Air preheating system

Abstract

The utility model discloses a preheater, in particular 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 circulating heat exchange units, the heat exchange amount of each heat exchange unit is independently controllable, and the first transfer device and the second transfer device are connected with each other when the system runs. 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 utility model relates to the technical field of heat exchange equipment, in particular to an air preheating system. Background Art

[0002] As an important device in boilers to improve heat exchange performance and reduce energy consumption, the role of air preheaters is becoming increasingly prominent. The use of air preheaters significantly improves boiler combustion efficiency and reduces emissions of harmful substances such as nitrogen oxides.

[0003] At present, the 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 shortcomings during operation:

[0005] 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.

[0006] 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.

[0007] The rotary air preheater has air leakage problems due to its structure (1. The rotation of the heating surface brings the air remaining in the flow section of the heating element into the flue gas, or brings the remaining flue gas into the air. 2. The gap between the moving and static parts of the air preheater causes air leakage through the pressure difference between the air and the flue gas.). A large amount of air leakage will increase the heat loss of the flue gas and the power consumption of the induced draft fan, affecting the output of the boiler.

[0008] The heat exchange unit of the traditional air preheater is prone to dust accumulation, resulting in insufficient ventilation, reducing actual working efficiency and causing the exhaust gas temperature to continue to rise.

[0009] The heat transfer rate of traditional air preheaters is limited, and the adjustment range of performance parameters is small. When some heat exchange units cannot operate normally or the combustion load increases due to environmental factors, the waste heat in the flue gas cannot be fully utilized. This results in partial heat discharge, high flue gas discharge temperature, energy waste and environmental pollution. Utility Model Content

[0010] In order to solve the problems existing in the above-mentioned prior art, the utility model provides an air preheating system to solve the current technical problems.

[0011] The technical solution adopted by the utility model to solve its technical problems is:

[0012] The utility model 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 amount of each heat exchange unit is individually controllable, and also includes a first transfer device and a second transfer device. When the system is running, the heat exchange unit is transferred from the first transfer device to the heat absorption exchange device to exchange heat with the flue gas, and the heated heat exchange unit is transferred to the heat release exchange device via the second transfer device to preheat the air; wherein the total heat exchange amount 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.

[0013] Preferably, the outer shell of the heat exchange unit is a sphere or a spherical body, and the outer shell is a shell made of anti-corrosion material.

[0014] 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.

[0015] 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, and the preheating device is also connected to a steam turbine and a condenser.

[0016] Preferably, the heat exchange device is a closed space for heat exchange between the heat exchange unit and the high-temperature flue gas, and the heat exchange device is provided with a flue gas input port and a flue gas output port, and the heat exchange device is also provided with a heat exchange unit input device and a heat exchange unit output device.

[0017] 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.

[0018] Preferably, the air preheated by the heat exchange device is output to the combustion chamber.

[0019] Preferably, the heat exchange unit comprises a shell, and a phase change material is encapsulated in the shell.

[0020] Preferably, the heat absorption exchange device is arranged at the tail end of the flue after the economizer.

[0021] The beneficial effects of the utility model are:

[0022] Independent heat exchange units are used to continuously circulate in the system, which facilitates repair and maintenance, expands equipment performance, and improves equipment reliability and flexibility.

[0023] 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.

[0024] As a separate system, the transfer device has strong expandability.

[0025] The present application also includes a method for optimizing the startup of a boiler unit, thereby improving the flexibility and economy of boiler startup, effectively shortening the boiler startup time, and preventing the problem of boiler startup failure.

[0026] 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

[0027] The above aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0028] Figure 1 is a schematic diagram of an air preheating system without a preheating device according to an embodiment of the utility model;

[0029] Figure 2 is a schematic diagram of an air preheating system according to an embodiment of the utility model;

[0030] Figure 3 It is a structural schematic diagram of a heat exchange unit of an air preheating system according to an embodiment of the utility model;

[0031] Figure 4 The coating structure of the heat exchange unit shell of the air preheating system of the utility model embodiment;

[0032] Figure 5 It is a structural schematic diagram of the shell of the ellipsoidal heat exchange unit of the air preheating system of the embodiment of the utility model;

[0033] Figure 6 It is a schematic cross-sectional structural diagram of the shell of the ellipsoid heat exchange unit of the air preheating system of the embodiment of the utility model;

[0034] Figure 7 It is a structural schematic diagram of the shell of the hole groove sphere heat exchange unit of the air preheating system of the embodiment of the utility model;

[0035] Figure 8 It is a schematic cross-sectional view of the outer shell of the hole groove sphere heat exchange unit of the air preheating system of the embodiment of the utility model;

[0036] Fig. 9 It is a structural schematic diagram of the housing of the convex sphere heat exchange unit of the air preheating system of the embodiment of the utility model;

[0037] Fig.10 It is a schematic cross-sectional structural diagram of the housing of the convex sphere heat exchange unit of the air preheating system of the embodiment of the utility model;

[0038] Fig.11 It is a structural schematic diagram of a polyhedral heat exchange unit shell of an air preheating system of an embodiment of the utility model;

[0039] Fig.12 It is a schematic cross-sectional structural diagram of a polyhedral heat exchange unit shell of an air preheating system of an embodiment of the utility model.

[0040] Description of reference numerals:

[0041] exist Figure 1-Figure 12 In the figure, the shell 1; the phase change material 2; and the anti-corrosion coating 3. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0043] The utility model provides an air preheating system, which utilizes the flow of an independent heat exchange unit to realize the heat conversion of boiler flue gas waste heat to 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.

[0044] Heat exchange unit: an individual medium that exchanges heat with flue gas, air and steam in a system device. The outer shell 1 is selected to have an external structure such as a sphere or a spheroid (including but not limited to an ellipsoid, a hole groove sphere, a convex point sphere, a polyhedron, etc.). Compared with other shape structures, the use of a sphere or a spheroid can ensure full contact with the heat exchange medium, provide a circulation channel for the heat exchange medium, and make the heat exchange medium contact longer in the channel where the heat exchange unit is stacked, thereby further enhancing the heat transfer and storage effect.

[0045] 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.

[0046] Optimized, the heat exchange unit shell material can also be made of PPS alloy (polyphenylene sulfide alloy). PPS is a special engineering plastic with excellent physical and chemical properties. It has excellent performance in terms of high mechanical strength, high temperature resistance, high flame retardancy, corrosion resistance, high hardness, and thermal stability. By blending or compounding with other polymers or fillers to make PPS alloy, while retaining the original performance, it can solve its shortcomings of fragility and low wear resistance.

[0047] Optimally, the components of the heat exchange medium and the phase change material 2 may cause corrosion to the heat exchange unit. In order to prevent corrosion, anti-corrosion coatings can be applied to the inner and outer walls of the heat exchange unit. For example, corrosion-resistant silicone coatings, arc spraying of rare earth alloys, epoxy glass coatings, etc.

[0048] Optimized, in order to ensure better use effect and increase the heat exchange area, the heat exchange unit can choose to add single or combined structural features such as grooves, holes, and convex points. Groove: The groove-like part of the heat exchange unit surface that is concave on the periphery and far from the circle and close to the center of the circle. Hole: The inner surface part of the heat exchange unit, which can be a special-shaped hole or a closed hole. Convex point: The raised point-like part on the surface of the heat exchange unit.

[0049] The heat exchange unit shell 1 can be filled with heat storage medium or can be empty. When selecting the diameter value of the shell 1, factors such as heat exchange amount and heat exchange area, heat exchange time, type and chemical composition of heat storage medium need to be considered, and optimization should be performed to achieve the best performance. Based on comprehensive considerations, the selected diameter of the shell 1 shall not be less than 25mm, and can be selected between 30mm-150mm to meet the functional requirements of the system.

[0050] Preferably, the heat exchange unit housing 1 encapsulates a phase change material 2. The formulation and quality of the phase change material 2 encapsulated in each heat exchange unit are the same. Therefore, the time and heat load required for the phase change process of each heat exchange unit during the heat storage and heat transfer process are basically consistent.

[0051] Optimally, the phase change materials 2 in the heat exchange units have different formulas and different 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.

[0052] 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.

[0053] Heat exchange device: A closed 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 provided with a flue gas input port and a flue gas output port, a heat exchange unit input device and a heat exchange unit output device.

[0054] 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.

[0055] The function of the heat exchange unit input and output devices in the heat absorption exchange device and the heat release exchange device is to control the heat exchange unit flow rate and seal rotation. For example, a rotary valve with good sealing performance is suitable for large-sized solid discharge valves.

[0056] Preferably, in the heat absorption exchange device and the heat release exchange device, the smoke input port and the air input port are arranged at the lower part of the device, and the smoke output port and the air output port are arranged at the upper part of the device. The heat exchange unit input device is arranged at the top of the device, and the heat exchange unit output device is arranged at the bottom of the device. The heat exchange units fall into the device from the heat exchange unit input device at the top of the device in turn, and the heat exchange medium is input from the bottom of the device, so that the lower heat exchange unit closest to the heat exchange medium input port has the longest relative contact heat exchange time, a higher contact heat exchange medium load, and completes the heat exchange first. After completing the heat exchange, the lower heat exchange unit first falls into the transfer device through the heat exchange unit output device at the bottom of the device under the action of gravity.

[0057] The first transfer device and the second transfer device are devices for transporting heat exchange units between the heat absorption exchange device and the heat release exchange device. For example, a feeding device that can transport solids, such as a bucket elevator, a screw feeder, and a belt conveyor. An input end and an output end are provided in the transfer device, wherein the input end of the first transfer device is connected to the output device of the heat exchange unit in the heat release space, and the output end of the first transfer device is connected to the input device of the heat exchange unit in the heat absorption space. The input end of the second transfer device is connected to the output device of the heat exchange unit in the heat absorption space, and the output end of the second transfer system is connected to the input device of the heat exchange unit in the heat release space.

[0058] 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.

[0059] Preferably, a transfer device is provided in the system, which is used to store 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.

[0060] Optimized, add a preheating device, a device that introduces steam to exchange heat with the low-temperature heat exchange unit when the boiler unit is started.

[0061] The operating principle of the air preheating system is: the air preheater is set at the tail end of the flue after the economizer. After the fuel is burned in the combustion chamber, flue gas is generated. Before heat exchange with the air preheating system, it needs to flow through the heat exchanger or economizer and other equipment to become high-temperature flue gas. The high-temperature flue gas continuously flows into the heat exchange device from the flue gas input port of the heat exchange device. The low-temperature heat exchange unit enters the heat exchange device from the heat exchange unit input device of the heat exchange device, and fully contacts with the high-temperature flue gas circulating in the heat exchange device for heat exchange. After the heat exchange, the high-temperature flue gas is cooled down and becomes low-temperature flue gas, which is continuously discharged into the flue dust removal device from the flue gas output port of the heat exchange device for the next process treatment. The low-temperature heat exchange unit that exchanges heat with the high-temperature flue gas undergoes a phase change in the phase change material 2 in its shell, and completes the heat absorption process after the phase change, and becomes a high-temperature heat exchange unit. The high-temperature heat exchange unit flows to the second transfer device through the heat exchange unit output device of the heat exchange device. The second transfer device transfers the high-temperature heat exchange unit to the heat exchange unit input device of the heat release exchange device, and the heat exchange unit input device flows into the heat release exchange device. The air is continuously sent in from the air input end of the heat release exchange device by the blower, and fully contacts with the high-temperature heat exchange unit in the heat release exchange device for heat exchange. The normal temperature air after heat exchange becomes preheated air and is continuously input into the combustion chamber to help fuel ignition, enhance combustion stability and improve combustion efficiency. The high-temperature heat exchange unit that exchanges heat with normal temperature air undergoes a phase change in the phase change material 2 in its shell, and completes the heat release process after the phase change, and becomes a low-temperature heat exchange unit. The low-temperature heat exchange unit flows to the first transfer device through the heat exchange unit input device at the bottom of the heat release exchange device; the first transfer device continuously transfers the low-temperature heat exchange unit to the heat exchange unit input device of the heat release exchange device at a specified rate. Through the heat exchange unit input device, the low-temperature heat exchange unit is transferred to the heat absorption exchange 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.

[0062] 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 unit in the exchange device matches the heat exchange required by the load.

[0063] As mentioned above, the high-temperature flue gas temperature refers to the monitored temperature at the flue gas inlet of the air preheater. Depending on the process of different uses, the heating furnace is also different, generally between 200℃ and 400℃. Correspondingly, the temperature of the high-temperature heat exchange unit after heat exchange (for example, the temperature is between 180℃ and 380℃) is determined by its thermal conductivity and heat exchange time. The transformation of a high-temperature heat exchange unit into a low-temperature heat exchange unit refers to the change in the phase state of its internal phase change material 2 (for example, from liquid to solid) and the change in its temperature. The temperature of the heat exchange unit drops from high temperature to low temperature after heat exchange with normal temperature air; conversely, the transformation of a low-temperature heat exchange unit into a high-temperature heat exchange unit is also the same.

[0064] During the operation of the system, the changes in the material state of the phase change material 2 in the heat exchange unit in the heat absorption exchange device and the heat release exchange device are opposite. For example, in the heat absorption exchange device, when the low-temperature heat exchange unit stores heat and becomes a high-temperature heat exchange unit, the phase change material 2 in the heat exchange unit will gradually change from solid to liquid, absorbing and storing heat; while in the heat release exchange device, when the high-temperature heat exchange unit releases heat and becomes a low-temperature heat exchange unit, the phase change material 2 in the heat exchange unit will gradually change from liquid to solid, releasing and transferring the stored heat.

[0065] During the operation of the above system, the principle of maintaining the heat exchange stability of the heat exchange unit is: the heat exchange unit adopts a sphere or spheroid shell 1 of the same diameter and is randomly stacked in the device space to form a stacked bed; because the heat exchange unit adopts a sphere or spheroid with the same shape and size, the stacked bed can ensure a minimum void ratio of 25.95%, and the voids are usually interconnected. Due to the large degree of distortion of the random stacking arrangement space, the flow path of the medium between the voids of the heat exchange unit in the stacked bed is random and disordered. Sufficient flow channels are reserved for the heat source and heat load, extending the flow time. This improves the reliability of the phase change process control.

[0066] Based on the addition of preheating devices, a method for optimizing the start-up of boiler units is also proposed: when the boiler is started, the air preheater preheats the air at a low temperature. The boiler is prone to long start-up time and the possibility of failure due to low ambient temperature, high humidity or wet fuel that is not easy to ignite. Nowadays, boiler units usually adopt sliding parameter start-up. That is, during the process of boiler ignition, steam pressure increase and temperature increase, low-temperature and low-pressure steam is used to warm the steam pipe. When a certain parameter is reached, the turbine is rushed and connected to the grid, and the load of the turbine is gradually increased as the temperature and pressure increase. Combined with the above process, a bypass can be drawn from the turbine to the preheating device. When the boiler is started, part of the clean low-temperature heat exchange unit is transferred from the transfer device to the preheating device, and the low-temperature heat exchange unit in the transfer space is preheated by a small amount of steam introduced by the turbine. After heat exchange, the steam condenses into water and is discharged. After the low-temperature heat exchange unit is heated up, it becomes a preheating heat exchange unit and is transferred to the heat release exchange device for heat exchange with normal temperature air. Normal temperature air becomes preheated air after being heated up, which shortens the furnace start-up time and prevents furnace start-up failure by accelerating fuel drying and strengthening radiation heat transfer in the furnace.

[0067] Technical Effects

[0068] As an independent entity, the heat exchange unit continuously circulates in the system device to achieve efficient heat exchange between flue gas and air, improve heat transfer efficiency, facilitate cleaning, maintenance and replacement, and reduce equipment maintenance costs.

[0069] Independent heat exchange units circulate in the system to avoid the possibility of dust accumulation; reduce 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.

[0070] Through the flowing heat exchange unit, the heat energy transmission and heat transfer are realized in two closed spaces, which effectively avoids the transfer of excess impurities and ensures the purity of the heat exchange medium. At the same time, the heat exchange unit is transferred through the heat exchange unit output and input device to avoid the increase of air leakage and reduce the exhaust heat loss caused by air leakage.

[0071] The heat exchange unit is designed as an independent sphere or spherical body, and the transfer space is increased, which facilitates the expansion of the heat exchange performance of the air preheater and enables it to adapt to different operating environments. This flexibility enables the air preheater to maintain efficient operation under various conditions.

[0072] The heat exchange unit housing 1 is made of a sphere or a spherical 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 sphere or spherical structure is conducive to identifying damage, easy to clean, and convenient to separate from the heat exchange medium.

[0073] The heat exchange unit selects to fill the shell 1 with a heat storage medium to increase the heat storage and release capacity of the heat exchange unit. For example, the heat exchange unit selects to fill the shell 1 with phase change material 2, which can store or release a large amount of heat energy with a small temperature change. It has high energy density, high thermal conductivity and controllable temperature change range. (Phase change material 2 can repeatedly exchange heat, and has lower environmental impact and better sustainable development than other technologies. Phase change material 2 has a wider range of options, and the type and ratio can be optimized according to the needs of specific applications to achieve the best heat storage and transfer effect.)

[0074] 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.

[0075] On the heat absorption exchange device and the heat release exchange device, the input end of the heat exchange medium is installed at the bottom, and the output end is installed at the top. This installation position selection can effectively control the heat exchange completion sequence of the heat exchange units in the space, thereby improving the stability and reliability of the system.

[0076] 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 protection scope of the present invention.

Claims

1. An air preheating system, characterized in that: The invention comprises a heat exchange system, which comprises a heat absorption exchange device, a heat release exchange device and a plurality of transferable heat exchange units. The heat exchange amount of each heat exchange unit is individually controllable. The invention also comprises 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 amount 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 outer shell of the heat exchange unit is a sphere or a spherical body, and the outer shell is made of anti-corrosion material.

3. The air preheating system according to claim 1, characterized in that: A transfer device is arranged on the movement track of the heat exchange unit, and the transfer device is arranged 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 arranged on the movement track of the heat exchange unit. The preheating device is arranged 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 exchanging device is output to the combustion chamber.

8. The air preheating system according to claim 1, characterized in that: The heat exchange unit comprises 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.

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