A paper machine dryer section moist heat steam waste heat recovery system

Abstract

The application discloses a paper machine drying section wet heat steam waste heat recovery system and relates to the technical field of waste heat recovery in the papermaking industry. The system comprises a heat source tracking module, a multi-stage heat exchange module and a condensation recycling module. The heat source tracking module is used for constructing a transient heat source topology matrix of wet heat steam based on real-time heat radiation flux of each dryer area of the paper machine drying section and density distribution of wet air in the air hood, and generating a waste heat recovery priority ranking table. The multi-stage heat exchange module is used for distributing the wet heat steam to high-temperature, medium-temperature and low-temperature heat exchange units according to a heat source temperature gradient, and outputting heat carrier fluids at different levels. The condensation recycling module is used for carrying out multi-stage flash evaporation separation on the mixed heat carrier medium, extracting three-stage flash steam and respectively conveying the three-stage flash steam to a pulping section preheater, a wire part cleaning water heater and a workshop heating radiator according to pressure grades.

Description

Technical Field

[0001] This invention relates to the field of waste heat recovery technology in the papermaking industry, specifically a wet steam waste heat recovery system for the drying section of a paper machine. Background Technology

[0002] The humid steam within the drying section hood of a paper machine contains a large amount of low-grade waste heat, and its efficient recovery is of great value for reducing energy consumption in the papermaking process. Existing methods for recovering waste heat from humid steam mostly employ fixed gas-liquid heat exchangers to centrally recover heat from the exhaust air of the hood, or use single-stage heat pumps to pressurize and utilize the humid steam. These technical solutions rely solely on the average temperature or humidity at the hood outlet for overall heat recovery control during operation, failing to reflect the dynamic changes in heat radiation flux and humid air density distribution within different local areas of the drying cylinder group. When fluctuations occur in the basis weight of the paper produced, the machine speed, or the steam pressure in the drying cylinder, the thermal and humid state within the hood exhibits non-uniform and transient characteristics. Fixed recovery systems, lacking precise perception of the spatial distribution and temporal evolution of heat sources, result in the mixing of high-grade and low-grade heat sources, leading to a significant amount of usable energy being degraded and dissipated during heat exchange, resulting in low overall efficiency. Furthermore, existing condensation and reuse processes typically employ single-stage flash evaporation or direct condensation, resulting in a uniform flash steam pressure. This makes it difficult to match the varying steam pressure requirements of different process hotspots within the paper mill, often necessitating the addition of steam pressurization or pressure-reducing valve assemblies, increasing system complexity and energy consumption. Simultaneously, the pipelines transporting the mixed heat transfer medium from the centralized heat recovery station to each heat-using terminal experience velocity attenuation and temperature loss along the way. Conventional systems lack online sensing and heat exchange area compensation mechanisms for dynamic deterioration of transport conditions, leading to deviations in terminal heating parameters. This not only affects the heat stability of processes such as pulping, wire cleaning, and heating but also reduces the overall system's actual usable heat recovery rate.

[0003] To address the aforementioned issues, a technical means is needed to construct a transient heat source topology in real time based on the thermal radiation of the drying cylinder and the enthalpy distribution of humid air, and to generate a recovery priority ranking. This would solve the challenges of dynamic identification and energy level matching of the waste heat enrichment area of ​​humid steam. Simultaneously, multi-stage flash separation of the mixed heat transfer medium is required, and the flash steam should be directionally transported to different heat-using equipment according to pressure levels. Furthermore, the heat exchange area ratio of the multi-stage heat exchange units should be adjusted based on feedback from the flow rate attenuation and temperature drop rate within the transport pipeline to address the issues of output parameter drift and heat attenuation compensation under varying operating conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a waste heat recovery system for wet steam in the drying section of a paper machine. This system can perform transient topology identification and priority sorting of wet steam heat sources in the drying cylinder group, realize graded heat exchange of wet steam according to temperature gradient, and adaptively adjust the input ratio of heat exchange area through multi-stage flash separation and conveying pipeline status feedback, so as to ensure the high efficiency of waste heat recovery, the accuracy of graded utilization, and the stability of end-use heat parameters.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a waste heat recovery system for wet steam in the drying section of a paper machine, comprising: a heat source tracking module, a multi-stage heat exchange module, a heat pump compensation module, a condensation reuse module, and a medium control module. The heat source tracking module is used to construct a transient heat source topology matrix of wet steam based on the real-time heat radiation flux of each drying cylinder area in the paper machine drying section and the humid air density distribution within the hood, and to generate a waste heat recovery priority ranking table based on the transient heat source topology matrix, thereby dynamically identifying the waste heat recovery value of wet steam in different areas and achieving precise tracking as needed. The multi-stage heat exchange module responds to the waste heat recovery priority ranking table, diverting the wet steam to a high-temperature stage heat exchange unit, a medium-temperature stage heat exchange unit, and a low-temperature stage heat exchange unit according to the heat source temperature gradient, and outputting high-temperature heat transfer fluid, medium-temperature heat transfer fluid, and low-temperature heat transfer fluid respectively, completing the cascade heat exchange of the wet steam and improving the depth of heat energy extraction. The heat pump compensation module receives the high-temperature, medium-temperature, and low-temperature heat transfer fluids. It dynamically adjusts the injection coefficient based on the real-time flow ratio and pressure fluctuation amplitude of each fluid to generate a mixed heat transfer medium. This suppresses parameter disturbances during the convergence of multiple fluids, ensuring stable mixed medium quality. The condensation and reuse module performs multi-stage flash evaporation separation on the mixed heat transfer medium, extracting primary, secondary, and tertiary flash steam. These flash steams are then delivered to the preheater in the pulping section, the cleaning water heater in the mesh section, and the workshop heating radiators, respectively, according to their pressure levels. This ensures that steam at different pressure levels is fully utilized, achieving graded utilization of waste heat. The medium control module monitors the velocity decay and temperature drop rate of the mixed heat transfer medium in the delivery pipeline. Based on these parameters, it adjusts the heat exchange area ratio of the multi-stage heat exchange modules, actively compensating for energy losses and flow resistance changes during delivery, and maintaining the system in its high-efficiency range.

[0006] As a preferred embodiment of the present invention, the specific implementation of the heat source tracking module in constructing the transient heat source topology matrix of humid steam includes: collecting infrared thermal imaging temperature field data of the surface of each drying cylinder in the paper machine drying section and humid air enthalpy data of each measurement section inside the hood; establishing a directed graph of drying cylinder thermal radiation using the center coordinates of each drying cylinder as nodes and the thermal radiation angle coefficient between adjacent drying cylinders as edge weights; generating a thermal-humid coupling diffusion path network using the humid air enthalpy gradient direction of each measurement section as the flow vector, combined with the directed graph of drying cylinder thermal radiation; constructing a heat flux density distribution matrix using the heat flux density distribution matrix as matrix elements; normalizing the heat flux density distribution matrix and sorting it according to the matrix element values ​​from largest to smallest to generate a priority ranking table for waste heat recovery. This method couples radiative heat transfer with humid air convection diffusion, fully reflecting the transient distribution characteristics of humid steam in the drying section, making the ranking table closely follow the actual operating conditions, and significantly improving the targeting and real-time performance of waste heat recovery.

[0007] Furthermore, the specific implementation of the multi-stage heat exchange module diverting humid heat steam to each heat exchange unit according to the heat source temperature gradient is as follows: humid heat steam sources with a priority higher than a first preset priority threshold in the waste heat recovery priority ranking table are extracted as the first diversion queue, and the humid heat steam corresponding to the first diversion queue is input into the high-temperature stage heat exchange unit; humid heat steam sources with a priority between the first preset priority threshold and the second preset priority threshold are extracted as the second diversion queue, and the humid heat steam corresponding to the second diversion queue is input into the medium-temperature stage heat exchange unit; humid heat steam sources with a priority lower than the second preset priority threshold are extracted as the third diversion queue, and the humid heat steam corresponding to the third diversion queue is input into the low-temperature stage heat exchange unit; electrically adjustable butterfly valves are respectively installed at the inlet of the high-temperature stage heat exchange unit, the medium-temperature stage heat exchange unit, and the low-temperature stage heat exchange unit, and the opening degree of the electrically adjustable butterfly valves is adjusted in real time according to the instantaneous steam flow feedback value of each diversion queue. Therefore, wet steam of different temperatures and grades enters the matching heat exchange unit, which prevents high-grade heat sources from being downgraded and used, avoids low-grade heat sources from occupying high-grade heat exchange resources, and maintains the flow distribution accuracy and system stability through flow feedback regulation.

[0008] Preferably, the process by which the heat pump compensation module dynamically adjusts the injection coefficient based on the real-time flow ratio and pressure fluctuation amplitude of each heat transfer fluid is as follows: The mass flow rates of the high-temperature heat transfer fluid at the outlet of the high-temperature stage heat exchange unit, the medium-temperature heat transfer fluid at the outlet of the medium-temperature stage heat exchange unit, and the low-temperature heat transfer fluid at the outlet of the low-temperature stage heat exchange unit are measured respectively, and the real-time flow ratios among the three are calculated; the pressures of the heat transfer fluids at each outlet are measured respectively, and the pressure fluctuation amplitudes of each pressure relative to its respective design reference pressure are calculated; the real-time flow ratios are compared with the preset optimal flow ratios to obtain the flow ratio deviation; the weighted sum of the flow ratio deviation and each pressure fluctuation amplitude is used as the injection coefficient adjustment factor; and the pre-stored injection coefficients are queried based on the injection coefficient adjustment factor. The adjustment factor mapping table yields the target injection coefficient for the current moment, and drives the nozzle opening actuator of the heat pump compensation module to the opening position corresponding to the target injection coefficient. This adjustment mechanism can promptly offset the impact of flow ratio imbalance and pressure fluctuations on the injection mixing effect, ensuring that the thermodynamic state of the mixed heat transfer medium remains close to the design conditions, thereby improving the heat pump's operating efficiency. Specifically, the weighting coefficients of the flow ratio deviation and the pressure fluctuation amplitude in the injection coefficient adjustment factor are adaptively adjusted in real time according to the heat pump performance coefficient under the current operating conditions, thereby automatically optimizing control parameters under partial load or variable operating conditions and enhancing the system's robustness.

[0009] In one specific embodiment, the condensate recycling module performs multi-stage flash evaporation separation on the mixed heat transfer medium as follows: The mixed heat transfer medium is introduced into a first-stage flash tank. The operating pressure of the first-stage flash tank is controlled at a first pressure value, causing saturated water in the mixed heat transfer medium with a pressure higher than the first pressure value to flash into first-stage flash steam. The unflashed remaining liquid is discharged to a second-stage flash tank. The operating pressure of the second-stage flash tank is controlled at a second pressure value, causing saturated water in the incoming remaining liquid with a pressure higher than the second pressure value to flash into second-stage flash steam. The unflashed remaining liquid is discharged to a third-stage flash tank, where the second pressure value is lower than the first pressure value. The operating pressure of the third-stage flash tank is controlled at a third pressure value, causing saturated water in the incoming remaining liquid with a pressure higher than the third pressure value to flash into tertiary-stage flash steam. The final condensate after flash evaporation is discharged, where the third pressure value is lower than the second pressure value. This staged flash evaporation method utilizes a pressure gradient to release flash steam step by step, fully extracting usable energy from the mixed heat transfer medium and obtaining multiple streams of steam at different pressure levels while reducing the condensate discharge temperature. Based on this, the specific method of conveying flash steam according to each flash steam pressure level is as follows: Measure the first-stage flash steam pressure value of the first-stage flash tank, compare the first-stage flash steam pressure value with the required pressure threshold of the pulping section preheater, and when the first-stage flash steam pressure value is greater than or equal to the required pressure threshold, open the first conveying pipeline to convey the first-stage flash steam to the pulping section preheater; measure the second-stage flash steam pressure value of the second-stage flash tank, compare it with the required pressure threshold of the mesh cleaning water heater, and when the condition is met, open the second conveying pipeline to convey the mesh cleaning water heater; measure the third-stage flash steam pressure value of the third-stage flash tank, compare it with the required pressure threshold of the workshop heating radiator, and when the condition is met, open the third conveying pipeline to convey the workshop heating radiator; and install pressure compensation valves on each conveying pipeline. When a flash steam pressure value is lower than the corresponding required pressure threshold, open the pressure compensation valve to introduce high-temperature heat transfer fluid from the medium control module for pressure compensation. This approach achieves both quality-based delivery of flash steam and ensures the continuity and stability of hot spot steam supply through pressure compensation, preventing process disruptions due to insufficient flash steam pressure.

[0010] As a further preferred embodiment of the present invention, the liquid level feedback values ​​of the first-stage flash tank, the second-stage flash tank, and the third-stage flash tank respectively form a cascade control loop with the opening degree of their respective inlet regulating valves, and the liquid level set value of each flash tank is dynamically corrected according to the inlet flow rate of the mixed heat transfer medium, thereby effectively suppressing the impact of incoming flow fluctuations on the liquid level of the flash tank, preventing water carryover in steam or excessively high liquid levels from affecting flash evaporation efficiency and operational safety.

[0011] The preferred implementation method for the medium control module to monitor the velocity decay and temperature drop rate of the mixed heat transfer medium in the delivery pipeline is as follows: a first ultrasonic flow meter and a first thermocouple are installed at the inlet section of the delivery pipeline to measure the inlet velocity and inlet temperature of the mixed heat transfer medium; a second ultrasonic flow meter and a second thermocouple are installed at the outlet section to measure the outlet velocity and outlet temperature; the difference between the inlet velocity and the outlet velocity is calculated as the velocity decay, and the difference between the inlet temperature and the outlet temperature is calculated and divided by the length of the delivery pipeline as the temperature drop rate; the velocity decay and temperature drop rate are continuously collected at multiple time points to generate a velocity decay time series curve and a temperature drop rate time series curve; the peak decay rate in the velocity decay time series curve and the maximum temperature drop slope in the temperature drop rate time series curve are extracted. Based on this, the specific logic for adjusting the heat exchange area input ratio of the multi-stage heat exchange module is as follows: The peak attenuation rate is compared with a preset attenuation rate upper limit. If the peak attenuation rate is greater than the preset attenuation rate upper limit, a first adjustment command to reduce the heat exchange area input ratio is generated. The maximum temperature drop slope is compared with a preset temperature drop slope upper limit. If the maximum temperature drop slope is greater than the preset temperature drop slope upper limit, a second adjustment command to increase the heat exchange area input ratio is generated. When both the first and second adjustment commands are received simultaneously, the first difference between the peak attenuation rate and the preset attenuation rate upper limit, and the second difference between the maximum temperature drop slope and the preset temperature drop slope upper limit are calculated. The magnitudes of the first and second differences are compared, and the first or second adjustment command is executed preferentially based on the comparison results. An opening control signal is sent to the bypass valve of each heat exchange unit in the multi-stage heat exchange module according to the final executed adjustment command. By adjusting the opening of the bypass valve, the number of heat exchange units in operation is changed, thereby adjusting the heat exchange area input ratio. This control logic ensures that the delivery pipeline is not blocked due to excessive flow rate attenuation, while also preventing excessive temperature drop from causing insufficient heat energy at the end. It also makes the optimal decision when the two demands conflict, thereby improving the system's adaptability and operational safety.

[0012] The technical effects and advantages provided by the present invention in the above technical solution are as follows: The heat source tracking module collects infrared thermal imaging temperature field data from the surface of each drying cylinder and enthalpy data of moist air from each measurement section. Using the center coordinates of the drying cylinder as nodes and the thermal radiation angle coefficient between adjacent cylinders as edge weights, it establishes a directed thermal radiation graph for the drying cylinders. Combined with the enthalpy gradient direction vector of the moist air, it generates a thermal-humidity coupling diffusion path network. The heat flux density at the path intersections is used as elements to construct a heat flux density distribution matrix, which, after normalization and sorting, forms a priority ranking table for waste heat recovery. This technical solution transforms the originally complex and changing heat and moisture transport process within the gas hood into a quantifiable transient heat source topology. The spatial morphology of heat sources in high-temperature, medium-temperature, and low-temperature zones is clearly separated, allowing multi-stage heat exchange modules to accurately divert moist steam to heat exchange units at corresponding temperature levels. During the recovery process, it avoids the exergy damage caused by high-grade heat sources being forced to participate in low-temperature heat exchange, ensuring that waste heat of different grades can be extracted in heat exchange stages at temperatures comparable to their own, significantly improving the exergy efficiency of the heat recovery process. The condensation and reuse module sequentially introduces the mixed heat transfer medium into the first-stage flash tank, the second-stage flash tank, and the third-stage flash tank, with gradually decreasing operating pressures. This allows saturated water to flash into first-stage, second-stage, and third-stage flash steam at different pressures. The pressure of each stage of flash steam is measured. When the pressure meets the threshold requirements of the preheater in the pulping section, the cleaning water heater in the mesh section, and the radiator in the workshop heating system, the corresponding delivery pipeline is opened to supply the flash steam to each hotspot in stages. Simultaneously, the medium control module installs ultrasonic flow meters and thermocouples at the inlet and outlet sections of the mixed heat transfer medium delivery pipeline to calculate the flow rate decay and temperature drop rate in real time, generating flow rate decay time-series curves and temperature drop rate time-series curves. The module extracts the peak decay rate and the maximum temperature drop slope. When the peak decay rate exceeds the upper limit, an adjustment command is generated to reduce the proportion of heat exchange area in operation. When the maximum temperature drop slope exceeds the upper limit, an adjustment command is generated to increase the proportion of heat exchange area in operation. The number of heat exchange units in operation is changed by adjusting the opening of the bypass valves of each heat exchange unit in the multi-stage heat exchange module. This scheme directly matches the output pressure level of flash steam with the terminal demand pressure level, eliminating the need for secondary pressurization or depressurization and reducing intermediate energy consumption. Simultaneously, by using closed-loop control of the heat exchange area allocation ratio based on flow and heat transfer attenuation data in the delivery pipeline, it can promptly compensate for insufficient or excessive heat energy of the heat transfer medium caused by pipeline friction losses, maintaining terminal heat consumption parameters within a reasonable range. This ensures that the system maintains stable heating quality even under load fluctuations and changes in pipeline conditions. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0014] Figure 1 This is a schematic diagram of the waste heat recovery system for the wet steam in the paper machine drying section; Figure 2 This is a schematic diagram of the multi-stage diversion and flow regulation control principle for waste heat recovery; Figure 3 This is a flowchart of the dynamic adjustment control of the injection coefficient based on the deviation between flow rate and pressure. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0016] See Figure 1 This invention provides a waste heat recovery system for wet steam in the drying section of a paper machine. The system includes: a heat source tracking module, a multi-stage heat exchange module, a heat pump compensation module, a condensation reuse module, and a medium control module. The heat source tracking module constructs a transient heat source topology matrix for wet steam based on the real-time heat radiation flux of each drying cylinder area and the humid air density distribution within the hood, and generates a waste heat recovery priority ranking table based on this matrix. The multi-stage heat exchange module responds to the waste heat recovery priority ranking table, diverting the wet steam to a high-temperature stage heat exchange unit, a medium-temperature stage heat exchange unit, and a low-temperature stage heat exchange unit according to the heat source temperature gradient, and outputs high-temperature, medium-temperature, and low-temperature heat transfer fluids respectively. The heat pump compensation module receives the high-temperature, medium-temperature, and low-temperature heat transfer fluids, and dynamically adjusts the injection coefficient based on the real-time flow ratio and pressure fluctuation amplitude of each heat transfer fluid to generate a mixed heat transfer medium. The condensation and reuse module performs multi-stage flash evaporation separation on the mixed heat transfer medium, extracting primary, secondary, and tertiary flash steam, which is then delivered to the preheater in the pulping section, the cleaning water heater in the mesh section, and the workshop heating radiators according to their respective pressure levels. The medium control module monitors the velocity decay and temperature drop rate of the mixed heat transfer medium in the delivery pipeline, and adjusts the heat exchange area ratio of the multi-stage heat exchange modules based on the velocity decay and temperature drop rate.

[0017] Example 1: In specific implementation, the method for collecting infrared thermal imaging temperature field data of the surface of each drying cylinder in the paper machine drying section is as follows: Infrared thermal imagers are arranged around each drying cylinder, with the field of view of the imagers covering the complete outer surface of the corresponding drying cylinder. The radiation temperature values ​​of each pixel on the surface of the drying cylinder are acquired at a preset sampling frequency, forming infrared thermal imaging temperature field data in time sequence. The method for collecting the enthalpy value data of moist air at each measurement section inside the gas hood is as follows: Multiple measurement sections perpendicular to the main direction of the moist steam are selected along the arrangement direction of the drying cylinders inside the gas hood. Temperature and humidity sensors and pressure sensors are arranged on each measurement section. Based on the measured moist air temperature, relative humidity, and pressure, the enthalpy value of the moist air at each measuring point on each measurement section is calculated using the thermodynamic relationship of moist air. The expression for calculating the enthalpy value of moist air is: in, Specific enthalpy of moist air, expressed in kilojoules per kilogram of dry air; The dry-bulb temperature of moist air, expressed in degrees Celsius. Moisture content of humid air, expressed in kilograms of water vapor per kilogram of dry air; constant. This represents the average isobaric specific heat capacity of dry air, expressed in kilojoules per kilogram of degree Celsius; a constant. The latent heat of vaporization of water at zero degrees Celsius, expressed in kilojoules per kilogram; constant. This represents the average isobaric specific heat capacity of water vapor, expressed in kilojoules per kilogram of degree Celsius.

[0018] The specific implementation of establishing a directed graph of drying cylinder thermal radiation, using the center coordinates of each drying cylinder as nodes and the thermal radiation angle coefficient between adjacent drying cylinders as edge weights, is as follows: Obtain the coordinates of the center point of each drying cylinder in three-dimensional space, and treat the center point of each drying cylinder as a node in the directed graph. For any two drying cylinders that are spatially adjacent, calculate the thermal radiation angle coefficient from one drying cylinder surface to the other. The thermal radiation angle coefficient is determined based on the relative geometric position of the two drying cylinders. When the line of sight between the surface elements of the two drying cylinders is unobstructed, the thermal radiation angle coefficient is obtained by integrating the angle between the surface normal vectors of the two drying cylinders and the distance between the surface elements of the two drying cylinders using the viewpoint factor integral formula. Use the calculated thermal radiation angle coefficient between each pair of adjacent drying cylinders as the weight of the directed edge pointing from the corresponding node of one drying cylinder to the corresponding node of the other drying cylinder, thereby establishing the directed graph of drying cylinder thermal radiation.

[0019] The specific implementation of generating a thermal-humidity coupled diffusion path network, using the enthalpy gradient direction of moist air at each measurement cross-section as the flow vector and combined with the directed thermal radiation graph of the drying cylinder, is as follows: For each measurement cross-section, using the enthalpy data of moist air at each measuring point on that cross-section, the rate of change of the enthalpy of moist air in the two orthogonal directions of the cross-section is calculated, and the enthalpy gradient vector of moist air at that measurement cross-section is synthesized. The direction of this enthalpy gradient vector is used as the flow vector for the transmission of enthalpy. The flow vector corresponding to each measurement cross-section is mapped to the node with the closest spatial position in the directed thermal radiation graph of the drying cylinder, and this flow vector is used as the dominant directional constraint for the diffusion of moist heat vapor at that node. Based on the existing directed edges in the directed thermal radiation graph of the drying cylinder, according to the dominant directional constraint, connecting edges representing the migration direction of enthalpy of moist air are added to form a thermal-humidity coupled diffusion path network that simultaneously includes the thermal radiation relationship of the drying cylinder and the migration relationship of enthalpy of moist air. In the aforementioned thermal-humidity coupled diffusion path network, the nodes still correspond to the centers of each drying cylinder, and the edges include directed edges weighted by the thermal radiation angle coefficient and directed edges weighted by the enthalpy gradient direction of the humid air.

[0020] The specific implementation of constructing a heat flux density distribution matrix by using the heat flux density at each intersection point in the heat-humidity coupled diffusion path network as matrix elements is as follows: In the heat-humidity coupled diffusion path network, identify all intersection points where two or more paths intersect. These intersection points correspond to the convergence areas of moist heat steam flow and radiative heat transfer between drying cylinders or near the measurement cross-section. Calculate the heat flux density at each intersection point, which is the heat passing through a unit area per unit time at that intersection point. This is obtained by summing the convective and radiative heat transfer from each connected path at that intersection point and dividing by the effective heat transfer area at that intersection point. Arrange all intersection points in the heat-humidity coupled diffusion path network according to their spatial distribution order to form the rows and columns of a two-dimensional matrix. Line number Column elements Indicates that it is located at the th The row corresponds to the horizontal coordinate and the first row. The column represents the heat flux density value at the path intersection point on the corresponding spatial vertical coordinate. When there is no path intersection point at a certain row or column position, the corresponding matrix element... The value is set to zero, thus constructing the heat flux density distribution matrix.

[0021] The specific implementation method for normalizing the heat flux density distribution matrix and sorting the matrix elements from largest to smallest to generate a waste heat recovery priority ranking table is as follows: extract the maximum value of all elements in the heat flux density distribution matrix. and minimum value Using a linear normalization method, for each element in the heat flux density distribution matrix Perform the transformation to obtain the normalized matrix elements. The normalization calculation formula is: in, Represents the th element in the normalized matrix. Line number The priority evaluation value of column elements, dimensionless, with a range of values. ; The heat flux density distribution matrix represents the first... Line number The heat flux density of the listed elements is expressed in watts per square meter. This represents the minimum value of all heat flux density values ​​in the heat flux density distribution matrix, expressed in watts per square meter. This represents the maximum value of all heat flux density values ​​in the heat flux density distribution matrix, expressed in watts per square meter.

[0022] All non-zero The elements are arranged in descending order of value, each... The wet heat steam source associated with the intersection position of the element is assigned a corresponding priority, and a waste heat recovery priority ranking table is generated. The waste heat recovery priority ranking table includes the wet heat steam source location identifier and the corresponding priority evaluation value, which is used for subsequent multi-stage heat exchange modules to distribute the heat in sequence.

[0023] Example 2: In specific implementation, please refer to Figure 2 The system's multi-stage heat exchange module obtains the waste heat recovery priority ranking table from the heat source tracking module. Each record in the waste heat recovery priority ranking table contains the location identifier of the wet heat steam source and the corresponding priority evaluation value. The priority evaluation value is a dimensionless value between 0 and 1. The first preset priority threshold and the second preset priority threshold are pre-stored in the system configuration parameters. The value of the first preset priority threshold is greater than the value of the second preset priority threshold. The specific values ​​of the two are determined before the system is put into operation according to the total heat allocation ratio of the waste heat recovery demand of the paper machine drying section: the first preset priority threshold is set to 0.7, which means that the top 30% of wet heat steam sources with priority evaluation values ​​are selected from all wet heat steam sources for high-temperature stage heat recovery; the second preset priority threshold is set to 0.3, which means that the bottom 30% of wet heat steam sources with priority evaluation values ​​are used for low-temperature stage heat recovery, and the remaining middle part of wet heat steam sources are used for medium-temperature stage heat recovery.

[0024] The first diversion queue is extracted as follows: All records in the waste heat recovery priority sorting table are traversed, and the priority evaluation value of each record is compared with a first preset priority threshold. When the priority evaluation value is greater than 0.7, the corresponding wet heat steam source is marked as a member of the first diversion queue, and the location identifier and pipeline channel information of the wet heat steam source are written into the first diversion queue list. The wet heat steam corresponding to the first diversion queue is centrally transported to the inlet header of the high-temperature heat exchange unit through a manifold with a switching valve.

[0025] The extraction of the second diversion queue is implemented as follows: Traverse the remaining records in the waste heat recovery priority sorting table that are not marked as members of the first diversion queue. Compare the priority evaluation value of each remaining record with the first preset priority threshold and the second preset priority threshold. When the priority evaluation value is greater than or equal to 0.3 and less than or equal to 0.7, mark the corresponding wet heat steam source as a member of the second diversion queue, and write the location identifier and pipeline channel information of the wet heat steam source into the second diversion queue list. The wet heat steam corresponding to the second diversion queue is centrally transported to the inlet header of the intermediate temperature heat exchange unit through another manifold.

[0026] The third diversion queue is extracted as follows: all wet heat steam sources with a priority evaluation value less than 0.3 in the waste heat recovery priority ranking table are marked as members of the third diversion queue, and the location identifier and pipeline channel information of the corresponding wet heat steam source are written into the third diversion queue list. The wet heat steam corresponding to the third diversion queue is centrally transported to the inlet header of the low-temperature stage heat exchange unit through the third manifold.

[0027] The specific implementation method for installing electrically controlled butterfly valves at the inlet of the high-temperature, medium-temperature, and low-temperature heat exchange units is as follows: a first electrically controlled butterfly valve is installed on the manifold before the inlet header of the high-temperature heat exchange unit; a second electrically controlled butterfly valve is installed on the manifold before the inlet header of the medium-temperature heat exchange unit; and a third electrically controlled butterfly valve is installed on the manifold before the inlet header of the low-temperature heat exchange unit. All three electrically controlled butterfly valves use actuators with continuously adjustable opening degrees, with an adjustment range of 0% to 100%, corresponding to the butterfly valve's state from fully closed to fully open.

[0028] The method for real-time adjustment of the electric regulating butterfly valve opening based on the instantaneous steam flow feedback value of each diversion queue is as follows: A first vortex flow meter is installed on the pipeline between the downstream of the inlet header of the high-temperature stage heat exchange unit and the first electric regulating butterfly valve. The first vortex flow meter measures the instantaneous steam flow feedback value of the first diversion queue in real time and transmits the instantaneous steam flow feedback value to the flow regulating controller. The flow regulating controller compares the instantaneous steam flow feedback value of the first diversion queue with the set flow value of the first diversion queue. The set flow value of the first diversion queue is calculated based on the rated heat exchange load of the high-temperature stage heat exchange unit and the inlet steam design parameters and is preset in the controller. When the instantaneous steam flow feedback value is less than the set flow value, the flow regulating controller outputs a control signal to increase the opening, driving the first electric regulating butterfly valve to move in the direction of increasing the opening; when the instantaneous steam flow feedback value is greater than the set flow value, the flow regulating controller outputs a control signal to decrease the opening, driving the first electric regulating butterfly valve to move in the direction of decreasing the opening, thereby maintaining the steam flow of the first diversion queue stable near the set flow value.

[0029] For the second electrically controlled regulating butterfly valve at the inlet of the intermediate-temperature heat exchange unit, the same method as described above is used. A second vortex flow meter is installed in the pipeline downstream of the inlet header of the intermediate-temperature heat exchange unit to measure the instantaneous steam flow feedback value of the second diversion queue. This value is compared with the set flow value of the second diversion queue, and the opening of the second electrically controlled regulating butterfly valve is adjusted by the corresponding flow control controller. For the third electrically controlled regulating butterfly valve at the inlet of the low-temperature heat exchange unit, a third vortex flow meter is installed in the pipeline downstream of the inlet header of the low-temperature heat exchange unit to measure the instantaneous steam flow feedback value of the third diversion queue. This value is compared with the set flow value of the third diversion queue, and the opening of the third electrically controlled regulating butterfly valve is adjusted by the corresponding flow control controller. The three flow control controllers operate independently, ensuring that the steam inlet flow of the high-temperature, intermediate-temperature, and low-temperature heat exchange units remains stable at their respective set values. This allows the multi-stage heat exchange module to stably divert wet hot steam of different qualities to the corresponding temperature-level heat exchange units for heat exchange and recovery, based on the heat source temperature gradient represented by the waste heat recovery priority ranking table.

[0030] Example 3: In specific implementation, please refer to Figure 3The method for measuring the mass flow rates of the high-temperature heat transfer fluid at the outlet of the high-temperature stage heat exchange unit, the medium-temperature heat transfer fluid at the outlet of the medium-temperature stage heat exchange unit, and the low-temperature heat transfer fluid at the outlet of the low-temperature stage heat exchange unit is as follows: A first Coriolis mass flow meter is installed on the outlet pipe of the high-temperature stage heat exchange unit. The measuring tube of the first Coriolis mass flow meter is made of stainless steel, which is compatible with the temperature and corrosiveness of the high-temperature heat transfer fluid. The first Coriolis mass flow meter outputs the mass flow rate of the high-temperature heat transfer fluid in kilograms per second, denoted as . A second Coriolis mass flow meter is installed on the outlet pipe of the intermediate-temperature heat exchange unit. This second Coriolis mass flow meter outputs the mass flow rate of the intermediate-temperature heat transfer fluid in kilograms per second, denoted as . A third Coriolis mass flow meter is installed on the outlet pipe of the cryogenic heat exchange unit. The third Coriolis mass flow meter outputs the cryogenic heat transfer fluid mass flow rate in kilograms per second, denoted as . The measurement signals from the three Coriolis mass flow meters are synchronously transmitted to the dedicated controller of the heat pump compensation module, which reads the signal once per control cycle. , and The instantaneous value.

[0031] The method for calculating the real-time flow ratio among the high-temperature heat transfer fluid mass flow rate, the medium-temperature heat transfer fluid mass flow rate, and the low-temperature heat transfer fluid mass flow rate is as follows: In the dedicated controller, the high-temperature heat transfer fluid mass flow rate is set. The mass flow rate of the intermediate-temperature heat transfer fluid corresponding to the first proportional component. Corresponding to the second proportional component, the mass flow rate of the low-temperature heat transfer fluid. Corresponding to the third proportional component, the calculation of the three proportional components adopts normalization processing, respectively using... , , Each value divided by the sum of the three. The high temperature flow rate ratio was obtained. Medium temperature flow rate ratio and low temperature flow rate ratio The sum of the three proportional values ​​is always equal to 1. The dedicated controller will control the triplet. Stored as a real-time traffic ratio value.

[0032] The method for measuring the high-temperature heat transfer fluid pressure at the outlet of the high-temperature stage heat exchange unit, the medium-temperature heat transfer fluid pressure at the outlet of the medium-temperature stage heat exchange unit, and the low-temperature heat transfer fluid pressure at the outlet of the low-temperature stage heat exchange unit is as follows: A first pressure transmitter is installed downstream of the first Coriolis mass flow meter on the outlet pipe of the high-temperature stage heat exchange unit. The first pressure transmitter outputs the high-temperature heat transfer fluid pressure in kilopascals, denoted as . A second pressure transmitter is installed downstream of the second Coriolis mass flow meter on the outlet pipe of the intermediate-temperature heat exchange unit. This second pressure transmitter outputs the pressure of the intermediate-temperature heat transfer fluid in kilopascals, denoted as [insert pressure here]. A third pressure transmitter is installed on the outlet pipe of the cryogenic heat exchange unit, downstream of the third Coriolis mass flow meter. This third pressure transmitter outputs the cryogenic heat transfer fluid pressure in kilopascals, denoted as [insert pressure here]. The measurement signals from the three pressure transmitters are synchronously transmitted to the dedicated controller of the heat pump compensation module.

[0033] The method for calculating the pressure fluctuation amplitude of each pressure relative to its respective design reference pressure is as follows: the design reference pressure of the high-temperature heat transfer fluid at the outlet of the high-temperature stage heat exchange unit is pre-stored in a dedicated controller. Design reference pressure of the intermediate-temperature heat transfer fluid at the outlet of the intermediate-temperature heat exchange unit and the design reference pressure of the cryogenic heat transfer fluid at the outlet of the cryogenic stage heat exchange unit These three design reference pressures are set based on the design pressure values ​​of each inlet of the heat pump compensation module under rated operating conditions, in kilopascals. The dedicated controller calculates the absolute value of the high-temperature pressure deviation in each control cycle. The absolute value of the temperature pressure deviation The absolute value of the deviation from the low temperature pressure The three absolute values ​​are used as the high-temperature pressure fluctuation amplitude, the medium-temperature pressure fluctuation amplitude, and the low-temperature pressure fluctuation amplitude, respectively.

[0034] The method for comparing the real-time flow ratio value with the preset optimal flow ratio value and calculating the flow ratio deviation is as follows: the preset optimal flow ratio value is pre-stored in a dedicated controller, and the preset optimal flow ratio value is a set of triplets. ,in This indicates the optimal flow rate ratio of the high-temperature heat transfer fluid. This indicates the optimal flow rate ratio of the medium-temperature heat transfer fluid. This indicates the optimal flow rate ratio of the low-temperature heat transfer fluid; all three values ​​are dimensionless and satisfy... The preset optimal flow ratio is determined based on the mixing ratio of the three heat transfer fluids required for the nozzles inside the heat pump compensation module to achieve the optimal injection coefficient under design conditions. This value is then calibrated through performance testing during the system commissioning phase and subsequently fixed to the dedicated controller. The dedicated controller calculates the flow ratio deviation. The method is as follows: calculate the high-temperature flow rate ratio deviation separately. Medium temperature flow rate ratio deviation and low temperature flow rate ratio deviation The maximum value among the three is taken as the flow ratio deviation. ,Right now .

[0035] The implementation method of using the weighted sum of the flow ratio deviation and the amplitude of each pressure fluctuation as the injection coefficient adjustment factor is as follows: In the dedicated controller, a first weighting coefficient is assigned to the flow ratio deviation. Assign a second weighting coefficient to the amplitude of high temperature pressure fluctuations. Assign a third weighting coefficient to the amplitude of intermediate temperature pressure fluctuations. Assign a fourth weighting coefficient to the amplitude of low-temperature pressure fluctuations. Injection coefficient adjustment factor The formula for calculation is: in, This represents the injection coefficient adjustment factor, which is a dimensionless value and takes the range of real numbers greater than or equal to 0. The weighting coefficient representing the deviation in flow ratio is a dimensionless value; This represents the flow rate deviation, a dimensionless value, with a range of values ​​ranging from [value missing]. ; The weighting coefficient representing the amplitude of high-temperature pressure fluctuations, expressed in kilopascals; This indicates the amplitude of high-temperature pressure fluctuation, expressed in kilopascals (kPa). The weighting coefficient representing the amplitude of pressure fluctuations at medium temperature, expressed in kilopascals; This indicates the amplitude of pressure fluctuation at medium temperature, expressed in kilopascals. The weighting coefficient representing the amplitude of low-temperature pressure fluctuations, expressed in kilopascals; This indicates the amplitude of low-temperature pressure fluctuation, expressed in kilopascals.

[0036] The weighting coefficients for the flow rate ratio deviation and the pressure fluctuation amplitudes in the injection coefficient adjustment factor are adaptively matched in real time based on the heat pump performance coefficient under the current operating conditions. This is achieved by programming a weighted adaptive matching algorithm in a dedicated controller. The dedicated controller acquires the heat pump performance coefficient under the current operating conditions from the heat pump compensation module within each control cycle. The coefficient of performance (COP) of a heat pump is defined as the ratio of the total heat output by the mixed heat transfer medium from the heat pump compensation module to the driving energy consumed by the heat pump compensation module. The COP is calculated in real time by a heat flow meter installed on the output main pipe of the heat pump compensation module and a power meter installed at the drive end. The weighted adaptive matching algorithm maintains a baseline set of weighted coefficients. When the COP... When the value exceeds the preset upper limit of the performance coefficient, it indicates that the heat pump is operating efficiently under the current conditions. In this case, the weighting factor of the flow ratio deviation should be increased. The proportion of each pressure fluctuation amplitude is reduced by decreasing the weighting coefficient. , , The proportion of this makes the injection coefficient adjustment factor more sensitive to the optimization of the mixing ratio; when the heat pump performance coefficient... When the pressure is below the preset lower limit of the performance coefficient, it indicates that the current operating condition deviates from the high-efficiency zone. In this case, the weighting coefficient of each pressure fluctuation amplitude should be increased. , , The proportion of, decrease The proportion of this factor ensures that the injection coefficient adjustment factor prioritizes pressure stability. The adaptive allocation of the weighting coefficients is achieved by linearly adjusting the magnitude of each weighting coefficient, and remains constant throughout all adjustments. The constraint relationship.

[0037] The method for obtaining the target injection coefficient at the current moment by querying the pre-stored injection coefficient-adjustment factor mapping table based on the injection coefficient adjustment factor is as follows: The injection coefficient-adjustment factor mapping table is pre-stored in the memory of a dedicated controller. The injection coefficient-adjustment factor mapping table is a one-dimensional lookup table with two columns of data. The first column is the injection coefficient adjustment factor. The second column contains the discrete values, and the third column contains the target injection coefficient corresponding to each discrete value. The injection coefficient-adjustment factor mapping table was established through offline experimental calibration: on the test platform of the heat pump compensation module, the injection coefficient adjustment factor was changed point by point. Adjust the nozzle opening of the heat pump compensation module according to the value until the optimal operating state is reached, and record the corresponding target injection coefficient. This establishes a mapping relationship. The dedicated controller calculates within the current control cycle... After obtaining the actual value, a linear interpolation method is used to look up the corresponding target injection coefficient in the injection coefficient-adjustment factor mapping table. ,when When the actual value exceeds the upper and lower limits of the mapping table, the target injection coefficient corresponding to the boundary value of the mapping table is taken.

[0038] The nozzle opening actuator of the heat pump compensation module is activated to the opening position corresponding to the target injection coefficient as follows: The nozzle opening actuator of the heat pump compensation module adopts a combination structure of an electric actuator and a needle nozzle. The electric actuator receives the opening command signal output by the dedicated controller, which expresses the nozzle opening as a percentage. The dedicated controller internally stores a calibration curve of nozzle opening versus injection coefficient. This calibration curve will determine the target injection coefficient. Mapped to nozzle opening percentage A dedicated controller will display the opening percentage. The signal is converted into a control current signal for the corresponding electric actuator. The electric actuator drives the valve core of the needle nozzle to move to the commanded position, thereby changing the nozzle throat area and realizing the dynamic adjustment of the injection coefficient.

[0039] Example 4: In practice, the condensation recovery module receives the mixed heat transfer medium generated by the heat pump compensation module. The mixed heat transfer medium enters the inlet manifold of the condensation recovery module through the delivery pipeline. Temperature and pressure sensors are installed on the inlet manifold to monitor the initial state parameters of the mixed heat transfer medium entering the flash separation unit.

[0040] The mixed heat transfer medium is introduced into the first-stage flash tank as follows: A liquid inlet pipe for the first-stage flash tank is connected downstream of the inlet main of the condensate recovery module. A first liquid inlet regulating valve is installed on the liquid inlet pipe. This first liquid inlet regulating valve is an electric V-type ball valve with an opening range of 0% to 100%, receiving opening command signals from the controller. The first-stage flash tank is a vertical pressure vessel, with the lower part of the tank containing the liquid phase and the upper part containing the gas phase. The tank's design pressure is determined based on the overall pressure rating of the paper machine's drying section's wet heat steam waste heat recovery system. The method for controlling the operating pressure of the first-stage flash tank to the first pressure value is as follows: A first pressure transmitter is installed at the top of the gas phase space of the first-stage flash tank. The first pressure transmitter measures the gas phase pressure inside the first-stage flash tank in real time and transmits the measured gas phase pressure signal to the flash pressure controller. The flash pressure controller has a pre-stored set value for the first pressure value. The set value for the first pressure value is calculated based on the required pressure threshold of the preheater in the pulping section plus the friction loss along the first conveying pipeline. The required pressure threshold of the preheater in the pulping section is determined by the process parameters of the pulping section during the system design stage. The flash pressure controller compares the internal gas phase pressure of the first-stage flash tank with the set value of the first pressure value. When the gas phase pressure is lower than the set value of the first pressure value, the flash pressure controller outputs a control signal to reduce the opening of the exhaust valve at the top of the first-stage flash tank, reducing the discharge of the first-stage flash steam and causing the pressure inside the tank to rise. When the gas phase pressure is higher than the set value of the first pressure value, the flash pressure controller outputs a control signal to increase the opening of the exhaust valve, increasing the discharge of the first-stage flash steam and causing the pressure inside the tank to decrease, thereby maintaining the operating pressure of the first-stage flash tank stable at the first pressure value.

[0041] The method for flashing saturated water with a pressure higher than a first pressure value in the mixed heat transfer medium into first-stage flash vapor is as follows: After the mixed heat transfer medium enters the first-stage flash tank, the operating pressure of the first-stage flash tank is controlled at the first pressure value, which is lower than the initial saturation pressure of the mixed heat transfer medium. The corresponding saturated water in the mixed heat transfer medium is in a superheated state and undergoes a flash phase change. The first-stage flash vapor generated by flashing rises into the gas phase space at the top of the first-stage flash tank, while the unflashed remaining liquid collects in the liquid phase region at the bottom of the first-stage flash tank due to gravity. The method for discharging the unflashed remaining liquid to the second-stage flash tank is as follows: A drain pipe is connected to the bottom of the first-stage flash tank, and the drain pipe is connected to the inlet of the second-stage flash tank. A first liquid level regulating valve is installed on the drain pipe at the bottom of the first-stage flash tank. The first liquid level regulating valve adjusts its opening according to the liquid level feedback value of the first-stage flash tank, discharging the unflashed remaining liquid to the second-stage flash tank.

[0042] The method for controlling the operating pressure of the second-stage flash tank to the second pressure value is as follows: The second-stage flash tank is also a vertical pressure vessel. A second pressure transmitter is installed at the top of the gas phase space of the second-stage flash tank. The second pressure transmitter measures the gas phase pressure inside the second-stage flash tank in real time and transmits the measured gas phase pressure signal to the second flash pressure controller. The second flash pressure controller has a pre-stored setpoint for the second pressure value. The setpoint for the second pressure value is calculated based on the required pressure threshold of the network cleaning water heater plus the friction loss along the second delivery pipeline. The required pressure threshold of the network cleaning water heater is determined by the network cleaning process. The second flash pressure controller maintains the operating pressure of the second-stage flash tank at the second pressure value by adjusting the opening of the exhaust valve at the top of the second-stage flash tank. The second pressure setting is lower than the first pressure setting, causing the saturated water in the remaining liquid entering the second-stage flash tank with a pressure higher than the second pressure to flash again into secondary flash steam. The secondary flash steam rises into the gas phase space at the top of the second-stage flash tank, while the unflashed remaining liquid collects in the liquid phase zone at the bottom of the second-stage flash tank and is discharged to the third-stage flash tank through the second liquid level regulating valve at the bottom of the second-stage flash tank.

[0043] The method for controlling the operating pressure of the third-stage flash tank to the third pressure value is as follows: A third pressure transmitter is installed at the top of the gas phase space of the third-stage flash tank. The third pressure transmitter measures the gas phase pressure inside the third-stage flash tank in real time and transmits the measured gas phase pressure signal to the third flash pressure controller. The third flash pressure controller has a pre-stored setpoint for the third pressure value. The setpoint for the third pressure value is calculated based on the required pressure threshold of the workshop heating radiator plus the friction loss along the third delivery pipeline. The required pressure threshold of the workshop heating radiator is determined by the workshop heating design parameters. The third flash pressure controller maintains the operating pressure of the third-stage flash tank at the third pressure value by adjusting the opening of the exhaust valve at the top of the third-stage flash tank. The set value of the third pressure value is less than the set value of the second pressure value, so that the saturated water with a pressure higher than the third pressure value in the remaining liquid entering the third-stage flash tank is flashed into third-stage flash steam. The third-stage flash steam rises into the gas phase space in the upper part of the third-stage flash tank. The final condensate after flashing collects in the liquid phase zone in the lower part of the third-stage flash tank and is discharged from the system through the drain port at the bottom of the third-stage flash tank.

[0044] The liquid level height of the first-stage flash tank, second-stage flash tank, and third-stage flash tank are measured separately as follows: A first guided wave radar level gauge is installed on the side of the first-stage flash tank. The waveguide rod of the first guided wave radar level gauge is inserted into the liquid phase zone from the top of the tank, emits an electromagnetic pulse, and receives the reflected echo from the liquid surface. The liquid level height of the first-stage flash tank is calculated based on the echo time, and a first liquid level height feedback value is output. A second guided wave radar level gauge is installed on the side of the second-stage flash tank, and a second liquid level height feedback value is output. A third guided wave radar level gauge is installed on the side of the third-stage flash tank, and a third liquid level height feedback value is output. The measuring range of the three guided wave radar level gauges is selected according to the corresponding height of the flash tank, and the output signal is a standard current signal of four to twenty milliamps.

[0045] The method for adjusting the opening of the inlet regulating valve of each flash tank based on the feedback value of each liquid level is as follows: The liquid level feedback value of the first-stage flash tank and the opening of the first inlet regulating valve form a cascade control loop, which includes a main controller and a secondary controller. The main controller receives the first liquid level feedback value output by the first guided wave radar level gauge, compares it with the first liquid level setpoint, and calculates the output value using a proportional-integral control algorithm. This output value serves as the setpoint for the secondary controller. The secondary controller receives the actual opening feedback value of the first inlet regulating valve, compares it with the output value of the main controller, and outputs an opening adjustment signal using a proportional control algorithm to drive the first inlet regulating valve to maintain the liquid level of the first-stage flash tank near the setpoint. The second liquid level feedback value of the second-stage flash tank and the opening of the second inlet regulating valve installed on the inlet pipe of the second-stage flash tank form a cascade control loop, with the same structure as that of the first-stage flash tank. The third liquid level height feedback value of the third-stage flash tank and the opening degree of the third liquid inlet regulating valve installed on the inlet pipe of the third-stage flash tank constitute a cascade control loop. The structure of the cascade control loop is the same as that of the first-stage flash tank.

[0046] The dynamic correction of the liquid level setpoint of each flash tank according to the inlet flow rate of the mixed heat transfer medium is achieved as follows: an inlet flow meter is installed on the inlet main of the condensate reuse module. The inlet flow meter measures the inlet flow rate of the mixed heat transfer medium in real time and transmits the inlet flow rate value to the liquid level setpoint correction controller. The liquid level setpoint correction controller pre-stores a relationship curve between the liquid level setpoint and the inlet flow rate. The function expression of the relationship curve is: in, Indicates the current time The flash tank level setpoint, in meters; This indicates the reference liquid level setting value of the flash tank under rated operating conditions, in meters, and is determined based on 50% of the height of each flash tank's volume. This represents the correction factor for the liquid level setpoint as the inlet flow rate changes. The unit is m·s per kilogram. The value of the correction factor is calculated by the ratio of the flash tank volume to the design residence time. Specifically, it is the ratio of the design residence time to the cross-sectional area of ​​each flash tank. Indicates the current time The inlet flow rate of the mixed heat transfer medium, in kilograms per second; This represents the reference inlet flow rate of the mixed heat transfer medium under rated operating conditions, expressed in kilograms per second. In each control cycle, the level setpoint correction controller calculates the corrected level setpoint based on the real-time inlet flow rate measured by the inlet flow meter, according to the aforementioned function expression. The corrected level setpoint is then written into the main controllers of the first-stage flash tank cascade control loop, the second-stage flash tank cascade control loop, and the third-stage flash tank cascade control loop, respectively, thus achieving dynamic correction of the level setpoint for each flash tank.

[0047] The method for measuring the primary flash steam pressure value of the first-stage flash tank is as follows: A first discharge pressure transmitter is installed on the exhaust pipe at the top of the first-stage flash tank, downstream of the exhaust valve. The first discharge pressure transmitter measures the pressure of the primary flash steam at the starting point of delivery to obtain the primary flash steam pressure value. The method for comparing the primary flash steam pressure value with the required pressure threshold of the pulping section preheater is as follows: The measurement signal from the first discharge pressure transmitter is transmitted to a first pressure comparison controller. The first pressure comparison controller has a pre-stored required pressure threshold for the pulping section preheater. The first pressure comparison controller internally executes numerical comparison logic to determine whether the primary flash steam pressure value is greater than or equal to the required pressure threshold of the pulping section preheater. When the primary flash steam pressure is greater than or equal to the required pressure threshold of the pulping section preheater, the first pressure comparison controller outputs a high-level signal to the first electric switch valve on the first delivery pipeline. The first electric switch valve is energized and opens, delivering the primary flash steam to the pulping section preheater. When the primary flash steam pressure is less than the required pressure threshold of the pulping section preheater, the first pressure comparison controller outputs a low-level signal, and the first electric switch valve remains closed.

[0048] The method for measuring the secondary flash steam pressure in the second-stage flash tank is as follows: A second discharge pressure transmitter is installed on the exhaust pipe at the top of the second-stage flash tank, downstream of the exhaust valve. The second discharge pressure transmitter measures the pressure of the secondary flash steam at the starting point of delivery, obtaining the secondary flash steam pressure value. This secondary flash steam pressure value is compared with the required pressure threshold of the network cleaning water heater. When the secondary flash steam pressure value is greater than or equal to the required pressure threshold of the network cleaning water heater, the second electrically operated valve on the second delivery pipe opens, delivering the secondary flash steam to the network cleaning water heater.

[0049] The method for measuring the tertiary flash steam pressure in the tertiary flash tank is as follows: A third discharge pressure transmitter is installed on the exhaust pipe at the top of the tertiary flash tank, downstream of the exhaust valve. This transmitter measures the pressure of the tertiary flash steam at the starting point of delivery, obtaining the tertiary flash steam pressure value. This pressure value is compared with the required pressure threshold of the workshop heating radiators. When the tertiary flash steam pressure value is greater than or equal to the required pressure threshold of the workshop heating radiators, the third electrically operated valve on the third delivery pipe opens, delivering the tertiary flash steam to the workshop heating radiators.

[0050] The installation of pressure compensation valves on the first, second, and third delivery pipelines is implemented as follows: A first pressure compensation valve is installed on the first delivery pipeline downstream of the first electrically operated valve. The inlet of the first pressure compensation valve is connected to the high-temperature heat transfer fluid supply pipeline in the media control module via a bypass pipeline. A second pressure compensation valve is installed on the second delivery pipeline downstream of the second electrically operated valve. The inlet of the second pressure compensation valve is also connected to the high-temperature heat transfer fluid supply pipeline via a bypass pipeline. A third pressure compensation valve is installed on the third delivery pipeline downstream of the third electrically operated valve. The inlet of the third pressure compensation valve is connected to the high-temperature heat transfer fluid supply pipeline.

[0051] The mechanism for opening pressure compensation valves to introduce high-temperature heat transfer fluid from the media control module to compensate for pressure when each flash steam pressure value is lower than the corresponding required pressure threshold is as follows: When the first-stage flash steam pressure value is determined to be lower than the required pressure threshold of the pulping section preheater, the first pressure comparison controller, in addition to keeping the first electric switch valve closed, simultaneously outputs an opening signal to the first pressure compensation valve. Upon receiving the signal, the first pressure compensation valve opens, introducing the high-temperature heat transfer fluid from the media control module into the first delivery pipeline, thereby increasing the fluid pressure entering the pulping section preheater to above the required pressure threshold of the pulping section preheater. The second pressure comparison controller uses the same logic; when the second-stage flash steam pressure value is lower than the required pressure threshold of the network cleaning water heater, it controls the second pressure compensation valve to open. The third pressure comparison controller controls the third pressure compensation valve to open when the third-stage flash steam pressure value is lower than the required pressure threshold of the workshop heating radiator. The pressure compensation valves automatically close after the flash steam pressure recovers to above the corresponding required pressure threshold.

[0052] Example 5: In practical implementation, the medium control module acquires measurement data reflecting the flow and temperature drop during the transport process by arranging sensors on the pipeline carrying the mixed heat transfer medium. A first ultrasonic flow meter and a first thermocouple are installed at the inlet section of the pipeline. The first ultrasonic flow meter uses an external clamp-on installation method, with a pair of ultrasonic transducers symmetrically installed on both sides of the outer wall of the inlet section. The ultrasonic transducers emit ultrasonic pulses that penetrate the pipe wall and the mixed heat transfer medium. The inlet velocity of the mixed heat transfer medium is calculated based on the propagation time difference between the forward and reverse flows, and the inlet velocity value is output in meters per second. The first thermocouple is inserted into the central region of the mixed heat transfer medium within the inlet section of the pipeline to measure the inlet temperature of the mixed heat transfer medium, and the inlet temperature value is output in degrees Celsius. A second ultrasonic flow meter and a second thermocouple are installed at the outlet section of the delivery pipeline. The installation method and output parameters of the second ultrasonic flow meter and the second thermocouple are the same as those of the corresponding equipment at the inlet section. The second ultrasonic flow meter outputs the outlet flow velocity of the mixed heat transfer medium in meters per second, and the second thermocouple outputs the outlet temperature of the mixed heat transfer medium in degrees Celsius.

[0053] The method for calculating the difference between the inlet and outlet velocities of the mixed heat transfer medium as the velocity attenuation is as follows: The signal processing unit in the medium control module synchronously acquires the inlet velocity value of the mixed heat transfer medium output by the first ultrasonic flow meter and the outlet velocity value of the mixed heat transfer medium output by the second ultrasonic flow meter. In each acquisition cycle, the inlet velocity value of the mixed heat transfer medium is subtracted from the outlet velocity value of the mixed heat transfer medium, and the difference is used as the velocity attenuation for that acquisition cycle. The unit of the velocity attenuation is meters per second.

[0054] The method for calculating the temperature drop rate by dividing the difference between the inlet and outlet temperatures of the mixed heat transfer medium by the length of the delivery pipeline is as follows: The signal processing unit simultaneously acquires the inlet temperature value of the mixed heat transfer medium output by the first thermocouple and the outlet temperature value output by the second thermocouple, and obtains the length value of the delivery pipeline. The length value of the delivery pipeline is a fixed parameter pre-stored in the signal processing unit, and its value is the actual length of the pipeline segment between the measurement points at the inlet and outlet sections, in meters. The expression for calculating the temperature drop rate is: in, This indicates the rate of temperature drop, expressed in degrees Celsius per meter. This indicates the inlet temperature of the mixed heat transfer medium, in degrees Celsius. This indicates the outlet temperature of the mixed heat transfer medium, in degrees Celsius. This indicates the length of the delivery pipeline, in meters.

[0055] The method for continuously collecting flow rate attenuation and temperature drop rate data at multiple time points to generate flow rate attenuation and temperature drop rate time series curves is as follows: The signal processing unit continuously samples the flow rate attenuation and temperature drop rate at a preset sampling interval of 1 second. The signal processing unit establishes a circular buffer in memory to store the flow rate attenuation values ​​and temperature drop rate values ​​at the most recent 600 sampling time points, corresponding to data within a 10-minute time window. The signal processing unit concatenates the stored flow rate attenuation values ​​in chronological order to generate a flow rate attenuation time series curve, with time on the horizontal axis and flow rate attenuation on the vertical axis; similarly, it concatenates the stored temperature drop rate values ​​in chronological order to generate a temperature drop rate time series curve, with time on the horizontal axis and temperature drop rate on the vertical axis.

[0056] The peak decay rate is extracted from the velocity decay time-series curve as follows: the signal processing unit iterates through all velocity decay values ​​in the velocity decay time-series curve within the current time window, extracts the largest velocity decay value as the peak decay rate, and the unit of the peak decay rate is meters per second. The peak decay rate reflects the most severe velocity loss of the mixed heat transfer medium in the pipeline during the statistical time period.

[0057] The method for extracting the maximum temperature drop slope from the temperature drop rate time-series curve is as follows: The signal processing unit performs point-by-point differential processing on the temperature drop rate time-series curve, calculates the change in temperature drop rate between two adjacent acquisition time points, divides it by the acquisition time interval, and obtains the temperature drop slope at each acquisition time point. The unit of the temperature drop slope is degrees Celsius per meter per second. The signal processing unit iterates through all the calculated temperature drop slope values ​​and extracts the temperature drop slope with the largest value as the maximum temperature drop slope. The maximum temperature drop slope reflects the fastest trend of temperature drop rate increase within a local time period.

[0058] The comparison between the peak decay rate in the flow rate decay time-series curve and the preset upper limit of decay rate is implemented as follows: The preset upper limit of decay rate is pre-stored in the signal processing unit. The preset upper limit of decay rate is determined based on the maximum allowable flow rate decay of the piping in each heat exchange unit of the multi-stage heat exchange module, and is specifically set to 0.5 m / s. In each analysis cycle, the signal processing unit compares the peak decay rate extracted within the current time window with the preset upper limit of decay rate, 0.5 m / s. When the peak decay rate is greater than 0.5 m / s, the signal processing unit generates a first adjustment command to reduce the proportion of heat exchange area input; when the peak decay rate is less than or equal to 0.5 m / s, no first adjustment command is generated.

[0059] The comparison between the maximum temperature drop slope in the temperature drop rate time-series curve and the preset upper limit of the temperature drop slope is implemented as follows: The preset upper limit of the temperature drop slope is pre-stored in the signal processing unit. The preset upper limit of the temperature drop slope is determined based on the maximum allowable rate of change of heat loss of the mixed heat transfer medium in the pipeline, specifically set to 0.02 degrees Celsius per meter per second. Within each analysis cycle, the signal processing unit compares the maximum temperature drop slope extracted within the current time window with the preset upper limit of the temperature drop slope of 0.02 degrees Celsius per meter per second. When the maximum temperature drop slope is greater than 0.02 degrees Celsius per meter per second, the signal processing unit generates a second adjustment command to increase the proportion of heat exchange area input; when the maximum temperature drop slope is less than or equal to 0.02 degrees Celsius per meter per second, no second adjustment command is generated.

[0060] When both the first and second adjustment commands are received simultaneously, the system calculates the first difference between the peak attenuation rate and the preset attenuation rate upper limit, and the second difference between the maximum temperature drop slope and the preset temperature drop slope upper limit. The comparison of these two differences is implemented as follows: In the signal processing unit, when both the first and second adjustment commands are generated within the same analysis cycle, the system calculates the first difference obtained by subtracting the preset attenuation rate upper limit of 0.5 meters per second from the peak attenuation rate, and the second difference obtained by subtracting the preset temperature drop slope upper limit of 0.02 degrees Celsius per meter per second from the maximum temperature drop slope. The unit for the first difference is meters per second, and the unit for the second difference is degrees Celsius per meter per second. The signal processing unit dimensionlessly assigns the first difference and divides it by the preset attenuation rate upper limit of 0.5 meters per second to obtain the first deviation ratio; similarly, it dimensionlessly assigns the second difference and divides it by the preset temperature drop slope upper limit of 0.02 degrees Celsius per meter per second to obtain the second deviation ratio. Compare the first deviation ratio with the second deviation ratio. If the first deviation ratio is greater than the second deviation ratio, the first adjustment command is executed first. If the second deviation ratio is greater than the first deviation ratio, the second adjustment command is executed second.

[0061] The implementation method for sending opening control signals to the bypass valves of each heat exchange unit in the multi-stage heat exchange module according to the final executed adjustment command is as follows: When the final executed adjustment command is the first adjustment command, the signal processing unit simultaneously sends an opening increase signal to the bypass valves of the high-temperature stage heat exchange unit, the intermediate-temperature stage heat exchange unit, and the low-temperature stage heat exchange unit. The opening increase of the bypass valve is carried out according to a preset step size, which is 5% of the current opening size. Each adjustment maintains one adjustment step size, waiting for the next analysis cycle for re-evaluation. After the bypass valve opening is increased, the proportion of mixed heat transfer medium diverted through the bypass pipeline increases, resulting in a decrease in the effective heat exchange area entering the corresponding heat exchange unit, thereby reducing the proportion of heat exchange area used. When the final executed adjustment command is the second adjustment command, the signal processing unit simultaneously sends opening reduction signals to the bypass valves of the high-temperature stage heat exchange unit, the intermediate-temperature stage heat exchange unit, and the low-temperature stage heat exchange unit. The opening reduction of the bypass valves is also in steps of 5% of the current opening. By reducing the bypass diversion ratio, the flow rate of the mixed heat transfer medium entering the heat exchange unit is increased, thereby increasing the effective heat exchange area and thus increasing the proportion of heat exchange area in operation. The specific method of changing the number of heat exchange units in operation by adjusting the bypass valve opening is as follows: when the bypass valve opening increases to exceed the preset bypass upper limit threshold (set to 90%), the corresponding heat exchange unit is determined to be out of effective heat exchange state, and the number of heat exchange units in operation decreases; when the bypass valve opening decreases to below the preset bypass lower limit threshold (set to 10%), the corresponding heat exchange unit is determined to be fully in effective heat exchange state, and the number of heat exchange units in operation increases. Through the aforementioned closed-loop regulation process, the media control module dynamically adjusts the heat exchange area ratio of the multi-stage heat exchange modules based on real-time monitoring results of flow rate attenuation and temperature drop rate.

[0062] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A waste heat recovery system for wet steam in the drying section of a paper machine, characterized in that, The system includes: The heat source tracking module is used to construct a transient heat source topology matrix of wet heat steam based on the real-time heat radiation flux of each drying cylinder area in the paper machine drying section and the density distribution of humid air in the hood, and to generate a waste heat recovery priority ranking table based on the transient heat source topology matrix. The multi-stage heat exchange module is used to respond to the waste heat recovery priority sorting table, and to divert the wet heat steam to the high-temperature stage heat exchange unit, the medium-temperature stage heat exchange unit and the low-temperature stage heat exchange unit according to the heat source temperature gradient, and output high-temperature heat transfer fluid, medium-temperature heat transfer fluid and low-temperature heat transfer fluid respectively. The heat pump compensation module is used to receive the high-temperature heat transfer fluid, the medium-temperature heat transfer fluid and the low-temperature heat transfer fluid, and dynamically adjust the injection coefficient according to the real-time flow ratio and pressure fluctuation amplitude of each heat transfer fluid to generate a mixed heat transfer medium. The condensation and reuse module is used to perform multi-stage flash evaporation separation treatment on the mixed heat transfer medium, extracting first-stage flash steam, second-stage flash steam and third-stage flash steam, and delivering them to the preheater of the pulping section, the cleaning water heater of the mesh section and the heating radiator of the workshop according to the pressure level of each flash steam. The medium control module is used to monitor the flow rate decrease and temperature drop rate of the mixed heat transfer medium in the delivery pipeline, and adjust the heat exchange area input ratio of the multi-stage heat exchange module according to the flow rate decrease and temperature drop rate.

2. The paper machine drying section wet heat steam waste heat recovery system according to claim 1, characterized in that, The specific implementation methods for constructing the transient heat source topology matrix of wet steam by the heat source tracking module include: Infrared thermal imaging temperature field data of the surface of each drying cylinder in the paper machine drying section and enthalpy data of moist air at each measurement section inside the air hood were collected. A directed graph of thermal radiation of drying cylinders is established with the center coordinates of each drying cylinder as nodes and the thermal radiation angle coefficient between adjacent drying cylinders as edge weights. Using the enthalpy gradient direction of moist air at each measurement section as the flow vector, and combining it with the directed thermal radiation diagram of the drying cylinder, a thermal-humidity coupling diffusion path network is generated. The heat flux density at each path intersection point in the thermal-humidity coupled diffusion path network is used as matrix elements to construct a heat flux density distribution matrix. The heat flux density distribution matrix is ​​normalized and sorted by matrix element values ​​from largest to smallest to generate a waste heat recovery priority ranking table.

3. The paper machine drying section wet heat steam waste heat recovery system according to claim 1, characterized in that, The specific implementation methods of the multi-stage heat exchange module that divert humid heat steam to the high-temperature stage heat exchange unit, the medium-temperature stage heat exchange unit, and the low-temperature stage heat exchange unit according to the heat source temperature gradient include: Extract the wet heat steam sources with a priority higher than the first preset priority threshold from the waste heat recovery priority sorting table as the first diversion queue, and input the wet heat steam corresponding to the first diversion queue into the high-temperature heat exchange unit; Extract the wet heat steam source with a priority between the first preset priority threshold and the second preset priority threshold from the waste heat recovery priority sorting table as the second diversion queue, and input the wet heat steam corresponding to the second diversion queue into the medium temperature stage heat exchange unit; Extract the wet heat steam sources with a priority lower than the second preset priority threshold from the waste heat recovery priority sorting table as the third diversion queue, and input the wet heat steam corresponding to the third diversion queue into the low temperature stage heat exchange unit; Electric regulating butterfly valves are installed at the inlet of the high-temperature heat exchange unit, the medium-temperature heat exchange unit, and the low-temperature heat exchange unit, respectively. The opening degree of the electric regulating butterfly valves is adjusted in real time according to the instantaneous steam flow feedback value of each diversion queue.

4. The paper machine drying section wet heat steam waste heat recovery system according to claim 1, characterized in that, The specific implementation methods of the heat pump compensation module dynamically adjusting the injection coefficient based on the real-time flow ratio and pressure fluctuation amplitude of each heat transfer fluid include: The mass flow rates of the high-temperature heat transfer fluid at the outlet of the high-temperature stage heat exchange unit, the medium-temperature heat transfer fluid at the outlet of the medium-temperature stage heat exchange unit, and the low-temperature heat transfer fluid at the outlet of the low-temperature stage heat exchange unit are measured respectively, and the real-time flow ratios among the high-temperature heat transfer fluid mass flow rates, the medium-temperature heat transfer fluid mass flow rates, and the low-temperature heat transfer fluid mass flow rates are calculated. The pressure of the high-temperature heat transfer fluid at the outlet of the high-temperature stage heat exchange unit, the pressure of the medium-temperature heat transfer fluid at the outlet of the medium-temperature stage heat exchange unit, and the pressure of the low-temperature heat transfer fluid at the outlet of the low-temperature stage heat exchange unit were measured respectively, and the pressure fluctuation amplitude of each pressure relative to its respective design reference pressure was calculated. The real-time traffic ratio value is compared with the preset optimal traffic ratio value to calculate the traffic ratio deviation. The weighted sum of the flow rate ratio deviation and the amplitude of each pressure fluctuation is used as the injection coefficient adjustment factor. The target injection coefficient at the current moment is obtained by querying the pre-stored injection coefficient-adjustment factor mapping table according to the injection coefficient adjustment factor, and the nozzle opening actuator of the heat pump compensation module is driven to move to the opening position corresponding to the target injection coefficient.

5. A waste heat recovery system for wet steam in a paper machine drying section according to claim 1, characterized in that, The specific implementation method of the multi-stage flash evaporation separation treatment of the mixed heat transfer medium by the condensation reuse module includes: The mixed heat transfer medium is introduced into the first-stage flash tank, and the operating pressure of the first-stage flash tank is controlled to a first pressure value. The saturated water in the mixed heat transfer medium with a pressure higher than the first pressure value is flashed into first-stage flash steam, and the remaining liquid that has not been flashed is discharged to the second-stage flash tank. The operating pressure of the second-stage flash tank is controlled to a second pressure value, so that the saturated water in the remaining liquid entering the second-stage flash tank with a pressure higher than the second pressure value is flashed into secondary flash steam, and the unflashed remaining liquid is discharged to the third-stage flash tank, wherein the second pressure value is less than the first pressure value; The operating pressure of the third-stage flash tank is controlled to a third pressure value, so that the saturated water in the remaining liquid entering the third-stage flash tank with a pressure higher than the third pressure value is flashed into third-stage flash steam, and the final condensate after flashing is discharged, wherein the third pressure value is less than the second pressure value. Measure the liquid level in the first-stage flash tank, the second-stage flash tank, and the third-stage flash tank respectively, and adjust the opening of the liquid inlet regulating valve of each flash tank according to the feedback value of each liquid level.

6. A waste heat recovery system for wet steam in a paper machine drying section according to claim 5, characterized in that, The specific implementation methods for the condensate recycling module to deliver flash steam to the preheater of the pulping section, the cleaning water heater of the mesh section, and the workshop heating radiator according to the pressure level of each flash steam include: Measure the first-stage flash steam pressure value of the first-stage flash tank, compare the first-stage flash steam pressure value with the required pressure threshold of the pulping section preheater, and when the first-stage flash steam pressure value is greater than or equal to the required pressure threshold, open the first delivery pipeline to deliver the first-stage flash steam to the pulping section preheater. Measure the secondary flash steam pressure value of the second-stage flash tank, compare the secondary flash steam pressure value with the required pressure threshold of the mesh cleaning water heater, and when the secondary flash steam pressure value is greater than or equal to the required pressure threshold of the mesh cleaning water heater, open the second delivery pipeline to deliver the secondary flash steam to the mesh cleaning water heater. Measure the tertiary flash steam pressure value of the tertiary flash tank, compare the tertiary flash steam pressure value with the required pressure threshold of the workshop heating radiator, and when the tertiary flash steam pressure value is greater than or equal to the required pressure threshold of the workshop heating radiator, open the third delivery pipeline to deliver the tertiary flash steam to the workshop heating radiator. Pressure compensation valves are installed on the first, second, and third delivery pipelines respectively. When the pressure value of each flash steam is lower than the corresponding required pressure threshold, the pressure compensation valve is opened to introduce high-temperature heat transfer fluid from the medium control module for pressure compensation.

7. A waste heat recovery system for wet steam in a paper machine drying section according to claim 1, characterized in that, The specific implementation methods of the medium control module for monitoring the flow rate attenuation and temperature drop rate of the mixed heat transfer medium in the delivery pipeline include: A first ultrasonic flow meter and a first thermocouple are installed at the inlet section of the delivery pipeline to measure the inlet flow velocity and inlet temperature of the mixed heat transfer medium. A second ultrasonic flow meter and a second thermocouple are installed at the outlet section of the delivery pipeline to measure the outlet flow rate and outlet temperature of the mixed heat transfer medium. The difference between the inlet flow velocity and the outlet flow velocity is calculated as the flow velocity attenuation, and the difference between the inlet temperature and the outlet temperature is divided by the length of the delivery pipeline as the temperature drop rate. The flow rate decay and temperature drop rate are continuously collected at multiple time points to generate flow rate decay time series curves and temperature drop rate time series curves. Extract the peak decay rate from the flow rate decay time series curve and the maximum temperature drop slope from the temperature drop rate time series curve.

8. A waste heat recovery system for wet steam in a paper machine drying section according to claim 7, characterized in that, The specific implementation methods of the medium control module adjusting the heat exchange area input ratio of the multi-stage heat exchange module according to the flow rate attenuation and the temperature drop rate include: The peak decay rate in the flow rate decay time series curve is compared with the preset decay rate upper limit. If the peak decay rate is greater than the preset decay rate upper limit, a first adjustment command to reduce the proportion of heat exchange area input is generated. The maximum temperature drop slope in the temperature drop rate time series curve is compared with the preset upper limit of the temperature drop slope. If the maximum temperature drop slope is greater than the preset upper limit of the temperature drop slope, a second adjustment command is generated to increase the proportion of heat exchange area input. When the first adjustment command and the second adjustment command are received simultaneously, the first difference between the peak attenuation rate and the preset attenuation rate upper limit and the second difference between the maximum temperature drop slope and the preset temperature drop slope upper limit are calculated. The magnitudes of the first difference and the second difference are compared, and the first adjustment command or the second adjustment command is executed first based on the comparison result. According to the final executed adjustment command, the opening control signal is sent to the bypass valve of each heat exchange unit in the multi-stage heat exchange module. By adjusting the opening of the bypass valve, the number of heat exchange units put into operation is changed, thereby adjusting the proportion of heat exchange area put into operation.

9. A waste heat recovery system for wet steam in a paper machine drying section according to claim 4, characterized in that, The weighting coefficients of the flow rate ratio deviation and the pressure fluctuation amplitude in the injection coefficient adjustment factor are adaptively matched in real time according to the heat pump performance coefficient under the current operating conditions.

10. A waste heat recovery system for wet steam in a paper machine drying section according to claim 5, characterized in that, The liquid level feedback values ​​of the first-stage flash tank, the second-stage flash tank, and the third-stage flash tank respectively form a cascade control loop with the opening degree of their respective inlet regulating valves, and the liquid level set value of each flash tank is dynamically corrected according to the inlet flow rate of the mixed heat transfer medium.

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