Anti-fouling flue gas waste heat recovery system and control method

Abstract

This invention relates to the field of flue gas waste heat recovery and utilization technology, and discloses a flue gas waste heat recovery system and control method for preventing scaling. The flue gas waste heat recovery system includes multiple heat exchange units, a resistance monitoring module, a flow path switching valve group, and a control module. The resistance monitoring module is used to acquire the flow channel resistance status on the flue gas side, and the flow path switching valve group is set on the cold medium flow path of the multiple heat exchange units. The control module is configured to determine whether the thermal regeneration trigger condition is met based on the flow channel resistance status on the flue gas side; and when the thermal regeneration trigger condition is met, control the flow path switching valve group to cut off the cold medium supply to the target heat exchange unit, so that the target heat exchange unit enters the thermal regeneration mode; and alternately execute the heat exchange mode and the thermal regeneration mode among the multiple heat exchange units. This invention achieves precise on-demand ash removal, effectively eliminating ash accumulation and blockage while minimizing the number of ineffective thermal regenerations, and reducing the risk of thermal fatigue damage to the equipment.

Description

Technical Field

[0001] This invention relates to the field of flue gas waste heat recovery and utilization technology, and specifically to a flue gas waste heat recovery system and control method for preventing scaling. Background Technology

[0002] In flue gas treatment systems of coal-fired power plants and industrial boilers, heat exchange equipment downstream of selective catalytic reduction (SCR) denitrification units often becomes clogged due to the reaction of ammonia escape with sulfur trioxide, forming viscous ammonium salt deposits such as ammonium bisulfate. Current technologies typically employ online heating to gasify and decompose the deposits, thus removing the ash buildup. However, existing cleaning methods largely rely on manual experience or fixed time intervals, lacking real-time awareness of the actual scaling status of the heat exchange units. This can easily lead to delayed cleaning, causing severe blockage, or excessively frequent cleaning, resulting in unnecessary thermal fatigue damage to the equipment. Furthermore, when cleaning a single heat exchange unit, it is often necessary to cut off the air supply to that side. This causes fluctuations in the overall waste heat recovery efficiency of the system and may even cause parameter disturbances in the downstream flue gas system, making it difficult to maintain continuous and stable system heat load operation while ensuring effective cleaning. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of blind timing of dust removal and poor continuity of waste heat recovery during dust removal in the existing technology. It provides a flue gas waste heat recovery system and control method to prevent scaling, realize adaptive heat regeneration based on resistance feedback and alternating peak operation of multiple heat exchange units, so as to ensure the stability of the overall heat load of the system while accurately eliminating scaling.

[0004] To achieve the above objectives, the present invention provides a flue gas waste heat recovery system for preventing scaling, comprising multiple heat exchange units, a resistance monitoring module, a flow path switching valve group, and a control module; wherein, the resistance monitoring module is used to acquire the flow path resistance status on the flue gas side, and the flow path switching valve group is disposed on the cold medium flow path of the multiple heat exchange units; the control module is configured to: determine whether the thermal regeneration triggering condition is met based on the flow path resistance status on the flue gas side; and when the thermal regeneration triggering condition is met, control the flow path switching valve group to cut off the cold medium supply to the target heat exchange unit, so that the target heat exchange unit enters the thermal regeneration mode; and alternately execute the heat exchange mode and the thermal regeneration mode among the multiple heat exchange units.

[0005] Preferably, the resistance monitoring module includes a differential pressure monitoring unit, which is used to acquire the flow channel differential pressure on the flue gas side; when the flow channel differential pressure on the flue gas side exceeds a preset differential pressure threshold and the duration reaches a preset time threshold, it is determined that the thermal regeneration triggering condition is met.

[0006] Preferably, the flue gas waste heat recovery system further includes a temperature monitoring unit, and the control module is further configured to: after the target heat exchange unit enters the thermal regeneration condition, obtain the real-time temperature of the target heat exchange unit through the temperature monitoring unit, and when the real-time temperature reaches the preset decomposition temperature and is maintained for a preset time, control the flow path switching valve group to restore the cold medium supply to the target heat exchange unit.

[0007] Preferably, the multiple heat exchange units are connected in series on the flue gas main pipe and in parallel on the air main pipe; each heat exchange unit has a main shut-off valve in the flow path switching valve group at its air-side inlet and outlet; the air main pipe is provided with an air bypass pipe that crosses each heat exchange unit, and the air bypass pipe is provided with a bypass regulating valve in the flow path switching valve group.

[0008] Preferably, the main flue gas pipe is provided with a flue gas bypass pipe corresponding to each group of heat exchange units, and the flue gas bypass pipe is provided with a flue gas bypass valve.

[0009] Preferably, the multiple heat exchange units include a first heat exchange unit and a second heat exchange unit arranged sequentially along the flue gas flow direction; the control module is further configured to: when the first heat exchange unit meets the thermal regeneration trigger condition and enters the thermal regeneration operating condition, control the second heat exchange unit to maintain the heat exchange operating condition, and adjust the flow path switching valve group so that the total air flow rate through the second heat exchange unit and / or the air bypass pipe is kept constant.

[0010] Preferably, when the first heat exchange unit switches operating conditions, the control module first opens the bypass regulating valve and then closes the main shut-off valve of the first heat exchange unit; when the first heat exchange unit exits the heat regeneration operating condition, the control module first opens the main shut-off valve of the first heat exchange unit and then closes the bypass regulating valve.

[0011] Preferably, the heat exchange unit includes a tube box and heat exchange tubes, and the surface of the heat exchange tubes is provided with an anti-corrosion coating or is made of an acid-resistant dew point corrosion-resistant material.

[0012] The present invention also provides a control method for the flue gas waste heat recovery system as described above, comprising:

[0013] Obtain the flow resistance status on the flue gas side;

[0014] Based on the flow channel resistance state on the flue gas side, determine whether the thermal regeneration triggering condition is met;

[0015] In response to the fulfillment of the thermal regeneration triggering condition, the control flow path switching valve group cuts off the cold medium supply to the target heat exchange unit so that the target heat exchange unit enters the thermal regeneration condition;

[0016] The heat exchange condition and the heat regeneration condition are alternately executed between multiple heat exchange units.

[0017] Preferably, the flow path switching valve group includes a main shut-off valve and a bypass regulating valve. During the process of alternating between the heat exchange condition and the heat regeneration condition among the multiple heat exchange units, real-time flow feedback of the air main pipe is obtained. Based on the real-time flow feedback, the opening of the bypass regulating valve is dynamically adjusted to compensate for the flow fluctuation caused by the action of the main shut-off valve.

[0018] In the flue gas waste heat recovery system provided by this invention, by using the flow resistance state on the flue gas side as the criterion for triggering thermal regeneration, a direct causal relationship between the degree of scaling and the cleaning action is established. This overcomes the blindness of traditional timed or manual cleaning, achieving precise cleaning on demand. While effectively eliminating ash accumulation and blockage, it minimizes the number of ineffective thermal regenerations and reduces the risk of thermal fatigue damage to the equipment. Simultaneously, by constructing a flow path topology combining multiple sets of heat exchange units in series with parallel bypasses on the air side, and coordinating with alternating peak-shifting operation and dynamic flow compensation control strategies, the system can maintain a constant total air flow and total heat exchange capacity on the air side through the remaining units and bypasses even when any heat exchange unit is undergoing thermal regeneration and descaling. This completely solves the industry problem of interrupted or fluctuating waste heat recovery during cleaning, ensuring the continuous and stable operation of the downstream flue gas system and production processes, and significantly improving the overall economy and reliability of the unit. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a flue gas waste heat recovery system for preventing scaling, provided in an embodiment of the present invention;

[0020] Figure 2 This is a flowchart of a control method for a flue gas waste heat recovery system to prevent scaling, provided in an embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures:

[0022] 100. Heat exchange unit; 101. Tube box; 102. Heat exchange tube; 110. First heat exchange unit; 120. Second heat exchange unit; 200. Resistance monitoring module; 210. Differential pressure monitoring unit; 300. Flow path switching valve group; 310. Main shut-off valve; 320. Bypass regulating valve; 400. Control module; 500. Temperature monitoring unit; 600. Flue gas main pipe; 610. Flue gas bypass pipe; 611. Flue gas bypass valve; 700. Air main pipe; 800. Air bypass pipe. Detailed Implementation

[0023] To make the technical means, creative features, objectives, and effects of this invention readily understandable, the invention is further illustrated below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention.

[0024] like Figure 1 As shown, this embodiment of the invention provides a flue gas waste heat recovery system for preventing scaling, including multiple heat exchange units 100, a resistance monitoring module 200, a flow path switching valve group 300, and a control module 400. The resistance monitoring module 200 is used to acquire the flow path resistance status on the flue gas side, and the flow path switching valve group 300 is disposed on the cold medium flow path of the multiple heat exchange units 100. The control module 400 is configured to: determine whether the thermal regeneration triggering condition is met based on the flow path resistance status on the flue gas side; and when the thermal regeneration triggering condition is met, control the flow path switching valve group 300 to cut off the cold medium supply to the target heat exchange unit, so that the target heat exchange unit enters the thermal regeneration condition; and alternately execute the heat exchange condition and the thermal regeneration condition among the multiple heat exchange units 100.

[0025] In this embodiment of the invention, the resistance monitoring module 200 can be installed on the main flue gas pipe 600, or at the flue gas inlet and outlet of each heat exchange unit 100, to sense the smoothness of flue gas flow in each heat exchange unit 100 in real time. In this invention, the flow resistance state on the flue gas side is a direct physical quantity reflecting the degree of ash or scale buildup inside the heat exchange unit 100. When viscous ammonium salt deposits in the flue gas accumulate on the surface of the heat exchange tubes, it leads to a reduction in the flow cross-section, thereby causing an increase in resistance. By using this resistance state as a feedback signal, the system can break free from dependence on fixed time periods or manual experience, achieving accurate quantitative sensing of the scaling state and providing a reliable data basis for subsequent adaptive cleaning.

[0026] In this embodiment of the invention, the cold medium is usually air, and the flow path switching valve group 300 is installed on the connecting branch between the air main pipe 700 and each heat exchange unit 100, for independently adjusting or cutting off the flow rate of cold air entering a specific heat exchange unit 100.

[0027] It should be noted that, Figure 1 The diagram only schematically shows the arrangement of the flow path switching valve assembly 300. The specific form of the flow path switching valve assembly 300 can be an electric butterfly valve, a damper, or other valve combination with flow regulation and shut-off functions, as long as it can achieve flow regulation or shut-off control of the cold medium supply to the heat exchange unit 100. This design, which places the actuator on the cold medium side, allows the system to flexibly change the thermal balance state of the heat exchange unit without affecting the continuous flow of high-temperature flue gas.

[0028] In this embodiment of the invention, the control module 400 is the decision-making core of the entire system, and its internal control logic or algorithm program is pre-stored. When the control module 400 determines, based on the data fed back by the resistance monitoring module 200, that the scaling degree of a certain group of heat exchange units 100 (i.e., the target heat exchange unit) has reached the level requiring cleaning, it will automatically issue a command to drive the corresponding flow path switching valve group 300 to act, blocking the entry of cold air into the target heat exchange unit. At this time, due to the loss of the cooling effect of the cold medium, the heat carried by the high-temperature flue gas will rapidly heat the pipe wall and deposits of the target heat exchange unit, raising its temperature above the decomposition point of ammonium salt deposits, thereby achieving in-situ thermal regeneration descaling. This process is entirely driven by the resistance state, avoiding energy waste caused by premature cleaning or the risk of serious blockage caused by late cleaning.

[0029] More importantly, in this embodiment of the invention, the control module 400 is also responsible for coordinating the operating sequence of multiple heat exchange units 100 to ensure that they can alternately perform heat exchange and heat regeneration operations.

[0030] In a specific embodiment of the present invention, the multiple heat exchange units 100 include a first heat exchange unit 110 and a second heat exchange unit 120 arranged sequentially along the flue gas flow direction. When the first heat exchange unit 110 enters the heat regeneration mode due to excessive resistance, the control module 400 maintains the second heat exchange unit 120 in the normal heat exchange mode, continuing to absorb waste heat from the flue gas and heat the cold air. This alternating peak-shifting control logic fundamentally solves the industry pain point that the system must be shut down or its load significantly reduced during traditional single-sided dry-burning ash removal. It ensures that at any given time, at least some of the heat exchange units 100 in the system are in an effective working state, thereby achieving the continuity and stability of the waste heat recovery process and preventing drastic fluctuations in the parameters of the downstream flue gas system due to ash removal operations. Through the synergistic cooperation of the above-mentioned resistance feedback trigger and multiple alternating peak-shifting, this embodiment constructs an adaptive system that can both accurately remove scale and ensure continuous heating.

[0031] In some embodiments, the resistance monitoring module 200 includes a differential pressure monitoring unit 210, which is used to acquire the flow channel differential pressure on the flue gas side; when the flow channel differential pressure on the flue gas side exceeds a preset differential pressure threshold and the duration reaches a preset time threshold, it is determined that the thermal regeneration triggering condition is met.

[0032] In this embodiment of the invention, the differential pressure monitoring unit 210 can specifically employ high-precision sensing devices such as a micro differential pressure transmitter or a U-tube manometer. Its positive and negative pressure measuring points are respectively connected to the inlet and outlet of the heat exchange unit 100 on the flue gas side, or connected to two pressure measuring sections spanning the heat exchange unit 100 on the main flue gas pipe 600, for real-time acquisition of pressure loss values ​​before and after flue gas flow. This differential pressure value directly reflects the unobstructedness of the flue gas passage and is one of the most sensitive physical indicators for quantifying the state of ash accumulation and blockage.

[0033] Understandably, during actual operation, rapid increases or decreases in boiler load, soot blowing operations of upstream SCR denitrification units, and even the occasional passage of large fly ash particles in the flue gas can all cause instantaneous pressure spikes. If only a single pressure difference threshold is used as the triggering criterion, the system is prone to frequent start-ups and shutdowns of thermal regeneration under these instantaneous fluctuations caused by non-scaling factors. This not only wastes resources but also subjectes the heat exchange unit to repeated thermal shocks, accelerating material fatigue and aging. This invention introduces a preset time threshold as a second filtration condition. The control module can integrate or delay the pressure difference signal over time. Only when the high resistance state is stably and continuously present, and it is determined to be a steady-state blockage formed by the gradual accumulation of viscous ammonium salt deposits, can the thermal regeneration condition be finally triggered. For example, under typical coal-fired power plant tail flue conditions, the preset pressure difference threshold can be set between 500 Pa and 800 Pa, and the preset time threshold can be set between 10 minutes and 30 minutes. It should be understood that the above values ​​are merely illustrative examples and are not intended to limit the scope of protection of this invention. In practical applications, they can be flexibly adjusted according to factors such as fuel type, flue gas flow rate, and heat exchanger type, as long as the function of filtering out transient interference and accurately identifying steady-state scaling can be achieved.

[0034] Furthermore, in some embodiments of the present invention, the flue gas waste heat recovery system further includes a temperature monitoring unit 500. The temperature monitoring unit 500 may be disposed on the outer wall of the tube box of the heat exchange unit 100, on the surface of the heat exchange tube, or arranged at the flue gas outlet of the heat exchange unit 100, for real-time sensing of changes in metal wall temperature or flue gas temperature during the heat regeneration stage.

[0035] The control module 400 is further configured to: after the target heat exchange unit enters the thermal regeneration condition, obtain the real-time temperature of the target heat exchange unit through the temperature monitoring unit 500, and when the real-time temperature reaches the preset decomposition temperature and is maintained for a preset time, control the flow path switching valve group 300 to restore the cold medium supply to the target heat exchange unit.

[0036] In this embodiment of the invention, the aforementioned exit mechanism is crucial for ensuring effective dust removal and preventing equipment overheating. The gasification and decomposition of viscous deposits such as ammonium bisulfate is an endothermic chemical reaction process that requires sufficient activation energy and reaction time. If the exit is based solely on reaching a certain temperature point, situations may arise where the local temperature of the pipe wall reaches the target but the internal ash has not been completely decomposed, resulting in incomplete dust removal and requiring the system to be regenerated quickly. Conversely, without time constraints, prolonged exposure to high temperatures may lead to overheating creep or accelerated oxidation of the metal material. Therefore, the combination of preset decomposition temperature and preset duration ensures that heat has sufficient time to conduct to the deep ash layer and complete chemical decomposition. For example, for common ammonium bisulfate deposits, the preset decomposition temperature is typically set in the range of 300°C to 400°C, and the preset maintenance time can be set to 20 to 60 minutes. Maintaining sufficient duration within this temperature range ensures that the ammonium salt fully sublimates into a gaseous state and is discharged with the flue gas, while also controlling the metal wall temperature within a safe and permissible range.

[0037] In this embodiment of the invention, the temperature monitoring unit 500 can be in the form of a thermocouple, a resistance temperature detector (RTD), or an infrared thermometer, etc., as long as it can accurately report the temperature status of the regeneration area, it is within the protection scope of this invention. Through the dual closed-loop logic of pressure difference and time triggering and temperature and time-based exit, this embodiment of the invention achieves precise on-demand start-up and reliable termination of the thermal regeneration process, maximizing the service life of the equipment while ensuring the descaling effect.

[0038] In some embodiments, the multiple heat exchange units 100 are connected in series on the flue gas main pipe 600 and in parallel on the air main pipe 700; each heat exchange unit 100 has a main shut-off valve 310 in the flow path switching valve group 300 at its air-side inlet and outlet; the air main pipe 700 is provided with an air bypass pipe 800 that crosses each heat exchange unit 100, and the air bypass pipe 800 is provided with a bypass regulating valve 320 in the flow path switching valve group 300.

[0039] like Figure 1 As shown, the main flue gas pipe 600 passes sequentially through the tube box 101 of each heat exchange unit 100, forming a multi-stage series flue gas flow. This series arrangement on the flue gas side is designed because the flue gas at the tail end of a coal-fired power plant typically has a large temperature drop range. Series connection allows high-temperature flue gas to flow sequentially through each stage of the heat exchange unit 100, fully utilizing the heat from flue gas at different temperature levels, thereby maximizing the overall heat exchange efficiency of the system. In contrast, if a parallel arrangement is also used on the flue gas side, it is not only difficult to ensure a uniform distribution of flue gas flow among the heat exchange units 100, but it may also lead to insufficient heat exchange in some heat exchange units 100 due to flue gas short-circuiting, while others may experience accelerated wear due to excessively high flow velocities. Therefore, series flue gas connection is the fundamental architecture for ensuring waste heat recovery performance.

[0040] Before entering the heat exchange area, the main air pipe 700 branches into multiple branches, each branch connecting to the air inlet of a set of heat exchange units 100, and then rejoining at the outlet to the downstream section of the main air pipe 700. A main shut-off valve 310 is installed on each air branch to independently control the flow of cold air into the corresponding heat exchange unit 100. The air bypass pipe 800 directly connects the branching and rejoining points of the main air pipe 700, forming a backup flow channel in parallel with all heat exchange units 100.

[0041] It should be noted that, in the appendix of this invention Figure 1 The diagram schematically shows the air bypass pipe 800 located on one side of the heat exchange unit 100. However, in other embodiments, the air bypass pipe 800 can also be arranged above or below the heat exchange unit, as long as its two ends are connected to the inlet header and outlet header of the air main pipe 700 respectively, so as to realize the bridging function.

[0042] In this embodiment of the invention, when a group of heat exchange units 100 needs to enter the thermal regeneration state due to severe scaling, the control module 400 can close the main shut-off valve 310 on the corresponding air branch of that group, cutting off the supply of cold medium to allow it to heat up and remove scale. At this time, since the air side adopts a parallel design and is equipped with an air bypass pipe 800, the cold air that originally flowed through that group of heat exchange units 100 can be guided to the other normally operating heat exchange units 100, or flow directly downstream via the air bypass pipe 800 by opening the bypass regulating valve 320. In this way, even if some heat exchange units 100 are in an offline regeneration state, the total flow cross section on the air side does not undergo a drastic change, and the total air resistance of the system remains relatively stable, effectively avoiding problems such as fan surge, pipeline pressure buildup, or sudden reduction in downstream air volume caused by unilateral isolation. That is, in this invention, by setting a parallel bypass on the air side, the system is given the ability to perform independent thermal regeneration of any single group of heat exchange units 100 without interrupting the overall process flow, realizing the decoupling of dust removal and heat exchange.

[0043] Furthermore, in this embodiment of the invention, to enhance the operational flexibility and safety of the system under extreme operating conditions, a flue gas bypass pipe 610 is provided on the main flue gas pipe 600 corresponding to each group of heat exchange units 100, and a flue gas bypass valve 611 is provided on the flue gas bypass pipe 610. Specifically, the two ends of the flue gas bypass pipe 610 are respectively connected to the inlet and outlet of the flue gas side of the group of heat exchange units 100, forming a flue gas short-circuit channel in parallel with the group of heat exchange units 100. During normal operation, the flue gas bypass valve 611 is in the fully closed state, and all flue gas flows through the heat exchange unit 100 for heat exchange. However, under special operating conditions, such as a serious leak inside a heat exchange unit 100 requiring emergency isolation and repair, or an abnormal rise in flue gas inlet temperature exceeding the equipment safety limit requiring rapid cooling protection, the control module 400 can open the corresponding flue gas bypass valve 611 and simultaneously close the isolation baffle (not shown in the figure) on the flue gas side of that heat exchange unit 100, allowing the high-temperature flue gas to bypass the faulty or unprotected heat exchange unit 100 and directly enter the next stage. This design not only provides convenient conditions for online maintenance of the equipment, allowing the isolation and replacement of a single heat exchange unit 100 to be completed without shutting down the furnace, but also serves as a safety barrier to prevent local overheating damage from affecting the entire waste heat recovery system.

[0044] It is understood that the flue gas bypass valve 611 may be in the form of a high-temperature resistant electric butterfly valve, a pneumatic damper, or other regulating valve suitable for high-temperature flue gas environments. This invention does not impose any special limitations on this.

[0045] In this embodiment of the invention, the multiple heat exchange units 100 include a first heat exchange unit 110 and a second heat exchange unit 120 arranged sequentially along the flue gas flow direction; the control module 400 is further configured to: when the first heat exchange unit 110 meets the heat regeneration trigger condition and enters the heat regeneration working condition, control the second heat exchange unit 120 to maintain the heat exchange working condition, and adjust the flow path switching valve group 300 so that the total air flow rate through the second heat exchange unit 120 and / or the air bypass pipe 800 is kept constant.

[0046] The aforementioned control strategy aims to address the issues of fluctuating total system airflow and decreasing heat load that inevitably occur during single-sided isolation and cleaning in traditional waste heat recovery systems. When the first heat exchange unit 110 is removed from normal operation due to severe scaling, the physical topology of the airflow path changes, and the total system flow resistance typically increases. If no active intervention is taken at this time, the operating point of the blower will shift along the performance curve towards lower flow rate and higher pressure head, resulting in a reduction in the total amount of air entering subsequent process stages, which in turn causes disturbances in the operating conditions of downstream drying, combustion, or environmental protection equipment.

[0047] In this embodiment of the invention, the control module 400 does not simply execute valve switching actions, but rather coordinates the opening of the second heat exchange unit 120 and the bypass regulating valve 320 in operation based on a preset flow conservation algorithm or real-time feedback signal. For example, while cutting off the first heat exchange unit 110, the control module 400 can simultaneously increase the opening of the bypass regulating valve 320, using the low-resistance channel of the air bypass pipe 800 to divert the amount of air originally flowing through the first heat exchange unit 110; or, if the second heat exchange unit 120 still has margin, its air inlet valve opening can be appropriately increased to improve flow capacity. Through this dynamic flow redistribution mechanism, the system can maintain the total flow rate at the outlet of the main air pipe within the allowable deviation range of the design value (e.g., within ±5%) during the offline regeneration of any set of heat exchange units 100. This not only ensures the continuity of the total amount of waste heat recovery, but more importantly, maintains the pressure balance of the downstream flue gas system, achieving truly uninterrupted online dust removal. It should be understood that although the above example focuses on the compensation function of the bypass regulating valve 320, in actual applications, the control module 400 can also flexibly choose to regulate only the bypass, only the operating unit, or both, according to the real-time load rate and resistance characteristics of each heat exchange unit 100. As long as the macroscopic constant total air flow can be achieved, it falls within the protection scope of this invention.

[0048] To ensure the safe and stable operation of the aforementioned flow switching process and to avoid equipment accidents caused by valve malfunctions or improper timing, this embodiment of the invention also specifies strict valve operation logic. Specifically, when the first heat exchange unit 110 switches operating conditions, the control module 400 first opens the bypass regulating valve 320 and then closes the main shut-off valve 310 of the first heat exchange unit 110; when the first heat exchange unit 110 exits the heat regeneration operating condition, the control module 400 first opens the main shut-off valve 310 of the first heat exchange unit 110 and then closes the bypass regulating valve 320.

[0049] When the first heat exchange unit 110 needs to be switched to heat regeneration mode, if its corresponding main shut-off valve 310 is closed first, the airflow path will be instantly cut off or forced entirely into the not-yet-fully-open bypass channel, causing a sharp increase in local system resistance. For centrifugal or axial flow fans with high inertia, this sudden back pressure can easily induce surge, causing fatigue damage to the fan blades or even bearing burnout. At the same time, the throttling effect of high-speed airflow in narrow gaps will generate strong aerodynamic noise and pipe vibration. Conversely, by adopting the strategy of opening the bypass regulating valve 320 first, it is equivalent to pre-establishing a low-resistance backup venting channel before the main line is cut off, allowing the airflow to transition smoothly. After the bypass flow stabilizes, the main shut-off valve 310 can be calmly closed, thus completely eliminating the risk of pressure shock caused by the sudden change in flow path. Similarly, when the first heat exchange unit 110 completes regeneration and is ready to resume heat exchange mode, if the bypass regulating valve 320 is closed first, the system will again face the risk of instantaneous flow interruption or high resistance. Therefore, the main shut-off valve 310 corresponding to the first heat exchange unit 110 must be opened slowly first. After the first heat exchange unit 110 re-establishes a stable airflow path, the bypass regulating valve 320 is gradually closed to smoothly transfer the flow from the bypass to the main heat exchange channel. This bidirectional soft switching sequence not only effectively prevents pressure buildup, water hammer (air hammer), and mechanical impact, protecting the valve actuator, seals, and pipeline support structure, but also avoids heat exchange tube bundle-induced vibration caused by airflow pulsation, significantly improving the operational reliability and service life of the entire anti-scaling flue gas waste heat recovery system.

[0050] In some embodiments, the heat exchange unit 100 includes a tube box 101 and a heat exchange tube 102, wherein the surface of the heat exchange tube 102 is provided with an anti-corrosion coating or is made of an acid-resistant dew point corrosion-resistant material.

[0051] In this invention, the tube box 101 serves as a partition cavity between the flue gas and air flow channels and a supporting and fixing component for the heat exchange tubes 102. It is typically welded from carbon steel or low-alloy steel plates. The heat exchange tubes 102 are installed inside the tube box 101, with both ends sealed to the tube sheet via expansion joints or welding, forming independent gas-side and air-side channels. In the technical solution of this invention, because the system adopts an adaptive thermal regeneration strategy based on resistance feedback, the heat exchange unit 100 periodically undergoes temperature cycles from a normal low-temperature state (typically between 100°C and 200°C) to a high-temperature state (above 300°C and 400°C) during thermal regeneration. This frequent thermal shock not only places demands on the mechanical strength of the materials, but more importantly, during the thermal regeneration process, the sticky deposits such as ammonium bisulfate adhering to the tube wall decompose upon heating, releasing high concentrations of sulfur trioxide and water vapor. When hot regeneration ends and cold medium is reintroduced, causing the tube wall temperature to drop rapidly, these acidic gases easily condense into highly corrosive acid on the tube wall surface, forming a typical acid dew point corrosion environment. If only ordinary carbon steel is used, under the coupled effect of this alternating thermal stress and chemical corrosion, heat exchange tube 102 is very prone to perforation and leakage, leading to system failure.

[0052] To address the aforementioned operating conditions, the specific type of anti-corrosion coating can be selected based on the actual flue gas composition and the thermal regeneration temperature range. For example, an enamel coating can be used. After high-temperature sintering, the enamel coating forms a strong chemical bond with the metal substrate, exhibiting extremely high density and excellent resistance to acid and alkali corrosion, effectively isolating acidic condensate from contact with the metal substrate. Simultaneously, the heat resistance temperature of the enamel coating typically reaches over 450℃, completely covering the temperature range of the thermal regeneration conditions described in this invention, and it is not easily peeled off under repeated rapid heating and cooling conditions. As another option, a fluoroplastic coating (such as a PFA, FEP, or PTFE modified coating) can also be used. Fluoroplastics not only possess excellent chemical inertness, resisting the erosion of almost all strong acids and alkalis, but also have extremely low surface energy. This low surface energy characteristic gives the heat exchange tube surface a non-stick effect, significantly reducing the adhesion of fly ash and sticky ammonium salts during normal operation and slowing down the ash accumulation rate; during the thermal regeneration stage, it facilitates the rapid removal and discharge of decomposition products, thereby indirectly improving the ash removal efficiency. It should be understood that, regardless of the type of coating used, its thickness and application process must ensure that it does not carbonize, decompose, or lose its protective function at the highest temperature of heat regeneration.

[0053] It is understood that, in this embodiment of the invention, in addition to surface coating protection, the heat exchange tube 102 can also be directly made of an acid-resistant dew point corrosion-resistant material to improve durability from the substrate level. For example, the heat exchange tube 102 can be made of ND steel (grade 09CrCuSb). ND steel is a special steel developed specifically to resist sulfuric acid dew point corrosion. By adding trace alloying elements such as copper (Cu) and antimony (Sb), it can promote the formation of a dense passivation film rich in Cu and Sb oxides on the metal surface in a corrosive environment. This passivation film can effectively inhibit the anodic dissolution process, and its resistance to sulfuric acid dew point corrosion is usually several times or even more than ten times that of ordinary carbon steel, and its cost is relatively low, making it suitable for large-scale industrial applications. For scenarios with high chloride ion content in flue gas or more severe corrosive environments, the heat exchange tube 102 can also be made of 316L austenitic stainless steel. The molybdenum (Mo) element contained in 316L endows it with excellent resistance to pitting and crevice corrosion. Combined with its good high-temperature mechanical properties, it can maintain structural integrity in the extremely harsh acidic atmosphere of thermal regeneration. This invention, through the aforementioned material-level protection design and deep adaptation to thermal regeneration conditions, effectively solves the problem of shortened lifespan due to accelerated corrosion during online ash removal in traditional waste heat recovery equipment, ensuring the safe and reliable operation and stable heat exchange performance of the anti-scaling flue gas waste heat recovery system throughout its entire life cycle.

[0054] like Figure 2 As shown, this embodiment of the invention also provides a control method for an anti-scaling flue gas waste heat recovery system, comprising the following steps:

[0055] Step S100: Obtain the flow resistance status on the flue gas side.

[0056] This step is the starting point of the entire control method, and its core lies in the real-time acquisition of physical quantities that characterize the unobstructed flow of the flue gas passage. In this embodiment of the invention, the resistance state of the flue gas side passage is a broad data concept, and its acquisition method is not limited to a specific sensor type or installation location. For example, it can be obtained by directly measuring the pressure difference between the flue gas inlet and outlet, or indirectly estimated by monitoring changes in the current, power, or speed of the induced draft fan, or even by using acoustic sensors to detect changes in the airflow noise spectrum to inversely determine the degree of blockage. Regardless of the data acquisition method used, as long as the data can sensitively and accurately reflect the changes in the flow cross-section caused by ash or scale buildup inside the heat exchange unit, it can be used as a valid input for this step.

[0057] Step S200: Based on the flow channel resistance state on the flue gas side, determine whether the thermal regeneration triggering condition is met.

[0058] This step is a crucial logical step in transforming raw monitoring data into control decisions. The control algorithm internally stores a mapping relationship or judgment model between resistance status and the severity of scaling. When the acquired resistance status data indicates that the flow channel blockage has reached a level affecting system safety or efficiency, it is determined that the thermal regeneration trigger condition is met. It should be understood that the judgment logic here can be multi-dimensional, ranging from simple threshold comparisons (such as resistance values ​​exceeding a set upper limit) to complex algorithms incorporating time integration, rate of change analysis, or machine learning predictions. For example, to prevent misjudgments caused by load fluctuations, the algorithm can introduce a delayed confirmation mechanism or filtering; to prevent severe blockages in advance, predictive triggering can also be performed based on resistance growth trends. Through this flexible logical judgment, the system can achieve precise on-demand cleaning, avoiding the blindness and lag of traditional timed cleaning modes.

[0059] In step S300, in response to the fulfillment of the thermal regeneration triggering condition, the control flow path switching valve group 300 cuts off the cold medium supply to the target heat exchange unit so that the target heat exchange unit enters the thermal regeneration condition.

[0060] This step is the execution action of the thermal regeneration process. Once step S200 makes a positive judgment, the control system immediately sends a command to the flow path switching mechanism to block the flow of cold medium (usually air) to the target heat exchange unit. From a thermodynamic point of view, this action essentially changes the thermal equilibrium boundary conditions of the heat exchange unit 100: after removing the cold-side heat absorber, the heat carried by the high-temperature flue gas is no longer carried away by the cold air, but is entirely used to heat the heat exchange element body and the deposits on its surface. As the wall temperature gradually rises above the decomposition temperature of viscous deposits such as ammonium salts, the scale undergoes a vaporization or cracking reaction, thereby achieving in-situ removal. This step emphasizes the control action of cutting off the cold medium itself and the resulting thermal state change, rather than being limited to the specific valve form (such as butterfly valves, baffle gates, or louvers) that implements this action. This descaling method based on thermal equilibrium reconstruction makes full use of the waste heat energy of the flue gas itself, without the need to introduce an external heat source, significantly reducing the system's operating energy consumption.

[0061] In step S400, heat exchange mode and heat regeneration mode are alternately executed among multiple heat exchange units 100.

[0062] This step aims to resolve the conflict between cleaning individual heat exchange units and continuous system heating. In systems with multiple heat exchange units 100 connected in parallel or a hybrid series-parallel configuration, the control algorithm coordinates the operational sequence of each unit, ensuring that at least some heat exchange units 100 are in normal heat exchange conditions to maintain the system's basic heat load within the same time period, while other heat exchange units 100 take turns entering the thermal regeneration mode for descaling based on the judgment result of step S200. This alternating execution logic includes not only simple rotation and sorting but also dynamic scheduling optimization based on the real-time resistance status of each unit, cumulative operating time, or downstream heat demand priority. For example, when multiple units approach the triggering condition simultaneously, the algorithm can automatically arrange the regeneration order according to urgency; or prioritize regeneration during low-load periods and maintain full operation during high-load periods. Through this spatiotemporal staggered peak coordination, this method completely breaks the limitations of traditional technologies where cleaning necessarily requires boiler shutdown or load reduction, achieving continuous and stable operation of the waste heat recovery process around the clock, greatly improving the overall economy and reliability of the unit.

[0063] In some embodiments, the flow path switching valve group 300 includes a main shut-off valve 310 and a bypass regulating valve 320. During the alternating execution of the heat exchange condition and the thermal regeneration condition among the multiple heat exchange units 100, real-time flow feedback of the air main pipe 700 is obtained. In this embodiment of the invention, obtaining this real-time flow feedback is a prerequisite for constructing high-precision closed-loop control. In terms of implementation, high-precision flow sensing devices, such as thermal gas mass flow meters, Pitot tube array flow meters, or Venturi flow meters, can be installed at the outlet header or downstream straight pipe section of the air main pipe 700. These sensing devices can continuously collect actual volumetric flow rate or mass flow rate data flowing through the air main pipe 700 with a sampling period of milliseconds or seconds, and convert it into a standard electrical signal for transmission to the control module. It should be understood that although the preferred embodiment of the present invention is to measure at the outlet of the air main pipe 700 to obtain the true value closest to the system output, in other embodiments, it is also possible to measure at the inlet of the air main pipe 700, or to indirectly estimate the flow rate by monitoring the power and speed of the blower motor and combining it with the blower performance curve, as long as the feedback data can accurately characterize the current actual ventilation volume of the system and meet the control response speed requirements.

[0064] Furthermore, based on the real-time flow feedback, the opening of the bypass regulating valve 320 is dynamically adjusted to compensate for flow fluctuations caused by the action of the main shut-off valve 310. During the dynamic process of switching operating conditions, relying solely on preset valve opening correspondences often fails to achieve the ideal constant flow effect. This is because industrial valves generally exhibit nonlinear flow characteristics (such as equal percentage characteristics, parabolic characteristics, etc.), and the resistance characteristics of the entire air-side pipeline network change in real time as the heat exchange unit 100 is switched in or out. If open-loop control is used, the same valve opening increment may correspond to drastically different flow increments under different operating conditions, leading to overshoot or undershoot compensation. Therefore, this embodiment of the invention introduces a dynamic compensation algorithm based on real-time deviation. The control module 400 runs a closed-loop control program. Its core logic is to compare the acquired real-time flow feedback value with the preset target flow setpoint and calculate the flow deviation e(t). Then, using the proportional-integral-derivative (PID) algorithm or a more advanced feedforward-feedback composite control algorithm, the target opening correction amount Δu(t) of the bypass regulating valve 320 is calculated in real time according to the magnitude, accumulation and trend of the deviation, and then superimposed on the basic opening command and output to the valve actuator.

[0065] In a preferred embodiment, an incremental PID control strategy with feedforward compensation can be employed. When the control module 400 issues a command to close the main shut-off valve 310 of the first heat exchange unit 110, the algorithm first calculates a coarse adjustment increment of the bypass regulating valve 320 based on the current load rate or historical flow ratio of the first heat exchange unit 110 using a feedforward model, so that the bypass flow quickly approaches the gap value. At the same time, the PID feedback loop performs fine adjustment based on the residual between the real-time flow feedback and the target value, eliminating steady-state errors caused by valve nonlinearity, pipeline resistance drift, and sensor noise. In this algorithm, the proportional coefficient Kp can be set between 0.5 and 2.0 to ensure response speed, the integral time Ti can be set between 5s and 20s to eliminate steady-state error, and the derivative time Td can be set between 0s and 2s to suppress overshoot. In addition, to prevent frequent valve jitter, an appropriate deadband can be set in the algorithm, for example, pausing integral accumulation or maintaining the current opening when the flow deviation is less than ±1% of the target value. It should be understood that the above PID parameters and control strategies are merely illustrative examples. In practical engineering applications, fuzzy PID, adaptive PID, model predictive control (MPC), or other advanced control algorithms suitable for nonlinear time-varying systems can also be used. As long as their core idea is to dynamically correct the opening of the bypass regulating valve 320 based on real-time flow feedback to offset disturbances, they all fall within the protection scope of this invention.

[0066] Through the aforementioned dynamic compensation algorithm based on real-time flow feedback, this embodiment of the invention upgrades traditional position control to flow servo control. From a microscopic perspective, the algorithm establishes a rapid negative feedback path for real-time sensing, deviation calculation, dynamic correction, and steady-state flow. When the action of the main shut-off valve 310 causes a sudden change in system resistance, the algorithm can identify the flow deviation trend within several control cycles and drive the bypass regulating valve 320 to perform a reverse compensation action, limiting the flow fluctuation amplitude to a very small allowable range (e.g., within ±3%). This not only effectively overcomes the control difficulties caused by the inherent nonlinear characteristics of the valve and the time-varying nature of system resistance, significantly improving the stability and control accuracy of the total air flow during off-peak operation, but more importantly, it provides an extremely stable air source condition for the downstream flue gas system and production process, completely eliminating the potential negative impact of airflow pulsation caused by ash removal operations on combustion efficiency, drying quality, or environmental emission indicators.

[0067] The foregoing has shown and described the basic principles, main features, and characteristics of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A flue gas waste heat recovery system with anti-scaling properties, characterized in that, It includes multiple heat exchange units (100), a resistance monitoring module (200), a flow path switching valve group (300), and a control module (400). The resistance monitoring module (200) is used to obtain the flow resistance status on the flue gas side, and the flow path switching valve group (300) is set on the cold medium flow path of the multiple heat exchange units (100). The control module (400) is configured to: determine whether the thermal regeneration triggering condition is met based on the flow resistance state of the flue gas side; and when the thermal regeneration triggering condition is met, control the flow path switching valve group (300) to cut off the cold medium supply of the target heat exchange unit so that the target heat exchange unit enters the thermal regeneration condition; and alternately execute the heat exchange condition and the thermal regeneration condition among the multiple heat exchange units (100).

2. The flue gas waste heat recovery system according to claim 1, characterized in that, The resistance monitoring module (200) includes a differential pressure monitoring unit (210), which is used to acquire the flow channel differential pressure on the flue gas side; When the flow channel pressure difference on the flue gas side exceeds a preset pressure difference threshold and the duration reaches a preset time threshold, it is determined that the thermal regeneration triggering condition is met.

3. The flue gas waste heat recovery system according to claim 2, characterized in that, It also includes a temperature monitoring unit (500), and the control module (400) is further configured to: After the target heat exchange unit enters the thermal regeneration mode, the real-time temperature of the target heat exchange unit is obtained by the temperature monitoring unit (500). When the real-time temperature reaches the preset decomposition temperature and is maintained for a preset time, the flow path switching valve group (300) is controlled to restore the cold medium supply to the target heat exchange unit.

4. The flue gas waste heat recovery system according to claim 1, characterized in that, The multiple heat exchange units (100) are connected in series on the flue gas main pipe (600) and in parallel on the air main pipe (700); Each heat exchange unit (100) is equipped with a main shut-off valve (310) in the flow path switching valve group (300) at its air-side inlet and outlet. The main air pipe (700) is provided with an air bypass pipe (800) that crosses each of the heat exchange units (100), and the air bypass pipe (800) is provided with a bypass regulating valve (320) in the flow path switching valve group (300).

5. The flue gas waste heat recovery system according to claim 4, characterized in that, The flue gas main pipe (600) is provided with a flue gas bypass pipe (610) corresponding to each group of heat exchange units (100), and a flue gas bypass valve (611) is provided on the flue gas bypass pipe (610).

6. The flue gas waste heat recovery system according to claim 4, characterized in that, The multiple heat exchange units (100) include a first heat exchange unit (110) and a second heat exchange unit (120) arranged sequentially along the flue gas flow direction. The control module (400) is further configured to: when the first heat exchange unit (110) meets the heat regeneration trigger condition and enters the heat regeneration working condition, control the second heat exchange unit (120) to maintain the heat exchange working condition, and adjust the flow path switching valve group (300) so that the total air flow rate through the second heat exchange unit (120) and / or the air bypass pipe (800) remains constant.

7. The flue gas waste heat recovery system according to claim 6, characterized in that, When the first heat exchange unit (110) switches operating conditions, the control module (400) first opens the bypass regulating valve (320) and then closes the main shut-off valve (310) of the first heat exchange unit (110). When the first heat exchange unit (110) exits the heat regeneration mode, the control module (400) first opens the main shut-off valve (310) of the first heat exchange unit (110), and then closes the bypass regulating valve (320).

8. The flue gas waste heat recovery system according to claim 1, characterized in that, The heat exchange unit (100) includes a tube box (101) and a heat exchange tube (102), the surface of which is provided with an anti-corrosion coating or is made of an acid-resistant dew point corrosion-resistant material.

9. A control method for a flue gas waste heat recovery system as described in any one of claims 1-8, characterized in that, include: Obtain the flow resistance status on the flue gas side; Based on the flow channel resistance state on the flue gas side, determine whether the thermal regeneration triggering condition is met; In response to the fulfillment of the thermal regeneration triggering condition, the control flow path switching valve group (300) cuts off the cold medium supply to the target heat exchange unit so that the target heat exchange unit enters the thermal regeneration condition; The heat exchange condition and the heat regeneration condition are alternately executed among multiple heat exchange units (100).

10. The control method according to claim 9, characterized in that, The flow path switching valve group (300) includes a main path shut-off valve (310) and a bypass regulating valve (320). During the process of alternately executing the heat exchange condition and the heat regeneration condition among the multiple heat exchange units (100), the real-time flow feedback of the air main pipe (700) is obtained. Based on the real-time flow feedback, the opening of the bypass regulating valve (320) is dynamically adjusted to compensate for the flow fluctuations caused by the action of the main shut-off valve (310).

Images