to the ratio of the actual heat transfer between the two fluids to the theoretically maximum possible heat transfer.

[0137] Reference Figure 3 As shown, the total cost of the heat exchange structure is the sum of the equipment investment cost and the operating cost, and this cost is output as the objective function of the heat exchange structure model. Specifically, this includes:

[0138] The total cost of a heat exchange structure includes equipment investment costs and operating costs;

[0139] The equipment investment cost is the investment cost of the heat exchange area;

[0140] Operating costs are the energy costs incurred by the pump to overcome pressure drop;

[0141] Obtain the heat transfer area parameters of the material selected for the heat exchange structure, namely the heat transfer area parameters of stainless steel;

[0142] Based on the heat exchange area parameters of stainless steel, the equipment investment cost is calculated using the investment cost formula.

[0143] Calculate operating costs using the energy cost formula;

[0144] The sum of the investment cost and operating cost of the output equipment is the objective function of the heat exchange structure model;

[0145] The investment cost formula is as follows:

[0146]

[0147] In the formula, C1 is the equipment investment cost, and a1, a2, and a3 are the first, second, and third heat exchange area parameters of stainless steel, respectively.

[0148] The energy cost formula is as follows:

[0149]

[0150] In the formula, C2 represents the operating cost, η represents the pump efficiency, and ΔP t , △P s These are the pressure losses on the tube side and the shell side, respectively.

[0151] The material selected for the heat exchange structure in this paper is stainless steel, and the corresponding values ​​of the first, second and third heat exchange area parameters are 8500, 409 and 0.85, respectively.

[0152] Reference Figure 4 As shown, based on the objective function of the heat transfer structure model, the genetic algorithm is used to realize the structural optimization process of the initial heat transfer structure model, resulting in the optimized heat transfer structure model, which specifically includes:

[0153] S101: Randomly generate a heat exchanger structure model and combine it with the initial heat exchanger structure model as the initial population;

[0154] S102: Evaluate all individuals in the population based on the objective function of the heat exchange structure model to obtain the fitness value of each individual;

[0155] S103: Select superior individuals as parents based on fitness values;

[0156] S104: Perform non-equipotential exchange operations between parent individuals to exchange the position and content of heat transfer structure model parameters and generate new offspring individuals;

[0157] S105: Perform random mutation operations on offspring individuals to introduce new parameter values ​​as genetic genes;

[0158] S106: Replace the non-superior individuals in the population with newly generated offspring individuals;

[0159] S107: Determine whether the preset maximum number of iterations has been reached. If yes, end the iteration and output the current population as the heat exchange structure optimization model. If no, return to step S102.

[0160] Genetic algorithms are adaptive global optimization probabilistic search algorithms that simulate the genetic and evolutionary processes of organisms in the natural environment. Starting from any initial population, this method generates a group of individuals that are better adapted to the environment through random selection, crossover, and mutation operations, allowing the population to evolve into increasingly better regions in the search space. This process continues generation after generation until it converges to a group of individuals that are best adapted to the environment, thus obtaining the optimal solution to the problem.

[0161] Reference Figure 5 As shown, based on the separator design principle, a design model of the distillation main unit is established. Based on the process parameters in the heat exchange structure optimization model, the structural parameters of the distillation main unit matching the MVR system are calculated. The specific construction of the distillation main unit structural model includes:

[0162] The main distillation unit consists of a cylinder, feed pipe, heat exchanger tube, concentrated liquid outlet, demister and steam outlet;

[0163] Obtain distillation parameters, waste liquid density, and vapor density;

[0164] Calculate the maximum permissible steam velocity using the critical velocity formula;

[0165] The diameter of the distillation main cylinder is calculated based on the maximum allowable steam velocity.

[0166] The height of the distillation main body is set to twice the diameter of the distillation main body.

[0167] Set the diameter of each interface to the inner diameter of the heat exchange tube;

[0168] A wire mesh demister is used to eliminate liquid droplets entrained in the steam;

[0169] The formula for the critical velocity is:

[0170]

[0171] In the formula, v max The maximum allowable velocity of steam is given by m, which is a distillation parameter, and ρ1 and ρ2 are the density of the waste liquid and the density of the steam, respectively.

[0172] The diameter of the distillation main unit cylinder is:

[0173]

[0174] In the formula, D is the diameter of the distillation main body cylinder, and F' is the steam flow rate inside the distillation main body.

[0175] The steam generated by the distillation unit inevitably carries a small amount of liquid as it rises. These droplets will be sucked into the compressor along with the steam and will damage the high-speed rotating parts. Therefore, it is necessary to remove the entrained droplets before the steam enters the compressor. This process is generally accomplished by a demister installed inside the distillation unit.

[0176] Reference Figure 6 As shown, a Roots compressor is used to compress the steam generated by the distillation unit, and the structure of the Roots compressor is analyzed, specifically including:

[0177] A Roots compressor is a positive displacement compressor with two rotors whose axes are parallel to each other;

[0178] The rotor is composed of a shaft and impellers, and there are pre-set gaps between the impellers and between the impellers and the casing and baffles;

[0179] The two rotors are driven by a pair of meshing synchronous gears and rotate in opposite directions at the same angular velocity;

[0180] The compressor's inlet and outlet are not directly connected, and the volume of the basic unit of the enclosed space formed by the impeller, casing, and baffles remains constant during rotation.

[0181] When the basic volume is connected to the exhaust port, the high-pressure gas flows back to the basic volume to equalize the pressure, thereby compressing the steam generated by the distillation unit.

[0182] Roots compressors are positive displacement compressors. They work by using two lobe-shaped rotors moving relative to each other within a cylinder to compress and transport gas. These compressors are simple in structure and easy to manufacture. They are widely used in aquaculture oxygenation, sewage treatment aeration, and cement conveying. They are also suitable for gas conveying and pressurization systems in low-pressure applications and can be used as vacuum pumps.

[0183] Reference Figure 7 As shown, the use of mechanical vapor recompression technology to recover and utilize the potential energy of discharged secondary steam as a heat source for the MVR system specifically includes:

[0184] In the distillation unit, a collector is used to collect the secondary steam generated by the heating and evaporation of the concentrated liquid;

[0185] The collected secondary steam is fed into a Roots compressor for compression. During the compression process, the pressure and temperature of the steam increase.

[0186] The compressed steam is sent back to the heat exchange structure to provide a heat source for the MVR system.

[0187] During the evaporation process, the heat released by the secondary steam generated by the evaporation of the concentrated liquid is recovered and can be input into the heat exchange structure. This efficient heat recovery and utilization technology not only improves energy utilization efficiency but also reduces production costs.

[0188] Reference Figure 8 As shown, the structure of the MVR waste liquid treatment evaporator is summarized and integrated, and the overall process integration diagram of the MVR system is drawn, specifically including:

[0189] Waste liquid is fed into the inlet of the MVR waste liquid treatment evaporator;

[0190] Waste liquid is fed into the distillation unit;

[0191] The waste liquid undergoes heat exchange through a heat exchange structure;

[0192] The distillation unit outputs steam and concentrated liquid;

[0193] Steam is fed into a Roots compressor for compression to produce distilled water.

[0194] The secondary steam generated by the heating and evaporation of the concentrated liquid is collected and fed into a Roots compressor for compression. The compressed steam is then sent back to the heat exchange structure.

[0195] System process integration design is one of the important tasks in overall system design. Establishing an overall process integration diagram for the MVR system makes the overall system integration and coordination work more flexible, adjustable and visible, thereby improving design quality and reducing design costs.

[0196] Furthermore, this solution also proposes a computer-readable storage medium storing a computer-readable program, which, when invoked, executes the aforementioned design method for a low-energy MVR waste liquid treatment evaporator structure.

[0197] It is understandable that the storage medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; an optical medium, such as a DVD; or a semiconductor medium, such as a solid-state drive (SSD).

[0198] In summary, the advantages of this invention are as follows: during the evaporation process, the heat released by the secondary steam generated by the heating and evaporation of the concentrated liquid is recovered, and this heat can be input into the heat exchange structure. This efficient heat energy recovery and utilization technology not only improves energy utilization efficiency but also reduces production costs. The modular design results in a compact structure, small footprint, and easy installation and transportation. At the same time, its integrated design tightly combines the various components, improving the overall performance and stability of the equipment.

[0199] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A design method for a low-energy MVR waste liquid treatment evaporator structure, characterized in that, include: Using the heat transfer effectiveness-number of heat transfer units theory of heat exchangers, the relevant structural parameters of the heat exchange structure are calculated, the heat exchange structure of the MVR system is matched and designed, and an initial model of the heat exchange structure is established. The total cost of the heat exchange structure is the sum of the equipment investment cost and the operating cost, and this sum is output as the objective function of the heat exchange structure model. Based on the objective function of the heat transfer structure model, a genetic algorithm is used to optimize the initial heat transfer structure model, resulting in an optimized heat transfer structure model. Based on the design principles of separators, a design model of the distillation unit is established. Based on the process parameters in the heat exchange structure optimization model, the structural parameters of the distillation unit that match the MVR system are calculated, and a structural model of the distillation unit is constructed. A Roots compressor is used to compress the steam generated by the distillation unit, and the structure of the Roots compressor is analyzed. Mechanical vapor recompression technology is used to recover and utilize the potential energy of the discharged secondary steam as heating steam to provide a heat source for the MVR system; Summarize and integrate the structures of MVR waste liquid treatment evaporators, and draw an overall process integration diagram of the MVR system. The process of applying the heat transfer effectiveness-number of heat transfer units theory to calculate relevant structural parameters of the heat exchange structure, matching and designing the heat exchange structure of the MVR system, and establishing an initial model of the heat exchange structure specifically includes: The steam in the heat exchange structure consists of two parts: steam cooling and steam condensation. The heat exchange structure is set as a cooling sensible heat section and a condensation latent heat section. The heat transfer effectiveness of the two heat exchange structures is calculated based on the heat transfer effectiveness-number of heat transfer units theory. Calculate the number of heat transfer units in the heat exchange structure; Obtain the empirical range of the overall heat transfer coefficient, and preset the overall heat transfer coefficient of the heat exchange structure based on this empirical range; Calculate the initial heat transfer area using the heat transfer area formula; The inner diameter of the pipe in the pre-designed heat exchange structure; Determine the flow area of ​​the tube; Calculate the number of heat exchange tubes and the length of each heat exchange tube; The heat transfer effectiveness-number of heat transfer units theory is as follows: In the formula, ε is the heat transfer efficiency, and t si t is the inlet temperature of the hot end. ti Δt represents the cold end inlet temperature. s Δt represents the temperature difference between the inlet and outlet of the hot end. t The temperature difference between the inlet and outlet of the cold end; The number of heat transfer units is: In the formula, N is the number of heat transfer units, and f is the function relating heat transfer effectiveness to the number of heat transfer units in the pre-defined non-mixed countercurrent heat exchange structure. The formula for the heat exchange area is: In the formula, k is the overall heat transfer coefficient, A is the initial heat transfer area, and W min This represents the minimum heat capacity of the waste liquid; The flow area of ​​the tube is: In the formula, S is the tube-side flow area, F is the steam flow rate, v is the tube-side velocity, and ρ is the steam density. The number of heat exchange tubes is: In the formula, n is the number of heat exchange tubes, and r is the preset inner diameter of the heat exchange tubes; The length of each heat exchange tube is: In the formula, L is the length of each heat exchange tube.

2. The design method for a low-energy MVR waste liquid treatment evaporator structure according to claim 1, characterized in that, The method of using the sum of equipment investment cost and operating cost as the total cost of the heat exchange structure, and outputting it as the objective function of the heat exchange structure model, specifically includes: The total cost of a heat exchange structure includes equipment investment costs and operating costs; The equipment investment cost is the investment cost of the heat exchange area; Operating costs are the energy costs incurred by the pump to overcome pressure drop; Obtain the heat transfer area parameters of the material selected for the heat exchange structure, namely the heat transfer area parameters of stainless steel; Based on the heat exchange area parameters of stainless steel, the equipment investment cost is calculated using the investment cost formula. Calculate operating costs using the energy cost formula; The sum of the investment cost and operating cost of the output equipment is the objective function of the heat exchange structure model; The investment cost formula is as follows: In the formula, C1 is the equipment investment cost, and a1, a2, and a3 are the first, second, and third heat exchange area parameters of stainless steel, respectively. The energy cost formula is as follows: In the formula, C2 represents the operating cost, η represents the pump efficiency, and ΔP t ΔP s These are the pressure losses on the tube side and the shell side, respectively.

3. The design method for a low-energy MVR waste liquid treatment evaporator structure according to claim 2, characterized in that, The objective function based on the heat transfer structure model is used to implement the structural optimization process of the initial heat transfer structure model using a genetic algorithm, resulting in the optimized heat transfer structure model, which specifically includes: S101: Randomly generate a heat exchanger structure model and combine it with the initial heat exchanger structure model as the initial population; S102: Evaluate all individuals in the population based on the objective function of the heat exchange structure model to obtain the fitness value of each individual; S103: Select superior individuals as parents based on fitness values; S104: Perform non-equipotential exchange operations between parent individuals to exchange the position and content of heat transfer structure model parameters and generate new offspring individuals; S105: Perform random mutation operations on offspring individuals to introduce new parameter values ​​as genetic genes; S106: Replace the non-superior individuals in the population with newly generated offspring individuals; S107: Determine whether the preset maximum number of iterations has been reached. If yes, end the iteration and output the current population as the heat exchange structure optimization model. If no, return to step S102.

4. The design method for a low-energy MVR waste liquid treatment evaporator structure according to claim 3, characterized in that, Based on the separator design principles, a design model for the distillation main unit is established. Based on the process parameters in the heat exchange structure optimization model, the structural parameters of the distillation main unit matching the MVR system are calculated. The construction of the distillation main unit structural model specifically includes: The main distillation unit consists of a cylinder, feed pipe, heat exchanger tube, concentrated liquid outlet, demister and steam outlet; Obtain distillation parameters, waste liquid density, and vapor density; Calculate the maximum permissible steam velocity using the critical velocity formula; The diameter of the distillation main cylinder is calculated based on the maximum allowable steam velocity. The height of the distillation main body is set to twice the diameter of the distillation main body. Set the diameter of each interface to the inner diameter of the heat exchange tube; A wire mesh demister is used to eliminate liquid droplets entrained in the steam; The formula for the critical velocity is: In the formula, v max The maximum allowable velocity of steam is given by m, which is a distillation parameter, and ρ1 and ρ2 are the density of the waste liquid and the density of the steam, respectively. The diameter of the distillation main unit cylinder is: In the formula, D is the diameter of the distillation main body cylinder, and F' is the steam flow rate inside the distillation main body.

5. The design method for a low-energy MVR waste liquid treatment evaporator structure according to claim 4, characterized in that, The method of using a Roots compressor to compress the steam generated by the distillation unit, and the analysis of the structure of the Roots compressor, specifically includes: A Roots compressor is a positive displacement compressor with two rotors whose axes are parallel to each other; The rotor is composed of a shaft and impellers, and there are pre-set gaps between the impellers and between the impellers and the casing and baffles; The two rotors are driven by a pair of meshing synchronous gears and rotate in opposite directions at the same angular velocity; The compressor's inlet and outlet are not directly connected, and the volume of the basic unit of the enclosed space formed by the impeller, casing, and baffles remains constant during rotation. When the basic volume is connected to the exhaust port, the high-pressure gas flows back to the basic volume to equalize the pressure, thereby compressing the steam generated by the distillation unit.

6. The design method for a low-energy MVR waste liquid treatment evaporator structure according to claim 5, characterized in that, The specific steps of using mechanical vapor recompression technology to recover and utilize the potential energy of discharged secondary steam as heating steam to provide a heat source for the MVR system include: In the distillation unit, a collector is used to collect the secondary steam generated by the heating and evaporation of the concentrated liquid; The collected secondary steam is fed into a Roots compressor for compression. During the compression process, the pressure and temperature of the steam increase. The compressed steam is sent back to the heat exchange structure to provide a heat source for the MVR system.

7. The design method for a low-energy MVR waste liquid treatment evaporator structure according to claim 6, characterized in that, The process of summarizing and integrating the structure of the MVR waste liquid treatment evaporator and drawing the overall process integration diagram of the MVR system specifically includes: Waste liquid is fed into the inlet of the MVR waste liquid treatment evaporator; Waste liquid is fed into the distillation unit; The waste liquid undergoes heat exchange through a heat exchange structure; The distillation unit outputs steam and concentrated liquid; Steam is fed into a Roots compressor for compression to produce distilled water. The secondary steam generated by the heating and evaporation of the concentrated liquid is collected and fed into a Roots compressor for compression. The compressed steam is then sent back to the heat exchange structure.

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