Control method and system for thermal pressure type multi-effect evaporation device based on working condition of ejector

Abstract

The application discloses a thermal pressure type multi-effect evaporation device control method and system based on an ejector working condition, relates to the technical field of thermal vapor compression multi-effect distillation devices, and determines an optimal working condition interval of an ejector in a high-grade steam pressure fluctuation interval according to an ejector and a multi-effect evaporation device mechanism model and in combination with device trial operation data; in the optimal working condition interval of the ejector, an optimal control target point of the ejector working condition is searched for according to a current state of the device through an optimization algorithm; according to the optimal control target point of the ejector working condition, model predictive control is adopted to perform optimal control of the ejector working condition under the condition of meeting the operation state constraints of the multi-effect evaporation device, and corresponding control values are obtained; the control values are input into a PID controller, the PID controller adjusts the operation frequency of a pump body, closed-loop regulation and control of a controlled variable are realized, the influence of high-grade steam pressure on the operation effect of the thermal pressure type multi-effect evaporation device is effectively reduced, operation energy consumption is reduced, and control effect and safety performance are improved.

Description

Technical Field

[0001] This invention relates to the field of thermal vapor compression multi-effect distillation (MED-TVC) equipment technology, and in particular to a control method and system for a thermo-compression multi-effect evaporator based on ejector operating conditions. Background Technology

[0002] The statements in this section are merely background information relating to this disclosure and do not necessarily constitute prior art.

[0003] With the rapid development of intelligent manufacturing and Industry 4.0, industrial equipment is also undergoing a transformation towards intelligent development. Multi-effect evaporators are widely used in chemical, petroleum, pharmaceutical, food, and environmental protection industries. These devices significantly reduce live steam consumption by repeatedly utilizing the vaporization and condensation of secondary steam, thereby improving the economic efficiency of the evaporation unit. Thermopressurized multi-effect evaporators are multi-effect evaporators equipped with steam ejectors. They use a high-grade heat source to irradiate a low-grade heat source in the final effect evaporator, achieving steam reuse and further energy savings.

[0004] In practical use, because the steam ejector itself has no moving parts, and the mechanical design is based on the application scenario and high-grade steam pressure, the operation of the thermocompressed multi-effect evaporator will be greatly affected when the high-grade steam pressure fluctuates or changes significantly due to external factors. Existing thermocompressed multi-effect evaporators are typically equipped with conventional PID control systems. While these systems can ensure safe operation under conditions of significant fluctuations in high-grade steam pressure, the energy-saving effect of the thermocompressed multi-effect evaporator will be significantly reduced due to changes in the ejector's operating conditions. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a control method and system for a thermo-pressed multi-effect evaporator based on ejector operating conditions. It develops an optimized control system for ejector operating conditions, and combines advanced control algorithms to achieve optimized control of ejector operating conditions, reduce the impact of high-grade steam pressure fluctuations on the thermo-pressed multi-effect evaporator, and expand the application fields of the thermo-pressed multi-effect evaporator.

[0006] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: In a first aspect, the present invention provides a control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions, comprising: Based on the mechanism model of the ejector and the multi-effect evaporator, and combined with the trial operation data of the device, the optimal operating condition range of the ejector within the high-grade steam pressure fluctuation range is determined; within the optimal operating condition range of the ejector, the target point for optimizing the ejector operating condition is searched by an optimization algorithm according to the current state of the device. Based on the target point of the ejector operating condition optimization control, model predictive control is adopted to carry out the ejector operating condition optimization control under the condition of satisfying the operating state constraints of the multi-effect evaporator, and obtain the corresponding control quantity values. The control value is input to the PID controller, which adjusts the pump operating frequency to achieve closed-loop control of the controlled variable.

[0007] A further technical solution is that the trial operation data of the device includes high-grade steam pressure, ejector outlet pressure, ejector suction pressure, current concentration, temperature, and feed flow rate of the medium in each effect evaporator.

[0008] A further technical solution is that the optimal operating range of the ejector is composed of the ejector critical pressure curve under the corresponding high-grade steam pressure and the pressure controllable domain of the multi-effect evaporator.

[0009] A further technical solution is that the optimization algorithm maximizes the suction pressure within the optimal operating range of the ejector.

[0010] A further technical solution is that the model predictive control is adaptive model predictive control, and its optimized performance index is:

[0011] in, To optimize performance metrics, For the first time, To predict the time domain, For prediction of the time domain The Middle One predicted moment, To the degree of suppression of tracking error, To optimize the control target point for injector operating conditions, In the first At the nth moment, for the first The predicted value output at time step. To control the time domain, To control the time domain The Middle One control moment, To determine the degree of suppression of changes in the control quantity, For the first Changes in control quantity at any given time To the degree of inhibition of the control quantity, For the first The amount of control at any given moment.

[0012] A further technical solution involves adaptive model predictive control where the controlled variables include feed flow rate, cooling water flow rate, and final-effect concentrate discharge flow rate; the controlled variables include ejector outlet pressure and ejector suction pressure; and the constraint variables include first-effect medium concentration and final-effect evaporator liquid level.

[0013] Further technical solutions include adding upper and lower limits for control quantity constraints, upper and lower limits for control quantity change constraints, upper and lower limits for liquid level constraints, and upper and lower limits for liquid level constraints, to the feed flow rate, cooling water flow rate, and final effect concentrate discharge flow rate; adding upper and lower limits for liquid level constraints, to the liquid level of the final effect evaporator; and adding upper limits for concentration constraints, to the concentration of the medium in the first effect.

[0014] Secondly, the present invention provides a control system for a thermo-pressurized multi-effect evaporator based on ejector operating conditions, comprising: The optimized control target module is configured to: determine the optimal operating condition range of the ejector within the high-grade steam pressure fluctuation range based on the mechanism model of the ejector and the multi-effect evaporator, combined with the trial operation data of the device; and within the optimal operating condition range of the ejector, search for the optimized control target point of the ejector operating condition through an optimization algorithm according to the current state of the device. The outer loop control module is configured to: optimize the control target point based on the ejector operating condition, adopt model predictive control, and perform ejector operating condition optimization control under the condition of satisfying the operating state constraints of the multi-effect evaporator to obtain the corresponding control value; The inner loop control module is configured to input the control value to the PID controller, which then adjusts the pump operating frequency to achieve closed-loop control of the controlled variable.

[0015] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in the first aspect.

[0016] Fourthly, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the control method for a thermo-pressurized multi-effect evaporator based on ejector conditions as described in the first aspect.

[0017] The above one or more technical solutions have the following beneficial effects: This invention provides an optimized control system for the operating conditions of ejectors in a thermo-pressed multi-effect evaporator. By introducing the optimal operating range of the ejector and combining it with an optimization algorithm to determine the optimal control target point of the ejector, and then entrusting the control target point to cascade adaptive model predictive control, the system effectively reduces the impact of high-grade steam pressure on the operating performance of the thermo-pressed multi-effect evaporator, reduces operating energy consumption, improves control performance and safety performance, and realizes the scientific control and management of the device.

[0018] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 This is a flowchart of the control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions according to an embodiment of the present invention; Figure 2 This is a control system diagram of the hot-pressing multi-effect evaporator according to an embodiment of the present invention; Figure 3 These are the critical state curves for different high-grade steam pressures in embodiments of the present invention; Figure 4 This is a schematic diagram of the target point for injector operating condition optimization control in an embodiment of the present invention; Figure 5 This is a graph showing the relationship between the ejector injection ratio and the changes in motive steam pressure and suction steam pressure in an embodiment of the present invention. Figure 6 This is a schematic diagram of the evaporator and flash tank according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the final-effect evaporator and condenser in an embodiment of the present invention; Figure 8 This is a schematic diagram of a preheater according to an embodiment of the present invention; Figure 9 This is a diagram showing the fluctuation of power steam pressure in an embodiment of the present invention; Figure 10 This is a diagram showing the tube-side temperature of the first-effect evaporator and the shell temperature of each effect evaporator under conventional PID control in an embodiment of the present invention. Figure 11 This is a diagram showing the tube-side temperature of the first-effect evaporator and the shell temperature of each effect evaporator under the injector operating condition control strategy of this invention embodiment; Figure 12 This is a comparison chart of the output of traditional PID control and injector condition control in an embodiment of the present invention. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0024] Example 1 like Figure 1 As shown, this embodiment discloses a control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions. The method includes the following steps: Based on the mechanism model of the ejector and the multi-effect evaporator, and combined with the trial operation data of the device, the optimal operating condition range of the ejector within the high-grade steam pressure fluctuation range is determined; within the optimal operating condition range of the ejector, the target point for optimizing the ejector operating condition is searched by an optimization algorithm according to the current state of the device. Based on the target point of the ejector operating condition optimization control, model predictive control is adopted to carry out the ejector operating condition optimization control under the condition of satisfying the operating state constraints of the multi-effect evaporator, and obtain the corresponding control quantity values. The control value is input to the PID controller, which adjusts the pump operating frequency to achieve closed-loop control of the controlled variable.

[0025] Specifically, the control process of this invention consists of three main steps. Step 1: Combining the pressure controllable range of the multi-effect evaporator... Based on the critical state curve, the target control point for injector operation condition optimization is determined using advanced optimization algorithms. Step 2: Control target point The feed is then fed to the MPC control system. The control steps of the MPC control system are the same as those of traditional MPC control; the differences lie only in the setting of the cost function, control parameters and constraints, and input / output settings. The third step: The MPC processes the feed flow rate... The calculation results are output to the PID controller, which controls the pump frequency to regulate the feed flow rate. Product water flow rate and concentrate flow rate Control.

[0026] In this embodiment, the system mainly comprises three parts: data acquisition, optimized control, and control execution. The data acquisition and control execution parts are not significantly different from traditional PID control systems; the main innovation and functional implementation come from its optimized control architecture and control methods. This optimized control system can select a suitable control target based on the high-grade steam pressure and achieve the control effect by scheduling the underlying actuators using advanced control methods. This system optimizes the control effect of the thermostatic multi-effect evaporator when dealing with high-grade steam pressure fluctuations, improves system stability, and reduces energy waste caused by pressure fluctuations.

[0027] To achieve the above objectives, the optimized control system employs feedforward cascade model predictive control. The inner loop control still uses traditional PID control to achieve a rapid response to the control objective and ensure control speed. The outer loop control uses model predictive control, combining feedback data from the thermocompression multi-effect evaporator and pressure fluctuation disturbances of high-grade steam to determine the setpoint for the inner loop control, thus achieving optimized control of the entire system. See the control system documentation. Figure 2 As shown, based on the target point of the injector operating condition optimization control, a parameter setting trajectory for the device operation is constructed, and model predictive control is used to optimize the operating condition of the multi-effect evaporator. First, the deviation between the parameter setting trajectory and the actual system output feedback value is fed into the model predictive control module. The model predictive control module uses the system optimization performance index as the objective function. Under the condition of satisfying the device operating state constraints, it solves the optimal control sequence online through rolling optimization and takes the control solution at the current moment as the setpoint of the PID controller. Simultaneously, the adaptive predictive model predicts the future output trend based on the current system state, and through a feedback correction loop, it updates the predictive model using the error between the actual output and the predicted value, correcting the optimization problem and forming a closed-loop correction mechanism to improve control robustness. Second, the setpoint of the model predictive control output and the feedback value of the controlled variable form the control error, which is fed into the PID controllers of each loop to calculate the control quantity and apply it to the controlled object. The system also introduces feedforward control to compensate for external disturbances in advance. Combined with the multi-level feedback mechanism of PID and model predictive control, a feedforward-feedback composite control structure is formed, ultimately achieving stable tracking of the actual system output to the parameter setting trajectory and completing the optimized control of the injector operating condition.

[0028] One of the key innovations of this invention is to determine the optimal operating range of the ejector within the high-grade steam pressure fluctuation range based on the mechanism model of the ejector and the multi-effect evaporator, combined with the trial operation data of the device. Within the optimal operating range, the target point for optimized control of the ejector is searched through an optimization algorithm based on the current state of the device (the current operating state of the device).

[0029] The optimal operating range was determined using data from the unit's trial operation (collected in real-time during factory testing). This trial operation data included high-grade steam pressure. Injector outlet pressure ejector suction pressure Current concentration of medium in each effect evaporator ,temperature Feed flow rate During actual operation of the hot-press multi-effect evaporator, real-time data is collected, including the pressure of high-grade steam. Injector outlet pressure ejector suction pressure Current concentration of medium in each effect evaporator ,temperature Feed flow rate The device's operating status is obtained based on real-time data acquisition.

[0030] The optimal operating range of the ejector specifically refers to the range between the ejector's suction and outlet pressures, which is a range based on the ejector's suction pressure. The x-axis represents the pressure at the injector outlet. The vertical axis represents the interval on the plane. This interval has two characteristics: firstly, different high-grade steam pressures. The lower interval is also different; the range of the second interval is determined by the corresponding high-grade steam pressure. The critical pressure curve of the ejector and the controllable pressure range of the multi-effect evaporator are constituted.

[0031] Furthermore, the ejector critical pressure curve refers to the pressure at which high-grade steam is pressurized. Under constant conditions, the injector outlet pressure when the injector is in a critical state. With suction pressure Curve. For an ejector with a fixed structure, when the high-grade steam pressure is constant, the ejector's ejection performance will reach its maximum value at the current high-grade steam pressure when the ejector outlet pressure is less than the critical ejector outlet pressure obtained by bringing the suction pressure into the critical state curve. Different high-grade steam pressures The critical state curve is as follows Figure 3 As shown.

[0032] Furthermore, the ejector critical state curve refers to the pressure of a given high-grade steam. Below, the injector outlet pressure that causes the injector to operate at the critical point between the double-blocking and non-double-blocking regions. and ejector suction pressure The curve is plotted from the set of values. Under critical conditions, the ejector's ejection performance is highest, with each ejector's suction pressure... There will always be an ejector outlet pressure Make the ejector operate at high-grade steam pressure The system is currently operating in a critical state. This critical state needs to be obtained through CFD modeling of the injector under all operating conditions.

[0033] Furthermore, the pressure controllable range of the multi-effect evaporator Specifically, it refers to the ejector outlet pressure. With the suction pressure of the ejector The controllable range, which is also subject to the pressure of high-grade steam. The effects can be derived from the heat and mass transfer mechanism of the multi-effect evaporator, and are influenced by the evaporation medium, the mechanical structure of the device, the suction position, and the feed flow rate. Influence.

[0034] Different evaporation media have different boiling point elevations during heat exchange, and the boiling point elevation is also affected by the current concentration of the medium. and temperature The effect, its impact on stress, can be expressed as: (1) in, For the first The pressure change in an efficient evaporator due to the boiling point rise This represents the current concentration of the evaporating medium. For temperature.

[0035] The mechanical structure of the device determines the pressure loss per effect. and heat exchange temperature difference Its effect on pressure can be expressed as: (2) in, For the first The pressure changes in an efficient evaporator due to pressure loss and heat exchange temperature difference For each effect pressure loss, This refers to the temperature difference during heat exchange.

[0036] The ejector suction position determines the ejector outlet pressure. With suction pressure The difference will be determined by the specific number of evaporators. and It is decided that, assuming the ejector suction port is installed in the Nth effect, and considering the aforementioned outlet pressure... With suction pressure The relation is: (3) The feed flow rate will affect the medium concentration, pressure loss, and heat exchange temperature difference. However, since multi-effect evaporators often use spray feeding, the adjustable range of the feed rate is limited. Therefore, the minimum feed flow rate is used as the basis for determining the optimal feed rate. and maximum feed flow rate The effect of pressure, and the final relationship between the outlet pressure and the suction pressure, is as follows: (4) In summary, based on the optimal operating range of the ejector in a multi-effect evaporator, an advanced optimization algorithm is used to determine the target control point for optimizing the ejector's operating conditions. ,in, Optimal ejector suction pressure The value, For optimal injector outlet pressure The value of this invention, based on the stability of the multi-effect evaporator, introduces the following optimized performance index into an optimization algorithm: (5) The optimization algorithm maximizes the suction pressure within the optimal operating range of the ejector. For the selected optimization performance index, the interior point method of the barrier function is chosen as the optimization algorithm to achieve pressure controllability within the multi-effect evaporator. Internally determine the optimal control target point for the current operating condition. See results Figure 4 As shown.

[0037] The second key innovation of this invention is that model predictive control is adopted based on the target point of ejector condition optimization control, so as to achieve the effect of ejector condition optimization control under the condition of satisfying the operating state constraints of the multi-effect evaporator.

[0038] Because multi-effect evaporators are inherently large time-delay, nonlinear systems, and ejector operating condition control includes ejector outlet pressure... and ejector suction pressure There are two control objectives. According to the heat and mass transfer mechanism, these two control objectives have a strong coupling relationship. Therefore, this invention proposes to use adaptive model predictive control to achieve the control effect.

[0039] Specifically, the feed flow rate is selected based on the conventional process flow of the multi-effect evaporator. Cooling water flow rate Final effect concentrate discharge flow rate There are three control variables: injector outlet pressure. and suction pressure For the two controlled variables, the first-effect medium concentration and the liquid level of the last-effect evaporator There are two constraint state variables.

[0040] Then the control vector ,in, For the first The feed flow rate at any given time. For the first Cooling water flow rate at any time For the first Final concentrate discharge flow rate at time; vector of control variable change ,in, For the first Changes in feed flow rate at any given time. For the first Changes in cooling water flow rate at any given time. For the first Change in final-effect concentrate discharge flow rate at time t; controlled variable vector ,in, For the first The constant suction pressure, For the first Injector outlet pressure at any given time; control target .

[0041] The optimal performance index of adaptive model predictive control is: (6) (7) in, To optimize performance metrics, For the first time, To predict the time domain, For prediction of the time domain The Middle One predicted moment, To the degree of suppression of tracking error, In the first At the nth moment, for the first The predicted value output at time step. To control the time domain, To control the time domain The Middle One control moment, To determine the degree of suppression of changes in the control quantity, For the first Changes in control quantity at any given time To the degree of inhibition of the control quantity, For the first The amount of control at any given moment; To the degree of inhibition of the control quantity, This is the lower limit of the constraint on the amount of change. The upper limit of the change constraint, To control the lower limit of the quantity constraint, To control the upper limit of the quantity, For the first The concentration of the first-effect medium at time of effect. This is the upper limit of the concentration constraint. This is the lower limit of the liquid level constraint. This is the upper limit of the liquid level constraint. For the first The liquid level in the final-effect evaporator at any given time.

[0042] To ensure the stability of flow control, upper limits for control parameters are added to the feed flow rate, cooling water flow rate, and final-effect concentrate discharge flow rate. and lower bound constraints Lower limit of change constraint and upper limit of constraints To ensure the operational safety of multi-effect evaporators, a lower limit for liquid level constraint is added to the liquid level of the last-effect evaporator. and upper limit of liquid level constraint Add a concentration limit constraint to the concentration of the first-effect medium. .

[0043] In this embodiment, the ejector mechanism model is constructed by: experimentally collecting data on different power steam pressures of the ejector used in the system within a certain operating range. and suction steam pressure The lower ejection ratio Based on the obtained data points, thin plate spline interpolation is used to determine all data within the operating range, completing the injector data modeling. Specifically, as follows... Figure 5 As shown.

[0044] In this embodiment, the multi-effect evaporator mechanism model (MED system dynamic model) is modeled using existing dynamic modeling methods.

[0045] The main assumptions used in the model are as follows: Three state parameters—temperature, liquid level, and salinity—were established for each evaporator effect. The vapor pressure of each evaporator effect was set to the saturated vapor pressure of water at the corresponding temperature, without considering the influence of non-condensable gases on the pressure. Ignore heat loss from system cooling and pressure loss from mechanical structure; Vapor loss due to the final-effect vacuum system is ignored; The steam does not contain salt.

[0046] (1) Evaporator and flash tank model The evaporator model includes external evaporation and internal condensation processes. Seawater is sprayed onto the heat exchange tubes to exchange heat with the steam inside. The generated steam travels to the next effect's tubes, while the remaining seawater, along with seawater from the previous effect, flows into the next effect. The steam inside the tubes condenses, and the condensate enters the flash tank. The flash tank collects the condensate from the tubes and the freshwater from the previous effect. A portion of the flashed steam flows into the next effect's tubes, while the remaining freshwater flows to the next effect's flash tank.

[0047] To simplify the dynamic model, the evaporator and its associated flash tank are modeled as a whole, and all evaporators except the last-effect evaporator adopt this treatment method. The entire system has four inputs: feed seawater, steam from the previous effect, concentrated brine from the previous effect, and freshwater from the previous effect, and three outputs: steam, concentrated brine, and freshwater, as detailed below. Figure 6 As shown.

[0048] Apart from the final-effect evaporator, the evaporator and flash tank together have five important state parameters: evaporator liquid level, evaporator vapor temperature, evaporator concentrate salinity, flash tank vapor temperature, and flash tank desalination level. Since pressure losses due to mechanical structures are ignored, the evaporator vapor temperature and flash tank vapor temperature are considered equal; therefore, vapor temperature is used uniformly. Instead, then the first State vector of efficient evaporator and flash tank Defined as: (8) in, For the first Effective evaporator and flash tank vapor phase temperature, For the first The salinity of concentrated brine in the efficient evaporator For the first The concentrated brine level in the efficient evaporator For the first Freshwater level in the flash evaporator.

[0049] Based on the system inputs, outputs, and state vectors, establish conservation equations for brine mass, freshwater and steam mass, energy, and salinity in the evaporator and flash tank.

[0050] Saltwater mass conservation: (9) in, For the first Effective evaporator brine quality, For the first Efficient evaporator feed flow rate.

[0051] Conservation of mass for freshwater and steam: (10) in, For the first Effective evaporator freshwater quality For the first Efficient evaporator steam quality.

[0052] Energy conservation:

[0053]

[0054] in, For the first Enthalpy of feed water to the evaporator.

[0055] Salt conservation law: (12) in, For the first Salinity of feed water to the efficient evaporator.

[0056] Then, the above formulas (9) to (12) can be written in the form of ordinary differential equations with four state variables, where formula (9) can be written as:

[0057]

[0058] Formula (10) can be written as:

[0059]

[0060] in, For the first The volume occupied by the gas phase in the efficient evaporator.

[0061] Formula (11) can be written as:

[0062]

[0063] Formula (12) can be written as:

[0064]

[0065] in, and Here, represents the density and enthalpy of the concentrated brine, and represents the temperature of the concentrated brine. and salinity of concentrated salt water The function, , , and The density and enthalpy of steam and fresh water are given, both at the vapor phase temperature. The function, and The volumes of concentrated salt water and fresh water can be expressed as: (17) (18) in, and The length and diameter of the evaporator; and The length and diameter of the flash tank.

[0066] Because the temperature of the concentrated brine and the vapor phase temperature of the evaporator satisfy: (19) in, It is the gas phase temperature. and salinity of concentrated salt water The function, therefore: (19) Substituting equation (19) into equations (13) through (16) and rearranging them, we can write them in matrix form: (20) (twenty one) in, Calculate the coefficient matrix for the evaporator state changes. Calculate the constant vector for the evaporator state changes.

[0067] in,

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086] To prevent incomplete condensation of steam before it enters the next effect, which could prevent the establishment of an inter-effect temperature difference, both the concentrated liquid and freshwater pipes between effects employ a U-shaped bend design. For non-final-effect evaporators, the inter-effect concentrated brine flow rate... and freshwater flow It can be represented as:

[0087]

[0088] in, and The throttling coefficient represents the flow rate of the concentrated brine and freshwater pipelines. and This represents the pipe diameter for concentrated brine and freshwater pipelines. and This represents the height of the U-bend in the concentrated brine and freshwater pipelines. For the first Effective evaporator gas phase pressure, This is the acceleration due to gravity.

[0089] Since the actual heat exchange process is not adiabatic, a heat loss coefficient is considered in the heat exchange process model. This parameter is used to simulate the impact of evaporator heat loss on system operation. Efficient evaporator evaporation capacity for:

[0090] in, This is the heat loss coefficient per effect of the evaporator. For the first The heat exchange efficiency of an evaporator can be expressed as:

[0091] in, and The first Effective evaporator heat exchange area and heat transfer coefficient, For heat exchange and condensation consumption Effective steam flow rate, The parameter is introduced to represent the heat transfer coefficient loss ratio per evaporator effect, and is used to simulate the impact of evaporator heat transfer coefficient loss on system operation.

[0092] (2) Model of the last-effect evaporator and condenser The final-effect evaporator and condenser are similar in function and structure to the evaporator and flash tank mentioned earlier. To simplify the dynamic model of the final-effect evaporator and condenser, only the phase change heat transfer process between the feed water and the final-effect steam is considered in the condenser model. Only the heat exchanger area involved in the phase change heat transfer process is included in the condenser's heat exchange area; the remaining heat exchange area is included in the preheater where the feed water and fresh water undergo non-phase change heat transfer processes.

[0093] The final-effect evaporator and condenser have four inputs: feed seawater, steam from the previous effect, concentrated brine from the previous effect, and freshwater from the previous effect; and three outputs: ejector-drawn steam, concentrated brine, and freshwater. (Details are as follows...) Figure 7 As shown.

[0094] Similar to the modeling of evaporators and flash tanks, the state vectors of the last-effect evaporator and condenser... Defined as: (26) in, The vapor phase temperature of the last-effect evaporator and condenser. The salinity of the concentrated brine in the final-effect evaporator. The concentrated brine level in the final-effect evaporator. This refers to the freshwater level in the condenser.

[0095] Based on the system inputs, outputs, and state vectors, establish conservation equations for brine mass, freshwater and steam mass, energy, and salinity in the final-effect evaporator and condenser.

[0096] Saltwater mass conservation: (27) in, For the quality of brine in the final effect evaporator, This refers to the feed flow rate of the final-effect evaporator. This refers to the evaporation rate of the final-effect evaporator.

[0097] Conservation of mass for freshwater and steam: (28) in, For the quality of freshwater from the last-effect evaporator, This refers to the steam volume of the final-effect evaporator.

[0098] Energy conservation:

[0099]

[0100] in, The enthalpy of the brine in the last-effect evaporator. This refers to the enthalpy of freshwater from the last-effect evaporator. This refers to the enthalpy of steam in the last-effect evaporator. This is the enthalpy value of the feed water to the final-effect evaporator.

[0101] Salt conservation law:

[0102] in, The brine and salt content of the final-effect evaporator. Salt is used as feed salt for the final-effect evaporator.

[0103] Similar to evaporators and flash tanks, the formulas can be rearranged into a matrix form: (31) in, Calculation of the state change of the last-effect evaporator. Calculation of the state change of the last-effect evaporator.

[0104] in, and and and Having similar compositional structures, it can and In Replace with That's all, I won't repeat it here. However, due to differences in mechanical structure and technological processes, some symbols in the modeling process and their meanings will differ.

[0105] First, compared to the evaporator and flash tank, the condenser is larger in overall volume than the flash tank, but the mechanical structure is similar, and its condenser freshwater volume is... It can be represented as: (32) in, and This refers to the length and diameter of the condenser.

[0106] Furthermore, unlike evaporators and flash tanks, both concentrated brine and fresh water in the final-effect evaporator and condenser are extracted from the system via water pumps, and the discharge pipes for concentrated brine and fresh water typically do not employ U-bend structures. Therefore, the flow rate of concentrated brine in the final-effect evaporator is relatively low. and condenser freshwater flow rate It can be represented as:

[0107]

[0108] in, and The throttling coefficient for the final-effect concentrated brine and condenser freshwater pipelines. and The diameter of the pipes for the final-effect concentrated brine and the condenser freshwater is [not specified]. This refers to the pump suction pressure. For the pipeline outlet pressure, This refers to the gas phase pressure of the final-effect evaporator. The density of the brine in the final-effect evaporator. It is the acceleration due to gravity. The density of fresh water in the final-effect evaporator.

[0109] Finally, the steam consumption of the last-effect evaporator originates from the condensation of cooling water and the suction of the ejector, thus the steam consumption of the last effect... It can be represented as: (35) in, For heat exchange of the condenser, The steam flow rate drawn by the ejector can be expressed as:

[0110]

[0111]

[0112] in, For the condenser heat exchange area, The heat transfer coefficient of the condenser. The heat transfer coefficient of the condenser is the proportion of heat loss. and The inlet and outlet temperatures of the feed seawater. The primary steam flow rate of the ejector. For ejector ejection ratio, This refers to the heat exchange temperature difference in the condenser.

[0113] (3) Preheater model Seawater needs to be preheated before entering each effect evaporator. The system consists of three preheaters, all of which are single-tube shell-and-tube heat exchangers using a counter-current heat exchange method, with the hot fluid flowing through the shell and the cold fluid flowing through the tubes. The first preheater is used for initial preheating of the feed seawater, with the heat source being the concentrated brine from the last effect. The second preheater is used for secondary preheating of the feed seawater, with the heat source being the fresh water from the condenser. The third preheater is used for preheating the feed seawater from the first effect, with the heat source being steam from the vacuum suction system.

[0114] The preheater includes two inputs (hot and cold fluids before heat exchange) and two outputs (hot and cold fluids after heat exchange), such as... Figure 8 As shown.

[0115] The preheater includes the cold fluid outlet temperature. and hot fluid outlet temperature Two key state parameters. Based on the input, output, and convective heat transfer mechanism, an energy conservation equation is established.

[0116]

[0117]

[0118] in, For the preheater shell volume, For thermal fluid density, The enthalpy of the hot fluid outlet. For hot fluid flow rate, The enthalpy of the hot fluid outlet. For the preheater tube side volume, For the density of cold fluid, This represents the enthalpy of the cold fluid outlet. For cold fluid flow rate, This represents the enthalpy of the cold fluid inlet. It is used for heat exchange in the preheater. It can be represented as:

[0119]

[0120] in, The heat exchange area of ​​the preheater. The heat transfer coefficient of the preheater. This represents the proportion of heat transfer coefficient loss in the preheater. and The inlet and outlet temperatures of the hot fluid. and The inlet and outlet temperatures of the cold fluid. This refers to the heat exchange temperature difference in the preheater.

[0121] In summary, the advantages of this invention are: The optimal operating range of the ejector was determined by combining data and mechanistic models, which reduced the impact of high-grade steam pressure on the operation of the hot-pressed multi-effect evaporator and lowered the energy consumption of the unit.

[0122] By replacing traditional PID control with cascade adaptive model predictive control, the control effect and safety performance of the device are improved while ensuring the same response speed as PID control.

[0123] An optimization objective function was introduced for the hot-pressed multi-effect evaporator, which enabled the evaluation of the operating status of the hot-pressed multi-effect evaporator by optimizing the objective function value. This quantified the evaluation indicators of the device and enabled the scientific control and management of the device.

[0124] Experimental example: This invention provides an optimized control system for a thermo-pressurized multi-effect evaporator operating under specific conditions. The system mainly comprises three parts: data acquisition, optimized control, and control execution. The data acquisition section includes sensors conventionally installed on the thermo-pressurized multi-effect evaporator; in actual use, some data that is difficult to measure will be determined through state estimation. The control execution section mainly consists of various water pumps; in actual use, if some water sources have high pressure, the water pumps will be replaced with regulating valves.

[0125] Seawater desalination is a common application of thermocompressive multi-effect evaporators (TCVAs), and this example illustrates the process. Taking a four-effect TVA for seawater desalination as an example, the design temperature of the first-effect tube side is 85℃, the design temperature of the last-effect shell side is 70℃, the design pressure of the high-grade steam driving the equipment is 10 bar, the design capacity is 4 t / h, the design steam consumption is 500 kg / h, and the water production ratio is 8. After simple filtering of the trial operation data, the following results were obtained during the trial operation: high-grade steam pressure 10.13 bar, first-effect tube side temperature 84.27℃ (corresponding to a saturation pressure of 56.22 kPa), last-effect shell side temperature 70.41℃ (corresponding to a saturation pressure of 31.76 kPa), capacity 4.398 t / h, steam consumption 510.1 kg / h, and actual water production ratio 8.62.

[0126] Based on the trial operation data, a dynamic simulation model of the MED-TVC device was constructed, and... Figure 9 The power steam pressure fluctuation shown is used as the simulation test pressure source to compare the performance of the traditional PID control method and the injector operating condition control strategy proposed in this invention.

[0127] Under traditional PID control, the tube-side temperature of the first-effect evaporator and the shell temperature of each effect evaporator are as follows: Figure 10 As shown. Reducing the high-grade steam pressure to 8 bar results in a first-effect tube-side temperature of 75.8℃, corresponding to a saturation pressure of 40.1 kPa, and a last-effect shell temperature of 64.6℃, corresponding to a saturation pressure of 24.6 kPa. The production capacity is 3.548 t / h, the first-effect tube-side steam consumption is 421.9 kg / h, and the actual water production ratio is 8.41. Increasing the high-grade steam pressure to 12 bar results in a first-effect tube-side temperature of 94.9℃, corresponding to a saturation pressure of 84.3 kPa, and a last-effect shell temperature of 81.8℃, corresponding to a saturation pressure of 51.1 kPa. The production capacity is 4.413 t / h, the first-effect tube-side steam consumption is 598.7 kg / h, and the actual water production ratio is 7.37.

[0128] Under the ejector operating condition control strategy, the tube-side temperature of the first-effect evaporator and the shell temperature of each effect evaporator are as follows: Figure 11 As shown. Combined with Figure 12 The comparison of freshwater production under the two control methods shows that, compared with the traditional PID control method, the new optimized control system of the hot-pressing multi-effect evaporator achieves the following results when the high-grade steam pressure decreases from 10 bar to 8 bar: first-effect tube temperature of 81.3℃ (corresponding to a saturation pressure of 50.1 kPa), last-effect shell temperature of 68.8℃ (corresponding to a saturation pressure of 29.6 kPa), production capacity of 3.881 t / h, first-effect tube steam consumption of 421.9 kg / h, actual water production ratio of 9.20, and a production increase of 9.39% compared with the traditional control method. Similarly, it can be measured that when the high-grade steam pressure increases from 10 bar to 12 bar, the first-effect tube temperature is 88.8℃, corresponding to a saturation pressure of 67.1 kPa, the last-effect shell temperature is 73.1℃, corresponding to a saturation pressure of 35.6 kPa, the production capacity is 4.983 t / h, the first-effect tube steam consumption is 598.7 kg / h, the actual water production ratio is 8.33, and the output is increased by 12.91% compared with the traditional control method.

[0129] Example 2 This embodiment discloses a control system for a thermo-pressurized multi-effect evaporator based on ejector operating conditions, including: The optimized control target module is configured to: determine the optimal operating condition range of the ejector within the high-grade steam pressure fluctuation range based on the mechanism model of the ejector and the multi-effect evaporator, combined with the trial operation data of the device; and within the optimal operating condition range of the ejector, search for the optimized control target point of the ejector operating condition through an optimization algorithm according to the current state of the device. The outer loop control module is configured to: optimize the control target point based on the ejector operating condition, adopt model predictive control, and perform ejector operating condition optimization control under the condition of satisfying the operating state constraints of the multi-effect evaporator to obtain the corresponding control value; The inner loop control module is configured to input the control value to the PID controller, which then adjusts the pump operating frequency to achieve closed-loop control of the controlled variable.

[0130] Example 3 The purpose of this embodiment is to provide a computing device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method of Embodiment 1.

[0131] Example 4 The purpose of this embodiment is to provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the steps of the method of Embodiment 1.

[0132] The steps and methods involved in the apparatuses of Embodiments 3 and 4 above correspond to those in Embodiment 1. For specific implementation details, please refer to the relevant description section of Embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood as including any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and enabling the processor to perform any of the methods in this invention.

[0133] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0134] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0135] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A control method for a thermal pressure type multiple effect evaporation apparatus based on the working condition of an ejector, characterized by, include: Based on the mechanism model of the ejector and the multi-effect evaporator, and combined with the trial operation data of the unit, the optimal operating range of the ejector within the pressure fluctuation range of high-grade steam was determined. Within the optimal operating range of the injector, the target point for optimizing the injector's operating condition is searched using an optimization algorithm based on the current state of the device. Based on the target point of the ejector operating condition optimization control, model predictive control is adopted to carry out the ejector operating condition optimization control under the condition of satisfying the operating state constraints of the multi-effect evaporator, and obtain the corresponding control quantity values. The control value is input to the PID controller, which adjusts the pump operating frequency to achieve closed-loop control of the controlled variable.

2. The control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in claim 1, characterized in that, The trial operation data of the device includes high-grade steam pressure, ejector outlet pressure, ejector suction pressure, current concentration and temperature of the medium in each evaporator, and feed flow rate.

3. The control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in claim 1, characterized in that, The optimal operating range of the ejector is composed of the ejector critical pressure curve under the corresponding high-grade steam pressure and the pressure controllable range of the multi-effect evaporator.

4. The control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in claim 1, characterized in that, The optimization algorithm maximizes the suction pressure within the optimal operating range of the ejector.

5. The control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in claim 1, characterized in that, The model predictive control is an adaptive model predictive control, and its optimization performance index is: in, To optimize performance metrics, For the first time, To predict the time domain, For prediction of the time domain The Middle One predicted moment, To the degree of suppression of tracking error, To optimize the control target point for injector operating conditions, In the first At the nth moment, for the first The predicted value output at time step. To control the time domain, To control the time domain The Middle One control moment, To determine the degree of suppression of changes in the control quantity, For the first Changes in control quantity at any given time To the degree of inhibition of the control quantity, For the first The amount of control at any given moment.

6. The control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in claim 5, characterized in that, In adaptive model predictive control, the controlled variables include feed flow rate, cooling water flow rate, and final-effect concentrate discharge flow rate; the controlled variables include ejector outlet pressure and ejector suction pressure; and the constraint variables include first-effect medium concentration and final-effect evaporator liquid level.

7. The control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in claim 6, characterized in that, The upper and lower limits of control quantity constraints, as well as the upper and lower limits of control quantity change constraints, are added to the feed flow rate, cooling water flow rate, and final effect concentrate discharge flow rate. The upper and lower limits of liquid level constraints are added to the liquid level of the final effect evaporator. The upper limit of concentration constraint is added to the concentration of the medium in the first effect.

8. A control system for a thermo-pressurized multi-effect evaporator based on ejector operating conditions, characterized in that: include: The optimized control target module is configured to: determine the optimal operating condition range of the ejector within the high-grade steam pressure fluctuation range based on the mechanism model of the ejector and the multi-effect evaporator, combined with the trial operation data of the device; and within the optimal operating condition range of the ejector, search for the optimized control target point of the ejector operating condition through an optimization algorithm according to the current state of the device. The outer loop control module is configured to: optimize the control target point based on the ejector operating condition, adopt model predictive control, and perform ejector operating condition optimization control under the condition of satisfying the operating state constraints of the multi-effect evaporator to obtain the corresponding control value; The inner loop control module is configured to input the control value to the PID controller, which then adjusts the pump operating frequency to achieve closed-loop control of the controlled variable.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the control method for a thermo-pressurized multi-effect evaporator based on ejector conditions as described in any one of claims 1-7.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the control method for a thermo-pressurized multi-effect evaporator based on ejector operating conditions as described in any one of claims 1-7.

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