CN113028864A

CN113028864A - Preparation method of graphite impregnated tetrafluoro shell and tube heat exchanger

Info

Publication number: CN113028864A
Application number: CN202110215930.9A
Authority: CN
Inventors: 孙建军; 王俊飞; 刘畅; 刘仍礼; 何志峰; 许亮
Original assignee: Nantong Star Graphite Co ltd
Current assignee: Nantong Star Graphite Co ltd
Priority date: 2021-02-26
Filing date: 2021-02-26
Publication date: 2021-06-25
Anticipated expiration: 2041-02-26
Also published as: CN113028864B

Abstract

The invention discloses a preparation method of a graphite impregnated tetrafluoro shell and tube heat exchanger, which comprises the steps of pressing carbon raw materials into bars through a die, roasting, machining to prepare standard graphite shell and tube, impregnating tetrafluoroethylene, and taking the graphite shell and tube as a heat exchange tube in the shell and tube heat exchanger. The graphite pipe has high flatness, smooth surface, high corrosion resistance and high interchangeability.

Description

Preparation method of graphite impregnated tetrafluoro shell and tube heat exchanger

Technical Field

The invention relates to a heat exchanger manufacturing technology used in the chemical industry.

Background

The graphite tube adopted in the traditional graphite tube type heat exchanger is formed by extruding carbon raw materials, roasting and graphitizing, and the graphite tube is easy to have the problems of eccentricity, bending and the like. And the machining is not carried out after the forming, and due to the existence of eccentric bending, the local wall is too thin and the strength is insufficient in the machining.

Application No.: 2011101548753 the invention discloses a liquid distribution tube for a graphite heat exchanger, which comprises a liquid distribution tube body and is characterized in that: the liquid distribution pipe body is made of a tetrafluoroethylene pipe. The graphite material and the tetrafluoroethylene material have larger property difference and are not organically combined.

Application No. of the present applicant: 201410372284, the invention relates to a tube type graphite heat exchanger, the inner graphite tube is formed by connecting an upper tube plate, a heat exchange tube and a lower tube plate from top to bottom in sequence, the heat exchange tube is arranged between the upper tube plate and the lower tube plate in parallel, and two ends of the heat exchange tube are respectively fixed in the upper tube plate and the lower tube plate; although the heat exchange effect of the invention is good, the strength of the heat exchange tube is not high enough, the dimensional accuracy and the straightness are not reliably ensured, the surface corrosion resistance is weak, and the heat exchange effect is to be improved.

Disclosure of Invention

The purpose of the invention is as follows:

the invention provides a tetrafluoro-impregnated graphite tubular heat exchanger which has high strength, high dimensional accuracy and good corrosion resistance and can be manufactured in a standardized way.

The technical scheme is as follows:

the invention provides a preparation method of a tetrafluoro-impregnated graphite tubular heat exchanger, which adopts carbon raw materials, the carbon raw materials are pressed into bar stock (round bars or polygonal bars) through a mould, then the bar stock is roasted into graphite bars, and then standard graphite tubes (the surface of the graphite tubes is turned and milled into tubes with the same external diameter, so that the graphite tubes can be conveniently and fixedly assembled with a partition plate or other tubes, and deep holes are drilled in the interior of the graphite tubes). The graphite tube array is used as a heat exchange tube in the tube type heat exchanger.

Preferably, short carbon fibers (basically axially or obliquely preset and non-radially preset) are added into the carbon raw materials of the graphite tube array, and a C-C composite material is formed after roasting, so that the specific strength and specific rigidity of the tube in the length direction are increased, and the difficulty of radial cutting processing and the roughness of the surface are avoided being increased; in the subsequent machining such as turning, the partial wall becomes thin, but the pressure resistance is sufficient.

Typical metal heat exchange tubes are drawn and typical graphite heat exchange tubes are extruded and have the same tube diameter and wall thickness throughout. In the invention, preferably, a boring process is adopted in the graphite tube array, and a numerical control boring and milling tool is adopted for boring in the tube cavity, so that uniformly-changed tapered holes can be formed, the inner diameter of the bored hole in one end is smaller, the wall is thicker, namely the end with high gas temperature and high pressure at a heat medium inlet is provided, the flow rate of the heat medium is high, and the heat medium is not easy to crack; the other end has a large inner diameter and a thin wall, namely the end with low temperature and low pressure, the flow rate of the heating medium is low, the mass and heat transfer are convenient, the heating medium after heat exchange flows out smoothly, and scaling is not easy to generate.

After machining, the graphite tubes are dipped in tetrafluoroethylene solution (polymerization is carried out in the form of aqueous emulsion, the process obtains suspension of polymer particles, tetrafluoroethylene can be exploded and decomposed into tetrafluoromethane and carbon, so special polymerization equipment is needed to prevent hot spots which can cause dangerous side reactions from generating) standard tubes, then the standard tubes are cooled after heat treatment at the temperature of 360 plus 380 ℃ (slightly higher than the melting point of tetrafluoroethylene, so that the graphite surfaces can be easily melted and permeated, and the temperature is not too high, the decomposition of the tetrafluoroethylene is avoided, and energy is saved and consumption is reduced), and radiation crosslinking permeation (especially microcracks and micro-depressions of mechanical machining) is carried out under the oxygen-free condition to enable the graphite tubes to become impermeable graphite, and the corrosion resistance and the surface mechanical strength of the tubes are improved.

The polytetrafluoroethylene pipe is firstly machined and then impregnated with tetrafluoroethylene, so that a tetrafluoroethylene coating (an impregnation layer) is complete and not damaged, the good corrosion resistance of the whole outer surface of the pipe is ensured, and the crosslinked polytetrafluoroethylene improves the high-temperature mechanical property and the corrosion resistance, is used for pipelines of various corrosive chemical substances, and is particularly suitable for heat exchange pipes in heat exchange equipment. The tube array and the tube plate are sealed by a single tube O-shaped sealing ring (preferably high-temperature-resistant elastic rubber such as fluorinated silicone rubber, temperature resistance, buffering, sealing and affinity with tetrafluoroethylene and graphite), so that the defect of low bonding strength of the tetrafluoro impregnated graphite is overcome.

Meanwhile, the inner surface and the outer surface of the pipe are smooth, so that fluid can flow through the inner side and the outer side (refrigerant can pass between the pipelines). The polytetrafluoroethylene surface is used as lubricant, so that the friction, the abrasion and the machine energy consumption can be reduced. The tube plate and the graphite tube nest cannot be bonded, and the gap between the tube plate and the tube plate can be accurately controlled due to the accurate machining of the outer wall surface, so that good mechanical seal is obtained, and meanwhile, the tube plate is convenient to tightly install, connect and disassemble and replace easily.

Has the advantages that:

the graphite pipe has high flatness, no eccentricity and high dimensional precision; the surface is smooth, and the corrosion resistance is high; the tube has high thermodynamic strength and good mass and heat transfer effects; the pipe is conveniently and closely matched with other pipe fittings. Fluid flows smoothly in the whole device, and the service life is long.

Drawings

Fig. 1 is a schematic view of an axial sectional structure of the present invention.

In the figure, 1-heat medium inlet; 2-high temperature end of graphite tube; 3-a tube plate; 4-low temperature end of graphite tube; 5-a refrigerant inlet; 6-graphite tube wall.

Detailed Description

The preparation method of the graphite-impregnated tetrafluoro shell and tube heat exchanger shown in figure 1 comprises the following steps: the graphite tube is used as the heat exchange tube inside the tube type heat exchanger, the graphite tube is made of carbon raw materials through die pressing to form a bar blank, the bar blank is baked to form a graphite bar, and the graphite tube is machined through surface turning and milling and internal boring to form a graphite tube, so that a uniformly-changed conical hole is bored inside the graphite tube, the internal diameter of the internal boring hole in one end of a heating medium inlet is small, the wall thickness of the internal boring hole is small, and the internal diameter of the other end is large and the wall thickness of the internal diameter of the internal boring hole. Then dipping the graphite tube into tetrafluoroethylene dispersion, carrying out heat treatment at 365-375 ℃, carrying out radiation crosslinking under the condition of isolating oxygen, and then cooling to form a tetrafluoroethylene surface dipping layer to form an impermeable graphite tube.

Claims

1. A graphite impregnated tetrafluoro shell and tube heat exchanger preparation method, which adopts graphite pipe as the heat exchange pipe inside the shell and tube heat exchanger, is characterized in that: the graphite tube is made by pressing carbon raw materials into a bar stock through a die, then roasting into a graphite bar, and then machining through turning and milling the outer surface and boring the inner part to prepare a graphite tube; then, the graphite tubes were immersed in the tetrafluoroethylene dispersion to form a tetrafluoroethylene surface-impregnated layer, thereby forming impermeable graphite tubes.

2. The method of manufacturing a graphite-impregnated tetrafluoro shell-and-tube heat exchanger as claimed in claim 1, wherein: the carbon raw material is added with short carbon fibers which are basically preset axially or obliquely, and the graphite made of the C-C composite material is formed after roasting.

3. The method of manufacturing a graphite-impregnated tetrafluoro shell-and-tube heat exchanger as claimed in claim 1, wherein: the graphite tube is dipped in a tetrafluoroethylene solution, and then heat treatment is carried out at the temperature of 360 plus 380 ℃ under the condition of isolating oxygen to generate radiation crosslinking and then cooling is carried out, so that a firm tetrafluoroethylene surface dipping layer is formed on the surface of the graphite tube.

4. The method of manufacturing a graphite-impregnated tetrafluoro shell-and-tube heat exchanger as claimed in claim 1, wherein: uniformly-changed conical holes are bored in the graphite tube, the inner diameter of the bored hole in one end of the heating medium inlet is small, the wall thickness of the bored hole is small, and the inner diameter of the other end of the graphite tube is large and the wall thickness of the bored hole is thin.

5. The method of manufacturing a graphite-impregnated tetrafluoro shell-and-tube heat exchanger as claimed in claim 1, wherein: and an O-shaped fluorosilicone rubber seal ring is used for sealing between the tube array and the tube plate.