Multi-backhaul air and flue gas heat exchange system

Abstract

The application discloses a multi-return flue gas and air heat exchange system and belongs to the technical field of flue gas heat exchange. The application comprises a flue gas channel and an air channel which are independent of each other. The air channel is a multi-return channel, and the flue gas channel is perpendicular to the plane where the multi-return channel is located as a whole, so that the same isothermal flue gas section of the flue gas channel covers each return channel of the multi-return channel at the same time. The air channel of the application is horizontally distributed as a whole, and the flue gas is perpendicular to the plane where the air channel is located, so that the same isothermal flue gas section can synchronously cover and heat the outer walls of the tube bundles of different temperature sections of the multi-return channel, and the heat exchange efficiency can be effectively improved. Meanwhile, the horizontally distributed air channel is beneficial to the settlement of fly ash, thereby reducing the risk of forming an ash dirt heat insulation layer attached to the tube wall, and further improving the heat exchange efficiency.

Description

Technical Field

[0001] This invention belongs to the field of flue gas heat exchange technology, and more specifically, relates to a multi-pass flue gas heat exchange system. Background Technology

[0002] During the operation of high-temperature equipment such as industrial boilers, solid waste incinerators, and various industrial kilns, the exhaust gas typically carries a large amount of high-quality waste heat. If this high-temperature exhaust gas is directly released into the atmosphere, it will not only cause air pollution but also waste energy significantly.

[0003] To recover and effectively utilize the heat from high-temperature flue gas, existing technologies have proposed a series of flue gas heat exchange systems. These systems transfer heat from the flue gas to combustion air or process air through indirect heat exchange, thereby improving energy efficiency. Among these, cross-flow heat exchange systems are commonly used. These systems involve arranging the flue gas and air heat exchange media in mutually perpendicular flow directions. The flue gas laterally washes over the outer wall of the heat exchange tube bundle, while the air flows longitudinally inside the bundle. The overall flow direction of the flue gas is either co-current or counter-current to the overall airflow, and heat transfer is completed through the heat exchange tube walls. Against this backdrop, further improving the heat exchange efficiency between high-temperature flue gas and the air to be preheated has been a crucial area of ​​continuous research and optimization within the industry.

[0004] A search revealed a flue gas heat exchanger in patent CN108036660A. This application includes: an air outlet header, an air inlet header, a flue gas pipe group, an air pipe group, and a flue gas outlet header; the lower part of the air outlet header is welded to the inner flue gas cylinder, and the upper part is welded to a flange; the air inlet header is a hollow cylinder, with its upper and lower parts welded to the outer flue gas cylinder to form a cavity; an annular seam formed by the inside of the inner cylinder, the inside of the upper flue gas pipe group, the outside of the inner flue gas cylinder, and the inside of the outer flue gas cylinder, the inside of the flue gas pipe group, the flue gas header formed by the sealing plate and the flange, and the flue gas outlet device constitute a flue gas channel; the air inlet device, the air inlet header, the annular seam formed by the inside of the outer cylinder and the outside of the outer flue gas cylinder, the annular seam formed by the inside of the air pipe group, the outside of the inner flue gas cylinder, and the outside of the inner cylinder, and the air outlet header constitute an air channel. In this application, the structural design achieves the intersection of flue gas loop flow and air loop flow, realizing efficient heat exchange during the flow process.

[0005] For example, patent CN217715033U discloses a heat exchange device with a cross-arranged flue gas duct. In this application, by arranging flat refrigerant channels and flat heat medium channels in an interlaced manner, the flow field of the heat exchange medium is made more uniform, and heat exchange is carried out twice through the heat exchanger and the flat channels, thereby further improving the heat exchange efficiency.

[0006] The above applications all involve technical improvements to flue gas heat exchange systems, but the industry still needs more diverse designs to further improve the heat exchange efficiency between high-temperature flue gas and air to be preheated. Summary of the Invention

[0007] The problem to be solved To address at least some of the problems existing in the prior art, this invention proposes a multi-pass flue gas heat exchange system, the purpose of which is to further improve the heat exchange efficiency between high-temperature flue gas and air to be preheated.

[0008] Technical solution To solve the above problems, the technical solution adopted by the present invention is as follows: The present invention provides a multi-pass flue gas heat exchange system, comprising independent flue gas passages and primary air passages; The primary air duct is a multi-pass duct, and the flue gas duct is perpendicular to the plane of the multi-pass duct, so that the same isothermal flue gas cross section of the flue gas duct simultaneously covers each pass of the multi-pass duct.

[0009] In some implementations, the primary air duct consists of at least two primary air return ducts, with adjacent primary air return ducts connected end-to-end by a turning duct.

[0010] In some embodiments, the device includes a housing, within which are arranged a plurality of heat exchange tube bundles that are laterally distributed and sequentially connected. The inner cavity of the heat exchange tube bundles forms the primary air return channel, and the inner cavity of the housing and the outer wall of the heat exchange tube bundles form the flue gas channel.

[0011] In some embodiments, the heat exchange tube bundle is equipped with an independent expansion compensation mechanism between itself and the shell.

[0012] In some embodiments, a dust collection device is provided below the primary air duct.

[0013] In some embodiments, a flue gas collection box connected to the flue gas passage is also included, and a secondary air passage is provided behind the primary air passage along the extension direction of the flue gas passage.

[0014] In some embodiments, the secondary air duct is a multi-pass duct, and the multiple secondary air return passages of the secondary air duct are distributed sequentially along the extension direction of the flue gas duct.

[0015] In some embodiments, a heat exchanger is provided in front of the primary air duct along the extension direction of the flue gas duct.

[0016] In some implementations, the flow rate of primary air in the primary air duct is less than the flow rate of secondary air in the secondary air duct, and the pressure of primary air in the primary air duct is greater than the pressure of secondary air in the secondary air duct.

[0017] Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The multi-pass flue gas heat exchange system of the present invention, compared with the traditional multi-pass channel which is distributed longitudinally, can only heat each pass channel sequentially along the flow direction; while the primary air channel of the present invention is distributed transversely, and the flue gas is perpendicular to the plane of the primary air channel, so that the same isothermal flue gas cross section can simultaneously cover and heat different temperature sections of multiple passes, which can effectively improve the heat exchange efficiency. At the same time, the transversely distributed primary air channel is conducive to the settling of fly ash, thereby reducing the risk of forming a ash insulation layer on the pipe wall, further improving the heat exchange efficiency.

[0018] (2) In the multi-pass flue gas heat exchange system of the present invention, each pass heat exchange tube bundle is equipped with an independent expansion compensation mechanism, which can individually compensate for the differential thermal deformation of heat exchange tube bundles in different temperature ranges, avoid the problems of sealing leakage, tube bundle deformation and cracking caused by the mutual pulling of different thermal expansion amounts when multiple pass tube bundles share the expansion structure, and effectively improve the operational reliability of the equipment under high temperature and variable load conditions.

[0019] (3) The multi-pass flue gas heat exchange system of the present invention, through the setting of the heat exchanger, can first cool down the ultra-high temperature flue gas before it enters the primary air channel and the secondary air channel, avoiding the ultra-high temperature flue gas directly scouring the heat exchange tube bundle and causing the tube material to overheat and deform. At the same time, through the setting of the dust collection device, the settled fly ash can be collected and discharged in time, reducing the ash accumulation on the surface of the tube bundle and maintaining a stable heat transfer coefficient for a long time; at the same time, it reduces the frequency of equipment cleaning and maintenance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a multi-pass flue gas heat exchange system according to the present invention; Figure 2 This is a main sectional view of the assembly between the flue gas passage and the primary air passage in this invention; Figure 3 This is a side sectional view of the assembly between the flue gas passage and the primary air passage in this invention; Figure 4 This is a schematic diagram of the assembly between the flue gas passage and the primary air passage in the prior art.

[0021] In the diagram: 100, flue gas passage; 200, heat exchange tube bundle; 300. Primary air duct; 310. Primary air return duct; 320. Turning duct; 400. Secondary air duct; 410. Secondary air return duct; 500. Expansion compensation mechanism; 600. Dust collection device; 700. Heat exchanger; 800. Flue gas collection box. Detailed Implementation

[0022] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings.

[0023] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] As described in the background section, existing flue gas cross-flow heat exchange systems have been widely used in fields such as industrial waste heat recovery and boiler air preheating due to their large flue gas side flow cross-sectional area and low flow resistance.

[0025] Specifically, refer to Figure 4 As shown, existing flue gas cross-flow heat exchange systems are generally divided into single-pass cross-flow (… Figure 1 (as shown in a) and multi-path crossflow ( Figure 1 (as shown in b, c, and d).

[0026] As shown in the figure, in the existing multi-pass flue gas cross-flow heat exchange system, the overall direction of the air multi-pass flow path is basically counter-current to the flue gas flow direction; of course, some are distributed in the same direction (not shown in the figure). The temperature of the high-temperature flue gas gradually decreases along the flue gas flow direction, and it can only heat the low-temperature section, medium-temperature section and high-temperature section of the air step by step along the path. It is impossible to use flue gas at the same temperature level (i.e., isothermal flue gas cross section) to simultaneously heat air sections at different temperature levels. Under this layout, the matching between the heat release gradient of the flue gas and the heat absorption gradient of the air is poor, and the energy level of the high-temperature flue gas is not fully utilized, which restricts the further improvement of the system's heat exchange efficiency and waste heat recovery capacity.

[0027] Therefore, the present invention aims to provide a multi-pass flue gas heat exchange system, so as to realize the simultaneous heating of multiple passes of air at different temperature ranges by flue gas on the same flue gas temperature cross section, thereby further improving the heat exchange efficiency.

[0028] The present invention will be further described below with reference to specific embodiments.

[0029] like Figure 2 , Figure 3 As shown, a multi-pass flue gas heat exchange system according to this embodiment includes a flue gas passage 100 and a primary air passage 300. The primary air passage 300 is a multi-pass passage; and the flue gas passage 100 is perpendicular to the plane in which the primary air passage 300 is located, so that the same isothermal flue gas cross section of the flue gas passage 100 can simultaneously cover each pass of the primary air passage 300.

[0030] It is not difficult to understand that the aforementioned multi-pass channel does not refer to a single straight-through channel where air enters and exits directly, but rather to a meandering channel in which air completes at least one flow reversal and detour within the channel.

[0031] It is worth mentioning that the aforementioned "vertical" is not an absolute state in a strict geometric sense. A certain angular deviation is allowed in the actual manufacturing and installation process. Usually, when the offset angle is within ±5°, the technical effect of this embodiment can be achieved, which is within the tolerance range allowed by this solution.

[0032] Furthermore, the aforementioned primary air duct 300 consists of at least two primary air return ducts 310, and adjacent primary air return ducts 310 are connected end to end by a turning duct 320.

[0033] Specifically, a multi-pass flue gas heat exchange system according to this embodiment includes a shell, and a plurality of heat exchange tube bundles 200 arranged laterally (perpendicular to the flue gas flow direction) and connected in sequence are arranged inside the shell. The inner cavity of the heat exchange tube bundles 200 forms the aforementioned primary air return channel 310, and the aforementioned flue gas channel 100 is formed between the inner cavity of the shell and the outer wall of the heat exchange tube bundles 200.

[0034] Specifically, in this embodiment, the aforementioned primary air duct 300 is a double-return duct. That is, along the path perpendicular to... Figure 2 In the direction shown on the paper, the heat exchange tube bundle 200 is configured with two passes. Primary air first enters the first pass heat exchange tube bundle 200 to exchange heat with the high-temperature flue gas in the flue gas passage 100. Then, it changes its flow direction through the turning duct 320 and returns to enter the other pass heat exchange tube bundle 200 to continue heat exchange before finally exiting. It is important to note that the two pass heat exchange tube bundles 200 do not exchange heat sequentially within the flue gas passage 100, but rather perform synchronous heat exchange at the same isothermal flue gas cross-section within the flue gas passage 100.

[0035] Compared to the traditional overall vertical distribution (such as...) Figure 1As shown, in a multi-pass flue gas heat exchange system, multiple return channels are sequentially distributed along the flue gas flow direction. The flue gas within the flue gas channel 100 can only heat each return channel sequentially along the flow direction. However, in this embodiment, the primary air channel 300 is horizontally distributed, and the flue gas is perpendicular to the plane containing the primary air channel 300. This allows the same isothermal flue gas cross-section to simultaneously cover and heat different temperature ranges across multiple passes, effectively improving heat exchange efficiency.

[0036] Furthermore, in the traditional longitudinally distributed multi-pass channel structure, each pass forms an obstruction in the direction of flue gas flow, reducing the probability of collision between fly ash and the outer wall of the subsequent pass, thus hindering ash settling. The vast majority of dust remains suspended in the flue gas and cannot settle in time. Simultaneously, because the multi-pass channel is distributed along the flue gas flow direction, the flow on both sides of the channel is a narrow, elongated channel, easily forming local eddies and backflow, which also hinders fly ash settling. After prolonged operation, the pipe walls easily accumulate ash, forming a thick layer of ash and heat insulation, resulting in high thermal resistance and a rapid decline in heat exchange efficiency over time.

[0037] In this embodiment, the primary air duct 300 is generally horizontally distributed, and each return duct has no obstruction in the direction of flue gas flow. This increases the probability of collision between fly ash and the duct wall, allowing the fly ash to settle rapidly under gravity after its kinetic energy decays. Simultaneously, since the primary air duct 300 does not extend along the direction of flue gas flow, the flow channels on both sides of the primary air duct 300 are naturally not too long, thus avoiding the formation of local eddies and backflows, which also facilitates ash settling.

[0038] In other words, the primary air duct 300 is horizontally distributed, which is conducive to the settling of fly ash, thereby reducing the risk of fly ash adhering to the pipe wall and further improving the heat exchange effect.

[0039] Furthermore, traditional devices that heat small-flow-rate air with large-volume flue gas suffer from an excessively large aspect ratio on the air side, resulting in an unreasonable structure. This embodiment, however, effectively achieves a reasonably adjustable aspect ratio for the air-side channel, improving the uniformity of the airflow field and enhancing heat exchange efficiency.

[0040] In summary, this embodiment optimizes the distribution of the primary air ducts 300, changing the traditional longitudinal arrangement along the flue gas flow direction to a transverse arrangement. This allows for simultaneous heating of multiple return air passes using the same flue gas cross-section, fully utilizing waste heat to improve heat exchange efficiency. It also enhances the impact and settling effect of fly ash against the pipe wall, mitigating fly ash adhesion and accumulation defects. This dual benefit results in significantly improved long-term heat exchange efficiency and continuous operational stability of the entire heat exchange system, far exceeding expectations. Furthermore, by varying the number and diameter of the primary air return ducts 310 according to different return air temperatures, a non-uniform cross-section design can be implemented, leading to a more rational airflow velocity, improved heat exchange efficiency, and reduced system air-side resistance.

[0041] In some other embodiments, each pass heat exchanger tube bundle 200 is equipped with an independent expansion compensation mechanism 500, which is prior art and will not be described in detail here.

[0042] In this embodiment, by setting the expansion compensation mechanism 500, the differential thermal deformation of the heat exchange tube bundle 200 in different temperature ranges can be compensated separately, avoiding problems such as sealing leakage and tube bundle deformation and cracking caused by the mutual pulling of different thermal expansion amounts when multiple tube bundles share the expansion structure, effectively improving the operational reliability of the equipment under high temperature and variable load conditions.

[0043] Furthermore, a dust collection device 600 is provided below the heat exchange tube bundle 200, and the dust collection device 600 covers the area occupied by the heat exchange tube bundle 200, so that the settled fly ash can fall directly into the dust collection device 600 for centralized collection and discharge, reducing dust accumulation and blockage on the surface of the tube bundle, maintaining a stable heat transfer coefficient for a long time, and reducing the frequency of equipment cleaning and maintenance.

[0044] like Figure 1 As shown, as another embodiment of a multi-pass flue gas heat exchange system in this example, the heat exchange system includes a flue gas collection box 800 connected to the flue gas passage 100, and a secondary air passage 400 is provided behind the primary air passage 300 along the extension direction of the flue gas passage 100, that is, the flue gas flow direction.

[0045] The secondary air duct 400 is also a multi-pass duct, but the secondary air return ducts 410 of the secondary air duct 400 are distributed sequentially along the extension direction of the flue gas duct 100. That is, the secondary air duct 400 is distributed longitudinally as a whole.

[0046] Furthermore, along the extension direction of the flue gas passage 100, a heat exchanger 700 is installed in front of the primary air passage 300. Because the flue gas discharged from the solid waste incineration radiant heat exchange chamber is extremely hot, it first flows through the heat exchanger 700, where the high-temperature flue gas heats the feed water and generates saturated / superheated steam, recovering the heat from the highest temperature section of the flue gas. The generated steam is used for power generation, heating, and process gas in the plant area, achieving priority utilization of high-grade thermal energy. The flue gas temperature is significantly reduced before being sent into the primary air passage 300 and secondary air passage 400, preventing the ultra-high temperature flue gas from directly scouring the heat exchange tube bundle and causing overheating and thermal deformation of the tubes.

[0047] This embodiment presents a multi-pass flue gas heat exchange system, primarily used in boiler flue gas heat exchange and solid waste powder incineration operations. Furnace combustion is divided into primary air feeding and secondary combustion support. The primary air mainly transports materials to the solid waste powder burner. High-temperature, high-pressure, and low-flow-rate primary air feeding simultaneously raises the material temperature, aiding in fuel ignition. Furthermore, the low volatility of solid waste powder fuel necessitates a low-flow-rate primary air requirement.

[0048] Secondary air primarily serves as combustion aid air in the burner, ensuring complete combustion of combustibles and degradation of pollutants; therefore, its flow rate is significantly higher than that of primary air. However, as a swirling combustion aid air, secondary air has low resistance in the flue gas passage, allowing for complete mixing without high pressure. Using high pressure would cause flame instability, severe fluctuations in furnace negative pressure, and flue gas leakage from the furnace door, increasing the risk of environmental air leakage. Therefore, low pressure is selected.

[0049] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A multi-pass flue gas heat exchange system, comprising independent flue gas passages (100) and primary air passages (300). Its features are: The primary air duct (300) is a multi-pass duct, and the flue gas duct (100) is perpendicular to the plane of the multi-pass duct, so that the same isothermal flue gas cross section of the flue gas duct (100) simultaneously covers each pass of the multi-pass duct.

2. The multi-pass flue gas heat exchange system according to claim 1, characterized in that: The primary air duct (300) consists of at least two primary air return ducts (310), and adjacent primary air return ducts (310) are connected end to end by a turning duct (320).

3. The multi-pass flue gas heat exchange system according to claim 2, characterized in that: The device includes a housing, within which are arranged a plurality of heat exchange tube bundles (200) arranged laterally and connected in sequence. The inner cavity of the heat exchange tube bundles (200) forms the primary air return channel (310), and the inner cavity of the housing and the outer wall of the heat exchange tube bundles (200) form the flue gas channel (100).

4. A multi-pass flue gas heat exchange system according to claim 3, characterized in that: The heat exchange tube bundle (200) is equipped with an independent expansion compensation mechanism (500) between itself and the shell.

5. A multi-pass flue gas heat exchange system according to claim 4, characterized in that: A dust collection device (600) is provided below the primary air duct (300).

6. A multi-pass flue gas heat exchange system according to any one of claims 1-5, characterized in that: It also includes a flue gas collection box (800) that is connected to the flue gas passage (100), and a secondary air passage (400) is provided behind the primary air passage (300) along the extension direction of the flue gas passage (100).

7. A multi-pass flue gas heat exchange system according to claim 6, characterized in that: The secondary air duct (400) is a multi-pass duct, and the multiple secondary air return ducts (410) of the secondary air duct (400) are distributed sequentially along the extension direction of the flue gas duct (100).

8. A multi-pass flue gas heat exchange system according to claim 7, characterized in that: A heat exchanger (700) is provided in front of the primary air passage (300) along the extension direction of the flue gas passage (100).

9. A multi-pass flue gas heat exchange system according to claim 7, characterized in that: The flow rate of primary air in the primary air channel (300) is less than the flow rate of secondary air in the secondary air channel (400), and the pressure of primary air in the primary air channel (300) is greater than the pressure of secondary air in the secondary air channel (400).

Images