A coated heat exchanger and a process for producing a heat exchanger

Abstract

This invention discloses a coated heat exchanger and its manufacturing process, belonging to the technical field of flue gas treatment equipment. It solves the problem of wear, corrosion, and blockage on the heat exchanger surface caused by ash accumulation. The technical solution mainly includes a heat exchanger comprising heat exchange plates, with a flue gas channel formed between adjacent heat exchange plates. Each heat exchange plate comprises two thin plates arranged side-by-side, with the unwelded portions of the two plates far apart to form an air channel. Each thin plate includes a front and a rear section. The length of the front section along the airflow direction is L1, and the length of the thin plate along the airflow direction is L, where 0.25L > L1. The surface of the front section is provided with heat-resistant elements to increase the heat transfer resistance of the front section, making the heat transfer resistance of the front section greater than that of the rear section. This invention effectively prevents the liquefaction, adhesion, and deposition of ammonium bisulfate, reduces ash accumulation, lowers the possibility of blockage, corrosion, and wear on the heat exchanger surface, and improves heat exchange efficiency and service life.

Description

Technical Field

[0001] This invention relates to the technical field of flue gas treatment equipment, and in particular to a coated heat exchanger and a manufacturing process for the heat exchanger. Background Technology

[0002] As a crucial heat exchange device at the tail end of a coal-fired power plant boiler, the air preheater's operating condition directly impacts the unit's economy and safety. While existing technologies combining rotary air preheaters and tubular heat exchangers can improve heat exchange efficiency, they still face a serious problem of ammonium bisulfate ash accumulation. This issue primarily stems from the reaction of ammonia escaping during selective catalytic reduction (SCR) denitrification with flue gas components to form ammonium bisulfate. This substance forms a viscous liquid state at temperatures between 150-200°C, readily adhering to the heated surfaces of heat exchange elements and forming an ash layer.

[0003] The thermal resistance of ash deposits is much higher than that of metallic materials, and their presence significantly reduces the heat transfer performance of heat exchangers. More seriously, ash accumulation reduces the flow area of ​​flue gas passages, causing localized increases in flow velocity and exacerbating wear and corrosion of heated surfaces. Simultaneously, ash accumulation increases flue gas flow resistance, leading to higher exhaust gas temperatures and directly impacting the safe and stable operation of the boiler system.

[0004] In traditional heat exchangers, flue gas and cold air flow in a vertical, cross-flow pattern. This arrangement results in the lowest temperature at the junction of the flue gas outlet and the cold air inlet, which falls precisely within the critical temperature range for ammonium bisulfate liquefaction. This area therefore becomes the most prone to ash accumulation, leading to channel blockage after prolonged operation and severely impacting the equipment's heat exchange performance and lifespan. Summary of the Invention

[0005] The objective of this invention is to provide a coated heat exchanger and its manufacturing process, which solves the problem of wear, corrosion, and blockage of the heat exchanger surface caused by the adhesion and accumulation of ash from liquid ammonium bisulfate at the junction of the flue gas outlet area and the cold air inlet area. This invention effectively prevents the liquefaction, adhesion, and deposition of ammonium bisulfate, reduces ash accumulation, and thereby reduces the possibility of blockage, corrosion, and wear on the heat exchanger surface, thus improving heat exchange efficiency and service life.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a coated heat exchanger, comprising multiple heat exchange plates arranged side by side, with a flue gas channel formed between adjacent heat exchange plates. Each heat exchange plate comprises two thin plates arranged side by side, with the welding position of the two thin plates forming a welded column and the unwelded positions forming an air channel away from each other. Each thin plate comprises a front part and a rear part distributed along the airflow direction, the length of the front part along the airflow direction being L1, the length of the thin plate along the airflow direction being L, and 0.25L>L1. The surface of the front part is provided with a heat-resistant element for increasing the heat transfer resistance of the front part, so that the heat transfer resistance of the front part is greater than that of the rear part.

[0007] Using the aforementioned technical solution, a flue gas channel is formed between two adjacent heat exchange plates. Simultaneously, the heat exchange plates are formed by welding two thin plates together, with an air channel formed between them. When flue gas and air enter the flue gas channel and air channel respectively, the flue gas contacts the outer wall of the thin plate, and the air contacts the inner wall of the thin plate. This allows heat in the flue gas to be transferred to the air through the thin plate, thereby reducing heat loss after flue gas emission and improving the heat recovery efficiency of the flue gas. When the flue gas exchanges heat with the air in the air channel, the air flows from the front to the rear of the thin plate. Therefore, the temperature of the air at the front is lower than that at the rear, and the flue gas... When the flue gas exchanges heat with the air, the temperature of the flue gas after heat exchange is lower than that of the flue gas after heat exchange in the rear section. Furthermore, the flue gas in the front section continuously exchanges heat along its flow path, which may cause the temperature of the flue gas at the junction of the air inlet and the flue gas outlet to be lower than the liquefaction temperature of ammonium bisulfate. By installing heat-insulating elements on the front surface of the thin plate, the heat exchange efficiency at the front of the heat exchange plate is reduced. This ensures that the temperature of the flue gas at the junction of the air inlet and the flue gas outlet is higher than the liquefaction temperature of ammonium bisulfate, reducing the possibility of blockage, corrosion, or wear on the heated surface of the front of the thin plate due to the continuous flow of flue gas caused by the adhesion of liquid ammonium bisulfate.

[0008] Furthermore, the heat-resistant element is an enamel coating.

[0009] Furthermore, the enamel coating is located on the outer side of the thin plate and comes into contact with the flue gas in the flue gas passage.

[0010] Furthermore, the enamel coating is located on the inner side of the thin plate and comes into contact with the air in the air channel.

[0011] Furthermore, the enamel coating includes a first enamel coating and a second enamel coating. The first enamel coating is located on the inner side of the thin plate and contacts the air in the air channel, while the second enamel coating is located on the inner side of the thin plate and contacts the flue gas in the flue gas channel.

[0012] Furthermore, the heat-resistant element is a metal overlay.

[0013] Furthermore, the length of the heat-insulating element along the airflow path gradually increases along the flue gas flow path.

[0014] To achieve the above objectives, the present invention also adopts the following technical solution: a heat exchanger manufacturing process for producing heat exchangers with enamel-coated heat-resistant elements, comprising the following steps:

[0015] S01. Weld two thin plates together, and introduce a high-pressure medium between the two thin plates so that the unwelded parts of the two thin plates are far apart to form an air channel.

[0016] S02. Weld the two adjacent thin plates of the two heat exchange plates at both ends of the air channel to form a flue gas channel between the two heat exchange plates.

[0017] S03. Repeat step S02 to weld multiple heat exchange plates together to form a semi-finished heat exchanger.

[0018] S04. Immerse one end of the air passage of the semi-finished heat exchanger in enamel liquid;

[0019] S05. Remove the semi-finished heat exchanger that has been immersed in enamel liquid, drain it, and let it stand.

[0020] S06. Install the semi-finished heat exchanger after step S05 on the frame to form a heat exchanger.

[0021] Step S06 can also be between steps S03 and S04.

[0022] To achieve the above objectives, the present invention also adopts the following technical solution: a heat exchanger manufacturing process for producing heat exchangers with a metal covering layer as the heat-resistant element, comprising the following steps:

[0023] a. A metal ion stream is sprayed onto one side of one end of the two thin plates to form a metal coating layer;

[0024] b. Place the metal covering layers on the two thin plates facing each other or back to back, with the metal covering layers on the two thin plates placed at the same end, and then weld the two thin plates together.

[0025] c. High-pressure medium is introduced between the two thin plates after welding to make the unwelded parts of the two thin plates separate and form an air channel;

[0026] d. Place multiple heat exchange plates side by side with intervals, and weld the two adjacent thin plates between two adjacent heat exchange plates at both ends of the air channel. After welding, the multiple heat exchange plates are installed on the frame to form a heat exchanger.

[0027] To achieve the above objectives, the present invention also adopts the following technical solution: a heat exchanger manufacturing process for producing heat exchangers with enamel-coated heat-resistant elements, comprising the following steps:

[0028] a. A metal ion flow is sprayed onto both sides of one end of the two thin plates to form a metal coating layer;

[0029] b. Weld the metal overlays of the two thin plates that have been sprayed with double layers to the same end;

[0030] c. High-pressure medium is introduced between the two thin plates after welding to make the unwelded parts of the two thin plates separate and form an air channel;

[0031] d. Two heat exchange plates are spaced apart and the two ends of the air passage are welded together to form a heat exchanger. Multiple heat exchange plates are welded together and installed on the frame to form a heat exchanger.

[0032] As can be seen from the above, the coating heat exchanger and the manufacturing process of the heat exchanger provided by the present invention reduce the heat transfer efficiency of the air inlet section of the heat exchange plate by setting heat-insulating elements, so that the temperature gradient in the area tends to be gentle, avoiding the critical temperature range for the formation of ammonium bisulfate liquefaction deposition, and has the advantages of effectively inhibiting the formation of ash accumulation, improving heat exchange efficiency and extending the service life of equipment. Attached Figure Description

[0033] The present invention will be further described below with reference to the accompanying drawings:

[0034] Figure 1 This is a schematic diagram of the heat exchanger in this invention;

[0035] Figure 2 This is a schematic diagram of the heat exchange plate in this invention;

[0036] Figure 3 This is a schematic diagram of the structure of the thin plate and the heat-insulating element in this invention;

[0037] Figure 4 This is a schematic diagram showing the inclination of the inner end of the heat-insulating element of the present invention;

[0038] Figure 5 This is a schematic diagram showing that the inner end of the heat-resistant element of the present invention is curved. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0040] The terms "first," "second," etc. (if present) in the specification and claims of this invention are used to distinguish similar objects, not to describe a specific order or sequence. Even if "second" is used before a technical feature for distinction, it does not necessarily imply the presence of "first." It should be understood that in this invention, "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. It should be understood that in this invention, "a plurality of" refers to two or more. "And / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, X and / or Y can represent: X alone, X and Y simultaneously, and Y alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "Containing X, Y, and Z," "Containing X, Y, and Z" means that all three X, Y, and Z are included; "Containing X, Y, or Z" means that one of X, Y, and Z is included; "Containing X, Y, and / or Z" means that any one, two, or three of X, Y, and Z are included.

[0041] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The following specific embodiments may be selected to be combined or substituted with each other according to the actual situation, and the same or similar concepts or processes may not be described again in some embodiments.

[0042] like Figure 1 and Figure 2 As shown, the present invention provides a coated heat exchanger, including multiple heat exchange plates 11 arranged side by side. A flue gas passage 113 for flue gas circulation is formed between adjacent heat exchange plates 11. Each heat exchange plate 11 includes two thin plates 111 arranged side by side. The welding position of the two thin plates 111 forms a weld column, and the unwelded positions of the two thin plates 111 are far apart to form an air passage 112. Specifically, in this embodiment, the air passage 112 and the flue gas passage 113 are orthogonally arranged. In the direction of the flue gas passage 113, the flue gas temperature... The temperature gradually decreases along the flow path of the flue gas; within the airflow direction of air passage 112, as the flue gas exchanges heat with the air, the air temperature gradually increases, and the flue gas temperature also shows a gradual upward trend numerically. This results in the lowest temperature of the flue gas at the junction of the inlet and outlet of air passage 112. Specifically, to effectively prevent the flue gas temperature from falling below the liquefaction temperature of ammonium bisulfate at the junction of the inlet and outlet of air passage 112, such as... Figure 1 , Figure 2 and Figure 3As shown, the thin plate 111 includes a front part and a rear part distributed along the airflow direction. The length of the front part along the airflow direction is L1, and the length of the thin plate 111 along the airflow direction is L, where 0.25L>L1. A heat-insulating element 2 is provided on the surface of the front part to increase the heat transfer resistance of the front part, so that the heat transfer resistance of the front part is greater than that of the rear part. The heat-insulating element 2 refers to a heat conduction suppression component provided on the thin plate 111. By increasing the thermal resistance, the heat transfer rate is reduced, which can slow down the cooling effect of cold air on the metal thin plate 111. The heat-insulating element 2 is provided in the front part to reduce the heat transfer efficiency of the front part. Specifically, when cold air enters the air channel 112 from the air intake section, the heat-insulating element 2 reduces the heat transfer efficiency of the area covered by the heat-insulating element 2, thereby reducing the heat exchange between the flue gas and the thin plate 111, and thus reducing the heat exchange between the thin plate 111 and the air. This slows down the rate of temperature drop of the surface of the front part of the thin plate 111, and the overall temperature is maintained above the critical temperature for liquefaction of ammonium bisulfate. Simultaneously, as the flue gas flows within the flue gas channel 113 formed by adjacent heat exchange plates 11, the heat exchange efficiency at the front of the thin plate 111 is effectively reduced, preventing the flue gas outlet area from contacting the overcooled surface of the thin plate 111 and avoiding the formation of local low-temperature zones. This ensures that the temperature of the area prone to ash accumulation is higher than the liquefaction temperature of ammonium bisulfate, eliminating the temperature conditions required for ammonium bisulfate adhesion; effectively inhibiting the liquefaction and deposition of ammonium bisulfate on the surface of the thin plate 111, reducing the formation of ash layers, and lowering the risk of blockage in the flue gas channel 113. The optimized temperature distribution of the heated surface mitigates low-temperature corrosion and extends the service life of the heat exchange plate 11. Under the control of the heat-insulating element 2, the cross-heat exchange structure of the air channel 112 and the flue gas channel 113 only reduces the heat exchange efficiency locally while maintaining the overall heat exchange efficiency, achieving a balance between ash accumulation control and heat exchange performance.

[0043] In this embodiment, to improve the corrosion resistance of the heated surface of the thin plate 111, the heat-insulating element 2 is an enamel coating. Specifically, the enamel coating refers to an inorganic non-metallic covering layer formed by melting and solidifying a glassy material at high temperature. It can be formed as a continuous covering layer on the surface of the heat exchange plate 11 by spraying or impregnation. The thermal conductivity of the enamel coating is lower than that of the thin plate 111, which can form a stable thermal resistance layer in the air intake section. The enamel coating has good heat insulation and corrosion resistance, which can effectively reduce the heat transfer efficiency of the air intake section. When the high-temperature flue gas flows through the coating surface, the inherent low thermal conductivity of the coating material slows down the heat transfer efficiency to the thin plate 111. This delaying effect prevents the temperature of the thin plate 111 in the air intake section from dropping sharply due to the rapid heat absorption of cold air, thereby maintaining the metal surface temperature above the critical temperature for the liquefaction of ammonium bisulfate and eliminating the necessary conditions for the formation of liquid ammonium bisulfate.

[0044] In another embodiment, the enamel coating is located on the outer side of the thin plate 111 and contacts the flue gas in the flue gas passage 113. It should be noted that in this embodiment and subsequent embodiments, the side wall of the thin plate 111 that contacts the flue gas in the flue gas passage 113 is considered the outer side wall, and the side wall of the thin plate 111 that contacts the air in the air passage 112 is considered the inner side wall. By controlling the coating thickness to be in the range of 0.2 to 0.5 mm, the coating completely covers the heated surface of the thin plate 111 in the flue gas flow path. When high-temperature flue gas containing ammonium bisulfate flows through this area, the relatively smooth surface of the enamel coating makes it difficult for liquid ammonium bisulfate to adhere stably, and its smooth surface promotes the removal of the deposits formed under the scouring action of the flue gas. Moreover, the silica component in the enamel coating undergoes a passivation reaction with the acidic substances in the flue gas, forming a chemical protective layer on the surface of the metal substrate, blocking the penetration of corrosive media, improving the corrosion resistance of the thin plate 111, and thus improving the service life of the thin plate 111. By precisely positioning the enamel coating on the heated surface of the thin plate 111, while maintaining the thermal conductivity of the metal substrate, the matching characteristics of the thermal expansion coefficient of the enamel material and the thin metal plate 111 are utilized to avoid coating cracking caused by thermal stress. This effectively blocks the direct contact between corrosive media in the flue gas and the thin metal plate 111, reduces the adhesion strength of ammonium bisulfate on the surface of the thin metal plate 111, and makes the deposits easier to be peeled off by the airflow, thereby reducing the formation of ash layer, maintaining the flow of flue gas channel 113, and extending the service life of heat exchange plate 11 in sulfur-containing flue gas environment.

[0045] In another embodiment, the enamel coating is located on the inner side of the thin plate 111 and contacts the air in the air channel 112; the thickness of the enamel coating can be set to 0.1 to 0.5 mm; the coating covers the inner surface of the air channel 112 and directly contacts the flowing cold air, weakening the heat conduction intensity by reducing the thermal conductivity of the metal surface; specifically, when the cold air enters the air channel 112 at the front of the thin plate 111, it first contacts the inner wall of the channel with the enamel coating. Since the thermal conductivity of the enamel material is much lower than that of the thin plate 111, the heat exchange rate between the cold air and the thin plate 111 is effectively controlled. This controlled heat exchange process reduces the temperature drop of the thin plate 111 in the cold air inlet area, ensuring that the temperature in this area is higher than the liquefaction critical temperature of ammonium bisulfate; during the air flow, the enamel coating continuously plays a heat-insulating role along the flow direction, ensuring the necessary heat exchange requirements while avoiding local overcooling that leads to the formation of liquid ammonium bisulfate.

[0046] To ensure that the temperature of the flue gas in the intake section is not lower than the liquefaction temperature of ammonium bisulfate, the enamel coating includes a first enamel coating and a second enamel coating. The first enamel coating is located on the inner side of the thin plate 111 and contacts the air in the air passage 112, while the second enamel coating is located on the inner side of the thin plate 111 and contacts the flue gas in the flue gas passage 113. Specifically, when the flue gas and cold air flow in the flue gas passage 113 and the air passage 112 respectively, the first enamel coating can inhibit the heat conduction of the high-temperature flue gas to the thin plate 111, while the second enamel coating hinders the cold air from reaching the thin plate 111. Rapid cooling; this bidirectional heat-insulating design ensures that the internal temperature field distribution of the thin plate 111 tends to be uniform when subjected to alternating heat flow impacts; in the cold end region, the synergistic effect of the double coating can eliminate the abrupt temperature gradient caused by unilateral heat transfer, keeping the overall temperature of the thin plate 111 above the critical liquefaction temperature of ammonium bisulfate; especially under start-up and shutdown conditions, the double coating structure can mitigate thermal stress impacts and avoid coating cracking failure caused by unilateral thermal expansion differences; effectively balancing the heat conduction rate in the cold end region of the heat exchange plate 11, preventing phase changes of ammonium bisulfate caused by sudden drops in local temperature. Under fluctuating boiler load conditions, the double coating structure can maintain the overall temperature of the thin plate 111 above the critical liquefaction value, avoiding the adhesion and deposition of viscous liquid ammonium bisulfate on the heat exchange surface, thereby significantly reducing the probability of ash accumulation.

[0047] In another embodiment, the heat-insulating element 2 is a metal coating layer; the metal coating layer refers to a metal material layer formed on the surface of the thin plate 111 by physical or chemical methods, specifically achieved by thermal spraying, electroplating, or vapor deposition processes, such as forming a nickel-based alloy layer on the surface of the thin plate 111 by plasma spraying. This metal coating layer reduces the thermal conductivity of the thin plate 111, forming local thermal resistance at the front of the thin plate 111, thereby reducing the thermal conductivity of that area; specifically, the metal coating layer is applied to the surface of the front end of the thin plate 111, and by adjusting the thickness of the metal coating layer and the thermal conductivity of different metal materials, the heat transfer rate at the front is lower than that at the rear. When cold air flows through the front, due to the heat-insulating effect of the metal coating layer, the front end temperature is always higher than the liquefaction temperature of ammonium bisulfate. The metal coating layer and the thin plate 111 form a stable interface through metallurgical bonding, maintaining structural integrity under operating conditions of 200-400℃ and avoiding interlayer delamination caused by differences in thermal expansion coefficients. Simultaneously, the high-temperature oxidation resistance of the metal coating layer prevents the surface oxide layer from peeling off, eliminating secondary dust accumulation caused by foreign matter buildup. It effectively prevents the front-end temperature from dropping below the liquefaction temperature of ammonium bisulfate, fundamentally inhibiting the formation of sticky substances. The metal coating layer maintains a stable adhesion state under high-temperature conditions, avoiding flow channel blockage caused by the shedding of heat-insulating materials. While maintaining overall heat exchange efficiency, the metal coating layer raises the front-end temperature above the critical liquefaction temperature of ammonium bisulfate, significantly extending the service life of the heat exchange plate 11.

[0048] Air passage 112 and flue gas passage 113 are orthogonally arranged. In the direction of flue gas passage 113, the flue gas temperature gradually decreases along the flue gas flow path. In the air flow direction within air passage 112, as the flue gas exchanges heat with the air, the air temperature gradually increases, and the flue gas temperature also shows a gradual upward trend along the air flow path. This results in the lowest flue gas temperature at the junction of the inlet and outlet of air passage 112; more specifically, the flue gas temperature is lower at the outlet of heat exchanger 1. Figure 4 and Figure 5 As shown, to ensure that the temperature of the flue gas at the outlet of heat exchanger 1 is higher than that of ammonium bisulfate, the length of the heat-resistant element 2 along the airflow path gradually increases along the flue gas flow path. As the flue gas flows in the flue gas channel 113 toward the outlet of heat exchanger 1, the size of the heat-resistant element 2 along the airflow path gradually increases. This effectively prevents the flue gas from maintaining a high heat exchange efficiency as it gradually approaches the outlet of heat exchanger 1, thus avoiding the flue gas temperature from falling below the liquefaction temperature of ammonium bisulfate. This also effectively prevents the accumulation of ash at the outlet of flue gas channel 113, which could lead to blockage, corrosion, or wear of the heated surface of heat exchange plate 11. In one embodiment, as... Figure 4 As shown, the heat-insulating element 2 forms a straight line inclined relative to the flue gas flow path at the end of the airflow path; in another embodiment, as... Figure 5 As shown, the heat-insulating element 2 has a smooth curve at the end of the airflow path that is inclined relative to the flue gas flow path.

[0049] In another embodiment, the present invention also provides a manufacturing process for a heat exchanger, for producing a heat exchanger 1 in which the heat-insulating element 2 is an enamel coating, comprising the following steps:

[0050] S01. Weld the two thin plates 111 together, and introduce a high-pressure medium between the two thin plates 111 so that the unwelded parts of the two thin plates 111 are far apart to form an air channel 112.

[0051] S02. Weld the two adjacent thin plates 111 of the two heat exchange plates 11 to both ends of the air passage 112 so that a flue gas passage 113 is formed between the two heat exchange plates 11.

[0052] S03. Repeat step S02 to weld multiple heat exchange plates 11 together to form a semi-finished heat exchanger.

[0053] S04. Immerse one end of the air passage 112 of the semi-finished heat exchanger in enamel liquid;

[0054] S05. Drain the semi-finished heat exchanger that has been immersed in enamel liquid and let it stand.

[0055] S06. Install the semi-finished heat exchanger on the frame to form heat exchanger 1; wherein, step S06 can also be between step S03 and step S04; that is, the semi-finished heat exchanger can also be installed on the frame first to form heat exchanger 1, and then one end of heat exchanger 1 is lifted and immersed in enamel liquid so that the front surface is coated with enamel liquid, and then heat exchanger 1 is taken out, drained and left to stand so that enamel liquid forms enamel coating on the front surface.

[0056] In this embodiment, the high-pressure medium refers to the medium that separates the unwelded areas of the thin plate 111 to form a channel through pressure. Specifically, it can be compressed air, inert gas, or liquid. When the heat-insulating element 2 is an enamel coating, the two ends of the two thin plates 111 are first sealed and welded to form a heat exchange plate 11, and the ends of multiple heat exchange plates 11 are then sealed and welded together to form a semi-finished heat exchanger. Specifically, when the enamel coating includes a first enamel coating and a second enamel coating, the semi-finished heat exchanger is lifted by a crane and lowered into a container containing enamel liquid, so that the enamel liquid adheres to the semi-finished heat exchanger. Then, the semi-finished heat exchanger is drained and left to stand, so that the enamel liquid can adhere well to the semi-finished heat exchanger. The ends of the heat exchanger are coated with an enamel layer. This enamel layer has excellent heat insulation and corrosion resistance, effectively reducing the heat exchange efficiency between flue gas and air, thereby reducing heat loss of the flue gas at the enamel layer. This ensures that the temperature of the flue gas at the enamel layer is not lower than the liquefaction temperature of ammonium bisulfate, thus effectively preventing the formation of a dust layer on the heat exchanger plate 11, which can lead to blockage, corrosion, and wear. In addition, the enamel layer has good smoothness, which can effectively prevent dust from accumulating on the heat exchanger plate 11. Even if liquid ammonium bisulfate accumulates and adheres to the heat exchanger plate 11, it is easily carried away by the flue gas when it flows through, greatly reducing the adhesion of ammonium bisulfate to the heat exchanger 1's heat exchanger surface, thereby improving the service life of the heat exchanger plate 11. When the size of the enamel coating in the air passage 112 gradually increases along the flue gas flow path, the semi-finished heat exchanger can be appropriately rotated or tilted and lifted after one end of the semi-finished heat exchanger is immersed in the enamel liquid; when the enamel coating is only attached to one side wall of the thin plate 111, the side that does not need to be attached to the enamel coating can be covered with a film or other material to prevent the enamel coating from being attached to the side wall of the thin plate 111 that does not need to be attached to the enamel coating.

[0057] In another embodiment, the present invention also provides a manufacturing process for a heat exchanger, used to produce a heat exchanger 1 in which the heat-insulating element 2 is a metal covering layer. In this embodiment, the metal covering layer is located on one side of the inner or outer side of the front portion of the thin plate 111, and includes the following steps:

[0058] a. A metal ion stream is sprayed onto one side of one end of the two thin plates 111 to form a metal coating layer;

[0059] b. Place the metal covering layers on the two thin plates 111 facing each other or back to back, and place the metal covering layers on the two thin plates 111 at the same end, and then weld the two thin plates 111.

[0060] c. High-pressure medium is introduced between the two thin plates 111 after welding to make the unwelded parts of the two thin plates 111 separate from each other to form an air channel 112;

[0061] d. Place multiple heat exchange plates 11 side by side with intervals, and weld the two adjacent thin plates 111 between two adjacent heat exchange plates 11 at both ends of the air channel 112. After welding, the multiple heat exchange plates 11 are installed on the frame to form a heat exchanger 1.

[0062] In another embodiment, the present invention also provides a manufacturing process for a heat exchanger, used to produce a heat exchanger 1 in which the heat-insulating element 2 is a metal covering layer. In this embodiment, the metal covering layer is located on the inner and outer side walls of the front part of the thin plate 111, and includes the following steps:

[0063] a. A metal ion flow is sprayed onto both sides of one end of the two thin plates 111 to form a metal coating layer;

[0064] b. Weld the metal covering layers of the two thin plates 111 that have been sprayed with double layers to the same end;

[0065] c. High-pressure medium is introduced between the two thin plates 111 after welding to make the unwelded parts of the two thin plates 111 separate from each other to form an air channel 112;

[0066] d. Two heat exchange plates 11 are spaced apart and the two ends of the air passage 112 are welded together to form a heat exchanger 1. Multiple heat exchange plates 11 are welded together and installed on the frame to form a heat exchanger 1.

[0067] In the two embodiments described above, metal ion jetting refers to the process of depositing metal material onto the surface of thin plate 111 using a high-energy beam. Specifically, it can be achieved using thermal spraying or cold spraying techniques. The thickness and distribution area of ​​the metal coating layer are controlled by adjusting the ion flow parameters. After the metal coating layer is formed on the surface of thin plate 111 in the cold air inlet area, the interfacial thermal resistance between the coating layer and the substrate material reduces the heat transfer efficiency in that area, making the cold-end temperature gradient more gradual. When the two thin plates 111 expand through a high-pressure medium to form an air channel 112, the coating layer is concentrated at a specific location at the channel inlet, forming a localized thermal barrier. When adjacent heat exchange plates 11 are welded, the welding points in the coating layer area avoid the high-temperature flue gas scouring surface, preventing the metal layer from peeling off due to thermal stress. After multiple heat exchange plates 11 are assembled, the coating layer forms a continuous heat-resistant zone in the overall structure, suppressing the sudden temperature drop at the cold air inlet and keeping the temperature in that area above the liquefaction critical point of ammonium bisulfate. In some specific embodiments, the metal ion jet can be produced using a pulse deposition process to create a gradient structure in the capping layer; when the high-pressure medium is introduced, it can be pressurized in stages, first pre-forming with low-pressure gas and then performing high-pressure shaping.

[0068] In addition to the preferred embodiments described above, the present invention has other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection claimed by the present invention.

Claims

1. A coated heat exchanger, comprising multiple heat exchange plates arranged side by side, with a flue gas passage formed between adjacent heat exchange plates, each heat exchange plate comprising two thin plates arranged side by side, the welded positions of the two thin plates forming a weld column, and the unwelded positions forming an air passage away from each other, characterized in that... The thin plate includes a front part and a rear part distributed along the airflow direction. The length of the front part along the airflow direction is L1, and the length of the thin plate along the airflow direction is L, where 0.25L>L1. The surface of the front part is provided with a heat-insulating element to increase the heat transfer resistance of the front part, so that the heat transfer resistance of the front part is greater than that of the rear part. The length of the heat-insulating element along the airflow path gradually increases along the flue gas flow path. The heat-insulating element is an enamel coating. The enamel coating is located on the inner side of the thin plate and contacts the air in the air channel, or the enamel coating includes a first enamel coating and a second enamel coating, the first enamel coating is located on the inner side of the thin plate and contacts the air in the air channel, and the second enamel coating is located on the outer side of the thin plate and contacts the flue gas in the flue gas channel.

2. A manufacturing process for a heat exchanger, used to produce the heat exchanger as claimed in claim 1, comprising the following steps: S01, welding two thin plates together, and introducing a high-pressure medium between the two thin plates, so that the unwelded portions of the two thin plates are far apart to form an air channel; S02, welding two adjacent thin plates of two heat exchange plates at both ends of the air channel, so that a flue gas channel is formed between the two heat exchange plates; S03, repeating step S02, welding multiple heat exchange plates together to form a semi-finished heat exchanger; S04, immersing one end of the air channel of the semi-finished heat exchanger in enamel liquid; S05, removing the semi-finished heat exchanger immersed in enamel liquid, draining it, and letting it stand; S06, installing the semi-finished heat exchanger on a frame to form a heat exchanger; wherein step S06 is after step S05, or between step S03 and step S04.

Images