Boiler waste heat recovery system

Abstract

The invention belongs to the field of heat-engine plant boiler flue gas waste heat recycling, and discloses a boiler waste heat recycling system which comprises an air preheater and a boiler, and a flue gas outlet of the boiler is communicated with a flue gas channel inlet of the air preheater through a pipeline; an outlet of an air channel of the air preheater communicates with a combustion-supporting air inlet of the boiler through a pipeline, and an inlet of the air channel is used for introducing air to be heated. The air preheater further comprises a preheating unit, the preheating unit comprises a compartment, and the compartment is arranged on the air side of the air preheater and located between the smoke channel and the air channel. The air inlet end and the air outlet end of the compartment are communicated through a circulating pipeline; the circulating fan is arranged on the circulating pipeline and is used for driving the gas in the compartment to circulate; according to the scheme, by means of the buffer area formed by the compartments and the circulating fan, the temperature shock amplitude of the heat accumulator in the alternate heat absorption and heat release process is reduced, and deformation of the heat accumulator caused by too large local thermal stress is relieved; the problem that the heat accumulator is heated unevenly is solved.

Description

TECHNICAL FIELD

[0001] The present scheme belongs to the field of waste heat recovery and utilization of boiler flue gas in thermal power plants, and particularly relates to a boiler waste heat recovery system. BACKGROUND

[0002] Thermal power plants need to use boilers as energy conversion equipment to generate high-temperature and high-pressure steam by burning fuel, and the steam drives the steam turbine to rotate, thereby driving the generator to generate electricity. Due to the fact that 100% energy conversion cannot be achieved during the fuel combustion process, and the high-temperature flue gas needs to be discharged through the flue to maintain the normal operation of the boiler, tail gas is generated. These tail gas still carries a large amount of heat (i.e. waste heat) that has not been fully utilized when it is discharged, and if it is directly discharged, it will not only cause a huge waste of energy, but also exacerbate environmental heat pollution. Therefore, the waste heat in the tail gas can be recovered and used for preheating air, heating feed water or other production links, which can improve the thermal efficiency of the entire power plant.

[0003] In waste heat recovery, the air preheater is a key equipment that connects the waste heat of the tail gas and the combustion demand of the boiler. By transferring the waste heat in the tail gas to the cold air entering the boiler, the temperature of the combustion air can be increased, which not only utilizes the heat in the tail gas that would otherwise be wasted, reduces energy loss, improves fuel combustion, and improves the thermal efficiency of the boiler, but also reduces the heat loss of the furnace caused by the direct entry of cold air, thereby optimizing the operation of the entire combustion system while achieving waste heat recovery.

[0004] For example, see the existing document (announcement) No. CN112212356A, which discloses a multi-channel regenerative air preheater, which includes a regenerative chamber, the regenerative chamber is multiple and even, the regenerative chamber includes a regenerative body, a regenerative chamber intermediate partition plate and a tail part passage, the regenerative chamber intermediate partition plate divides the regenerative chamber into upper and lower two layers of regenerative chambers, the upper and lower regenerative chambers are filled with regenerative bodies, the upper and lower regenerative chambers are communicated through the tail part passage, the regenerative body is a plate type, preferably a metal plate, and can also be a non-plate type honeycomb ceramic.

[0005] The regenerative chamber of the above-mentioned rotary air preheater can make air and flue gas flow through the regenerative chamber alternately, so that the regenerative chamber realizes self-cleaning. However, during the operation of the preheater, the cold medium (air) and the hot medium (boiler flue gas) pass through the two sides of the preheater respectively, and the flow directions of the cold medium and the hot medium are opposite, which adopts a counterflow form. In actual use, there is a large temperature difference between the boiler flue gas side and the air side. Along the flow direction of the original flue gas, the temperature near the flue gas side is high, and the radial deformation of the rotor is large; while on the air side, the situation is the opposite, so that the temperature of the upper regenerative body is always higher than that of the lower regenerative body, and the temperature affects the thermal deformation of the metal. After a period of operation, the regenerative body begins to deform downward, forming a "mushroom" shape (as shown in Figure 1After the deformation of the heat storage body, the spacing between adjacent heat storage bodies increases, forming an air leakage area, which gradually increases with the increase of the running time, causing a large amount of air leakage, and ultimately leading to the reduction of the heat exchange efficiency of the air preheater. SUMMARY

[0006] The purpose of the present scheme is to provide a boiler waste heat recovery system to alleviate the problem of uneven heating of the heat storage body.

[0007] In order to achieve the above purpose, the present scheme provides a boiler waste heat recovery system, comprising an air preheater and a boiler, the flue gas outlet of the boiler is communicated with the flue gas passage inlet of the air preheater through a pipeline, and the flue gas passage outlet of the air preheater is connected with a waste heat utilization system; the outlet of the air passage of the air preheater is communicated with the combustion air inlet of the boiler through a pipeline, and the inlet of the air passage is used for introducing air to be heated; further comprising a preheating unit, the preheating unit comprises: a compartment, the compartment is arranged on the air side of the air preheater, and the compartment is located between the flue gas passage and the air passage; the air inlet end and the air outlet end of the compartment are communicated through a circulating pipeline; a circulating fan, the circulating fan is arranged on the circulating pipeline and is used for driving the circulation of the gas in the compartment.

[0008] The principle of the present scheme is that the high-temperature flue gas generated by the boiler first enters the flue gas passage of the air preheater, transfers heat to the heat storage body (such as a heat exchange element) in the air preheater, and completes the first waste heat recovery; the cooled flue gas enters the subsequent waste heat utilization system for further recovery of the remaining heat; and the air to be heated introduced by the air passage flows through the heat storage body, becomes high-temperature combustion air after absorbing the stored heat, and enters the boiler, completing the conversion of heat from flue gas to air and forming a waste heat recovery closed loop. In this process, the heat storage body needs to alternately enter the high-temperature flue gas passage (heat absorption) and the low-temperature air passage (heat release) with the rotation of the rotor, and the large temperature difference between the two is easy to cause local thermal stress concentration and uneven heating; the compartment arranged between the flue gas passage and the air passage drives the circulation of the internal gas through the circulating fan, forming a buffer area with a temperature between the flue gas and the air, and the heat storage body passes through the compartment before entering the air passage after turning out of the flue gas passage, the circulating gas can appropriately adjust the temperature of the heat storage body, and reduce the sudden change amplitude from high temperature to low temperature, thereby alleviating the problem of uneven heating.

[0009] The effect of the scheme is that: (1) The buffer area formed by the partition between the flue gas passage and the air passage and the circulating fan reduces the temperature sudden change amplitude of the heat storage body in the alternating heat absorption and heat release process, slows down the deformation, damage or heat exchange efficiency reduction of the heat storage body caused by excessive local thermal stress, and prolongs the service life of the air preheater. (2) The circulating gas exchanges heat with the heat storage body, which can diffuse the excess heat brought out by the heat storage body from the flue gas passage in the partition, avoid the heat concentration in a certain area to affect the heat exchange with the cold air in the air passage, and the flow of circulating air can also reduce the ash accumulation in the partition.

[0010] Further, the waste heat utilization unit comprises a first heat exchanger and a second heat exchanger, the air side inlet of the first heat exchanger is communicated with the outlet of the flue gas passage, the heat exchange medium outlet of the first heat exchanger is communicated with the heat exchange medium inlet of the second heat exchanger, the heat exchange medium outlet of the second heat exchanger is communicated with the heat exchange medium inlet of the first heat exchanger, the air side inlet of the second heat exchanger is used for preheating the air to be heated, and the air side outlet of the second heat exchanger is communicated with the inlet of the air passage through a pipeline; the air side outlet of the first heat exchanger is sequentially connected with a desulfurization device, a denitration device and an induced draft fan, and the outlet of the induced draft fan is communicated with a chimney.

[0011] The principle and effect of the scheme are that: the cooled flue gas discharged from the flue gas passage of the air preheater first enters the first heat exchanger, the residual waste heat is transferred to the circulating heat exchange medium, the heat exchange medium brings heat into the second heat exchanger, the air to be heated at the inlet of the air passage is preheated, the air carries part of the heat before entering the air preheater, and the temperature difference with the heat storage body is reduced. At the same time, the flue gas further cooled by the first heat exchanger is sequentially purified by the desulfurization and denitration devices, and after removing the pollutants, it is sent into the chimney by the induced draft fan for discharge, realizing the environmental protection treatment of the flue gas.

[0012] Further, the air preheater comprises a shell, a rotor and a heat exchange element, the shell is divided to form a flue gas passage and an air passage, the air passage comprises a primary air passage, a secondary air passage and a partition; the rotor is arranged in the shell, and the rotating shaft of the rotor extends out of the shell; the heat exchange element is distributed in the cavity of the rotor along the radial direction and the circumferential direction of the rotor; the rotating shaft of the rotor is fixedly connected with a driven gear, the driven gear is engaged with a driving gear, and the driving gear is connected with a driving assembly.

[0013] The principle and effect of the scheme are that: the smoke passage and the air passage (including the primary air passage, the secondary air passage and the compartment) formed by the shell are separated, and when the driving assembly drives the rotor to rotate the heat exchange elements distributed in the radial and circumferential directions, the heat exchange elements can alternately enter the high-temperature smoke passage to absorb heat and then enter different air passages (primary air and secondary air) to release heat to heat the corresponding combustion-supporting air. At the same time, the heat exchange elements pass through the compartment before entering the air passage, and the temperature is adjusted by the buffer of the compartment.

[0014] Further, the driving assembly comprises a motor and a driving rod, the output shaft of the motor is coaxially fixedly connected with one end of the driving rod, the free end of the driving rod is hingedly connected with a driving gear, the driving gear is coaxially provided with a support disc, the support disc is fixedly arranged on the shell, the support disc is eccentrically hingedly connected with a connecting rod, the free end of the connecting rod is provided with a support frame, the connecting rod is slidably connected with the support frame, and the first eccentric hinged end of the driving rod and the driving gear is arranged in the support frame.

[0015] The principle and effect of the scheme are that: (1) the driving rod is rotated at one end by the motor, the output shaft drives the one end of the driving rod to do circular motion, and the other end of the driving rod drives the driving gear to rotate around the center of the support disc, and the driving gear drives the driven gear to rotate, thereby driving the rotor to rotate. (2) Because the smoke contains water and acidic gases such as sulfur dioxide, when the smoke flows through the low-temperature section of the air preheater, if the temperature of the heating surface is lower than the dew point of the smoke (especially the acid dew point), the water in the smoke will combine with the acidic gases to condense into corrosive liquid, which not only corrodes the heat exchange elements, but also adsorbs fly ash particles in the smoke, gradually deposits on the heat exchange elements, and causes the air preheater to be blocked. In the scheme, the hinged point of the support disc and the connecting rod is eccentrically arranged, and the free end of the connecting rod is slidably connected with the hinged end of the driving rod through the support frame, forming a crank rocker structure. During the rotation of the driving gear, when the driving rod moves from the minimum transmission angle position to the maximum transmission angle position (working stroke), the angular velocity of the driving gear is slow; when the driving rod returns from the maximum transmission angle to the minimum transmission angle position (return stroke), due to the geometric characteristics of the eccentric structure, the angular velocity of the driving gear is accelerated, forming a quick return motion, and because the driving gear and the driven gear are meshed, the driven gear also has the quick return characteristic, thereby making the rotor rotate at a non-uniform speed. Through the above quick return characteristic, the region where the driven gear drives the rotor to rotate at a high speed corresponds to the air side of the air preheater, and the region where the rotor rotates at a low speed corresponds to the smoke side of the air preheater, thereby shortening the residence time of the heat exchange elements in the air side, avoiding excessive temperature drop of the heat exchange elements below the dew point of the smoke due to long-time heat exchange with low-temperature air, and reducing the risk of blockage; at the same time, the large temperature difference between the excessive temperature drop of the heat exchange elements in the air side and the high temperature of the smoke side will produce greater thermal stress.

[0016] Further, the support disc and the second eccentric hinge end of the connecting rod form a first eccentric distance with the shaft center of the driving gear, the first eccentric distance is 0.2 times of the radius of the driving gear, and the length of the driving rod is 0.6 times of the length of the connecting rod, so that the driving gear generates an angular velocity difference in the circumferential direction, and the average angular velocity of the half stroke is greater than the average angular velocity of the other half stroke.

[0017] The principle and effect of the scheme are that: through the above setting, the circumferential angular velocity difference is generated in the rotation process of the driving gear due to the change of the force arm and the stroke, that is, the average angular velocity of the half stroke is greater than the other half stroke, and the speed difference is transmitted to the driven gear through gear meshing, and then the rotor forms the quick return characteristic. When the rotor rotates to the flue gas side, corresponding to the half stroke with smaller average angular velocity of the driven gear, the rotation speed is slower, and the contact time of the heat exchange element and the high-temperature flue gas can be prolonged to fully absorb heat; when rotating to the air side, corresponding to the half stroke with larger average angular velocity of the driven gear, the rotation speed is faster, and the contact time of the heat exchange element and the low-temperature air can be shortened to avoid excessive cooling below the flue gas dew point to cause corrosion and blockage, and reduce the thermal stress caused by the temperature difference on both sides.

[0018] Further, the heat exchange element comprises a heat exchange chamber and a heat exchange plate, the heat exchange chamber is an open and through heat exchange chamber, and the number of the heat exchange plates is multiple groups, and the multiple groups of heat exchange plates are distributed along the inner wall of the heat exchange chamber, so that the heat exchange channels for medium flow are formed between adjacent heat exchange plates.

[0019] The principle and effect of the scheme are that: the open and through heat exchange chamber provides a flow channel for flue gas or air, when the medium (flue gas or air) flows through the heat exchange channel, heat can be transmitted through the heat exchange plate, and the interval distribution of the heat exchange plates can guide the medium to form turbulent flow and enhance heat exchange.

[0020] Further, each group of the heat exchange plates comprises two first heat exchange plates and second heat exchange plates arranged above and below, the first heat exchange plate and the second heat exchange plate are both in sliding connection with the side wall of the heat exchange chamber; the first heat exchange plate is located above the second heat exchange plate, and the first heat exchange plate is arranged outside the second heat exchange plate, the top end of the first heat exchange plate is fixedly connected with a traction rope, the free end of the traction rope is fixedly connected with the top end of the second heat exchange plate, the top end of the side wall of the heat exchange chamber is provided with a fulcrum, the traction rope passes through the fulcrum, and a driving unit for driving the first heat exchange plate to move downward is further arranged.

[0021] The principle and effect of the scheme are that: (1) when the air preheater is running, since the boiler flue gas flows from top to bottom, the first heat exchange plate located at the top contacts the flue gas with higher temperature first and absorbs more heat, and when the flue gas flows to the bottom and contacts the second heat exchange plate, the temperature of the flue gas has been lowered due to heat exchange with the first heat exchange plate, and the heat release is reduced, so the second heat exchange plate absorbs less heat than the first heat exchange plate. Therefore, the first heat exchange plate and the second heat exchange plate need to be transposed on the air side to make the heat release more uniform. (2) In the scheme, when the rotor rotates to the air side, the first heat exchange plate is driven to slide downward along the side wall of the heat exchange chamber by the driving unit, and since the first heat exchange plate and the second heat exchange plate are connected by the traction rope that bypasses the top pivot of the chamber side wall, when the first heat exchange plate moves downward, it pulls the second heat exchange plate to slide upward along the side wall through the traction rope, so that the positions of the first heat exchange plate and the second heat exchange plate are interchanged. At this time, the first heat exchange plate that absorbs more heat is located at the bottom and preferentially contacts the low-temperature air flowing from bottom to top on the air side to fully release heat, and the second heat exchange plate that absorbs less heat is located at the top and contacts the air that has been preliminarily heated to release the remaining heat, so that the heat is released more uniformly, thereby improving the heat exchange efficiency.

[0022] Further, the driving unit includes a support plate, a fixed pulley and a sliding block, the support plate is arranged between the first heat exchange plate and the second heat exchange plate, the support plate is provided with a through slot for the first heat exchange plate and the second heat exchange plate to pass through, the support plate is provided with a cavity, the fixed pulley is fixedly arranged in the cavity, and the sliding block is slidingly arranged in the cavity.

[0023] The principle and effect of the scheme are that: when the rotor rotates to the air side, under the action of the quick return characteristic, the sliding block slides along the cavity of the support plate under the centrifugal force, thereby pulling the connected traction rope, the traction rope changes the force direction by bypassing the fixed pulley in the cavity, and drives the first heat exchange plate to move downward along the side wall of the heat exchange chamber, while the first heat exchange plate synchronously pulls the second heat exchange plate to slide upward through the traction rope that bypasses the pivot, so as to realize the position interchanging of the two. When the rotor rotates to the flue gas side, the centrifugal force acting on the sliding block is reduced to slide back along the cavity due to the slow rotation speed on the flue gas side, the traction rope is relaxed, and the first heat exchange plate and the second heat exchange plate are reset to the initial upper and lower positions under the action of gravity, so that the heat exchange plates in different positions on the flue gas side and the air side are corresponded.

[0024] Further, the inner side of the bottom of the first heat exchange plate is attached to the outer side of the top of the second heat exchange plate.

[0025] The principle and effect of the scheme are that when the first heat exchange plate moves downward and the second heat exchange plate moves upward, the adhered plate surface slides relatively, and the flue gas dust adhered to the plate surface is scraped off through the friction force of the contact surface of the two plates, so that the cleaning of the contact surface of the two plates is completed at each position switching, the dust accumulation is avoided to form a stubborn scale layer, and the dust accumulation is reduced.

[0026] Further, the first heat exchange plate is connected with a spring, a free end of the spring is fixedly connected with a side wall of the heat exchange chamber, a sliding table is arranged in the cavity, a sliding block is slidingly connected with the sliding table, and the sliding block is connected with a tension spring, and a free end of the tension spring is fixedly connected with an inner wall of the cavity.

[0027] The principle and effect of the scheme are that the spring and the tension spring are used for driving the first heat exchange plate and the sliding block to reset respectively, and the sliding table is used for providing positioning and guiding for the movement of the sliding block. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the prior art; Figure 2 It is a structural schematic diagram of a boiler waste heat recovery system of the present application; Figure 3 It is a top view of the air preheater of the present application; Figure 4 It is a structural schematic diagram of the driving assembly of the present application Figure 1 ; Figure 5 It is a structural schematic diagram of the driving assembly of the present application Figure 2 ; Figure 6 It is a top view of the rotor of the present application; Figure 7 It is a structural schematic diagram of the heat exchange element of the present application.

[0029] The reference signs in the drawings of the specification include: air preheater 1, flue gas passage 11, flue gas passage 12, primary air passage 121, secondary air passage 122, shell 13, rotor 14, heat exchange element 15, heat exchange chamber 151, heat exchange plate 152, first heat exchange plate 153, second heat exchange plate 154, traction rope 155, fulcrum 156, support plate 157, fixed pulley 158, sliding block 159, tension cable 160, sliding table 161, driven gear 16, driving gear 17, preheating unit 2, compartment 21, circulating fan 22, waste heat utilization unit 3, first heat exchanger 31, second heat exchanger 32, driving assembly 4, motor 41, driving rod 42, eccentric hinged end 421, support disc 43, eccentric hinged end 431, connecting rod 44, support frame 45. DETAILED DESCRIPTION

[0030] The concept and the technical effects of the present application will be described clearly and completely in combination with the embodiments, so as to fully understand the purposes, features and effects of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application: Embodiment 1 Please refer to Figure 2 and Figure 3 The boiler waste heat recovery system of the present embodiment comprises an air preheater 1, a boiler, a preheating unit 2 and a waste heat utilization unit 3. The flue gas outlet of the boiler is connected to the flue gas passage 11 inlet of the air preheater 1 through a pipeline, and the flue gas passage 11 outlet of the air preheater 1 is connected to the waste heat utilization unit 3. The air passage 12 outlet of the air preheater 1 is connected to the combustion air inlet of the boiler through a pipeline, and the air passage 12 inlet is used to introduce the air to be heated. The preheating unit 2 comprises a compartment 21 and a circulating fan 22. The compartment 21 is arranged on the air side of the air preheater 1 and is located between the flue gas passage 11 and the air passage 12. The air inlet end and the air outlet end of the compartment 21 are connected through a circulating pipeline, and the circulating fan 22 is installed on the circulating pipeline. During the operation of the system, the circulating fan 22 drives the gas in the compartment 21 to circulate, forming a buffer area with a temperature between the flue gas and the air. When the heat storage body rotates with the rotor 14 and is transferred from the flue gas passage 11 to the air passage 12, it will first pass through the compartment 21. The circulating gas can adjust the temperature of the heat storage body, reduce the sudden change amplitude from high temperature to low temperature, and slow down the deformation of the heat storage body caused by excessive local thermal stress.

[0031] Please continue to refer to Figure 2 and Figure 3The waste heat utilization unit 3 comprises a first heat exchanger 31 and a second heat exchanger 32. The air side inlet of the first heat exchanger 31 is communicated with the outlet of the flue gas passage 11, the heat exchange medium outlet of the first heat exchanger 31 is communicated with the heat exchange medium inlet of the second heat exchanger 32, the heat exchange medium outlet of the second heat exchanger 32 is communicated with the heat exchange medium inlet of the first heat exchanger 31, and the air side inlet of the second heat exchanger 32 is used for introducing the air to be heated, and the air side outlet is communicated with the inlet of the air passage 12 through a pipeline; the air side outlet of the first heat exchanger 31 is sequentially connected with a desulfurization device, a denitration device and an induced draft fan, and the outlet of the induced draft fan is communicated with a chimney (not shown), which is a prior art and will not be described in detail here. The cooling flue gas discharged from the flue gas passage 11 of the air preheater 1 first enters the first heat exchanger 31, and the remaining waste heat is transferred to the circulating heat exchange medium, and the heat exchange medium brings heat to the second heat exchanger 32, preheats the air to be heated at the inlet of the air passage 12, so that the air has part of the heat before entering the air preheater 1, and the temperature difference with the heat storage body is reduced. The flue gas further cooled by the first heat exchanger 31 is sequentially purified by the desulfurization and denitration devices, and after removing the pollutants, it is sent into the chimney by the induced draft fan for emission, realizing environmental protection treatment.

[0032] Please refer to Figure 3 、 Figure 4 and Figure 6 , the air preheater 1 is composed of a shell 13, a rotor 14 and a heat exchange element 15. The shell 13 is divided to form a flue gas passage 11 and an air passage 12, the air passage 12 includes a primary air passage 121, a secondary air passage 122 and a compartment 21; the rotor 14 is arranged in the shell 13, and the rotating shaft thereof extends out of the shell 13; the heat exchange element 15 is distributed in the cavity of the rotor 14 along the radial direction and the circumferential direction of the rotor 14, and can adopt a plate or corrugated plate structure; the rotating shaft of the rotor 14 is coaxially fixedly connected with a driven gear 16, the driven gear 16 is engaged with a driving gear 17, and the driving gear 17 is connected with a driving assembly 4, which in the embodiment adopts a servo motor. Different passages formed by the shell 13 enable the driving assembly 4 to drive the rotor 14 and the heat exchange element 15 to rotate, so that the heat exchange element 15 can alternately enter the high-temperature flue gas passage 11 to absorb heat, and then enter different air passages 12 to release heat, and the air first passes through the compartment 21 to adjust the temperature before entering the air passage 12. It should be noted that the rotor 14, the heat exchange element 16 and the like are prior art, and the corresponding structures in the patent document CN112212356A can be referred to.

[0033] The boiler waste heat recovery system of the embodiment operates as follows: the high-temperature flue gas generated by the boiler combustion is first delivered to the flue gas passage 11 of the air preheater 1 through a pipeline, and in the process of flowing in the flue gas passage 11, the high-temperature flue gas transfers heat to the heat exchange elements 15 distributed in the cavity of the rotor 14, so that the heat exchange elements 15 absorb heat to complete preliminary heat storage. At the same time, the air to be heated is introduced from the air side inlet of the second heat exchanger 32, and the flue gas preliminarily cooled by the air preheater 1 is discharged from the outlet of the flue gas passage 11 and then enters the first heat exchanger 31 of the waste heat utilization unit 3, in which the flue gas transfers the remaining waste heat to the circulating heat exchange medium, and the heat exchange medium carrying the heat enters the second heat exchanger 32 to preheat the introduced air to be heated, and the preheated air enters the air passage 12 inlet of the air preheater 1 through a pipeline. The flue gas further cooled by the first heat exchanger 31 flows through the desulfurization device and the denitration device in turn for purification treatment, and is sent into the chimney for emission under the action of the induced draft fan after the pollutants are removed. Under the action of the driving assembly 4, the driving gear 17 drives the driven gear 16 to rotate, and then the rotor 14 drives the heat exchange elements 15 to rotate. When the heat exchange elements 15 rotate with the rotor 14 to the flue gas passage 11, they continuously absorb the heat of the high-temperature flue gas; when the heat exchange elements 15 rotate out of the flue gas passage 11, they first enter the compartment 21 of the preheating unit 2, at which time the circulating fan 22 drives the gas in the compartment 21 to circulate, forming a buffer area with a temperature between that of the flue gas and the air, to adjust the temperature of the heat exchange elements 15 and reduce the sudden change amplitude from high temperature to low temperature. The heat exchange elements 15 adjusted by the compartment 21 continue to rotate with the rotor 14, enter the primary air passage 121 or the secondary air passage 122 of the air passage 12, and exchange heat with the air preheated by the second heat exchanger 32 and introduced from the inlet of the air passage 12, to release the stored heat and heat the air. The heated air is delivered to the combustion air inlet of the boiler through the outlet of the air passage 12 to participate in the combustion process of the boiler as combustion air, realizing effective utilization of waste heat.

[0034] Embodiment 2 The difference between the embodiment and the previous embodiment is that the driving assembly 4 in the previous embodiment rotates at a uniform speed, thereby driving the rotor 14 to rotate at a uniform speed, but because the heat exchange elements 15 are in long-term heat exchange with the low-temperature air and are excessively cooled below the dew point of the flue gas, they are easy to be blocked, and a huge temperature difference formed thereby will generate greater thermal stress. Therefore, the driving assembly 4 and the heat exchange elements 15 are further improved in the embodiment to solve the problem.

[0035] Please refer to FIG Figure 4 and Figure 5The drive assembly 4 includes a motor 41 and a drive rod 42. The output shaft of the motor 41 is coaxially and fixedly connected to one end of the drive rod 42. The free end of the drive rod 42 is hinged to the drive gear 17. The drive gear 17 is coaxially connected to a support disk 43, which is fixed to the housing 13 (the support disk 43 does not rotate with the drive gear 17). The support disk 43 is eccentrically hinged to a connecting rod 44, the free end of which is connected to a support frame 45. The connecting rod 44 and the support frame 45 are slidably connected to form a sliding pair structure. The first eccentrically hinged end 421 of the drive rod 42 and the drive gear 17 is located inside the support frame 45. The motor 41 drives one end of the drive rod 42 to rotate, and the output shaft drives one end of the drive rod 42 to perform a circular motion. The other end of the drive rod 42 pushes the drive gear 17 to rotate around the center of the support disk 43. The drive gear 17 drives the driven gear 16 to rotate, thereby driving the rotor 14 to rotate. Because the hinge point between the support plate 43 and the connecting rod 44 is eccentrically set, forming a crank-rocker structure, the drive gear 17 generates a rapid return motion during rotation, causing the rotor 14 to rotate at a non-uniform speed. This shortens the residence time of the heat exchange element 15 on the air side, preventing it from excessively cooling below the flue gas dew point due to prolonged heat exchange with low-temperature air, mitigating the risk of blockage, and reducing thermal stress caused by the temperature difference between the two sides. Furthermore, a first eccentricity is formed between the second eccentric hinge end 431 of the support plate 43 and the connecting rod 44 and the axis of the drive gear 17. This first eccentricity is 0.2 times the radius of the drive gear 17, and the length of the drive rod 42 is 0.6 times the length of the connecting rod 44. This arrangement causes a circumferential angular velocity difference when the drive gear 17 rotates, half a circumference ( Figure 6 The average angular velocity of the travel in region B is greater than that in the other half of the journey. Figure 6 The heat exchange element 15 rotates to the high-temperature flue gas side (region A) and is transmitted to the driven gear 16 through gear meshing, driving the rotor 14 to form a quick-return characteristic. When the rotor 14 rotates to the flue gas side, the speed is slower, which prolongs the contact time between the heat exchange element 15 and the high-temperature flue gas to fully absorb heat; when it rotates to the air side, the speed is faster, which shortens the contact time with the low-temperature air, avoids excessive cooling that could cause corrosion and blockage, and reduces thermal stress.

[0036] Please see Figure 7The heat exchange element 15 includes a heat exchange chamber 151 and heat exchange plates 152. The heat exchange chamber 151 has an open and continuous structure. There are multiple sets of heat exchange plates 152, which are distributed at intervals along the inner wall of the heat exchange chamber 151, forming heat exchange channels for medium flow between adjacent heat exchange plates 152. In this embodiment, the heat exchange plates 152 adopt a rectangular plate structure. The open heat exchange chamber 151 provides a flow channel for flue gas or air. When the medium flows through the heat exchange channel, heat is transferred through the heat exchange plates 152. Each heat exchange plate 152 includes a first heat exchange plate 153 and a second heat exchange plate 154 arranged vertically. Both the first heat exchange plate 153 and the second heat exchange plate 154 are slidably connected to the side wall of the heat exchange chamber 151. The first heat exchange plate 153 is located above the second heat exchange plate 154 and is located outside the second heat exchange plate 154. A traction rope 155 is fixedly connected to the top of the first heat exchange plate 153, and the free end of the traction rope 155 is fixedly connected to the top of the second heat exchange plate 154. A fulcrum 156 is provided at the top of the side wall of the heat exchange chamber 151, and the traction rope 155 passes around the fulcrum 156. A drive unit for driving the first heat exchange plate 153 to move downward is also provided. Since the boiler flue gas flows from top to bottom, the upper first heat exchange plate 153 comes into contact with the high-temperature flue gas first and absorbs more heat, while the lower second heat exchange plate 154 absorbs less heat. When the rotor 14 rotates to the air side, the drive unit drives the first heat exchange plate 153 to slide downwards and pulls the second heat exchange plate 154 upwards via the traction rope 155, so that the positions of the two are interchanged. The first heat exchange plate 153, which absorbs more heat, is located at the bottom and makes preferential contact with the low-temperature air flowing from bottom to top on the air side to fully release heat. The second heat exchange plate 154, which absorbs less heat, is located at the top and makes contact with the pre-heated air to release the remaining heat, so that the heat release is more uniform and the heat exchange efficiency is improved.

[0037] Please continue reading. Figure 7The driving unit comprises a support plate 157, a fixed pulley 158 and a sliding block 159. The support plate 157 is arranged between the first heat exchange plate 153 and the second heat exchange plate 154. The support plate 157 is provided with a through slot for the first heat exchange plate 153 and the second heat exchange plate 154. The support plate 157 is provided with a cavity. The fixed pulley 158 is fixed in the cavity. The sliding block 159 is slidingly arranged in the cavity. The sliding block 159 is connected with a cable 160. The cable 160 passes around the fixed pulley 158. The free end of the cable 160 is fixedly connected with the top end of the first heat exchange plate 153. When the rotor 14 rotates to the air side, the air side rotates faster due to the effect of the quick return characteristic. The sliding block 159 slides along the cavity of the support plate 157 under the action of the centrifugal force. The cable 160 is pulled. The cable 160 passes around the fixed pulley 158 and drives the first heat exchange plate 153 to move downward. The first heat exchange plate 153 synchronously pulls the second heat exchange plate 154 to slide upward through the traction rope 155, so as to realize the position exchange. When the rotor 14 rotates to the flue gas side, the flue gas side rotates slower. The centrifugal force acting on the sliding block 159 decreases. The sliding block 159 slides back along the cavity. The cable 160 is relaxed. The first heat exchange plate 153 and the second heat exchange plate 154 are reset under the action of the gravity. The inner side of the bottom of the first heat exchange plate 153 is attached to the outer side of the top of the second heat exchange plate 154. When the first heat exchange plate 153 moves downward and the second heat exchange plate 154 moves upward, the attached plate surfaces slide relative to each other. The flue gas dust on the plate surfaces is scraped off through the friction force of the contact surface. The cleaning of the contact surfaces of the two plates is completed at each position switching. The dust accumulation is avoided to form a stubborn scale layer. The accumulation of the dust is reduced. The cleaning effect is good. The first heat exchange plate 153 is connected with a spring (not shown). The free end of the spring is fixedly connected with the side wall of the heat exchange chamber 151. The spring is mainly used to drive the first heat exchange plate 153 to reset to the initial position when the first heat exchange plate 153 is subjected to a smaller centrifugal force. The cavity is provided with a sliding table 161. The sliding block 159 is slidingly connected with the sliding table 161. The sliding block 159 is connected with a tension spring (not shown). The free end of the tension spring is fixedly connected with the inner wall of the cavity. The tension spring is used to drive the sliding block 159 to reset to the left side of the sliding table 161 when the sliding block 159 is subjected to a smaller centrifugal force.

[0038] The working process of the present embodiment is basically the same as that of Embodiment 1, and the difference lies in the driving assembly 4 and the heat exchange element 15. After the system is started, the high-temperature flue gas generated by the boiler still flows through the original path of the flue gas passage 11, the air preheater 1, and the waste heat utilization unit 3 in sequence, and the heated air enters the air passage 12 after being preheated by the second heat exchanger 32, and finally returns to the boiler as combustion air. The difference is that the operation mode of the driving assembly 4 has changed: the motor 41 drives one end of the driving rod 42 to move in a circular motion, and the other end of the driving rod 42 pushes the driving gear 17 to rotate around the center of the support disc 43. Due to the eccentric setting of the hinge point of the support disc 43 and the connecting rod 44, a crank rocker structure is formed, and the driving gear 17 produces a quick return motion during rotation, which, through the meshing transmission with the driven gear 16, makes the rotor 14 exhibit a non-uniform rotation characteristic. Specifically, when the rotor 14 rotates to the flue gas side (corresponding to Figure 6 Area A), the rotation speed is slow, prolonging the contact time of the heat exchange element 15 with the high-temperature flue gas and ensuring that the heat exchange plate 152 fully absorbs heat; when it rotates to the air side (corresponding to Figure 6 Area B), the rotation speed is fast, shortening the contact time of the heat exchange element 15 with the low-temperature air, avoiding excessive cooling below the dew point of the flue gas, thereby reducing the risk of blockage and reducing thermal stress. At the same time, the heat exchange element 15 is also adjusted accordingly. When the rotor 14 drives the heat exchange element 15 to rotate to the flue gas side, the high-temperature flue gas flows from top to bottom through the heat exchange chamber 151, and the first heat exchange plate 153 above first contacts the high-temperature flue gas and absorbs more heat than the second heat exchange plate 154 below. As the rotor 14 rotates to the air side, affected by the quick return characteristic, the slider 159 slides along the slide 161 of the support plate 157 under the action of centrifugal force, pulling the cable 160, which passes around the fixed pulley 158 to drive the first heat exchange plate 153 to move downward, while pulling the second heat exchange plate 154 upward through the traction rope 155, so that the positions of the two are interchanged. At this time, the first heat exchange plate 153, which absorbs more heat, is located below and preferentially contacts and fully releases heat with the low-temperature air flowing from bottom to top, and the second heat exchange plate 154, which absorbs less heat, is located above and contacts the already preliminarily heated air to release the remaining heat, making the heat release more uniform and improving the heat exchange efficiency. During the relative sliding of the first heat exchange plate 153 and the second heat exchange plate 154, the plate surfaces of the two are scraped to remove the flue gas dust on each other's surfaces through friction force, avoiding the formation of stubborn scale layer by accumulated dust. When the rotor 14 rotates to the flue gas side again, the rotation speed slows down, the centrifugal force acting on the slider 159 decreases, and the slider 159 slides back along the slide 161 under the action of the tension spring, the cable 160 relaxes, the first heat exchange plate 153 is reset upward under the action of the spring, and the second heat exchange plate 154 is reset downward under the action of gravity, restoring the initial position to reabsorb the heat of the flue gas.

[0039] The above-mentioned are only embodiments of the present application, and the common knowledge of specific structures and characteristics in the scheme is not described too much. It should be pointed out that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, which will not affect the effect and practicality of the patent. The protection scope claimed in this application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A boiler waste heat recovery system, comprising an air preheater (1) and a boiler, wherein the flue gas outlet of the boiler is connected to the inlet of the flue gas passage (11) of the air preheater (1) via a pipe, and the outlet of the flue gas passage (11) of the air preheater (1) is connected to a waste heat utilization system (3); the outlet of the air passage (12) of the air preheater (1) is connected to the combustion air inlet of the boiler via a pipe, and the inlet of the air passage (12) is used to introduce air to be heated; characterized in that, It also includes a preheating unit (2), which comprises: The compartment (21) is located on the air side of the air preheater (1) and is located between the flue gas passage (11) and the air passage (12); the air inlet and air outlet of the compartment (21) are connected by a circulation pipe. A circulating fan (22) is installed on a circulating pipe and is used to drive the gas circulation in the compartment (21).

2. The boiler waste heat recovery system according to claim 1, characterized in that: The waste heat utilization unit (3) includes a first heat exchanger (31) and a second heat exchanger (32). The air-side inlet of the first heat exchanger (31) is connected to the outlet of the flue gas passage (11). The heat exchange medium outlet of the first heat exchanger (31) is connected to the heat exchange medium inlet of the second heat exchanger (32). The heat exchange medium outlet of the second heat exchanger (32) is connected to the heat exchange medium inlet of the first heat exchanger (31). The air-side inlet of the second heat exchanger (32) is used to preheat the air to be heated. The air-side outlet of the second heat exchanger (32) is connected to the inlet of the air passage (12) through a pipe. The air-side outlet of the first heat exchanger (31) is sequentially connected to a desulfurization device, a denitrification device, and an induced draft fan. The outlet of the induced draft fan is connected to a chimney.

3. The boiler waste heat recovery system according to claim 1, characterized in that: The air preheater (1) includes a shell (13), a rotor (14) and heat exchange elements (15). The shell (13) is divided to form a flue gas passage (11) and an air passage (12). The air passage (12) includes a primary air passage (121), a secondary air passage (122) and a compartment (21). The rotor (14) is located inside the shell (13), and the shaft of the rotor (14) extends outside the shell (13). The heat exchange elements (15) are distributed radially and circumferentially in the cavity of the rotor (14). The shaft of the rotor (14) is coaxially fixedly connected to a driven gear (16), which meshes with a driving gear (17). The driving gear (17) is connected to a drive assembly (4).

4. A boiler waste heat recovery system according to claim 3, characterized in that: The drive assembly (4) includes a motor (41) and a drive rod (42). The output shaft of the motor (41) is coaxially fixedly connected to one end of the drive rod (42). The free end of the drive rod (42) is hinged to the drive gear (17). The drive gear (17) is coaxially provided with a support plate (43). The support plate (43) is fixedly mounted on the housing (13). The support plate (43) is eccentrically hinged with a connecting rod (44). The free end of the connecting rod (44) is provided with a support frame (45). The connecting rod (44) is slidably connected to the support frame (45). The first eccentric hinge end (421) of the drive rod (42) and the drive gear (17) is located inside the support frame (45).

5. A boiler waste heat recovery system according to claim 4, characterized in that: The second eccentric hinge end (431) of the support plate (43) and the connecting rod (44) forms a first eccentricity with the axis of the drive gear (17). The first eccentricity is 0.2 times the radius of the drive gear (17). The length of the drive rod (42) is 0.6 times the length of the connecting rod (44), so that the drive gear (17) generates an angular velocity change in the circumferential direction, wherein the average angular velocity of half a stroke is greater than the average angular velocity of the other half stroke.

6. A boiler waste heat recovery system according to claim 5, characterized in that: The heat exchange element (15) includes a heat exchange chamber (151) and a heat exchange plate (152). The heat exchange chamber (151) is an open and continuous heat exchange chamber (151) with openings at the top and bottom. The heat exchange plate (152) is in multiple sets. The multiple sets of heat exchange plates (152) are distributed at intervals along the inner wall of the heat exchange chamber (151) so that heat exchange channels for medium flow are formed between adjacent heat exchange plates (152).

7. A boiler waste heat recovery system according to claim 6, characterized in that: Each heat exchange plate (152) includes two heat exchange plates (153) and (154) arranged vertically. The first heat exchange plate (153) and the second heat exchange plate (154) are slidably connected to the side wall of the heat exchange chamber (151). The first heat exchange plate (153) is located above the second heat exchange plate (154) and is located outside the second heat exchange plate (154). A traction rope (155) is fixedly connected to the top of the first heat exchange plate (153). The free end of the traction rope (155) is fixedly connected to the top of the second heat exchange plate (154). A fulcrum (156) is provided at the top of the side wall of the heat exchange chamber (151). The traction rope (155) passes around the fulcrum (156). The heat exchange chamber (151) also includes a drive unit for driving the first heat exchange plate (153) to move downward.

8. A boiler waste heat recovery system according to claim 7, characterized in that: The drive unit includes a support plate (157), a fixed pulley (158), and a slider (159). The support plate (157) is located between the first heat exchange plate (153) and the second heat exchange plate (154). The support plate (157) has a through groove for the passage of the first heat exchange plate (153) and the second heat exchange plate (154). The support plate (157) has a cavity. The fixed pulley (158) is fixedly located in the cavity. The slider (159) is slidably located in the cavity. The slider (159) is connected to a cable (160). The cable (160) passes around the fixed pulley (158), and its free end is fixedly connected to the top end of the first heat exchange plate (153).

9. A boiler waste heat recovery system according to claim 8, characterized in that: The bottom inner side of the first heat exchange plate (153) is in contact with the top outer side of the second heat exchange plate (154).

10. A boiler waste heat recovery system according to claim 8, characterized in that: The first heat exchange plate (153) is connected to a spring, and the free end of the spring is fixedly connected to the side wall of the heat exchange chamber (151); a slide (161) is provided in the cavity, and the slider (159) is slidably connected to the slide (161); the slider (159) is connected to a tension spring, and the free end of the tension spring is fixedly connected to the inner wall of the cavity.

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