A low-temperature heat pump evaporator multi-mode control system and intelligent cleaning method

Abstract

The application relates to the technical field of wastewater treatment, and specifically discloses a low-temperature heat pump evaporator multi-mode control system and an intelligent cleaning method, wherein the system comprises an evaporation tank and liquid inlet pneumatic valves, circulating pneumatic valves, liquid discharge pneumatic valves, cleaning pneumatic valves and defoaming agent liquid inlet valves arranged on the evaporation tank; the evaporation tank is internally provided with liquid level sensors and foam sensors; the cleaning pipeline is provided with a first cleaning valve and a second cleaning valve with fan-shaped nozzles, which are respectively opposite to the surfaces of the liquid level sensors and the foam sensors to realize directional high-pressure water flushing and descaling; the control system controls the time sequence of the pneumatic valves according to the sensor signals, realizes automatic switching of three modes of evaporation, liquid discharge and cleaning, and controls the opening and closing of the defoaming agent liquid inlet valve to inject the defoaming agent in a pulse mode when the foam sensor detects that the foam exceeds the standard, so that closed-loop precise defoaming is realized. The application realizes full-automatic multi-mode switching, online sensor cleaning and precise defoaming agent dosing, and significantly improves the system reliability and energy efficiency ratio.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a multimodal control system and intelligent cleaning method for a low-temperature heat pump evaporator. Background Technology

[0002] Low-temperature heat pump evaporators are widely used in the treatment of high-concentration wastewater in industries such as chemical, pharmaceutical, and electroplating. Their basic principle is to heat and evaporate the wastewater under negative pressure through a heat pump system, so that the water vaporizes and is condensed and discharged, thereby achieving wastewater reduction or even zero discharge.

[0003] However, traditional low-temperature heat pump evaporators face three major technical bottlenecks when treating high-concentration wastewater: First, during evaporation, the solution concentration continuously increases, leading to scaling (such as salt crystallization and organic matter deposition) on the surfaces of level and foam sensors, resulting in measurement errors of up to ±20% and requiring frequent manual cleaning. Second, during low-temperature heat pump evaporation, when wastewater (especially wastewater containing surfactants, proteins, or high organic matter) is concentrated, the surface tension of the liquid phase decreases, continuously generating a large amount of foam. This foam can cause water pollution, equipment blockage, and reduced evaporation efficiency. Traditional systems rely on manual observation or the addition of fixed doses of defoamer, which is both delayed and wasteful. Third, the switching efficiency between evaporation, cleaning, and drainage modes is low, resulting in significant heat energy loss.

[0004] Utility model patent CN202420939387.6 discloses a low-temperature heat pump evaporator to prevent inner wall adhesion, which uses a scraping mechanism to scrape and clean solid waste from the inner wall of the casing. Utility model patent CN202322462633.1 discloses a three-stage vapor-liquid separation module for a low-temperature heat pump evaporator, which extends the bubble flow path through multi-stage baffles and Z-shaped baffle channels to achieve a defoaming effect. While the above-mentioned prior art has improved the hardware structure, none of it involves a system-level automated control scheme, and therefore cannot solve systemic problems such as intelligent switching between multiple modes, online sensor cleaning, and precise dosing of defoaming agent.

[0005] Therefore, this invention proposes a multi-modal control system and intelligent cleaning method for a low-temperature heat pump evaporator. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-modal control system and intelligent cleaning method for low-temperature heat pump evaporators, thereby solving the above-mentioned technical problems: The objective of this invention can be achieved through the following technical solutions: A multi-modal control system for a low-temperature heat pump evaporator includes an evaporator, a circulating pump, a filter press, a heating coil, a condensate discharge device, and a control system. The evaporator is connected to an inlet pipe, a circulation pipe, a drain pipe, a cleaning pipe, and a defoamer filling pipe. The inlet pipe is equipped with an inlet pneumatic valve, the circulation pipe is equipped with a solution circulation pneumatic valve, the drain pipe is equipped with a drain pneumatic valve, the cleaning pipe is equipped with a cleaning pneumatic valve, a first cleaning valve, and a second cleaning valve, and the defoamer filling pipe is equipped with a defoamer inlet valve. The evaporator is equipped with a liquid level sensor and a foam sensor. The signal output terminals of the liquid level sensor and the foam sensor are connected to the control system. The control signal output terminals of the control system are respectively connected to the control terminals of each pneumatic valve. The outlet ends of the first cleaning valve and the second cleaning valve are respectively connected to fan-shaped nozzles, which are respectively positioned facing the surfaces of the liquid level sensor and the foam sensor, for directional rinsing of the sensor surfaces with high-pressure water. In the evaporation operation mode, the control system controls the timing of the inlet pneumatic valve and the circulation pneumatic valve based on the liquid level sensor signal. When the cumulative number of condensate discharges reaches a preset threshold, the control system automatically switches the system to the drainage mode and automatically switches to the cleaning mode after the drainage is completed. In the probe cleaning stage of the cleaning mode, the control system simultaneously opens the first cleaning valve and the second cleaning valve to perform high-pressure water directional flushing on the liquid level sensor and the foam sensor to ensure the accuracy of liquid level detection and foam detection in the next evaporation cycle. The control system controls the defoamer inlet valve to open in a pulse manner based on the detection signal from the foam sensor, thereby achieving closed-loop precise dosing of the defoamer.

[0007] As a further description of the technical solution of the present invention, the multimodal control logic of the control system includes an evaporation operation mode. In the evaporation operation mode: the evaporator is in a negative pressure state, the control system opens the liquid inlet pneumatic valve, the liquid level sensor detects the liquid level in real time, when the liquid level reaches the set liquid level value, the control system closes the liquid inlet pneumatic valve, opens the solution circulation pneumatic valve, starts the circulation pump and filter press, and begins the evaporation circulation of the solution; when the liquid level sensor detects that the liquid level is lower than the replenishment set value, the control system opens the liquid inlet pneumatic valve again to replenish the evaporator.

[0008] As a further description of the technical solution of the present invention, in the evaporation operation mode, when the cumulative number of times the condensate discharged by the condensate discharge device reaches the preset discharge number threshold, it is determined that the solution in the evaporator is saturated, and the system switches to the discharge mode.

[0009] As a further description of the technical solution of the present invention, the multimodal control logic of the control system includes a draining mode, in which: the control system controls the evaporator to release the negative pressure state, closes the inlet pneumatic valve and the solution circulation pneumatic valve, opens the draining pneumatic valve, starts the circulation pump, and drains the concentrated liquid in the evaporator to the waste liquid tank; the draining stops when the draining time reaches the preset draining time value or the waste liquid tank reaches the high liquid level.

[0010] As a further description of the technical solution of the present invention, the multimodal control logic of the control system includes a cleaning mode, which includes a probe cleaning stage and a chemical cleaning stage: During the probe cleaning stage, the control system opens the first cleaning valve and the second cleaning valve, and high-pressure water with a pressure of 0.3 to 0.5 MPa is used to rinse the surface of the liquid level sensor and the foam sensor through the fan-shaped nozzle. The cleaning time is controlled according to the preset cleaning time value. During the chemical cleaning stage, the control system closes the first cleaning valve and the second cleaning valve, opens the cleaning pneumatic valve, controls the evaporator to be in a negative pressure state to draw in the cleaning liquid to the set liquid level, opens the solution circulation pneumatic valve to start the circulation pump, and performs circulation cleaning according to the preset chemical cleaning time. After the cleaning time is reached, the cleaning waste liquid is discharged. The spray angle of the fan-shaped nozzle is 60°, and the installation position of the fan-shaped nozzle is set so that the spray coverage area completely covers the outer surface of the liquid level sensor and the foam sensor; the water pressure of the high-pressure water is 0.3 to 0.5 MPa, the flow rate of a single nozzle is ≥12 L / min, and the duration of the probe cleaning stage is 20 seconds.

[0011] As a further description of the technical solution of the present invention, the foam sensor is a capacitive foam sensor or an optical foam sensor, used to detect changes in foam layer height or dielectric constant in real time, and output a 0-10V analog signal; when the amplitude of the detected signal is greater than 5V, it is determined that the foam exceeds the standard.

[0012] As a further description of the technical solution of the present invention, the control system has a built-in foam detection delay confirmation logic: when the foam sensor detects a signal exceeding a set threshold and the duration reaches 5 seconds, the defoaming action is triggered; after the defoaming action is triggered, the control system controls the defoamer inlet valve to open in a pulse manner, opening for 2 seconds each time, for a total of 3 times; after the injection is completed, a second detection is performed after a 5-second delay, and if the signal still exceeds the threshold, additional injection is performed.

[0013] As a further description of the technical solution of the present invention, the outer surfaces of the liquid level sensor and the foam sensor are coated with... A nano-hydrophobic coating, wherein the contact angle of the hydrophobic coating is greater than 160°; The heating coil maintains an evaporation temperature of 40±5℃; the preset threshold for the number of drainage cycles is 400; and the running time of the circulating pump during the chemical cleaning stage is 30 to 60 minutes.

[0014] A smart cleaning method for a multimodal control system of a low-temperature heat pump evaporator, the smart cleaning method comprising the following steps: S1: The control system opens the inlet pneumatic valve to draw in wastewater to be evaporated under negative pressure in the evaporator. When the liquid level sensor detects that the set liquid level value has been reached, the inlet pneumatic valve is closed, the solution circulation pneumatic valve is opened, and the circulation pump and filter press are started to begin the evaporation cycle. During the evaporation process, when the liquid level is lower than the replenishment set value, the inlet pneumatic valve is opened again to replenish the liquid. When the cumulative number of condensate discharges reaches the preset discharge number threshold, the evaporation mode ends. S2: The control system controls the evaporator to release the negative pressure, closes the liquid inlet pneumatic valve and the solution circulation pneumatic valve, opens the liquid draining pneumatic valve and starts the circulation pump to drain the concentrate to the waste liquid tank. The liquid draining stops when the liquid draining time reaches the preset liquid draining time value or when the waste liquid tank reaches the high liquid level. S3: The system automatically enters cleaning mode after drainage is complete. S31: During the probe cleaning stage, the control system opens the first cleaning valve and the second cleaning valve. High-pressure water with a pressure of 0.3 to 0.5 MPa is flushed through a fan-shaped nozzle with a spray angle of 60° for 20 seconds to clean the surface of the level sensor and the foam sensor. S32: In the chemical cleaning stage, the control system closes the first and second cleaning valves, opens the cleaning pneumatic valve, and draws in the cleaning liquid to the set level under the negative pressure of the evaporator. The solution circulation pneumatic valve is opened to start the circulation pump to circulate and clean for 30 to 60 minutes. After the cleaning time is reached, the cleaning waste liquid is drained and the system automatically switches back to the evaporation mode. As a further description of the technical solution of the present invention, the foam sensor detects the height of the foam layer in real time. When the detection signal exceeds the set threshold, the control system controls the defoamer inlet valve to open and inject defoamer in a pulse manner, thereby realizing closed-loop control of the foam.

[0015] The beneficial effects of this invention are as follows: This invention achieves automatic and seamless switching between three working modes—evaporation, drainage, and cleaning—through the timing control of pneumatic valve groups, effectively reducing the time consumed during mode switching, significantly reducing the frequency of manual intervention, and significantly improving the continuity and automation of system operation. Simultaneously, by utilizing a foam sensor in conjunction with a closed-loop control algorithm, on-demand dynamic addition of defoamer is achieved, solving the problems of delayed defoaming response and excessive agent consumption in traditional methods, and effectively reducing the false alarm probability of foam detection. Furthermore, the fan-shaped nozzle installed on the top of the evaporator, combined with high-pressure water, performs directional rinsing of the sensor surface. Combined with the anti-adhesion properties of the hydrophobic coating on the sensor surface, the problem of scale buildup on the sensor is effectively suppressed, the maintenance cycle is significantly extended, and measurement data drift is well controlled. Attached Figure Description

[0016] The invention will now be further described with reference to the accompanying drawings.

[0017] Figure 1 This is a schematic diagram of part of the multi-modal control system for the low-temperature heat pump evaporator of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figure 1 As shown, the present invention provides a multi-modal control system for a low-temperature heat pump evaporator, including an evaporator, a circulating pump, a filter press, a heating coil, a condensate discharge device, and a control system; The evaporator is connected to an inlet pipe, a circulation pipe, a drain pipe, a cleaning pipe, and a defoamer dosing pipe, with pneumatic valves installed on each pipe. The evaporator is equipped with a liquid level sensor and a foam sensor. The control system is a PLC or microcontroller, which is connected to the signals of each sensor and to the control terminal of each pneumatic valve. It is used to control the opening and closing sequence of each pneumatic valve according to the sensor signals, so as to realize the automatic switching of evaporation mode, cleaning mode, and draining mode. The cleaning pipeline includes a first cleaning valve and a second cleaning valve installed on the top of the evaporator. The outlet ends of the first cleaning valve and the second cleaning valve are respectively connected to fan-shaped nozzles. The fan-shaped nozzles are respectively positioned facing the surfaces of the liquid level sensor and the foam sensor, and are used to directionally rinse the sensor surfaces with high-pressure water. The defoamer filling pipeline is equipped with a defoamer inlet valve, and the signal output terminal of the foam sensor is connected to the control system. The control system controls the opening and closing of the defoamer inlet valve and the pulse injection time according to the detection signal of the foam sensor.

[0020] The pneumatic valve includes: The liquid inlet pneumatic valve V03 is installed on the liquid inlet pipeline and is used to control the liquid inlet of the wastewater to be evaporated; A solution circulation pneumatic valve V02 is installed on the circulation pipeline to control the solution circulation during the evaporation process; A pneumatic drain valve V05 is installed on the drain pipeline to control the discharge of the concentrate; A cleaning pneumatic valve V04 is installed on the cleaning pipeline to control the inlet of cleaning fluid; The first cleaning valve V06 and the second cleaning valve V07 are respectively installed on two branch pipes of the cleaning pipeline and are respectively connected to the fan-shaped nozzles facing the liquid level sensor and the foam sensor to control the spraying of high-pressure cleaning water. The defoamer inlet valve V01 is installed on the defoamer filling pipeline and is used to control the pulse injection of defoamer.

[0021] The heating coil maintains an evaporation temperature of 40±5℃.

[0022] Through the above technical solution, the present invention provides a multi-modal control system for a low-temperature heat pump evaporator, mainly comprising an evaporator tank, a circulating pump, a filter press, a heating coil, a condensate discharge device, and an electrical control system composed of a PLC or microcontroller. The evaporator tank is connected to an inlet pipe, a circulation pipe, a drain pipe, a cleaning pipe, and a defoamer filling pipe. Each pipe is equipped with a pneumatic valve: the inlet pipe has an inlet pneumatic valve V03 for controlling the inflow of wastewater to be evaporated; the circulation pipe has a solution circulation pneumatic valve V02 for controlling the circulation of the solution during evaporation; the drain pipe has a drain pneumatic valve V05 for controlling the discharge of concentrated liquid; the cleaning pipe has a cleaning pneumatic valve V04 for controlling the inflow of cleaning liquid, and a first cleaning valve V06 and a second cleaning valve V07 installed on the top of the evaporator tank; the defoamer filling pipe has a defoamer inlet valve V01. The evaporator is equipped with a liquid level sensor and a foam sensor. Both sensors have fan-shaped nozzles (60° spray angle) directly opposite their surfaces, connected to the outlets of V06 and V07, respectively. High-pressure water (0.3–0.5 MPa) is used for directional flushing and descaling. The control system is connected to the control terminals of all sensors and pneumatic valves. Based on the liquid level sensor signal, it controls the switching sequence of V03, V02, and V05, achieving seamless automatic switching between evaporation, drainage, and cleaning modes. Simultaneously, based on the foam sensor's detection signal (0–10V analog signal, amplitude > 5V indicates an over-limit), it controls V01 to precisely add defoamer in a pulse manner (2 seconds per pulse, 3 times in total), forming a closed-loop control. The sensor surface is also coated with... The nano-hydrophobic coating (contact angle > 160°) further reduces scale buildup.

[0023] The multimodal control logic of the control system is as follows: 1. Evaporation Operation Mode The evaporator is under negative pressure. The control system opens the inlet pneumatic valve V03 to draw the wastewater to be evaporated into the evaporator through negative pressure. The liquid level sensor LD01 detects the liquid level in real time. When the liquid level reaches the set liquid level value, the control system closes the inlet pneumatic valve V03, opens the solution circulation pneumatic valve V02, starts the circulation pump and filter press, and maintains the evaporation temperature through the heating coil to start the evaporation circulation of the solution. During the evaporation process, the solution in the evaporator gradually decreases. When the liquid level sensor LD01 detects that the liquid level is lower than the replenishment set value, the control system opens the inlet pneumatic valve V03 again to draw in replenished wastewater to the evaporator. The mixture is repeatedly circulated and concentrated until the evaporation tank reaches a low liquid level or the solution in the evaporator reaches the concentration endpoint judgment condition, at which point the evaporation mode ends.

[0024] The concentration endpoint determination condition is: when the cumulative number of times the condensate is discharged through the condensate discharge device reaches the preset discharge number threshold, it is determined that the solution in the evaporator is saturated and needs to be discharged.

[0025] Through the above technical solution, the evaporator is maintained under negative pressure. The control system first opens the inlet pneumatic valve V03 to draw the wastewater to be evaporated into the tank. When the liquid level sensor detects that the set liquid level value (e.g., 80%) has been reached, V03 is closed. Then, the solution circulation pneumatic valve V02 is opened and the circulation pump and filter press are started. The evaporation temperature of 40±5℃ is maintained by the heating coil for circulation evaporation. As evaporation proceeds, the liquid level in the tank gradually decreases. When it is lower than the replenishment set value (e.g., 30%), the system opens V03 again to replenish the liquid. This cycle of concentration is repeated. When the cumulative number of discharges by the condensate discharge device reaches the preset threshold (e.g., the preset discharge number threshold is 400 times, corresponding to a concentration rate of 92%), the solution is determined to be saturated, and the system automatically ends the evaporation mode and switches to the discharge mode.

[0026] 2. Drainage Mode When the concentration endpoint determination conditions are met, the system automatically enters the draining mode: the control system first controls the exhaust to release the negative pressure state of the evaporator; closes the liquid inlet pneumatic valve V03 and the solution circulation pneumatic valve V02, opens the liquid draining pneumatic valve V05, and restarts the circulation pump to drain the concentrated liquid in the evaporator to the waste liquid tank through the draining pipeline. The drainage process is controlled by the drainage time. Drainage stops when the preset drainage time value is reached or when the waste liquid tank reaches a high level.

[0027] Using the above technical solution, when the solution in the evaporator reaches the concentration endpoint (determined by the cumulative number of condensate discharges reaching a preset threshold), the system automatically enters the drainage mode. The control system first opens the exhaust valve to release the negative pressure in the evaporator and restore it to normal pressure. Simultaneously, it closes the inlet pneumatic valve V03 and the solution circulation pneumatic valve V02, prohibiting replenishment and circulation. Then, it opens the drain pneumatic valve V05 and restarts the circulation pump, forcibly draining the high-concentration concentrate in the evaporator into the wastewater tank via the drain pipeline. The drainage process employs dual protection logic for endpoint control: drainage stops when the drainage time reaches the preset drainage time value (e.g., 15-20 minutes) or when the wastewater tank level reaches the high-level interlock signal. After drainage, the system automatically enters the cleaning mode, thus completing the entire concentration cycle.

[0028] 3. Cleaning Mode After the system finishes draining, it automatically enters the cleaning mode, which includes a probe cleaning stage and a chemical cleaning stage. Probe cleaning stage: The control system opens the first cleaning valve V06 and the second cleaning valve V07. High-pressure water with a pressure of 0.3 to 0.5 MPa is used to rinse the surface of the liquid level sensor and the foam sensor through the fan-shaped nozzles. The cleaning time is controlled according to the preset cleaning time value. After the cleaning time is reached, the chemical cleaning stage is entered. Chemical cleaning stage: The control system closes the first cleaning valve V06 and the second cleaning valve V07, opens the cleaning pneumatic valve V04, controls the evaporator to be under negative pressure to draw in cleaning liquid to the set level, and then closes V04; opens the solution circulation pneumatic valve V02, starts the circulation pump, and performs circulation cleaning according to the preset chemical cleaning time; after the cleaning time is reached, closes the solution circulation pneumatic valve V02, opens the drain pneumatic valve V05, and discharges the cleaning waste liquid in the evaporator to the waste liquid tank; after emptying, the system automatically switches back to evaporation mode. During the chemical cleaning stage, the running time of the circulation pump is 30 to 60 minutes.

[0029] The foam sensor is a capacitive foam sensor or an optical foam sensor, used to detect changes in foam layer height or dielectric constant in real time and output a 0-10V analog signal; when the amplitude of the detected signal is greater than 5V, it is determined that the foam exceeds the standard.

[0030] The control system has a built-in foam detection delay confirmation logic: the defoaming action is only triggered when the foam sensor detection signal exceeds the set threshold and the duration reaches 5 seconds, so as to avoid malfunctions caused by momentary interference.

[0031] The defoamer inlet valve is controlled as follows: when the defoaming action is triggered, the control system controls the defoamer inlet valve to open in a pulse manner, opening for 2 seconds each time, for a total of 3 times, to inject defoamer into the evaporator; after the injection is completed, there is a 5-second delay, and the control system reads the foam sensor signal again for secondary detection. If the signal still exceeds the threshold, additional injection is performed.

[0032] The spray angle of the fan-shaped nozzle is 60°, and the installation position and orientation of the fan-shaped nozzle are set such that the spray coverage area completely covers the outer surface of the liquid level sensor and the foam sensor.

[0033] The outer surfaces of the liquid level sensor and the foam sensor are coated with... A nano-hydrophobic coating, wherein the contact angle of the hydrophobic coating is greater than 160°.

[0034] Using the above technical solution, the system automatically enters the cleaning mode after drainage. The entire cleaning process is divided into two stages: physical cleaning of the probe and chemical circulation cleaning. In the probe cleaning stage, the control system first opens the first cleaning valve V06 and the second cleaning valve V07 installed on the top of the evaporator. High-pressure water with a pressure of 0.3-0.5MPa is sprayed through fan-shaped nozzles with a spray angle of 60°, directly rinsing the surfaces of the level sensor and the foam sensor. The flow rate of a single nozzle is ≥12L / min, and the spraying continues for 20 seconds. The impact force of the high-pressure water flow thoroughly removes the salt crystals and organic scale adhering to the probe surface, ensuring the measurement accuracy of the sensor. After this stage, the control system closes V06 and V07. The chemical cleaning stage then begins: The control system maintains negative pressure in the evaporator by controlling the exhaust, opens the cleaning pneumatic valve V04, and uses the negative pressure to draw the cleaning agent (such as 5% citric acid solution, 2% sodium hydroxide solution, or 3% oxalic acid solution) prepared according to the solution type into the evaporator until the set liquid level (e.g., 30% of the tank capacity) is reached. Then, V04 is closed, and the solution circulation pneumatic valve V02 is opened and the circulation pump is started, allowing the cleaning solution to circulate within the evaporator and circulation pipelines. This chemically dissolves and cleans the inner wall of the tank, the heating coil, and the inside of the pipelines. The circulation cleaning time can be set as needed, from 30 to 60 minutes. After the cleaning time is reached, V02 is closed, and the drain pneumatic valve V05 is opened to discharge the cleaning waste liquid in the evaporator into the waste liquid tank. After emptying, the system automatically switches back to evaporation mode and enters the next evaporation and concentration cycle. The entire cleaning process requires no manual disassembly or shutdown, achieving online sensor cleaning and fully automatic system operation.

[0035] As a further optimization of the above cleaning mode, the control system also integrates a scaling trend prediction module and a cleaning parameter adaptive adjustment module. The scaling trend prediction module records the time required for the liquid level sensor signal to drift from the initial value to exceed the set error threshold within each complete evaporation cycle. This time is used as the scaling characteristic value of that evaporation cycle. The module also performs trend analysis on the scaling characteristic values ​​of multiple consecutive evaporation cycles. When it is determined that scaling is accelerating, an early warning signal is generated and output to the cleaning parameter adaptive adjustment module. After receiving the warning signal, the adaptive adjustment module for cleaning parameters dynamically adjusts at least one of the high-pressure water jet duration, high-pressure water jet pressure, and chemical cleaning cycle duration for the current cleaning cycle.

[0036] The scaling trend prediction module stores the scaling characteristic value of the first complete evaporation cycle after the system is put into operation for the first time or after the sensor is manually calibrated as the baseline scaling characteristic value; the scaling characteristic value of each subsequent evaporation cycle is compared with the baseline scaling characteristic value to calculate the scaling acceleration coefficient, which is the ratio obtained by dividing the difference between the baseline scaling characteristic value and the current cycle scaling characteristic value by the baseline scaling characteristic value.

[0037] When the scaling acceleration coefficient shows an increasing trend for two or more consecutive evaporation cycles, the scaling trend prediction module determines that scaling is accelerating.

[0038] The adaptive adjustment module for cleaning parameters uses a tiered adjustment method. Upon receiving the first warning signal, it increases the high-pressure water jet duration by a first increment and the high-pressure water jet pressure by a second increment. If the scaling acceleration coefficient in the next evaporation cycle continues to increase, it further increases the chemical cleaning cycle duration by a third increment. The first increment is 5–10 seconds, the second increment is 0.05–0.1 MPa, and the third increment is 10–20 minutes.

[0039] The system, based on the above technical solution, also includes a scaling trend prediction module and a cleaning parameter adaptive adjustment module, both integrated within the control system. The scaling trend prediction module dynamically monitors and determines the scaling rate and trend of the liquid level sensor within the evaporator. During long-term operation, the surface of the liquid level sensor gradually scales due to salt crystallization or organic matter deposition, causing the output signal to drift. The more severe the scaling, the faster the signal drift rate, and the shorter the time required for the sensor to drift from its initial value to exceeding the allowable error threshold. Based on this mechanism, the scaling trend prediction module records the time taken for the liquid level sensor signal to change from its initial value to exceeding the set error threshold within each complete evaporation cycle, defining this time as the scaling characteristic value for that cycle. The scaling characteristic values ​​acquired during the first complete evaporation cycle after the system is first put into operation or after the sensor has been manually calibrated are stored as baseline scaling characteristic values.

[0040] The scaling trend prediction module performs trend analysis on scaling characteristic values ​​across multiple consecutive evaporation cycles. Specifically, it compares the scaling characteristic values ​​of subsequent evaporation cycles with a baseline scaling characteristic value to calculate a scaling acceleration coefficient. This coefficient is the ratio of the difference between the baseline scaling characteristic value and the current cycle's scaling characteristic value to the baseline scaling characteristic value. When the scaling acceleration coefficient shows an increasing trend for two or more consecutive evaporation cycles, the scaling trend prediction module determines that scaling is accelerating, generates an early warning signal, and transmits it to the cleaning parameter adaptive adjustment module.

[0041] The scaling trend prediction module can also obtain the false alarm frequency of the foam sensor over multiple consecutive evaporation cycles as an auxiliary judgment condition. The surface of the foam sensor also presents a risk of scaling, and the increasing trend of its false alarm frequency can reflect, to some extent, the deterioration of the overall scaling condition inside the evaporator. When the false alarm frequency shows an upward trend, this information, together with the deceleration rate of the aforementioned scaling characteristic values, is used to generate an early warning signal to improve the reliability of scaling trend judgment.

[0042] Upon receiving a warning signal, the adaptive cleaning parameter adjustment module dynamically adjusts the cleaning parameters for the current cleaning cycle. The adjusted cleaning parameters include at least one of the following: high-pressure water jet duration, high-pressure water jet pressure, and chemical cleaning cycle duration. The module employs a tiered adjustment strategy: upon receiving the first warning signal, the module increases the high-pressure water jet duration by a first increment and the high-pressure water jet pressure by a second increment. If the scaling acceleration coefficient continues to increase in the next evaporation cycle, indicating that the existing adjustment is insufficient to effectively suppress scaling acceleration, the module further increases the chemical cleaning cycle duration by a third increment.

[0043] The first increment is 5 to 10 seconds, the second increment is 0.05 to 0.1 MPa, and the third increment is 10 to 20 minutes. The specific increment values ​​can be set by the operator based on the actual wastewater quality and system operating conditions.

[0044] The advantage of this tiered adjustment strategy is that physical cleaning (high-pressure water jet) is prioritized over chemical cleaning (cleaning fluid circulation). Generally, increasing the intensity and duration of high-pressure water jet is sufficient to effectively remove scale from the sensor surface without consuming additional chemical agents. Chemical cleaning intensity is only adjusted when the accelerating scaling trend is still not effectively curbed after physical cleaning adjustments, thus ensuring cleaning effectiveness while minimizing cleaning costs.

[0045] A smart cleaning method for a multimodal control system of a low-temperature heat pump evaporator, the smart cleaning method comprising the following steps: S1: The control system opens the inlet pneumatic valve to draw in wastewater to be evaporated under negative pressure in the evaporator. When the liquid level sensor detects that the set liquid level value has been reached, the inlet pneumatic valve is closed, the solution circulation pneumatic valve is opened, and the circulation pump and filter press are started to begin the evaporation cycle. During the evaporation process, when the liquid level is lower than the replenishment set value, the inlet pneumatic valve is opened again to replenish the liquid. When the cumulative number of condensate discharges reaches the preset discharge number threshold, the evaporation mode ends. S2: The control system controls the evaporator to release the negative pressure, closes the liquid inlet pneumatic valve and the solution circulation pneumatic valve, opens the liquid draining pneumatic valve and starts the circulation pump to drain the concentrate to the waste liquid tank. The liquid draining stops when the liquid draining time reaches the preset liquid draining time value or when the waste liquid tank reaches the high liquid level. S3: The system automatically enters cleaning mode after drainage is complete. S31: During the probe cleaning stage, the control system opens the first cleaning valve and the second cleaning valve. High-pressure water with a pressure of 0.3 to 0.5 MPa is flushed through a fan-shaped nozzle with a spray angle of 60° for 20 seconds to clean the surface of the level sensor and the foam sensor. S32: In the chemical cleaning stage, the control system closes the first and second cleaning valves, opens the cleaning pneumatic valve, and draws in the cleaning liquid to the set level under the negative pressure of the evaporator. The solution circulation pneumatic valve is opened to start the circulation pump to circulate and clean for 30 to 60 minutes. After the cleaning time is reached, the cleaning waste liquid is drained and the system automatically switches back to the evaporation mode. The following are specific examples of the present invention. Example 1 This embodiment uses heavy metal cleaning wastewater from an electroplating company as the treatment object. The main components of the wastewater are copper ions, nickel ions, and surfactants, with a TDS concentration of 35,000 mg / L, a COD concentration of 1,200 mg / L, and a pH value of 3.5.

[0046] The system configuration is as follows: Evaporator heat exchange area 25m² 2 The cylinder has a diameter of 1200mm, a height of 1700mm, and a wall thickness of 5mm. It is made of 316L stainless steel, with titanium for the internal parts in contact with the liquid. The operating pressure is -0.09MPa. The cooling water circulation pump has a power of 7.5kW and is equipped with a vacuum ejector, achieving a vacuum degree of -0.096MPa. The compressor unit consists of two 20P compressors, including an air-cooled compressor condenser and evaporator. The cooling water circulation tank has a volume of 0.35m³. 3 It has a built-in 4kW preheater. The distilled water pump has a flow rate of 2.0m³ / h. 3 The pump has a flow rate of 12L / min per hour, a head of 20m, and a power of 0.5kW. It features a fan-shaped nozzle with a spray angle of 60°, a single nozzle flow rate of 12L / min, a working water pressure of 0.4MPa, and a quantity of 2 nozzles. The control system uses a Siemens S7-1200 PLC and is equipped with a 7-inch touchscreen.

[0047] The operation process is as follows: The evaporator is maintained under negative pressure. The inlet pneumatic valve V03 is opened, and wastewater is drawn into the tank under negative pressure. The liquid level sensor LD01 monitors the liquid level in real time, and closes V03 when the tank reaches 80% capacity. The solution circulation pneumatic valve V02 is opened, and the circulation pump and filter press are started. The heating coil maintains the evaporation temperature at 40℃, and the evaporation rate is 250L / h.

[0048] During evaporation, foam gradually forms. The foam sensor LS01 is capacitive, detecting the change in dielectric constant corresponding to the foam layer height and outputting a 0-10V analog signal. A signal amplitude greater than 5V corresponds to a foam layer height of 8cm. If the signal exceeds the limit for 5 seconds, the PLC determines that the foam is excessive and triggers a defoaming action. The defoamer inlet valve V01 opens in a pulse manner, opening for 2 seconds each time, for a total of 3 times, with a 1-second interval between each opening, injecting polysiloxane-based defoamer. After a 5-second delay after injection, the PLC reads the sensor signal again for a second detection. If the signal is still greater than 5V, an additional pulse cycle is injected.

[0049] When the condensate drain device has discharged condensate 400 times cumulatively, the system determines that the solution in the evaporator is saturated, corresponding to a concentration rate of 92%, and automatically switches to drain mode. The control system opens the vent valve to release the negative pressure in the evaporator to atmospheric pressure, closes VO3 and VO2, opens the drain pneumatic valve VO5, and starts the circulation pump to run for 15 minutes to drain the concentrate into the waste liquid tank. Drainage stops after the designated time has elapsed.

[0050] After the drainage is complete, the system automatically enters the cleaning mode: Probe cleaning stage: Open the first cleaning valve V06 and the second cleaning valve V07. 0.4MPa high-pressure water is sprayed directly onto the surfaces of the level sensor and foam sensor through two fan-shaped nozzles for 20 seconds to rinse away the scale buildup on the sensor surfaces. After the cleaning time is up, close V06 and V07.

[0051] Chemical cleaning stage: Open the cleaning pneumatic valve V04, and the evaporator will draw in 5% citric acid cleaning solution under negative pressure until the liquid level reaches 30% of the tank capacity, then close V04. Open the solution circulation pneumatic valve V02 and start the circulation pump to circulate the solution for 30 minutes. After the cleaning time is up, close V02 and open the drain pneumatic valve V05 to discharge the cleaning waste liquid into the waste liquid tank. After emptying, the system will automatically switch back to evaporation mode.

[0052] In this embodiment, the system operated continuously for 500 hours with a liquid level sensor measurement error of ±2.8%, and no downtime for maintenance due to sensor scaling occurred. The average daily consumption of defoamer was 73L. The system operated fully automatically without the need for manual mode switching.

[0053] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A multi-modal control system for a low-temperature heat pump evaporator, comprising an evaporator tank, a circulating pump, a filter press, a heating coil, a condensate drain device, and a control system, characterized in that: The evaporator is connected to an inlet pipe, a circulation pipe, a drain pipe, a cleaning pipe, and a defoamer filling pipe. The inlet pipe is equipped with an inlet pneumatic valve, the circulation pipe is equipped with a solution circulation pneumatic valve, the drain pipe is equipped with a drain pneumatic valve, the cleaning pipe is equipped with a cleaning pneumatic valve, a first cleaning valve, and a second cleaning valve, and the defoamer filling pipe is equipped with a defoamer inlet valve. The evaporator is equipped with a liquid level sensor and a foam sensor. The signal output terminals of the liquid level sensor and the foam sensor are connected to the control system. The control signal output terminals of the control system are respectively connected to the control terminals of each pneumatic valve. The outlet ends of the first cleaning valve and the second cleaning valve are respectively connected to fan-shaped nozzles, which are respectively positioned facing the surfaces of the liquid level sensor and the foam sensor, for directional rinsing of the sensor surfaces with high-pressure water. In the evaporation operation mode, the control system controls the timing of the inlet pneumatic valve and the circulation pneumatic valve based on the liquid level sensor signal. When the cumulative number of condensate discharges reaches a preset threshold, the control system automatically switches the system to the drainage mode and automatically switches to the cleaning mode after the drainage is completed. In the probe cleaning stage of the cleaning mode, the control system simultaneously opens the first cleaning valve and the second cleaning valve to perform high-pressure water directional flushing on the liquid level sensor and the foam sensor to ensure the accuracy of liquid level detection and foam detection in the next evaporation cycle. The control system controls the defoamer inlet valve to open in a pulse manner based on the detection signal of the foam sensor, thereby achieving closed-loop precise dosing of the defoamer.

2. The multi-modal control system for a low-temperature heat pump evaporator according to claim 1, characterized in that, The multimodal control logic of the control system includes an evaporation operation mode. In the evaporation operation mode, the evaporator is under negative pressure. The control system opens the liquid inlet pneumatic valve, and the liquid level sensor detects the liquid level in real time. When the liquid level reaches the set liquid level value, the control system closes the liquid inlet pneumatic valve, opens the solution circulation pneumatic valve, starts the circulation pump and filter press, and begins the evaporation circulation of the solution. When the liquid level sensor detects that the liquid level is lower than the replenishment set value, the control system opens the liquid inlet pneumatic valve again to replenish the evaporator.

3. The multi-modal control system for a low-temperature heat pump evaporator according to claim 2, characterized in that, In the evaporation operation mode, when the cumulative number of times the condensate is discharged through the condensate discharge device reaches the preset discharge number threshold, it is determined that the solution in the evaporator is saturated, and the system switches to the discharge mode.

4. The multi-modal control system for a low-temperature heat pump evaporator according to claim 1, characterized in that, The multimodal control logic of the control system includes a drainage mode, in which: the control system controls the evaporator to release the negative pressure state, closes the inlet pneumatic valve and the solution circulation pneumatic valve, opens the drainage pneumatic valve, starts the circulation pump, and drains the concentrated liquid in the evaporator to the waste liquid tank; drainage stops when the drainage time reaches the preset drainage time value or the waste liquid tank reaches the high liquid level.

5. The multi-modal control system for a low-temperature heat pump evaporator according to claim 1, characterized in that, The multimodal control logic of the control system includes a cleaning mode, which includes a probe cleaning stage and a chemical cleaning stage. During the probe cleaning stage, the control system opens the first cleaning valve and the second cleaning valve, and high-pressure water with a pressure of 0.3 to 0.5 MPa is used to rinse the surface of the liquid level sensor and the foam sensor through the fan-shaped nozzle. The cleaning time is controlled according to the preset cleaning time value. During the chemical cleaning stage, the control system closes the first cleaning valve and the second cleaning valve, opens the cleaning pneumatic valve, controls the evaporator to be in a negative pressure state to draw in the cleaning liquid to the set liquid level, opens the solution circulation pneumatic valve to start the circulation pump, and performs circulation cleaning according to the preset chemical cleaning time. After the cleaning time is reached, the cleaning waste liquid is discharged. The spray angle of the fan-shaped nozzle is 60°, and the installation position of the fan-shaped nozzle is set so that the spray coverage area completely covers the outer surface of the liquid level sensor and the foam sensor; the water pressure of the high-pressure water is 0.3 to 0.5 MPa, the flow rate of a single nozzle is ≥12 L / min, and the duration of the probe cleaning stage is 20 seconds.

6. The multi-modal control system for a low-temperature heat pump evaporator according to claim 1, characterized in that, The foam sensor is a capacitive foam sensor or an optical foam sensor, used to detect changes in foam layer height or dielectric constant in real time and output a 0-10V analog signal; when the amplitude of the detected signal is greater than 5V, it is determined that the foam exceeds the standard.

7. A multi-modal control system for a low-temperature heat pump evaporator according to claim 6, characterized in that, The control system has a built-in foam detection delay confirmation logic: the defoaming action is triggered only when the foam sensor detection signal exceeds the set threshold and the duration reaches 5 seconds; after the defoaming action is triggered, the control system controls the defoamer inlet valve to open in a pulse manner, opening for 2 seconds each time, for a total of 3 times; After injection, a second check is performed after a 5-second delay. If the signal still exceeds the threshold, additional injection is performed.

8. The multi-modal control system for a low-temperature heat pump evaporator according to claim 1, characterized in that, The outer surfaces of the liquid level sensor and the foam sensor are coated with... A nano-hydrophobic coating, wherein the contact angle of the hydrophobic coating is greater than 160°; The heating coil maintains an evaporation temperature of 40±5℃; the preset threshold for the number of drainage cycles is 400; and the running time of the circulating pump during the chemical cleaning stage is 30 to 60 minutes.

9. A smart cleaning method for a low-temperature heat pump evaporator multimodal control system based on any one of claims 1 to 8, characterized in that, The method includes the following steps: S1: The control system opens the inlet pneumatic valve to draw in wastewater to be evaporated under negative pressure in the evaporator. When the liquid level sensor detects that the set liquid level has been reached, the inlet pneumatic valve is closed, the solution circulation pneumatic valve is opened, and the circulation pump and filter press are started to begin the evaporation cycle. During the evaporation process, when the liquid level is lower than the replenishment set value, the inlet pneumatic valve is opened again to replenish the liquid. When the cumulative number of condensate discharges reaches the preset discharge number threshold, the evaporation mode ends. S2: The control system controls the evaporator to release the negative pressure, closes the liquid inlet pneumatic valve and the solution circulation pneumatic valve, opens the liquid draining pneumatic valve and starts the circulation pump to drain the concentrate to the waste liquid tank. The liquid draining stops when the liquid draining time reaches the preset liquid draining time value or when the waste liquid tank reaches the high liquid level. S3: The system automatically enters cleaning mode after drainage is complete. S31: During the probe cleaning stage, the control system opens the first cleaning valve and the second cleaning valve. High-pressure water with a pressure of 0.3 to 0.5 MPa is flushed through a fan-shaped nozzle with a spray angle of 60° for 20 seconds to clean the surface of the level sensor and the foam sensor. S32: In the chemical cleaning stage, the control system closes the first and second cleaning valves, opens the cleaning pneumatic valve, and draws in the cleaning liquid to the set level under the negative pressure of the evaporator. The solution circulation pneumatic valve is opened to start the circulation pump to circulate and clean for 30 to 60 minutes. After the cleaning time is reached, the cleaning waste liquid is drained, and the system automatically switches back to the evaporation mode.

10. The intelligent cleaning method for the multi-modal control system of a low-temperature heat pump evaporator according to claim 9, characterized in that, The foam sensor detects the height of the foam layer in real time. When the detection signal exceeds the set threshold, the control system controls the defoamer inlet valve to open and inject defoamer in a pulse manner, thereby realizing closed-loop control of the foam.

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