Control method and related device for steam condensate waste heat recovery and waste water heating

Abstract

The invention discloses a control method for steam condensate waste heat recovery and waste water heating, a control device for steam condensate waste heat recovery and waste water heating, control equipment and a computer readable storage medium. The thermal load and the logarithmic average temperature difference are calculated based on the energy conservation principle, and the needed heat exchange area is calculated through a logarithmic average temperature difference method. A flow combination scheme of the plate heat exchanger is determined according to the heat exchange area and the flow parameters, a steam condensate side adopts a single flow, and a waste water side adopts asymmetric configuration of double flows or multiple flows so as to adapt to the flow difference of the two sides. In addition, a real-time monitoring mechanism is further established, when the total heat transfer coefficient is decreased by more than 10%, a cleaning program is automatically triggered, continuous and stable operation of the system is guaranteed, and efficient utilization of waste heat resources is achieved.

Description

Technical Field

[0001] This invention pertains to waste heat recovery technology in the chemical industry, and more specifically, relates to a control method for waste heat recovery of steam condensate and wastewater heating, a control device for waste heat recovery of steam condensate and wastewater heating, a control equipment, and a computer-readable storage medium. Background Technology

[0002] In energy-intensive industrial production processes such as polysilicon, chemical, and metallurgical manufacturing, steam is widely used as a crucial heat source in various process heating stages. The condensate produced after steam use typically still carries sensible heat of 60°C to 90°C; direct discharge would result in significant energy waste. Simultaneously, the reverse osmosis process in industrial wastewater treatment systems has high requirements for influent water temperature; increasing the temperature can significantly improve membrane flux and permeate efficiency. Therefore, utilizing the waste heat from steam condensate to preheat wastewater, achieving synergistic utilization of thermal energy and water resources, has become an important way for enterprises to reduce costs and increase efficiency.

[0003] In related technologies, waste heat recovery technology mainly uses plate heat exchangers for indirect heat exchange. However, in actual engineering projects involving heat exchange between steam condensate and wastewater, there are generally two defects: First, there is a serious imbalance in flow rate, with the flow rate of steam condensate on the hot side being much smaller than that of wastewater on the cold side, resulting in uneven flow velocities and pressure drop mismatch on both sides. Traditional equal flow configurations cannot take into account the flow characteristics on both sides, resulting in low heat exchange efficiency. Second, there is a lack of scientific design and calculation models. In engineering practice, for the condition of heating a large flow of low-temperature medium from a small flow high-temperature heat source, there is a lack of targeted criteria for selecting the overall heat transfer coefficient, temperature drop control range, and process combination optimization methods, leading to blind equipment selection, wasted investment, or unstable operation.

[0004] Therefore, how to achieve efficient and stable heat exchange between a small-flow-rate high-temperature heat source and a large-flow-rate low-temperature medium, and how to increase the water production of the subsequent reverse osmosis system by increasing the wastewater temperature, are key issues of concern to those skilled in the art. Summary of the Invention

[0005] The purpose of this application is to provide a control method, a control device, a control equipment, and a computer-readable storage medium for recovering waste heat from steam condensate and heating wastewater, to achieve efficient and stable heat exchange between a small-flow-rate high-temperature heat source and a large-flow-rate low-temperature medium, and to increase the water production of the subsequent reverse osmosis system by increasing the wastewater temperature.

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a control method for waste heat recovery from steam condensate and wastewater heating, comprising: S1 collects the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. S2, based on the principle of energy conservation, calculate the heat load according to the hot side inlet temperature, hot side outlet temperature, hot side flow rate of the steam condensate and the cold side inlet temperature, cold side outlet temperature, cold side flow rate of the wastewater, and calculate the logarithmic mean temperature difference based on the hot side inlet temperature, hot side outlet temperature, cold side inlet temperature, and cold side outlet temperature. S3. Calculate the required heat exchange area using the logarithmic mean temperature difference method based on the overall heat transfer coefficient, the logarithmic mean temperature difference, and the heat load. S4. Based on the heat exchange area and flow parameters, determine the process combination scheme of the plate heat exchanger; wherein, the process combination scheme includes a single process on the steam condensate side and a dual or multiple process on the wastewater side. S5, according to the process combination scheme, a waste heat recovery system is set up, and the flow velocity of the steam condensate side is controlled within the range of 0.2m / s to 0.8m / s, the flow velocity of the wastewater side is controlled within the range of 0.3m / s to 0.5m / s, and the pressure drop of the wastewater side is controlled to be less than or equal to 30kPa; S6. Monitor the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, trigger the cleaning procedure.

[0007] Optionally, S1 includes: collecting the hot-side inlet temperature, the hot-side outlet temperature, the cold-side inlet temperature, and the cold-side outlet temperature through a temperature sensor; and collecting the hot-side flow rate of the steam condensate and the cold-side flow rate of the wastewater through a flow meter, with a sampling period of 1 second to 10 seconds.

[0008] Optionally, in step S3, the overall heat transfer coefficient is determined according to the process combination scheme: when a single process is used on the steam-condensate side, the value of U is in the range of 2500 W / (m³). 2 ·K) to 3500W / (m 2 ·K); When a dual-pass system is used on the steam condensate side, the value of U ranges from 3000 W / (m³). 2 ·K) to 4000W / (m 2 ·K).

[0009] Optionally, S5 includes: adjusting the frequency of the wastewater-side circulation pump through a frequency conversion control unit to control the wastewater-side flow rate; and adjusting the steam condensate-side flow rate through a regulating valve to control the steam condensate-side flow rate.

[0010] Optionally, S5 further includes: when the cold-side outlet temperature of the wastewater deviates from the target temperature by more than ±2℃, dynamically adjusting the steam condensate flow rate or the frequency of the wastewater-side circulation pump to restore the cold-side outlet temperature to the target temperature range.

[0011] Optionally, it also includes: inputting the heat-exchanged wastewater into the reverse osmosis system, and adjusting the operating pressure of the reverse osmosis system according to the increase in wastewater temperature relative to the initial temperature, so as to maintain the desalination rate within a set range; wherein, when the increase is 10°C, the operating pressure is reduced by 5% to 10%.

[0012] Optionally, the method is applied to wastewater treatment systems in the polysilicon, chemical, or metallurgical industries, and the ratio of the hot-side flow rate of the steam condensate to the cold-side flow rate of the wastewater is 1:5 to 1:20, and the single-plate area of ​​the plate heat exchanger is 0.3 m². 2 up to 0.8m 2 .

[0013] This application also provides a control device for waste heat recovery of steam condensate and heating of wastewater, comprising: The data acquisition module is used to collect the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. The parameter calculation module is used to calculate the heat load based on the principle of energy conservation, according to the hot-side inlet temperature, hot-side outlet temperature, hot-side flow rate of the steam condensate and the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of the wastewater, and to calculate the logarithmic mean temperature difference based on the hot-side inlet temperature, hot-side outlet temperature, cold-side inlet temperature, and cold-side outlet temperature. The heat transfer area calculation module is used to calculate the required heat transfer area based on the overall heat transfer coefficient, the logarithmic mean temperature difference, and the heat load using the logarithmic mean temperature difference method. The process scheme determination module is used to determine the process combination scheme of the plate heat exchanger based on the heat exchange area and flow parameters; wherein, the process combination scheme includes a single process on the steam condensate side and a dual or multiple process on the wastewater side. The system setting module is used to set up the waste heat recovery system according to the process combination scheme, and control the flow velocity of the steam condensate side within the range of 0.2m / s to 0.8m / s, control the flow velocity of the wastewater side within the range of 0.3m / s to 0.5m / s, and control the pressure drop of the wastewater side to be less than or equal to 30kPa. The cleaning module is used to monitor the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, the cleaning procedure is triggered.

[0014] This application also provides a control device, including: Memory, used to store computer programs; A processor is used to implement the control method described above when executing the computer program.

[0015] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the control method described above.

[0016] This application provides a control method for waste heat recovery of steam condensate and wastewater heating, comprising: S1 collects the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. S2, based on the principle of energy conservation, calculate the heat load according to the hot side inlet temperature, hot side outlet temperature, hot side flow rate of the steam condensate and the cold side inlet temperature, cold side outlet temperature, cold side flow rate of the wastewater, and calculate the logarithmic mean temperature difference based on the hot side inlet temperature, hot side outlet temperature, cold side inlet temperature, and cold side outlet temperature. S3. Calculate the required heat exchange area using the logarithmic mean temperature difference method based on the overall heat transfer coefficient, the logarithmic mean temperature difference, and the heat load. S4. Based on the heat exchange area and flow parameters, determine the process combination scheme of the plate heat exchanger; wherein, the process combination scheme includes a single process on the steam condensate side and a dual or multiple process on the wastewater side. S5, according to the process combination scheme, a waste heat recovery system is set up, and the flow velocity of the steam condensate side is controlled within the range of 0.2m / s to 0.8m / s, the flow velocity of the wastewater side is controlled within the range of 0.3m / s to 0.5m / s, and the pressure drop of the wastewater side is controlled to be less than or equal to 30kPa; S6. Monitor the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, trigger the cleaning procedure.

[0017] It has the following beneficial effects: By precisely calculating the heat exchange area and optimizing the process combination scheme, the flow rate mismatch caused by the steam condensate flow rate being much smaller than the wastewater flow rate was solved. This ensured sufficient flow velocity on the hot side to enhance heat exchange and prevent fouling, while keeping the flow velocity on the cold side within a reasonable range to avoid excessive pressure drop. The wastewater temperature increased after being preheated by waste heat, improving the water flux and desalination performance of the subsequent reverse osmosis membrane. Under the same water production conditions, the operating pressure of the reverse osmosis system could be reduced, decreasing the energy consumption of the high-pressure pump. Simultaneously, by monitoring changes in the heat transfer coefficient in real time, fouling of the heat exchanger could be detected promptly, triggering the cleaning process and maintaining the long-term stable and efficient operation of the system. Overall, this invention achieves the cascade utilization of waste heat resources, reduces the overall energy consumption and operating costs of the wastewater treatment system, and improves the economic and environmental benefits of enterprises, demonstrating significant engineering application value. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 A flowchart of a control method for recovering waste heat from steam condensate and heating wastewater, provided as an embodiment of this application; Figure 2 This application provides a control device for recovering waste heat from steam condensate and heating wastewater. Figure 3 This is a schematic diagram of the control device provided in an embodiment of this application. Detailed Implementation

[0020] The purpose of this application is to provide a control method, a control device, a control equipment, and a computer-readable storage medium for recovering waste heat from steam condensate and heating wastewater, to achieve efficient and stable heat exchange between a small-flow-rate high-temperature heat source and a large-flow-rate low-temperature medium, and to increase the water production of the subsequent reverse osmosis system by increasing the wastewater temperature.

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] The following embodiment illustrates a control method for waste heat recovery of steam condensate and heating of wastewater provided in this application.

[0023] Please refer to Figure 1 , Figure 1 This is a flowchart of a control method for recovering waste heat from steam condensate and heating wastewater, provided as an embodiment of this application.

[0024] The core equipment of the waste heat recovery system is a plate heat exchanger, made of 316L stainless steel to withstand the corrosive environment of industrial wastewater. The plates of the plate heat exchanger adopt a herringbone corrugated structure, and the plate spacing is selected according to the suspended solids content of the wastewater. In this embodiment, plates with a spacing of 3mm to 5mm are selected to balance heat transfer efficiency and anti-clogging performance. The plate thickness is 0.5mm to 0.8mm, and the area of ​​a single plate is selected according to the on-site installation space and flow requirements.

[0025] Regarding pipeline configuration, a PT100 platinum resistance temperature sensor is installed on the steam condensate inlet pipe, with a temperature measurement range of 0℃ to 150℃ and a standard 4-20mA current signal output. The outlet pipe is also equipped with a temperature sensor of the same specification. One temperature sensor is installed on each of the wastewater inlet and outlet pipes, with a temperature measurement range of 0℃ to 100℃. All temperature sensors are installed on straight pipe sections, at least 10 times the pipe diameter away from bends, valves, and other flow-obstructing components to ensure accurate temperature measurements.

[0026] Flow measurement is performed using an electromagnetic flow meter. The flow meter range for the steam condensate side is selected to be 1.2 to 1.5 times the maximum flow rate on the hot side, and the flow meter range for the wastewater side is selected to be 1.2 times the maximum flow rate on the cold side. The flow meter is installed on a horizontal or vertical pipe, with sufficient straight pipe sections upstream and downstream. The upstream straight pipe section is no less than 5 times the pipe diameter, and the downstream straight pipe section is no less than 2 times the pipe diameter.

[0027] An electric regulating valve is installed on the steam condensate side. The valve diameter is selected according to the pipe size, the adjustment ratio is not less than 30:1, and the response time is less than 15 seconds. The regulating valve adopts an equal percentage characteristic to achieve precise flow control. A centrifugal circulating pump is installed on the wastewater side. The pump head and flow rate are selected according to the system resistance and flow requirements. The motor is equipped with a frequency converter, and the frequency range covers 30Hz to 50Hz.

[0028] For pressure monitoring, pressure transmitters are installed at the wastewater inlet and outlet pipes, with a measurement range of 0 to 100 kPa. The system pressure drop is calculated by differential pressure.

[0029] The control system uses a PLC (Programmable Logic Controller) as the core control unit. An industrial-grade PLC is selected, equipped with analog input modules to receive signals from temperature sensors and flow meters, and analog output modules to control the opening degree of the regulating valve and the frequency of the frequency converter. The PLC's scan cycle is set to 100ms to 500ms to ensure real-time response.

[0030] The host computer system uses configuration software to develop a human-machine interface that displays parameters such as temperature, flow rate, and pressure drop at each measuring point in real time, plots historical trend curves, sets alarm thresholds, and records alarm events. Operators can adjust control parameters, such as target temperature, upper and lower limits of flow rate, and cleaning trigger conditions, through the host computer interface.

[0031] The data acquisition cycle is set in the PLC program. Temperature and flow signals are acquired and stored in the data buffer at fixed time intervals. To filter out measurement noise, a moving average filtering algorithm is used, taking the average of several consecutive sampled values ​​as the valid data.

[0032] In this embodiment, the method may include: S1 collects the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. After the system is powered on, the PLC begins executing the data acquisition program. During each sampling cycle, the PLC reads the current signals from the temperature sensor and flow meter from the analog input module, converts them into digital values ​​after A / D conversion, and sets signal conversion formulas in the program to convert the current signals into actual temperature and flow rates.

[0033] To ensure data reliability, the program includes logic for determining data validity. When the temperature sensor signal is below 4mA or above 20mA, a sensor malfunction is detected, and the system issues a fault alarm and activates a backup sensor or enters a safety mode. When the flow meter signal is abnormal, the system retains the previous flow rate value or calculates the flow rate based on the control valve opening and pump frequency.

[0034] After data acquisition, the data enters the filtering stage, where first-order lag filtering or moving average filtering algorithms are used to eliminate measurement fluctuations. The time constant of the filtering algorithm can be adjusted according to the stability of the operating conditions. A larger time constant is used when the operating conditions are stable to smooth the data, while a smaller time constant is used when the operating conditions change rapidly to improve the response speed.

[0035] S2, based on the principle of energy conservation, calculates the heat load according to the hot side inlet temperature, hot side outlet temperature, hot side flow rate of steam condensate and the cold side inlet temperature, cold side outlet temperature, cold side flow rate of wastewater, and calculates the logarithmic mean temperature difference based on the hot side inlet temperature, hot side outlet temperature, cold side inlet temperature, and cold side outlet temperature. The PLC control program includes a function block for calculating heat load, which calculates the system's heat exchange power based on the principle of energy conservation. This function block reads the inlet and outlet temperatures, flow rate, and medium properties (density and specific heat capacity) from the data buffer. The medium properties can be corrected for temperature; the program has a built-in property table, and the density and specific heat capacity at the current temperature are obtained through interpolation.

[0036] After the heat load calculation is completed, the program performs an energy balance check. It calculates the heat absorbed by the cold side using cold-side parameters and compares the difference between the heat released by the hot side and the heat absorbed by the cold side. If the difference exceeds a set threshold (typically 10% to 15% of the total heat load), the system determines it as a measurement anomaly or excessive heat loss and issues a warning to maintenance personnel for inspection.

[0037] The logarithmic mean temperature difference calculation function block calculates ΔTLM based on the countercurrent heat transfer model. Boundary conditions are set in the program to use the arithmetic mean temperature difference instead of the logarithmic mean temperature difference when the temperature difference is close to zero, thus avoiding calculation overflow. The calculation results are used for subsequent heat transfer area estimation and heat transfer coefficient monitoring.

[0038] S3, calculate the required heat exchange area using the logarithmic mean temperature difference method based on the overall heat transfer coefficient, logarithmic mean temperature difference, and heat load; During the system design phase, a suitable overall heat transfer coefficient is selected based on the process conditions. The selection of the overall heat transfer coefficient needs to consider factors such as the process flow combination scheme, medium flow rate, and fouling thermal resistance. For heat exchange between steam condensate and wastewater, the program has built-in empirical correlations to estimate the convective heat transfer coefficient based on parameters such as flow rate and Reynolds number, thereby deducing a reasonable range for the overall heat transfer coefficient.

[0039] The heat exchange area is calculated using the logarithmic mean temperature difference method. A safety factor is set in the program, and the actual area configured is the calculated area multiplied by the safety factor. The size of the safety factor is determined based on factors such as operating condition fluctuations, fouling growth rate, and future expansion needs, and is generally taken as 1.1 to 1.2.

[0040] The calculation formula can be: .

[0041] Where A is the heat exchange area, in m². 2 U is the overall heat transfer coefficient, with units of W / (m²). 2 ·K); Q is the heat load, in kW; This is the logarithmic mean temperature difference, in °C. When selecting a heat exchanger, the required number of plates is determined based on the calculated total heat exchange area and the area of ​​each plate. The number of plates should be an even number and meet the requirements of the flow combination. For example, a single flow on the hot side requires at least two plates to form one heat exchange channel, while a dual flow on the cold side requires at least four plates to form two heat exchange channels.

[0042] S4. Based on the heat exchange area and flow parameters, determine the process combination scheme of the plate heat exchanger; wherein, the process combination scheme includes a single process on the steam condensate side and a dual or multiple process on the wastewater side. Determining the process combination scheme is a crucial step in this embodiment. Since the steam condensate flow rate is much smaller than the wastewater flow rate, using the same number of processes would result in either excessively low flow velocity on the hot side or excessively high flow velocity on the cold side. To balance the flow velocities on both sides, an asymmetric process configuration is adopted.

[0043] In practice, the process combination is first determined based on the flow ratio. When the flow ratio is in the range of 1:5 to 1:10, a single hot-side process and a dual cold-side process are preferred; when the flow ratio is in the range of 1:10 to 1:20, a single hot-side process and a triple or quadruple cold-side process are preferred.

[0044] After determining the initial plan, flow rate verification is performed. Calculate the flow rate on each side based on the number of flow paths and the area of ​​the flow channels between the plates, and check if it meets the flow rate control requirements. If the flow rate does not meet the requirements, adjust the flow path combination or increase / decrease the number of plates. Pressure drop constraints must also be considered during flow rate verification to ensure that the cold-side pressure drop does not exceed the upper limit.

[0045] Once the process combination scheme is determined, gaskets and plates are installed on the connecting tube sheet of the plate heat exchanger according to the designed process path. The arrangement of the gaskets determines the flow path of the medium, and the process combination can be flexibly adjusted by changing the position of the gaskets.

[0046] S5. Set up a waste heat recovery system according to the process combination scheme, and control the flow velocity of steam condensate on the side within the range of 0.2m / s to 0.8m / s, control the flow velocity of wastewater on the side within the range of 0.3m / s to 0.5m / s, and control the pressure drop on the wastewater side to be less than or equal to 30kPa. After the system is put into operation, the PLC executes the real-time control program. The control program includes three subroutines: flow rate control, temperature control, and pressure drop monitoring.

[0047] The flow rate control subroutine adjusts the inverter frequency and regulating valve opening using a PID control algorithm. Wastewater-side flow rate control primarily relies on the circulating pump's frequency converter. The program reads the actual flow rate measured by the flow meter, compares it with the set flow rate to obtain the deviation, and the PID controller calculates the output value based on the deviation and sends it to the inverter. Upon receiving the frequency setting signal, the inverter adjusts the motor speed, thereby changing the pump's outlet flow rate. The proportional, integral, and derivative parameters of the PID controller need to be tuned according to the system characteristics, which can be done using the critical proportional gain method or empirical formulas.

[0048] The flow rate control on the steam condensate side is achieved through a regulating valve. The PLC outputs a 4-20mA signal to the regulating valve actuator, which adjusts the valve opening according to the signal strength. To avoid frequent valve actuation, a dead zone and delay are set in the control program. No adjustment is made when the flow rate deviation is less than the dead zone value, and the adjustment action is only performed when the deviation duration exceeds the delay time.

[0049] The temperature control subroutine uses the wastewater outlet temperature as the controlled variable and achieves precise control through cascade control or feedforward-feedback composite control. When the outlet temperature deviates from the target temperature, the program first determines the direction and magnitude of the deviation. If the temperature is too high, it indicates that the heat exchange is too large, requiring a reduction in the steam condensate flow rate or an increase in the wastewater flow rate; if the temperature is too low, it indicates that the heat exchange is insufficient, requiring an increase in the steam condensate flow rate or a decrease in the wastewater flow rate.

[0050] The program selects an adjustment strategy based on the magnitude of the deviation. When the deviation is within the allowable range, it performs only fine-tuning or no adjustment; when the deviation exceeds the allowable range but does not reach the alarm value, it adjusts at the normal adjustment rate; when the deviation exceeds the alarm value, it accelerates the adjustment rate or switches to manual mode to request manual intervention.

[0051] The pressure drop monitoring subroutine calculates the inlet and outlet pressure difference on the wastewater side in real time and compares it with the set upper limit of pressure drop. When the pressure drop exceeds the upper limit, it indicates that there may be blockage or scaling inside the heat exchanger, and the program issues an alarm signal and suggests cleaning. Pressure drop monitoring is also used to determine the operating status of the system; an abnormally high pressure drop may indicate faults such as plate breakage or gasket aging.

[0052] S6 monitors the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, the cleaning procedure is triggered.

[0053] During system operation, fouling gradually accumulates on the heat exchanger surface, leading to a decrease in the heat transfer coefficient. To detect heat transfer performance degradation in a timely manner, an online heat transfer coefficient monitoring function is configured in the PLC program.

[0054] The monitoring method involves using measured heat load, logarithmic mean temperature difference, and heat transfer area to inversely deduce the overall heat transfer coefficient using the heat transfer calculation formula. The program compares the current heat transfer coefficient with the baseline value at the initial stage of system operation and calculates the percentage decrease. To eliminate the impact of operating condition fluctuations, a sliding time window statistical method is used, taking the average value over a period of time for comparison.

[0055] When the decrease in heat transfer coefficient reaches the cleaning trigger threshold, the program initiates the cleaning process. There are two cleaning methods: online cleaning and offline cleaning. Online cleaning is achieved through circulating cleaning fluid and does not require system shutdown. The program controls the switching valves to pump the cleaning fluid from the cleaning tank into the heat exchanger, circulates it for a certain period, then discharges it, and finally rinses with clean water. Offline cleaning requires stopping the system, disassembling the heat exchanger plates for manual cleaning or replacement.

[0056] The cleaning process includes steps such as cleaning solution selection, cleaning temperature control, and circulation time control. For organic scale in the wastewater, an alkaline cleaning solution is used; for inorganic salt scale, an acidic cleaning solution is used. The concentration and temperature of the cleaning solution are determined according to the type of scale, and the flow rate of the circulating pump should ensure sufficient flow velocity between the plates to flush away the scale. After cleaning, the program control system resumes normal operation, and the heat transfer coefficient is re-measured as a new baseline value.

[0057] Furthermore, this embodiment also includes: The wastewater after heat exchange is transported to the reverse osmosis system for further treatment. The water flux and desalination rate of the reverse osmosis membrane are significantly affected by temperature. Increased temperature increases the diffusion rate of water molecules and improves the water flux, but may also affect the desalination rate.

[0058] The integrated control system automatically adjusts the reverse osmosis operating parameters based on changes in wastewater temperature. The program incorporates a temperature-pressure correlation curve, and the optimal operating pressure is determined by looking up a table or calculation based on the influent temperature. When the influent temperature rises, the program reduces the outlet pressure of the reverse osmosis high-pressure pump through frequency conversion speed regulation or a regulating valve. The magnitude of the pressure adjustment is determined based on the temperature increase and membrane performance parameters, ensuring that the desalination rate is maintained within the set range while reducing energy consumption.

[0059] The linkage control also includes flow balance control. When the waste heat recovery system shuts down due to a malfunction or is being cleaned, the temperature of the wastewater entering the reverse osmosis system decreases, and the program automatically increases the operating pressure to compensate for the decrease in water flux. At the same time, the program adjusts the opening of the reverse osmosis concentrate discharge valve to maintain a stable system recovery rate.

[0060] In summary, this embodiment solves the velocity mismatch problem caused by the steam condensate flow rate being much smaller than the wastewater flow rate by accurately calculating the heat exchange area and optimizing the process combination scheme. This ensures sufficient flow velocity on the hot side to enhance heat exchange and prevent fouling, while keeping the cold side flow velocity within a reasonable range to avoid excessive pressure drop. The wastewater temperature increases after being preheated by waste heat, improving the water flux and desalination performance of the subsequent reverse osmosis membrane. Under the same water production conditions, this reduces the operating pressure of the reverse osmosis system and decreases the energy consumption of the high-pressure pump. Simultaneously, real-time monitoring of heat transfer coefficient changes allows for timely detection of heat exchanger fouling and triggers the cleaning process, maintaining the system's long-term stable and efficient operation. Overall, this invention achieves cascade utilization of waste heat resources, reduces the overall energy consumption and operating costs of wastewater treatment systems, and improves the economic and environmental benefits for enterprises, demonstrating significant engineering application value.

[0061] The following describes a control device for waste heat recovery of steam condensate and wastewater heating provided in an embodiment of this application. The control device and control method for waste heat recovery of steam condensate and wastewater heating described below can be referred to in correspondence with each other.

[0062] Please refer to Figure 2 , Figure 2 This application provides a control device for recovering waste heat from steam condensate and heating wastewater.

[0063] In this embodiment, the device may include: The data acquisition module 100 is used to acquire the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. The parameter calculation module 200 is used to calculate the heat load based on the principle of energy conservation, according to the hot side inlet temperature, hot side outlet temperature, hot side flow rate of the steam condensate and the cold side inlet temperature, cold side outlet temperature, and cold side flow rate of the wastewater, and to calculate the logarithmic mean temperature difference based on the hot side inlet temperature, hot side outlet temperature, cold side inlet temperature, and cold side outlet temperature. The heat transfer area calculation module 300 is used to calculate the required heat transfer area based on the total heat transfer coefficient, the logarithmic mean temperature difference, and the heat load using the logarithmic mean temperature difference method. The process scheme determination module 400 is used to determine the process combination scheme of the plate heat exchanger based on the heat exchange area and flow parameters; wherein, the process combination scheme includes a single process on the steam condensate side and a dual process or multiple processes on the wastewater side. The system setting module 500 is used to set up the waste heat recovery system according to the process combination scheme, and control the flow velocity of the steam condensate side to be within the range of 0.2m / s to 0.8m / s, control the flow velocity of the wastewater side to be within the range of 0.3m / s to 0.5m / s, and control the pressure drop of the wastewater side to be less than or equal to 30kPa. The cleaning module 600 is used to monitor the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, the cleaning program is triggered.

[0064] This application also provides control equipment, please refer to... Figure 3 , Figure 3 This is a schematic diagram of the structure of the control device provided in the embodiments of this application. The control device may include: Memory, used to store computer programs; The processor, when executing a computer program, can implement the steps of any of the control methods described above for steam condensate waste heat recovery and wastewater heating.

[0065] like Figure 3 The diagram shows the structural composition of a control device, which may include a processor 10, a memory 11, a communication interface 12, and a communication bus 13. The processor 10, memory 11, and communication interface 12 communicate with each other via the communication bus 13.

[0066] In this embodiment, the processor 10 may be a central processing unit (CPU), an application-specific integrated circuit, a digital signal processor, a field-programmable gate array, or other programmable logic devices.

[0067] The processor 10 can call the program stored in the memory 11. Specifically, the processor 10 can execute the operations in the embodiment of the abnormal IP identification method.

[0068] The memory 11 is used to store one or more programs. The programs may include program code, which includes computer operation instructions. In this embodiment, the memory 11 stores at least a program for implementing the following functions: S1 collects the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. S2, based on the principle of energy conservation, calculates the heat load according to the hot side inlet temperature, hot side outlet temperature, hot side flow rate of steam condensate and the cold side inlet temperature, cold side outlet temperature, cold side flow rate of wastewater, and calculates the logarithmic mean temperature difference based on the hot side inlet temperature, hot side outlet temperature, cold side inlet temperature, and cold side outlet temperature. S3, calculate the required heat exchange area using the logarithmic mean temperature difference method based on the overall heat transfer coefficient, logarithmic mean temperature difference, and heat load; S4. Based on the heat exchange area and flow parameters, determine the process combination scheme of the plate heat exchanger; wherein, the process combination scheme includes a single process on the steam condensate side and a dual or multiple process on the wastewater side. S5. Set up a waste heat recovery system according to the process combination scheme, and control the flow velocity of steam condensate on the side within the range of 0.2m / s to 0.8m / s, control the flow velocity of wastewater on the side within the range of 0.3m / s to 0.5m / s, and control the pressure drop on the wastewater side to be less than or equal to 30kPa. S6 monitors the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, the cleaning procedure is triggered.

[0069] In one possible implementation, the memory 11 may include a program storage area and a data storage area, wherein the program storage area may store the operating system and applications required for at least one function; and the data storage area may store data created during use.

[0070] In addition, memory 11 may include high-speed random access memory, and may also include non-volatile memory, such as at least one disk storage device or other volatile solid-state storage device.

[0071] Communication interface 12 can be an interface for the communication module, used to connect with other devices or systems.

[0072] Of course, it should be noted that, Figure 3 The structure shown does not constitute a limitation on the control device in the embodiments of this application. In practical applications, the control device may include more than Figure 3 More or fewer components as shown, or combinations of certain components.

[0073] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, can implement the steps of any of the control methods described above for steam condensate waste heat recovery and wastewater heating.

[0074] The computer-readable storage medium may include various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0075] For a description of the computer-readable storage medium provided in this application, please refer to the above method embodiments; further details will not be repeated here.

[0076] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0077] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0078] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0079] The foregoing has provided a detailed description of a control method, control device, control equipment, and computer-readable storage medium for waste heat recovery of steam condensate and wastewater heating, as well as the control method and the control device for waste heat recovery of steam condensate and wastewater heating provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and its core ideas. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A control method for waste heat recovery of steam condensate and wastewater heating, characterized in that, include: S1 collects the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. S2, based on the principle of energy conservation, calculate the heat load according to the hot side inlet temperature, hot side outlet temperature, hot side flow rate of the steam condensate and the cold side inlet temperature, cold side outlet temperature, cold side flow rate of the wastewater, and calculate the logarithmic mean temperature difference based on the hot side inlet temperature, hot side outlet temperature, cold side inlet temperature, and cold side outlet temperature. S3. Calculate the required heat exchange area using the logarithmic mean temperature difference method based on the overall heat transfer coefficient, the logarithmic mean temperature difference, and the heat load. S4. Based on the heat exchange area and flow parameters, determine the process combination scheme of the plate heat exchanger; wherein, the process combination scheme includes a single process on the steam condensate side and a dual or multiple process on the wastewater side. S5, according to the process combination scheme, a waste heat recovery system is set up, and the flow velocity of the steam condensate side is controlled within the range of 0.2m / s to 0.8m / s, the flow velocity of the wastewater side is controlled within the range of 0.3m / s to 0.5m / s, and the pressure drop of the wastewater side is controlled to be less than or equal to 30kPa; S6. Monitor the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, trigger the cleaning procedure.

2. The control method according to claim 1, characterized in that, S1 includes: collecting the hot-side inlet temperature, the hot-side outlet temperature, the cold-side inlet temperature, and the cold-side outlet temperature through a temperature sensor; and collecting the hot-side flow rate of the steam condensate and the cold-side flow rate of the wastewater through a flow meter, with a sampling period of 1 second to 10 seconds.

3. The control method according to claim 2, characterized in that, In step S3, the overall heat transfer coefficient is determined based on the process combination scheme: when a single process is used on the steam-condensate side, the value of U ranges from 2500 W / (m³). 2 ·K) to 3500W / (m 2 ·K); When a dual-pass system is used on the steam condensate side, the value of U ranges from 3000 W / (m³). 2 ·K) to 4000W / (m 2 ·K).

4. The control method according to claim 3, characterized in that, S5 includes: adjusting the frequency of the wastewater-side circulation pump through a frequency conversion control unit to control the wastewater-side flow rate; and adjusting the steam condensate-side flow rate through a regulating valve to control the steam condensate-side flow rate.

5. The control method according to claim 4, characterized in that, S5 further includes: when the cold-side outlet temperature of the wastewater deviates from the target temperature by more than ±2℃, dynamically adjusting the steam condensate flow rate or the frequency of the wastewater-side circulation pump to restore the cold-side outlet temperature to the target temperature range.

6. The control method according to claim 5, characterized in that, Also includes: The wastewater after heat exchange is input into the reverse osmosis system. The operating pressure of the reverse osmosis system is adjusted according to the increase in wastewater temperature relative to the initial temperature in order to maintain the desalination rate within the set range. Specifically, when the increase is 10°C, the operating pressure is reduced by 5% to 10%.

7. The control method according to claim 6, characterized in that, The method is applied to wastewater treatment systems in the polysilicon, chemical, or metallurgical industries, wherein the ratio of the hot-side flow rate of the steam condensate to the cold-side flow rate of the wastewater is 1:5 to 1:20, and the single-plate area of ​​the plate heat exchanger is 0.3 m². 2 up to 0.8m 2 .

8. A control device for waste heat recovery of steam condensate and wastewater heating, characterized in that, include: The data acquisition module is used to collect the hot-side inlet temperature, hot-side outlet temperature, and hot-side flow rate of steam condensate, as well as the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of wastewater. The parameter calculation module is used to calculate the heat load based on the principle of energy conservation, according to the hot-side inlet temperature, hot-side outlet temperature, hot-side flow rate of the steam condensate and the cold-side inlet temperature, cold-side outlet temperature, and cold-side flow rate of the wastewater, and to calculate the logarithmic mean temperature difference based on the hot-side inlet temperature, hot-side outlet temperature, cold-side inlet temperature, and cold-side outlet temperature. The heat transfer area calculation module is used to calculate the required heat transfer area based on the overall heat transfer coefficient, the logarithmic mean temperature difference, and the heat load using the logarithmic mean temperature difference method. The process scheme determination module is used to determine the process combination scheme of the plate heat exchanger based on the heat exchange area and flow parameters; wherein, the process combination scheme includes a single process on the steam condensate side and a dual or multiple process on the wastewater side. The system setting module is used to set up the waste heat recovery system according to the process combination scheme, and control the flow velocity of the steam condensate side within the range of 0.2m / s to 0.8m / s, control the flow velocity of the wastewater side within the range of 0.3m / s to 0.5m / s, and control the pressure drop of the wastewater side to be less than or equal to 30kPa. The cleaning module is used to monitor the change in the total heat transfer coefficient in real time. When the total heat transfer coefficient decreases by more than or equal to 10%, the cleaning procedure is triggered.

9. A control device, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the steps of the control method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the control method as described in any one of claims 1 to 7.

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