Air preheating system

Abstract

The invention discloses a preheater, and particularly relates to an air preheating system which comprises a heat exchange system, a first transfer device and a second transfer device, the heat exchange system comprises a heat absorption exchange device, a heat release exchange device and a plurality of heat exchange units capable of flowing, the heat exchange amount of each heat exchange unit is independently controllable, and when the system runs, the first transfer device and the second transfer device are connected with each other; the heat exchange unit is transferred to the heat absorption exchange device from the first transfer device and exchanges heat with flue gas, and the heated heat exchange unit is transferred to the heat release exchange device through the second transfer device to preheat air; the total heat exchange amount of the heat exchange units transferred to the heat absorption exchange device and the heat release exchange device is matched with the heat exchange demand quantity of the corresponding devices. And the independent heat exchange unit continuously flows in the system device, so that the maintenance is convenient, the equipment performance is expanded, and the reliability and flexibility of the equipment are improved. The heat exchange units are selected from spheres or similar spheres, maintenance and cleaning are convenient, meanwhile, circulation of heat exchange media can be guaranteed, and the heat exchange efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchange equipment, and in particular to an air preheating system. Background Art

[0002] With the global energy transition and rising environmental awareness, the energy efficiency and pollutant emissions of traditional coal-fired boilers have become key factors restricting their development. Against this backdrop, the role of air preheaters, a crucial component in boilers that improves heat exchange performance and reduces energy consumption, has become increasingly prominent. The use of air preheaters significantly improves boiler combustion efficiency and reduces emissions of harmful substances such as nitrogen oxides, not only meeting environmental regulations but also promoting the sustainable development of the boiler industry.

[0003] China's air preheater industry encompasses a wide range of economic sectors, including thermal power generation, coal chemical industry, and petrochemical industry. In recent years, with the steady development of China's power plant boiler industry, the market size of air preheaters has continued to expand. Guided by national energy-saving and environmental protection policies, the manufacturing industry of new energy-saving and environmentally friendly equipment has also ushered in new development opportunities. However, due to the long history of traditional air preheaters, the industry has now entered a mature stage, and the production processes and technologies of traditional products are relatively complete. As a result, the overall industrial technology level and R&D and innovation capabilities of the air preheater industry are relatively lagging behind. With the shift in energy structure and environmental awareness, the position of air preheaters in the boiler industry is becoming increasingly important. Currently, the most commonly used types of air preheaters on the market are tubular air preheaters and rotary air preheaters.

[0004] The above two different types of air preheaters each have their own characteristics. Although they can meet the current market demand, they still have the following deficiencies during operation: The heat exchange unit of the traditional air preheater is fixed in the flue, which is inconvenient to clean and repair. It requires the furnace to be shut down, which increases maintenance costs.

[0005] Due to the low metal wall temperature of the tubular air preheater, low-temperature corrosion is prone to occur at the air inlet. The air leakage will increase rapidly with low-temperature corrosion and wear and perforation, resulting in a decrease in thermal efficiency.

[0006] Rotary air preheaters are subject to air leakage due to their structure (1. The rotation of the heating surface draws air remaining in the heated element's cross-section into the flue gas, or draws retained flue gas into the air; 2. The gap between the moving and static parts of the air preheater causes air leakage due to the pressure difference between the air and the flue gas). Excessive air leakage increases exhaust heat loss and induced draft fan power consumption, affecting boiler output.

[0007] The heat exchange unit of traditional air preheaters is prone to dust accumulation, resulting in insufficient ventilation, reduced actual working efficiency, and a continuous increase in exhaust gas temperature.

[0008] Traditional air preheaters have limited heat transfer rates and a narrow range of performance parameter adjustments. When some heat exchange units fail to operate normally or when combustion loads increase due to environmental factors, they cannot fully utilize the waste heat in the flue gas. This results in partial heat discharge, high flue gas temperatures, energy waste, and environmental pollution. Summary of the Invention

[0009] In order to solve the problems existing in the above-mentioned prior art, the present invention provides an air preheating system to solve the current technical problems.

[0010] The technical solution adopted by the present invention to solve its technical problem is: The present invention provides an air preheating system, including a heat exchange system, which includes a heat absorption exchange device, a heat release exchange device and a plurality of transferable heat exchange units. The heat exchange capacity of each heat exchange unit is individually controllable. The system also includes a first transfer device and a second transfer device. When the system is in operation, the heat exchange unit is transferred from the first transfer device to the heat absorption exchange device to exchange heat with the flue gas. The heated heat exchange unit is transferred to the heat release exchange device via the second transfer device to preheat the air. The total heat exchange capacity of the heat exchange units transferred to the heat absorption exchange device and the heat release exchange device is adapted to the heat exchange demand of the corresponding device.

[0011] Preferably, the outer shell of the heat exchange unit is a sphere or a spherical-like body, and the outer shell is made of an anti-corrosion material.

[0012] Preferably, a transfer device is provided on the movement trajectory of the heat exchange unit, and the transfer device is provided between the heat release exchange device and the heat absorption exchange device.

[0013] Preferably, a preheating device is provided on the movement track of the heat exchange unit, and the preheating device is provided between the transfer device and the heat release exchange device. The preheating device is also connected to a steam turbine and a condenser.

[0014] Preferably, the heat absorption exchange device is a closed space for heat exchange between the heat exchange unit and the high-temperature flue gas, and the heat absorption exchange device is provided with a flue gas input port and a flue gas output port, and the heat absorption exchange device is also provided with a heat exchange unit input device and a heat exchange unit output device.

[0015] Preferably, the heat exchange device is a closed space for heat exchange between the heat exchange unit and the air, and the heat exchange device is provided with an air input port and an air output port, and the heat exchange device is also provided with a heat exchange unit input device and a heat exchange unit output device.

[0016] Preferably, the air preheated by the heat exchange device is output to the combustion chamber.

[0017] Preferably, the heat exchange unit comprises a shell, in which a phase change material is encapsulated.

[0018] Preferably, the heat absorption exchange device is arranged at the tail end of the flue after the economizer.

[0019] The beneficial effects of the present invention are: The independent heat exchange unit is used to continuously circulate in the system device, which facilitates repair and maintenance, expands equipment performance, and improves equipment reliability and flexibility.

[0020] The heat exchange unit is made of a sphere, which is convenient for maintenance and cleaning. At the same time, it can ensure the circulation of the heat exchange medium, enhance the heat transfer effect and improve the heat exchange efficiency.

[0021] As a separate system, the transfer device has strong scalability.

[0022] The present application also includes a method for optimizing boiler unit startup, which improves the flexibility and economy of boiler startup, effectively shortens boiler startup time, and prevents boiler startup failure.

[0023] Based on the first transfer device and the second transfer device, circulation within the heat exchange unit system is achieved, thereby improving the utilization rate and efficiency of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an air preheating system without a preheating device according to an embodiment of the present invention; Figure 2 is a schematic diagram of an air preheating system according to an embodiment of the present invention; Figure 3 2 is a schematic structural diagram of a heat exchange unit of an air preheating system according to an embodiment of the present invention; Figure 4 The heat exchange unit shell coating structure of the air preheating system according to an embodiment of the present invention; Figure 5 2 is a schematic structural diagram of an ellipsoidal heat exchange unit housing of an air preheating system according to an embodiment of the present invention; Figure 6 is a schematic cross-sectional structural diagram of the shell of the ellipsoidal heat exchange unit of the air preheating system according to an embodiment of the present invention; Figure 7 2 is a schematic structural diagram of a housing of a hole-groove sphere heat exchange unit of an air preheating system according to an embodiment of the present invention; Figure 8 2 is a schematic cross-sectional view of the outer shell of the hole-groove sphere heat exchange unit of the air preheating system according to an embodiment of the present invention; Figure 92 is a schematic structural diagram of a housing of a convex sphere heat exchange unit of an air preheating system according to an embodiment of the present invention; Figure 10 2 is a schematic cross-sectional view of the housing of a convex sphere heat exchange unit of an air preheating system according to an embodiment of the present invention; Figure 11 2 is a schematic structural diagram of a polyhedron heat exchange unit housing of an air preheating system according to an embodiment of the present invention; Figure 12 It is a schematic cross-sectional structural diagram of the polyhedron heat exchange unit shell of the air preheating system according to an embodiment of the present invention. Description of Reference Numerals

[0025] exist Figures 1-12 In the figure, the shell 1; the phase change material 2; and the anti-corrosion coating 3. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] The present invention provides an air preheating system that utilizes the flow of an independent heat exchange unit to convert waste heat from boiler flue gas into combustion air. The air preheater includes a heat exchange unit, a heat absorption exchange device, a heat release exchange device, a first transfer device, a second transfer device, and a transfer device.

[0028] Heat exchange unit: An individual medium within a system that exchanges heat with flue gas, air, and steam. The housing 1 may have a spherical or spheroidal shape (including but not limited to ellipsoids, spheres with holes and grooves, spheres with convex points, and polyhedrons). Compared to other shapes, a spherical or spheroidal shape ensures sufficient contact with the heat exchange medium, providing a flow channel for the heat exchange medium while extending its contact time within the channels of the heat exchange unit, thereby further enhancing heat transfer and storage.

[0029] Optimally, the heat exchange unit shell can be made of materials with high strength, good thermal conductivity, high temperature resistance, and certain corrosion resistance, such as ordinary carbon steel, stainless steel, polytetrafluoroethylene, etc.

[0030] Alternatively, the heat exchange unit shell can be made of PPS alloy (polyphenylene sulfide alloy). PPS is a premium engineering plastic with excellent physical and chemical properties. It boasts high mechanical strength, high temperature resistance, flame retardancy, corrosion resistance, high hardness, and thermal stability. By blending or compounding with other polymers or fillers to create a PPS alloy, PPS can address its inherent fragility and low wear resistance while retaining its original properties.

[0031] Optimized, the composition of the heat exchange medium and phase change material 2 may cause corrosion to the heat exchange unit. To prevent corrosion, the inner and outer walls of the heat exchange unit can be coated with anti-corrosion coatings. For example, corrosion-resistant silicone coatings, arc spraying of rare earth alloys, epoxy glass coatings, etc. can be used.

[0032] To optimize heat exchange units and increase heat transfer area for better performance, you can add single or combined structural features such as grooves, holes, and bumps. A groove is a recessed groove on the surface of a heat exchange unit that extends farther from the circle and closer to the center of the circle. A hole is a portion of the heat exchange unit's inner surface that can be either a special-shaped hole or a closed hole. A bump is a raised point on the surface of a heat exchange unit.

[0033] The heat exchange unit housing 1 can be filled with a heat storage medium or left empty. When selecting the diameter of housing 1, factors such as heat transfer capacity and area, heat transfer time, and the type and chemical composition of the heat storage medium should be considered, and optimized for optimal performance. Based on these considerations, the diameter of housing 1 should be no less than 25 mm, and can range from 30 mm to 150 mm to meet the system's functional requirements.

[0034] Preferably, a phase change material 2 is encapsulated within the heat exchange unit housing 1. The phase change material 2 encapsulated in each heat exchange unit has the same formulation and quality. Therefore, the time required for heat storage and heat transfer, as well as the heat load required for phase change, remains substantially consistent across each heat exchange unit.

[0035] Optimally, the phase change materials 2 in the heat exchange units have different formulas and qualities, but different formulas are selected to fill different qualities of phase change materials 2, so that the heat exchange capacity of each heat exchange unit is the same.

[0036] Optimized, the heat transfer capacity of the heat exchange unit is mainly related to the formulation of the phase change material 2 and the quality of the filling. The heat transfer capacity of each heat exchange unit is individually controllable, which is convenient for system calculation and regulation.

[0037] Heat exchange device: An enclosed space where the heat exchange unit exchanges heat with the high-temperature flue gas, such as a sealable container such as a tank. It is equipped with a flue gas input port, a flue gas output port, a heat exchange unit input device, and a heat exchange unit output device.

[0038] Heat exchange device: A closed space where the heat exchange unit exchanges heat with the air, which is provided with an air input port and an air output port, a heat exchange unit input device and a heat exchange unit output device.

[0039] The input and output devices of the heat exchange units in the heat absorption and heat release exchange devices are used to control the flow rate of the heat exchange units and to seal them. For example, rotary valves with good sealing properties are suitable for large-scale solid discharge.

[0040] Preferably, in the heat absorption and heat release exchange devices, the flue gas input and air input ports are located at the bottom of the device, while the flue gas output and air output ports are located at the top. The heat exchange unit input device is located at the top of the device, and the heat exchange unit output device is located at the bottom. Heat exchange units are sequentially dropped into the device from the heat exchange unit input device at the top of the device, and heat exchange medium is input from the bottom of the device. This ensures that the lower-level heat exchange units closest to the heat exchange medium input port have the longest relative heat exchange contact time, a higher heat exchange medium load, and complete heat exchange first. After completing heat exchange, the lower-level heat exchange units are the first to fall into the transfer device through the heat exchange unit output device at the bottom of the device under the action of gravity.

[0041] The first and second transfer devices are devices that transport heat exchange units between the heat-absorbing and heat-releasing exchange units. Examples include bucket elevators, screw loaders, and belt conveyors. Each transfer device has an input and an output. The first transfer device's input is connected to the output of the heat exchange unit in the heat-releasing space, while the first transfer device's output is connected to the input of the heat exchange unit in the heat-absorbing space. The second transfer device's input is connected to the output of the heat exchange unit in the heat-absorbing space, while the second transfer device's output is connected to the input of the heat exchange unit in the heat-releasing space.

[0042] Optimally, the first transfer device can be open or semi-open, for example, the outer shell 1 of the transport device has an opening so that the deformed or damaged heat exchange unit can be observed and replaced; secondly, the transfer system is closed and has a heat-insulating effect, for example, heat-insulating cotton or other heat-insulating materials are wrapped on the outer shell 1 of the transport device.

[0043] Preferably, a transfer device is provided in the system for storing idle low-temperature heat exchange units, and is located on the movement trajectory of the heat exchange unit from the heat release exchange device to the heat absorption exchange device.

[0044] Optimized, a preheating device is added, which introduces steam to exchange heat with the low-temperature heat exchange unit when the boiler unit is started.

[0045] The air preheating system operates as follows: The air preheater is located at the tail end of the flue after the economizer. Fuel combustion in the combustion chamber generates flue gas, which must flow through a heat exchanger or economizer to become high-temperature flue gas before exchanging heat with the air preheating system. The high-temperature flue gas continuously flows into the heat exchanger from the flue gas input port. A low-temperature heat exchange unit enters the heat exchanger from the heat exchange unit input device, where it fully contacts and exchanges heat with the high-temperature flue gas circulating within the heat exchanger. After heat exchange, the high-temperature flue gas cools down to low-temperature flue gas, which is continuously discharged from the flue gas output port of the heat exchanger into the flue dust removal device for further processing. The phase change material 2 within the shell of the low-temperature heat exchange unit undergoes a phase change, completing the heat absorption process after the phase change, transforming into a high-temperature heat exchange unit. The high-temperature heat exchange unit then flows to the second transfer device through the heat exchange unit output device of the heat exchanger. The second transfer device transfers the high-temperature heat exchange unit to the heat exchange unit input device of the heat release device. From there, it flows into the heat release device. Air is continuously supplied by a blower from the air input end of the heat release device, allowing it to fully contact and exchange heat with the high-temperature heat exchange unit within the heat release device. After heat exchange, the ambient temperature air becomes preheated air and is continuously input into the combustion chamber to aid fuel ignition, enhance combustion stability, and improve combustion efficiency. The phase change material 2 within the high-temperature heat exchange unit undergoes a phase change during heat exchange with the ambient temperature air. After the phase change, the heat release process is completed, transforming it into a low-temperature heat exchange unit. The low-temperature heat exchange unit flows through the heat exchange unit input device at the bottom of the heat release device to the first transfer device. The first transfer device continuously transfers the low-temperature heat exchange unit to the heat exchange unit input device of the heat release device at a specified rate. Through the heat exchange unit input device, the low-temperature heat exchange unit is transferred to the heat absorption device for the next cycle. Under conditions where the combustion load is reduced, a portion of the low-temperature heat exchange units can also be stored in the transfer device and transferred when there is a heat load demand.

[0046] Optimized, the transfer rate of the transfer device is adjustable. Sensor devices can be installed at the flue gas and air input and output ends of the heat absorption exchange device and the heat release exchange device to collect temperature, flow rate and other data and upload them to the system to calculate and control the transfer rate of the heat exchange unit, so that the heat exchange rate of the heat exchange unit in the exchange device matches the heat exchange rate required by the load.

[0047] The high-temperature flue gas temperature mentioned above refers to the monitored temperature at the flue gas inlet of the air preheater. Depending on the process used, the heating furnace temperature varies, generally ranging from 200°C to 400°C. Correspondingly, the temperature of the high-temperature heat exchange unit after heat exchange (for example, between 180°C and 380°C) is determined by its thermal conductivity and heat exchange time. The conversion of a high-temperature heat exchange unit to a low-temperature heat exchange unit refers to a phase change (for example, from liquid to solid) in the internal phase change material (PCM) and a temperature change. The temperature of the heat exchange unit drops from high temperature to low temperature after heat exchange with ambient air; the same applies to converting a low-temperature heat exchange unit to a high-temperature unit.

[0048] During system operation, the phase change material 2 in the heat exchange unit changes state in opposite directions between the heat-absorbing and heat-releasing units. For example, in the heat-absorbing unit, when the low-temperature heat exchange unit stores heat and becomes the high-temperature heat exchange unit, the phase change material 2 in the heat exchange unit gradually changes from solid to liquid, absorbing and storing heat. Conversely, in the heat-releasing unit, when the high-temperature heat exchange unit releases heat and becomes the low-temperature heat exchange unit, the phase change material 2 in the heat exchange unit gradually changes from liquid to solid, releasing and transferring the stored heat.

[0049] During operation of the aforementioned system, the principle for maintaining stable heat transfer within the heat exchange units is as follows: the heat exchange units utilize spherical or spheroidal shells (1) of identical diameter, randomly stacked within the device space to form a stacked bed. Because the heat exchange units utilize spherical or spheroidal shells of identical shape and size, the stacked bed maintains a minimum void ratio of 25.95%, with the voids generally interconnected. Due to the significant spatial distortion of the random stacking arrangement, the flow paths of the medium within the stacked bed's heat exchange units are random and disordered. This maintains sufficient flow channels for both the heat source and the heat load, extending the flow time and thereby improving the reliability of phase change process control.

[0050] Based on the addition of a preheating device, a method for optimizing boiler unit startup has been proposed. During boiler startup, the air preheater preheats the air at a low temperature. Boiler startup can be delayed and potentially cause startup failures due to low ambient temperature, high humidity, or damp fuel that hinders ignition. Currently, boiler units typically utilize sliding parameter startup. This involves using low-temperature, low-pressure steam to warm the steam pipes during boiler ignition and steam pressure and temperature increase. Once certain parameters are reached, the turbine is started up and connected to the grid. The turbine load is gradually increased as air temperature and pressure rise. Integrating this process, a bypass can be created within the turbine to connect to the preheating device. During boiler startup, a portion of the clean, low-temperature heat exchanger is transferred from the transfer unit to the preheating unit. A small amount of steam introduced from the turbine preheats the low-temperature heat exchanger within the transfer space. After heat exchange, the steam condenses into water and is discharged. The low-temperature heat exchanger heats up, transforming into a preheating heat exchanger and transferring it to the heat exchanger for heat exchange with ambient air. After the room temperature air is heated up, it becomes preheated air, which shortens the furnace start-up time and prevents furnace start-up failure by accelerating the drying of the fuel and strengthening the radiation heat transfer in the furnace.

[0051] Technical Effects As an independent unit, the heat exchange unit continuously circulates within the system, achieving efficient heat exchange between flue gas and air, improving heat transfer efficiency. It is easy to clean and repair, reducing equipment maintenance costs.

[0052] Independent heat exchange units circulate in the system to avoid the possibility of dust accumulation; reducing the contact time of each low-temperature heat exchange unit with the high-temperature flue gas dew point corrosion, thereby extending the service life of the heat exchange unit.

[0053] The flowing heat exchange unit achieves thermal energy and heat transfer within two enclosed spaces, effectively preventing the transfer of excess impurities and ensuring the purity of the heat exchange medium. Furthermore, the heat exchange unit's input and output devices are used to transfer the heat exchange unit, preventing increased air leakage and reducing exhaust heat loss caused by air leakage.

[0054] The heat exchange units are designed as independent spheres or quasi-spheres, with additional transfer space, facilitating the expansion of the air preheater's heat exchange performance and adapting it to different operating environments. This flexibility enables the air preheater to maintain efficient operation under various conditions.

[0055] The heat exchange unit housing 1 is spherical or spherical in shape to ensure the circulation of the heat exchange medium, ensure sufficient contact and heat exchange with the heat exchange medium, and further enhance the heat exchange effect. In addition, the spherical or spherical structure is easy to identify damage, easy to clean, and convenient to separate from the heat exchange medium.

[0056] The heat exchange unit's outer shell 1 is filled with a heat storage medium to increase its heat storage and release capabilities. For example, if the heat exchange unit's outer shell 1 is filled with phase change material 2, it can store or release large amounts of heat energy with minimal temperature fluctuations. This material exhibits high energy density, high thermal conductivity, and controllable temperature range. (Phase change material 2 can perform repeated heat exchange, resulting in lower environmental impact and greater sustainability compared to other technologies. Phase change material 2 offers a wider range of options, allowing for optimized types and ratios based on specific application requirements to achieve optimal heat storage and transfer.) By optimizing the boiler unit startup method, accelerating fuel drying, and strengthening radiation heat transfer in the furnace, the startup time can be shortened and startup failure can be prevented.

[0057] The heat transfer medium input is installed at the bottom of the heat transfer unit and the heat transfer medium output is installed at the top of the heat transfer unit. This installation position effectively controls the heat transfer sequence of the heat transfer units within the space, thereby improving the stability and reliability of the system.

[0058] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An air preheating system, characterized in that: The heat exchange system includes a heat absorption exchange device, a heat release exchange device and several transferable heat exchange units. The heat exchange capacity of each heat exchange unit is individually controllable. The system also includes a first transfer device and a second transfer device. When the system is in operation, the heat exchange unit is transferred from the first transfer device to the heat absorption exchange device to exchange heat with the flue gas. The heated heat exchange unit is transferred to the heat release exchange device via the second transfer device to preheat the air. The total heat exchange capacity of the heat exchange units transferred to the heat absorption exchange device and the heat release exchange device is adapted to the heat exchange demand of the corresponding device.

2. The air preheating system according to claim 1, characterized in that: The shell of the heat exchange unit is a sphere or a spherical shape, and is made of an anti-corrosion material.

3. The air preheating system according to claim 1, characterized in that: A transfer device is provided on the movement track of the heat exchange unit, and the transfer device is provided between the heat release exchange device and the heat absorption exchange device.

4. The air preheating system according to claim 1, characterized in that: A preheating device is provided on the movement track of the heat exchange unit. The preheating device is provided between the transfer device and the heat release exchange device. The preheating device is also connected to a steam turbine and a condenser.

5. The air preheating system according to claim 1, characterized in that: The heat exchange device is a closed space for heat exchange between the heat exchange unit and the high-temperature flue gas. The heat exchange device is provided with a flue gas input port and a flue gas output port. The heat exchange device is also provided with a heat exchange unit input device and a heat exchange unit output device.

6. The air preheating system according to claim 1, characterized in that: The heat exchange device is a closed space for heat exchange between the heat exchange unit and the air. The heat exchange device is provided with an air input port and an air output port. The heat exchange device is also provided with a heat exchange unit input device and a heat exchange unit output device.

7. The air preheating system according to claim 1, characterized in that: The air preheated by the heat exchange device is output to the combustion chamber.

8. The air preheating system according to claim 1, characterized in that: The heat exchange unit includes a shell in which a phase change material is encapsulated.

9. The air preheating system according to claim 1, characterized in that: The heat absorption exchange device is arranged at the tail end of the flue after the economizer.

Images