A graphite impregnation method

Abstract

The application discloses a kind of graphite impregnation methods, using solidification kettle system to furan resin impregnation to graphite;The solidification kettle system is by solidification kettle, PLC controller, gas inlet control system, exhaust control system composition;Solidification kettle, gas inlet control system will pressure, temperature and flow transmitter to PLC transmission time signal, and time signal with the preset program signal in PLC is compared, and PLC sends drive signal to heater and related valve, so that the temperature, pressure and flow of system mutually cooperate, complete the heat curing process of impregnated graphite.The application takes away residual gas and reaction dehydration gas generated by high temperature in graphite piece in time, solves the problem of return and vomit;The application generates byproduct by making airflow channel in kettle in time, makes reaction positive, and solidifies fully.

Description

Technical Field

[0001] The invention relates to a graphite impregnation method. Background Art

[0002] Graphite, an inorganic carbon material, boasts excellent corrosion resistance and is resistant to attack by strong inorganic acids, strong bases, and most organic compounds, making it an ideal corrosion-resistant alternative to metals. Its sp2 conjugated ring structure allows for easy electron flow within the graphite sheets, resulting in excellent thermal conductivity. Drilling channels within graphite blocks for feeding materials and heating media (called feed and water pores) makes them ideal components for heat exchangers. However, during the firing process of artificial graphite, volatilization of gases can form interconnected micropores within the blocks, short-circuiting the feed and water pores. Therefore, before use, graphite requires an impregnant to fill these micropores and react to form a solid seal, completely separating the water and feed pores. The choice of impregnant and the development of supporting impregnation and curing technologies are closely tied to the operating conditions of the heat exchanger. Strong acid heat exchange is a common practice in the corrosion protection industry. The development and use of phenolic resins, which are resistant to strong acid corrosion, as impregnants are becoming increasingly common, and the corresponding impregnation and curing processes are well-established. As the market for pure strong acids becomes increasingly saturated, the environmental protection industry is increasingly targeting the strong alkali and acid-base alternating corrosion protection markets. The current development direction for highly corrosion-resistant impregnated graphite, both domestically and internationally, is to improve the impregnating agent to achieve high-corrosion resistance. The impregnating agents studied primarily include furan resins such as furfuryl alcohol and furfuryl ketone. Furan resins possess excellent corrosion resistance, boasting superior temperature resistance, corrosion resistance, chemical stability, and other physical properties compared to phenolic resin-impregnated graphite. Furan resin-impregnated graphite is applicable to nearly all media operating conditions and can withstand long-term operation under demanding conditions.

[0003] Research on the process of furan resin impregnation of graphite has been going on for many years at home and abroad. The production process characteristics of furan resin lead to a huge difference in the quality of furan resin produced by different manufacturers. In addition, the curing system of furan resin is different in terms of latentness and non-latentness. Therefore, the development of this process needs to start from the screening and modification of resin, and then determine the process parameters such as impregnation and heat treatment. At present, the development of furan resin impregnation graphite process at home and abroad is progressing slowly.

[0004] Currently, the primary development approach for furan resin impregnation in China is to study the mixing of furan resin and phenolic resin, using the mixed resin as an impregnating agent to impregnate graphite, thereby achieving corrosion-resistant and impermeable graphite. While this mixed resin approach can improve the success rate of graphite impregnation to a certain extent, it also reduces corrosion resistance, with severe corrosion in alkaline conditions. Even when pure furan resin is used for graphite impregnation, various issues remain, including minimal pressure resistance, which cannot meet practical application requirements.

[0005] The traditional impregnation process of furan resin impregnated graphite has the following main problems:

[0006] (1) Furan resin is difficult to impregnate into graphite pores

[0007] The overall weight gain rate of furan resin impregnated graphite is low, and after heat treatment, the impregnant will spit back, and the amount of furan resin impregnated and preserved in the graphite is small;

[0008] (2) It is difficult to combine furan resin and graphite interface well

[0009] When using furan resin-impregnated graphite materials in heat exchange conditions, a large amount of impregnant overflows and peels off, and the bonding strength between the furan resin and the graphite material is low after curing;

[0010] (3) Furan resin combines with graphite and is not alkali-resistant.

[0011] Repeated testing revealed that pure furan resin castings exhibit excellent corrosion resistance in alkaline solutions. High-purity furan resin exhibits only very slight discoloration after soaking in alkaline solutions for a period of time, and this discoloration persists over a long period. However, repeating the process with graphite coupons soaked in furan resin quickly results in a more pronounced discoloration of the medium.

[0012] (4) The curing agent used in the traditional process will react quickly with the furan resin, which has extremely high requirements for the operation of the addition process. It is difficult to control in production, and uneven addition can easily cause local reactions. Summary of the Invention

[0013] The object of the present invention is to provide a graphite impregnation method which can promptly remove residual gas in the graphite piece and gas generated by reaction dehydration at high temperature, solve the back-spitting problem, and promptly remove by-products generated by curing of furan resin, so that the reaction proceeds in a forward direction and the graphite is fully cured.

[0014] The technical solution of the present invention is:

[0015] A graphite impregnation method is characterized by using a curing kettle system to impregnate graphite with furan resin; the curing kettle system comprises a curing kettle, a PLC controller, an air intake control system, and an exhaust control system; the curing kettle and the air intake control system transmit real-time signals from pressure, temperature, and flow transmitters to the PLC, and compare the real-time signals with program signals preset in the PLC. The PLC then sends drive signals to a heater and related valves, so that the system's temperature, pressure, and flow coordinate with each other to complete the thermal curing process of the impregnated graphite.

[0016] The curing kettle is equipped with a pressure sensor, a temperature sensor, a heating control line, and an electric heater. The air intake control system includes a manual valve and an electric valve controlled by a PLC signal, wherein the electric valve is only used for pressure stabilization during the ventilation process; a protective valve is installed at each end of the electric valve; the inlet pipeline of the air intake control system is also provided with a manual ball valve for switching between hot compressed air and cold compressed air. After the compressed air is discharged from the buffer tank, it can enter the air intake control system from two pipelines respectively: the unheated compressed air is directly input into the air intake control system through the first pipeline and the first manual valve, and is used for the pressurization and leak detection stages of the curing kettle. Another pipeline preheats the compressed air through the preheater, and then enters the air intake control system through the second pipeline and the second manual valve. During the production process, the hot compressed air is mainly used to control the speed of slow vaporization of volatile liquids;

[0017] There are two parallel pipelines in the exhaust control system 4. One pipeline has a third manual valve for quick release of air at the end of production. The other pipeline is used for flow and pressure control during the production process. It has three core components: a flow transmitter responsible for outputting signals to the PLC; another controlled valve that controls the flow by adjusting the opening; and a pressure transmitter that sends signals to the PLC to reflect pressure changes in the system. The first needle valve, the second needle valve and the pressure gauge form a pressure stabilizing device in the reactor.

[0018] The interior of the curing kettle is equipped with a gas flow and distribution control system to allow the flowing air to fully contact the raw materials of furan resin-impregnated graphite accumulated in the middle of the curing kettle, thereby increasing the contact area and forming surface gas flow.

[0019] By adjusting the opening ratio of the first needle valve and the second needle valve, the pressure of the pressure gauge is positioned at 90% of the pressure transmitter value. During the production process, the relative opening of the first needle valve and the second needle valve does not change.

[0020] The working method of the gas flow and distribution control system is as follows: after the gas enters the curing kettle from the air inlet hole on the wall of the curing kettle, it is introduced through the pipeline and guided downward to the center of the bottom, and then multiple air guide pipes that are attached to the wall and upward are led out to the four sides. Some small holes with different outlet directions are pre-drilled on the pipes as gas distributors, and the gas is evenly blown toward the material area in the middle. After passing through the material, it flows to the upper part through the circular baffle above and is discharged from the gas outlet on the side to the outflow exhaust control system.

[0021] The method includes the following steps: putting the washed and dried graphite material into a curing kettle, covering the top, sealing the kettle, reducing the pressure to a vacuum degree of 0.094 MPa, maintaining the pressure for half an hour, ensuring no air leakage, opening the feed valve, sucking the furan resin into the curing kettle, the liquid level being 10 cm higher than the top of the graphite, reducing the vacuum degree to 0.088 MPa, and maintaining the pressure for half an hour; then, opening the air inlet valve, introducing compressed air to a pressure of 0.65 MPa, maintaining the pressure for 4 hours, opening the exhaust valve, adjusting the system pressure to slightly above one atmosphere, opening the discharge valve, and using the pressure to discharge the remaining material back to the furan resin trough; the impregnated graphite is left to rest for 12 hours, allowing excess furan resin on the surface to flow back to the trough for re-impregnation.

[0022] Before impregnation, the furan resin is modified by adding one or more auxiliary agents selected from furfural, butyl acetate, n-butanol and water to the furan resin. The amount of the auxiliary agent added is 1-20% of the mass of the furan resin.

[0023] The present invention timely removes residual gas in the graphite parts and gas generated by high-temperature reaction dehydration by forming an air flow channel in the kettle, thereby solving the back-spitting problem and eliminating the need for subsequent mechanical processing, greatly saving processing costs and improving production efficiency. The main reason for poor interface bonding between furan resin and graphite is that the furan resin is not completely cured during heat treatment. The present invention timely removes by-products generated by the curing of the furan resin by forming an air flow channel in the kettle, allowing the reaction to proceed in a forward direction and fully cure.

[0024] The present invention solves the instability factor in the production process by modifying the furan resin, thereby greatly improving product quality and qualified rate.

[0025] The present invention coordinates the heating curve, pressure curve and flow curve of the system during the thermal curing process. It can use the continuous passage of hot compressed air at a specific stage of the reaction process to reduce the partial pressure of the volatile liquid in the air of the curing kettle, increase the driving force for the stable vaporization of the volatile liquid, and reduce the thickness of the air mold resistance layer on the surface of the furan resin-impregnated graphite through the flow of air, thereby increasing the overflow speed of the volatile liquid to match the curing film-forming speed of the resin, thereby achieving the following advantages.

[0026] This prevents volatile liquids from vaporizing and overflowing when the viscosity is very high during the resin thickening process, causing the resin to be squeezed out of the air in the graphite and form sags on the outer surface and in the water and material pores. This avoids the extra work of polishing the outer surface and re-drilling the holes before the third impregnation.

[0027] This prevents the volatile liquid from heating up again and vaporizing and expanding after forming a solid crust on the outer surface. The enormous pressure would burst the outer shell or the graphite body, and the remaining pressure would impact the wall of the curing kettle, forming a shock wave and a loud noise. The sudden high pressure could even break the safety valve (or bursting disc), terminating the production process and affecting production efficiency.

[0028] While preventing the volatile liquid from forming a solid on the outer surface, even if it does not break the shell, it will still vibrate violently, causing the resin surrounding the volatile gas to form cracks, weaken its strength, and reduce the bonding strength between different resin layers (the first layer and the second layer, the second layer and the third layer). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below with reference to the accompanying drawings and examples.

[0030] Figure 1 It is a schematic diagram of the composition of the curing kettle system adopted in the present invention.

[0031] Figure 2 This is a schematic diagram of a gas flow and distribution control system installed inside a curing kettle.

[0032] Figure 3 yes Figure 2 Schematic cross-section diagram. DETAILED DESCRIPTION

[0033] A graphite impregnation method employs a curing kettle system to impregnate graphite with furan resin. The curing kettle system comprises a curing kettle 1, a PLC controller 2, an intake control system 3, and an exhaust control system 4. Systems 1, 3, and 4 transmit real-time signals from pressure, temperature, and flow transmitters to the PLC via multiple data lines. The real-time signals are compared with pre-set program signals in the PLC. At appropriate times, the PLC sends drive signals to heaters and related valves, aligning the system's temperature, pressure, and flow to complete the thermal curing process of the impregnated graphite, thereby addressing various drawbacks of current furan resin-impregnated graphite curing methods.

[0034] The curing kettle system includes the pressure sensor 1-1, temperature sensor 1-2, heating control line 1-3, and an annular electric heater 1-4. The air intake control system 3 includes a manual valve 3-1 and an electric valve 3-3 controlled by a PLC signal. Valve 3-3 is used only for pressure stabilization during ventilation. Protective valves 3-2 and 3-4 are installed at each end of the controlled valve 3-3 to extend the service life of the electric valve 3-3. Manual ball valves 3-5 and 3-6 are also installed in the inlet pipeline to switch between hot and cold compressed air.

[0035] After being discharged from the buffer tank, the compressed air can enter the air intake control system 3 through two pipelines: the unheated compressed air is directly input into the air intake control system 3 through pipeline 5-2 and manual valve 3-6, and is used for pressurization and leak detection of the curing kettle. Another pipeline preheats the compressed air after passing it through the preheater, and then enters the air intake control system 3 through pipeline 5-1 and valve 3-5. During the production process, the hot compressed air is mainly used to control the speed of slow vaporization of volatile liquids.

[0036] The exhaust control system 4 contains two parallel pipelines. One contains a manual valve 4-1, used for quick release at the end of production. The other controls flow and pressure during the production process. It has three core components: flow transmitter 4-6, which outputs signals to the PLC; controlled valve 4-5, which controls flow by adjusting its opening; and pressure transmitter 4-8, which sends signals to the PLC reflecting pressure changes within the system. Needle valves 4-3 and 4-4, along with a pressure gauge 4-9, form a pressure stabilization device within the reactor (which reduces pressure). By adjusting the opening ratio of valves 4-3 and 4-4, the pressure at valve 4-9 is set at 90% of the value at valve 4-8. The relative openings of valves 4-3 and 4-4 do not change during production.

[0037] The interior of the curing kettle 1 is equipped with a gas flow direction and distribution control system, which allows the flowing air to fully contact the raw materials of furan resin-impregnated graphite accumulated in the middle of the curing kettle, thereby increasing the contact area, forming surface gas flow, and slowly, evenly and steadily vaporizing and overflowing the volatile liquid, thereby suppressing the occurrence of vomiting and implosion, thereby improving production efficiency. Figure 3 After the neutral gas enters the curing kettle from the air inlet hole on the wall of the curing kettle, it is introduced through pipeline 1-5 and guided downward to the center of the bottom. Then, four air guide pipes 1-6 (only one is drawn) that are attached to the wall and pointed upward are led out to the four sides. Some small holes 1-8 with different outlet directions are pre-drilled on the pipe as a gas distributor. The gas is evenly blown to the material area in the middle, passes through the material, flows to the upper part through the circular baffle above, and is discharged from the gas outlet on the side to the outflow control system 4.

[0038] Usage: Before impregnation, the furan resin is modified by adding furfural, butyl acetate, n-butanol, or one or more additives in water to the furan resin. The amount of additive added is 1-20% (e.g., 1%, 10%, 19%) of the mass of the furan resin.

[0039] The pretreatment process for furan resin impregnation of graphite: Place the cleaned and dried graphite into the impregnation kettle, cover and seal the kettle, and reduce the vacuum to 0.094 MPa. Maintain the pressure for half an hour to ensure airtightness. Open the feed valve and draw the furan resin into the kettle until the liquid level is 10 cm above the top of the graphite. Reduce the vacuum to 0.088 MPa and maintain the pressure for half an hour. Then, open the air inlet valve and introduce compressed air to a pressure of 0.65 MPa. After maintaining the pressure for 4 hours, open the exhaust valve to adjust the system pressure to slightly above 1 atmosphere. Open the discharge valve and use the pressure to drain the remaining material back into the furan resin tank. The impregnated graphite is allowed to rest for 12 hours to allow any excess furan resin on the surface to flow back into the tank for further impregnation.

[0040] The total heating time of the production process is 20 hours, and different temperatures, pressures, and flow rates are set at different times. This production process is set based on a 3.2 cubic meter furan resin curing kettle. If the volume of the curing kettle changes, the relevant parameters need to be adjusted. The pretreated furan-impregnated graphite block is transferred from the impregnation kettle to the curing kettle 1, and then the upper curing kettle cover is covered. After checking that the seal is good, the air compressor is turned on and its compressed air is introduced from the high-pressure storage tank through 5-2 in the form of cold air and enters the input control system 3 through valve 3-6. It is directly introduced into the curing kettle 1 through valve 3-1. The pressure of the curing kettle is transmitted to the PLC controller 2 through the pressure transmitter 1-1 and displayed. When the pressure reaches 0.75 MPa, valve 3-1 is closed and it is checked that 4-1 is closed. The PLC pre-sets the heat treatment process's pressure, temperature, and flow curves. Heat treatment begins, opening protective valves 3-2, 3-4, 4-2, and 4-7, ensuring the controlled valves operate normally upon receiving the command. Simultaneously, the temperature, pressure, and flow control programs are activated, ensuring synchronization. Before reaching 120°C, if the pressure falls below 0.75 MPa, the PLC (Programmable Logic Controller) commands automatic valve 3-3 to replenish the system with cold compressed air. If the pressure exceeds this value, the PLC disables the inlet valve 3-3. After reaching 120°C, the cold compressed air line 5-2 is disconnected, and valve 3-5 is opened to allow 120°C hot compressed air from line 5-1 to enter. From the second to third hour, the PLC controls the flow rate based on the settings and compares it with data monitored by a flow transmitter. It then commands automatic valve 4-5 to adjust the valve opening, gradually increasing the flow rate from 0 to 200 nl / min. If the pressure drops below 0.7 MPa, the PLC signals automatic valve 3-3 to open and replenish air. If the pressure exceeds 0.75 MPa, valve 3-3 closes. In between, fine-tuning can be performed based on the speed of the pressure change. From the 12th to the 13th hour, the flow rate is ramped down from 200 nl / min to 175 nl / min, while the pressure is ramped up from 0.75 MPa to 1.0 MPa. From the 13th to the 14th hour, the flow rate is ramped down from 175 nl / min to 150 nl / min, while the pressure is ramped up from 1.0 MPa to 1.1 MPa. From the 15th to the 16th hour, the flow rate is ramped down from 150 nl / min to 0 nl / min. From the 16th hour until the end of the heating process, if the system pressure falls below 1.1 MPa, inlet valve 3-3 opens to replenish compressed gas. If the system pressure exceeds 1.15 MPa, outlet valves 4-5 open and close when the pressure falls below 1.13 MPa. When the heating process ends, the pressure and flow control program remains at the last instruction, maintaining the final pressure stable until the temperature drops to 140°C. All pressure and flow control valves are closed.After the temperature naturally drops to 90 degrees, close the inlet protection valves 3-2, 3-4 and the outlet protection valves 4-2 and 4-7, open the manual start valve 4-1 to release the air to normal pressure, and then carry out the loading and unloading operations of the solidified product.

Claims

1. A graphite impregnation method, characterized in that: Graphite is impregnated with furan resin using a curing kettle system, which consists of a curing kettle, a PLC controller, an air intake control system, and an exhaust control system. The curing kettle and air intake control system transmit real-time signals from pressure, temperature, and flow transmitters to the PLC, which compares these real-time signals with program signals preset in the PLC. The PLC then sends drive signals to the heater and related valves, aligning the system's temperature, pressure, and flow to complete the thermal curing process of the impregnated graphite. The interior of the curing kettle is equipped with a gas flow and distribution control system to allow the flowing air to fully contact with the furan resin-impregnated graphite raw materials accumulated in the middle of the curing kettle, thereby increasing the contact area and forming surface gas flow. The working method of the gas flow and distribution control system is as follows: after the gas enters the curing kettle from the air inlet hole on the wall of the curing kettle, it is introduced through the pipeline and guided downward to the center of the bottom, and then multiple air guide pipes that are attached to the wall and upward are led out to the four sides. Some small holes with different outlet directions are pre-drilled on the pipes as gas distributors, and the gas is evenly blown toward the material area in the middle. After passing through the material, it flows to the upper part through the circular baffle above and is discharged from the gas outlet on the side to the outflow exhaust control system.

2. A graphite impregnation method according to claim 1, characterized in that: The curing kettle is equipped with a pressure sensor, a temperature sensor, a heating control line, and an electric heater. The air intake control system includes a manual valve and an electric valve controlled by a PLC signal, wherein the electric valve is only used for pressure stabilization during the ventilation process; a protective valve is installed at each end of the electric valve.

3. A graphite impregnation method according to claim 2, characterized in that: The inlet pipeline of the air intake control system is also equipped with a manual ball valve to convert hot compressed air and cold compressed air. After the compressed air is discharged from the buffer tank, it can enter the air intake control system from two pipelines respectively: the unheated compressed air is directly input into the air intake control system through the first pipeline and the first manual valve, which is used for the pressurization and leak detection stages of the curing kettle. Another pipeline preheats the compressed air after passing through the preheater, and then enters the air intake control system through the second pipeline and the second manual valve. During the production process, the hot compressed air is mainly used to control the speed of slow vaporization of volatile liquids.

4. A graphite impregnation method according to claim 1, characterized in that: There are two parallel pipelines in the exhaust control system. One pipeline is provided with a third manual valve for quick air release at the end of production; the other pipeline is used for flow and pressure control during the production process.

5. A graphite impregnation method according to claim 4, characterized in that: The other pipeline used for flow and pressure control in the production process has three core components: one is a flow transmitter, which is responsible for outputting signals to the PLC; another is a controlled valve, which controls the flow by adjusting the opening; and there is also a pressure transmitter, which is used to send signals to the PLC to reflect the pressure changes in the system; the first needle valve, the second needle valve and the pressure gauge constitute an air pressure stabilizing device in the reactor.

6. A graphite impregnation method according to claim 5, characterized in that: By adjusting the opening ratio of the first needle valve and the second needle valve, the pressure of the pressure gauge is positioned at 90% of the pressure transmitter value. During the production process, the relative opening of the first needle valve and the second needle valve does not change.

7. A graphite impregnation method according to claim 1, 2, 3, 4, 5 or 6, characterized in that: The pretreatment process of impregnating graphite with furan resin is as follows: the washed and dried graphite material is placed in a curing kettle, the lid is sealed, the vacuum degree is reduced to 0.094 MPa, the pressure is maintained for half an hour to ensure that there is no air leakage, the feed valve is opened, and the furan resin is sucked into the curing kettle. The liquid level is 10 cm higher than the top of the graphite, the vacuum degree is reduced to 0.088 MPa, and the pressure is maintained for half an hour; Then, open the air inlet valve and introduce compressed air to a pressure of 0.65 MPa. After maintaining the pressure for 4 hours, open the exhaust valve, adjust the system pressure to slightly above one atmosphere, open the discharge valve, and use the pressure to discharge the remaining material back to the furan resin tank; the impregnated graphite is left to stand for 12 hours to allow excess furan resin on the surface to flow back to the tank for re-impregnation.

8. A graphite impregnation method according to claim 7, characterized in that: Before impregnation, the furan resin is modified by adding one or more auxiliary agents selected from furfural, butyl acetate, n-butanol and water to the furan resin. The amount of the auxiliary agent added is 1-20% of the mass of the furan resin.

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