Monitoring, recovery and control method and system for sensible heat and latent heat of grain dryer exhaust gas

Abstract

The application discloses a kind of grain dryer waste gas sensible heat and latent heat monitoring recovery control method and system, belong to waste heat recovery and utilization technical field, to solve the initial stage of drying waste gas state instability, to cause the problem of recovery system concussion;Sensible heat and latent heat proportion dynamic change in whole cycle of drying, and single parameter control cannot realize efficient and stable recovery problem.The method of the present application sets initial operation stage, adjusts the inlet temperature of dryer by the second combustion machine, so that the waste gas reaches stable state;Set normal adjustment stage, according to the temperature and humidity of waste gas, the double PID closed loop adjustment of first combustion machine opening degree is realized by long cycle enthalpy optimization and short cycle humidity ratio tracking, efficient and stable recovery is realized.The system for realizing heat recovery cooperated with the method, the system includes double combustion machine, generator, dryer, sensible and latent heat recovery device, sensor assembly and controller;Realize the efficient and stable recovery of waste gas sensible heat and latent heat, improve energy utilization.

Description

Technical Field

[0001] This invention relates to the field of waste heat recovery and utilization technology, and in particular to a method and system for monitoring, recovering and controlling the sensible heat and latent heat of waste gas from a grain dryer. Background Technology

[0002] Grain dryers typically use hot air to heat and dry the grain during operation, and then the hot air, after heat exchange with the grain, is discharged as exhaust gas. Although the temperature of this exhaust gas decreases due to heat exchange with the grain, it is still higher than the ambient temperature, representing sensible heat. Secondly, because grains contain moisture, during the drying process, this moisture absorbs heat and changes from a liquid to a gaseous state, which is then discharged with the hot air, carrying a significant amount of latent heat. Therefore, grain dryers generate a large amount of exhaust gas during operation, containing considerable sensible and latent heat. The proper recovery and utilization of this heat is crucial for improving energy efficiency, reducing drying costs, and minimizing environmental pollution.

[0003] For sensible heat recovery, a common approach is to install heat exchangers in the exhaust pipes of the dryer, allowing the exhaust gas to exchange heat with the fresh air or water entering the dryer. For example, in a shell-and-tube heat exchanger, the exhaust gas flows inside the tubes while fresh air or water flows outside, transferring heat through the tube walls to preheat the fresh air or heat the water, thus recovering and utilizing sensible heat. For latent heat recovery, the common method is to lower the temperature of the exhaust gas, causing water vapor in the exhaust gas to condense into liquid water, releasing latent heat. This can be achieved using solution absorption heat recovery devices or mixed condensers. In solution absorption heat recovery devices, the exhaust gas and a cooling medium (such as water or air) exchange heat through the metal walls, causing water vapor to condense. Mixed condensers directly mix the exhaust gas with cooling water, causing water vapor to condense. The latent heat released during condensation can be used to preheat the fresh air entering the dryer or for other process flows.

[0004] However, some problems still exist in the actual process of waste gas recovery and utilization. For example, the waste gas state is unstable in the initial stage of drying, which can easily lead to vibration of the recovery system; the ratio of sensible heat to latent heat changes dynamically throughout the drying cycle, and traditional single-parameter control, such as temperature or humidity, cannot achieve efficient and stable heat recovery. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a waste heat energy recovery and compensation system for grain dryers, which is mainly used for waste heat recovery and utilization of grain dryers, so as to achieve the purpose of efficiently recovering heat energy in drying exhaust gas.

[0006] This invention discloses a method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer. It is applied to a drying system including a first burner, a second burner, a generator, a dryer, a latent heat recovery device, and a sensible heat recovery device. The method includes the following steps: S1. Initial running phase, The first burner is fully open, inputting hot air into the dryer. The heat exchange contact surface between the first burner and the generator is closed, and the latent heat recovery device is on standby. Obtain the real-time temperature T at the air inlet of the dryer. sc And transmit it to the controller, the controller based on the real-time temperature T sc The opening of the second burner is adjusted according to the preset drying temperature threshold until the drying exhaust gas reaches the preset stable state. S2. Normal adjustment phase The latent heat recovery device is activated, and the heat exchange contact area between the first burner and the generator is adjusted in real time based on the enthalpy recovery rate to regulate the recovery efficiency of the latent heat recovery device. S21. Calculate the actual enthalpy recovery rate of the drying system in the first control cycle, use the PID algorithm to dynamically calculate the deviation between the actual enthalpy recovery rate and the set target recovery rate, and update the target absolute moisture content. S211. Real-time parameter acquisition and transmission to the processor, the parameter acquisition includes the exhaust gas temperature T before the dryer exhaust gas recovery. in and humidity RH in The temperature T of the exhaust gas after the dryer exhaust gas recovery out and humidity RH out The temperature of the ambient air, T amb and humidity RH amb ; S212. Calculate the enthalpy h of moist air before waste gas recovery. in Enthalpy of moist air h after exhaust gas recovery out Enthalpy of ambient air (h) amb ; ; Where h is the enthalpy of moist air (kJ / kg dry air); T is the gas temperature (°C); d is the moisture content (g / kg dry air); 1.006×T is the sensible heat of 1 kg dry air; d×2501 is the latent heat of water vapor; and d×1.86×T is the sensible heat of water vapor. S213. Calculate the actual enthalpy recovery rate η of the drying system. device ; ; Among them, h in —Enthalpy of moist air before exhaust gas recovery; h out —Enthalpy of moist air after exhaust gas recovery; hamb —The enthalpy of humid air in the environment; S214. Based on the actual enthalpy value recovery rate η device With target recovery rate η target The deviation is dynamically calculated to determine the target absolute moisture content d. target , The absolute moisture content correction increment is obtained using a PID algorithm. ; Where Δd is the output increment of the controller; e is the deviation signal. ;de—represents the minute change in the deviation signal e; dt—the differential increment of time; —This reflects the rate and direction of change of the deviation over time; K p —Quickly respond to current recovery rate deviations; K i —Eliminate steady-state deviation; K d —Suppress volatility; S215. Add the current target absolute moisture content to the correction increment to obtain the updated target absolute moisture content. , ; S22. Obtain the actual absolute moisture content of the exhaust gas during the second control cycle, and update the target absolute moisture content. To set a value, a closed-loop control algorithm is used to dynamically adjust the opening of the first burner, thereby adjusting the heat exchange contact area between the first burner and the generator, and adjusting the evaporation capacity of the generator. The second control cycle is shorter than the first control cycle.

[0007] Furthermore, in step S1, the adjustment method for the second burner includes: If the real-time temperature T sc Below the preset minimum temperature T min Then increase the opening degree of the second burner; If the real-time temperature T sc Higher than the preset maximum temperature T max If so, then reduce the opening degree of the second burner; If the real-time temperature T sc At the preset minimum temperature T min With the preset maximum temperature T max In between, the opening degree of the second burner remains unchanged; The stable state is determined by the condition that the running time reaches a preset duration and the drying exhaust gas has a stable latent heat.

[0008] Furthermore, the method for calculating the updated target absolute moisture content in step S21 is as follows: As a preferred method, the correction amount The updated target absolute moisture content A safety constraint interval is defined, wherein the lower limit of the safety constraint interval is the physical limit lower limit to prevent system anomalies, and the upper limit of the safety constraint interval is the dynamic performance upper limit calculated based on the minimum allowable recovery rate. .

[0009] Furthermore, prior to the normal adjustment phase, the initial opening degree of the heat exchange contact area between the first burner and the generator is adjusted, including the following steps: S201. Obtain the exhaust gas outlet temperature T1 and humidity RH1 at the exhaust gas outlet of the dryer; S202. Calculate the initial absolute moisture content d; ; ; ; Where 611.2 is the saturated vapor pressure at 0℃, in Pa; 17.67 is the empirical coefficient of the Magnus formula, dimensionless; and 243.5 is the empirical coefficient of the Magnus formula, in ℃. —Saturated vapor pressure, Pa; exp—Natural exponential function; —Actual water vapor pressure, Pa; —Standard atmospheric pressure, Pa; 622—Molar mass ratio of water vapor to dry air; S203. Compare the calculated initial absolute moisture content d with the preset moisture content range to match the opening value corresponding to the corresponding moisture content range; S204. The opening value obtained by matching is used as the initial opening of the heat exchange contact area between the first burner and the generator for adjustment. Then, the opening of the first burner is dynamically adjusted using the closed-loop control algorithm to adjust the heat exchange contact area between the first burner and the generator.

[0010] As a preferred approach, the closed-loop control algorithm employs a positional PID algorithm. ; Where A is the first burner opening degree output by the algorithm, 20%≤A≤100%; init —Initial opening; K p K i K d —PID parameters, K p =1.0~2.0, % / (g / kg); K i=0.005~0.02%, % / (g / kg) s); K d =0 (set to 0.1~0.5 when overshooting).

[0011] Furthermore, during the normal adjustment phase, step S3 is also included, which involves dynamically switching the heat recovery mode based on the exhaust gas moisture content and temperature. If the moisture content of the inlet exhaust gas is greater than the preset high threshold for inlet exhaust gas moisture content, it is determined to be the latent heat-dominant stage, and the latent heat is fully recovered, and a first target recovery rate is set. If the moisture content of the inlet exhaust gas is between the preset low threshold and the preset high threshold of the inlet exhaust gas moisture content, it is determined to be a transitional stage, and a second target recovery rate is set. If the moisture content of the inlet exhaust gas is less than or equal to the preset low threshold of the moisture content of the inlet exhaust gas, it is determined to be the sensible heat-dominant stage, the sensible heat recovery device is activated, and the third target recovery rate is set. Wherein, the first target recovery rate is greater than the second target recovery rate and the third target recovery rate; during the latent heat-dominant stage, when the difference between the exhaust gas temperature and the ambient temperature is less than the preset temperature difference threshold, the sensible heat recovery device is in standby mode and the exhaust gas directly enters the latent heat recovery device; when the difference between the exhaust gas temperature and the ambient temperature is greater than or equal to the preset temperature difference threshold, the exhaust gas is controlled to first flow through the sensible heat recovery device and then enter the latent heat recovery device.

[0012] Furthermore, it also includes a method for preventing solution crystallization in a latent heat recovery device, wherein the latent heat recovery device is a solution absorption heat recovery device, the solution absorption heat recovery device includes a steam heat recovery pipeline and a solution heat recovery pipeline, and the solution heat recovery pipeline is equipped with a solution cooling heat exchange device, a solution pump and a dilution valve; The method for preventing solution crystallization includes: The actual solution temperature T is obtained after the solution is cooled by the heat exchanger and before it enters the absorption unit. y ; Obtain the crystallization temperature T corresponding to the current solution concentration. j ; Calculate the actual solution temperature T y With the crystallization temperature T j The actual temperature difference △T y1 ; ; With a preset safe temperature difference as the target, a closed-loop control algorithm is used to dynamically adjust the opening of the solution cooling heat exchange device to adjust the cooling capacity of the solution cooling heat exchange device so that the actual temperature difference meets the preset safe temperature difference.

[0013] As a preferred embodiment, the method for preventing solution crystallization further includes multi-level safety over-limit release logic: Level 1 warning: When the actual temperature difference is less than or equal to the first alarm threshold, increase the speed of the solution pump and maintain closed-loop control algorithm adjustment; Level 2 warning: When the actual temperature difference is less than or equal to the second alarm threshold, the cooling capacity of the solution cooling heat exchange device is forcibly limited to a preset safety value, the dilution valve is opened, the speed of the solution pump is increased to the maximum value, and the closed-loop control algorithm output is paused. Level 3 warning: When the actual temperature difference is less than or equal to the third alarm threshold, the solution cooling heat exchange device will be forcibly shut down, and the dilution valve and solution pump will be kept open at maximum speed. Wherein, the first alarm threshold > the second alarm threshold > the third alarm threshold.

[0014] This invention also provides a monitoring and control system for the recovery of sensible and latent heat in the exhaust gas of a grain dryer, comprising a first burner, a second burner, a generator, a dryer, a latent heat recovery device, a sensible heat recovery device, a sensor assembly, and a controller. The first burner and the second burner are disposed in the combustion chamber, and the combustion chamber is provided with a first air inlet pipe connected to the air inlet of the dryer; the generator is disposed above the first burner. The first burner is used to supply the heat required by the dryer and to heat the generator. The first burner is provided with a first adjusting baffle for adjusting the heat exchange contact area between the first burner and the generator. The second burner is provided with a second adjusting baffle for adjusting the opening degree of the second burner to quickly adjust the air inlet temperature of the dryer in order to obtain a stable exhaust gas temperature. The latent heat recovery device is connected to the generator and the dryer outlet via a pipeline system to recover latent heat. The sensible heat recovery device includes a sensible heat recovery heat exchanger and a sensible heat recovery valve. The sensible heat recovery heat exchanger is located between the latent heat recovery device and the drying outlet of the dryer. The sensible heat recovery valve is located at the air outlet of the dryer to control the direction of waste airflow. The dryer's air outlet is also connected to an exhaust pipe for discharging the waste gas after heat recovery treatment; The sensor assembly includes a temperature sensor and a humidity sensor for collecting temperature and humidity data. The temperature sensor is installed at the air inlet of the dryer, the air outlet of the dryer, the inside of the exhaust pipe, the outside of the exhaust pipe, and the liquid outlet of the solution cooling heat exchange device to monitor the real-time temperature T at the air inlet of the dryer. sc The exhaust gas outlet temperature T1 at the dryer's exhaust gas outlet or the exhaust gas temperature T before dryer exhaust gas recovery. in The temperature T of the exhaust gas after the dryer exhaust gas recovery out The temperature of the ambient air, T ambThe actual solution temperature T after cooling by the solution cooling heat exchanger y The humidity sensors are installed at the air outlet, inside the exhaust pipe, and outside the exhaust pipe of the dryer to monitor the exhaust gas outlet humidity RH1 or the exhaust gas humidity RH1 before exhaust gas recovery. in The humidity (RH) of the exhaust gas after the dryer exhaust gas recovery out RH of ambient air amb ; The controller is communicatively connected to the first regulating baffle, the second regulating baffle, the sensible heat recovery device, the latent heat recovery device, and the sensor assembly. The controller is configured to execute the monitoring and recovery control method for sensible heat and latent heat of the grain dryer exhaust gas as described above.

[0015] Furthermore, the latent heat recovery device includes a steam heat recovery pipeline and a solution heat recovery pipeline. One end of the steam heat recovery pipeline is positioned above the generator to absorb the water vapor generated by the generator, and the other end is connected to the solution absorption device. A condenser heat exchanger, a throttling valve, and an evaporator are sequentially arranged on the steam heat recovery pipeline between the generator and the solution absorption device. The condenser heat exchanger is positioned behind the generator to recover the latent heat of the water vapor. A second air inlet pipeline connected to the air inlet of the dryer is provided outside the condenser heat exchanger. The evaporator is located at the air outlet of the dryer to recover the latent heat of the exhaust gas. A fourth air inlet pipeline connected to the air inlet of the dryer is provided outside the solution absorption device. The solution heat recovery pipeline is a circulation pipeline located below the generator. The solution heat recovery pipeline is equipped with a solution cooling heat exchange device and a solution pump in sequence. A third air inlet pipeline connected to the air inlet of the dryer is located outside the solution cooling heat exchange device.

[0016] The beneficial effects of this invention are as follows: This invention constructs a complete control system for the recovery of waste heat and latent heat from grain drying exhaust gas through phased control, dual-layer closed-loop regulation, multi-mode automatic switching, and multi-level safety protection. It adopts a two-stage design of initial operation and normal adjustment. First, the second burner quickly stabilizes the drying inlet temperature to avoid system oscillations caused by start-up fluctuations. Then, by monitoring the exhaust gas temperature and humidity, a dual-layer PID architecture using long-cycle enthalpy optimization and short-cycle moisture content tracking is used to regulate the heat exchange contact area between the first burner and the generator, thereby adjusting the generator's evaporation capacity to achieve control over the recovery capacity. Through multi-parameter control of temperature and humidity, a synergy between recovery efficiency and execution accuracy is achieved, effectively utilizing the sensible and latent heat in the exhaust gas and reducing heat loss. It ensures stable control while rapidly responding to changes in operating conditions, and the staggered cycle avoids adjustment conflicts, improving system operational stability.

[0017] The second burner adopts a three-stage temperature regulation logic, coupled with temperature thresholds that can be adjusted according to grain type and clear stability judgment conditions, making temperature control more reliable and adaptable to operating conditions. With enthalpy and recovery rate as the core control targets, a standardized wet air parameter calculation formula is used to achieve quantitative control and dynamic correction of heat energy recovery. Combined with correction limit and physical and dynamic dual safety constraints, it can prevent over-adjustment from causing system fluctuations, and ensure equipment safety and minimum energy efficiency.

[0018] Before normal adjustment, an initial opening degree lookup table setting step based on the moisture content of exhaust gas is set up to enable the system to quickly match the operating conditions and shorten the time to meet the standards. Position-type PID is adopted and the opening degree range and engineering parameters of the first burner are limited to reduce the difficulty of on-site commissioning and improve the service life of the actuator.

[0019] Based on the automatic switching between three recovery modes—latent heat as the primary mode, transitional mode, and sensible heat as the primary mode—based on the moisture content and temperature difference of the exhaust gas, the system achieves efficient utilization of heat energy in stages throughout the drying cycle, solving the problem of insufficient energy efficiency of a single recovery method.

[0020] For solution absorption latent heat recovery devices, the safe temperature difference between the solution temperature and the crystallization temperature is the controlled object. With the help of graded early warning and automatic recovery logic, the system progresses from normal adjustment to extreme protection. Through multiple means such as cooling control, solution pump speed-up, and dilution valve opening, solution crystallization is prevented from the source, ensuring long-term continuous and stable operation of the system.

[0021] The control system for recovering sensible and latent heat from the exhaust gas of grain dryers features an integrated hardware architecture with dual burners for zoned heating, switchable sensible and latent heat recovery, and comprehensive sensor layout. The method and structure support each other, with a complete heat recovery process and a reasonable hot air circuit design. It can be directly applied to the construction and energy-saving renovation of grain dryers, achieving a comprehensive effect of efficient heat recovery, stable and reliable system, safe and durable equipment, and adaptability to multiple grain types and all operating conditions. Attached Figure Description

[0022] Figure 1 This invention provides a schematic diagram of a control system for the recovery and latent heat of sensible heat from waste gas in a grain dryer. Figure 2 Schematic diagram of the layout of the first and second burners; Reference numerals: 1-Combustion chamber; 11-First burner; 12-Second burner; 13-First regulating baffle; 14-Second regulating baffle; 3-Generator; 4-Dryer; 41-Dryer air inlet; 42-Dryer air outlet; 421-Exhaust pipe; 5-Latent heat recovery device; 51-Steam heat recovery pipeline; 511-Condensing heat exchanger; 512-Throttle valve; 513-Evaporator; 514-Solution absorption device; 52-Solution heat recovery pipeline; 521-Solution cooling heat exchanger; 522-Solution pump; 6-Sensible heat recovery device; 61-Sensible heat recovery heat exchanger; 62-Sensible heat recovery valve; 7-PLC controller; 8-Temperature and humidity sensor assembly; 81-Temperature sensor; 82-Humidity sensor; 91-First air inlet pipeline; 92-Second air inlet pipeline; 93-Third air inlet pipeline; 94-Fourth air inlet pipeline; 95-Fifth air inlet pipeline. Detailed Implementation

[0023] The present invention will be further described below.

[0024] This invention provides a method for monitoring, recovering, and controlling the sensible and latent heat of waste gas from a grain dryer. It is mainly used for waste heat recovery and utilization in grain dryers, and is applied to a grain drying system including a first burner 11, a second burner 12, a generator 3, a dryer 4, a latent heat recovery device 5, a sensible heat recovery device 6, a PLC controller 7, and a temperature and humidity sensor assembly 8. The method includes the following steps: S1. Initial running phase, The first burner 11 is fully open, inputting hot air into the dryer 4. The heat exchange contact surface between the first burner 11 and the generator 3 is closed, and the latent heat recovery device 5 is on standby. Obtain the real-time temperature T at the air inlet 41 of the dryer. sc And transmit it to controller 7, controller 7 based on the real-time temperature T sc The opening of the second burner 12 is adjusted according to the preset drying temperature threshold until the drying exhaust gas reaches the preset stable state. The adjustment methods for the second burner 12 include: If the real-time temperature T sc Below the preset minimum temperature T min Then the opening degree of the second burner 12 is increased; If the real-time temperature T sc Higher than the preset maximum temperature T max If so, the opening degree of the second burner 12 is reduced; If the real-time temperature T sc At the preset minimum temperature T min With the preset maximum temperature T max Between these points, the opening degree of the second burner 12 remains unchanged; The stable state is determined by the condition that the running time reaches a preset duration and the drying exhaust gas has a stable latent heat.

[0025] S2. Normal adjustment phase The latent heat recovery device 5 is activated, and the heat exchange contact area between the first burner 11 and the generator 3 is adjusted in real time based on the enthalpy recovery rate to regulate the recovery efficiency of the latent heat recovery device 5. The initial opening adjustment of the heat exchange contact area between the first burner 11 and the generator 3 includes the following steps: S201. Obtain the exhaust gas outlet temperature T1 and humidity RH1 at the exhaust gas outlet of dryer 4; S202. Calculate the initial absolute moisture content d; ; ; ; Where 611.2 is the saturated vapor pressure at 0℃, in Pa; 17.67 is the empirical coefficient of the Magnus formula, dimensionless; and 243.5 is the empirical coefficient of the Magnus formula, in ℃. —Saturated vapor pressure, Pa; exp—Natural exponential function; —Actual water vapor pressure, Pa; —Standard atmospheric pressure, Pa; 622—Molar mass ratio of water vapor to dry air; S203. Compare the calculated initial absolute moisture content d with the preset moisture content range to match the opening value corresponding to the corresponding moisture content range; S204. The opening value obtained by matching is used as the initial opening of the heat exchange contact area between the first burner 11 and the generator 3 for adjustment. Then, the opening of the first burner 11 is dynamically adjusted using the closed-loop control algorithm to adjust the heat exchange contact area between the first burner 11 and the generator 3. S21. Calculate the actual enthalpy recovery rate of the drying system in the first control cycle, use the PID algorithm to dynamically calculate the deviation between the actual enthalpy recovery rate and the set target recovery rate, and update the target absolute moisture content. S211. Real-time parameter acquisition and transmission to the processor, the parameter acquisition includes the exhaust gas temperature T before exhaust gas recovery in dryer 4. in and humidity RH in The temperature T of the exhaust gas after the waste gas recovery of the dryer 4 out and humidity RH out The temperature of the ambient air, T amb and humidity RH amb ; S212. Calculate the enthalpy h of moist air before waste gas recovery. inEnthalpy of moist air h after exhaust gas recovery out Enthalpy of ambient air (h) amb ; ; Where h is the enthalpy of moist air (kJ / kg dry air); T is the gas temperature (°C); d is the moisture content (g / kg dry air); 1.006×T is the sensible heat of 1 kg dry air; d×2501 is the latent heat of water vapor; and d×1.86×T is the sensible heat of water vapor. S213. Calculate the actual enthalpy recovery rate η of the drying system. device ; ; Among them, h in —Enthalpy of moist air before exhaust gas recovery; h out —Enthalpy of moist air after exhaust gas recovery; h amb —The enthalpy of humid air in the environment; S214. Based on the actual enthalpy value recovery rate η device With target recovery rate η target The deviation is dynamically calculated to determine the target absolute moisture content d. target , The absolute moisture content correction increment is obtained using a PID algorithm. ; Where Δd is the output increment of PLC controller 7; e is the deviation signal. ;de—represents the minute change in the deviation signal e; dt—the differential increment of time; —This reflects the rate and direction of change of the deviation over time; K p —Quickly respond to current recovery rate deviations; K i —Eliminate steady-state deviation; K d —Suppress volatility; Wherein, the target recovery rate It is based on the corresponding setting of the heat recovery mode, which is dynamically switched according to the moisture content and temperature of the waste gas before recovery; If the moisture content of the exhaust gas at the inlet of the dryer 4 is greater than the preset high threshold for the moisture content of the exhaust gas, it is determined to be the stage dominated by latent heat, and the latent heat is fully recovered, and the first target recovery rate is set. If the moisture content of the exhaust gas at the inlet of the dryer 4 before recovery is between the preset low threshold of the inlet exhaust gas moisture content and the preset high threshold of the inlet exhaust gas moisture content, it is determined to be a transitional stage, and a second target recovery rate is set. If the moisture content of the exhaust gas at the inlet of the dryer 4 is less than the preset low threshold for the moisture content of the exhaust gas, it is determined to be the stage dominated by sensible heat, the sensible heat recovery device 6 is turned on, and the third target recovery rate is set. Wherein, the first target recovery rate is greater than the second target recovery rate and the third target recovery rate; during the latent heat-dominant stage, when the difference between the exhaust gas temperature and the ambient temperature is less than the preset temperature difference threshold, the sensible heat recovery device 6 is on standby and the exhaust gas directly enters the latent heat recovery device 5; when the difference between the exhaust gas temperature and the ambient temperature is greater than or equal to the preset temperature difference threshold, the exhaust gas is controlled to first flow through the sensible heat recovery device 6 and then enter the latent heat recovery device 5.

[0026] S215. Add the current target absolute moisture content to the correction increment to obtain the updated target absolute moisture content. , ; The updated target absolute moisture content is used as the set value in S22, and the heat exchange contact area between the first burner 11 and the generator 3 is dynamically adjusted using a closed-loop control algorithm to adjust the evaporation capacity of the generator 3. The correction amount The updated target absolute moisture content A safety constraint interval is defined, wherein the lower limit of the safety constraint interval is the physical limit lower limit to prevent system anomalies, and the upper limit of the safety constraint interval is the dynamic performance upper limit calculated based on the minimum allowable recovery rate. .

[0027] S22. Obtain the actual absolute moisture content of the exhaust gas in the second control cycle, and use the updated target absolute moisture content as the set value. Use a closed-loop control algorithm to dynamically adjust the opening of the first burner 11, so as to adjust the heat exchange contact area between the first burner 11 and the generator 3 and the heat exchange contact area between the generator 3, and adjust the evaporation capacity of the generator 3 so that the actual absolute moisture content tracks the set value. The closed-loop control algorithm uses a positional PID algorithm. ; Where A is the opening degree of the first burner 11 output by the algorithm, 20%≤A≤100%; A init —Initial opening; K p K i K d —PID parameters, K p =1.0~2.0, % / (g / kg); K i =0.005~0.02%, % / (g / kg) s); K d =0, and set it to 0.1~0.5 if it exceeds the opening adjustment range.

[0028] The second control cycle is shorter than the first control cycle.

[0029] Specifically, such as Figures 1-2 As shown, the present invention provides a method for monitoring, recovering, and controlling the sensible and latent heat of exhaust gas from a grain dryer. This method is applied to a grain drying system comprising a first burner 11, a second burner 12, a generator 3, a dryer 4, a latent heat recovery device 5, a sensible heat recovery heat exchanger 61, a PLC controller 7, and a set of temperature and humidity sensors 82. The grain drying system adopts an overall architecture featuring dual-burner zoned heating, steam circulation with latent heat recovery, switchable sensible heat recovery, and solution anti-crystallization safety protection.

[0030] After the grain drying system starts, it enters the initial operation stage S1. During this stage, the flow rate, temperature, and humidity of the drying exhaust gas are not stable, and waste heat recovery is not performed to avoid control oscillations. At this time, the first burner 11 is fully open, inputting hot air into the dryer 4. The heat exchange contact surface between the first burner 11 and the generator 3 is first reset to the fully closed state, and the latent heat recovery device 5 is not activated to avoid frequent adjustments caused by initial fluctuations. The second burner 12 serves as a rapid adjustment module for the drying temperature. The PLC controller 7 receives the real-time temperature T at the dryer air inlet 41 collected by the temperature and humidity sensor assembly 8. sc The real-time temperature T sc The temperature is compared with a preset drying temperature threshold, and the opening of the second burner 12 is adjusted until the drying exhaust gas reaches a preset stable state. The preset drying temperature threshold mentioned above can be set according to the type and quantity of grain crop to be dried, such as rice: T max =61℃, T min =59℃; Corn: T max =81℃, T min =79℃. Specifically, taking rice as an example, if T sc <59℃, increase the opening of the second burner 12; that is, adjust the second adjusting baffle 14 to reduce the contact area between the second adjusting baffle 14 and the heat output end of the second burner 12, so as to increase the heat supply of the second burner 12; if T sc If the temperature is >61℃, reduce the opening of the second burner 12; that is, adjust the second adjusting baffle 14 to increase the contact area between the second adjusting baffle 14 and the heat output end of the second burner 12, thereby reducing the heat supply of the second burner 12; if 59℃ ≤ T sc ≤61℃, maintain the current opening degree of the second burner 12 stable. The initial running time involved in the stable state mentioned above can be set to 10 minutes, at which time the drying exhaust gas has a stable latent heat. By adding an initial running stage to adjust the opening degree of the second burner 12, the exhaust gas discharged from the dryer 4 can have a stable latent heat, avoiding control oscillations.

[0031] When the initial operation phase reaches the preset 10-minute operating time, the exhaust gas has stable latent heat and automatically enters the S2 normal adjustment phase, activating the latent heat recovery device 5. At this time, the PLC controller 7 transmits control action information to the driver based on the received latent heat recovery status of the drying exhaust gas. The driver controls the contact area between the first adjusting baffle 13 and the heat output end of the first burner 11, thereby adjusting the contact area between the flame of the first burner 11 and the generator 3, thus regulating the evaporation capacity of the generator 3 and consequently the recovery capacity. Specifically, the control is executed in the following sequence: adjusting the position of the first adjusting baffle 13 according to the pre-set heat exchange contact area between the first burner 11 and the generator 3 → dynamically correcting the target moisture content based on the enthalpy recovery rate → adjusting the opening degree of the first burner 11 based on the updated target moisture content.

[0032] Specifically, temperature and humidity sensor component 8 collects the exhaust gas outlet temperature T1 and humidity RH1 at the exhaust gas outlet of dryer 4, and calculates the saturated water vapor pressure according to Magnus's formula. In calculating actual water vapor pressure Finally, the initial absolute moisture content was calculated. The initial opening degree of the first burner 11 is matched with the calculated initial moisture content of the exhaust gas and the set moisture content range. Specifically, the initial opening degree of the first burner 11 corresponding to the set moisture content range is as follows: when d ≥ 120 g / kg, the initial opening degree is 70%; when 80 ≤ d < 120 g / kg, the initial opening degree is 60%; when 40 ≤ d < 80 g / kg, the initial opening degree is 50%; when 25 ≤ d < 40 g / kg, the initial opening degree is 40%; when 15 ≤ d < 25 g / kg, the initial opening degree is 30%; and when d < 15 g / kg, the initial opening degree is 0%.

[0033] After adjusting the initial opening of the first burner 11, the system continues to operate. At this point, step S21 is executed, with enthalpy recovery rate as the core control target, while also considering sensible heat and latent heat recovery effects, dynamically correcting the target moisture content of the lower layer, and adapting to changes in the drying cycle conditions. The first control cycle is set to 10 minutes / cycle.

[0034] Temperature and humidity sensor component 8 collects the temperature T of the exhaust gas before exhaust gas recovery in real time from dryer 4. in and humidity RH in The temperature T of the exhaust gas after the waste gas recovery of the dryer 4 out and humidity RH out The temperature of the ambient air, T amb and humidity RH amb Calculate the enthalpy h of the moist air before waste gas recovery. in Enthalpy of moist air h after exhaust gas recovery out Enthalpy of ambient air (h) amb; then calculate the actual enthalpy recovery rate η of the device. device Then, based on the actual enthalpy value recovery rate η device With target recovery rate η target The deviation is dynamically calculated to determine the target absolute moisture content d. target Specifically, the PID algorithm is used to calculate the moisture content correction increment Δd, and the correction amount is... The correction amount Δd is limited to ±2 g / kg to avoid over-adjustment. The current target absolute moisture content is added to the correction increment to obtain the updated target absolute moisture content. The updated target absolute moisture content is used as the setpoint in S22. A closed-loop control algorithm is employed to dynamically adjust the heat exchange contact area between the first burner 11 and the generator 3, thereby adjusting the evaporation capacity of the generator 3. The first control cycle is set to 10 minutes, meaning the target absolute moisture content is updated every 10 minutes. The heat exchange contact area between the first burner 11 and the generator 3 is adjusted as a set value in S22.

[0035] Where the target recovery rate η target This is based on the corresponding settings of the heat recovery mode, which dynamically switches according to the moisture content and temperature of the exhaust gas before recovery. The heat recovery mode includes a latent heat-dominant stage, a transition stage, and a sensible heat-dominant stage, which dynamically switch according to the moisture content and temperature of the exhaust gas before recovery, wherein the moisture content of the exhaust gas before recovery is d. in The temperature of the exhaust gas before the recovery of the exhaust gas from the dryer is T. in and humidity RH in Calculations show that when the moisture content of the exhaust gas before recovery at the dryer's inlet is greater than the preset high threshold for inlet exhaust gas moisture content, i.e., d... in >d high At this time, the heat recovery mode is dominated by latent heat, and the target recovery rate η is... target The corresponding first target recovery rate; when the moisture content of the inlet exhaust gas before recovery is between the preset low threshold and the preset high threshold of the inlet exhaust gas moisture content, i.e., d low ≤d in ≤d high During this period, the heat recovery mode is in a transition phase, at which time the target recovery rate η is... target The corresponding second target recovery rate; when the moisture content of the exhaust gas before recovery at the dryer 4 inlet is less than the preset low threshold for inlet exhaust gas moisture content, i.e., d in <d low At this time, the heat recovery mode is dominated by sensible heat, and the target recovery rate η is... target This corresponds to the set third target recovery rate. Where d high Take 80, d lowTaking 25, the first target recovery rate is 75%~80%, the second target recovery rate is 65%~70%, and the third target recovery rate is 60%~65%. It should be noted that regardless of the stage of heat recovery mode, when the exhaust gas temperature T before the dryer's exhaust gas recovery... in Reduce ambient temperature T amb When the temperature is above 8℃, the sensible heat recovery device 6 must be turned on.

[0036] The above-mentioned updated target absolute moisture content A safety constraint interval is defined, wherein the lower limit of the safety constraint interval is the physical limit lower limit to prevent system anomalies, and the upper limit of the safety constraint interval is the dynamic performance upper limit calculated based on the minimum allowable recovery rate. The lower limit of the aforementioned safety constraint range is no less than 10 g / kg to prevent excessive recovery from causing freezing and excessive solution concentration. The upper limit of the safety constraint range is the dynamic performance upper limit calculated based on the minimum allowable recovery rate. This is to ensure that the recovery rate is always no less than the performance requirements.

[0037] The above dynamic performance limit The calculation steps include: Based on the minimum allowable recovery rate η min Calculate the maximum permissible enthalpy after exhaust gas recovery: ; The outlet temperature T after the collected waste gas is recovered out Calculate the corresponding maximum allowable moisture content: ; Among them, h in —Enthalpy of moist air before exhaust gas recovery; h amb —The enthalpy of moist air in the ambient air.

[0038] The updated target absolute moisture content output by S21 As the setpoint for S22, the opening degree of the first burner 11 is dynamically adjusted using a closed-loop control algorithm. After the initial 10 minutes of operation and transition to normal adjustment, the target moisture content is updated every 10 minutes in step S21. In step S22, the contact area between the first burner 11 and the generator 3 needs to be adjusted in real time to ensure the actual moisture content d. actual Track the target moisture content In step S22, a positional PID algorithm is used to measure the moisture content deviation e. d The output contact area opening degree A is set, and the output limit and safety constraint for the contact area opening degree A are set, namely 20%≤A≤100%; the lower limit is set to 20% to avoid large system fluctuations caused by the contact area being completely closed; where the actual moisture content d actualThe temperature T of the exhaust gas after waste gas recovery in dryer 4 out and humidity RH out Real-time calculation. To ensure system stability, a rate of change limit is set, meaning the opening degree of the first burner 11 changes by no more than ±5% every 2 seconds; when A reaches the limit and the deviation e... d When moving in the same direction, the integral accumulation is paused. The second control cycle in step S22 is 2 seconds, that is, the position of the first adjusting baffle 13 is adjusted every 2 seconds, thereby adjusting the heat exchange contact area between the first burner 11 and the generator 3. When the actual moisture content d actual Enter settings Within the range and maintain for 30 seconds, the adjustment frequency can be reduced; when the humidity deviation... If the disturbance persists for more than one minute, an alarm will be triggered to alert the system to the abnormality.

[0039] Through upper-level optimization of S21, the value is corrected and updated every 10 minutes based on the enthalpy recovery rate. Then, through the lower-level control of S22, with the updated With the goal of achieving stable recovery of waste heat and latent heat, the contact area A between the first burner 11 and the generator 3 is adjusted every 2 seconds using PID control. The upper tube efficiency and lower tube tracking are controlled, with both layers operating independently to achieve stable recovery of waste heat and latent heat. Through this adjustment method, the stable recovery of drying waste heat and latent heat is achieved.

[0040] Furthermore, to prevent the latent heat recovery device 5 from being affected by solution crystallization during use, the monitoring and recovery control method for sensible heat and latent heat in the waste gas of the grain dryer also includes a solution crystallization prevention control method for the latent heat recovery device 5. The latent heat recovery adopts lithium bromide aqueous solution circulation, and the system operates synchronously with anti-crystallization control, which is executed independently in parallel with the main control logic.

[0041] The temperature T after the solution cooling heat exchanger 521 is collected. y The PLC uses a table lookup function to calculate the crystallization temperature T corresponding to the current solution concentration ξ. j , ; Wherein, ξ—lithium bromide mass concentration ; ; ; .

[0042] Calculate the actual solution temperature T y With the crystallization temperature T j The actual temperature difference △T y1 ; ; With a preset safe temperature difference as the target, a closed-loop control algorithm is used to dynamically adjust the opening of the solution cooling heat exchange device 521 to adjust the cooling capacity of the solution cooling heat exchange device 521 so that the actual temperature difference meets the preset safe temperature difference.

[0043] The above closed-loop control algorithm dynamically adjusts the opening degree u of the solution cooler. cool It can quickly and directly affect T y This changes ΔT yl The standard positional PID algorithm is used, and the output is the opening degree of the solution cooler; ; in, The deviation at the current moment; when e>0, the actual temperature difference is less than the set target, i.e., it is too cold, and there is a risk of crystallization. Cooling needs to be reduced, i.e., the cooling fan speed needs to be adjusted to reduce T. y The temperature rises; when e < 0, the actual temperature difference is greater than the target, meaning it's too hot. This is safe but may result in low energy efficiency. Adjusting the airflow and fan speed can increase cooling. bias —Manually set feedforward offset is optional, such as preset reference opening based on load; K p —Proportional coefficient, ranging from 2 to 5% / ℃, adjusted according to the intensity of the cooling device's influence on temperature; K i —Integral coefficient, ranging from 0.08 to 0.17% / (℃·s), to eliminate steady-state deviation and prevent integral saturation; K d — Differential coefficient, ranging from 6% to 30%. s / ℃; the derivative term easily amplifies noise, so it can be temporarily set to zero. The control cycle is set to 1~5 seconds; due to the slow temperature response, it can be appropriately extended. The opening limit of the cooling device is 0 < u. cool <100%; with increased cooling capacity, the variation per cycle should not exceed ±5% / s to prevent excessive valve switching action. Integral saturation protection, when u cool Reaching the limit of 0% or 100% and e t When moving in the same direction, the accumulation of integral terms is paused; when the over-limit release logic is activated, the accumulation is also paused.

[0044] To ensure the normal operation of the solution heat recovery device, this solution crystallization prevention control method also includes multi-level safety over-limit release logic; based on the normal PID regulation, multi-level safety protection is added, and ΔT is independently monitored. yl In extreme cases, mandatory intervention is required. The first alarm threshold is set to 8℃, the second alarm threshold to 3℃, and the third alarm threshold to 2℃. Safe zone, ΔT yl >8℃, PID adjustment is normal; Level 1 warning, ΔT yl≤8℃, increase the speed of solution pump 522 by 10% to accelerate circulation and prevent local overcooling; PID continues to adjust. Level II warning, ΔT yl ≤3℃, the solution cooler is forced to open to 30%, the dilution valve is opened, water is added to dilute and lower the crystallization temperature, the solution pump 522 is accelerated to 100%, and the PID integral is paused; Level 3 warning, ΔT yl At ≤2℃, the solution cooler is forcibly shut off (0%), while the dilution valve remains open and the pump runs at full speed to urgently prevent crystallization.

[0045] Recovery logic: When ΔT yl Rebound to the safe zone, i.e., ΔT yl After maintaining a temperature above 8°C for 3 minutes, gradually restore the temperature in sequence: The first step is to return control of the solution cooler to the PID controller, and switch without disturbance, starting from the current actual opening degree. The second step is to close the dilution valve (if it is already open). The third step is to restore the solution pump 522 to its normal operating setpoint or the value before PID adjustment.

[0046] If any warning is triggered again during the recovery process, the recovery will be stopped immediately, and the corresponding level of action will be re-executed.

[0047] This method for preventing solution crystallization uses PID to adjust the opening of the solution cooler in real time, combined with graded over-limit protection, to achieve precise temperature control while maintaining an absolute safety baseline. It operates in parallel with the PID real-time adjustment of the opening of the first burner 11, without direct coupling, but sharing a sensor to ensure the recovery efficiency of sensible and latent heat of the drying exhaust gas from the grain dryer.

[0048] The present invention also provides a control system for the recovery and control of sensible heat and latent heat of exhaust gas from a grain dryer, including a controller 7 and a first burner 11, a second burner 12, a generator 3, a dryer 4, a latent heat recovery device 5, a sensible heat recovery device 6, and a temperature and humidity sensor assembly 8, all electrically connected to the controller 7. The first burner 11 and the second burner 12 are disposed in the combustion chamber 1. The combustion chamber 1 is provided with a first air inlet pipe 91 connected to the air inlet of the dryer 4. The generator 3 is disposed above the first burner 11. The first burner 11 is used to supply the heat required by the dryer 4 and to heat the generator 3. The first burner 11 is provided with a first adjusting baffle 13 for adjusting the heat exchange contact area between the first burner 11 and the generator 3. The second burner 12 is provided with a second adjusting baffle 14 for adjusting the opening degree of the second burner 12 to quickly adjust the air inlet temperature of the dryer 4 to obtain a stable exhaust gas temperature. The latent heat recovery device 5 is connected to the generator 3 and the dryer outlet 42 via a pipeline system to recover latent heat. The sensible heat recovery device 6 includes a sensible heat recovery heat exchanger 61 and a sensible heat recovery valve 62. The sensible heat recovery heat exchanger 61 is located between the latent heat recovery device 5 and the drying outlet of the dryer 4. The sensible heat recovery valve 62 is located at the air outlet of the dryer to control the direction of waste airflow. The sensible heat recovery device is provided with a fifth air inlet pipe 95 that is connected to the air inlet 41 of the dryer. The dryer outlet 42 is also connected to an exhaust pipe 421 for discharging the waste gas after heat recovery treatment; The temperature and humidity sensor assembly 8 includes a temperature sensor 81 and a humidity sensor 82 for collecting temperature and humidity data. The temperature sensor 81 is installed at the air inlet 41 of the dryer 4, the air outlet 4, the inside of the exhaust pipe, the outside of the exhaust pipe, and the liquid outlet of the solution cooling heat exchange device 521 to monitor the real-time temperature T at the air inlet 41 of the dryer. sc The exhaust gas outlet temperature T1 at the exhaust gas outlet of dryer 4 or the exhaust gas temperature T before exhaust gas recovery of dryer 4. in The temperature T of the exhaust gas after the waste gas recovery of the dryer 4 out The temperature of the ambient air, T amb The actual solution temperature T after cooling by the solution cooling heat exchanger 521 y The humidity sensor 82 is installed at the air outlet, inside the exhaust pipe, and outside the exhaust pipe of the dryer 4 to monitor the exhaust gas outlet humidity RH1 at the exhaust gas outlet of the dryer 4 or the exhaust gas humidity RH1 before exhaust gas recovery of the dryer 4. in The humidity (RH) of the exhaust gas after the dryer's exhaust gas recovery is 4. out RH of ambient air amb ; The controller 7 is communicatively connected to the first adjusting baffle 13, the second adjusting baffle 14, the sensible heat recovery device 6, the latent heat recovery device 5, and the sensor assembly. The controller 7 is configured to execute the monitoring and recovery control method for sensible heat and latent heat of the grain dryer exhaust gas as described above.

[0049] Furthermore, the latent heat recovery device 5 includes a steam heat recovery pipeline 51 and a solution heat recovery pipeline 52. One end of the steam heat recovery pipeline 51 is located above the generator 3 to absorb the water vapor generated by the generator 3, and the other end is connected to the solution absorption device 514. The steam heat recovery pipeline 51 is sequentially provided with a condenser heat exchanger 511, a throttle valve 512, and an evaporator 513 located between the generator 3 and the solution absorption device 514. The condenser heat exchanger 511 is located behind the generator 3 to recover the latent heat of water vapor. A second air inlet pipeline 92 connected to the air inlet 41 of the dryer is provided on the outside of the condenser heat exchanger 511. The evaporator 513 is located at the air outlet 42 of the dryer to recover the latent heat of the exhaust gas. A fourth air inlet pipeline 94 connected to the air inlet 41 of the dryer is provided on the outside of the solution absorption device 514. The solution heat recovery pipeline 52 is a circulation pipeline located below the generator 3. The solution heat recovery pipeline 52 is provided with a solution cooling heat exchange device 521 and a solution pump 522 in sequence. The outside of the solution cooling heat exchange device 521 is provided with a third air inlet pipeline 93 that is connected to the air inlet 41 of the dryer.

[0050] After the grain dryer 4 is powered on, the controller 7 collects the temperature and humidity signals of the sensor components and drives the first burner 11, the second burner 12, the latent heat recovery device 5, and the sensible heat recovery device 6 to work together according to the preset logic. The entire process realizes initial temperature stabilization, graded recovery of sensible and latent heat, double-layer closed-loop regulation, and solution anti-crystallization safety protection. All the recovered heat is sent back to the dryer air inlet 41 for recycling.

[0051] Upon system startup and initial operation, controller 7 fully activates the first burner 11, and hot air is delivered to the dryer 4 via the first air inlet duct 91. Simultaneously, the first regulating baffle 13 between the first burner 11 and the generator 3 is reset to the fully closed state, and the latent heat recovery device 5 remains in standby mode to prevent control oscillations caused by fluctuating exhaust gases during startup. During this stage, the temperature T is collected in real time by the temperature sensor 81 at the dryer air inlet 41. sc The controller 7 quickly adjusts the opening of the second burner 12 via the second adjusting baffle 14: T sc If the temperature is below the set lower limit, the opening degree is increased; if it is above the set upper limit, the opening degree is decreased, maintaining stability within the target range to ensure that the inlet temperature of dryer 4 quickly and steadily reaches the standard. After the system runs continuously for a preset time and the exhaust gas has a stable latent heat, it automatically enters the normal adjustment stage.

[0052] During the normal adjustment phase, the latent heat recovery device 5 is started. The controller 7 calculates the absolute moisture content of the exhaust gas based on the temperature T1 and humidity RH1 of the dryer outlet 42. According to the moisture content range, the controller sets the initial heat exchange contact area between the first burner 11 and the generator 3 through the first adjustment baffle 13 to quickly match the recovery conditions. The generator 3 is heated by the first burner 11 to produce high-temperature and high-pressure steam, which enters the condenser heat exchanger 511 along the steam heat recovery pipeline 51. The steam releases latent heat in the condenser heat exchanger 511 and condenses into liquid water. The heat is sent to the dryer air inlet 41 through the second air inlet pipeline 92 to form a second hot air source. After passing through the throttle valve 512, the liquid water and steam are connected to the evaporator 513. The liquid water exchanges heat with the high-temperature and high-humidity exhaust gas discharged from the dryer 4, absorbing the latent heat of the exhaust gas and evaporating into steam. At this time, the steam is absorbed by the solution absorption device 514 located behind the evaporator 513. Because the solution absorption device 514 absorbs the steam located at the rear end of the evaporator 513, a vacuum is generated in the steam heat recovery pipeline 51. The generation of this vacuum causes the pressure inside the pipeline to drop sharply, which lowers the saturation temperature of the liquid water. The water can boil and evaporate at low temperature, that is, the liquid water evaporates rapidly in the evaporator 513 and absorbs heat to recover the heat in the exhaust gas. When the solution absorbs water vapor, it releases dilution heat, which is sent to the dryer air inlet 41 through the fourth air inlet pipe 94 to form the fourth hot air source.

[0053] The solution heat recovery pipeline 52 circulates under the drive of the solution pump 522. The high-temperature solution flows through the solution cooling heat exchange device 521 to release heat, and is sent into the dryer air inlet 41 through the third air inlet pipeline 93 to form a third hot air source. The cooled solution flows back to the generator 3 to complete the closed cycle.

[0054] During system operation, controller 7 collects the temperature T of the waste gas before recovery in real time. in RH humidity in The temperature of the waste gas after recycling, T out RH humidity out and ambient temperature and humidity T amb RH amb The system calculates enthalpy and enthalpy recovery rate, corrects the target moisture content over a long period, and adjusts the opening of the first regulating baffle 13 using a positional PID algorithm over a short period to precisely control the evaporation capacity and latent heat recovery intensity of the generator 3. Simultaneously, the controller 7 controls the sensible heat recovery valve 62 based on the exhaust gas moisture content and temperature difference, automatically switching the exhaust gas flow direction: during the latent heat-dominant stage and when the temperature difference is small, the exhaust gas bypasses and directly enters the latent heat recovery device 5; during the transition stage and the sensible heat-dominant stage, the exhaust gas first flows through the sensible heat recovery heat exchanger 61 to recover sensible heat, and the heat is then sent through the fifth air inlet duct 95 to the dryer air inlet 41 to form the fifth hot air source, before entering the latent heat recovery device 5, achieving full recovery of sensible and latent heat.

[0055] The system performs solution anti-crystallization control in parallel throughout the process, and the temperature sensor 81 at the outlet of the solution cooling heat exchange device 521 collects the solution temperature T in real time. y The PLC controller 7 obtains the crystallization temperature T based on the current solution concentration. j Calculate the safe temperature difference ΔT yl =T y -T j The cooling capacity of the solution cooling heat exchanger 521 is adjusted via PID control to maintain a stable safe temperature difference. When ΔT yl Upon entering the warning zone, controller 7 initiates protection in stages: Level 1 warning increases the speed of solution pump 522; Level 2 warning forcibly limits the cooling opening, opens the dilution valve, and keeps solution pump 522 running at full speed; Level 3 warning shuts down the cooling device to completely avoid the risk of solution crystallization. Once the temperature difference returns to a safe range and stabilizes, the system automatically deactivates protection and gradually resumes normal operation.

[0056] After sensible heat and latent heat recovery treatment, the low-temperature and low-humidity exhaust gas is discharged from the system through the exhaust pipe 421. The first to fifth hot air sources are collected at the air inlet 41 of the dryer and mixed with the hot air in the combustion chamber 1 for continuous use in grain drying, so as to realize the heat recycling and efficient, stable and safe operation of the system.

Claims

1. A method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer, characterized in that, A grain drying system comprising a first burner (11), a second burner (12), a generator (3), a dryer (4), a latent heat recovery device (5), a sensible heat recovery device (6), a PLC controller (7), and a temperature and humidity sensor assembly (8) includes the following steps: S1. Initial running phase, The first burner (11) is fully open and inputs hot air into the dryer (4). The heat exchange contact surface between the first burner (11) and the generator (3) is closed, and the latent heat recovery device (5) is on standby. Obtain the real-time temperature T of the air inlet (41) of the dryer. sc And transmit it to the PLC controller (7), the PLC controller (7) based on the real-time temperature T sc The opening of the second burner (12) is adjusted according to the preset drying temperature threshold control until the drying exhaust gas reaches the preset stable state; S2. Normal adjustment phase The latent heat recovery device (5) is started, and the heat exchange contact area between the first burner (11) and the generator (3) is adjusted in real time based on the enthalpy recovery rate to adjust the recovery efficiency of the latent heat recovery device (5), including: S21. Calculate the actual enthalpy recovery rate of the drying system in the first control cycle, use the PID algorithm to dynamically calculate the deviation between the actual enthalpy recovery rate and the set target recovery rate, and update the target absolute moisture content. S211. Real-time parameter acquisition and transmission to controller (7), the parameter acquisition includes the exhaust gas temperature T before exhaust gas recovery of dryer (4). in and humidity RH in The temperature T of the waste gas after waste gas recovery in the dryer (4) out and humidity RH out The temperature of the ambient air, T amb and humidity RH amb ; S212. Calculate the enthalpy h of moist air before waste gas recovery. in Enthalpy of moist air h after exhaust gas recovery out Enthalpy of ambient air (h) amb ; ； Where h is the enthalpy of moist air (kJ / kg dry air); T is the gas temperature (°C); d is the moisture content (g / kg dry air); 1.006×T is the sensible heat of 1 kg dry air; d×2501 is the latent heat of water vapor; and d×1.86×T is the sensible heat of water vapor. S213. Calculate the actual enthalpy recovery rate η of the drying system. device ; ； Among them, h in —Enthalpy of moist air before exhaust gas recovery; h out —Enthalpy of moist air after exhaust gas recovery; h amb —The enthalpy of humid air in the environment; S214. Based on the actual enthalpy value recovery rate η device With target recovery rate η target The deviation is dynamically calculated to determine the target absolute moisture content d. target , The absolute moisture content correction increment is obtained using a PID algorithm. ； Where Δd is the output increment of the PLC controller (7); e is the deviation signal. ;de—represents the minute change in the deviation signal e; dt—the differential increment of time; —This reflects the rate and direction of change of the deviation over time; K p —Quickly respond to current recovery rate deviations; K i —Eliminate steady-state deviation; K d —Suppress volatility; S215. Add the current target absolute moisture content to the correction increment to obtain the updated target absolute moisture content. , ； S22. Obtain the actual absolute moisture content of the exhaust gas during the second control cycle, and update the target absolute moisture content. To set the value, a closed-loop control algorithm is used to dynamically adjust the opening of the first burner (11) to adjust the heat exchange contact area between the first burner (11) and the generator (3), thereby adjusting the evaporation capacity of the generator (3) so that the actual absolute moisture content tracks the set value. The second control cycle is shorter than the first control cycle.

2. The method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer as described in claim 1, characterized in that: In step S1, the adjustment method of the second burner (12) includes: If the real-time temperature T sc Below the preset minimum temperature T min If so, the opening degree of the second burner (12) is increased; If the real-time temperature T sc Higher than the preset maximum temperature T max If so, the opening degree of the second burner (12) is reduced; If the real-time temperature T sc At the preset minimum temperature T min With the preset maximum temperature T max Between these points, the opening degree of the second burner (12) remains unchanged; The stable state is determined by the condition that the running time reaches a preset running duration.

3. The method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer as described in claim 1, characterized in that, The correction amount The updated target absolute moisture content A safety constraint interval is defined, wherein the lower limit of the safety constraint interval is the physical limit lower limit to prevent system anomalies, and the upper limit of the safety constraint interval is the dynamic performance upper limit calculated based on the minimum allowable recovery rate. .

4. The method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer as described in claim 1, characterized in that, The target recovery rate η target It is based on the corresponding setting of the heat recovery mode, which is dynamically switched according to the moisture content and temperature of the waste gas before recovery; If the moisture content of the inlet exhaust gas before the dryer (4) is greater than the preset maximum moisture content of the inlet exhaust gas, it is determined to be the latent heat-dominant stage, and the latent heat is fully recovered, and the first target recovery rate is set. If the moisture content of the inlet exhaust gas before recovery of the dryer (4) is between the preset minimum moisture content of the inlet exhaust gas and the preset maximum moisture content of the inlet exhaust gas, it is determined to be a transitional stage, and a second target recovery rate is set. If the moisture content of the inlet exhaust gas before the dryer (4) is less than the preset minimum moisture content of the inlet exhaust gas, it is determined to be the sensible heat-dominant stage, the sensible heat recovery device (6) is turned on, and the third target recovery rate is set. The first target recovery rate is greater than the second target recovery rate and the third target recovery rate; when the latent heat is the main stage, when the difference between the exhaust gas temperature and the ambient temperature is less than the preset temperature difference threshold, the sensible heat recovery device (6) is on standby and the exhaust gas directly enters the latent heat recovery device (5); when the difference between the exhaust gas temperature and the ambient temperature is greater than or equal to the preset temperature difference threshold, the exhaust gas is controlled to flow through the sensible heat recovery device (6) first and then enter the latent heat recovery device (5).

5. The method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer as described in claim 1, characterized in that, Before step S21, the initial opening degree of the heat exchange contact area between the first burner (11) and the generator (3) is adjusted, including the following steps: S201. Obtain the exhaust gas outlet temperature T1 and humidity RH1 at the exhaust gas outlet of the dryer (4); S202. Calculate the initial absolute moisture content d; ； ； ； Where 611.2 is the saturated vapor pressure at 0℃, in Pa; 17.67 is the empirical coefficient of the Magnus formula, dimensionless; and 243.5 is the empirical coefficient of the Magnus formula, in ℃. —Saturated vapor pressure, Pa; exp—Natural exponential function; —Actual water vapor pressure, Pa; —Standard atmospheric pressure, Pa; 622—Molar mass ratio of water vapor to dry air; S203. Compare the calculated initial absolute moisture content d with the moisture content range to match the opening value corresponding to the corresponding moisture content range; S204. The opening value obtained by matching is used as the initial opening of the heat exchange contact area between the first burner (11) and the generator (3) for adjustment. Then, the opening of the first burner (11) is dynamically adjusted by the closed-loop control algorithm to adjust the heat exchange contact area between the first burner (11) and the generator (3).

6. The method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer as described in claim 5, characterized in that, The closed-loop control algorithm uses a positional PID algorithm. ； Where A is the opening degree of the first burner (11) output by the algorithm, 20%≤A≤100%; A init —Initial opening; e d —Moisture content deviation, K p K i K d —PID parameters, K p =1.0~2.0, % / (g / kg); K i =0.005~0.02%, % / (g / kg) s); K d =0.

7. The method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer as described in claim 1, characterized in that, It also includes a method for preventing solution crystallization for a latent heat recovery device (5), wherein the latent heat recovery device (5) is a solution absorption heat recovery device, the solution absorption heat recovery device includes a steam heat recovery pipeline (51) and a solution heat recovery pipeline (52), and the solution heat recovery pipeline (52) is provided with a solution cooling heat exchange device (521), a solution pump (522) and a dilution valve; The method for preventing solution crystallization includes: The actual solution temperature T after the solution cooling heat exchanger (521) and before entering the solution absorption device (514) is obtained. y ; Obtain the crystallization temperature T corresponding to the current solution concentration. j ; Calculate the actual solution temperature T y With the crystallization temperature T j The actual temperature difference △T y1 ; ； With a preset safe temperature difference as the target, the opening degree of the solution cooling heat exchange device (521) is dynamically adjusted using a closed-loop control algorithm to adjust the cooling capacity of the solution cooling heat exchange device (521) so that the actual temperature difference meets the preset safe temperature difference.

8. The method for monitoring, recovering, and controlling the sensible heat and latent heat of waste gas from a grain dryer as described in claim 7, characterized in that, The method for preventing solution crystallization also includes multi-level safety over-limit release logic: Level 1 warning: When the actual temperature difference is less than or equal to the first alarm threshold, increase the speed of the solution pump (522) and maintain the closed-loop control algorithm adjustment; Level 2 warning: When the actual temperature difference is less than or equal to the second alarm threshold, the cooling capacity of the solution cooling heat exchange device (521) is forcibly limited to a preset safety value, the dilution valve is opened, the speed of the solution pump (522) is increased to the maximum value, and the closed-loop control algorithm output is paused. Level 3 warning: When the actual temperature difference is less than or equal to the third alarm threshold, the solution cooling heat exchange device (521) is forcibly shut down, and the dilution valve and solution pump (522) are kept at maximum speed. Wherein, the first alarm threshold > the second alarm threshold > the third alarm threshold.

9. A monitoring and control system for the recovery of sensible heat and latent heat in the exhaust gas of a grain dryer, characterized in that, It includes a combustion chamber (1), a first burner (11), a second burner (12), a generator (3), a dryer (4), a latent heat recovery device (5), a sensible heat recovery device (6), a PLC controller (7), and a temperature and humidity sensor assembly (8); The first burner (11) and the second burner (12) are installed in the combustion chamber (1). The combustion chamber (1) is provided with a first air inlet pipe (91) connected to the air inlet of the dryer (4). The generator (3) is installed above the first burner (11). The first burner (11) is used to supply the heat required by the dryer (4) and to heat the generator (3). The first burner (11) is provided with a first adjusting baffle (13) for adjusting the heat exchange contact area between the first burner (11) and the generator (3). The second burner (12) is provided with a second adjusting baffle (14) for adjusting the opening degree of the second burner (12) to quickly adjust the air inlet temperature of the dryer (4) to obtain a stable exhaust gas temperature. The latent heat recovery device (5) is connected to the generator (3) and the dryer outlet (42) through a pipeline system to recover latent heat; The sensible heat recovery device (6) includes a sensible heat recovery heat exchanger (61) and a sensible heat recovery valve (62). The sensible heat recovery heat exchanger (61) is located between the latent heat recovery device (5) and the dryer outlet (42). The sensible heat recovery valve (62) is located at the dryer outlet to control the direction of waste gas flow. The sensible heat recovery device (61) is provided with a fifth air inlet pipe (95) connected to the dryer inlet (41). The dryer outlet (42) is also connected to an exhaust pipe (421) for discharging the waste gas after heat recovery treatment. The temperature and humidity sensor assembly (8) includes a temperature sensor (81) and a humidity sensor (82) for collecting temperature and humidity data. The temperature sensor (81) is installed at the air inlet of the dryer (4), the air outlet of the dryer (4), the inside of the exhaust pipe, the outside of the exhaust pipe, and the liquid outlet of the solution cooling heat exchange device (521) to monitor the real-time temperature T of the air inlet (41) of the dryer. sc The exhaust gas outlet temperature T1 at the exhaust gas outlet of the dryer (4) or the exhaust gas temperature T before exhaust gas recovery of the dryer (4) in The temperature T of the waste gas after waste gas recovery in the dryer (4) out The temperature of the ambient air, T amb The actual solution temperature T after cooling by the solution cooling heat exchanger (521) y The humidity sensor (82) is installed at the air outlet, inside the exhaust pipe, and outside the exhaust pipe of the dryer (4) to monitor the exhaust outlet humidity RH1 of the dryer (4) or the exhaust gas humidity RH before the dryer (4) exhaust gas is recovered. in The humidity (RH) of the waste gas after waste gas recovery from the dryer (4) out RH of ambient air amb ; The PLC controller (7) is communicatively connected to the first adjusting baffle (13), the second adjusting baffle (14), the sensible heat recovery device (6), the latent heat recovery device (5), and the temperature and humidity sensor assembly (8). The PLC controller (7) is configured to perform the monitoring and recovery control method for sensible heat and latent heat of grain dryer exhaust gas as described in any one of claims 1-9.

10. The monitoring and control system for the recovery of sensible heat and latent heat in the exhaust gas of a grain dryer as described in claim 9, characterized in that, The latent heat recovery device (5) includes a steam heat recovery pipeline (51) and a solution heat recovery pipeline (52). One end of the steam heat recovery pipeline (51) is located above the generator (3) to absorb the water vapor generated by the generator (3), and the other end is connected to a solution absorption device (514). The steam heat recovery pipeline (51) is provided with a condenser heat exchanger (511), a throttle valve (512), and an evaporator (513) located between the generator (3) and the solution absorption device (514). The condenser heat exchanger (511) is located behind the generator (3) to recover the latent heat of water vapor. A second air inlet pipeline (92) connected to the air inlet (41) of the dryer is provided on the outside of the condenser heat exchanger (511). The evaporator (513) is located at the air outlet (42) of the dryer to recover the latent heat of the exhaust gas. A fourth air inlet pipeline (94) connected to the air inlet (41) of the dryer is provided on the outside of the solution absorption device (514). The solution heat recovery pipeline (52) is a circulation pipeline located below the generator (3). The solution heat recovery pipeline (52) is provided with a solution cooling heat exchange device (521) and a solution pump (522) in sequence. The outside of the solution cooling heat exchange device (521) is provided with a third air inlet pipeline (93) connected to the air inlet (41) of the dryer.

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