Baking waste heat recovery method and system based on multistage heat exchange

Abstract

The embodiment of the invention provides a baking waste heat recovery method and system based on multistage heat exchange, and belongs to the technical field of waste heat recovery and utilization. The method comprises the steps that exhaust operation parameters in the baking process are obtained, and a plurality of thermotechnical stages and stage identifiers corresponding to the thermotechnical stages are obtained; determining a heat grade index and a dew point difference of each thermal stage based on the stage identifier, and generating a cascade sequence and a valve position control parameter corresponding to each thermal stage; calling the corresponding cascading sequence and the valve position control parameters according to the stage identifiers to execute sequential heat exchange, and calculating to obtain a heat recovery result of each thermal stage; and according to the stage identifier and the production line rhythm, the heat recovery result is distributed to the heat utilization link according to the priority matrix, and the priority matrix and the distribution quantity are dynamically corrected based on the energy demand during stage switching. According to the scheme, dynamic matching of heat energy and self-adaptive control of condensation risks in the baking process are achieved, so that the waste heat utilization rate is increased, and the temperature field in the furnace is kept stable.

Description

Technical Field

[0001] This invention relates to the field of waste heat recovery and utilization technology, specifically to a baking waste heat recovery method and a baking waste heat recovery system based on multi-stage heat exchange. Background Technology

[0002] In the food processing industry, baking ovens, as key heat treatment equipment, account for a significant proportion of overall production energy consumption. The high-temperature exhaust generated during baking contains a large amount of recoverable heat, but existing waste heat recovery technologies generally suffer from low energy utilization efficiency. Traditional devices often employ single-stage heat exchange structures or constant heat exchange modes, recovering a portion of sensible or latent heat through fixed pipelines and valves. Their operation control primarily relies on steady-state heat recovery and fails to dynamically respond to the periodic changes in the baking process.

[0003] However, the baking process is not a stable operating condition. With the continuous fluctuations in production line cycle time, furnace temperature distribution, and exhaust humidity, the heat grade and dew point conditions of the exhaust gas vary significantly at each stage. If a fixed heat exchange strategy is still adopted, problems such as condensation and oil accumulation and decreased heat exchange efficiency are likely to occur during high humidity and high temperature stages. On the other hand, a large amount of recoverable heat cannot be effectively utilized during low load stages, resulting in large fluctuations in recovery efficiency and low heat energy matching. At the same time, baking production lines typically operate with continuous feeding, intermittent start-up and shutdown, or variable speed conveying. Their operating rhythm directly affects the heat load distribution, but existing waste heat recovery systems generally lack a coordinated control mechanism with the production line cycle time, making it impossible to adjust the recovery and utilization strategy in a timely manner when operating conditions change.

[0004] Therefore, existing technologies suffer from the problem of failing to establish a dynamic waste heat recovery and distribution mechanism that coordinates with changes in baking conditions and production line rhythm. In other words, existing solutions often use static parameters or a fixed sequence for heat exchange and distribution, lacking the identification and response to the thermal characteristics of different stages of baking. This leads to a disconnect between the heat recovery process and the production line's operating status, affecting recovery efficiency and increasing the risk of condensation. How to achieve dynamic and coordinated control of multi-stage heat exchange units under varying operating conditions, and how to ensure that the recovered heat is distributed synchronously with the baking rhythm, is a core technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for recovering baking waste heat based on multi-stage heat exchange, so as to at least solve the problems of low waste heat recovery efficiency and asynchronous heat distribution with production line cycle time in the baking process.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for recovering baking waste heat based on multi-stage heat exchange. The method is applied to a baking oven equipped with an exhaust gas collection pipeline and multi-stage heat exchange units. The method includes: acquiring exhaust gas operating parameters of the baking process, establishing a hierarchical operating condition model, obtaining multiple thermal stages and corresponding stage identifiers for each thermal stage; determining the heat grade index and dew point difference of each thermal stage based on the stage identifiers, generating a cascading sequence and valve position control parameters corresponding to each thermal stage; performing time-sequential heat exchange according to the stage identifiers and calling the corresponding cascading sequence and valve position control parameters, calculating the recovered heat results for each thermal stage, and switching the thermal stage to a sensible heat recovery sub-mode when the dew point difference of any stage is lower than a preset threshold; allocating the recovered heat results to heat-using links according to a priority matrix based on the stage identifiers and production line cycle time, and dynamically correcting the priority matrix and allocation amount based on energy demand during stage switching.

[0007] Optionally, the exhaust operating parameters of the baking process are obtained, a hierarchical operating condition model is established, and multiple thermal stages and corresponding stage identifiers for each thermal stage are obtained. This includes: collecting temperature, humidity, and flow information from the exhaust operating parameters of the baking oven based on the exhaust collection pipeline, and calculating the corresponding exhaust temperature rise rate, humidity change rate, and flow fluctuation amplitude to form a comprehensive criterion for reflecting the dynamic characteristics of the baking process; determining the boundary moments of each stage based on the comprehensive criterion, and dividing the continuous baking process into multiple thermal stages; wherein, the thermal stages include a preheating stage, a steady-state baking stage, a steam peak stage, and a cooling stage; and assigning a unique stage identifier to each thermal stage.

[0008] Optionally, based on the stage identifier, the heat quality index and dew point difference of each thermal stage are determined, and the cascading sequence and valve position control parameters corresponding to each thermal stage are generated. This includes: using the stage identifier as the trigger index, calling the exhaust operating parameters and heat exchange unit operating parameters of the corresponding stage to construct a stage input set; calculating the recoverable enthalpy difference in the heat balance model based on the stage input set to determine the heat quality index, and calculating the heat exchange wall temperature and exhaust dew point temperature in combination with the wall thermal model to obtain the dew point difference; generating the cascading sequence and valve position control parameters of the stage under the constraints of heat quality index sorting and dew point difference and pressure drop; when the dew point difference is lower than the preset threshold, correcting the cascading configuration of the stage to prioritize sensible heat and updating the valve position control parameters.

[0009] Optionally, the heat quality index is determined by calculating the recoverable enthalpy difference in the heat balance model based on the stage input set, and the heat exchange wall temperature and exhaust dew point temperature are calculated in combination with the wall thermal model to obtain the dew point difference. This includes: inputting the exhaust temperature, humidity, and flow rate parameters from the stage input set into the stage heat balance model, calculating the recoverable enthalpy difference per unit mass of exhaust gas to obtain the heat quality index characterizing the degree of thermal energy utilization; using the heat exchange unit wall parameters and airflow boundary conditions from the stage input set as inputs, and obtaining the corresponding heat exchange wall temperature based on the wall thermal model; substituting the exhaust humidity and temperature data into the dew point calculation model to obtain the exhaust dew point temperature, and comparing it with the heat exchange wall temperature to obtain the dew point difference; and establishing a correspondence between the heat quality index and the dew point difference and the stage identifier.

[0010] Optionally, under the constraints of heat quality index ranking and dew point difference and pressure drop, the cascading sequence and valve position control parameters for this stage are generated, including: calling the heat quality index, dew point difference, and pressure drop data of the current thermal stage to construct a stage constraint set; generating candidate cascading sequences in descending order of heat quality index under the condition of meeting the preset safety threshold, and filtering the stage cascading configuration by combining the dew point difference and pressure drop constraints; outputting the valve position opening degree and air volume ratio of each heat exchange unit based on the stage cascading configuration and calling the valve position calculation rules; when the stage constraints do not meet the preset safety threshold, switching to a sensible heat priority downgraded configuration and updating the valve position control parameters.

[0011] Optionally, according to the stage identifier, the corresponding cascade sequence and valve position control parameters are invoked to perform time-sequential heat exchange, calculate the recovered heat results of each thermal stage, and switch the thermal stage to sensible heat recovery sub-mode when the dew point difference of any stage is lower than a preset threshold. This includes: retrieving the cascade sequence and valve position control parameters associated with the current thermal stage, and performing heat exchange cycles according to preset time slices; collecting the operating parameters of the heat exchange unit and updating the dew point difference estimate in each time slice, comparing it with a preset safety threshold, and forming a dew point difference criterion within the stage; when the dew point difference meets the lower-than-threshold condition of the preset continuous criterion, triggering the sensible heat recovery sub-mode, shutting down the latent heat stage or placing a bypass, and resetting the valve position control parameters to sensible heat priority configuration; when the dew point difference meets the hysteresis criterion and recovers to above the threshold and the pressure drop meets the safety limit, exiting the sub-mode, restoring the original cascade sequence and valve position control parameters of the thermal stage, and continuing time-sequential heat exchange.

[0012] Optionally, based on the stage identifier and production line cycle time, the recovered heat results are allocated to the heat-using links according to a priority matrix, and the priority matrix and allocation amount are dynamically adjusted based on energy demand during stage switching. This includes: obtaining the production line cycle time reflecting the operating rhythm of the baking production line; wherein the production line cycle time signal consists of at least one of the conveyor belt running speed, feeding interval time, or oven door opening and closing cycle, used to characterize the time sequence of baked products passing through the baking oven; establishing a time synchronization relationship based on the production line cycle time and stage identifier, aligning the stage recovered heat results with the corresponding production line operating conditions to form a heat allocation cycle within the time window; within each heat allocation cycle, calling the pre-constructed heat-using link priority matrix to allocate the recovered heat results, and outputting heat allocation instructions for each heat-using link; when a change in the production line cycle time signal is detected that causes the stage duration or energy demand to deviate from the set range, triggering the weight update of the heat-using link priority matrix and recalculating the allocation amount to maintain the dynamic matching between the production line cycle time and heat utilization.

[0013] Optionally, the construction rules for the priority matrix of heat-using links are as follows: Calculate the weighted combination value of recoverable enthalpy difference, dew point margin, and available temperature difference based on the stage input set to determine the heat grade score characterizing the availability of heat energy in the stage; establish a receiving function for each heat-using link, and calculate the heat absorption preference based on the return water temperature matching degree, temperature stability coefficient, and minimum guaranteed flow constraint; superimpose the heat grade score and heat absorption preference according to the stage identifier to generate an initial priority matrix, and introduce a synchronization factor and switching penalty term corresponding to the production line cycle time to constrain frequent adjustments; when the dew point margin is lower than the safety threshold or the production line cycle time fluctuation causes energy distribution deviation, recalculate the heat absorption weight of each heat-using link and correct the heat flow distribution path, and output the priority matrix after energy balance correction.

[0014] The second aspect of this invention provides a baking waste heat recovery system based on multi-stage heat exchange. The system is applied to a baking oven equipped with exhaust gas collection pipelines and multi-stage heat exchange units. The system includes: a collection unit for acquiring exhaust gas operating parameters of the baking process, establishing a hierarchical operating condition model, and obtaining multiple thermal stages and corresponding stage identifiers for each thermal stage; a processing unit for determining the heat grade index and dew point difference of each thermal stage based on the stage identifiers, generating a cascading sequence and valve position control parameters corresponding to each thermal stage; a switching unit for executing time-sequential heat exchange according to the stage identifiers and corresponding cascading sequence and valve position control parameters, calculating the recovered heat results for each thermal stage, and switching the thermal stage to a sensible heat recovery sub-mode when the dew point difference of any stage is lower than a preset threshold; and an execution unit for allocating the recovered heat results to heat-using links according to a priority matrix based on the stage identifiers and production line cycle time, and dynamically correcting the priority matrix and allocation amount based on energy demand during stage switching.

[0015] On the other hand, the present invention provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described method for recovering baking waste heat based on multi-stage heat exchange.

[0016] Through the above technical solution, the present invention achieves dynamic and coordinated control of waste heat recovery and production line operation during the baking process. By establishing a hierarchical operating condition model and extracting stage identifiers, the temperature and humidity characteristics of each thermal stage can be accurately identified, providing targeted control basis for multi-stage heat exchange units. Based on the stage identifiers, heat quality indicators and dew point differences are generated, enabling adaptive adjustment of the heat exchange cascade sequence and valve position parameters, avoiding condensation and energy waste. During heat exchange execution, when the dew point difference is lower than the threshold, the sensible heat recovery mode is automatically switched to ensure system operation safety and heat exchange stability. Finally, the recovered heat is prioritized and allocated according to the production line cycle time, so that the utilization of recovered heat is synchronized with the actual energy demand, thereby achieving integrated optimization of waste heat recovery efficiency, balanced heat load distribution, and production line thermal energy management.

[0017] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of a baking waste heat recovery method based on multi-stage heat exchange provided by one embodiment of the present invention; Figure 2 This is a detailed flowchart of step S20 provided in one embodiment of the present invention; Figure 3 This is a detailed flowchart of step S30 provided in one embodiment of the present invention; Figure 4 This is a system structure diagram of a baking waste heat recovery system based on multi-stage heat exchange provided by one embodiment of the present invention. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0020] like Figure 1 As shown, embodiments of the present invention provide a method for recovering baking waste heat based on multi-stage heat exchange, the method comprising: Step S10: Obtain the exhaust operation parameters of the baking process, establish a working condition layering model, and obtain multiple thermal stages and the corresponding stage identifiers for each thermal stage.

[0021] This invention relates to baking ovens equipped with exhaust gas collection pipelines and multi-stage heat exchange units. It is an optimized structural form based on traditional hot air circulating baking ovens, designed to achieve waste heat recovery and thermal energy reuse. Such baking ovens generally include an oven body, exhaust channels, exhaust gas collection pipelines, heat exchange modules, and control components. The exhaust gas collection pipelines are used to draw high-temperature, high-humidity exhaust gas from the upper or lower part of the oven cavity without affecting the airflow organization within the oven. Multi-stage heat exchange units are typically arranged sequentially within the exhaust pipelines, with different stages corresponding to different heat grade ranges. They often employ finned tube, plate-fin, or shell-and-tube structures, achieving cascaded recovery of sensible and latent heat through series connection or bypass. Temperature, humidity, and flow rate detection interfaces are reserved between each stage of the heat exchange units for the execution of subsequent heat exchange control strategies.

[0022] For existing baking ovens lacking this structure, compatibility can be achieved through modification. Specifically, a detachable exhaust gas collection pipe is added to the oven's exhaust outlet, with a branch interface equipped with a regulating valve to guide some exhaust gas into the heat exchange module. One to three heat exchange units are connected in series along the exhaust path, equipped with temperature and humidity sensors, pressure sensors, and electric valve assemblies. The output of the heat exchange units can be connected to the baking air preheating pipe, process hot water circuit, or insulation heating circuit. If the original oven exhaust system's power is insufficient, an induced draft fan can be added to the main exhaust pipe to maintain stable flow. After the above modifications, the traditional baking oven can possess multi-stage heat exchange and waste heat collection capabilities, providing the hardware foundation for implementing the present invention.

[0023] Specifically, the temperature, humidity, and flow rate information of the baking oven exhaust is collected from the exhaust collection pipeline, and the corresponding exhaust temperature rise rate, humidity change rate, and flow fluctuation amplitude are calculated to form a comprehensive criterion for reflecting the dynamic characteristics of the baking process. Based on the comprehensive criterion, the boundary moments of each stage are determined, and the continuous baking process is divided into multiple thermal stages. The thermal stages include a preheating stage, a steady-state baking stage, a steam peak stage, and a cooling stage. A unique stage identifier is assigned to each thermal stage.

[0024] In this embodiment of the invention, during the thermal management of the baking process, changes in exhaust parameters often best reflect the dynamic characteristics of heat transfer within the oven cavity. To more accurately identify different thermal stages of the baking process, continuous acquisition and feature analysis of exhaust flow and thermal-humidity conditions are necessary. By installing temperature sensors, humidity probes, and flow meters on the exhaust collection pipeline of the baking oven, real-time data on changes in exhaust temperature, moisture content, and flow rate can be obtained. After time synchronization and data cleaning, key characteristic parameters such as the exhaust temperature rise rate, humidity change rate, and flow fluctuation amplitude are extracted from these raw signals. These parameters reflect the transient response of heat release and material moisture content changes within the oven cavity, serving as a direct basis for judging the transition of the baking state.

[0025] During the data processing phase, the inflection points of the trends in temperature rise rate and humidity change rate are calculated through simultaneous analysis to identify the critical turning points in heat input and moisture evaporation. For example, a rapid increase in temperature rise rate and a significant increase in humidity often correspond to the transition from preheating to steady-state baking; while a peak in humidity change rate followed by a decrease indicates the transition from the peak steam stage to the cooling stage. Simultaneously, the amplitude of flow rate fluctuations is used to correct for local disturbances caused by exhaust fan speed or oven door opening, thus ensuring the stability and repeatability of the stage division. Based on these characteristic parameters, a comprehensive criterion model is constructed, which can generate stage division signals through multi-dimensional threshold superposition, enabling the baking process to form a clear hierarchical structure in time sequence.

[0026] Specifically, the continuous baking cycle is divided into four main thermal stages based on the boundary moments determined by this comprehensive criterion: the preheating stage, the steady-state baking stage, the steam peak stage, and the cooling stage. Each stage corresponds to different exhaust heat grade and humidity characteristics, providing input for subsequent heat exchange optimization. To facilitate subsequent control logic calls and data indexing, a unique stage identifier is assigned to each stage after the stage division, and this identifier is stored in a one-to-one correspondence with the time series. Through this modeling process, the thermal state evolution during the baking process is transformed from a continuous signal into discrete and identifiable stage units, thereby achieving a precise hierarchical and traceable description of the thermal process.

[0027] This method transforms the complex and variable baking exhaust behavior into quantifiable and categorizable stage information, providing accurate input conditions for subsequent adaptive control of multi-stage heat exchange. By introducing stage identifiers, heat exchange control can call differentiated parameters at different stages, enabling dynamic matching between waste heat recovery and furnace conditions. This not only improves thermal energy utilization efficiency but also avoids the problems of condensation and oil accumulation and energy waste that easily occur under traditional constant heat exchange strategies.

[0028] In another possible implementation, the establishment of the stratified operating condition model can be based on the joint analysis of exhaust acoustic characteristics and infrared radiation characteristics, rather than solely relying on temperature, humidity, and flow rate data. During the actual baking process, the acoustic signals carried by the airflow in the furnace cavity implicitly contain information about flow field disturbances and changes in evaporation rates. By installing miniature acoustic pickups on the exhaust collection pipeline, the exhaust sound pressure level and spectral distribution characteristics can be obtained. Simultaneously, by deploying infrared temperature sensors to monitor the surface radiation intensity of the exhaust channel, the changing trends of the gas's average temperature and moisture content can be reflected under non-contact conditions. By using the acoustic frequency band energy change rate and the infrared radiation intensity change rate as new dynamic feature dimensions, and jointly constructing a three-dimensional feature space with the exhaust flow rate signal, the transition boundaries of the evaporation stage within the furnace can be identified more sensitively.

[0029] In model implementation, acoustic and infrared signals are first normalized, and the main frequency band energy is extracted using short-time Fourier transform to calculate the acoustic spectrum energy change rate. Then, the temperature change rate is obtained by differentiating the infrared radiation curve, and multidimensional cluster analysis is performed in conjunction with flow fluctuation information. By identifying the stage boundaries through the migration trend of cluster centers, the abrupt evaporation rate change stage and the airflow rebalancing stage can be effectively distinguished. Compared with traditional methods that rely solely on temperature and humidity thresholds, this scheme is less sensitive to local disturbances and is particularly suitable for baking conditions involving frequent opening and closing of oven doors or large load variations.

[0030] Step S20: Determine the heat quality index and dew point difference of each thermal stage based on the stage identifier, and generate the cascade sequence and valve position control parameters corresponding to each thermal stage.

[0031] Specifically, by determining the heat grade index and dew point difference of each thermal stage based on stage identifiers, a quantitative characterization and dynamic classification of the thermal energy state during baking can be achieved. Each thermal stage corresponds to specific exhaust temperature and humidity characteristics and recoverable enthalpy difference. By analyzing these parameters, the heat energy grade and condensation risk can be accurately determined, thereby generating matching cascade heat exchange sequence and valve position control parameters. This process enables multi-stage heat exchange units to no longer operate in a fixed mode, but rather adaptively adjust the sensible heat and latent heat recovery ratio according to stage changes. This achieves differentiated heat exchange control, fully utilizing high-grade heat energy in the high-temperature stage and avoiding condensation in the low-temperature stage, ultimately achieving a dynamic balance between safety and efficiency in the waste heat recovery process. Specifically, it includes the following steps: Step S201: Using the stage identifier as the trigger index, call the exhaust operation parameters and heat exchange unit operation parameters of the corresponding stage to construct the stage input set.

[0032] Specifically, the signals collected by temperature, humidity, and flow sensors installed on the exhaust gas collection pipeline are synchronized with parameters such as inlet and outlet temperature difference, pressure drop, and valve opening of each heat exchange unit, and then packaged into a stage input set. This input set not only includes instantaneous measurements but also retains the moving average value within a certain time window to reflect the thermal dynamic characteristics of that stage.

[0033] During the data retrieval process, the stage identifier triggers data update logic, automatically extracting all operating parameters of the heat exchange units and the exhaust heat and humidity status corresponding to the current stage, and eliminating redundant data not belonging to the current stage. In this way, the stage input set can fully reflect the airflow heat content, heat transfer resistance, and available energy distribution under the current thermal conditions, providing accurate boundary conditions for subsequent heat grade calculations and valve position calculations. This process establishes a data retrieval mechanism centered on stage identification, ensuring that heat exchange parameters and operating condition characteristics remain in real-time correspondence, thereby improving the timeliness and specificity of multi-stage heat exchange control.

[0034] Step S202: Calculate the recoverable enthalpy difference in the thermal balance model based on the stage input set to determine the heat grade index, and calculate the heat exchange wall temperature and exhaust dew point temperature in combination with the wall thermal model to obtain the dew point difference.

[0035] Specifically, the exhaust temperature, humidity, and flow rate parameters from the stage input set are input into the stage heat balance model to calculate the recoverable enthalpy difference per unit mass of exhaust gas, thus obtaining a heat grade index characterizing the degree of thermal energy utilization. The heat exchange unit wall parameters and airflow boundary conditions from the stage input set are used as inputs to obtain the corresponding heat exchange wall temperature based on the wall thermal model. The exhaust humidity and temperature data are substituted into the dew point calculation model to obtain the exhaust dew point temperature, which is then compared with the heat exchange wall temperature to calculate the dew point difference. Finally, a correspondence is established between the heat grade index and the dew point difference and the stage identifier.

[0036] In this embodiment of the invention, to quantitatively analyze the exhaust heat energy during the baking process, a heat balance model needs to be constructed based on a stage input set to calculate the recoverable enthalpy difference and determine the heat grade index. The stage input set includes the exhaust temperature. relative humidity Volumetric flow rate and gas pressure These parameters collectively determine the distribution characteristics of sensible and latent heat in the airflow. First, based on the characteristics of the humid air exhaust from the baking oven, the specific enthalpy of the humid air is calculated at both the inlet and outlet of the heat exchange unit. and Specific enthalpy It can be obtained by superimposing the partial enthalpy values ​​of dry air and water vapor, and its physical meaning is the total heat content carried by a unit mass of exhaust gas. Stage recoverable enthalpy difference. The following is calculated using the enthalpy difference between the inlet and outlet:

[0037] in, This represents the energy per unit mass that the exhaust gas can release after passing through the heat exchange process in this stage, and is used to characterize the degree of thermal energy recovery in this stage. Furthermore, the recoverable enthalpy difference is correlated with the stage exhaust gas density. Correlation, defining heat grade index :

[0038] Heat grade index It reflects the unit mass thermal energy level of the exhaust gas. The higher the value, the higher the proportion of high-grade thermal energy in the airflow at this stage, which is suitable for priority allocation to the inlet air preheating or process hot water stages.

[0039] After calculating the heat grade index, in order to further assess the safety margin of latent heat recovery, it is also necessary to calculate the heat exchange wall temperature in conjunction with the wall thermal model. The wall temperature depends on the air-side heat transfer intensity and the wall's thermal conductivity, and can be expressed by an energy balance equation:

[0040] in, The heat flux density per unit area is calculated from the exhaust mass flow rate and the recoverable enthalpy difference. The gas-side heat transfer coefficient is related to the flow state, gas thermal conductivity, and channel geometry. By calculating the heat exchange wall temperature, the true heat exchange temperature difference between the wall and the airflow can be obtained, providing a basis for judging whether there is a risk of condensation.

[0041] Subsequently, the exhaust temperature of the stage input is concentrated. With relative humidity Substituting the values ​​into the empirical dew point calculation model, the dew point temperature of the exhaust gas at this stage is obtained. The dew point temperature is calculated using the modified Magnus formula, in the following form:

[0042]

[0043] In the formula, a and b are empirical constants (a=17.27, b=237.7); Relative humidity (%); This refers to the exhaust temperature (K or °C).

[0044] The dew point difference is calculated by comparing the heat exchanger wall temperature with the dew point temperature. :

[0045] Dew point difference Used to determine the safe range for latent heat recovery processes: when When the temperature is greater than 0, the wall temperature is higher than the dew point, condensation does not occur, and latent heat can be safely recovered; when When the temperature is not greater than 0, the wall temperature is below the dew point, and the sensible heat recovery mode needs to be triggered to avoid liquid accumulation or oil stains caused by condensation.

[0046] Finally, the calculated heat grade index and dew point difference A stage thermal characteristic mapping table is formed by mapping the stage identifiers. This mapping table is called in subsequent control to determine the cascading sequence of multi-stage heat exchange and the direction of valve position adjustment. Through this process, the exhaust energy level and condensation margin of each thermal stage can be expressed in quantitative data form, providing a precise basis for dynamic regulation.

[0047] This method enables quantifiable modeling of the energy characteristics of baking exhaust, allowing for full utilization of latent heat during the high-grade stage and automatic adjustment to sensible heat recovery mode during the low-margin stage, thus avoiding condensation and efficiency degradation on the heat exchange surface. By establishing a mapping relationship between heat grade indicators and dew point differences, the entire heat exchange process is transformed from experience-based regulation to data-driven hierarchical control, achieving the dual goals of improving energy utilization efficiency and maintaining safety margins.

[0048] Step S203: Generate the cascading sequence and valve position control parameters for this stage under the constraints of heat quality index ranking, dew point difference, and pressure drop.

[0049] Specifically, the system calls upon the heat quality index, dew point difference, and pressure drop data of the current thermal stage to construct a stage constraint set; under the condition of meeting the preset safety threshold, it generates a candidate cascade sequence in descending order of heat quality index, and combines the dew point difference and pressure drop constraints to filter and obtain the stage cascade configuration; based on the stage cascade configuration, it calls the valve position calculation rules to output the valve position opening degree and air volume ratio of each heat exchange unit; when the stage constraint does not meet the preset safety threshold, it switches to a sensible heat priority downgrade configuration and updates the valve position control parameters.

[0050] In this embodiment of the invention, during the execution phase control, a dynamic energy distribution sequence needs to be established among different heat exchange units to match the heat transfer path with the current operating conditions. To this end, key operating data such as heat grade indicators, dew point difference, and pressure drop for the current thermal stage need to be extracted to construct a constraint set for that stage. Heat grade indicators reflect the level of recoverable energy, dew point difference characterizes the condensation safety margin, and pressure drop reflects the resistance of airflow through the heat exchange unit. These three factors together constitute the constraints, used to limit the feasible combination range of cascaded heat exchange.

[0051] After the constraint set is constructed, the heat exchange units are initially ranked according to the numerical value of the heat grade index. The ranking rule adopts a descending order, that is, heat exchange units with higher heat energy levels participate in upstream energy exchange first, so as to ensure the full utilization of high-grade heat in the transfer path. During the ranking process, the dew point difference and pressure drop of the corresponding units need to be checked in real time. If they are lower than the preset safety threshold or exceed the allowable limit, the unit is removed or transferred to the standby sequence to prevent a sudden drop in heat exchange efficiency due to condensation or excessive air resistance. Through the above screening, candidate cascade sequences that meet the safety and energy efficiency requirements are obtained.

[0052] Based on the candidate sequence, cascade configuration calculations are further performed. This process is not simply a sequential arrangement; it also requires consideration of the heat flow distribution capacity of each heat exchange unit, flow coupling relationships, and stage energy balance conditions. Specifically, the inlet and outlet temperature differences of each unit are fitted to determine the functional relationship between the target heat exchange power and the valve opening. The valve control parameters can be calculated using linear proportional or piecewise regression methods, combined with the calibrated airflow-opening characteristic curve, to obtain the valve opening and airflow ratio that meets the stage heat load requirements. For example, when the outlet temperature of the upstream unit is close to the inlet dew point of the downstream unit, the downstream valve position can be appropriately increased to enhance the flow rate and suppress the risk of local condensation.

[0053] If any indicator in the stage constraint set exceeds the preset safety threshold, such as a dew point difference that remains below zero or a pressure drop exceeding a set limit, the degradation control logic is immediately triggered, switching the current configuration to sensible heat priority mode. At this time, the latent heat recovery unit is partially bypassed or shut down to ensure that condensate does not accumulate during the heat exchange process. The valve position control parameters under the degradation configuration are updated synchronously, typically manifesting as a reduction in gas-side flow rate and heat flux density, with overall operation tending towards a steady-state safety zone.

[0054] After the above calculations and adjustments, each thermal stage forms an independent cascade sequence and corresponding valve position control parameters. It not only considers the optimal utilization of thermal energy levels but also takes into account condensation risk and flow stability, achieving maximum energy recovery within the safety boundary. Unlike traditional fixed sequences or manual valve position settings, this scheme can automatically rearrange the cascade structure during stage switching, dynamically adjusting the energy flow direction based on real-time changes in heat grade. This improves the response speed and energy utilization rate of multi-stage heat exchange, ensuring that the waste heat recovery process of baking exhaust always remains in a highly efficient and safe operating state.

[0055] Step S204: When the dew point difference is lower than the preset threshold, correct the cascade configuration of this stage to prioritize sensible heat and update the valve position control parameters.

[0056] Specifically, during the phased operation, if the difference between the heat exchange wall temperature and the exhaust dew point temperature gradually decreases, it indicates that the latent heat recovery process is approaching the condensation critical zone. When the dew point difference is lower than the preset safety threshold, it is determined that the wall temperature may be lower than the airflow dew point, and the current cascade configuration needs to be corrected immediately. The principle of correction is to prioritize keeping the airflow channel dry and the heat exchange surface clean. Therefore, the energy recovery ratio of the latent heat stage is reduced or temporarily bypassed, switching the cascade structure of the entire phase to a sensible heat priority mode. At this time, the heat flow and valve opening of each heat exchange unit need to be recalculated to ensure that the heat exchange capacity balance is not disrupted. In terms of specific operation, the energy demand of the current phase is redistributed through the heat balance model, reducing the airflow of the wet zone unit and increasing the heat exchange load of the dry zone unit; then, the valve control parameters are re-output according to the new heat load distribution, so that the high-temperature section maintains a larger opening and the low-temperature section gradually reduces the opening.

[0057] This adjustment prevents condensation from forming on the pipe walls while maintaining a stable rise in exhaust temperature. This strategy allows for a rapid response to sudden increases in humidity or temperature reversals, preventing contamination of the heat exchange surfaces and improving operational safety and long-term heat exchange efficiency.

[0058] Step S30: Perform time-sequential heat exchange by calling the corresponding cascade sequence and valve position control parameters according to the stage identifier, calculate the recovered heat results of each thermal stage, and switch the thermal stage to sensible heat recovery sub-mode when the dew point difference of any stage is lower than the preset threshold.

[0059] In this embodiment of the invention, by sequentially calling the corresponding cascade sequence and valve position control parameters under the guidance of stage identifiers, the heat exchange process of each thermal stage can form a clear time sequence, realizing the orderly scheduling of energy transfer. Each stage performs a heat exchange cycle under a predetermined cascade structure, calculates the corresponding recovered heat result, and thus quantifies the thermal energy utilization level of different stages. When the dew point difference of any stage is continuously lower than a preset threshold, it indicates that the wall temperature is approaching or lower than the airflow dew point, and latent heat recovery will face the risk of condensation. At this time, by switching to the sensible heat recovery sub-mode, the latent heat exchange unit is suspended or bypassed to maintain the heat exchange surface in the dry range and avoid liquid accumulation and energy loss. This strategy enables the multi-stage heat exchange process to achieve adaptive switching within a safe threshold, ensuring the stability of the recovered heat calculation and the thermal efficiency of the baking process. Specifically, it includes the following steps: Step S301: Retrieve the cascade sequence and valve position control parameters associated with the current thermal stage, and execute the heat exchange cycle according to the preset time slice.

[0060] Specifically, to ensure the heat exchange process accurately matches the rhythm of the baking conditions, it is necessary to retrieve the cascading sequence and valve position control parameters corresponding to the current thermal stage according to the stage identifier, and execute cyclic heat exchange operations in units of time slices. A time slice divides a complete stage into several equal-time intervals, maintaining constant valve position and airflow configuration within each interval to achieve stable heat transfer and data acquisition. Before the start of each time slice, the cascading configuration table for the current stage is read, and the airflow path through each heat exchange unit is determined according to the order of heat grade indicators. Simultaneously, the valve position control parameters are calculated into specific opening commands, ensuring a larger ventilation cross-section in high-heat-grade sections and moderately reduced flow in low-temperature sections, forming a temperature gradient for staged heat exchange.

[0061] In the heat exchange cycle, dynamic stability within each time segment is achieved through smooth transitions in temperature and flow rate. Specifically, when the outlet temperature or dew point difference of the previous time segment deviates too much from the target value, the valve opening increment can be adjusted in the next time segment to gradually bring the heat load towards equilibrium. At the end of each time segment, the inlet and outlet temperatures and airflow parameters of the heat exchange unit are recorded to calculate the cumulative recovered heat for the stage and update the operating trend.

[0062] This time-slice-based sequential execution method makes heat exchange control predictable and adjustable. By periodically calling the stage configuration, it not only ensures that each stage of the heat exchange unit operates under reasonable heat load, but also suppresses energy loss caused by temperature fluctuations. It achieves continuity and self-correction characteristics in the heat exchange process, enabling multi-stage heat exchange units to maintain a highly efficient and stable energy recovery state under dynamic operating conditions, providing a reliable staged data foundation for subsequent energy allocation and mode switching.

[0063] Step S302: Collect the operating parameters of the heat exchange unit at each time slice and update the dew point difference estimate. Compare it with the preset safety threshold to form the dew point difference criterion within the stage.

[0064] Specifically, within each time slice, the operating status of the heat exchange unit needs to be collected and assessed in real time to dynamically evaluate the condensation risk and latent heat recovery safety margin for that stage. In practice, the collected operating parameters include the inlet and outlet temperatures of the heat exchange unit, airflow humidity, pressure difference, and flow rate data. These parameters collectively reflect the heat and moisture exchange status of the airflow as it passes through each stage of the heat exchange unit. The collected temperature and humidity data, after time synchronization and instantaneous smoothing, are used to calculate the estimated dew point difference for that stage. The core idea of ​​dew point difference estimation is to compare the current airflow dew point temperature with the wall temperature in real time, and then use a dynamic calculation model to fit and predict the temperature difference between the two, thereby capturing subtle changes in the condensation trend.

[0065] During the calculation, the dew point temperature can be obtained in real time using a modified Magnus formula, while the wall temperature is calculated inversely from the heat flux density of the heat exchange unit and the air-side heat transfer coefficient. To avoid misjudgments caused by data fluctuations, a moving average or first-order filter can be introduced when calculating the dew point difference to make the change in the dew point difference more stable. Subsequently, this estimated dew point difference value is compared with a preset safety threshold. When the dew point difference is consistently lower than the preset safety threshold, it is considered a condensation risk signal within the stage. This comparison result constitutes the stage dew point difference criterion, which is used as the trigger for subsequent mode switching or valve position adjustment.

[0066] By continuously updating the dew point difference estimate over a time slice scale, the risk of condensation caused by rising humidity or sudden drops in temperature can be identified in a timely manner, enabling early intervention in the thermal state. This improves the safety and control sensitivity of phased operation, allowing multi-stage heat exchange units to avoid condensate buildup and wall contamination without affecting energy efficiency, thus maintaining long-term stable and efficient heat exchange processes.

[0067] Step S303: When the dew point difference meets the preset continuous criterion condition of being below the threshold, the sensible heat recovery sub-mode is triggered, the latent heat stage is shut down or a bypass is set, and the valve position control parameters are reset to sensible heat priority configuration.

[0068] Specifically, during phased operation, when the monitored dew point difference consistently remains below the preset safety threshold, it indicates that the margin between the airflow temperature and the dew point temperature is insufficient, and the latent heat recovery process enters a critical state. To prevent wall condensation and pipe accumulation, the sensible heat recovery sub-mode should be triggered immediately. The core idea of ​​this sub-mode is to prioritize ensuring that the airflow temperature is higher than the dew point temperature, thereby avoiding condensation caused by moisture heat exchange. After triggering, the operating status of each heat exchange unit is first assessed. Latent heat exchange units with a persistently negative or near-zero dew point difference are temporarily removed from the main heat exchange loop, which can be achieved by closing the valve or switching to a bypass.

[0069] When performing bypass or shutdown operations, the valve position control parameters must be simultaneously reset to sensible heat priority configuration. At this time, the control strategy will reallocate the heat flow path, ensuring that the upstream high-temperature section bears the main heat exchange load, while the downstream section with higher humidity participates less, thus forming an airflow structure dominated by sensible heat transfer. Specific adjustments typically include reducing the airflow ratio of the latent heat unit, increasing the flow cross-section of the dry zone unit, and resetting the valve opening curve to ensure a smooth decreasing distribution of heat flow along the pipeline direction. If the risk of condensation persists, the stage time slice can be further shortened to accelerate temperature recovery.

[0070] By continuously monitoring and confirming the trend of dew point difference changes, the mode switching becomes more stable and responsive. It can intervene in advance before condensation actually occurs, keeping the heat exchange surface dry at all times, preventing energy loss and equipment corrosion, and ensuring that the multi-stage heat exchange structure can safely and stably maintain energy recovery efficiency under high humidity conditions.

[0071] Step S304: When the dew point difference meets the hysteresis criterion and recovers to above the threshold and the pressure drop meets the safety limit, exit the sensible heat recovery sub-mode, restore the original cascade sequence and valve position control parameters of this thermal stage, and continue the time-sequential heat exchange.

[0072] Specifically, after operating in the sensible heat recovery sub-mode for a period of time, as the heat distribution rebalances, the airflow temperature gradually rises and the humidity decreases, causing the dew point difference to rebound. When the dew point difference is consistently higher than the preset threshold and simultaneously meets the stability requirements of the hysteresis criterion—that is, the dew point difference has remained within the safe range for multiple consecutive sampling cycles—the condensation risk can be determined to be eliminated. Based on this, it is also necessary to confirm that the pipeline pressure drop does not exceed the safety limit and ensure that the airflow in the heat exchange unit is normal and that there is no blockage or adhering liquid accumulation. After meeting these two conditions, the stage control enters the recovery process and exits the sensible heat recovery sub-mode.

[0073] The recovery process references the cascade structure of the original thermal stage. Specifically, according to the previously recorded stage identifiers, the corresponding cascade sequence and valve position control parameters for that stage are reloaded, and the participation ratio of the latent heat stage is gradually increased in a smooth transition. The valve opening does not jump directly to the target value, but is adjusted in stages according to the rate of heat flow change, generally using segmented proportional control or time-slice interpolation, to slowly restore the latent heat unit to its normal operating flow rate. During this process, continuous monitoring of dew point difference and pressure drop is maintained to prevent transient secondary condensation during recovery.

[0074] This hysteresis criterion control strategy eliminates the reliance on single threshold judgments for switching between sensible and latent heat recovery modes. Instead, it relies on continuous verification over time, avoiding energy waste and structural stress fluctuations caused by frequent oscillations. This method ensures the continuity and predictability of heat flow distribution in multi-stage heat exchange processes under dynamic conditions, achieving self-suppression of condensation risks and automatic rebalancing of energy recovery. This guarantees the heat exchange efficiency and stability of the baking process after the high humidity phase.

[0075] Step S40: Based on the stage identifier and production line cycle time, allocate the recovered heat results to the heat-using links according to the priority matrix, and dynamically adjust the priority matrix and allocation amount based on energy demand when switching stages.

[0076] Specifically, the process involves acquiring the production line cycle time, which reflects the operational rhythm of the baking production line. This cycle time signal is composed of at least one of the following: conveyor belt speed, feeding interval, or oven door opening / closing cycle, used to characterize the time sequence of baked products passing through the baking oven. A time synchronization relationship is established based on the production line cycle time and stage identifiers, aligning the stage's recovered heat results with the corresponding production line conditions to form a heat allocation cycle within a time window. Within each heat allocation cycle, a pre-constructed priority matrix for heat-using links is invoked to allocate the recovered heat results, outputting heat allocation instructions for each heat-using link. When a change in the production line cycle time signal is detected that causes the stage duration or energy demand to deviate from the set range, the weight update of the priority matrix for heat-using links and the recalculation of the allocation amount are triggered to maintain a dynamic match between the production line cycle time and heat utilization.

[0077] Furthermore, the construction rules for the priority matrix of heat-using links are as follows: Based on the stage input set, calculate the weighted combination value of recoverable enthalpy difference, dew point margin, and available temperature difference to determine the heat grade score characterizing the stage's thermal energy availability; establish a receiving function for each heat-using link, and calculate the heat absorption preference based on return water temperature matching degree, temperature stability coefficient, and minimum guaranteed flow constraint; superimpose the heat grade score and heat absorption preference according to the stage identifier to generate an initial priority matrix, and introduce a synchronization factor and switching penalty term corresponding to the production line cycle time to constrain frequent adjustments; when the dew point margin is lower than the safety threshold or the production line cycle time fluctuation causes energy allocation deviation, recalculate the heat absorption weight of each heat-using link and correct the heat flow allocation path, outputting the priority matrix after energy balance correction.

[0078] In this embodiment of the invention, in baking-type thermal equipment, there is often a complex dynamic coupling relationship between the production line's operating rhythm and heat recovery. To ensure the rational utilization of recovered waste heat across different stages, a heat distribution logic that can automatically adjust according to changes in the production line's cycle time is needed. This logic uses stage identifiers as the primary index and establishes time constraints through synchronization with the production line's cycle time signal, thereby achieving precise heat distribution and dynamic correction within different thermal operating stages.

[0079] In practical implementation, the first step is to acquire the production line cycle time signal, which characterizes the operating rhythm of the baking production line. The production line cycle time is not a single parameter, but a time-series signal formed by a combination of variables such as conveyor belt speed, feeding interval, and oven door opening and closing cycle. For example, conveyor belt speed directly affects the residence time of the product in the baking oven, while the oven door opening and closing frequency determines the periodicity of heat loss. By unifying these discrete signals to a single time scale, a continuous cycle time curve can be formed to reflect the real-time movement rhythm of the product in the oven and the changing patterns of heat load. This cycle time signal is paired with the time coordinates corresponding to the stage markers to establish a time synchronization relationship, ensuring that the output of heat recovery at each stage is aligned in time with the production line's heat demand window.

[0080] Based on synchronization, the recovered heat results of each thermal stage are divided into multiple heat allocation cycles according to time windows. Within each allocation cycle, a pre-constructed priority matrix of heat-using links is invoked to perform heat allocation. The row vectors of the priority matrix typically correspond to heat source levels (such as high, medium, and low grade heat), the column vectors correspond to the heat-using links (such as inlet air preheating, process hot water, and insulation heating), and the matrix elements represent the heat absorption weight of that link in the current stage. After the matrix calculation is completed, heat allocation instructions can be directly generated, indicating the heat flow ratio or target temperature range that each link should receive.

[0081] However, production line cycle time is not constant in actual production. For example, changes in product thickness, fluctuations in raw material moisture content, or equipment maintenance operations can all cause changes in the duration of a stage. If these changes are not addressed in a timely manner, they will lead to delayed energy allocation, decreased heat utilization, or even localized overheating. Therefore, it is necessary to monitor the drift trend of the production line cycle time signal in real time during each stage switch. When a change in cycle time causes the stage duration or energy demand to deviate from the preset range, the priority matrix weight update mechanism should be triggered immediately. This mechanism will recalculate the energy absorption priority of each heat-consuming link and correct the allocation amount so that the heat output is rematched with the production rhythm.

[0082] The construction of the priority matrix also possesses physical rigor. First, a weighted combination of recoverable enthalpy difference, dew point margin, and available temperature difference needs to be calculated based on the stage input set. The recoverable enthalpy difference represents the usable heat potential in the exhaust gas, the dew point margin reflects the risk of gas flow condensation, and the available temperature difference reflects the effective temperature span between different thermal stages. The weighted combination of these three can be expressed as:

[0083] in, Rate the heat quality. To recover the enthalpy difference, For dew point margin, For usable temperature difference, These are the weighting coefficients. The weighting coefficients can be set based on experience with different equipment types and operating strategies to ensure the model balances thermal efficiency and safety margins.

[0084] Subsequently, an endothermic receiving function is established for each heat-consuming stage. This receiving function takes into account the thermophysical characteristics and operational constraints of each stage, and typically takes the following form:

[0085] in, Let be the heat absorption preference function of the i-th stage. Indicates the degree of matching of return water temperature. Indicates the temperature fluctuation stability coefficient. For minimum flow constraint term, This is an empirical coefficient. This function is used to evaluate the feasibility and priority of absorbing heat at the current stage.

[0086] An initial priority matrix can be generated by superimposing heat grade scores with endothermic preferences. To prevent frequent adjustments to heat allocation within short cycles, two key adjustment terms need to be introduced during matrix construction: one is a synchronization factor corresponding to the production line cycle time, used to ensure that the matrix change frequency is consistent with the production rhythm; the other is a switching penalty term, used to suppress frequent weight oscillations and avoid repeated adjustments to the allocation strategy during slight fluctuations. The matrix update rule is usually expressed in the following form:

[0087] in, The updated priority matrix, To adjust the step size, To switch the penalty option.

[0088] During operation, when the dew point margin drops below the safety threshold or the production line cycle time fluctuates significantly, the heat distribution path needs to be recalculated. In this case, the energy balance equation is first used to verify whether the current total heat flow meets the stage requirements, and then the heat flow is redistributed using a priority matrix as a weighting factor. If the heat absorption in any stage exceeds the set upper limit, the system will automatically execute a reduction strategy, transferring some of the high-temperature heat flow to low-temperature stages or energy storage media to maintain overall energy balance.

[0089] Traditional waste heat recovery solutions often employ fixed valve positions or constant ratio control, lacking the ability to respond to changes in operating conditions, thus limiting energy utilization. This solution, however, utilizes the dual constraints of production line cycle time and stage markers to enable flexible adjustment of heat distribution over time. Whether the cycle time is accelerated or the stage is extended, the heat flow distribution can be adjusted in real time according to the current energy demand, thereby maintaining a stable and balanced temperature field within the baking oven.

[0090] Its phase-based heat distribution makes the waste heat utilization strategy more targeted at different stages, avoiding energy waste in low-temperature stages and overheating in high-temperature stages. On the other hand, by synchronizing with the production line rhythm, it can achieve dynamic coordination between energy release and product throughput rhythm, making the temperature distribution inside the furnace more uniform and significantly improving the consistency of product quality.

[0091] In one specific embodiment, the multi-stage heat exchange-based waste heat recovery method for baking proposed in this invention is applied to a tunnel-type baking oven with a rated power of 60kW. The oven is equipped with a three-section heating zone and a two-stage exhaust channel. The exhaust collection pipeline is laid along the main exhaust channel and is equipped with five temperature and humidity sensors, two flow meters, and one differential pressure gauge. The multi-stage heat exchange units adopt a series-parallel combined structure. The first heat exchange stage is a high-temperature sensible heat recovery section (using a finned heat exchanger), and the second heat exchange stage is a low-temperature latent heat recovery section (using a corrugated plate heat exchanger). Each heat exchange unit is equipped with an electric valve assembly and an airflow regulating valve for valve position control.

[0092] During one operation, the exhaust temperature ranged from 150℃ to 230℃, and the humidity fluctuated between 28% and 75%. Based on the exhaust operating parameters, the calculated temperature rise rate was approximately 0.8~1.3℃ / s, and the humidity change rate was approximately 0.4% / s. Four thermal stages were determined through comprehensive criteria: a preheating stage lasting approximately 90 seconds, a steady-state baking stage lasting approximately 420 seconds, a steam peak stage lasting approximately 150 seconds, and a cooling stage lasting approximately 100 seconds. These stages were designated as S1, S2, S3, and S4, respectively.

[0093] In stage S2, the calculated recoverable enthalpy difference of the exhaust gas is approximately 145 kJ / kg, corresponding to a heat grade index of 0.86 (relative scale 1.0). The dew point temperature is approximately 68℃, the heat exchange wall temperature is 74℃, and the dew point difference is 6℃, which is within a safe range. When the steam peak stage (S3) is activated, the dew point temperature rises to 92℃, the wall temperature drops to 89℃, and the dew point difference drops to -3℃, triggering the sensible heat recovery sub-mode. This automatically closes the latent heat recovery section valve and adjusts the airflow ratio, allowing the wall temperature to recover to above 94℃ within 15 seconds.

[0094] In the energy distribution process, the production line cycle time is determined by the conveyor belt speed (0.24 m / s) and the furnace door opening and closing cycle (once every 180 seconds). After time synchronization correction, each cycle time corresponds to a heat distribution window. Through priority matrix calculation, 70% of the high-grade heat flow is allocated to the inlet air preheating stage, 20% to the process hot water, and 10% to the insulation heating stage. After five batches of actual measurements, and with dynamic adjustments to the distribution weights based on production line cycle time fluctuations (±8%), the production line's heat utilization rate increased from 71.4% in the original scheme to 83.2%, the condensate accumulation rate decreased from 5.2 times per hour to 0.7 times per hour, and the pressure drop fluctuation decreased from ±6.3 Pa to ±2.1 Pa.

[0095] Further statistics show that the sensible heat recovery sub-mode was triggered 27 times during an 8-hour continuous operation cycle, with an average duration of 22 seconds. After adopting this mode, the drying rate of the heat exchange surface in the low-temperature section increased from 78% to 96%, effectively extending the heat exchanger cleaning cycle by approximately 1.7 times. Experimental results demonstrate that the implementation method of this invention can achieve synchronous adjustment of stage heat flow and energy demand under dynamic cycle time, thereby simultaneously improving thermal stability and heat recovery rate.

[0096] In summary, this embodiment achieves intelligent waste heat distribution in continuous baking scenarios through quantitative cycle signal coupling and multi-stage valve position control logic. Verification shows that this method can reduce energy consumption by 8% to 15% in typical food production lines and significantly reduce secondary energy loss caused by condensation, demonstrating significant energy-saving performance and industrial application potential.

[0097] like Figure 4 As shown, this invention provides a baking waste heat recovery system based on multi-stage heat exchange. The system includes: a data acquisition unit for acquiring exhaust operating parameters of the baking process, establishing a hierarchical operating condition model, and obtaining multiple thermal stages and corresponding stage identifiers for each thermal stage; a processing unit for determining the heat grade index and dew point difference of each thermal stage based on the stage identifiers, and generating cascading sequence and valve position control parameters corresponding to each thermal stage; a switching unit for executing time-sequential heat exchange according to the stage identifiers and calling the corresponding cascading sequence and valve position control parameters, calculating the recovered heat results of each thermal stage, and switching the thermal stage to a sensible heat recovery sub-mode when the dew point difference of any stage is lower than a preset threshold; and an execution unit for allocating the recovered heat results to the heat-using links according to a priority matrix based on the stage identifiers and production line cycle time, and dynamically correcting the priority matrix and allocation amount based on energy demand during stage switching.

[0098] The present invention also provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described method for recovering baking waste heat based on multi-stage heat exchange.

[0099] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0100] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe the various possible combinations.

[0101] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the embodiments of the present invention, they should also be regarded as the content disclosed by the embodiments of the present invention.

Claims

1. A method for recovering baking waste heat based on multi-stage heat exchange, characterized in that, The method is applied to a baking oven equipped with an exhaust gas collection pipeline and a multi-stage heat exchange unit, and the method includes: Obtain the exhaust operation parameters of the baking process, establish a working condition hierarchical model, and obtain multiple thermal stages and the corresponding stage identifiers for each thermal stage. Based on the stage identifier, the heat quality index and dew point difference of each thermal stage are determined, and the cascade sequence and valve position control parameters corresponding to each thermal stage are generated. According to the stage identifier, the corresponding cascade sequence and valve position control parameters are called to perform time-sequential heat exchange, calculate the recovered heat results of each thermal stage, and switch the thermal stage to sensible heat recovery sub-mode when the dew point difference of any stage is lower than the preset threshold. Based on the stage identifier and production line cycle time, the recovered heat results are allocated to the heat-using links according to the priority matrix, and the priority matrix and allocation amount are dynamically adjusted based on energy demand when switching stages.

2. The baking waste heat recovery method based on multi-stage heat exchange according to claim 1, characterized in that, The exhaust operation parameters of the baking process are obtained, a hierarchical operating condition model is established, and multiple thermal stages and corresponding stage identifiers for each thermal stage are obtained, including: Based on the temperature, humidity and flow rate information of the oven exhaust operating parameters collected by the exhaust collection pipeline, the corresponding exhaust temperature rise rate, humidity change rate and flow rate fluctuation amplitude are calculated to form a comprehensive criterion for reflecting the dynamic characteristics of the baking process. Based on the aforementioned comprehensive criteria, the boundary moments of each stage are determined, dividing the continuous baking process into multiple thermal stages; among which, The thermal process includes a preheating stage, a steady-state baking stage, a steam peak stage, and a cooling stage. Each thermal stage is assigned a unique stage identifier.

3. The baking waste heat recovery method based on multi-stage heat exchange according to claim 1, characterized in that, Based on the stage identifier, the heat quality index and dew point difference of each thermal stage are determined, and the cascading sequence and valve position control parameters corresponding to each thermal stage are generated, including: Using the stage identifier as the trigger index, the exhaust operation parameters and heat exchange unit operation parameters of the corresponding thermal stage are called to construct the stage input set; Based on the stage input set, the recoverable enthalpy difference is calculated in the heat balance model to determine the heat grade index, and the heat exchange wall temperature and exhaust dew point temperature are calculated in combination with the wall thermal model to obtain the dew point difference. The cascading sequence and valve position control parameters for this thermal stage are generated under the constraints of thermal quality index ranking, dew point difference, and pressure drop. When the dew point difference is lower than the preset threshold, the cascade configuration of this thermal stage is corrected to prioritize sensible heat and the valve position control parameters are updated.

4. The method for recovering baking waste heat based on multi-stage heat exchange according to claim 3, characterized in that, Based on the stage input set, the recoverable enthalpy difference is calculated in the thermal equilibrium model to determine the heat grade index, and the heat exchange wall temperature and exhaust dew point temperature are calculated in combination with the wall thermal model to obtain the dew point difference, including: The exhaust temperature, humidity, and flow rate parameters of the stage input set are input into the stage heat balance model to calculate the recoverable enthalpy difference per unit mass of exhaust gas, and obtain the heat grade index characterizing the degree of thermal energy utilization. Using the heat exchange unit wall parameters and airflow boundary conditions in the stage input set as input, the corresponding heat exchange wall temperature is obtained based on the wall thermal model; Substitute the exhaust humidity and temperature data into the dew point calculation model to obtain the exhaust dew point temperature, and compare it with the heat exchange wall temperature to obtain the dew point difference; Establish a correspondence between the heat grade index and the dew point difference and the stage identifier.

5. The method for recovering baking waste heat based on multi-stage heat exchange according to claim 3, characterized in that, The cascading sequence and valve position control parameters for this stage are generated under the constraints of thermal grade index ranking and dew point difference and pressure drop, including: Use the heat grade index, dew point difference, and pressure drop data of the current thermal stage to construct the stage constraint set; Candidate cascade sequences are generated in descending order of heat grade index under the condition of meeting the preset safety threshold, and the stage cascade configuration is obtained by combining dew point difference and pressure drop constraints. Based on the stage-cascaded configuration, the valve position calculation rules are invoked to output the valve position opening degree and air volume ratio of each heat exchange unit; When the stage constraint does not meet the preset safety threshold, switch to the sensible heat priority degradation configuration and update the valve position control parameters.

6. The method for recovering baking waste heat based on multi-stage heat exchange according to claim 1, characterized in that, According to the stage identifier, the corresponding cascade sequence and valve position control parameters are invoked to perform time-sequential heat transfer, calculate the recovered heat results of each thermal stage, and switch the thermal stage to sensible heat recovery sub-mode when the dew point difference of any stage is lower than a preset threshold, including: Retrieve the cascade sequence and valve position control parameters associated with the current thermal stage, and execute the heat exchange cycle according to the preset time slot; At each time slice, the operating parameters of the heat exchange unit are collected and the dew point difference estimate is updated. This estimate is then compared with a preset safety threshold to form the dew point difference criterion for that stage. When the dew point difference meets the preset continuous criterion condition of being below the threshold, the sensible heat recovery sub-mode is triggered, the latent heat stage is shut down or a bypass is set, and the valve position control parameters are reset to sensible heat priority configuration; When the dew point difference meets the hysteresis criterion and recovers to above the threshold and the pressure drop meets the safety limit, the sensible heat recovery sub-mode is exited, the original cascade sequence and valve position control parameters of this thermal stage are restored, and the time-sequential heat exchange continues.

7. The method for recovering baking waste heat based on multi-stage heat exchange according to claim 1, characterized in that, Based on the stage identifier and production line cycle time, the recovered heat results are allocated to the heat-using links according to a priority matrix, and the priority matrix and allocation amount are dynamically adjusted based on energy demand during stage switching, including: Obtain the production line cycle time that reflects the operating rhythm of the baking production line; wherein, the production line cycle time signal is composed of at least one of the conveyor belt running speed, feeding interval time or oven door opening and closing cycle, and is used to characterize the time sequence of baked products passing through the baking oven; Based on the production line cycle time and stage identifier, a time synchronization relationship is established, and the stage heat recovery results are aligned with the production line operating conditions to form a heat distribution cycle within the time window. Within each heat allocation cycle, the pre-constructed priority matrix of heat use links is invoked to allocate the recovered heat results and output the heat allocation instructions for each heat use link. When a change in the production line cycle signal is detected that causes the stage duration or energy demand to deviate from the set range, the weight update and recalculation of the priority matrix of the heat use link are triggered to maintain the dynamic matching between the production line cycle and heat utilization.

8. The method for recovering baking waste heat based on multi-stage heat exchange according to claim 7, characterized in that, The rules for constructing the priority matrix of the thermal link are as follows: The weighted combination of recoverable enthalpy difference, dew point margin, and available temperature difference is calculated based on the stage input set to determine the heat grade score that characterizes the availability of thermal energy in the stage. Establish receiving functions for each heat-consuming link, and calculate heat absorption preference based on return water temperature matching degree, temperature stability coefficient and minimum guaranteed flow constraint; The heat grade score and endothermic preference are superimposed according to the stage identifier to generate an initial priority matrix, and a synchronization factor and switching penalty term corresponding to the production line cycle time are introduced to constrain frequent adjustments; When the dew point margin is lower than the safety threshold or the production line cycle time fluctuates, causing the energy distribution to shift, the heat absorption weight of each heat-using link is recalculated and the heat flow distribution path is corrected, and the priority matrix after energy balance correction is output.

9. A baking waste heat recovery system based on multi-stage heat exchange, characterized in that, The system is applied to a baking oven equipped with an exhaust gas collection pipeline and a multi-stage heat exchange unit, and the system includes: The data acquisition unit is used to acquire the exhaust operation parameters of the baking process, establish a hierarchical model of operating conditions, and obtain multiple thermal stages and the corresponding stage identifiers for each thermal stage. The processing unit is used to determine the heat grade index and dew point difference of each thermal stage based on the stage identifier, and generate the cascading sequence and valve position control parameters corresponding to each thermal stage. The switching unit is used to call the corresponding cascade sequence and valve position control parameters according to the stage identifier to perform time-sequential heat exchange, calculate the recovered heat results of each thermal stage, and switch the thermal stage to sensible heat recovery sub-mode when the dew point difference of any stage is lower than the preset threshold. The execution unit is used to allocate the recovered heat results to the heat-using links according to the priority matrix based on the stage identifier and production line cycle time, and dynamically adjust the priority matrix and allocation amount based on energy demand when switching stages.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed on a computer, cause the computer to perform the baking waste heat recovery method based on multi-stage heat exchange as described in any one of claims 1-8.

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