Emergency repair method and repair structure of air preheater

Abstract

The invention discloses an emergency repair method and structure of an air preheater, the air preheater comprises a shell defining a flue gas channel and a tube bundle structure arranged in the shell and used for separating flue gas and air, the tube bundle structure comprises an upper tube plate, a lower tube plate and a plurality of first heat exchange tubes connected between the upper tube plate and the lower tube plate, the method comprises the following steps: S1, determining a plurality of damaged heat exchange tubes in a plurality of first heat exchange tubes; s2, the damaged heat exchange tubes are removed, so that a plurality of first tube holes corresponding to the damaged heat exchange tubes are formed in the upper tube plate and the lower tube plate respectively; s3, the multiple first pipe holes are blocked; and S4, a plurality of second pipe holes are formed in the upper pipe plate and the lower pipe plate, a plurality of bypass pipelines are installed, and the two ends of each bypass pipeline penetrate through the second pipe holes in the upper pipe plate and the lower pipe plate correspondingly and are fixed. By establishing the flue gas bypass, the problem of air leakage caused by large-area damage of the heat exchange tube is solved quickly at low cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of boiler auxiliary equipment, in particular to an emergency repair method and repair structure of an air preheater. BACKGROUND

[0002] The shell-and-tube air preheater (abbreviated as air preheater) is a key energy-saving equipment in a coal-fired or gas-fired boiler system. In this structure, high-temperature flue gas usually flows outside the heat exchange tube (shell side), while the combustion air flows inside the heat exchange tube (tube side), or vice versa.

[0003] However, during long-term operation, especially in the low-temperature section of the air preheater (i.e., the area where the flue gas temperature is relatively low), acid substances such as sulfur oxides in the flue gas easily combine with water vapor to form acid liquid, causing serious corrosion to the heat exchange tube made of metal material. Over time, corrosion can cause the heat exchange tube wall to have perforation or even breakage. Once the heat exchange tube has perforation, high-pressure air for combustion will leak in large quantities to the low-pressure flue gas passage through the damaged part, which is called "air leakage". When the corrosion area expands, causing a large number of heat exchange tubes to have perforation at the same time, it will cause catastrophic air leakage, so that even if the air blower is running at full load, it cannot meet the air quantity required for boiler combustion, resulting in a serious shortage of boiler output, and even forced shutdown for repair, causing huge economic losses to production.

[0004] For such serious air leakage caused by large-area physical damage of the heat exchange tube, the traditional existing treatment method is usually to replace the entire tube bundle structure of the air preheater. Although this method can fundamentally solve the problem, it has the disadvantage of extremely long procurement and replacement period, usually several months, during which the unit cannot operate, causing huge economic losses.

[0005] In view of the above problems, there is an urgent need for an emergency repair scheme that can solve such sudden and catastrophic air leakage problems in a short time and at a low cost. SUMMARY

[0006] Therefore, the present application provides an emergency repair method and repair structure of an air preheater. The main purpose is to solve the technical problem that the repair scheme has a long period, high cost, and cannot meet the rapid recovery of production demand when facing the serious air leakage problem caused by large-area damage of the heat exchange tube of the air preheater in the prior art.

[0007] According to a first aspect of the present invention, an emergency repair method for an air preheater is provided. The air preheater includes a shell defining a flue gas passage and a tube bundle structure disposed within the shell for separating flue gas from air. The tube bundle structure includes an upper tube sheet, a lower tube sheet, and a plurality of first heat exchange tubes connected between the upper and lower tube sheets. The method includes the following steps: S1: identifying a plurality of damaged heat exchange tubes among the plurality of first heat exchange tubes; S2: removing the plurality of damaged heat exchange tubes from the upper and lower tube sheets to... S3: Form multiple first tube holes corresponding to the damaged heat exchange tubes on the upper tube sheet and the lower tube sheet; S4: Seal the multiple first tube holes; S5: Set multiple second tube holes on the upper tube sheet and the lower tube sheet, and install multiple bypass pipes, wherein each of the bypass pipes passes through a second tube hole on the upper tube sheet and the lower tube sheet at both ends and is fixed, so as to form a flue gas bypass in the flue gas passage that bypasses the tube bundle structure and directly connects the space above the upper tube sheet and the space below the lower tube sheet.

[0008] Furthermore, in S4, the total flow cross-sectional area of ​​the multiple bypass pipes is smaller than the total flow cross-sectional area of ​​the multiple damaged heat exchange tubes before they were removed. In this application, this saves material costs on the one hand, and provides more operating space for drilling holes and installation on the tube sheet on the other hand.

[0009] Furthermore, in S4, the basis for determining the number of the multiple bypass pipes and the cross-sectional area of ​​each pipe is to ensure that the design flow rate of the flue gas through the bypass is not lower than a preset value, wherein the design flow velocity of the flue gas in the bypass pipe is higher than its original design flow velocity in the first heat exchange tube. This invention cleverly utilizes fluid mechanics principles to compensate for the reduced cross-sectional area by actively increasing the flow velocity of the flue gas in the bypass pipe, thereby ensuring the total flue gas volume required for boiler operation.

[0010] Furthermore, in S4, in order to facilitate subsequent welding and sealing operations and ensure the reliability of the connection, after the bypass pipe is installed, both ends of it extend beyond the outer surfaces of the upper tube sheet and the lower tube sheet.

[0011] Furthermore, the method further includes the step of fixing and sealing the portion of the bypass pipe extending beyond the outer surfaces of the upper and lower tube sheets to the upper pipe and the lower tube sheet, respectively.

[0012] Furthermore, the damaged heat exchange tube is located in the low-temperature section of the air preheater.

[0013] Furthermore, the bypass pipe is a straight pipe, which makes manufacturing and installation simple and convenient.

[0014] Furthermore, according to a second aspect of the present invention, an air preheater structure repaired using the emergency repair method described in any of the preceding inventions is provided. The original air preheater structure includes a shell defining a flue gas passage and a tube bundle structure disposed within the shell for separating flue gas from air. The tube bundle structure includes an upper tube sheet, a lower tube sheet, and multiple first heat exchange tubes connected between the upper tube sheet and the lower tube sheet. The repaired air preheater structure includes: a sealed first tube hole originally belonging to multiple damaged heat exchange tubes, the first tube hole being located on the upper tube sheet and the lower tube sheet; and multiple bypass pipes, each of which has both ends passing through the upper tube sheet and the lower tube sheet and being fixed to form a flue gas bypass within the flue gas passage that bypasses the tube bundle structure and directly connects the space above the upper tube sheet and the space below the lower tube sheet.

[0015] Furthermore, the total flow cross-sectional area of ​​the multiple bypass pipes is smaller than the total flow cross-sectional area of ​​the multiple damaged heat exchange tubes before they were repaired.

[0016] Furthermore, both ends of the bypass pipe extend beyond the outer surfaces of the upper tube sheet and the lower tube sheet, and are fixedly and sealed to the upper tube sheet and the lower tube sheet.

[0017] This invention provides an emergency repair method and structure for an air preheater. The method bypasses the time-consuming process of customizing and replacing the entire tube bundle, directly isolating and constructing a bypass on-site for the damaged section. Repair can be completed within a few days, allowing the unit to quickly resume operation and significantly reducing downtime losses. Compared to replacing the entire tube bundle structure, this invention only requires a small number of large-diameter pipes and sealing welding, resulting in extremely low material and labor costs and significant economic advantages.

[0018] On the other hand, this application fundamentally eliminates the catastrophic air leakage caused by tube corrosion and perforation by sealing all damaged pipe holes and establishing a brand-new, well-sealed bypass pipe, thus restoring the air supply system to normal and ensuring the boiler's load-bearing capacity. This application provides a novel emergency repair approach that is applicable not only to gas-fired boilers but also to all shell-and-tube heat exchange equipment suffering severe internal leakage due to extensive damage to heat exchange tubes, and has high promotion and application value. Practice shows that after repair using this invention, the resistance to flue gas flow is actually reduced due to the smooth inner wall and direct path of the new bypass pipe, which helps to reduce the power consumption of the induced draft fan.

[0019] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0020] The accompanying drawings, as part of this invention, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation thereof. Clearly, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0021] In the attached diagram:

[0022] Fig. 1 A flowchart of an emergency repair method for an air preheater provided by an embodiment of the present invention is shown;

[0023] Fig. 2 This diagram shows a top view of an emergency repair structure for an air preheater according to an embodiment of the present invention.

[0024] Fig. 3 The diagram shows a schematic of the bypass pipe in an emergency repair structure of an air preheater provided by an embodiment of the present invention.

[0025] Reference numerals: 1. Tube bundle area; 2. First tube hole; 3. Second tube hole; 4. Bypass pipe.

[0026] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0028] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and 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 limiting this invention.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Example

[0031] like Figs. 1-3 As shown, this embodiment relates to the emergency repair of an air preheater in a boiler that suffered from large-scale air leakage due to severe corrosion of the low-temperature heat exchange tubes. The air preheater is a shell-and-tube structure, with flue gas flowing outside the tubes (shell side) and combustion air flowing inside the tubes (tube side). Its tube bundle structure 1 mainly includes an upper tube sheet and a lower tube sheet, as well as tens of thousands of spiral grooved tubes connecting them, which serve as the first heat exchange tubes.

[0032] After shutting down the boiler for inspection, it was found that the 6,800 first heat exchange tubes located in the low-temperature section of the air preheater, which are φ40*1.5mm in size, had varying degrees of corrosion and perforation. This was the root cause of the boiler’s serious insufficient air supply and inability to operate at full load.

[0033] The emergency repair method provided by this invention refers to... Figs. 1 to 3 Specifically, it includes the following steps:

[0034] S1: Identify multiple damaged heat exchange tubes among the multiple first heat exchange tubes.

[0035] In this embodiment, through internal inspection, taking 6800 first heat exchange tubes as an example, a thorough inspection is conducted to identify and mark all 6800 first heat exchange tubes with corrosion perforations.

[0036] S2: Using a cutting tool, cut off the 6800 damaged heat exchange tubes from the position adjacent to the upper tube sheet and the lower tube sheet to form a plurality of first tube holes 2 corresponding to the damaged heat exchange tubes on the upper tube sheet and the lower tube sheet respectively.

[0037] S3: Seal the plurality of first pipe holes 2.

[0038] After removing the damaged heat exchange tubes, 6800 pairs of first tube holes will remain at the original connection points with the upper and lower tube sheets. Using steel plates of the same material as the tube sheets, these 13600 first tube holes 2 on the upper and lower tube sheets will be sealed one by one and completely by welding to ensure that the air side and flue gas side are completely isolated at these locations.

[0039] S4: Construct a flue gas bypass.

[0040] After sealing all damaged pipes, the original flue gas flow path was partially blocked. To restore smooth flue gas flow, this invention constructs a completely new flue gas bypass.

[0041] In this embodiment, the determination of the number of bypass pipes and the cross-sectional area of ​​each pipe is based on ensuring that the design flow rate of the flue gas through the bypass is not lower than a preset value. Specifically, the design flow velocity of the flue gas in the bypass pipe is higher than its original design flow velocity in the first heat exchange tube, first determined through theoretical calculations. The total internal cross-sectional area of ​​the 6800 φ401.5mm first heat exchange tubes removed is approximately 7.91m². 2 Considering that the resistance decreases and the flow velocity increases significantly when the flue gas flows through a large-diameter straight pipe, specifically, the flow velocity in the original small-diameter first heat exchange tube is increased from 12 m / s to 20 m / s in the large-diameter flue gas bypass. Calculations show that only 24 carbon steel pipes with a specification of φ5126mm (DN500) are needed as bypass pipes to handle almost the same total flue gas flow as the original 6800 small pipes. That is, calculations show that the flue gas velocity achieved by using the existing 24 carbon steel pipes with a specification of φ5126mm (DN500) as bypass pipes is 96 m / s. 3 / s, the original flow velocity of the 6800 φ401.5mm first heat exchange tubes was 94.92m / s. 3 / s.

[0042] After calculating and determining the scheme, on the upper and lower tube sheets, avoiding the still-operating heat exchange tubes and the sealed first tube hole 2, select suitable locations to drill 24 pairs, or a total of 48, second tube holes 3 that match the diameter of the bypass pipes. Then, install 24 φ512*6mm bypass pipes (such as... Fig. 3 Large-diameter bypass pipes 4) are installed one by one. Each bypass pipe 4 enters from the second pipe hole of the lower tube sheet, passes directly through the entire original tube bundle area, and then exits from the corresponding second pipe hole of the upper tube sheet.

[0043] During installation, both ends of the control bypass pipe 4 extend approximately 100mm beyond the outer surfaces of the upper and lower tube sheets. This extension ensures sufficient space for subsequent welding operations and is crucial for ensuring welding quality.

[0044] Finally, the portion of each bypass pipe 4 extending out of the tube sheet is fully welded and sealed to the upper and lower tube sheets respectively. At this point, a flue gas bypass consisting of 24 large-diameter pipes, completely independent of the original tube bundle structure, and directly connected to the flue gas inlet and outlet of the air preheater (i.e., the space above the upper tube sheet and the space below the lower tube sheet), is completed.

[0045] In this embodiment, in step S4, the total flow cross-sectional area of ​​the multiple bypass pipes 4 is smaller than the total flow cross-sectional area of ​​the multiple damaged heat exchange tubes before they were removed. After the repair, a leakage test was conducted on the air preheater. Multiple tests showed that the original large-area leakage problem was completely resolved. After the boiler was put back into operation, its load-carrying capacity was significantly improved, easily reaching full load of 135MW with a margin. Furthermore, due to the smooth inner wall and unobstructed flow path of the new bypass pipes 4, the boiler tail flue resistance significantly decreased from -9.5kPa before the repair to approximately -4.5kPa, reducing the operating power consumption of the induced draft fan.

[0046] In one feasible implementation, the bypass pipe 4 is a straight pipe.

[0047] This embodiment fully demonstrates that the method of the present invention, based on the core idea of ​​"blocking + bypassing", successfully solved the catastrophic air leakage problem of the air preheater, which is difficult to deal with by traditional methods, in a very short time and at a very low cost. Its technical solution is feasible and efficient.

[0048] It should be noted that the number (24 pipes) and specifications (φ512*6mm) of bypass pipes in the above embodiment are preferred values ​​calculated based on specific operating conditions. In other applications, those skilled in the art can perform corresponding calculations based on the specific parameters of the air preheater to be repaired, flue gas flow requirements, etc., to determine the optimal number and specifications of bypass pipes. These changes do not depart from the protection scope of this invention. Similarly, the material of the bypass pipes can also be selected from carbon steel, stainless steel, or other corrosion-resistant alloy materials based on factors such as the corrosiveness of the flue gas.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An emergency repair method for an air preheater, the air preheater comprising a shell defining a flue gas passage and a tube bundle structure (1) disposed within the shell for separating flue gas from air, the tube bundle structure (1) comprising an upper tube sheet, a lower tube sheet, and a plurality of first heat exchange tubes connected between the upper tube sheet and the lower tube sheet, characterized in that, The method includes the following steps: S1: Identify multiple damaged heat exchange tubes among the multiple first heat exchange tubes; S2: Remove the multiple damaged heat exchange tubes from the upper tube sheet and the lower tube sheet to form multiple first tube holes (2) on the upper tube sheet and the lower tube sheet, respectively corresponding to the damaged heat exchange tubes; S3: Seal the plurality of first pipe holes (2); S4: Multiple second pipe holes (3) are provided on the upper pipe plate and the lower pipe plate, and multiple bypass pipes (4) are installed, wherein the two ends of each bypass pipe (4) pass through the second pipe holes on the upper pipe plate and the lower pipe plate respectively and are fixed.

2. The method according to claim 1, characterized in that: In S4, the total flow cross-sectional area of ​​the multiple bypass pipes (4) is less than the total flow cross-sectional area of ​​the multiple damaged heat exchange tubes before they were removed.

3. The method according to claim 1 or 2, characterized in that: In S4, the basis for determining the number of the multiple bypass pipes (4) and the cross-sectional area of ​​each pipe is to ensure that the design flow rate of the flue gas through the flue gas bypass is not lower than a preset value, wherein the design flow velocity of the flue gas in the bypass pipe (4) is higher than its original design flow velocity in the first heat exchange tube.

4. The method according to claim 1, characterized in that: In S4, after the bypass pipe (4) is installed, both ends of it extend out of the outer surfaces of the upper pipe sheet and the lower pipe sheet.

5. The method according to claim 4, characterized in that: The method further includes the step of fixing and sealing the portion of the bypass pipe (4) extending out of the outer surface of the upper and lower tube sheets to the upper pipe and the lower tube sheet, respectively.

6. The method according to claim 1, characterized in that: The damaged heat exchange tube is located in the low-temperature section of the air preheater.

7. The method according to claim 1, characterized in that: The bypass pipe (4) is a straight pipe.

8. An air preheater structure repaired using the emergency repair method described in any one of claims 1-7, wherein the original air preheater structure includes a shell defining a flue gas passage and a tube bundle structure (1) disposed within the shell for separating flue gas from air, the tube bundle structure (1) including an upper tube sheet, a lower tube sheet, and a plurality of first heat exchange tubes connected between the upper tube sheet and the lower tube sheet, characterized in that, The repaired air preheater structure includes: The first tube hole (2) that was blocked originally belonged to multiple damaged heat exchange tubes, and the first tube hole (2) is located on the upper tube sheet and the lower tube sheet; Multiple bypass pipes (4), each of which passes through the upper tube sheet and the lower tube sheet at both ends and is fixed, to form a flue gas bypass in the flue gas passage that bypasses the tube bundle structure and directly connects the space above the upper tube sheet and the space below the lower tube sheet.

9. The structure according to claim 8, characterized in that: The total cross-sectional area of ​​the multiple bypass pipes (4) is less than the total cross-sectional area of ​​the multiple damaged heat exchange tubes before they were repaired.

10. The structure according to claim 8 or 9, characterized in that: Both ends of the bypass pipe extend beyond the outer surfaces of the upper and lower tube sheets and are fixedly and sealed to the upper and lower tube sheets.

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