A widely-applied acid-resistant and wear-resistant metal matrix composite heat exchange tube and a manufacturing method thereof

Abstract

A kind of acid-resistant wear-resistant metal-based composite heat exchange tube and its manufacturing method, the composite heat exchange tube includes the metal-based pipe (1) by the intermediate heat exchange section (11) and the non-heat exchange sealing section (12) located at the both ends of heat exchange section respectively, four fluorine acid-resistant layer (2a) in heat exchange section is compounded outside the metal-based pipe, carbon fiber protective layer (3) is compounded outside four fluorine acid-resistant layer in heat exchange section, silicon carbide wear-resistant layer (4) is applied outside carbon fiber protective layer;Four fluorine acid-resistant layer (2b) in sealing section is compounded outside the non-heat exchange sealing section of metal-based pipe, the thickness of four fluorine acid-resistant layer (2b) in sealing section is greater than the thickness of four fluorine acid-resistant layer (2a) in heat exchange section;The thickness of four fluorine acid-resistant layer (2a) in heat exchange section does not exceed 3 mm, the thickness of carbon fiber protective layer (3) does not exceed 1mm, the thickness of silicon carbide wear-resistant layer (4) does not exceed 2mm.The acid-resistant wear-resistant metal-based composite heat exchange tube of the present application is widely applicable and has low production cost.

Description

Technical Field

[0001] This invention belongs to the technical field of heat exchanger tubes and their manufacturing methods. Background Technology

[0002] Currently, there are many types of heat exchange tubes available on the market. Metal heat exchange tubes include various acid-resistant stainless steel tubes, titanium tubes, zirconium tubes, etc., while non-metallic heat exchange elements include graphite heat exchange tubes. However, all commercially available heat exchange tubes share a common drawback: the applicable range of each type is very narrow. Once environmental conditions change slightly, such as temperature, pressure, acid type, acidity, or even a change in the concentration of a certain impurity element in the acid solution, all heat exchange tubes in the entire heat exchanger must be replaced with a new type. There are also heat exchange elements with a wide range of applications, such as tantalum tubes, but their extremely high production cost makes industrial-scale promotion impossible.

[0003] PTFE (polytetrafluoroethylene) possesses excellent broad-spectrum acid resistance, making PTFE-steel composite acid-resistant heat exchange tubes an ideal combination. However, due to PTFE's poor thermal conductivity and its expansion coefficient being more than ten times that of steel, PTFE+steel composite tubes have not yet entered the market. If the following three technical challenges can be solved, PTFE+steel composite acid-resistant heat exchange tubes could completely replace the vast majority of existing heat exchange tubes, becoming a cost-effective broad-spectrum acid-resistant heat exchange tube. First, the PTFE layer encasing the steel tube should be sufficiently thin while ensuring acid and corrosion resistance to meet thermal conductivity requirements. Second, the PTFE acid-resistant layer and the steel tube should be tightly bonded without gaps to meet thermal conductivity requirements. Third, the thermal expansion and contraction of the PTFE layer should be constantly controlled to ensure a sufficiently long service life for the relatively thin PTFE layer. Uncontrolled PTFE layers, especially when long, will randomly expand locally upon heating, commonly known as "bulging"; the thickness at the bulging points becomes significantly thinner, making them extremely prone to cracking and damage. Only when the PTFE layer expands and contracts uniformly and under controlled conditions can the relatively thin PTFE layer be guaranteed to be used safely for a long time. Summary of the Invention

[0004] The purpose of this invention is to solve the aforementioned technical problems and provide a widely applicable, low-cost, acid-resistant and wear-resistant metal-based composite heat exchanger tube. This invention also provides a method for manufacturing this acid-resistant and wear-resistant metal-based composite heat exchanger tube.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchanger tube includes a metal base tube consisting of a central heat exchange section and non-heat exchange sealing sections located at both ends of the heat exchange section. A PTFE acid-resistant layer is composited outside the heat exchange section of the metal base tube, and a carbon fiber protective layer is composited outside the PTFE acid-resistant layer. A silicon carbide wear-resistant layer is coated outside the carbon fiber protective layer. A sealing PTFE acid-resistant layer is composited outside the non-heat exchange sealing sections of the metal base tube, and the thickness of the sealing PTFE acid-resistant layer is greater than the thickness of the heat exchange PTFE acid-resistant layer. The thickness of the heat exchange PTFE acid-resistant layer does not exceed 3 mm, the thickness of the carbon fiber protective layer does not exceed 1 mm, and the thickness of the silicon carbide wear-resistant layer does not exceed 2 mm.

[0007] Furthermore, the combined thickness of the PTFE acid-resistant layer, the composite carbon fiber protective layer, and the silicon carbide wear-resistant layer in the heat exchange zone does not exceed 3 mm.

[0008] The preparation method of a broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchanger tube according to the present invention is as follows:

[0009] S1. Clean the outer surface of the metal base tube and roughen it.

[0010] S2. Tightly wrap the PTFE tape around the outside of the metal base tube. First, wrap the entire outer surface of the metal base tube with enough PTFE acid-resistant layer to meet the set thickness of the heat exchange zone. Then, wrap the non-heat exchange sealing sections at both ends with PTFE tape until the set thickness of the sealing zone PTFE acid-resistant layer is reached.

[0011] S3. Wrap a layer of carbon fiber material around the PTFE tape layer in the heat exchange section to form a carbon fiber protective layer. Use the carbon fiber protective layer to tightly wrap the PTFE acid-resistant layer in the heat exchange section.

[0012] S4. Starting from the pipe opening of the metal base pipe, a glass fiber tape layer is wrapped around the outside of the PTFE acid-resistant layer in the sealing area (including the non-heat exchange sealing sections at both ends) and the carbon fiber protective layer in the heat exchange section to form a composite pipe blank.

[0013] S5. The above-mentioned composite tube blank is sent into the kiln and sintered according to the set firing curve.

[0014] S6. After sintering, the furnace is cooled according to the set cooling curve;

[0015] S7. After cooling is complete, the composite tube blank is removed, the outermost glass fiber tape layer is removed, and then silica gel carbide mud is applied to the carbon fiber protective layer to form a silicon carbide wear-resistant layer, thus obtaining the broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchange tube.

[0016] The preparation method of the general-purpose acid-resistant and wear-resistant metal-based composite heat exchange tube can also be as follows:

[0017] S1. Clean the outer surface of the metal base tube and roughen it.

[0018] S2. Tightly wrap the PTFE tape around the outside of the metal base tube. First, wrap the entire outer surface of the metal base tube with the PTFE acid-resistant layer of the heat exchange zone to the set thickness, and then wrap the non-heat exchange sealing sections at both ends with PTFE tape until the set thickness of the PTFE acid-resistant layer of the sealing zone is reached;

[0019] S3. Starting from the pipe opening of the metal base pipe, a fiberglass tape layer is wrapped around the outside of the PTFE acid-resistant layer in the sealing area (including the non-heat exchange sealing sections at both ends) and the PTFE acid-resistant layer in the heat exchange section to form a composite pipe blank.

[0020] S4. The above-mentioned composite tube blank is sent into the kiln and sintered according to the set firing curve.

[0021] S5. After sintering, the furnace is cooled according to the set cooling curve.

[0022] S6. After cooling is completed, the composite tube blank is removed, the outermost glass fiber tape layer is removed, and then a carbon fiber protective layer is wrapped around the PTFE acid-resistant layer in the heat exchange zone; then a layer of silica carbide mud is applied on the carbon fiber protective layer to form a silicon carbide wear-resistant layer, thus obtaining the broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchange tube.

[0023] The present invention has at least the following advantages:

[0024] 1. The general-purpose acid-resistant and wear-resistant metal-based composite heat exchange tube of the present invention has a heat exchange zone of PTFE acid-resistant layer, carbon fiber protective layer and silicon carbide wear-resistant layer sequentially composited outside the heat exchange zone of the metal base tube. It has high heat exchange efficiency, good high temperature and high pressure resistance, excellent acid corrosion resistance, wide range of applications and low production cost.

[0025] 2. The present invention incorporates a polytetrafluoroethylene (PTFE) acid-resistant layer on the outside of the metal base tube. The thickness of the PTFE acid-resistant layer can be as thin as 0.2 mm, thereby maximizing the prevention of the PTFE acid-resistant layer from affecting the thermal conductivity of the heat exchange tube.

[0026] 3. The PTFE acid-resistant layer is made of PTFE material wound and sintered, which can make the PTFE acid-resistant layer tightly bonded to the outer surface of the metal base tube, with no gaps between them, which can effectively prevent the reduction of thermal conductivity.

[0027] 4. A layer of carbon fiber is wrapped around the PTFE acid-resistant layer in the heat exchange zone to form a protective carbon fiber layer. This prevents the PTFE tape from expanding outwards randomly during sintering, forcing the thermal expansion volume of the PTFE material to find deformation space within the carbon fiber layer. This makes it easier for the PTFE tape to melt and bond together, preventing incomplete sintering and weak adhesion between PTFE tape layers. Furthermore, by appropriately increasing the sintering temperature, the carbon fiber and PTFE material are bonded together, preventing gaps and further improving the thermal conductivity of the composite tube. Alternatively, the PTFE acid-resistant layer in the heat exchange zone can be directly wrapped with fiberglass tape for sintering, achieving the same effect. A layer of acid-resistant thermally conductive putty is then applied to the outside of the sintered PTFE acid-resistant layer in the heat exchange zone, followed by another layer of carbon fiber material to form protective layer 3. This layer also provides excellent control over the thermal expansion of the PTFE acid-resistant layer and good thermal conductivity. In the non-heat exchange sealing zone, there are no requirements for thermal conductivity; appropriately increasing the thickness of the PTFE layer is sufficient to meet the requirements for acid resistance, corrosion protection, and sealing. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the general-purpose acid-resistant and wear-resistant metal-based composite heat exchanger tube of the present invention;

[0029] Figure 2 This is a schematic diagram of the sintering of the composite tube blank. Detailed Implementation

[0030] The invention will now be further described in conjunction with the accompanying drawings.

[0031] like Figure 1 The diagram shows a broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchanger tube, comprising a metal base tube 1, which includes a central heat exchange section 11 and non-heat exchange sealed sections 12 located at both ends of the heat exchange section. A PTFE acid-resistant layer 2a is laminated outside the heat exchange section of the metal base tube, a carbon fiber protective layer 3 is laminated outside the PTFE acid-resistant layer, and a silicon carbide wear-resistant layer 4 is coated outside the carbon fiber protective layer. Only a sealing PTFE acid-resistant layer 2b is laminated outside the non-heat exchange sealed sections of the metal base tube; the thickness of the sealing PTFE acid-resistant layer 2b is greater than the thickness of the heat exchange PTFE acid-resistant layer 2a. Typically, the sum of the thicknesses of the heat exchange PTFE acid-resistant layer 2a, the composite carbon fiber protective layer 3, and the silicon carbide wear-resistant layer 4 does not exceed 3 mm, and can be as thin as 0.5 mm. The thickness of the heat exchange PTFE acid-resistant layer 2a does not exceed 3 mm, the thickness of the carbon fiber protective layer 3 does not exceed 1 mm, and the thickness of the silicon carbide wear-resistant layer 4 does not exceed 2 mm. The thickness of the PTFE acid-resistant layer in the heat exchange zone can be as thin as 0.2 mm, the thickness of the carbon fiber protective layer 3 can be as thin as 0.15 mm, and the thickness of the silicon carbide wear-resistant layer can be as thin as 0.15 mm.

[0032] The preparation method of the general-purpose acid-resistant and wear-resistant metal-based composite heat exchange tube is as follows:

[0033] S1. Clean the surface of the metal base pipe 1 and roughen it. The metal base pipe is usually made of steel pipe, and sandblasting or other methods are used to remove rust and roughen it.

[0034] S2. Tightly wrap the PTFE tape around the outside of the metal base tube. First, wrap the entire outer surface of the metal base tube 1 with the PTFE acid-resistant layer 2a of the heat exchange zone to the set thickness, and then wrap the sealing areas at both ends with PTFE tape until the thickness of the PTFE acid-resistant layer 2b of the sealing area is reached.

[0035] S3. Wrap a layer of carbon fiber material, such as carbon fiber cloth, tape or filament, around the outside of the PTFE acid-resistant layer 2a in the heat exchange zone to form a carbon fiber protective layer 3. Use the carbon fiber protective layer to tightly wrap the PTFE tape layer.

[0036] S4. Starting from the pipe opening of the metal base pipe, a glass fiber tape layer 5 is wrapped around the outside of the PTFE acid-resistant layer 2b in the sealing area at both ends and the carbon fiber protective layer 3 in the heat exchange section to form a composite pipe blank.

[0037] S5, such as Figure 2 As shown, the composite tube blank is fed into kiln 6 and sintered according to the set firing curve. Kiln 6 is existing technology equipment.

[0038] S6. After sintering, the furnace should be cooled according to the set cooling curve. During cooling, the temperature drop in the high-temperature zone above 300°C should not exceed 10°C per hour.

[0039] S7. After cooling is complete, remove the composite tube, remove the outermost fiberglass tape layer, and then apply silica gel sludge to the carbon fiber protective layer to form a silicon carbide wear-resistant layer 4, thus obtaining the broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchange tube.

[0040] The broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchange tube of the present invention can also be prepared by the following method:

[0041] S1. Clean the outer surface of the metal base tube 1 and roughen it.

[0042] S2. Tightly wrap the PTFE tape around the outside of the metal base tube. First, wrap the entire outer surface of the metal base tube 1 with the PTFE acid-resistant layer 2a of the heat exchange zone to the set thickness, and then wrap the sealing areas at both ends with PTFE tape until the thickness of the PTFE acid-resistant layer 2b of the sealing area is reached.

[0043] S3. Starting from the pipe opening of the metal base pipe, a fiberglass tape layer 5 is wrapped around the outside of the PTFE acid-resistant layer in the sealing area (including the non-heat exchange sealing areas at both ends) and the PTFE acid-resistant layer in the heat exchange section to form a composite pipe blank.

[0044] S4. The composite tube blank is fed into kiln 6 and sintered according to the set firing curve; the optimal firing temperature range is 375°C~385°C.

[0045] S5. After sintering, cool the furnace according to the set cooling curve; the cooling rate in the temperature zone above 300°C shall not exceed 10°C per hour;

[0046] S6. After cooling is completed, the composite tube blank is removed, the outermost glass fiber tape layer is removed, and then a carbon fiber protective layer 3 is wrapped around the PTFE acid-resistant layer in the heat exchange zone; then a layer of silica carbide mud is applied on the carbon fiber protective layer to form a silicon carbide wear-resistant layer 4, thus obtaining the broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchange tube.

[0047] Application examples:

[0048] The shell-and-tube waste acid concentrator uses heat exchange tubes in operation where 160°C superheated steam passes through the tubes to heat the waste acid solution in the heat exchanger shell. The waste acid inlet temperature is 45°C, and the outlet temperature is 98°C; the sulfuric acid concentration is 25%–35%, and the heating rate is 5 m³ / h. 3 .

[0049] The general-purpose acid-resistant and wear-resistant metal-based composite heat exchanger tube of this invention uses a φ32 x 1.5 mm heat-resistant steel pipe as the metal base tube. In the heat exchange section, a 0.35 mm thick polytetrafluoroethylene (PTFE) acid-resistant layer is wrapped around it, followed by a 0.2 mm thick carbon fiber protective layer and a 0.3 mm thick silicon carbide wear-resistant coating. In the non-heat exchange sealed section, a 1.5 mm thick PTFE acid-resistant layer is wrapped around it. The composite heat exchanger tube is 6 m long with an effective heat exchange area of ​​0.58 m². 2 A total of 13 tubes are sufficient to meet production requirements. After 300 days of use, no tube bursts or blockages occurred, and no maintenance or repairs were required. Furthermore, the heat exchange effect is excellent.

[0050] Using graphite heat exchange tubes of the same length (φ32x5 x6000 mm), with the same heat exchange area per tube, and employing a heat exchange method where waste acid flows inside the tubes and superheated steam flows inside the heat exchanger shell, 32 heat exchange tubes are required to meet production requirements. During use, scaling and clogging inside the tubes are severe problems, requiring cleaning on average every ten days. The average service life of graphite tubes is 183 days, and there is a risk of tube bursting.

[0051] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchanger tube, characterized in that, The metal base tube (1) consists of a heat exchange section (11) in the middle and non-heat exchange sealing sections (12) located at both ends of the heat exchange section. A heat exchange section PTFE acid-resistant layer (2a) is composited outside the heat exchange section of the metal base tube. A carbon fiber protective layer (3) is composited outside the heat exchange section PTFE acid-resistant layer. A silicon carbide wear-resistant layer (4) is coated outside the carbon fiber protective layer. A sealing section PTFE acid-resistant layer (2b) is composited outside the non-heat exchange sealing section of the metal base tube. The thickness of the sealing section PTFE acid-resistant layer (2b) is greater than the thickness of the heat exchange section PTFE acid-resistant layer (2a). The thickness of the heat exchange section PTFE acid-resistant layer (2a) does not exceed 3 mm, the thickness of the carbon fiber protective layer (3) does not exceed 1 mm, and the thickness of the silicon carbide wear-resistant layer (4) does not exceed 2 mm.

2. The widely acid-resistant and wear-resistant metal matrix composite heat exchange tube according to claim 1, characterized in that, The total thickness of the three layers in the heat exchange zone—the PTFE acid-resistant layer (2a), the carbon fiber protective layer (3), and the silicon carbide wear-resistant layer (4)—does not exceed 3 mm.

3. The method for preparing a broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchanger tube according to claim 1 or 2, characterized in that the method... as follows: S1. Clean the outer surface of the metal base tube (1) and roughen it; S2. Tightly wrap the PTFE tape around the outside of the metal base tube. First, wrap the entire metal base tube (1) with enough PTFE tape to reach the thickness set by the heat exchange zone PTFE acid-resistant layer (2a). Then, wrap the non-heat exchange sealing sections at both ends with PTFE tape until the thickness set by the sealing zone PTFE acid-resistant layer (2b) is reached. S3. Wrap a layer of carbon fiber material around the PTFE tape layer in the heat exchange section to form a carbon fiber protective layer (3). Use the carbon fiber protective layer to tightly wrap the PTFE acid-resistant layer (2a) in the heat exchange section. S4. Starting from the pipe opening of the metal base pipe, a glass fiber tape layer (5) is wrapped around the outside of the PTFE acid-resistant layer in the sealing area, which includes the non-heat exchange sealing sections at both ends, and the carbon fiber protective layer in the heat exchange section, to form a composite pipe blank. S5. The above composite tube blank is sent into the kiln (6) and sintered according to the set firing curve; S6. After sintering, the furnace is cooled according to the set cooling curve; S7. After cooling is completed, the composite tube blank is taken out, the outermost glass fiber tape layer is removed, and then carbonized silica gel mud is applied on the carbon fiber protective layer to form a silicon carbide wear-resistant layer (4), thus obtaining the broad-spectrum acid-resistant and wear-resistant metal-based composite heat exchange tube.

4. The method for preparing a widely acid-resistant and wear-resistant metal matrix composite heat exchange tube according to claim 1 or 2, characterized in that the method as follows: S1. Clean the outer surface of the metal base tube (1) and roughen it; S2. Tightly wrap the PTFE tape around the outside of the metal base tube. First, wrap the entire metal base tube (1) with enough PTFE tape to reach the thickness set by the heat exchange zone PTFE acid-resistant layer (2a). Then, wrap the non-heat exchange sealing sections at both ends with PTFE tape until the thickness set by the sealing zone PTFE acid-resistant layer (2b) is reached. S3. Starting from the pipe opening of the metal base pipe, a fiberglass tape layer (5) is wrapped around the outside of the PTFE acid-resistant layer in the sealing area of ​​the non-heat exchange sealing section at both ends and the PTFE acid-resistant layer in the heat exchange section to form a composite pipe blank. S4. The above composite tube blank is sent into the kiln (6) and sintered according to the set firing curve; S5. After sintering, the furnace is cooled according to the set cooling curve. S6. After cooling is completed, the composite tube blank is taken out, the outermost glass fiber tape layer is removed, and then a carbon fiber protective layer is wrapped around the PTFE acid-resistant layer in the heat exchange zone (3); then a layer of silica carbide mud is applied on the carbon fiber protective layer to form a silicon carbide wear-resistant layer (4), and the wide-spectrum acid-resistant and wear-resistant metal-based composite heat exchange tube is obtained.

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