Thermocompression multi-effect water distiller system and control method therefor

Abstract

The present invention relates to the technical field of water distillers, and disclosed are a thermocompression multi-effect water distiller system and a control method therefor. The thermocompression multi-effect water distiller system comprises a distillation unit and a control unit; the distillation unit comprises a multi-effect evaporator; the multi-effect evaporator is a horizontal tube falling film evaporator and has a side-by-side configuration, and the shell pass of a preceding effect evaporator is communicated with the tube pass of a following effect evaporator; the control unit controls the distillation unit during working, and the control unit is a feedforward-cascaded fuzzy PID model predictive control system and comprises an inner-loop control system and an outer-loop control system; the inner-loop control system uses fuzzy PID control, and the inner-loop control system is provided with a control system for fluctuations in industrial steam pressure Psteam; and the outer-loop control system uses model predictive control. In the present invention, by using the thermocompression multi-effect water distiller system and the control method therefor, the heat exchange efficiency is greatly improved; and a novel control system is provided, enabling normal operation within a range of 40-200% of a set operating condition.

Description

A hot-pressed multi-effect distilled water machine system and its control method Technical Field

[0001] The present invention relates to the technical field of distilled water machines, and in particular to a hot-pressed multi-effect distilled water machine system and a control method thereof. Background Art

[0002] Distillation is the only method for producing water for injection recognized by my country's Pharmacopoeia. How to reduce energy consumption in the production process and improve its automation level through technological innovation is a key issue that needs to be urgently addressed.

[0003] Currently, there are two types of equipment that are commonly used in the industry to prepare water for injection using the distillation method: multi-effect distilled water machine and hot-pressed distilled water machine.

[0004] The basic principle of a multi-effect distilled water machine is as follows: room-temperature raw water reaches a higher temperature after passing through multiple heat exchangers such as condensers and preheaters, and then enters the first-effect vertical tube evaporator tube side, where it is evenly distributed on the inner wall of the heat exchange tube to form a liquid film. At the same time, high-temperature steam enters the shell side of the heat exchanger. The steam temperature is higher than that of the raw water. The two media exchange heat through the heat exchange tube wall. The steam outside the tube releases heat and condenses into product water. The raw water inside the tube evaporates to produce steam that enters the shell side of the next effect. The unevaporated raw water enters the tube side of the next effect, and the above process is repeated until the last effect. The steam generated in the last effect all enters the condenser and condenses into product water. However, the inventors have found that the equipment has the following shortcomings: the evaporator uses vertical tube falling film technology to produce water, which has low heat exchange efficiency; the system inlet and outlet steam pressure difference is large, making it difficult to recycle the outlet steam, resulting in huge energy waste; the system control method is outdated, the control effect is poor, and it is difficult to maintain the optimal operating state.

[0005] Thermal compression water distillers have been gaining popularity in the industry in recent years. Using a steam compressor to circulate steam within the system can reduce water production costs by half. The basic principle is that industrial steam passes through a steam regenerator and enters the evaporator heat exchange tubes, exchanging heat with preheated, pure water sprayed onto the outside of the heat exchange tubes. The resulting steam is then boosted by a steam thermocompressor and re-enters the evaporator heat exchange tubes, completing the system's internal circulation. However, the inventors discovered that this device has the following disadvantages: the steam compressor impeller rotates at a high speed, requiring a high workload. This not only increases the cost, but also the impeller's susceptibility to damage, leading to high maintenance costs. Summary of the Invention

[0006] The purpose of the present invention is to provide a hot-pressed multi-effect distilled water machine system and a control method thereof, which greatly improves the heat exchange efficiency and proposes a new control system that can achieve normal operation within the set operating conditions range of 40% to 200%, ensuring that the equipment can be in a stable and efficient operating state.

[0007] To achieve the above-mentioned object, the present invention provides a hot-pressed multi-effect water distiller system, comprising a distillation unit and a control unit;

[0008] The distillation unit includes a multiple-effect evaporator;

[0009] The multiple-effect evaporator is a horizontal tube falling film evaporator, and is arranged side by side, with the shell side of the first-effect evaporator and the tube side of the second-effect evaporator being connected;

[0010] The control unit controls the distillation unit during operation. The control unit is a feedforward cascade fuzzy PID model predictive control system and includes an inner loop control system and an outer loop control system;

[0011] The inner loop control system is a fuzzy PID control, and the inner loop control system is provided with a control system for fluctuations in the industrial steam pressure Psteam;

[0012] The outer loop control system is model predictive control.

[0013] Preferably, the distillation unit further comprises a pure steam generator, a steam ejector, a raw material pure water buffer tank, a condensed water buffer tank and a waste heat recovery system;

[0014] The waste heat recovery system is used to preheat the raw pure water, and is sequentially provided with a raw pure water pump, a concentrated water preheater, an industrial condensate secondary preheater, a condenser, a product water preheater and an industrial condensate primary preheater from the raw pure water end;

[0015] The pure steam generator tube-side feed water end is connected to the raw pure water buffer tank through a steam generator pump, and the shell-side steam inlet end is connected to the industrial steam pipeline; the industrial condensate discharge end is connected to the industrial condensate primary preheater, and the concentrated drainage discharge end is connected to the concentrated drainage preheater.

[0016] Preferably, in the multiple-effect evaporator, the steam inlet of the first-effect evaporator is connected to the outlet of the steam ejector, and the secondary flow inlet of the steam ejector is connected to the steam outlet of the last-effect evaporator;

[0017] The last-effect evaporator is also connected to the condenser, the raw pure water buffer tank and the condensed water buffer tank respectively, wherein the steam outlet of the condensation side header of the last-effect evaporator is connected to the shell side inlet of the condenser, the residual water outlet of the middle cylinder of the last-effect evaporator is connected to the raw pure water buffer tank, and the condensed water outlet of the condensation side header of the last-effect evaporator is connected to the condensed water buffer tank;

[0018] The raw pure water buffer tank is connected to the industrial condensate primary preheater through a circulating water pump, and the industrial condensate primary preheater is connected to the spray liquid distribution system of the multiple-effect evaporator;

[0019] The spray liquid distribution system is provided with a liquid distributor;

[0020] The number of the liquid distributors is the same as the number of effects of the multi-effect evaporator, and each liquid distributor is located directly above each effect evaporator.

[0021] Preferably, the pure steam outlet end of the pure steam generator is connected to the primary flow inlet of the steam ejector.

[0022] Preferably, the last-effect evaporator is further connected to a condensed water buffer tank, which outputs product water through a product water discharge pipe. The product water discharge pipe includes a first row of pipes, the ends of which are respectively connected to a second row of pipes for qualified product water and a third row of pipes for unqualified product water. The water quality is tested by an online conductivity detector to determine whether it is qualified, thereby controlling the opening and closing of the valves in the second row of pipes and the valves in the third row of pipes.

[0023] The first row of pipes is provided with a product water pump.

[0024] The present invention also provides a control method for a hot-pressed multi-effect distilled water machine system. The inner loop control system is a single-input single-output control system. For controlling the flow rate through the pump and the steam pressure through the valve opening, a fuzzy control method is used to form a fuzzy control rule based on the deviation and deviation change rate of the current controlled quantity.

[0025] The outer loop control system is a model predictive control, with system performance, reference trajectory tracking performance, and the degree of change of the inner loop set value as optimization objectives. Based on the inner loop set value and the state constraints of the thermal compression multi-effect distilled water machine system, a rolling optimization model is established:

[0026] ;

[0027] ;

[0028] ;

[0029] ;

[0030] in, is the set optimization objective function; is the system performance evaluation function; and They are The reference trajectory at time Time for Prediction output at the moment; and are the minimum and maximum values ​​of the key state parameters of the system; For Time for Predicted values ​​of system state parameters at time t; and The minimum and maximum values ​​of the output values ​​given by the model predictive controller to the inner loop controller; for The output value of the model predictive controller to the inner loop controller at that moment; and The minimum and maximum rates of change of the output value of the inner loop controller given by the model predictive controller; for The rate of change of the output value given by the model predictive controller to the inner loop controller at each moment; is the prediction time domain; is the i-th moment in the prediction time domain; To control the time domain; is the jth moment in the control time domain; 、 and is the weight coefficient at the i-th moment.

[0031] Preferably, the control system for fluctuations in industrial steam pressure Psteam includes an ejector operating condition control system and an evaporator liquid level control system;

[0032] The ejector operating condition control system ensures that the system water production ratio is not less than 8;

[0033] The evaporator liquid level control system controls the opening of the effect regulating valve to make the industrial steam pressure During the fluctuation process, the liquid level in the effect is maintained between 5 and 35 cm.

[0034] Preferably, for the steam ejector operating condition control, the steam ejector is modeled to obtain the different primary flow inlet pressures. The steam ejector outlet pressure that meets the steam ejector injection performance is and secondary flow pressure , by controlling the steam ejector outlet pressure and secondary flow pressure , to control the steam ejector injection performance and achieve the purpose of system water production ratio not less than 8;

[0035] For the steam ejector modeling method, since the ejector is a nonlinear link, the modeling method is based on data-driven modeling; obtain industrial steam pressure Secondary flow pressure within the fluctuation range that meets the steam ejector injection performance and outlet pressure Data, in actual control, the secondary flow pressure is obtained by looking up the table and steam ejector outlet pressure Control target to achieve the purpose of linearizing the steam ejector;

[0036] Steam ejector outlet pressure The control method is to control the steam flow at the steam ejector outlet, control the temperature of the first-effect evaporator, and adjust the steam ejector outlet pressure. control;

[0037] Steam ejector outlet pressure The control method adopts cascade control system. The inner loop of the system controls the steam flow by PID control of the regulating valve opening, and the outer loop controls the steam ejector outlet pressure by adjusting the steam flow set value through model predictive control. Obtained by looking up the table;

[0038] Steam ejector secondary flow pressure The control method is to control the feed rate of raw water, control the steam pressure of the condenser, and further control the secondary flow pressure of the steam ejector. ;

[0039] Steam ejector secondary flow pressure The control method adopts cascade control system. The inner loop of the system controls the feed water flow rate by PID control of the feed pump frequency. The outer loop controls the feed water flow rate set value by model predictive control to control the steam ejector secondary flow pressure. The steam ejector secondary flow pressure set value Obtained by looking up the table.

[0040] Preferably, the evaporator liquid level control method is based on the model predictive control method, with the liquid level control system of each effect as a subsystem. The main system then combines the liquid level data of each effect and sends the control requirements to each subsystem to realize a distributed model predictive control structure.

[0041] The control requirements issued by the main system are the Nash optimal solutions obtained based on Nash optimization;

[0042] The subsystem control method uses mechanism modeling to establish the relationship equation between evaporator pressure, liquid level and inter-effect flow, so as to achieve the purpose of accurately controlling the liquid level by controlling the inter-effect flow;

[0043] The subsystem control method adopts feedforward plus cascade model predictive control. The inner loop adopts PID control to control the effect flow by controlling the effect valve opening. The outer loop adopts model predictive control to modify the PID set value of the effect flow according to the evaporator liquid level. The evaporator pressure further modifies the PID set value of the effect flow through feedforward control.

[0044] Therefore, the present invention adopts the above-mentioned hot-pressing multi-effect distilled water machine system and control method thereof, and its technical effects are as follows:

[0045] (1) Using horizontal tube falling film evaporation technology, pure steam enters the evaporator heat exchange tube, and the raw pure water is evenly sprayed on the outer wall of the heat exchange tube through the spray distribution system to form a uniform liquid film, which greatly improves the heat exchange efficiency;

[0046] (2) Introducing steam ejector technology to recover low-grade steam, recover low-grade steam from the final-effect evaporator, and realize steam internal circulation. The hot-pressed multi-effect distilled water machine system uses steam ejectors to replace the compressor in the hot-pressed distilled water machine system. The steam ejector is a purely mechanical structure with no moving parts inside, low processing cost and long service life.

[0047] (3) A new control system was proposed, which can achieve normal operation within the range of 40% to 200% of the set working conditions, ensuring that the equipment can operate in a stable and efficient state;

[0048] (4) The hot-pressed multi-effect distilled water machine can not only achieve the energy consumption level and water production cost of the hot-pressed distilled water machine, but also has a simple mechanical structure.

[0049] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is an overall schematic diagram of a hot-pressed multi-effect distilled water machine system according to the present invention;

[0051] FIG2 is a partial enlarged view of the steam ejector;

[0052] Figure 3 is an enlarged schematic diagram of part A in Figure 1;

[0053] Figure 4 is a schematic diagram of a horizontal tube falling film evaporator;

[0054] Figure 5 is a diagram of a feedforward cascade fuzzy PID model predictive control system;

[0055] FIG6 is a diagram of a steam ejector operating control system;

[0056] Figure 7 is a diagram of a single-effect liquid level control system.

[0057] Reference numerals

[0058] 1. Multi-effect evaporator; 101. Steam inlet side header; 102. Steam baffle; 103. Intermediate cylinder; 104. Defoamer; 105. Condensation side header; 2. Pure steam generator; 3. Steam ejector; 301. Outlet end; 302. Primary inlet; 303. Secondary inlet; 4. Raw pure water buffer tank; 5. Condensate buffer tank; 6. Waste heat recovery system; 601. Concentrated water preheater; 602. Secondary preheater for industrial condensate; 603. Condenser; 604. Product water preheater; 605. Primary preheater for industrial condensate; 7. Circulating water pump; 8. Spray liquid distribution system; 801. Liquid distributor; 9. Raw pure water pump; 10. Product water discharge pipe; 11. First row of pipes; 12. Second row of pipes; 13. Third row of pipes; 14. Product water pump; 15. Steam generator pump. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0060] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0061] Example 1

[0062] As shown in FIG1 , it is an overall schematic diagram of a hot-pressed multi-effect distilled water machine system of the present invention, including a distillation unit and a control unit;

[0063] The distillation unit includes a multi-effect evaporator 1; this embodiment is a five-effect evaporator; in Figure 1, I is industrial steam, B is non-condensable gas, C is industrial condensate, D is concentrated drainage, E is qualified injection water, F is unqualified injection water, G is a sampling port, and H is raw pure water.

[0064] Non-condensable gas is the gas in the system that cannot be condensed into liquid water. Here it mainly refers to the air remaining inside the system before the system is operated and the air mixed in the steam and raw water.

[0065] The multi-effect evaporator 1 is a horizontal tube falling film evaporator and is arranged side by side. The shell side of the previous effect evaporator and the tube side of the next effect evaporator are connected. Compared with the vertical tube falling film evaporation technology, the technology proposed in the present invention allows pure steam to enter the evaporator heat exchange tube, and the raw pure water is evenly sprayed on the outer wall of the heat exchange tube through the spray liquid distribution system to form a uniform liquid film, thereby greatly improving the heat exchange efficiency.

[0066] As shown in Figure 4, the horizontal tube falling film evaporator is the core component of the hot-pressed multi-effect water distiller, primarily consisting of a steam inlet head 101, a condensation head 105, and an intermediate cylinder 103. A steam baffle 102 is installed within the steam inlet head 101 to ensure uniform steam entry into the heat exchange tube bundle; a demister 104 is installed within the condensation head 105 to remove droplets of raw water from the steam; and the intermediate cylinder 103 is welded with heat exchange tubes for heat exchange between the raw pure water and pure steam. A spray liquid distribution system 8 is welded above the intermediate cylinder 103 to ensure uniform distribution of the raw pure water.

[0067] The distillation unit also includes a pure steam generator 2, a steam ejector 3, a raw pure water buffer tank 4, a condensed water buffer tank 5 and a waste heat recovery system 6; FIG2 is an enlarged view of the steam ejector 3.

[0068] The waste heat recovery system 6 is provided with a raw pure water pump 9, a concentrated water preheater 601, an industrial condensate secondary preheater 602, a condenser 603, a product water preheater 604 and an industrial condensate primary preheater 605 in sequence from the raw pure water end. The waste heat recovery system 6 is used to preheat the raw pure water. The raw pure water inlet temperature is 20°C. It first passes through the concentrated wastewater preheater 601 for heat exchange with the 160°C concentrated wastewater discharged from the pure steam generator 2. The raw pure water is preheated to about 22°C, and the concentrated wastewater temperature drops to about 40°C for low-temperature discharge; then the raw pure water passes through the industrial condensate secondary preheater 602 for heat exchange with the 110°C industrial condensate discharged from the industrial condensate primary preheater 605. The raw pure water is preheated to about 27°C, and the industrial condensate temperature drops to below 50°C for low-temperature discharge; then the raw pure water passes through the condenser 603 for heat exchange with the 102°C saturated steam discharged from the last-effect evaporator. The raw pure water is preheated to about 85°C, and the steam is condensed into 102°C condensate and enters the condensate buffer. Tank 5; then the raw pure water passes through the product water preheater 604 for heat exchange with the product water of about 102°C discharged from the condensate buffer tank 5. The raw pure water is preheated to 93°C and then enters the raw pure water buffer tank 4 to mix with the residual steam water from the last effect entering the buffer tank. The product water temperature is reduced to 80-95°C according to actual needs and then discharged from the system; the temperature of the raw pure water after mixing in the raw pure water buffer tank 4 is about 97°C, and then passes through the industrial condensate first-level preheater 605 for heat exchange with the industrial condensate of about 160°C discharged from the pure steam generator 2. The raw pure water is preheated to about 101°C and enters the spray liquid distribution system 8 of the first-effect evaporator. The industrial condensate temperature drops to 110°C and then enters the industrial condensate second-level preheater 602.

[0069] In the multi-effect evaporator 1, the steam inlet of the first-effect evaporator is connected to the outlet 301 of the steam ejector 3, and the secondary flow inlet 303 of the steam ejector 3 is connected to the steam outlet of the last-effect evaporator;

[0070] The final evaporator is also connected to the condenser 603 and the raw pure water buffer tank 4 respectively;

[0071] A circulating water pump 7 is provided on one side of the raw pure water buffer tank 4. The other end of the circulating water pump 7 is connected to the industrial condensate primary preheater 605. The industrial condensate primary preheater 605 is connected to the spray liquid distribution system 8 of the multi-effect evaporator 1.

[0072] As shown in FIG3 , the liquid spraying system 8 is provided with liquid distributors 801 ; the number of liquid distributors 801 is the same as the number of effects of the multi-effect evaporator 1 , and each liquid distributor 801 is located directly above each effect evaporator.

[0073] One end of the pure steam generator 2 is connected to industrial steam and a buffer water tank. The pure steam outlet end of the pure steam generator 2 is connected to the primary flow inlet 302 of the steam ejector 3. A steam generator pump 15 is provided between the pure steam generator 2 and the buffer water tank for generating steam.

[0074] The last-effect evaporator is also connected to the condensate buffer tank 5, which outputs product water through the product water discharge pipe 10. The product water discharge pipe 10 includes a first row of pipes 11. The ends of the first row of pipes 11 are respectively connected to the second row of pipes 12 for qualified product water and the third row of pipes 13 for unqualified product water. The water quality is tested by an online conductivity detector to determine whether it is qualified, and then the switches of the second row of pipe valves and the third row of pipe valves are controlled; a product water pump 14 is provided on the first row of pipes 11 for extracting product water.

[0075] During operation, the raw pure water is preheated by the waste heat recovery system 6 (concentrated water preheater 601, secondary industrial condensate preheater 602, condenser 603, product water preheater 604, and primary industrial condensate preheater 605). It is then evenly sprayed onto the outer walls of the heat exchange tubes via a liquid distributor, forming a uniform liquid film. Industrial steam and water from the buffer tank are converted into pure steam by the pure steam generator 2. This steam is then used as the power source for the steam ejector to inject steam from the last-effect evaporator. The two steam streams mix and enter the heat exchange tubes of the horizontal tube falling-film evaporator through the steam ejector outlet. Due to the temperature difference between the inside and outside of the heat exchange tubes, the steam inside the tubes condenses into water for injection, which is then discharged. The raw pure water outside the tubes evaporates, producing pure steam that enters the heat exchange tubes of the next-effect evaporator. The excess unevaporated raw pure water enters the outer surface of the heat exchange tubes of the next-effect evaporator, forming a uniform liquid film. This cycle continues until the last-effect evaporator.

[0076] The pipeline connections and various valves provided on the pipelines in the present invention are conventional settings and are well known to those skilled in the art.

[0077] The control unit controls the distillation unit during operation. The control unit is a feedforward cascade fuzzy PID model predictive control system and includes an inner loop control system and an outer loop control system;

[0078] The inner loop control system is fuzzy PID control, and the inner loop control system is equipped with a control system for fluctuations in industrial steam pressure Psteam;

[0079] The outer loop control system is model predictive control.

[0080] As shown in Figure 5, it is a feedforward cascade fuzzy PID model predictive control system diagram.

[0081] (1) According to the process flow of the equipment, the intermediate controlled quantity of the control system is mainly the circulating water flow , Raw water flow , feed water flow , product water flow , preheating steam pressure and heating steam pressure Since the flow control is realized by water pump and the pressure control is realized by steam pressure regulating valve, the control amount For each pump frequency and pressure regulating valve opening:

[0082] (1)

[0083] in, is the circulation pump frequency; is the feed pump frequency; is the steam generator feed pump frequency; is the product water pump frequency; The opening of the steam preheating pipeline valve; is the opening of industrial steam valve;

[0084] For this equipment, the performance of the steam ejector determines the steam recovery rate. For energy-saving optimization and control considerations, the control system needs to regulate the three-port pressure to ensure that the steam ejector operates in the optimal state. The final output of the system is is the primary flow pressure of the steam ejector , secondary flow pressure and outlet pressure :

[0085] (2)

[0086] In industrial applications, industrial steam and feed water are both provided by the factory. Affected by the peak period of steam use, the industrial steam pressure will fluctuate. Similarly, different feed water sources will also cause the feed water temperature to change. Therefore, the main disturbance variables of the system are Industrial steam pressure and feed water temperature :

[0087] (3)

[0088] Based on the analysis of the system process, there is a strong coupling relationship between the input and output of the system, among which the primary flow pressure of the steam ejector and heating steam pressure and feed water flow There is a strong coupling relationship, and the disturbed variable industrial steam pressure Influence: Secondary flow pressure and preheated steam pressure and raw water flow There is a strong coupling relationship, and the disturbed variable feed water temperature Impact; outlet pressure Circulating water flow and preheat steam pressure There is a strong coupling relationship, and the disturbed variable industrial steam pressure and feed water temperature Influence.

[0089] In summary, the system has a complex structure and obvious time-delay links. It is a large time-delay, strongly coupled, nonlinear multi-input and multi-output system.

[0090] (2) For multi-input and multi-output systems with large time delays, strong coupling, and nonlinearity, it is difficult to precisely control the system output by controlling only one input. Therefore, it is necessary to adopt a global coordinated control approach and select a global control method that can effectively eliminate the influence of time delay on control. Under these conditions, model predictive control is more appropriate. Compared with other control methods that are highly dependent on model accuracy, model predictive control does not require an overly accurate model. In practical applications, the system model will not remain unchanged. The feedback correction link in the model prediction can effectively reduce the impact of external interference and model mismatch, thereby improving the robustness of the control system.

[0091] When designing a specific control system, the presence of measurable external disturbances in the controlled object is first considered, necessitating the design of a feedforward control loop to mitigate the effects of these disturbances. Furthermore, for large-scale industrial system control, model predictive control (MPC) is computationally intensive and struggles to meet the underlying control speed requirements. Therefore, cascade MPC is often employed. PID control is used as the inner loop of the cascade control to meet the underlying control speed requirements, while MPC serves as the outer loop to modify the inner controller setpoint at a constant speed. Under these conditions, the inner loop control becomes a simple single-input, single-output control. Expert knowledge exists for controlling flow through pumps and steam pressure through valve openings. Fuzzy control methods can be employed based on the deviation and rate of change of the current controlled variable to form fuzzy control rules and enhance the inner loop control effectiveness.

[0092] In Figure 5, represents the expected output of the system, 、 and Represent the primary flow pressure of steam ejector , secondary flow pressure and outlet pressure The expected output; represents the inner loop controller set value, 、 、 、 、 and Represents the circulating water flow , Raw water flow , feed water flow , product water flow , preheating steam pressure and heating steam pressure The inner loop controller setting value; Represents the control quantity output of the inner loop controller; Output feedback for the inner loop; and The inner loop circulating water flow and heating steam pressure Control error; 、 and They represent the proportional coefficient, integral time and differential time of the inner loop PID controller derived by fuzzy reasoning respectively.

[0093] The selection of model predictive control optimization performance indicators will take system performance, reference trajectory tracking performance and the degree of change of inner loop set values ​​as optimization targets. Based on the inner loop set values ​​and system state constraints, a rolling optimization model will be established.

[0094] ;

[0095] ;

[0096] ;

[0097] ;

[0098] in, is the set optimization objective function; is the system performance evaluation function; and They are The reference trajectory at time Time for Prediction output at the moment; and are the minimum and maximum values ​​of the key state parameters of the system; For Time for Predicted values ​​of system state parameters at time t; and The minimum and maximum values ​​of the output values ​​given by the model predictive controller to the inner loop controller; for The output value of the model predictive controller to the inner loop controller at that moment; and The minimum and maximum rates of change of the output value of the inner loop controller given by the model predictive controller; for The rate of change of the output value given by the model predictive controller to the inner loop controller at each moment; is the prediction time domain; is the i-th moment in the prediction time domain; To control the time domain; is the jth moment in the control time domain; 、 and is the weight coefficient at the i-th moment.

[0099] Use intelligent optimization algorithms to solve constrained quadratic optimization problems and obtain Inner loop setpoint increments.

[0100] (3) Due to industrial steam pressure Fluctuations in steam pressure will have adverse effects on the operation of medical water for injection preparation equipment. Therefore, based on the above functions, the industrial steam pressure Conventional medical water preparation equipment relies on simple PID control. Rapid steam pressure fluctuations can severely impact the system's water production ratio and heat exchange efficiency, and can even cause production accidents.

[0101] The equipment is designed for widely varying operating conditions. When the steam generator pressure fluctuates between 0.4 and 0.8 MPa, manual control is eliminated, relying on the equipment control system to automatically complete the equipment control tasks, ensuring efficient and safe operation. In practical applications, this not only effectively reduces the impact of sudden pressure fluctuations on production, but also lowers the equipment's steam pressure requirements, expanding its application areas.

[0102] The equipment control system is characterized by its ability to adapt to 0.4~0.8Mpa steam generator pressure fluctuations and maintain the system water production ratio at no less than 8.

[0103] For the current process flow of the equipment, for industrial steam pressure The fluctuating control system consists of ejector working condition control and evaporator liquid level control. The ejector working condition control effect is achieved by controlling the ejector working condition to ensure that the ejector ejection coefficient does not fluctuate due to industrial steam pressure. The evaporator level control effect is achieved by controlling the opening of the regulating valve between the effects to make the industrial steam pressure During the fluctuation process, the liquid level in the effect is maintained between 5 and 35 cm, and empty tanks and flooded pipes will not occur.

[0104] As shown in Figure 6, it is a diagram of the steam ejector operating condition control system. For the ejector operating condition control, due to the ejector primary flow pressure and industrial steam pressure Highly correlated, it is an external disturbance that is out of control. Therefore, the characteristic of ejector operating condition control is that it does not affect the primary inlet pressure. Control, by modeling the ejector, obtain different primary flow inlet pressure The ejector outlet pressure that satisfies the ejector ejection performance is and secondary flow pressure , by controlling the ejector outlet pressure and secondary flow pressure , to control the ejector injection performance and ultimately achieve the goal of a system water production ratio of no less than 8.

[0105] As for the ejector modeling method, since the ejector is a nonlinear link, its modeling feature is based on a data-driven modeling method, and the industrial steam pressure is obtained through experiments. Secondary flow pressure within the fluctuation range that meets the ejector injection performance and outlet pressure Data, in actual control, the secondary flow pressure is obtained by looking up the table and outlet pressure Control target to achieve the purpose of linearizing the controlled object.

[0106] For the ejector outlet pressure The control method is characterized by controlling the steam flow at the ejector outlet, further controlling the temperature of the first-effect evaporator, and ultimately controlling the ejector outlet pressure. For the purpose of injector outlet pressure The control system is characterized by the use of a cascade control system. The inner loop of the system controls the steam flow rate by regulating the valve opening through PID control, and the outer loop controls the ejector outlet pressure by adjusting the steam flow set value through model predictive control. Obtained by table lookup method.

[0107] For the ejector secondary flow pressure Control, the control method is characterized by controlling the raw water feed rate, further controlling the condenser steam pressure, and further controlling the ejector secondary flow pressure For the ejector secondary flow pressure The control system is characterized by the use of a cascade control system. The inner loop of the system controls the feed water flow rate by controlling the feed pump frequency through PID, and the outer loop controls the feed water flow rate set value through model predictive control to control the ejector secondary flow pressure. The ejector secondary flow pressure set value Obtained by looking up the table.

[0108] Figure 7 shows a diagram of a single-effect liquid level control system. Evaporator level control is a multivariable coupled system because the level controls of each evaporator effect are highly coupled, and each evaporator effect requires an inter-effect valve with controlled opening. Therefore, evaporator level control is characterized by utilizing a model predictive control approach, treating each effect's liquid level control system as a subsystem. The main system, after integrating the liquid level data from each effect, issues control requirements to each subsystem, implementing a distributed model predictive control structure. The control requirements issued by the system are characterized by Nash optimal solutions obtained through Nash optimization, achieving control system decoupling. The main system, as the superior system that issues control commands to the subsystems, is well known to those skilled in the art.

[0109] The control method of the model predictive control subsystem is characterized by establishing the relationship equation between evaporator pressure, liquid level and inter-effect flow through mechanism modeling, so as to achieve the purpose of accurately controlling the liquid level by controlling the inter-effect flow.

[0110] Furthermore, the control system of the model predictive control subsystem is characterized by the use of feedforward plus cascade model predictive control. The inner loop adopts PID control to control the effect flow by controlling the effect valve opening. The outer loop adopts model predictive control to modify the PID set value of the effect flow according to the evaporator liquid level. The evaporator pressure further modifies the PID set value of the effect flow through feedforward control.

[0111] Therefore, the present invention adopts the above-mentioned hot-pressed multi-effect distilled water machine system and its control method, which greatly improves the heat exchange efficiency and proposes a new control system that can achieve normal operation within the set working conditions range of 40%~200%, ensuring that the equipment can be in a stable and efficient operation state.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A hot-pressed multi-effect distilled water machine system, characterized in that: including a distillation unit and a control unit; The distillation unit includes a multiple-effect evaporator; The multiple-effect evaporator is a horizontal tube falling film evaporator, and is arranged side by side, with the shell side of the first-effect evaporator and the tube side of the second-effect evaporator being connected; The control unit controls the distillation unit during operation. The control unit is a feedforward cascade fuzzy PID model predictive control system and includes an inner loop control system and an outer loop control system; The inner loop control system is a fuzzy PID control, and the inner loop control system is provided with a control system for fluctuations in the industrial steam pressure Psteam; The outer loop control system is model predictive control.

2. A hot-pressed multi-effect distilled water machine system according to claim 1, characterized in that: The distillation unit also includes a pure steam generator, a steam ejector, a raw material pure water buffer tank, a condensed water buffer tank and a waste heat recovery system; The waste heat recovery system is used to preheat the raw pure water, and is sequentially provided with a raw pure water pump, a concentrated water preheater, an industrial condensate secondary preheater, a condenser, a product water preheater and an industrial condensate primary preheater from the raw pure water end; The pure steam generator tube-side feed water end is connected to the raw pure water buffer tank through a steam generator pump, and the shell-side steam inlet end is connected to the industrial steam pipeline; the industrial condensate discharge end is connected to the industrial condensate primary preheater, and the concentrated drainage discharge end is connected to the concentrated drainage preheater.

3. A hot-pressed multi-effect distilled water machine system according to claim 2, characterized in that: In the multi-effect evaporator, the steam inlet of the first-effect evaporator is connected to the outlet of the steam ejector, and the secondary flow inlet of the steam ejector is connected to the steam outlet of the last-effect evaporator; The last-effect evaporator is also connected to the condenser, the raw pure water buffer tank and the condensed water buffer tank respectively, wherein the steam outlet of the condensation side header of the last-effect evaporator is connected to the shell side inlet of the condenser, the residual water outlet of the middle cylinder of the last-effect evaporator is connected to the raw pure water buffer tank, and the condensed water outlet of the condensation side header of the last-effect evaporator is connected to the condensed water buffer tank; The raw pure water buffer tank is connected to the industrial condensate primary preheater through a circulating water pump, and the industrial condensate primary preheater is connected to the spray liquid distribution system of the multiple-effect evaporator; The spray liquid distribution system is provided with a liquid distributor; The number of the liquid distributors is the same as the number of effects of the multi-effect evaporator, and each liquid distributor is located directly above each effect evaporator.

4. A hot-pressed multi-effect distilled water machine system according to claim 3, characterized in that: The pure steam outlet end of the pure steam generator is connected to the primary flow inlet of the steam ejector.

5. A hot-pressed multi-effect distilled water machine system according to claim 4, characterized in that: The last-effect evaporator is also connected to a condensed water buffer tank, which outputs product water through a product water discharge pipe. The product water discharge pipe includes a first row of pipes, the ends of which are respectively connected to a second row of pipes for qualified product water and a third row of pipes for unqualified product water. The water quality is tested by an online conductivity detector to determine whether it is qualified, thereby controlling the opening and closing of the valves in the second and third rows of pipes. The first row of pipes is provided with a product water pump.

6. A control method for a hot-pressing multi-effect distilled water machine system according to any one of claims 1 to 5, characterized in that: The inner loop control system is a single-input single-output control system. For controlling the flow rate through the pump and the steam pressure through the valve opening, the fuzzy control method is used to form fuzzy control rules based on the deviation and deviation change rate of the current controlled quantity. The outer loop control system is a model predictive control, with system performance, reference trajectory tracking performance, and the degree of change of the inner loop set value as optimization objectives. Based on the inner loop set value and the state constraints of the thermal compression multi-effect distilled water machine system, a rolling optimization model is established: ; ; ; ; in, is the set optimization objective function; is the system performance evaluation function; and They are The reference trajectory at time Time for Prediction output at the moment; and are the minimum and maximum values ​​of the key state parameters of the system; For Time for Predicted values ​​of system state parameters at time t; and The minimum and maximum values ​​of the output values ​​given by the model predictive controller to the inner loop controller; for The output value of the model predictive controller to the inner loop controller at that moment; and The minimum and maximum rates of change of the output value of the inner loop controller given by the model predictive controller; for The rate of change of the output value given by the model predictive controller to the inner loop controller at each moment; is the prediction time domain; is the i-th moment in the prediction time domain; To control the time domain; is the jth moment in the control time domain; 、 and is the weight coefficient at the i-th moment.

7. The control method of a hot-pressed multi-effect distilled water machine system according to claim 6, characterized in that: The control system for industrial steam pressure Psteam fluctuations includes an ejector operating condition control system and an evaporator liquid level control system; The ejector operating condition control system ensures that the system water production ratio is not less than 8; The evaporator liquid level control system controls the opening of the effect regulating valve to make the industrial steam pressure During the fluctuation process, the liquid level in the effect is maintained between 5 and 35 cm.

8. The control method of a hot-pressed multi-effect distilled water machine system according to claim 7, characterized in that: For steam ejector operating condition control, the steam ejector is modeled to obtain different primary flow inlet pressures. The steam ejector outlet pressure that meets the steam ejector injection performance is and secondary flow pressure , by controlling the steam ejector outlet pressure and secondary flow pressure , to achieve the purpose of controlling the steam ejector injection performance and achieving a system water production ratio of not less than 8; For the steam ejector modeling method, since the ejector is a nonlinear link, the modeling method is based on data-driven modeling; obtain industrial steam pressure Secondary flow pressure within the fluctuation range that meets the steam ejector injection performance and outlet pressure Data, in actual control, the secondary flow pressure is obtained by looking up the table and steam ejector outlet pressure Control target to achieve the purpose of linearizing the steam ejector; Steam ejector outlet pressure The control method is to control the steam flow at the steam ejector outlet, control the temperature of the first-effect evaporator, and adjust the steam ejector outlet pressure. control; Steam ejector outlet pressure The control method adopts cascade control system. The inner loop of the system controls the steam flow by PID control of the regulating valve opening, and the outer loop controls the steam ejector outlet pressure by adjusting the steam flow set value through model predictive control. Obtained by looking up the table; Steam ejector secondary flow pressure The control method is to control the feed rate of raw water, control the steam pressure of the condenser, and further control the secondary flow pressure of the steam ejector. ； Steam ejector secondary flow pressure The control method adopts cascade control system. The inner loop of the system controls the feed water flow rate by PID control of the feed pump frequency. The outer loop controls the feed water flow rate set value by model predictive control to control the steam ejector secondary flow pressure. The steam ejector secondary flow pressure set value Obtained by looking up the table.

9. The control method of a hot-pressing multi-effect distilled water machine system according to claim 8, characterized in that: The evaporator liquid level control method is based on the model predictive control method. The liquid level control system of each effect is used as a subsystem. The main system then combines the liquid level data of each effect and sends the control requirements to each subsystem to realize the distributed model predictive control structure. The control requirements issued by the main system are the Nash optimal solutions obtained based on Nash optimization; The subsystem control method uses mechanism modeling to establish the relationship equation between evaporator pressure, liquid level and inter-effect flow, so as to achieve the purpose of accurately controlling the liquid level by controlling the inter-effect flow; The subsystem control method adopts feedforward plus cascade model predictive control. The inner loop adopts PID control to control the effect flow by controlling the effect valve opening. The outer loop adopts model predictive control to modify the PID set value of the effect flow according to the evaporator liquid level. The evaporator pressure further modifies the PID set value of the effect flow through feedforward control.

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