A heat exchange type waste heat recovery device and control method for a wood-based panel drying line

Abstract

This invention discloses a heat exchange-type waste heat recovery device and control method for a wood-based panel drying line. The device includes an exhaust air classification and adjustment module, a primary sensible heat recovery module, a secondary condensation heat exchange module, a controller, and a sensor group. The exhaust air classification and adjustment module distributes high-temperature exhaust air to the primary sensible heat recovery module and high-humidity exhaust air to the secondary condensation heat exchange module according to the heat and humidity state of different exhaust air sections. Makeup air passes through the primary sensible heat recovery module and the secondary condensation heat exchange module sequentially before being returned to the drying line. The controller adjusts the exhaust air distribution, condensation heat exchange, makeup air volume, and auxiliary heating amount based on exhaust air temperature and humidity, dew point, enthalpy, moisture content deviation, pressure difference, and condensate state. This invention enables the graded recovery of sensible and latent heat under conditions where exhaust and makeup air are not mixed, reducing drying energy consumption.

Description

Technical Field

[0001] This invention relates to the field of waste heat recovery technology for wood-based panel drying equipment, specifically to a heat exchange type waste heat recovery device and control method for wood-based panel drying lines. Background Technology

[0002] During the drying of wood-based panels, heated external fresh air is introduced into the drying line. The hot air carries away the moisture from the panels, creating a high-temperature, high-humidity exhaust. This exhaust contains sensible heat as well as latent heat of water vapor. Direct discharge would result in heat loss and increase energy consumption for heating the make-up air.

[0003] Existing drying lines sometimes install air heat exchangers between exhaust and makeup air ducts to preheat the makeup air with exhaust air. This method typically only recovers a portion of the sensible heat and does not adequately consider exhaust air humidity, dew point temperature, and moisture content. Because exhaust air from wood-based panels contains wood dust, resin volatiles, and water vapor, existing equipment generally avoids cooling the exhaust air below the dew point within the heat exchanger to reduce corrosion, dirt accumulation, and blockage problems caused by condensation. This makes it difficult to utilize the latent heat of water vapor in the exhaust air.

[0004] Meanwhile, the exhaust conditions differ across different sections of the wood-based panel drying line. Some sections have higher exhaust temperatures, suitable for sensible heat recovery; others have higher humidity, suitable for condensation heat exchange. Directly mixing and uniformly treating the exhaust from each section would weaken the distinct thermal and humidity characteristics of the exhaust, impacting the waste heat recovery effect.

[0005] Furthermore, the moisture content of the sheet material, conveying speed, external air supply conditions, and drying process requirements all affect the drying heat demand. Existing waste heat recovery equipment mostly uses fixed air volume or simple temperature feedback control, which is difficult to adjust based on exhaust dew point, exhaust enthalpy, condensate state, and sheet material moisture content deviation. Therefore, it is necessary to provide a waste heat recovery device and control method that can utilize exhaust waste heat in stages and control the condensation heat exchange process. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a heat exchange type waste heat recovery device and control method for wood-based panel drying lines, so as to solve the problems of insufficient utilization of exhaust waste heat, difficulty in recovering latent heat of exhaust, lack of graded utilization of exhaust in different sections, lack of controlled area in condensation process, and insufficient correlation between waste heat recovery control and the drying state of the panels.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a heat exchange type waste heat recovery device for a wood-based panel drying line, which is used to connect with the exhaust section and air outlet of the wood-based panel drying line, including an exhaust stage adjustment module, a primary sensible heat recovery module, a secondary condensation heat exchange module, a controller and a sensor group; The exhaust grading and adjustment module has multiple exhaust input terminals for receiving exhaust air from different exhaust sections of the wood-based panel drying line, and at least two exhaust output branches. The primary sensible heat recovery module has a primary exhaust side and a primary air supply side that are isolated from each other. The primary exhaust side is connected to an exhaust output branch of the exhaust stage adjustment module, and the primary air supply side is connected to the air supply path. The secondary condensing heat exchange module has a secondary exhaust side and a secondary makeup air side that are isolated from each other. The secondary exhaust side is connected to another exhaust output branch of the exhaust stage adjustment module. The secondary makeup air side is connected to the makeup air passage. The secondary condensing heat exchange module is provided with a condensate discharge structure. The air supply passage is used to allow external fresh air to pass sequentially through the primary air supply side of the primary sensible heat recovery module and the secondary air supply side of the secondary condensation heat exchange module before being delivered to the air outlet. The sensor group is used to acquire at least one of the following: exhaust air temperature, exhaust air humidity, exhaust air volume, makeup air temperature, makeup air humidity, pressure difference of the secondary condensation heat exchange module, and condensate status. The controller is connected to the sensor group, the exhaust grading adjustment module, and the secondary condensation heat exchange module respectively. The controller is configured to obtain exhaust dew point information and / or exhaust enthalpy information based on the parameters obtained by the sensor group, and adjust the exhaust distribution state of the exhaust grading adjustment module and the condensation heat exchange state of the secondary condensation heat exchange module.

[0008] Furthermore, the plurality of exhaust input terminals are respectively connected to the first exhaust collection port, the second exhaust collection port and the third exhaust collection port, and the first exhaust collection port, the second exhaust collection port and the third exhaust collection port are respectively connected to different exhaust sections of the wood-based panel drying line; the exhaust grading adjustment module includes at least one of the following: exhaust manifold, diversion valve, bypass valve, mixing valve and frequency conversion exhaust fan.

[0009] Furthermore, the secondary condensation heat exchange module includes a bypass valve, a differential pressure sensor, a flushing nozzle, a corrosion-resistant heat exchange core, a drainage slope, a condensate collection tank, a liquid-sealed drain pipe, an exhaust inlet, and an exhaust outlet; The corrosion-resistant heat exchange core is disposed between the exhaust inlet and the exhaust outlet. The flushing nozzle is disposed facing the exhaust side of the corrosion-resistant heat exchange core. The drainage slope is located below the corrosion-resistant heat exchange core and slopes towards the condensate collection tank. The condensate collection tank is connected to the liquid-sealed drain pipe. The differential pressure sensor is used to detect the pressure difference between the upstream and downstream of the corrosion-resistant heat exchange core. The bypass valve is disposed on the bypass pipe that bypasses the corrosion-resistant heat exchange core.

[0010] Furthermore, it also includes a moisture-absorbing and heat-releasing heat exchange module and an absorbent regenerator; the moisture-absorbing and heat-releasing heat exchange module has a moisture-absorbing exhaust side and a moisture-absorbing makeup air side that are isolated from each other, the moisture-absorbing exhaust side is connected to the secondary exhaust side outlet of the secondary condensation heat exchange module, the moisture-absorbing makeup air side is connected to the makeup air passage, and an absorbent circulation passage is formed between the moisture-absorbing and heat-releasing heat exchange module and the absorbent regenerator.

[0011] Furthermore, a residual heat exhaust regeneration passage is provided between the primary exhaust outlet of the primary sensible heat recovery module and the absorbent regenerator. The residual heat exhaust regeneration passage is used to introduce the residual heat exhaust after the primary heat exchange into the absorbent regenerator.

[0012] Furthermore, it also includes a phase change thermal energy storage module, which is connected to the make-up air passage or to a circulating medium passage that exchanges heat with the make-up air passage; the phase change thermal energy storage module is signal-connected to the controller to charge heat when there is excess waste heat and release heat when there is insufficient waste heat.

[0013] Furthermore, a regeneration heat replenishment path is provided between the phase change thermal storage module and the absorbent regenerator, which is used to replenish the absorbent regenerator when the regeneration heat of the absorbent regenerator is insufficient.

[0014] This invention also provides a heat exchange-type waste heat recovery control method for a wood-based panel drying line, comprising the following steps: S1, collect operating parameters, including exhaust temperature, exhaust humidity and exhaust volume of different exhaust sections, as well as at least one of makeup air temperature, makeup air humidity, board moisture content, secondary condensation heat exchange pressure difference and condensate state; S2, based on the operating parameters, obtain at least one of the following: exhaust dew point temperature, moisture content, exhaust enthalpy, dew point margin, and moisture content deviation; S3, based on at least one of the exhaust dew point temperature, moisture content, exhaust enthalpy value and moisture content deviation, predict the drying heat demand and waste heat recovery capacity; S4, based on the exhaust temperature, exhaust humidity, exhaust dew point temperature, moisture content or exhaust enthalpy of different exhaust sections, distribute high-temperature exhaust to the primary sensible heat recovery branch and high-humidity exhaust to the secondary condensation heat exchange branch. S5, the high-temperature exhaust air and the makeup air in the first-stage sensible heat recovery branch are indirectly exchanged for sensible heat, and the high-humidity exhaust air and the makeup air or the circulating medium in the second-stage condensing heat exchange branch are indirectly condensed for heat exchange. S6, based on the drying heat demand, waste heat recovery capacity and moisture content deviation, adjust at least one of the following: exhaust distribution ratio, secondary condensation heat exchange state, make-up air volume, dehumidification volume and auxiliary heating volume; S7. When the secondary condenser heat exchange pressure difference, condensate status or absorbent status is abnormal, reduce the corresponding waste heat recovery load, open the bypass or start flushing. S8 records the actual operating results, updates the prediction correction coefficients, and enters the next control cycle.

[0015] Furthermore, in step S2, the exhaust dew point temperature is calculated based on the exhaust temperature and humidity, obtained by looking up a table, or obtained by a dew point sensor; the dew point margin includes the difference between the exhaust outlet temperature of the primary sensible heat recovery branch and the corresponding exhaust dew point temperature, and the difference between the exhaust outlet temperature of the secondary condensation heat exchange branch and the corresponding exhaust dew point temperature.

[0016] Furthermore, in step S6, the exhaust outlet temperature of the secondary condensation heat exchange branch is controlled to be 2°C to 8°C lower than the corresponding exhaust dew point temperature; when the predicted waste heat recovery capacity is greater than the drying heat demand, the excess waste heat is introduced into the phase change heat storage module for heating; when the predicted waste heat recovery capacity is less than the drying heat demand, the phase change heat storage module releases heat to the make-up air passage or absorbent regenerator for compensation.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: 1. By setting up an exhaust grading adjustment module, exhaust air from different sections is distributed to different recovery branches according to its heat and humidity status, so that high-temperature exhaust air is used for primary sensible heat recovery and high-humidity exhaust air is used for secondary condensation heat exchange, thereby reducing heat utilization loss caused by mixing of various exhaust air types.

[0018] 2. By having both the primary sensible heat recovery module and the secondary condensation heat exchange module have isolated exhaust and makeup air sides, the exhaust and makeup air can exchange heat indirectly without mixing, which helps to keep the makeup air clean and reduce the subsequent heating load of the makeup air.

[0019] 3. By setting up a two-stage condensation heat exchange module, the high-humidity exhaust air undergoes controlled condensation within a dedicated module. The heat released by the condensation of water vapor can be used for preheating of the make-up air or heating of the circulating medium, thereby improving the utilization of the latent heat of the exhaust air.

[0020] 4. By setting corrosion-resistant heat exchange cores, drainage slopes, condensate collection tanks and liquid-sealed drain pipes in the secondary condensation heat exchange module, condensate can be discharged along a set path, reducing the retention of condensate in the pipeline or heat exchange chamber.

[0021] 5. By installing differential pressure sensors, bypass valves, and flushing nozzles, the condensation heat exchange load can be reduced, the bypass can be opened, or flushing can be performed when the heat exchange core resistance increases, condensate discharge is abnormal, or maintenance is required, thereby improving the maintainability of the equipment operation.

[0022] 6. By setting up a moisture absorption and heat release heat exchange module and an absorbent regenerator, the residual wet exhaust air after the secondary condensation heat exchange can be further processed, and the residual hot exhaust air after the primary heat exchange can be used to regenerate the absorbent, further utilizing the waste heat inside the system.

[0023] 7. By setting up a phase change thermal storage module, heat can be stored when there is excess waste heat and released when there is insufficient waste heat. This heat can be used for preheating of make-up air or regeneration of absorbent, reducing load fluctuations of auxiliary heaters. Attached Figure Description

[0024] Figure 1 This is a system module block diagram of the heat exchange type waste heat recovery device for the wood-based panel drying line of the present invention; Figure 2 This is a flowchart of the control method of the present invention; Figure 3 This is a schematic diagram of the exhaust grading and energy flow direction of the present invention; Figure 4 This is a schematic diagram of the structure of the two-stage condensation heat exchange module of the present invention; Figure 5 This is a block diagram illustrating the input-output relationship of the rolling predictive control of this invention.

[0025] In the diagram: 1. Drying line; 2. First exhaust air collection port; 3. Second exhaust air collection port; 4. Third exhaust air collection port; 5. Exhaust air classification and adjustment module; 6. First-stage sensible heat recovery module; 7. Second-stage condensation heat exchange module; 8. Moisture absorption and heat release heat exchange module; 9. Phase change heat storage module; 10. Makeup air filter; 11. Makeup air fan; 12. Auxiliary heater; 13. Condensate collection and discharge module; 14. Absorbent regenerator; 15. Controller; 16. Sensor group; 17. Exhaust bypass branch; 18. Air supply outlet; 701. Bypass valve; 702. Differential pressure sensor; 703. Flushing nozzle; 704. Corrosion-resistant heat exchange core; 705. Drainage slope; 706. Condensate collection tank; 707. Liquid-sealed drain pipe; 708. Exhaust air inlet; 709. Exhaust air outlet. Detailed Implementation

[0026] The following is combined with Figures 1 to 5 This invention will now be described in detail with reference to a specific embodiment. In this embodiment, the waste heat recovery device is connected to a wood-based panel drying line 1. The drying line 1 can be a continuous conveyor drying line or a segmented hot air drying line. The drying line 1 itself can consist of a hot air box, a conveying device, an exhaust port, an air supply port, and an auxiliary heating unit. The waste heat recovery device is not required to be integrated into the entire drying line 1, but rather connected to the exhaust section and air supply port 18 of the drying line 1. Thus, the waste heat recovery device can be installed as a stand-alone unit beside an existing drying line, or it can be installed along with a newly constructed drying line.

[0027] like Figure 1 As shown, the drying line 1 is equipped with a first exhaust air collection port 2, a second exhaust air collection port 3, and a third exhaust air collection port 4 along the conveying direction of the sheet material. The first exhaust air collection port 2 can be located at the beginning of the drying line or near the high-temperature air supply area. The exhaust air temperature at this location is relatively high, and the moisture content is relatively stable, making it suitable for sensible heat recovery. The second exhaust air collection port 3 can be located in the middle of the drying line. The exhaust air at this location has a certain temperature and also carries a significant amount of water vapor. The third exhaust air collection port 4 can be located at the end of the drying line or in an area where moisture is concentrated. The exhaust air temperature at this location may be lower than at the beginning, but the humidity is higher, making it suitable for entering the condensation heat exchange branch. The arrangement of the three exhaust air collection ports ensures that the exhaust air maintains the different thermal and moisture characteristics of different sections before entering the recovery device, eliminating the need for pre-mixing.

[0028] The first exhaust air intake 2, the second exhaust air intake 3, and the third exhaust air intake 4 are connected to the exhaust air classification and regulation module 5 via exhaust branch pipes. Each exhaust branch pipe can be equipped with an electric air valve, a check valve, and an inspection port. The exhaust air classification and regulation module 5 can be equipped with an exhaust air manifold, a diverter valve, a mixing valve, a bypass valve, and a variable frequency exhaust fan. The exhaust air manifold is used to receive exhaust air from multiple exhaust air intakes. The diverter valve is used to control the proportion of each exhaust branch entering the primary sensible heat recovery module 6 or the secondary condensing heat exchange module 7. The mixing valve is used to mix a portion of the high-temperature exhaust air with the high-humidity exhaust air in a certain proportion when needed, so that the exhaust air temperature and dew point entering the secondary condensing heat exchange module 7 are within the range suitable for condensing heat exchange. The bypass valve is used to bypass exhaust air during abnormal exhaust, start-up and shutdown phases, or maintenance.

[0029] Sensor group 16 is installed on drying line 1, each exhaust branch pipe, exhaust stage adjustment module 5, primary sensible heat recovery module 6, secondary condensation heat exchange module 7, moisture absorption and heat release heat exchange module 8, phase change heat storage module 9, and makeup air passage. Sensor group 16 may include temperature sensors, humidity sensors, airflow sensors, differential pressure sensors, condensate level sensors, sheet moisture content detectors, absorbent concentration detectors, and heat storage status detectors. Temperature and humidity sensors are used to obtain the temperature and humidity status of each exhaust section. Airflow sensors are used to obtain the exhaust or makeup air flow rate. Sheet moisture content detectors can be installed at the inlet, middle, or outlet of the drying line to reflect the sheet drying process. Differential pressure sensors are used to determine whether there is dirt accumulation or blockage in the secondary condensation heat exchange module 7. Condensate level sensors are used to determine whether the condensate collection and discharge module 13 is draining smoothly.

[0030] The controller 15 can be a PLC, an industrial controller, or a control unit with data acquisition capabilities. The controller 15 is connected to the sensor group 16 and also to the exhaust fan staged regulation module 5, the secondary condensation heat exchange module 7, the moisture absorption and heat release heat exchange module 8, the phase change heat storage module 9, and the auxiliary heater 12. After receiving the detection signals, the controller 15 calculates the exhaust fan dew point, moisture content, enthalpy, moisture content deviation, and recoverable heat, and outputs control commands such as valve opening degree, fan frequency, circulating pump frequency, bypass opening and closing, flushing start and stop, and auxiliary heating amount.

[0031] The primary sensible heat recovery module 6 has a primary exhaust side and a primary makeup air side that are isolated from each other. The exhaust air grading and regulating module 5 sends high-temperature exhaust air into the primary exhaust side of the primary sensible heat recovery module 6. External fresh air enters the primary makeup air side of the primary sensible heat recovery module 6 after passing through the makeup air filter 10 and the makeup air fan 11. The high-temperature exhaust air and makeup air exchange heat indirectly through the heat exchange wall within the primary sensible heat recovery module 6. The two gases do not come into direct contact or mix. The primary sensible heat recovery module 6 can use a plate heat exchanger, a plate-fin heat exchanger, a finned tube heat exchanger, or a heat pipe heat exchanger. The exhaust side can be made of stainless steel, aluminum alloy anti-corrosion coating material, or other moisture- and heat-resistant materials. The primary sensible heat recovery module 6 is mainly used to utilize the sensible heat of the high-temperature exhaust air to raise the makeup air temperature to a higher level.

[0032] During operation, the primary sensible heat recovery module 6 does not undertake the main condensation task. The controller 15 can keep the exhaust outlet temperature of the primary sensible heat recovery module 6 above the corresponding exhaust dew point temperature. This can reduce the amount of condensation inside the primary heat exchanger. The residual hot exhaust air after the primary heat exchange still has a certain temperature, especially when the drying line is operating at high load. This residual hot exhaust air can enter the absorbent regenerator 14 through the residual hot exhaust air regeneration path for absorbent regeneration.

[0033] The secondary condensing heat exchange module 7 has a secondary exhaust side and a secondary makeup air side that are isolated from each other. The exhaust air classification and regulation module 5 sends high-humidity exhaust air into the secondary exhaust side of the secondary condensing heat exchange module 7. The makeup air, after being preheated by the primary sensible heat recovery module 6, enters the secondary makeup air side of the secondary condensing heat exchange module 7. The high-humidity exhaust air and the makeup air exchange indirectly through the corrosion-resistant heat exchange core 704. After the high-humidity exhaust air is cooled, its water vapor condenses in the controlled area and releases latent heat of condensation. This heat is transferred to the makeup air or circulating medium through the heat exchange core. Condensate is discharged through the condensate collection and discharge module 13.

[0034] like Figure 4As shown, the secondary condensation heat exchange module 7 includes a bypass valve 701, a differential pressure sensor 702, a flushing nozzle 703, a corrosion-resistant heat exchange core 704, a drainage slope 705, a condensate collection tank 706, a liquid-sealed drain pipe 707, an exhaust inlet 708, and an exhaust outlet 709. Exhaust air enters the secondary condensation heat exchange module 7 through the exhaust inlet 708, passes through the corrosion-resistant heat exchange core 704, and exits through the exhaust outlet 709. A hydrophilic anti-corrosion layer can be provided on the exhaust side surface of the corrosion-resistant heat exchange core 704 to facilitate the formation of a water film and its flow downwards. The corrosion-resistant heat exchange core 704 can be made of stainless steel plates, aluminum alloy plates coated with an anti-corrosion layer, fluoroplastic coated plates, or other moisture-resistant materials.

[0035] A drainage slope 705 is positioned below the corrosion-resistant heat exchange core 704 and slopes towards the condensate collection tank 706. Condensate flows into the condensate collection tank 706 along the corrosion-resistant heat exchange core 704 and the drainage slope 705. The condensate collection tank 706 is connected to a liquid-sealed drain pipe 707. The liquid-sealed drain pipe 707 has a curved liquid-sealed structure, which reduces exhaust leakage from the drain outlet and also reduces backflow of external air. The condensate collection tank 706 can be equipped with a removable filter screen to intercept wood dust and fine impurities. If necessary, the condensate can enter a sedimentation or filtration device after discharge.

[0036] Differential pressure sensor 702 is used to detect the pressure difference between the upstream and downstream of the corrosion-resistant heat exchange core 704. An increase in differential pressure usually indicates the presence of dirt, water accumulation, or blockage on the surface of the heat exchange core. Upon receiving an abnormal differential pressure signal, controller 15 can reduce the exhaust airflow into the secondary condenser heat exchange module 7, open bypass valve 701, or activate flushing nozzle 703. Flushing nozzle 703 is positioned above or to the side of the corrosion-resistant heat exchange core 704, with the spray direction directed towards the exhaust side surface of the corrosion-resistant heat exchange core 704. Flushing can use external clean water or filtered condensate. The flushing action can be performed during shutdown or briefly during low-load operation.

[0037] A bypass valve 701 is installed on the bypass pipeline that bypasses the corrosion-resistant heat exchange core 704. When the pressure differential of the secondary condensing heat exchange module 7 is too high, the condensate drainage is obstructed, or maintenance is required, the bypass valve 701 opens, allowing at least part of the exhaust air to bypass the corrosion-resistant heat exchange core 704 before being discharged. This ensures that the exhaust path of the drying line 1 is not blocked.

[0038] In the secondary condensation heat exchange process, controller 15 obtains the exhaust dew point temperature based on the exhaust air temperature and humidity. The exhaust dew point temperature can be obtained through formula calculation, table lookup, or direct measurement by a dew point sensor. When using formula calculation, the Magnus formula can be used:

[0039]

[0040] in, For the first The exhaust temperature of each exhaust section For the first The relative humidity of the exhaust air in each exhaust section, and Expressed as a percentage, For the first The exhaust dew point temperature of each exhaust section This represents intermediate computational costs. You can take 17.27. 237.7℃ can be used. The above coefficient is a preferred empirical coefficient. Under different altitudes, air pressures, or sensor conditions, other dew point estimation formulas, lookup table models, or empirical coefficients can also be used. The key is to obtain the exhaust dew point temperature based on the exhaust air temperature and humidity, and use it to adjust the condensation heat exchange process.

[0041] Controller 15 can also calculate the dew point margin. The dew point margin of the primary sensible heat recovery branch can be expressed as:

[0042] The dew point margin of the secondary condenser heat exchange branch can be expressed as:

[0043] in, This refers to the exhaust outlet temperature of the primary sensible heat recovery module 6. The exhaust outlet temperature of the secondary condensing heat exchange module 7. The exhaust dew point temperature for entering the primary sensible heat recovery module 6, The exhaust dew point temperature is the temperature of the air entering the secondary condenser heat exchange module 7. It can be controlled to a positive value, so that the first-stage sensible heat recovery module 6 is kept in a state of minimal condensation. The temperature can be controlled to be negative, causing controlled condensation in the secondary condensing heat exchange module 7. Preferably, the exhaust outlet temperature of the secondary condensing heat exchange module 7 is 2°C to 8°C lower than the corresponding exhaust dew point temperature. This range allows condensation to occur in the high-humidity exhaust air without causing excessive condensation or significant water accumulation.

[0044] The controller 15 can also calculate the exhaust air moisture content and exhaust air enthalpy based on the humid air parameters. The exhaust air moisture content can be calculated using the following formula:

[0045] in, For the first Moisture content of exhaust air For the first Section exhaust steam partial pressure, Atmospheric pressure. It can be calculated based on saturated water vapor pressure and relative humidity.

[0046] The exhaust enthalpy can be calculated using the following formula:

[0047] in, For the first The enthalpy of the exhaust air section can be expressed in kJ / kg dry air. For the first Section exhaust air temperature, in °C. For the first The enthalpy value of the exhaust air reflects the sensible heat of dry air, the sensible heat of water vapor, and the latent heat of water vapor. The controller 15 can determine whether the exhaust air section is suitable to enter the sensible heat recovery branch or the condensation heat exchange branch based on the enthalpy value of different exhaust air sections.

[0048] The theoretical recoverable heat in the corresponding module for each exhaust section can be estimated using the following formula:

[0049] in, For the first The section exhaust system can recover heat. For the first Sectional exhaust air mass flow rate For the first The enthalpy value of the exhaust air before it enters the corresponding module. This represents the outlet enthalpy value of the exhaust air after passing through the corresponding module. To determine the efficiency of the corresponding heat exchange modules: The primary sensible heat recovery module 6 can be primarily estimated based on the sensible heat from the temperature difference. The secondary condensation heat exchange module 7 can be estimated based on the enthalpy difference. The moisture absorption and heat release heat exchange module 8 can be estimated based on the amount of moisture absorbed and the amount of heat absorbed and released. The phase change heat storage module 9 can be estimated based on the currently available chargeable and releaseable heat.

[0050] The drying heat demand can be composed of the makeup air heating demand, the moisture evaporation demand of the sheet material, and a heat loss correction term. The drying heat demand in the next control cycle or the next forecast window can be expressed as:

[0051] in:

[0052]

[0053]

[0054] In the formula, To meet the drying heat requirements, To meet the demand for supplemental air and heating, To meet the moisture evaporation requirements of the board material. This is a correction term for heat loss. To supplement air mass flow rate, For the specific heat of air, For the target supply air temperature, For external air supply temperature, This is the correction factor for the heat of evaporation of moisture in the board material. This refers to the mass or area of ​​the boards entering the drying line per unit time. This represents the current moisture content of the board. For the target moisture content, This is a correction factor for heat dissipation in the drying line. This is the current temperature of the drying chamber. The ambient temperature.

[0055] Moisture content deviation can be expressed as:

[0056] in, For moisture content deviation, This represents the target moisture content of the drying process curve at the current time or location. When the value is positive and exceeds the set value, it indicates that the board is not dry enough. Controller 15 can increase the make-up air volume, dehumidification volume, or auxiliary heating volume; when When the value is negative and lower than the set value, it indicates that the board material is becoming too dry. Controller 15 can reduce the auxiliary heating amount or reduce the dehumidification intensity.

[0057] like Figure 1 and Figure 3 As shown, the moisture-absorbing and heat-releasing heat exchange module 8 can be connected after the exhaust outlet of the secondary condensation heat exchange module 7. After the high-humidity exhaust air undergoes secondary condensation heat exchange, it may still contain some water vapor. This residual wet exhaust air enters the moisture-absorbing exhaust side of the moisture-absorbing and heat-releasing heat exchange module 8. The moisture-absorbing and heat-releasing heat exchange module 8 is equipped with an absorbent spray section, a gas-liquid contact zone, an absorbent circulation pump, and an absorbent liquid heat exchange section. The absorbent can be an aqueous solution of lithium chloride, calcium chloride, or lithium bromide, or a compound absorbent suitable for humid air absorption. After absorbing the water vapor in the residual wet exhaust air, the absorbent's temperature rises, and the released heat is transferred to the makeup air side or the circulating medium through the absorbent liquid heat exchange section. This allows for the continued utilization of the remaining humid heat after secondary condensation.

[0058] After absorbing moisture, the absorbent's concentration decreases, forming a dilute absorbent. This dilute absorbent enters the absorbent regenerator 14. The absorbent regenerator 14 may include a regeneration heating section, a gas-liquid separation section, and a concentrated absorbent return section. A residual heat exhaust regeneration passage is provided between the primary exhaust outlet of the primary sensible heat recovery module 6 and the absorbent regenerator 14. The residual heat exhaust after the primary heat exchange enters the absorbent regenerator 14, heating the dilute absorbent and causing some of the moisture to evaporate, increasing the absorbent concentration and forming a concentrated absorbent. The concentrated absorbent then flows back to the moisture absorption and heat release heat exchange module 8. The exhaust after absorbent regeneration enters the exhaust gas discharge end.

[0059] The phase change thermal storage module 9 is connected to the make-up air passage, preferably positioned after the make-up air side of the moisture absorption and heat release heat exchange module 8 and before the auxiliary heater 12. The phase change thermal storage module 9 may include a phase change thermal storage box, a phase change material, heat exchange piping, a charging valve, a releasing valve, and a temperature sensor. The phase change material can be selected from materials whose phase change temperature matches the make-up air preheating temperature, such as hydrated salts, paraffin composite materials, or eutectic salts with a phase change temperature of 45℃ to 75℃. To improve the heat exchange rate, fins, a metal thermally conductive frame, or a tube bundle can be installed inside the phase change thermal storage box.

[0060] When the controller 15 determines that the waste heat recovery capacity is greater than the drying heat demand, some of the waste heat can be introduced into the phase change thermal storage module 9, causing the phase change material to absorb heat and undergo a phase change, thus completing the heat charging. When the controller 15 determines that the waste heat recovery capacity is less than the drying heat demand, the makeup air or circulating medium passes through the phase change thermal storage module 9, and the phase change material releases heat to compensate for the heat of the makeup air. The phase change thermal storage module 9 can also provide heat to the absorbent regenerator 14 through the regeneration heat supplementation path. When the residual heat exhaust air after the first-stage heat exchange is insufficient to complete the absorbent regeneration, the heat released by the phase change thermal storage module 9 can supplement the absorbent regenerator 14.

[0061] The operation of the make-up air passage is as follows: External fresh air first enters the make-up air filter 10 to remove particulate matter from the outside air. Then, it is delivered by the make-up air fan 11 to the primary make-up air side of the primary sensible heat recovery module 6. The make-up air absorbs the sensible heat of the high-temperature exhaust air in the primary sensible heat recovery module 6. Afterward, the make-up air enters the secondary make-up air side of the secondary condensation heat exchange module 7 to absorb the heat released by the condensation of the high-humidity exhaust air. If a moisture absorption and heat release heat exchange module 8 is installed, the make-up air continues to enter the moisture absorption make-up air side of the moisture absorption and heat release heat exchange module 8 to absorb the heat generated by moisture absorption and heat release. Subsequently, the make-up air enters the phase change heat storage module 9, absorbing the heat released by the heat storage module according to the operating state or storing excess heat in the heat storage module. Finally, the make-up air enters the auxiliary heater 12, where the auxiliary heater 12 corrects the make-up air temperature to the target supply air temperature, and then delivers it to the drying line 1 through the air outlet 18.

[0062] The auxiliary heater 12 can be a steam heat exchanger, a hot water heat exchanger, a thermal oil heat exchanger, a gas heater, or an electric heater. Since the makeup air has undergone multi-stage preheating before entering the auxiliary heater 12, the auxiliary heater 12 primarily serves a temperature compensation function. The controller 15 adjusts the heating capacity of the auxiliary heater 12 based on the target supply air temperature and the actual makeup air temperature. If the moisture content of the board material is too high, the auxiliary heater 12 can increase the heating capacity; if the moisture content of the board material is close to the target moisture content, the auxiliary heater 12 can decrease the heating capacity.

[0063] like Figure 2 As shown, the control method of this embodiment is executed cyclically according to a control cycle. The control cycle can be from 10 seconds to 60 seconds, or it can be set to other times according to the on-site response speed. The controller 15 first collects exhaust air temperature and humidity, air volume, makeup air temperature and humidity, board moisture content, pressure difference, condensate state, absorbent concentration, and phase change heat storage state. Then it calculates exhaust air dew point temperature, moisture content, enthalpy, dew point margin, and moisture content deviation. Then it predicts the drying heat demand and waste heat recovery capacity. The prediction window can be from 3 minutes to 10 minutes, or it can be adjusted according to the length of the drying line and the conveyor speed.

[0064] During exhaust air classification, controller 15 allocates exhaust air with higher temperature and suitable for sensible heat recovery to the primary sensible heat recovery module 6, and exhaust air with higher humidity and higher dew point to the secondary condensation heat exchange module 7. When a certain exhaust air has a high dust content, its temperature and humidity are unsuitable for heat exchange, or the equipment is in an abnormal state, controller 15 can allocate that part of the exhaust air to the exhaust bypass branch 17. The exhaust bypass branch 17 is ultimately connected to the exhaust gas emission end.

[0065] In the multi-stage waste heat recovery control, controller 15 adjusts the exhaust volume of the primary sensible heat recovery module 6 to stably recover the sensible heat from the high-temperature exhaust air. Controller 15 also adjusts the exhaust volume, bypass ratio, or heat exchange medium flow rate of the secondary condensing heat exchange module 7 to maintain the condensation process of the secondary condensing heat exchange module 7 within a set range. When further treatment of residual wet exhaust air is required, controller 15 adjusts the absorbent circulation rate of the moisture absorption and heat release heat exchange module 8. When the absorbent concentration is lower than the set value, controller 15 starts the absorbent regenerator 14 and prioritizes regeneration using the residual hot exhaust air after the primary heat exchange. If the regenerated heat is insufficient, the phase change heat storage module 9 is called in to supplement the heat.

[0066] In the abnormal protection mode, if the pressure difference of the secondary condensing heat exchange module 7 exceeds the set value, it indicates that there may be dirt, blockage, or water accumulation in the corrosion-resistant heat exchange core 704. The controller 15 can reduce the exhaust volume of the secondary condensing heat exchange branch, open the bypass valve 701, and start the flushing nozzle 703. If the condensate level rises or the liquid seal drain pipe 707 is not draining properly, the controller 15 can temporarily reduce the condensation intensity and issue a maintenance prompt. If the absorbent concentration is abnormal or the absorbent circulation pump is abnormal, the controller 15 can reduce the load of the moisture absorption and heat release heat exchange module 8 and allow the residual wet exhaust air to directly enter the tail gas emission end. In this way, when the waste heat recovery device is abnormal, the drying line 1 can still maintain basic exhaust and air supply.

[0067] like Figure 5 As shown, the inputs to the rolling predictive control include exhaust parameters, makeup air parameters, sheet material parameters, and module status. Exhaust parameters include temperature, humidity, airflow, and differential pressure. Makeup air parameters include temperature, humidity, and airflow. Sheet material parameters include inlet moisture content, current moisture content, target moisture content, and conveying speed. Module status includes absorbent concentration, heat storage status, and condensate status. The controller 15 calculates the moisture content deviation, drying heat demand, recoverable heat, dew point temperature, moisture content, exhaust enthalpy, and dew point margin based on these inputs. The controller 15 then performs thermal and humidity status identification and energy surplus / deficit judgment, and corrects the control parameters accordingly.

[0068] The control actions output by controller 15 include adjusting the exhaust stage valve, adjusting the secondary condenser bypass valve, adjusting the fan frequency, adjusting the absorbent circulation volume, controlling the charging and discharging of the phase change thermal storage module 9, adjusting the auxiliary heating amount, and initiating bypass, flushing, or alarm functions. At the end of each control cycle, controller 15 records the actual operating results. If the actual makeup air temperature is lower than the predicted value, controller 15 can reduce the corresponding heat exchange efficiency correction coefficient. If the rate of decrease in the moisture content of the sheet material is lower than the predicted value, controller 15 can increase the drying heat demand correction coefficient. In this way, the predicted results for the next control cycle will be corrected according to the actual operating conditions.

[0069] This embodiment utilizes an exhaust grading and adjustment module 5, a primary sensible heat recovery module 6, and a secondary condensation heat exchange module 7 to direct high-temperature exhaust and high-humidity exhaust into suitable heat exchange branches. The secondary condensation heat exchange module 7 ensures condensation occurs in a dedicated module with drainage, differential pressure detection, bypass, and flushing structures. The residual wet exhaust is further processed by the moisture absorption and heat release heat exchange module 8 and the absorbent regenerator 14, and regenerated using the residual heat exhaust after the primary heat exchange. The phase change heat storage module 9 buffers excess and insufficient waste heat. The controller 15 and sensor group 16 combine exhaust status, makeup air status, board moisture content, and equipment status to coordinate waste heat recovery and the drying process. This structure and method can be used for exhaust waste heat recovery in wood-based panel drying lines and reduce auxiliary heating load.

Claims

1. A heat exchange type waste heat recovery device for a wood-based panel drying line, used to connect with the exhaust section and air inlet (18) of the wood-based panel drying line (1), characterized in that, It includes an exhaust grading and adjustment module (5), a primary sensible heat recovery module (6), a secondary condensation heat exchange module (7), a controller (15), and a sensor group (16). The exhaust grading adjustment module (5) has multiple exhaust input terminals for receiving exhaust from different exhaust sections of the wood board drying line (1), and at least two exhaust output branches; The primary sensible heat recovery module (6) has a primary exhaust side and a primary air supply side that are isolated from each other. The primary exhaust side is connected to an exhaust output branch of the exhaust grade adjustment module (5), and the primary air supply side is connected to the air supply path. The secondary condensing heat exchange module (7) has a secondary exhaust side and a secondary makeup air side that are isolated from each other. The secondary exhaust side is connected to another exhaust output branch of the exhaust grade adjustment module (5). The secondary makeup air side is connected to the makeup air passage. The secondary condensing heat exchange module (7) is provided with a condensate discharge structure. The air supply passage is used to allow fresh air from outside to pass through the primary air supply side of the primary sensible heat recovery module (6) and the secondary air supply side of the secondary condensation heat exchange module (7) in sequence before being sent to the air outlet (18). The sensor group (16) is used to acquire at least one of the following: exhaust air temperature, exhaust air humidity, exhaust air volume, makeup air temperature, makeup air humidity, pressure difference of the secondary condensation heat exchange module (7), and condensate status. The controller (15) is connected to the sensor group (16), the exhaust grading adjustment module (5) and the secondary condensing heat exchange module (7) respectively. The controller (15) is configured to obtain exhaust dew point related information and / or exhaust enthalpy related information based on the parameters obtained by the sensor group (16), and adjust the exhaust distribution state of the exhaust grading adjustment module (5) and the condensing heat exchange state of the secondary condensing heat exchange module (7).

2. The heat exchange type waste heat recovery device for a wood-based panel drying line according to claim 1, characterized in that, The plurality of exhaust input terminals are respectively connected to the first exhaust collection port (2), the second exhaust collection port (3) and the third exhaust collection port (4), and the first exhaust collection port (2), the second exhaust collection port (3) and the third exhaust collection port (4) are respectively connected to different exhaust sections of the wood board drying line (1); the exhaust grade adjustment module (5) includes at least one of the following: exhaust manifold, diversion valve, bypass valve, mixing valve and frequency conversion exhaust fan.

3. The heat exchange type waste heat recovery device for a wood-based panel drying line according to claim 1, characterized in that, The secondary condensing heat exchange module (7) includes a bypass valve (701), a differential pressure sensor (702), a flushing nozzle (703), a corrosion-resistant heat exchange core (704), a drainage slope (705), a condensate collection tank (706), a liquid-sealed drain pipe (707), an exhaust inlet (708), and an exhaust outlet (709). The corrosion-resistant heat exchange core (704) is disposed between the exhaust inlet (708) and the exhaust outlet (709). The flushing nozzle (703) is disposed facing the exhaust side of the corrosion-resistant heat exchange core (704). The drainage slope (705) is located below the corrosion-resistant heat exchange core (704) and inclined towards the condensate collection tank (706). The condensate collection tank (706) is connected to the liquid seal drain pipe (707). The differential pressure sensor (702) is used to detect the differential pressure between the upstream and downstream of the corrosion-resistant heat exchange core (704). The bypass valve (701) is disposed on the bypass pipeline that bypasses the corrosion-resistant heat exchange core (704).

4. The heat exchange type waste heat recovery device for a wood-based panel drying line according to claim 1, characterized in that, It also includes a moisture-absorbing and heat-releasing heat exchange module (8) and an absorbent regenerator (14); the moisture-absorbing and heat-releasing heat exchange module (8) has a moisture-absorbing exhaust side and a moisture-absorbing makeup air side that are isolated from each other. The moisture-absorbing exhaust side is connected to the secondary exhaust side outlet of the secondary condensation heat exchange module (7). The moisture-absorbing makeup air side is connected to the makeup air passage. An absorbent circulation passage is formed between the moisture-absorbing and heat-releasing heat exchange module (8) and the absorbent regenerator (14).

5. The heat exchange type waste heat recovery device for a wood-based panel drying line according to claim 4, characterized in that, A residual heat exhaust regeneration passage is provided between the primary exhaust side outlet of the primary sensible heat recovery module (6) and the absorbent regenerator (14). The residual heat exhaust regeneration passage is used to introduce the residual heat exhaust after the primary heat exchange into the absorbent regenerator (14).

6. The heat exchange type waste heat recovery device for a wood-based panel drying line according to any one of claims 1 to 5, characterized in that, It also includes a phase change thermal storage module (9), which is connected to the make-up air passage or to a circulating medium passage that exchanges heat with the make-up air passage; the phase change thermal storage module (9) is signal-connected to the controller (15) to charge heat when there is excess waste heat and release heat when there is insufficient waste heat.

7. The heat exchange type waste heat recovery device for a wood-based panel drying line according to claim 6, characterized in that, A regeneration and heat replenishment passage is provided between the phase change thermal storage module (9) and the absorbent regenerator (14) for replenishing heat to the absorbent regenerator (14) when the regeneration heat of the absorbent regenerator (14) is insufficient.

8. A heat exchange-type waste heat recovery control method for a wood-based panel drying line, characterized in that, Includes the following steps: S1, collect operating parameters, including exhaust temperature, exhaust humidity and exhaust volume of different exhaust sections, as well as at least one of makeup air temperature, makeup air humidity, board moisture content, secondary condensation heat exchange pressure difference and condensate state; S2, based on the operating parameters, obtain at least one of the following: exhaust dew point temperature, moisture content, exhaust enthalpy, dew point margin, and moisture content deviation; S3, based on at least one of the exhaust dew point temperature, moisture content, exhaust enthalpy value and moisture content deviation, predict the drying heat demand and waste heat recovery capacity; S4, based on the exhaust temperature, exhaust humidity, exhaust dew point temperature, moisture content or exhaust enthalpy of different exhaust sections, distribute high-temperature exhaust to the primary sensible heat recovery branch and high-humidity exhaust to the secondary condensation heat exchange branch. S5, the high-temperature exhaust air and the makeup air in the first-stage sensible heat recovery branch are indirectly exchanged for sensible heat, and the high-humidity exhaust air and the makeup air or the circulating medium in the second-stage condensing heat exchange branch are indirectly condensed for heat exchange. S6, based on the drying heat demand, waste heat recovery capacity and moisture content deviation, adjust at least one of the following: exhaust distribution ratio, secondary condensation heat exchange state, make-up air volume, dehumidification volume and auxiliary heating volume; S7. When the secondary condenser heat exchange pressure difference, condensate status or absorbent status is abnormal, reduce the corresponding waste heat recovery load, open the bypass or start flushing. S8 records the actual operating results, updates the prediction correction coefficients, and enters the next control cycle.

9. The heat exchange-type waste heat recovery control method for a wood-based panel drying line according to claim 8, characterized in that, In step S2, the exhaust dew point temperature is calculated based on the exhaust temperature and humidity, obtained by looking up a table, or obtained by a dew point sensor; the dew point margin includes the difference between the exhaust outlet temperature of the primary sensible heat recovery branch and the corresponding exhaust dew point temperature, and the difference between the exhaust outlet temperature of the secondary condensation heat exchange branch and the corresponding exhaust dew point temperature.

10. The heat exchange-type waste heat recovery control method for a wood-based panel drying line according to claim 8, characterized in that, In step S6, the exhaust outlet temperature of the secondary condensation heat exchange branch is controlled to be 2°C to 8°C lower than the corresponding exhaust dew point temperature; when the predicted waste heat recovery capacity is greater than the drying heat demand, the excess waste heat is introduced into the phase change heat storage module (9) for heating; when the predicted waste heat recovery capacity is less than the drying heat demand, the phase change heat storage module (9) releases heat to the make-up air passage or absorbent regenerator (14) for compensation.

Images