Polytetrafluoroethylene impregnated graphite unitized heat exchanger

Abstract

The utility model discloses a unit body combined heat exchanger of polytetrafluoroethylene impregnated graphite. The heat exchanger includes upper head and lower head, and is provided with graphite heat exchange block between upper head and lower head, the center of upper head is equipped with material inlet and outlet pipe no.

Description

Technical Field

[0001] This utility model relates to a heat exchanger, and more particularly to a unit-type heat exchanger made of polytetrafluoroethylene impregnated with graphite. Background Technology

[0002] In the process of producing HF from fluorosilicic acid by decomposing sulfuric acid, concentrated sulfuric acid is added to the fluorosilicic acid solution, causing dehydration and decomposition to produce hydrogen fluoride and silicon tetrafluoride gas. During the decomposition process, the concentrated sulfuric acid is diluted to 70-75%. At this point, most of the HF is absorbed by the sulfuric acid and discharged as a sulfuric acid solution, with a small portion of the HF being converted into fluorosulfonic acid. Fluorosulfonic acid is a highly corrosive acid, and silicon tetrafluoride is sparingly soluble, escaping as a gas. The fluorinated sulfuric acid solution is heated to boiling in an evaporator, desorbing and releasing hydrogen fluoride. The hydrogen fluoride is then purified and condensed to obtain anhydrous hydrofluoric acid. The defluorinated hot sulfuric acid is cooled in a sulfuric acid cooler and then transferred to the phosphate rock decomposition process.

[0003] To utilize the waste heat from the defluorination-heated sulfuric acid, an acid-acid preheater is installed upstream of the sulfuric acid evaporator. The defluorination-heated sulfuric acid (approximately 75% concentration, containing trace amounts of hydrogen fluoride, at approximately 160°C) preheats the fluorinated sulfuric acid solution (approximately 70% concentration, containing approximately 7% hydrogen fluoride, at approximately 120°C), heating the solution to 135-140°C before it enters the sulfuric acid evaporator where steam heating is used to extract hydrogen fluoride. This process involves complex operating conditions, a highly corrosive environment, and is prone to scaling, placing stringent demands on the equipment. Currently, a suitable acid-acid heat exchanger capable of long-term stable operation is lacking.

[0004] Graphite materials possess strong corrosion resistance, but they also have inherent porosity. An impregnation and curing process is required to fill these voids, creating impermeable graphite composite materials for use in manufacturing chemical equipment such as graphite heat exchangers. Current impregnating agents for graphite materials primarily include phenolic resins, furan resins, and vinyl resins. However, the applications of impermeable graphite composite materials impregnated with these resins are very limited, especially in the case of waste heat recovery preheaters in the process of producing HF from fluorosilicic acid via sulfuric acid decomposition.

[0005] The applicant has applied for a patent with patent number ZL202111357870.0, entitled "A method for modifying graphite by dynamic isostatic pressing and impregnating it with polytetrafluoroethylene". This method can impregnate graphite heat exchange blocks with polytetrafluoroethylene, and the impregnated graphite heat exchange blocks can meet the high requirements of acid-acid preheaters.

[0006] However, this method can only process graphite components. Traditional heat exchange preheaters typically use a combination of a steel-lined shell and graphite heat exchange components. The graphite components alone are far from sufficient to meet the corrosion resistance requirements of acid-acid preheaters. Therefore, achieving high corrosion resistance for the entire heat exchanger remains a focus of research for those skilled in the art. Furthermore, the structure and dimensions of traditional heat exchangers are fixed and customized according to production needs, making mass production impossible and resulting in excessively high manufacturing costs.

[0007] Therefore, the structure of the heat exchanger in this application has been studied and improved. Utility Model Content

[0008] The purpose of this application is to provide a modular heat exchanger made of polytetrafluoroethylene (PTFE) impregnated with graphite. This heat exchanger features good corrosion resistance, meeting the requirements of acid-acid heat exchange systems in the process of producing HF from sulfuric acid by decomposing fluorosilicic acid. Furthermore, the heat exchanger has a novel structure, allowing for mass production and flexible combination, resulting in low manufacturing costs and suitability for widespread application. Additionally, the heat exchanger is easy to disassemble, maintain, and clean, making it more convenient to use.

[0009] A modular heat exchanger made of polytetrafluoroethylene-impregnated graphite, characterized in that: it includes an upper end cap and a lower end cap made of graphite, and at least one graphite heat exchange block is disposed between the upper end cap and the lower end cap; the upper end cap, the lower end cap and the graphite heat exchange block are all impregnated with polytetrafluoroethylene. The upper end cap has a material inlet / outlet pipe 1 running vertically through its center. The lower side of the upper end cap has an annular groove 1, which is separated from the material inlet / outlet pipe 1. The annular groove 1 is connected to the outer side of the upper end cap via a material inlet / outlet pipe 2. The lower end cap has a material inlet / outlet pipe 3 running vertically through its center. The upper side of the lower end cap has an annular groove 2, which is separated from the material inlet / outlet pipe 3. The annular groove 2 is connected to the outer side of the lower end cap via a material inlet / outlet pipe 4. The graphite heat exchange block has a vertically oriented flow collecting hole in the middle, which is coaxial with the material inlet / outlet pipe one and the material inlet / outlet pipe three. A transverse baffle is provided in the middle of the flow collecting hole. An annular cavity is provided inside the graphite heat exchange block near the outer side. Several transverse and longitudinal through holes are provided in the area between the flow collecting hole and the annular cavity. The transverse through holes connect the flow collecting hole and the annular cavity, and the longitudinal through holes penetrate the graphite heat exchange block vertically and are concentrated in the area covered by annular groove one and annular groove two.

[0010] In this heat exchanger design, the acid-acid channels are entirely located within the graphite heat exchange blocks, with no steel lining or outer shell. Therefore, the heat exchanger exhibits extremely high corrosion resistance, fully meeting the requirements of the acid-acid heat exchange system in the process of producing HF from sulfuric acid by decomposing fluorosilicic acid. Furthermore, this heat exchanger incorporates a novel graphite heat exchange block unit, which can be freely combined according to usage requirements to meet the needs of enterprises of different scales. This allows for mass production of the entire heat exchanger, significantly reducing manufacturing costs. Additionally, the heat exchanger in this design is easy to disassemble, maintain, and replace.

[0011] Preferably, in the aforementioned polytetrafluoroethylene-impregnated graphite unit-type heat exchanger, a sealing gasket is provided on the connecting surface of the upper end cap, the graphite heat exchange block, and the lower end cap.

[0012] This solution improves sealing by placing a sealing gasket on the connection surface.

[0013] Preferably, in the aforementioned polytetrafluoroethylene impregnated graphite unit combined heat exchanger, the outer sides of the upper end cap and the lower end cap are respectively provided with an upper cover plate and a lower cover plate, and the upper cover plate and the lower cover plate are connected and fixed by long bolts.

[0014] In this design, the upper end cap, graphite heat exchange block, and lower end cap are fixed together by an upper cover plate, a lower cover plate, and long bolts, making disassembly and assembly convenient.

[0015] Preferably, in the aforementioned polytetrafluoroethylene-impregnated graphite unit-type heat exchanger, one side of the annular cavity in the vertical direction is an open structure.

[0016] This design makes it easier to clean the channel by setting an open structure on one side of the annular cavity.

[0017] A method for processing a modular heat exchanger based on the aforementioned polytetrafluoroethylene-impregnated graphite unit includes the following steps: (1) Prefabricate the upper head, lower head and graphite heat exchange block according to the structure described above; (2) The graphite heat exchange block is placed in a polytetrafluoroethylene impregnation device according to conventional methods, and then the graphite heat exchange block is removed and dried to obtain polytetrafluoroethylene impregnated graphite heat exchange block. (3) Select the appropriate number of polytetrafluoroethylene impregnated graphite heat exchange blocks according to the actual situation. First, place the lower end cap at the bottom, then stack the graphite heat exchange blocks on the lower end cap, and finally cover the upper end cap and tighten the whole assembly. During the assembly process, the material inlet and outlet pipes on the lower end cap, the flow collection holes in the graphite heat exchange blocks, and the material inlet and outlet pipes on the upper end cap should be aligned coaxially, and the longitudinal through holes in adjacent graphite heat exchange blocks should be aligned coaxially.

[0018] Preferably, in the aforementioned processing method of the polytetrafluoroethylene impregnated graphite unit combined heat exchanger, a sealing gasket is provided on the contact surface between the upper end cap, the lower end cap, and the graphite heat exchange block, and the area of ​​the sealing gasket corresponding to the annular groove one, the material inlet / outlet pipe one, the flow collection hole, the longitudinal through hole, the annular groove two, and the material inlet / outlet pipe three is a hollow structure.

[0019] 1. In the heat exchanger of this utility model, the acid-acid channels are entirely located within the graphite heat exchange blocks, and there is no steel inner or outer shell in the structure. Therefore, the heat exchanger has extremely high overall corrosion resistance and can fully meet the usage requirements of the acid-acid heat exchange system in the process system of sulfuric acid decomposition of fluorosilicic acid to produce HF. In addition, the heat exchanger of this utility model is designed with a brand-new graphite heat exchange block unit, which can be freely combined according to usage requirements to meet the needs of enterprises of different scales, enabling the entire heat exchanger to be mass-produced and greatly reducing manufacturing costs. Furthermore, the heat exchanger of this utility model is easy to disassemble, maintain, and replace.

[0020] 2. This utility model achieves better sealing by setting a sealing gasket on the connecting surface.

[0021] 3. The upper end cap, graphite heat exchange block and lower end cap of this utility model are fixed together by the upper cover plate, the lower cover plate and long bolts, which makes disassembly and assembly convenient.

[0022] 4. This utility model makes it easier to clean the channel by setting an open structure on one side of the annular cavity.

[0023] In summary, the heat exchanger of this invention has good corrosion resistance and can meet the requirements of the acid-acid heat exchange system in the process system for producing HF by decomposing fluorosilicic acid with sulfuric acid. In addition, the heat exchanger of this invention has a novel structure, can be mass-produced and freely combined, has low manufacturing cost, and is suitable for widespread application. At the same time, the heat exchanger of this invention is easy to disassemble, maintain and clean, making it more convenient to use. Attached Figure Description

[0024] Appendix Figure 1 This is a front sectional view of the heat exchanger of this utility model along the longitudinal through-hole axis; Appendix Figure 2 This is a front sectional view of the heat exchanger of this utility model along the axis of the transverse through hole; Appendix Figure 3 This is a schematic diagram of the external structure of the heat exchanger of this utility model; Appendix Figure 4 This is a cross-sectional view of the graphite heat exchanger block of this utility model; Appendix Figure 5 This is a front sectional view of the graphite heat exchange block of this utility model along the axis of the transverse through hole; Appendix Figure 6 This is a front sectional view of the graphite heat exchange block of this utility model along the longitudinal through-hole axis; Appendix Figure 7 This is a plan view of the sealing gasket of this utility model; Appendix Figure 8 This is a vertical sectional view of the upper end cap of this utility model; the structure of the lower end cap is the same. Appendix Figure 9 This is a transverse sectional view of the upper end cap of this utility model; the structure of the lower end cap is the same.

[0025] Explanation of reference numerals in the attached drawings: 1-Upper head, 2-Lower head, 3-Graphite heat exchange block, 4-Material inlet / outlet pipe one, 5-Material inlet / outlet pipe three, 6-Material inlet / outlet pipe two, 7-Material inlet / outlet pipe four, 8-Annular groove one, 9-Collecting hole, 10-Annular cavity, 11-Transverse through hole, 12-Longitudinal through hole, 13-Baffle plate, 14-Sealing gasket, 15-Upper cover plate, 16-Lower cover plate, 17-Annular groove two. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments, but this should not be construed as limiting the present invention.

[0027] Embodiments of this utility model Example

[0028] A modular heat exchanger made of polytetrafluoroethylene impregnated with graphite, as shown in the attached figure. Figure 1-9 As shown, it includes an upper end cap 1 and a lower end cap 2, with at least one graphite heat exchange block 3 disposed between the upper end cap 1 and the lower end cap 2; the upper end cap 1, the lower end cap 2 and the graphite heat exchange block 3 are all made of graphite material, and are all impregnated with polytetrafluoroethylene according to the dynamic isostatic pressing method for modifying polytetrafluoroethylene and impregnating graphite disclosed in the patent with patent number ZL202111357870.0, so that it has good impermeability and corrosion resistance; The upper end cap 1 has a material inlet / outlet pipe 4 running vertically through its center. The lower side of the upper end cap 1 has an annular groove 8, which is separated from the material inlet / outlet pipe 4. The annular groove 8 is connected to the outer side of the upper end cap 1 via a material inlet / outlet pipe 6. The lower end cap 2 has a material inlet / outlet pipe 5 running vertically through its center. The upper side of the lower end cap 2 has an annular groove 17, which is separated from the material inlet / outlet pipe 5. The annular groove 17 is connected to the outer side of the lower end cap 2 via a material inlet / outlet pipe 7. The graphite heat exchange block 3 has a vertically oriented flow collecting hole 9 in the middle. The flow collecting hole 9 is coaxial with the material inlet / outlet pipe 4 and the material inlet / outlet pipe 5. A horizontal baffle 13 is provided in the middle of the flow collecting hole 9. An annular cavity 10 is provided inside the graphite heat exchange block 3 near the outer side. A number of horizontal through holes 11 and vertical through holes 12 are provided in the area between the flow collecting hole 9 and the annular cavity 10. The horizontal through holes 11 connect the flow collecting hole 9 and the annular cavity 10. The vertical through holes 12 penetrate the graphite heat exchange block 3 vertically and are concentrated in the area covered by the annular groove 8 and the annular groove 17. The material inlet / outlet pipe 1, material inlet / outlet pipe 3, and the collection hole 9 have the same diameter and are coaxially aligned to form an upper and lower channel; when the graphite heat exchange block 3 in the middle is installed, the longitudinal through holes 12 in the adjacent graphite heat exchange blocks 3 must be coaxially aligned.

[0029] In specific work: High-temperature acid flow path: The high-temperature acid enters the annular groove 17 in the lower head 2 through the material inlet / outlet pipe 4 7, and after being separated in the annular groove 17, it flows into the longitudinal through hole 12 of the graphite heat exchange block 3 at the bottom, and then flows through the graphite heat exchange block above and enters the annular groove 8 in the upper head 1, and finally is discharged through the material inlet / outlet pipe 2 6; the high-temperature acid heats the graphite heat exchange block 3 during the flow process.

[0030] Low-temperature acid flow path: The low-temperature acid is fed into the material inlet / outlet pipe 4 at the top of the upper end cap 1. It first enters the collection hole 9 at the center of the first graphite heat exchange block 3 below. Under the obstruction of the baffle plate 13, the low-temperature acid cannot flow directly downwards, but is forced to flow into the transverse through hole 11 on the side, and then into the annular cavity 10 on the outside of the graphite heat exchange block. It then flows into the transverse through hole 11 on the lower side of the baffle plate 13 and continues to flow into the collection hole 9 at the center of the graphite heat exchange block. The reciprocating cycle makes the low-temperature acid flow in an S-shaped curve in the graphite heat exchange block, and after heat exchange with the high-temperature acid on the high-temperature side, it is heated up. Finally, it is discharged through the material inlet / outlet pipe 5.

[0031] Further implementation, for example, is attached. Figure 1-9 As shown, a sealing gasket 14 is provided on the connecting surface of the upper end cap 1, the graphite heat exchange block 3, and the lower end cap 2. The sealing gasket 14 is made of a corrosion-resistant material commonly used in the heat exchanger field, which only needs to meet high corrosion resistance requirements. The sealing gasket 14 is placed on the connecting surface during the heat exchanger assembly process. When assembling the sealing gasket 14, care must be taken to prevent displacement and ensure that it does not obstruct the upper and lower flow channels.

[0032] Further implementation, for example, is attached. Figure 1-9As shown, the upper end cap 1 and the lower end cap 2 are respectively provided with an upper cover plate 15 and a lower cover plate 16 on their outer sides, and the upper cover plate 15 and the lower cover plate 16 are connected and fixed together by long bolts. The upper cover plate 15 and the lower cover plate 16 are made of steel and are used to hold and fix the upper end cap 1, the lower end cap 2 and the graphite heat exchange block 3 in the middle. The long bolts can be the bolts commonly used in heat exchangers.

[0033] Further implementation, for example, is attached. Figure 1-9 As shown, one side of the annular cavity 10 in the vertical direction is an open structure. The open structure can be located on the upper side or the lower side, and the open part is located in the solid part of the next graphite heat exchange block. When the sealing gasket 14 is installed, the sealing gasket 14 completely seals and blocks the open part to prevent sulfuric acid leakage. When cleaning the graphite heat exchange block 3, the inside of the annular cavity 10 and the transverse through hole 11 can be cleaned through the open part of the annular cavity 10.

[0034] The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be included within the protection scope of the present invention.

Claims

1. A modular heat exchanger composed of polytetrafluoroethylene impregnated graphite, characterized in that: It includes an upper end cap (1) and a lower end cap (2) made of graphite, and at least one graphite heat exchange block (3) is provided between the upper end cap (1) and the lower end cap (2); the upper end cap (1), the lower end cap (2) and the graphite heat exchange block (3) are all impregnated with polytetrafluoroethylene; The upper end cap (1) has a material inlet / outlet pipe 1 (4) running vertically through its center. The lower side of the upper end cap (1) has an annular groove 1 (8) which is separated from the material inlet / outlet pipe 1 (4). The annular groove 1 (8) is connected to the outer side of the upper end cap (1) via a material inlet / outlet pipe 2 (6). The lower end cap (2) has a material inlet / outlet pipe 3 (5) running vertically through its center. The upper side of the lower end cap (2) has an annular groove 2 (17) which is separated from the material inlet / outlet pipe 3 (5). The annular groove 2 (17) is connected to the outer side of the lower end cap (2) via a material inlet / outlet pipe 4 (7). The graphite heat exchange block (3) has a vertically oriented flow collection hole (9) in the middle. The flow collection hole (9) is coaxial with the material inlet / outlet pipe one (4) and the material inlet / outlet pipe three (5). The flow collection hole (9) has a horizontal baffle plate (13) in the middle. The graphite heat exchange block (3) has an annular cavity (10) in the inner part near the outer side. The area between the flow collection hole (9) and the annular cavity (10) has a number of horizontal through holes (11) and vertical through holes (12) arranged at intervals. The horizontal through holes (11) connect the flow collection hole (9) and the annular cavity (10). The vertical through holes (12) penetrate the graphite heat exchange block (3) vertically and are concentrated in the area covered by the annular groove one (8) and the annular groove two (17).

2. The PTFE impregnated graphite monoblock composite heat exchanger as claimed in claim 1, wherein: A sealing gasket (14) is provided on the connecting surface of the upper head (1), the graphite heat exchange block (3) and the lower head (2).

3. The PTFE impregnated graphite monoblock composite heat exchanger as claimed in claim 1 wherein: The upper end cap (1) and the lower end cap (2) are respectively provided with an upper cover plate (15) and a lower cover plate (16), and the upper cover plate (15) and the lower cover plate (16) are connected and fixed by long bolts.

4. The PTFE impregnated graphite monoblock composite heat exchanger as claimed in claim 1, wherein: The annular cavity (10) has an open structure on one side in the vertical direction.

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