CN113028864B

CN113028864B - Preparation method of graphite impregnated tetrafluoro shell and tube heat exchanger

Info

Publication number: CN113028864B
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: 2022-10-04
Anticipated expiration: 2041-02-26
Also published as: CN113028864A

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.: the invention discloses a 2011101548753 discloses a liquid distribution pipe for a graphite heat exchanger, which comprises a liquid distribution pipe 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 relates to a tube type graphite heat exchanger, wherein the inner graphite tube is formed by sequentially connecting an upper tube plate, a heat exchange tube and a lower tube plate from top to bottom, 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 slightly, and the heat exchange effect needs 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 is milled into tubes with the same outer diameter, so that the standard graphite tubes can be conveniently and replaceably assembled with a partition plate or other tubes, and the inner deep holes are bored). The graphite tube is used as a heat exchange tube in the tube type heat exchanger.

Preferably, short carbon fibers are added into the carbon raw materials of the graphite tube array (when the carbon raw materials are pressed into bar stock, the short carbon fibers are basically preset in the axial direction or the oblique direction and in the non-radial direction of the bar stock), and a C-C composite material is formed after roasting, so that the specific strength and the 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 in the tube cavity for boring, 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, and the end with high gas temperature and high pressure at a heat medium inlet has high flow rate of the heat medium and 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 heat medium after heat exchange flows out smoothly, and the scaling is not easy to generate.

After machining, the graphite tubes are dipped in a tetrafluoroethylene solution (polymerization is carried out in the form of aqueous emulsion, a suspension of polymer particles is obtained in the process, tetrafluoroethylene can be exploded into tetrafluoromethane and carbon, so special polymerization equipment is needed to prevent hot spots which can cause dangerous side reactions from being generated), then the standard tubes are subjected to heat treatment at the temperature of 360-380 ℃ (slightly higher than the melting point of tetrafluoroethylene so as to facilitate the melting and permeation of the graphite surface, and the temperature is not too high so as to avoid the decomposition of the tetrafluoroethylene, save energy and reduce consumption), and then cooled, radiation crosslinking and permeation (in particular micro cracks and micro recesses of mechanical machining) are carried out under the oxygen-free condition to enable the tubes to become impermeable graphite, and the corrosion resistance and the surface mechanical strength of the tubes are improved.

The polytetrafluoroethylene is firstly machined and then impregnated, so that a tetrafluoroethylene coating (an impregnation layer) is complete and is not damaged, the good corrosion resistance of the whole outer surface of the pipe is ensured, the high-temperature mechanical property and the corrosion resistance are improved by the crosslinked polytetrafluoroethylene, and the polytetrafluoroethylene is used for pipelines of various corrosive chemical substances, and is particularly suitable for heat exchange tubes in heat exchange equipment. The tube and the tube plate are sealed by a single-tube O-shaped sealing ring (preferably high-temperature-resistant elastic rubber such as fluorosilicone 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 friction, abrasion and 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. The fluid in the whole device flows smoothly, 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: adopt graphite tubular product as the inside heat exchange tube of shell and tube heat exchanger, graphite tubular product adopt the carbon element raw materials, press into the rod stock through the mould, the calcination is the graphite rod after that, graphite tubulation is made to the machining of rethread outward appearance turn-milling, inside boring through-hole for the inside boring of graphite tubulation has the toper through-hole of uniform variation, and the internal diameter of the inside boring through-hole of one end of heat medium entrance is little, the wall thickness, and the other end internal diameter is big, the wall is thin. Then dipping the graphite tubes into the tetrafluoroethylene dispersion liquid, carrying out heat treatment at 365-375 ℃ under the condition of isolating oxygen to generate radiation crosslinking, and then cooling to form a tetrafluoroethylene surface dipping layer to form impermeable graphite tubes.

Claims

1. A graphite impregnated tetrafluoro shell and tube heat exchanger preparation method, use graphite tubular product as the heat exchange tube in the shell and tube heat exchanger, the said graphite tubular product uses the carbon element raw materials, press into the bar stock through the mould first; the method is characterized in that:

the carbon raw material is added with short carbon fibers, and the short carbon fibers are basically preset in the axial direction of a bar blank; then, roasting the bar stock to obtain a graphite bar made of a C-C composite material; then, the graphite tube nest is manufactured by turning and milling the surface and boring a through hole inside; 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 graphite tube is dipped in tetrafluoroethylene solution, then heat treatment is carried out at the temperature of 360-380 ℃ under the condition of oxygen isolation 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.

3. The method of manufacturing a graphite-impregnated tetrafluoro shell-and-tube heat exchanger as claimed in claim 1, wherein:

the graphite shell and tube bores the toper through-hole of uniform change inside, and the internal diameter of the inside bore hole of one end at the heat medium entrance is little, the wall thickness, and the other end internal diameter is big, the wall is thin.