Multi-mode switching flue gas waste heat recovery device and method

Abstract

The invention discloses a multi-mode switching flue gas waste heat recovery device and method. The device comprises a tower body, a sensible heat recovery module, a latent heat recovery module and a flue gas path switching module, the sensible heat recovery module is used for indirectly exchanging heat with flue gas to recover sensible heat, and the latent heat recovery module is used for recovering latent heat in the flue gas through gas-liquid direct contact; the flue gas path switching module comprises a bypass pipe set arranged between the sensible heat recovery module and the latent heat recovery module and a switching valve set arranged on the bypass pipe set, and the bypass pipe set and the switching valve set are configured to guide flue gas to selectively flow through the sensible heat recovery module and the latent heat recovery module or sequentially flow through the sensible heat recovery module and the latent heat recovery module. According to the flue gas waste heat recovery device, the occupied area and the pipeline length are reduced, it is ensured that flue gas only flows through necessary modules under different working conditions through a switchable flue gas path, corrosion and blockage of non-working modules are effectively avoided while the flowing resistance and energy consumption are reduced, and efficient, stable and high-adaptability flue gas waste heat recovery is achieved.

Description

Technical Field

[0001] This invention relates to the fields of waste incineration power generation and industrial flue gas treatment and waste heat recovery technology, and particularly to a multi-mode switching flue gas waste heat recovery device and method. Background Technology

[0002] Waste-to-energy incineration plants produce flue gas containing significant amounts of sensible and latent heat, along with pollutants such as dust, SO2, and NOx, making waste heat recovery and environmental treatment urgently needed. Currently, most flue gas waste heat recovery devices are single sensible or latent heat recovery units, resulting in low heat recovery efficiency and significant energy waste. While some integrated devices combine multiple functions, their dispersed structure, large footprint, and fixed flue gas flow path mean that the gas still needs to flow through all modules under non-essential operating conditions, leading to high flow resistance, high energy consumption, and accelerated equipment corrosion and blockage. Furthermore, traditional devices employ simplistic control strategies, relying solely on rough operating parameters for on / off adjustments. They cannot accurately and adaptively coordinate control based on dynamic changes in flue gas temperature, humidity, and pollutant concentration, as well as complex factors such as start-up / shutdown transitions and seasonal environmental differences. This makes it difficult to simultaneously achieve high heat recovery efficiency, environmental benefits, and equipment operational stability. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, embodiments of the present invention propose a multi-mode switching flue gas waste heat recovery device, which has the advantages of compact structure, high heat recovery efficiency, and the ability to achieve intelligent multi-mode switching and optimized control.

[0005] The multi-mode switching flue gas waste heat recovery device of this invention includes a tower body, a sensible heat recovery module, a latent heat recovery module, and a flue gas path switching module. The bottom of the tower body is provided with a flue gas inlet, and the top of the tower body is provided with a flue gas outlet. The sensible heat recovery module is located in the tower body and is used to indirectly exchange heat with the flue gas to recover sensible heat. The latent heat recovery module is located in the tower body and is used to recover latent heat in the flue gas through direct gas-liquid contact. At least a portion of the latent heat recovery module is located above the sensible heat recovery module. The flue gas path switching module includes a bypass pipe assembly located between the sensible heat recovery module and the latent heat recovery module, and a switching valve assembly located on the bypass pipe assembly. The bypass pipe assembly and the switching valve assembly are configured to guide the flue gas to selectively flow through the sensible heat recovery module, the latent heat recovery module, or sequentially through both.

[0006] In some embodiments, the bottom of the tower body has a first chamber and a second chamber arranged in parallel, and the upper middle part of the tower body has a third chamber. The first chamber is connected to the third chamber via a guide pipe, and the second chamber is directly connected to the third chamber. The sensible heat recovery module is disposed in the first chamber, and the latent heat recovery module is disposed in the second chamber and the third chamber. The tower body is provided with a smoke inlet pipe and a smoke outlet pipe. One end of the smoke inlet pipe is connected to the first chamber, and the other end of the smoke inlet pipe is the flue gas inlet. One end of the smoke outlet pipe is connected to the third chamber, and the other end of the smoke outlet pipe is the flue gas outlet.

[0007] In some embodiments, the sensible heat recovery module includes a plate heat exchanger, the flow channel of which is a multi-pass S-shaped narrow slit flow channel. The plate heat exchanger is connected to an external cold water source through an inlet pipe, so that the external cold water source enters the plate heat exchanger through the inlet pipe and indirectly exchanges heat with the flue gas. The plate heat exchanger is connected to an external heat utilization system through an outlet pipe, so that the water that absorbs the sensible heat of the flue gas is transported to the external heat utilization system through the outlet pipe. The connection between the flue gas inlet pipe and the first chamber, and the connection between the guide pipe and the first chamber, are located on opposite sides of the plate heat exchanger.

[0008] In some embodiments, the latent heat recovery module includes a packing layer, a spraying unit, and a gas-liquid separation net arranged sequentially from bottom to top in the third chamber, so that the flue gas can fully contact the cooling water sprayed by the spraying unit in the packing layer to recover the latent heat of the flue gas, and the gas-liquid separation net is used to separate the liquid droplets carried in the flue gas after the latent heat has been recovered. The latent heat recovery module also includes a water tank, a circulation pump, and a stirring pump. The water tank is located in the second chamber so that the spray water for recovering the latent heat of the flue gas falls into the water tank. Parts of the circulation pump and part of the stirring pump are located in the water tank. The water in the water tank is transported to the spray unit through the circulation pump and pipeline. The stirring pump is used to stir the sludge deposited at the bottom of the water tank. The water tank is equipped with an overflow pipe, a drain pipe, and a latent heat recovery pipe. The overflow pipe is used to control the water level in the water tank. The drain pipe is used to discharge the sludge at the bottom of the water tank. The latent heat recovery pipe is used to output hot water after recovering the latent heat of the flue gas. A water supply pipe is provided on the pipeline between the circulating pump and the spray unit. The water supply pipe is used to replenish fresh cold water.

[0009] In some embodiments, the bypass pipe group includes a first bypass pipe and a second bypass pipe, one end of the first bypass pipe is connected to the smoke inlet pipe, the other end of the first bypass pipe is connected to the third chamber, one end of the second bypass pipe is connected to the guide pipe, and the other end of the first bypass pipe is connected to the smoke exhaust pipe. The switching valve assembly includes a first switching valve, a second switching valve, and a third switching valve. The first switching valve is located at the connection between the first bypass pipe and the smoke inlet pipe. The second switching valve is located at the connection between the second bypass pipe and the guide pipe. The third switching valve is located at the connection between the second bypass pipe and the smoke exhaust pipe.

[0010] The embodiments of the present invention also propose a method for recovering waste heat from flue gas with multiple modes switching, which is applicable to the multi-mode switching waste heat recovery device described in the above embodiments.

[0011] The multi-mode switching flue gas waste heat recovery method of this invention includes: Real-time acquisition of flue gas operating parameters; Based on the operating parameters, determine the current target operating mode. The target operating modes include pure sensible heat recovery mode, pure latent heat recovery mode, and total heat recovery mode. Based on the target operating mode, control commands are generated to drive the switching valve group to operate, so that the flue gas flows along the path corresponding to the target operating mode, and to control the start and stop of the corresponding recovery module.

[0012] In some embodiments, the operating parameters of the flue gas include at least flue gas temperature and flue gas humidity; When the flue gas temperature is higher than the first temperature threshold and the flue gas humidity is lower than the first humidity threshold, the target operating mode is determined to be the pure sensible heat recovery mode. When the flue gas temperature is lower than the second temperature threshold and the flue gas humidity is higher than the second humidity threshold, the target operating mode is determined to be the pure latent heat recovery mode. When the flue gas temperature is between the second temperature threshold and the first temperature threshold, and the flue gas humidity is higher than the second humidity threshold, the target operating mode is determined to be the total heat recovery mode.

[0013] In some embodiments, the operating parameters of the flue gas also include the concentration of pollutants in the flue gas, and the composition and / or spray flow rate of the spray water in the latent heat recovery module are dynamically adjusted according to the concentration of pollutants.

[0014] In some embodiments, the method further includes: Acquire environmental parameters and identify the current seasonal operating conditions based on these parameters; Adjust the threshold for determining the target operating mode or the switching strategy based on the identified seasonal operating conditions.

[0015] In some embodiments, the method further includes: During the start-up and shutdown of the unit, the trend of flue gas operating conditions is predicted based on the preset start-up and shutdown flue gas parameter change model. Based on the changing trends, adjust the target operating mode and the operating parameters of each recycling module in advance.

[0016] In summary, in the embodiments of this invention, the flue gas waste heat recovery device integrates three major functional modules—sensible heat recovery, latent heat recovery, and liquid circulation—through a vertical integrated structure, and incorporates a flue gas path switching module consisting of a bypass pipe and a switching valve. By flexibly adapting to flue gas with different temperatures and humidity levels through three modes, it achieves synergistic or independent efficient recovery of sensible and latent heat, improving heat recovery efficiency. The dry-wet separation design ensures that flue gas flows only through the necessary chambers in each mode, completely avoiding corrosion and blockage of non-working modules and extending equipment lifespan. It significantly reduces the footprint and pipeline resistance, while the latent heat module also has a deep cleaning and purification function, simultaneously removing pollutants while recovering energy.

[0017] The flue gas waste heat recovery method constructs a closed-loop control system of perception-prediction-decision-execution. Based on real-time flue gas parameters, pollutant concentrations, and environmental climate information, this method dynamically determines the optimal operating mode (pure sensible heat, pure latent heat, or total heat). Through seasonal strategy adjustments and predictive feedforward control during start-up and shutdown, the system automatically maintains high efficiency and stability across all operating conditions and time periods, maximizing transient energy recovery and protecting equipment. The composition and flow rate of the spray liquid are dynamically adjusted according to pollutant concentrations, minimizing reagent consumption while ensuring stable emissions compliance. Complex logic is embedded in the control system, enabling intelligent operation from one-button start-up and shutdown to all-weather adaptive optimization, significantly reducing operational difficulty and labor costs. Attached Figure Description

[0018] Figure 1 This is a first schematic diagram of a multi-mode switching flue gas waste heat recovery device according to an embodiment of the present invention.

[0019] Figure 2 This is a second schematic diagram of a multi-mode switching flue gas waste heat recovery device according to an embodiment of the present invention.

[0020] Figure 3 This is a top view schematic diagram of a multi-mode switching flue gas waste heat recovery device according to an embodiment of the present invention.

[0021] Figure label: 1-Tower body; 11-Inlet pipe; 12-Exhaust pipe; 13-Guide pipe; 101-Flue gas inlet; 102-Flue gas outlet; 103-First chamber; 104-Second chamber; 105-Third chamber; 21-Plate heat exchanger; 22-Inlet pipe; 23-Outlet pipe; 31-Packing layer; 32-Spray unit; 33-Gas-liquid separation network; 34-Water tank; 341-Overflow pipe; 342-Sewage pipe; 343-Late heat recovery pipe; 35-Circulating pump; 351-Water supply pipe; 36-Agitator pump; 41-First bypass pipe; 42-Second bypass pipe; 43-First switching valve; 44-Second switching valve; 45-Third switching valve. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] The following describes a multi-mode switching flue gas waste heat recovery device according to an embodiment of the present invention with reference to the accompanying drawings.

[0024] like Figures 1 to 3 As shown, the multi-mode switching flue gas waste heat recovery device of this invention includes: tower body 1, sensible heat recovery module, latent heat recovery module and flue gas path switching module.

[0025] The tower body 1 has a flue gas inlet 101 at its bottom and a flue gas outlet 102 at its top. A sensible heat recovery module is located inside the tower body 1 and is used for indirect heat exchange with the flue gas to recover sensible heat. A latent heat recovery module is also located inside the tower body 1 and is used for recovering latent heat in the flue gas through direct gas-liquid contact; at least a portion of the latent heat recovery module is located above the sensible heat recovery module.

[0026] The tower body 1 adopts a longitudinal stacked layout, with a flue gas inlet 101 at the bottom and a flue gas outlet 102 at the top. It integrates a sensible heat recovery module and a latent heat recovery module, and the latent heat recovery module is located at least partially above the sensible heat recovery module (such as the latent heat module being located directly above the sensible heat module or overlapping in some areas), which achieves compact space and avoids the problems of long pipelines and large footprint of traditional distributed devices.

[0027] Sensible heat recovery modules recover high-temperature sensible heat from flue gas through indirect heat exchange (such as plate heat exchangers and finned tubes) (no contact with flue gas required, avoiding corrosion), suitable for preliminary cooling before high-humidity flue gas or independent heat recovery for low-humidity flue gas. Latent heat recovery modules recover the latent heat of condensation of water vapor in flue gas through direct gas-liquid contact (such as spraying and packing) (contact with flue gas required, allowing for simultaneous pollutant purification), suitable for deep heat recovery of medium-low temperature and high-humidity flue gas.

[0028] The flue gas path switching module includes a bypass pipe assembly located between the sensible heat recovery module and the latent heat recovery module, and a switching valve assembly located on the bypass pipe assembly. The bypass pipe assembly and the switching valve assembly are configured to guide the flue gas to selectively flow through the sensible heat recovery module, the latent heat recovery module, or sequentially through both.

[0029] The path switching logic of the flue gas path switching module includes: When only sensible heat recovery is performed, the latent heat recovery module is turned off. After heat exchange in the sensible heat recovery module, the flue gas flows directly to the flue gas outlet 102 through the bypass pipe (without passing through the latent heat recovery module). This maximizes the sensible heat recovery efficiency and avoids low-humidity flue gas entering the latent heat module, which would lead to low heat exchange efficiency.

[0030] When only latent heat recovery is needed, the sensible heat recovery module is shut down, and the flue gas directly enters the latent heat recovery module (without flowing through the sensible heat recovery module). This efficiently recovers latent heat and synergistically purifies pollutants, reducing energy consumption from unnecessary modules.

[0031] During total heat recovery, the flue gas flows sequentially through the sensible heat recovery module (cooling) and the latent heat recovery module (condensation), and then exits from the flue gas outlet 102. Sensible and latent heat work together to maximize the total heat recovery efficiency.

[0032] In embodiments of the present invention, the path is dynamically switched according to the temperature and humidity of the flue gas to avoid a single module operating under inefficient conditions (such as low-humidity flue gas flowing through the latent heat recovery module, resulting in wasted heat exchange area). High-humidity flue gas passes through the sensible heat and latent heat modules in sequence, which can reduce the flue gas temperature to below the dew point, fully recover latent heat, improve heat recovery efficiency, and reduce energy waste.

[0033] Sensible and latent heat recovery modules are stacked vertically, eliminating the long pipelines of traditional decentralized devices, thus reducing floor space and pipeline costs. Switching valve groups ensure that flue gas only flows through necessary modules (e.g., in pure sensible heat mode, flue gas does not enter the latent heat recovery module), reducing flow resistance and reducing the power consumption of the induced draft fan at flue gas outlet 102.

[0034] Low-humidity / high-temperature flue gas does not flow through the latent heat recovery module (to prevent dry flue gas from washing over the spray unit 32 and causing scaling), and high-humidity / low-temperature flue gas does not flow through the sensible heat recovery module (to reduce condensate accumulation and blockage in the plate heat exchanger). Alkaline agents (such as NaOH) can be added to the spray water of the latent heat recovery module to absorb SO2 and NOx while recovering latent heat, reducing the load on subsequent environmental protection equipment and minimizing the corrosion of downstream equipment by pollutants.

[0035] By switching valve groups, the system can quickly respond to fluctuations in flue gas parameters (such as drastic changes in temperature and humidity during the start-up and shutdown of waste incinerators), avoiding module overload or inefficient operation. In the event of a single module failure, it can switch to another module for independent operation (such as switching to pure latent heat mode when the sensible heat recovery module leaks), ensuring continuous operation of the unit.

[0036] In some embodiments, such as Figure 1 and Figure 2As shown, the bottom of the tower body 1 has a first chamber 103 and a second chamber 104 arranged in parallel, and the upper middle part of the tower body 1 has a third chamber 105. The first chamber 103 is connected to the third chamber 105 via a guide pipe 13, and the second chamber 104 is directly connected to the third chamber 105. The sensible heat recovery module is located in the first chamber 103, and the latent heat recovery module is located in the second chamber 104 and the third chamber 105. The tower body 1 is provided with a flue gas inlet pipe 11 and a flue gas outlet pipe 12. One end of the flue gas inlet pipe 11 is connected to the first chamber 103, and the other end of the flue gas inlet pipe 11 is a flue gas inlet 101. One end of the flue gas outlet pipe 12 is connected to the third chamber 105, and the other end of the flue gas outlet pipe 12 is a flue gas outlet 102.

[0037] The first chamber 103 serves as a sensible heat recovery chamber, and a sensible heat recovery module such as a plate heat exchanger 21 can be installed inside the first chamber 103. The first chamber 103 is an indirect heat exchange environment. The first chamber 103 introduces the original flue gas through the flue gas inlet pipe 11, and the flue gas after heat exchange is discharged to the third chamber 105 through the guide pipe 13.

[0038] The second chamber 104 serves as a collection and buffer chamber (i.e., water tank 34) for the spray circulating liquid. It collects the spray liquid falling from the upper third chamber 105 and performs storage, buffering, chemical dosing, and hot water output. The flue gas itself does not flow directly through this chamber. The second chamber 104 is directly connected to the upper third chamber 105, forming a continuous space for liquid to fall and gas to rise. A submersible pump can be installed in the second chamber 104 to deliver the liquid to the spray unit 32 at the top of the third chamber 105.

[0039] The third chamber 105 serves as the main reaction chamber for latent heat recovery and gas-liquid contact. Both latent heat and total heat flue gas are ultimately processed and discharged in this chamber. The third chamber 105 receives flue gas from the first chamber 103 (after sensible heat exchange) through the guide pipe 13. The third chamber 105 can also receive raw flue gas that does not pass through the first chamber 103 directly through a bypass. The bottom of the third chamber 105 is connected to the second chamber 104, forming a natural liquid return channel. The top of the third chamber 105 is connected to the exhaust pipe 12.

[0040] In an embodiment of the invention, the first chamber 103 is a completely independent dry chamber, connected to the wet areas (second and third chambers) only by a guide pipe 13 and isolated by a valve. This ensures that the surface of the sensible heat exchanger remains absolutely dry in non-total heat mode, completely avoiding low-temperature corrosion and wet ash caking. The flue gas mainly contacts the spray liquid droplets in the third chamber 105, without entering the second chamber 104 containing a large amount of liquid, reducing the water content of the flue gas and minimizing the impact of the flue gas on the liquid level fluctuations in the second chamber 104. The first chamber 103, second chamber 104, and third chamber 105 are arranged in a parallel and stacked layout, forming a compact vertical structure with clear functional zones (dry heat exchange, wet reaction, and liquid storage), facilitating design, manufacturing, and maintenance.

[0041] Optionally, such as Figures 1 to 3 As shown, the bypass pipe group includes a first bypass pipe 41 and a second bypass pipe 42, and the switching valve group includes a first switching valve 43, a second switching valve 44 and a third switching valve 45.

[0042] One end of the first bypass pipe 41 is connected to the flue gas inlet pipe 11, and the other end of the first bypass pipe 41 is connected to the third chamber 105. The first bypass pipe 41 establishes a direct channel that bypasses the first chamber 103 (sensible heat recovery module), so that the original flue gas can enter the third chamber 105 directly for latent heat recovery or simply serve as a channel without passing through the sensible heat recovery module.

[0043] One end of the second bypass pipe 42 is connected to the guide pipe 13, and the other end of the first bypass pipe 41 is connected to the exhaust pipe 12. The second bypass pipe 42 establishes a direct channel that bypasses the third chamber 105 (latent heat reaction zone), so that the flue gas after heat exchange in the first chamber 103 can be discharged directly without entering the third chamber 105.

[0044] The first switching valve 43 is located at the connection between the first bypass pipe 41 and the smoke inlet pipe 11, controlling whether the original flue gas is diverted into the first bypass pipe 41. The second switching valve 44 is located at the connection between the second bypass pipe 42 and the guide pipe 13, controlling whether the flue gas exiting the first chamber 103 is diverted into the second bypass pipe 42. The third switching valve 45 is located at the connection between the second bypass pipe 42 and the smoke exhaust pipe 12, controlling whether the flue gas in the second bypass pipe 42 can flow into the smoke exhaust pipe 12.

[0045] When the device operates in pure sensible heat recovery mode, the flue gas flows directly into the first chamber 103 through the inlet pipe 11 for sensible heat recovery, and then flows sequentially through the guide pipe 13 and the second bypass pipe 42 to the exhaust pipe 12 to be discharged from the tower body 1. After completing heat exchange in the dry first chamber 103, the flue gas is directly discharged through the bypass, completely avoiding the humid third chamber 105, achieving absolute dry and wet separation, protecting the sensible heat recovery module and avoiding ineffective resistance.

[0046] When the device operates in pure latent heat recovery mode, the flue gas flows sequentially into the third chamber 105 through the inlet pipe 11 and the first bypass pipe 41 for latent heat recovery, and then exits the tower body 1 through the exhaust pipe 12. The high-temperature flue gas bypasses the easily scaled sensible heat recovery module and directly enters the wet spray section for rapid cooling and latent heat recovery, avoiding the risk of corrosion and ash accumulation of the sensible heat recovery module under high temperature and high humidity conditions.

[0047] When the device operates in total heat recovery mode, the flue gas flows into the first chamber 103 through the inlet pipe 11 for sensible heat recovery, then flows through the guide pipe 13 to the third chamber 105 for latent heat recovery, and finally exits the tower body 1 through the exhaust pipe 12. The flue gas undergoes dry and wet stage recovery in sequence, realizing the step utilization of heat energy and achieving the highest total heat recovery efficiency.

[0048] In the embodiments of the present invention, the flue gas follows the shortest necessary path in each mode. For example, in the pure sensible heat mode, the flue gas path is the shortest and completely avoids resistance components such as the packing layer 31 and the spray layer, resulting in the minimum total pressure loss of the system and the lowest power consumption of the induced draft fan.

[0049] In some embodiments, such as Figure 1 As shown, the sensible heat recovery module includes a plate heat exchanger 21. The flow channel of the plate heat exchanger 21 is a multi-pass S-shaped narrow slit flow channel. The plate heat exchanger 21 is connected to an external cold water source through an inlet pipe 22, so that the external cold water source enters the plate heat exchanger 21 through the inlet pipe 22 to indirectly exchange heat with the flue gas. The plate heat exchanger 21 is connected to an external heat utilization system through an outlet pipe 23, so that the water that absorbs the sensible heat of the flue gas is transported to the external heat utilization system through the outlet pipe 23.

[0050] Flue gas flows in one channel of the plate heat exchanger 21, while cooling water flows in the other channel. The two are physically isolated through metal plates, ensuring that the recovered sensible heat is output as clean hot water, while preventing flue gas from contaminating the cooling water and preventing the cooling water from entering the flue gas system.

[0051] The cooling water flow direction is opposite to the flue gas flow direction (i.e., the high-temperature flue gas inlet corresponds to the cooling water outlet, and the low-temperature flue gas outlet 102 corresponds to the cooling water inlet). This arrangement maximizes the average temperature difference across the entire heat exchange surface, thereby significantly improving heat exchange efficiency.

[0052] An external cold water source (such as ambient temperature tap water or circulating return water) is pumped into the cooling water channel of the plate heat exchanger 21 through the inlet pipe 22. After absorbing the sensible heat released by the flue gas, the temperature rises and becomes hot water. It is then transported to an external heat utilization system (such as heating network, process heating, lithium bromide refrigeration unit, etc.) through the outlet pipe 23.

[0053] Multi-pass S-shaped flow channels refer to the flow of flue gas (or water flow) within the plate heat exchanger 21 being divided by guide vanes, repeatedly turning 180 degrees to form a continuous S-shaped forward path. The S-shaped path increases the flow length of the flue gas within a limited space, allowing for longer contact time with the plates and more thorough heat exchange. Narrow-slit flow channels refer to flow channels with very small gaps between adjacent plates (typically only a few millimeters), resulting in a higher heat exchange area per unit volume and a more compact equipment structure.

[0054] Furthermore, the connection points between the flue gas inlet pipe 11 and the first chamber 103, and between the guide pipe 13 and the first chamber 103, are located on opposite sides of the plate heat exchanger 21. Flue gas enters from the bottom (or top) of one side of the plate heat exchanger and exits from the top (or bottom) of the other side, ensuring that the flue gas fills and flows through all the flow channels of the entire plate heat exchanger 21, avoiding short circuits or flow dead zones, and guaranteeing effective utilization of the heat exchange area.

[0055] In some embodiments, such as Figures 1 to 3 As shown, the latent heat recovery module includes a packing layer 31, a spray unit 32, and a gas-liquid separation net 33 arranged sequentially from bottom to top in the third chamber 105, so that the flue gas can fully contact the cooling water sprayed by the spray unit 32 in the packing layer 31 to recover the latent heat of the flue gas. The gas-liquid separation net 33 is used to separate the liquid droplets carried in the flue gas after the latent heat is recovered.

[0056] The spray unit 32 consists of multiple spiral nozzles, etc., and its function is to atomize the circulating water into fine droplets to maximize the gas-liquid contact area.

[0057] The packing layer 31 is located below the spray unit 32. It is composed of a large number of corrosion-resistant ceramic or plastic packing balls (or structured packing), providing a contact surface for falling droplets and rising flue gas, disrupting the laminar flow of flue gas and droplets, and enhancing heat and mass transfer. The flue gas is cooled to below the dew point in the packing layer 31, and water vapor condenses on the surface of the packing and droplets, releasing a large amount of latent heat. At the same time, the condensation process has a strong dissolution and absorption effect on pollutants such as SO2 and NOx.

[0058] The gas-liquid separation mesh 33 is composed of multiple layers of fine wire mesh or baffles. Its principle is that when flue gas carrying liquid droplets passes through the mesh, the droplets collide with the wire mesh due to inertia and agglomerate and fall, thereby efficiently separating the moisture in the flue gas, ensuring that the discharged flue gas is dry and clean, and preventing water corrosion of the induced draft fan and white smoke from the chimney.

[0059] The circulating water is atomized by nozzles and sprayed downwards, where it comes into full countercurrent contact with the flue gas entering from the bottom of the third chamber 105 in the packing layer 31, completing heat and mass exchange. The heat-exchanged, heated droplets that have absorbed pollutants fall down, while the purified and cooled flue gas rises and is discharged after being demisted by the gas-liquid separation network 33.

[0060] The latent heat recovery module also includes a water tank 34, a circulation pump 35, and a stirring pump 36. The water tank 34 is located in the second chamber 104 so that the spray water for recovering the latent heat of the flue gas falls into the water tank 34. Parts of the circulation pump 35 and the stirring pump 36 are located in the water tank 34. The water in the water tank 34 is transported to the spray unit 32 through the circulation pump 35 and pipeline. The stirring pump 36 is used to stir the sludge deposited at the bottom of the water tank 34.

[0061] Water tank 34 is located in the second chamber 104 and collects the spray water that falls back from the third chamber 105. Circulation pump 35 (usually a submersible pump) is installed in water tank 34, pressurizes the water in water tank 34, and delivers it through pipelines to the top spray unit 32 to drive the entire circulation.

[0062] The stirring pump 36 is used to agitate the deposited sludge and prevent solid sediment from caking, ensuring uniform concentration at the bottom of the water tank 34, avoiding localized corrosion and clogging of the drain pipe 342, and enabling the added reagents (such as alkaline solution) to mix quickly and evenly with the circulating water, maintaining a stable pH value for efficient absorption of acidic pollutants.

[0063] The water tank 34 is equipped with an overflow pipe 341, a drain pipe 342 and a latent heat recovery pipe 343. The overflow pipe 341 is used to control the water level of the water tank 34, the drain pipe 342 is used to discharge the sludge at the bottom of the water tank 34, and the latent heat recovery pipe 343 is used to output hot water after recovering the latent heat of the flue gas. A water supply pipe 351 is provided on the pipeline between the circulating pump 35 and the spray unit 32. The water supply pipe 351 is used to replenish fresh cold water.

[0064] The water supply pipe 351 connects to the outlet pipe of the circulating pump 35 to replenish the water lost due to evaporation, sewage discharge, and hot water output, and to introduce low-temperature cold water to maintain system thermal balance and spray cooling effect. The latent heat recovery pipe 343 extends from the top of the water tank 34 to continuously output hot water whose temperature has increased after recovering the latent heat of the flue gas for external use. The overflow pipe 341 is located at the highest water level in the water tank 34 to automatically maintain a safe liquid level and prevent the water tank 34 from overflowing. The sewage pipe 342 is located at the lowest point of the bottom of the water tank 34 to periodically or continuously discharge concentrated wastewater / sludge rich in dissolved salts, suspended solids, and reaction products, controlling the quality of the circulating water and preventing scaling and corrosion.

[0065] The following describes a multi-mode switching flue gas waste heat recovery method according to an embodiment of the present invention. This method is applicable to the multi-mode switching flue gas waste heat recovery device described in the above embodiments.

[0066] The multi-mode switching flue gas waste heat recovery method of this invention includes: S1: Real-time acquisition of flue gas operating parameters. High-precision, corrosion-resistant online sensors are installed at key nodes of the unit. For example, temperature and humidity sensors are installed at flue gas inlet 101 to acquire the core thermal parameters of the raw flue gas. Pollutant concentration sensors (such as SO2 and NOx analyzers) are installed before flue gas inlet 101 or the latent heat recovery module. Environmental temperature and humidity sensors are installed to provide data for seasonal strategies. Auxiliary temperature sensors are installed at the outlets of the sensible heat module and the latent heat module to verify heat transfer effects and perform model calibration.

[0067] Sensor signals are converted into standard signals by transmitters and transmitted to a central controller (such as a PLC or DCS). The data acquisition frequency is typically ≥ 1 time / second to ensure real-time control.

[0068] S2: Based on operating parameters, determine the current target operating mode, which includes pure sensible heat recovery mode, pure latent heat recovery mode, and total heat recovery mode.

[0069] For example, the operating parameters of flue gas include at least flue gas temperature and flue gas humidity.

[0070] When the flue gas temperature is higher than the first temperature threshold and the flue gas humidity is lower than the first humidity threshold, the target operating mode is determined to be the pure sensible heat recovery mode. This corresponds to the initial start-up of waste incineration or certain dry industrial kiln flue gas. At this time, the flue gas has low moisture content, low latent heat, and high temperature, making it suitable for efficient sensible heat recovery on its own, thus avoiding corrosion of the sensible heat recovery module by wet flue gas.

[0071] When the flue gas temperature is below the second temperature threshold and the flue gas humidity is above the second humidity threshold, the target operating mode is determined to be the pure latent heat recovery mode. This corresponds to the later stages of waste incineration operation or high-humidity, low-temperature exhaust gas. At this time, the sensible heat grade is not high, but the latent heat is abundant, and the flue gas may be highly acidic. Directly entering the latent heat recovery module can efficiently recover latent heat and synergistically purify it, while avoiding condensation and corrosion of high-temperature, high-humidity flue gas within the sensible heat recovery module.

[0072] When the flue gas temperature is between the second and first temperature thresholds, and the flue gas humidity is higher than the second humidity threshold, the target operating mode is determined to be the total heat recovery mode. The flue gas has both high-grade sensible heat and abundant latent heat (such as during the stable operation period of waste incineration). At this time, by passing through the two modules in sequence, the total heat energy recovery can be maximized.

[0073] Furthermore, this step can integrate more complex algorithms, such as fuzzy control, to handle situations where temperature and humidity are in a fuzzy boundary zone, achieving a smooth transition between modes. Multi-objective optimization combines pollutant concentration, hot water demand temperature, ambient temperature (seasonal factors), and even energy prices to perform comprehensive benefit calculations and select the most economical mode.

[0074] S3: Based on the target operating mode, generate control commands to drive the switching valve group to operate, so that the flue gas flows along the path corresponding to the target operating mode, and control the start and stop of the corresponding recovery module.

[0075] The PLC sends precise switching commands to the first switching valve 43, the second switching valve 44, the third switching valve 45 (or the corresponding valve group) according to the selected mode.

[0076] For example, if the system is determined to be in pure sensible heat mode, the control commands are as follows: the first switching valve 43 directly sends the flue gas into the first chamber 103; the second switching valve 44 connects the guide pipe 13 and the second bypass pipe 42; and the third switching valve 45 connects the second bypass pipe 42 and the exhaust pipe 12. The flue gas path is rigidly locked as sensible heat recovery module → second bypass pipe 42 → exhaust pipe 12.

[0077] Module start / stop control includes: The sensible heat recovery module controls the start and stop of its cooling water circulation pump 35 and the opening of the regulating valve of the inlet pipe 22 to regulate the water flow and output water temperature.

[0078] The latent heat recovery module controls the start and stop of the circulating pump 35, the opening degree of the spray pipeline valves (adjusting the spray volume), and the start and stop of the dosing pump (based on pH or pollutant concentration feedback).

[0079] In pure sensible heat mode, the circulating pump 35 and spray valve of the latent heat module should be closed to prevent dry flue gas from entering the humid environment.

[0080] In pure latent heat mode, the cooling water system of the sensible heat module should be shut off.

[0081] In total heat recovery mode, the two systems operate simultaneously and are coordinated and adjusted according to the inlet parameters (such as adjusting the outlet water temperature of the sensible heat section to provide the best air intake conditions for the latent heat section).

[0082] In embodiments of the present invention, traditional devices operate in a fixed mode, resulting in a sharp drop in efficiency when deviating from design conditions. This method, through real-time sensing and dynamic switching, ensures that the device always operates in the optimal or suboptimal mode under the current conditions, maximizing the average heat recovery efficiency throughout the year.

[0083] The method's embedded protective logic (such as preventing high-humidity flue gas from entering the sensible heat module) can proactively prevent damage to the equipment, such as low-temperature corrosion and ash accumulation, thus ensuring the long-term reliable operation of the core equipment from a control strategy perspective.

[0084] Complex path switching and equipment interlocking logic are embedded in the program and executed automatically by the controller, avoiding human error. The system has a fast response time (≤1 second), can smoothly cope with fluctuations in operating conditions, and operates more stably.

[0085] This method enables the same set of hardware equipment to flexibly cope with various complex scenarios such as furnace start-up and shutdown, fuel changes, seasonal changes, and production load fluctuations, thus expanding the applicability of the equipment and reducing the cost of repeated investment by users for different operating conditions.

[0086] In some embodiments, the operating parameters of the flue gas also include the concentration of pollutants in the flue gas, and the composition and / or spray flow rate of the spray water in the latent heat recovery module are dynamically adjusted according to the concentration of pollutants.

[0087] An online flue gas analyzer (such as a non-dispersive infrared spectroscopy (NDIR) or a differential ultraviolet absorption spectroscopy (DOAS) instrument) is installed on the flue gas inlet 101 or before the latent heat recovery module inlet to monitor the concentration signals of target pollutants such as SO2, NOx, and HCl in real time. This concentration signal, along with the flue gas temperature and humidity signals, is transmitted to the central controller to form a more comprehensive dataset for judging operating conditions. This ensures that the latent heat recovery efficiency meets environmental protection requirements while guaranteeing pollutant removal efficiency and achieving economical operation.

[0088] For example, the dynamic adjustment of the spray solution composition. When the pollutant level rises and exceeds a preset threshold, the control system determines that the current spray solution's absorption capacity may be insufficient. The controller sends a command to the dosing system (such as a NaOH solution dosing pump) to increase the pump's frequency or opening, thereby increasing the dosage of alkaline agents and thus raising the pH and alkalinity of the circulating spray solution.

[0089] Increasing the alkalinity of the spray solution can enhance its chemical absorption driving force and reaction rate for acidic gases (SO2, HCl, etc.), ensuring that the outlet emission concentration still meets the standards under high pollutant loads. Conversely, when the pollutant concentration decreases, the dosage should be reduced to avoid waste of chemicals and excessive salinity in the circulating water.

[0090] Dynamic adjustment of spray flow rate. Changes in pollutant concentration can also be addressed by adjusting the physical conditions of gas-liquid contact. Increased pollutant levels mean a larger gas-liquid mass transfer area or a longer contact time is required. The controller adjusts the frequency converter of the latent heat recovery module's circulating pump 35 or the regulating valve on the spray pipeline to increase the total flow rate of the spray water.

[0091] Higher spray flow rates mean an increased amount of liquid per unit volume of flue gas, providing more absorbent. Faster flow rates allow for more rapid renewal of the liquid film on the packing surface, maintaining its absorption activity and preventing failure due to liquid film saturation. Greater spray intensity can slightly alter the fluid dynamics within the tower, enhancing turbulence and improving mass transfer.

[0092] The spray solution composition and spray flow rate are synergistically regulated. Composition regulation (dosing) is precise and chemically driven, used to address slow changes in concentration; while flow rate regulation is rapid and physically driven, used to address instantaneous concentration surges. Both can be used independently or in combination.

[0093] In some embodiments, the method of the present invention further includes: Step 1: Obtain environmental parameters and identify the current seasonal operating conditions based on the environmental parameters.

[0094] Ambient temperature and humidity sensors are installed in the area where the device is located to monitor atmospheric temperature and humidity in real time. The device's control system can also access weather forecast data, historical climate data, or use a real-time clock to obtain monthly information for auxiliary judgment.

[0095] Thermodynamics and seasonal demand are identified based on environmental parameters. The controller's built-in algorithm model categorizes data into several typical operating modes based on the data flow, such as: Winter operating conditions: characterized by cold environment and high demand for heating.

[0096] Summer operating conditions: characterized by hot environment, with potentially greater demand for cooling or process cooling and less demand for heating.

[0097] Transitional season (spring and autumn) conditions: moderate temperature, unclear heat demand.

[0098] Rainy season / high humidity conditions: Humidity remains above the high threshold, and the ambient air moisture content is extremely high.

[0099] Step 2: Adjust the judgment threshold or switching strategy of the target operating mode based on the identified seasonal operating conditions.

[0100] Adjust the mode determination threshold (taking temperature and humidity thresholds as an example): In winter, the system prioritizes generating more heat, especially high-temperature heat. The trigger temperature threshold for the pure latent heat mode is lowered, while the priority of the total heat recovery mode is increased. For example, under standard settings, the pure latent heat mode is triggered below 120°C; however, in winter, this threshold is adjusted to 100°C. As long as the flue gas temperature is above 100°C, the system is more inclined to allow the flue gas to pass through the sensible heat recovery module (even with high humidity) to recover more high-grade sensible heat and produce more, hotter water for heating.

[0101] In summer, the strategy prioritizes efficient cooling and balanced heat output. This includes increasing the intensity of spray cooling in pure latent heat or total heat recovery modes. It also involves raising the trigger humidity threshold in pure sensible heat modes to allow the unit to enter wet mode earlier, utilizing evaporative cooling to rapidly reduce flue gas temperature and alleviate the heat load on downstream equipment.

[0102] Adjusting the switching strategy (more complex logic changes): In rainy season / high humidity environments, the system introduces a dehumidification priority sub-strategy. When the ambient humidity is extremely high, even if the flue gas temperature is moderate, the total heat recovery mode is prioritized, and the condensation of the latent heat section is enhanced. The aim is to condense the water vapor in the flue gas as much as possible, reduce visual pollution from white smoke, and recover more condensate.

[0103] Seasonal adjustments to start-up and shutdown strategies are made. In winter, when the ambient temperature is low and the flue gas cools down quickly, the unit will switch from the start-up mode to a heat-generating operation mode earlier. In summer, the low-load operation mode may be extended to avoid generating too much useless heat.

[0104] In some embodiments, the method of the present invention further includes: During the start-up and shutdown of the unit, the trend of flue gas operating conditions is predicted based on a pre-set start-up and shutdown flue gas parameter change model. This model describes the typical trajectory of key parameters such as flue gas temperature, humidity, and flow rate over time during standard start-up (from cold ignition to full load) and shutdown (from full load to shutdown).

[0105] By collecting massive amounts of data from multiple start-ups and shutdowns of the same furnace type or similar processes, statistical analysis and regression fitting are performed to generate a fingerprint curve for the specific device. Based on the principles of combustion and heat transfer, combined with the structural parameters of the boiler / kiln, a simplified physical model is established to calculate the theoretical trend of change.

[0106] The model can be one or more curves (or functions). For example, a start-up model represents the process of flue gas temperature rising from ambient temperature to the rated temperature (e.g., 200°C) over time, typically exhibiting an S-shaped increase. A shutdown model represents the process of flue gas temperature decreasing from the rated temperature. The model also incorporates humidity changes (extremely dry at start-up, becoming wetter later due to waste drying) and pollutant concentration changes (unstable combustion at start-up may produce high concentrations of CO and hydrocarbons).

[0107] Based on the changing trends, the target operating mode and the operating parameters of each recovery module are adjusted in advance. The controller no longer waits for the sensors to measure changes before taking action, but instead issues control commands in advance based on the predicted trends.

[0108] Example of furnace start-up process: Initial phase: The model predicts that the temperature will rise from 80℃ to 150℃ in the next 2 minutes. The system starts in advance (before the temperature reaches the threshold) from the pure latent heat preparation mode, gradually starting the cooling water circulation of the sensible heat module at a small flow rate to preheat the heat exchanger and avoid thermal shock.

[0109] Heating Phase: The model indicates the temperature will exceed 150°C in 5 minutes while humidity remains low. One minute prior, the system begins shutting off the latent heat module spray and prepares to switch valves. When the actual temperature reaches 150°C, the valves are in place, seamlessly switching to pure sensible heat mode to maximize the recovery of initial high-temperature sensible heat.

[0110] Stabilization phase: The model predicts that humidity will begin to rise. The system calculates in advance and slowly increases the preparation work of the latent heat module. When the temperature and humidity simultaneously meet the conditions of the total heat recovery mode, it is in the optimal state and smoothly switches to the total heat recovery mode.

[0111] Example of a shutdown process: The model predicts that as the load begins to decrease, the flue gas temperature will drop. The system proactively reduces the cooling water flow rate of the sensible heat module and activates the latent heat module spray system in advance to prevent condensation on the sensible heat module due to delayed switching during a sudden temperature drop.

[0112] When the model predicts that the temperature will be lower than the lower limit of the pure sensible heat mode, the system will switch from the total heat mode to the pure latent heat mode in advance to ensure the continuity of heat recovery.

[0113] Parameter Coordination Adjustment: Before and after mode switching, parameters such as the frequency of the circulating pump 35, the dosage, and the water replenishment rate are also adjusted in advance according to the predicted load to ensure a smooth transition of the system status.

[0114] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0115] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0116] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0117] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0118] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0119] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A multi-mode switching flue gas waste heat recovery device, characterized in that, include: The tower body has a flue gas inlet at its bottom and a flue gas outlet at its top; A sensible heat recovery module is located inside the tower and is used to indirectly exchange heat with the flue gas to recover sensible heat. A latent heat recovery module is disposed inside the tower body and is used to recover latent heat in flue gas through direct gas-liquid contact. At least a portion of the latent heat recovery module is located above the sensible heat recovery module. A flue gas path switching module includes a bypass pipe assembly disposed between the sensible heat recovery module and the latent heat recovery module, and a switching valve assembly disposed on the bypass pipe assembly. The bypass pipe assembly and the switching valve assembly are configured to guide flue gas to selectively flow through the sensible heat recovery module, the latent heat recovery module, or sequentially through both.

2. The multi-mode switching flue gas waste heat recovery device according to claim 1, characterized in that, The bottom of the tower has a first chamber and a second chamber arranged in parallel, and the upper middle part of the tower has a third chamber. The first chamber is connected to the third chamber via a guide pipe, and the second chamber is directly connected to the third chamber. The sensible heat recovery module is located in the first chamber, and the latent heat recovery module is located in the second chamber and the third chamber. The tower body is provided with a smoke inlet pipe and a smoke outlet pipe. One end of the smoke inlet pipe is connected to the first chamber, and the other end of the smoke inlet pipe is the flue gas inlet. One end of the smoke outlet pipe is connected to the third chamber, and the other end of the smoke outlet pipe is the flue gas outlet.

3. The multi-mode switching flue gas waste heat recovery device according to claim 2, characterized in that, The sensible heat recovery module includes a plate heat exchanger. The flow channel of the plate heat exchanger is a multi-pass S-shaped narrow slit flow channel. The plate heat exchanger is connected to an external cold water source through an inlet pipe, so that the external cold water source enters the plate heat exchanger through the inlet pipe and indirectly exchanges heat with the flue gas. The plate heat exchanger is connected to an external heat utilization system through an outlet pipe, so that the water that absorbs the sensible heat of the flue gas is transported to the external heat utilization system through the outlet pipe. The connection between the flue gas inlet pipe and the first chamber, and the connection between the guide pipe and the first chamber, are located on opposite sides of the plate heat exchanger.

4. The multi-mode switching flue gas waste heat recovery device according to claim 2, characterized in that, The latent heat recovery module includes a packing layer, a spraying unit, and a gas-liquid separation net arranged sequentially from bottom to top in the third chamber, so that the flue gas can fully contact the cooling water sprayed by the spraying unit in the packing layer to recover the latent heat of the flue gas. The gas-liquid separation net is used to separate the liquid droplets carried in the flue gas after the latent heat is recovered. The latent heat recovery module also includes a water tank, a circulation pump, and a stirring pump. The water tank is located in the second chamber so that the spray water for recovering the latent heat of the flue gas falls into the water tank. Parts of the circulation pump and part of the stirring pump are located in the water tank. The water in the water tank is transported to the spray unit through the circulation pump and pipeline. The stirring pump is used to stir the sludge deposited at the bottom of the water tank. The water tank is equipped with an overflow pipe, a drain pipe, and a latent heat recovery pipe. The overflow pipe is used to control the water level in the water tank. The drain pipe is used to discharge the sludge at the bottom of the water tank. The latent heat recovery pipe is used to output hot water after recovering the latent heat of the flue gas. A water supply pipe is provided on the pipeline between the circulating pump and the spray unit. The water supply pipe is used to replenish fresh cold water.

5. The multi-mode switching flue gas waste heat recovery device according to claim 2, characterized in that, The bypass pipe assembly includes a first bypass pipe and a second bypass pipe. One end of the first bypass pipe is connected to the smoke inlet pipe, and the other end of the first bypass pipe is connected to the third chamber. One end of the second bypass pipe is connected to the guide pipe, and the other end of the first bypass pipe is connected to the smoke exhaust pipe. The switching valve assembly includes a first switching valve, a second switching valve, and a third switching valve. The first switching valve is located at the connection between the first bypass pipe and the smoke inlet pipe. The second switching valve is located at the connection between the second bypass pipe and the guide pipe. The third switching valve is located at the connection between the second bypass pipe and the smoke exhaust pipe.

6. A method for recovering waste heat from flue gas using a multi-mode switching mechanism, characterized in that, The method is applicable to a multi-mode switching flue gas waste heat recovery device according to any one of claims 1-5, and the method includes: Real-time acquisition of flue gas operating parameters; Based on operating parameters, determine the current target operating mode, which includes pure sensible heat recovery mode, pure latent heat recovery mode, and total heat recovery mode. Based on the target operating mode, control commands are generated to drive the switching valve group to operate, so that the flue gas flows along the path corresponding to the target operating mode, and to control the start and stop of the corresponding recovery module.

7. The multi-mode switching flue gas waste heat recovery method according to claim 6, characterized in that, The operating parameters of flue gas include at least flue gas temperature and flue gas humidity; When the flue gas temperature is higher than the first temperature threshold and the flue gas humidity is lower than the first humidity threshold, the target operating mode is determined to be the pure sensible heat recovery mode. When the flue gas temperature is lower than the second temperature threshold and the flue gas humidity is higher than the second humidity threshold, the target operating mode is determined to be the pure latent heat recovery mode. When the flue gas temperature is between the second temperature threshold and the first temperature threshold, and the flue gas humidity is higher than the second humidity threshold, the target operating mode is determined to be the total heat recovery mode.

8. The multi-mode switching flue gas waste heat recovery method according to claim 6, characterized in that, The operating parameters of the flue gas also include the concentration of pollutants in the flue gas. Based on the concentration of pollutants, the composition and / or flow rate of the spray water in the latent heat recovery module are dynamically adjusted.

9. The multi-mode switching flue gas waste heat recovery method according to claim 6, characterized in that, Also includes: Acquire environmental parameters and identify the current seasonal operating conditions based on these parameters; Adjust the threshold for determining the target operating mode or the switching strategy based on the identified seasonal operating conditions.

10. The multi-mode switching flue gas waste heat recovery method according to claim 6, characterized in that, Also includes: During the start-up and shutdown of the unit, the trend of flue gas operating conditions is predicted based on the preset start-up and shutdown flue gas parameter change model. Based on the changing trends, adjust the target operating mode and the operating parameters of each recycling module in advance.

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