KR20220160724A - Method of pfa impregnation for block type graphite heat exchanger - Google Patents

Abstract

The present invention relates to a block type graphite heat exchanger PFA immersion method. The method includes: a graphite block preparation step (S10) of removing foreign substances from the surface of a graphite block to be impregnated through pneumatic washing; a primary thermal treatment step (S20) of charging the graphite block having passed through the graphite block preparation step (S10) into an air drying furnace and maintaining the graphite block therein at 90-140℃ for 4-12 hours to dry and thermally treat the graphite block; a coupling agent immersion step (S30) of inputting the graphite block having passed through the primary thermal treatment step (S20) into a coupling agent immersion machine and pressing the graphite block in a vacuum condition to immerse the graphite block in coupling agent immersion liquid; a secondary thermal treatment step (S40) of charging the graphite block having passed through the coupling agent immersion step (S30) into the air drying furnace and maintaining the graphite block at 80-120℃ for 4-12 hours to dry and thermally treat the graphite block; an immersion preparation step (S50) of inputting the graphite block having passed through the secondary thermal treatment step (S40) into a container and filling the container with PFA pellets such that the graphite block is submerged therein; a PFA immersion step (S60) of charging the container filled with the graphite block and the PFA into a PFA immersion furnace and thermally treating the container in a vacuum condition to press the PFA after melting the PFA to immerse the PFA; and a cooling step (S70) of cooling the graphite block having passed through the PFA immersion step (S60) at a room temperature. Therefore, a PFA immersion block type graphite heat exchanger product applied to a high-temperature and high-pressure corrosion environment can be more efficiently manufactured.

Description

Block type graphite heat exchanger PFA impregnation method {METHOD OF PFA IMPREGNATION FOR BLOCK TYPE GRAPHITE HEAT EXCHANGER}

The present invention relates to a PFA impregnation method for a block-type graphite heat exchanger, and more particularly, constitutes a method of impregnating a PFA (Per Fluoro Alkoxy) resin in the manufacture of a block-type graphite heat exchanger applied to a high-temperature and high-pressure corrosive environment. It relates to a technology for manufacturing a PFA-impregnated graphite heat exchanger product applicable to industrial fields requiring high temperature and high chemical resistance by improving mechanical properties and increasing acid resistance.

In general, a heat exchanger is a device used to exchange energy between two fluids with different thermal energies. It is a key device to increase savings and efficiency.

In a situation where interest and investment in the efficient use of thermal energy such as industrial waste heat, geothermal heat, and solar heat are increasing along with the recent increase in the supply of new and renewable energy in earnest, efforts to develop technologies related to thermal energy are expanding in each country, and as part of this, the need for heat exchange technology is increasing. is also rising.

Heat exchangers can be classified into shell & tube type, plate & frame type, block type, etc. by shape. Demand for the block type, in particular, is continuously increasing as an ultra-efficient, compact, high value-added heat exchanger that can be used in extreme environments.

Graphite has excellent thermal conductivity after aluminum and is resistant to corrosion and thermal shock, so it is applied to acid washing tanks, metal processing industries where hydrochloric acid, sulfuric acid, hydrofluoric acid, and nitric acid are used, heat recovery from pigments and corrosive processes, various chemical industries, fine chemicals, and pharmaceutical fields. do.

Since graphite is porous, it is impregnated with a thermosetting resin to make it impermeable. Graphite heat exchangers are classified into phenolic resin, carbon resin, and PFA resin impregnated graphite heat exchangers, respectively, depending on the usage environment corresponding to the temperature and characteristics.

As an example of a known technique, Korean Patent Registration No. 10 - 0907042 discloses a first step of cleaning the surface of a heat exchanger, a second step of stirring a thermosetting coating agent having a phenolic resin and a solvent, and mounting a ring jig on the heat exchanger. The third step, the fourth step of polishing the inside of the tube of the heat exchanger using a synthetic abrasive, the fifth step of mounting the polished heat exchanger on the inclined rotation device, and the phenolic resin thermal curing coating agent inside the heat exchanger tube The 6th step of applying, the 7th step of drying the thermosetting coating agent by operating the air cooler disposed around the heat exchanger when the heat exchanger is rotated according to the operation of the inclined rotation device, and the corresponding to the preset temperature graph information The eighth step of performing intermediate baking of the heat exchanger, the ninth step of performing a pinhole test on the tubes of the heat exchanger after intermediate baking, and the fifth to ninth steps are repeated a preset number of times to obtain intermediate A heat exchanger including a 10th step of completing baking and an 11th step of performing final baking of the heat exchanger in accordance with preset temperature graph information after performing the 5th to 7th steps a finite number of times Construct the coating method.

Korean Registered Patent No. 10 - 0907042 (2009.07.09) Korean Registered Patent No. 10 - 0974532 (2010.08.10) Korea Utility Model Registration No. 20 - 0475201 (2014.11.27) Korean Registered Patent No. 10 - 2100785 (2020.04.14)

Graphite heat exchangers according to the prior art are mostly produced using a thermosetting phenolic resin as an impregnation material.

However, phenolic resin-impregnated graphite heat exchangers have lower characteristics such as temperature, corrosion resistance, and thermal shock resistance than carbon resins or, in particular, PFA resins. In the case of , there is a disadvantage that is not suitable for use environments that require convenience of maintenance, reliability, and high corrosion resistance.

In addition, the level of industrial technology of phenolic resin heat exchangers is in the order of Europe, the United States, Japan, Korea, and China. If Europe is 100%, Korea is about 90%, but PFA-impregnated graphite heat exchangers that exhibit superior mechanical properties than phenolic resins In the case of PFA, impregnation technology is virtually non-existent, and as competitors handling phenolic resin impregnated products increase, competition intensifies and it is difficult to increase sales, so the development of PFA-impregnated graphite heat exchanger technology is urgently needed.

On the other hand, when replacing the PFA resin in the phenolic resin impregnation process according to the prior art, there was a problem that the PFA resin was impregnated only on the surface of the graphite and was not impregnated to the deep inside, and the PFA resin was pressed into the impregnation device, contaminating the device There is a limitation that the PFA resin cannot be impregnated with the existing impregnation process, such as causing

Accordingly, the present invention was invented to solve the problems of the prior art as described above,

A graphite block preparation step (S10) of pneumatically washing the graphite block to be impregnated to remove foreign substances from the surface;

A first heat treatment step (S20) of charging the graphite block that has passed through the graphite block preparation step (S10) into an air drying furnace and holding it at 90 to 140 ° C. for 4 to 12 hours to dry and heat treat;

A coupling agent impregnation step (S30) of impregnating the coupling agent impregnating solution by putting the graphite block that has undergone the first heat treatment step (S20) into a coupling agent impregnating machine and pressurizing it in a vacuum state;

A second heat treatment step (S40) of loading the graphite block that has passed through the coupling agent impregnation step (S30) into an air drying furnace and drying and heat treatment by maintaining it at 80 to 120 ° C. for 4 to 12 hours;

An impregnation preparation step (S50) of putting the graphite block that has undergone the second heat treatment step (S40) into a container and filling the graphite block with PFA pellets so that the graphite block is submerged;

A PFA impregnation step (S60) of loading the graphite block and the container filled with PFA into a PFA impregnation furnace, heat-treating in a vacuum state to melt the PFA, and then pressurizing to impregnate the PFA;

By including a cooling step (S70) of cooling the graphite block that has passed through the PFA impregnation step (S60) to room temperature, it is possible to more efficiently manufacture a PFA-impregnated block-type graphite heat exchanger product applied to a high-temperature and high-pressure corrosive environment. purpose can be achieved.

The present invention provides a method of impregnating a graphite part of a block type graphite heat exchanger applied to a high temperature and high pressure corrosive environment with a PFA resin.

In particular, the present invention constitutes a PFA impregnation method differentiated from the conventionally well-known phenol resin impregnation method in order to impart impermeability to the porous graphite heat exchanger, resulting in the case of replacing the PFA resin in the existing phenol resin impregnation process There is an advantage in securing product competitiveness by resolving various problems and significantly increasing process efficiency and corrosion resistance.

In addition, the present invention improves the properties such as temperature, corrosion resistance, and thermal shock resistance of the block-type graphite heat exchanger to manufacture a PFA-impregnated graphite heat exchanger product applicable to a use environment requiring high temperature or chemical resistance, especially in the chemical industry. By doing so, there is an effect of localizing PFA-impregnated graphite heat exchanger products that have been supplied exclusively overseas.

1 is a process flow diagram of a PFA impregnation method for a block type graphite heat exchanger according to the present invention.

Hereinafter, the configuration and operation according to a preferred embodiment of the block type graphite heat exchanger PFA impregnation method of the present invention will be described in detail with reference to the accompanying drawings. In the following description, detailed descriptions of parts that can be easily implemented by those skilled in the art may be omitted. In addition, since the following description describes the present invention with respect to preferred embodiments, the present invention is not limited by the following examples, and it is natural that various modifications may be provided within a range that does not depart from the scope of the present invention. something to do.

1 shows a process flow diagram of a PFA impregnation method for a block type graphite heat exchanger according to the present invention.

Block-type graphite heat exchanger PFA impregnation method to which the technology of the present invention is applied constitutes a method of impregnating block-type graphite heat exchanger applied to high temperature and high pressure corrosive environment with PFA resin to improve mechanical properties and increase process efficiency and productivity. Note that it is about the technology that makes it possible.

For this purpose, the block-type graphite heat exchanger PFA impregnation method of the present invention constitutes a block-type graphite heat exchanger PFA impregnation method applicable to a use environment of a temperature of 220 ° C and a design pressure of 10 bar, specifically as follows.

The block-type graphite heat exchanger PFA impregnation method of the present invention is largely divided into a graphite block pretreatment process and a PFA resin impregnation process, and each detailed process is largely a graphite block preparation step (S10) and a first heat treatment step (S20). , A coupling agent impregnation step (S30), a second heat treatment step (S40), an impregnation preparation step (S50), a PFA impregnation step (S60), and a cooling step (S70).

The graphite block preparation step to the second heat treatment step (S10 to S40) is a pretreatment process for the graphite block, and the heat treatment temperature, holding time, vacuum degree, and pressure are controlled under specific conditions to optimize the physical properties of the graphite block for impregnation with the PFA resin. make up

The graphite block preparation step (S10) is a step of removing foreign substances from the surface of the graphite block to be impregnated by air washing.

The graphite material for a heat exchanger is formed by extruding/isostatically pressing a powder mixture of fine graphite particles and pitch, heat-treating at about 1300°C, impregnating the pitch, and graphitizing at 2500°C. Before impregnation, the graphite block has about 21% of open pores, so that airtightness and high mechanical properties as a heat exchanger material are secured while providing impermeability by filling the pores through the PFA resin impregnation method according to the present invention.

To this end, first, in the graphite block preparation step (S10), the graphite block to be impregnated is washed with air to remove foreign substances attached to the surface, and in subsequent steps, a coupling agent, an impregnation solution, etc. are applied to open pores formed on the surface of the graphite block. Prepare to be effectively impregnated.

The first heat treatment step (S20) is a step of charging the graphite block that has passed through the graphite block preparation step (S10) into an air drying furnace and maintaining it at 90 to 140 ° C. for 4 to 12 hours to dry and heat-treat it.

The first heat treatment step (S20) processes the graphite block together with the subsequent coupling agent impregnation step (S30) and the second heat treatment step (S40) to improve wettability and adhesion between the graphite block and the PFA resin.

The wetting angle is an index for evaluating the wettability, coverage, and reactivity of a liquid to a solid, and is variously displayed depending on processing conditions such as temperature and gas as well as characteristics of a material. Since hydrophobic PFA and hydrophilic graphite have a large wetting angle, in the first heat treatment step (S20), the coupling agent impregnation step (S30), and the second heat treatment step (S40) to be described later, graphite before impregnation with PFA In order to lower the interfacial wetting angle with the block, it is configured to improve the flowability of the PFA resin by inducing a change in interface properties.

The coupling agent impregnation step (S30) is a step of impregnating the coupling agent impregnating solution by putting the graphite block that has passed through the first heat treatment step (S20) into a coupling agent impregnating machine and pressurizing it in a vacuum state, Determine the wetting angle and softening point according to the treatment conditions included, and set and configure the optimal conditions.

The coupling agent impregnation step (S30) consists of a vacuum treatment step (S31), a coupling agent injection step (S32), and a coupling agent pressure step (S33).

The vacuum treatment step (S31) is a step of putting the graphite block into the coupling agent impregnating machine and maintaining it in a vacuum state for 4 to 24 hours.

In the vacuum treatment step (S31), a vacuum state is created and maintained at a pressure of less than 1 torr in the coupling agent impregnator into which the graphite block is introduced.

The coupling agent injection step (S32) is a step of injecting a coupling agent impregnating solution into a coupling agent impregnator in a vacuum state so that the graphite block is submerged.

In the coupling agent injection step (S32), the coupling agent impregnation solution is composed of a mixture of a silane coupling agent in an amount of 1 to 25 wt% of the weight of the graphite block and an ethanol diluent.

The silane coupling agent has a reactive group capable of bonding with an organic functional group and a reactive group capable of bonding with an inorganic material in a molecule and acts as a binder between organic and inorganic materials.

The ethanol diluent consists of a mixture of 85 to 99 parts by weight of ethanol and 1 to 15 parts by weight of distilled water.

In the coupling agent injection step (S32), the coupling agent impregnation solution composed of the mixture as described above is left at room temperature for 4 hours or more to allow a sufficient hydrolysis reaction of the silane coupling agent to occur, and then injected into the coupling agent impregnator.

The coupling pressure step (S33) is a step of pressurizing the coupling agent impregnator into which the coupling agent impregnating liquid is injected using air, nitrogen, or argon gas and maintaining it for 4 to 24 hours.

In the coupling reducing pressure step (S33), the gas atmosphere is formed to form functional groups such as -OH, -COOH, -NH ₂ at the interface of the graphite block, and is configured to pressurize and maintain at 5 to 30 bar.

In the second heat treatment step (S40), the graphite block subjected to the coupling agent impregnation step (S30) is loaded into an air drying furnace and maintained at 80 to 120 ° C. for 4 to 12 hours to dry and heat-treat.

In the second heat treatment step (S40), the coupling agent impregnator is depressurized, the graphite block is taken out, charged into an air drying furnace, and subjected to dry heat treatment, thereby reducing the coupling agent. By attaching through heat treatment, the graphite block is effectively impregnated with PFA in a later PFA impregnation process.

The impregnation preparation step or cooling step (S50 to S70) is a process of impregnating the pretreated graphite block with PFA. Since the block-type graphite heat exchanger according to the present invention is applied to an environment in which strong acidic and basic solutions such as hydrofluoric acid, sulfuric acid, hydrochloric acid, and potassium hydroxide at about 220 ° C are used, considering that leakage of the solution can cause serious problems, each It is configured to produce a high-density PFA-impregnated graphite block by deriving high airtight characteristics by controlling the temperature, holding time, vacuum degree, and pressing force in each step under specific conditions.

The impregnation preparation step (S50) is a step of putting the graphite block that has passed through the second heat treatment step (S40) into a container and filling the graphite block with PFA pellets so that the graphite block is submerged.

In the impregnation preparation step (S50), a wire mesh or the like is installed so that the bottom of the container does not come into contact with the graphite block, PFA pellets are poured onto the bottom, then a graphite block is installed, and the graphite block is filled so that it is sufficiently submerged. Depending on the size of the PFA particles, there is a volume reduction of 10 to 40% during the treatment process, so it is added taking this into account.

The PFA impregnation step (S60) is a step of impregnating the PFA by charging the graphite block and the container filled with PFA into a PFA impregnation furnace and heating and pressurizing it in a vacuum state.

In the PFA impregnation step (S60), the PFA used for impregnation of the graphite block is a crystalline polymer having a melting point of about 327 ° C. The continuous use temperature is 260 ° C. It can be stably used from low temperature (-286 ° C.) to high temperature range. . In particular, it has the highest chemical resistance among organic materials, and it is soluble in special chemicals such as fluorine gas, molten alkali metal, and chlorine trifluoride without being affected by various acids and alkali solvents.

In the phenolic resin impregnation process according to the prior art, since phenol is a thermosetting resin, an impregnation process device and a heat treatment process device are separately used, but since PFA is a thermoplastic resin, impregnation and heat treatment are performed simultaneously in the PFA impregnation step (S60).

Therefore, in the PFA impregnation step (S60), it is possible to continuously heat the PFA resin at a melting temperature of about 260 to 375 ° C. during impregnation, and to minimize corrosion caused by florine gas generated when PFA is melted. Use a PFA impregnation furnace made of a suitable material.

The PFA impregnation furnace is provided to implement a high degree of vacuum and temperature to increase the flowability of the PFA resin, which is a thermoplastic material. In order to optimize the PFA impregnation furnace, a DB for grasping the material properties according to graphite and PFA types was established, the appropriate temperature setting section and tank temperature deviation were set, and an induction heating coil was installed in the impregnation tank for PFA heating and impregnation. do. In addition, a vacuum port is installed so that the vacuum pump can be set to less than 1 torr, and a thermocouple and port are provided to measure the impregnated temperature.

The PFA impregnation step (S60) consists of a vacuum pump operation step (S61), a temperature raising step (S62), and a PFA pressurization step (S63).

The vacuum pump operating step (S61) is a step of operating the vacuum pump in the PFA impregnation furnace into which the graphite block and the container filled with PFA are charged.

In the vacuum pump operation step (S61), a vacuum state is created and maintained at a pressure of less than 1 torr inside the PFA impregnation furnace.

The temperature raising step (S62) is a step of raising the temperature of the PFA impregnation furnace to a range of 220 to 390 ° C.

In the temperature raising step (S62), the temperature of the PFA impregnation furnace is raised at a rate of 0.5 to 5 ° C per minute and configured to maintain a vacuum state at a pressure of less than 1 torr.

The PFA pressurization step (S63) is a step of pressurizing the heated PFA impregnation furnace using air, nitrogen, or argon gas and maintaining it for 4 to 36 hours.

In the PFA pressurization step (S63), the gas atmosphere is created to activate and attach the interface between the graphite block and the PFA, and the pressure is set to 5 to 30 bar.

The cooling step (S70) is a step of cooling the graphite block that has passed through the PFA impregnation step (S60) to room temperature.

In the cooling step (S70), after cooling to room temperature while maintaining the pressure in the PFA pressurization step (S63), the pressure is decompressed and the graphite block is taken out. After completing a series of processes as described above, the graphite block is manufactured as a heat exchanger product through external diameter processing and hole processing.

Table 1 below shows the results of testing and comparing the characteristics of each item of a phenol resin graphite heat exchanger, a carbon resin graphite heat exchanger, and a PFA resin graphite heat exchanger for each impregnated resin.

division phenolic resin
graphite heat exchanger carbon resin
graphite heat exchanger PFA resin
graphite heat exchanger microstructure

usable temperature 220℃ 430℃ 250℃ bending strength 27 MPa 32 MPa 32 MPa compressive strength 65 MPa 80 MPa 90 MPa thermal shock resistance lowness good Great Main purpose of use universal
(normal temperature & corrosive environment) High temperature high chemical resistance

The block-type graphite heat exchanger PFA impregnation method according to the present invention having the configuration described above provides a series of processes for more effectively impregnating the graphite block with the PFA resin having the characteristics shown in Table 1, and has a density of 1.92 g. /cm ³ or more, porosity 0.38% or less, bending strength 32.0MPa or more, compressive strength 91.0MPa or more, thermal conductivity 100W/mK or more, leak pressure 4 bar or more, used for manufacturing high-quality block-type graphite heat exchangers with no leakage do.

The block-type graphite heat exchanger PFA impregnation method according to the present invention as described above is differentiated from the conventionally well-known phenolic resin impregnation method, and a method of impregnating a block-type graphite heat exchanger applied to a high-temperature and high-pressure corrosive environment with PFA resin By constituting, there is an advantage in securing product competitiveness by significantly increasing process efficiency and productivity as well as solving all problems caused by replacing the PFA resin in the existing phenolic resin impregnation process.

Therefore, the present invention is to more efficiently manufacture PFA-impregnated graphite heat exchanger products that are applicable to use environments requiring high temperature and high chemical resistance, especially in the chemical industry, so that PFA-impregnated graphite heat exchanger products that have been exclusively supplied overseas Since it has effects such as being able to be localized, it is expected that the possibility of industrial use will be very high.

S10: Graphite block preparation step
S20: 1st heat treatment step
S30: coupling agent impregnation step
S31: vacuum treatment step
S32: coupling agent injection step
S33: coupling pressure step
S40: 2nd heat treatment step
S50: impregnation preparation step
S60: PFA impregnation step
S61: vacuum pump operation step
S62: temperature rising step
S63: PFA pressurization step
S70: cooling step

Claims (5)

A graphite block preparation step (S10) of pneumatically washing the graphite block to be impregnated to remove foreign substances from the surface;
A first heat treatment step (S20) of charging the graphite block that has passed through the graphite block preparation step (S10) into an air drying furnace and holding it at 90 to 140 ° C. for 4 to 12 hours to dry and heat treat;
A coupling agent impregnation step (S30) of impregnating the coupling agent impregnating solution by putting the graphite block that has undergone the first heat treatment step (S20) into a coupling agent impregnating machine and pressurizing it in a vacuum state;
A second heat treatment step (S40) of loading the graphite block that has passed through the coupling agent impregnation step (S30) into an air drying furnace and drying and heat treatment by maintaining it at 80 to 120 ° C. for 4 to 12 hours;
An impregnation preparation step (S50) of putting the graphite block that has undergone the second heat treatment step (S40) into a container and filling the graphite block with PFA pellets so that the graphite block is submerged;
A PFA impregnation step (S60) of loading the graphite block and the container filled with PFA into a PFA impregnation furnace, heat-treating in a vacuum state to melt the PFA, and then pressurizing to impregnate the PFA;
A block-type graphite heat exchanger PFA impregnation method comprising a cooling step (S70) of cooling the graphite block that has passed through the PFA impregnation step (S60) to room temperature. According to claim 1,
In the coupling agent impregnation step (S30),
A vacuum treatment step (S31) of putting the graphite block into a coupling agent impregnator and maintaining it in a vacuum state for 4 to 24 hours;
A coupling agent injection step (S32) of injecting a coupling agent impregnating liquid into a coupling agent impregnator in a vacuum state so that the graphite block is immersed;
Block-type graphite heat exchanger PFA, characterized in that it comprises a coupling depressurization step (S33) of pressurizing the coupling agent impregnator into which the coupling agent impregnation liquid is injected using air, nitrogen, or argon gas and maintaining it for 4 to 24 hours impregnation method. According to claim 2,
In the vacuum treatment step (S31), a vacuum state is created at a pressure of less than 1 torr,
In the coupling agent injection step (S32), the coupling agent impregnation solution is composed of a mixture of a silane coupling agent and an ethanol diluent at 1 to 25 wt% of the weight of the graphite block,
In the coupling pressure step (S33), block type graphite heat exchanger PFA impregnation method, characterized in that made to pressurize at 5 to 30 bar. According to claim 1,
The PFA impregnation step (S60),
A vacuum pump operation step (S61) of operating a vacuum pump in a PFA impregnation furnace into which a graphite block and a container filled with PFA are charged.
A temperature raising step (S62) of raising the temperature of the PFA impregnation furnace to a range of 220 to 390 ° C and maintaining it for 4 to 36 hours;
A block-type graphite heat exchanger PFA impregnation method comprising a PFA pressurization step (S63) of pressurizing the heated PFA impregnation furnace using air, nitrogen, or argon gas and maintaining it for 4 to 36 hours. According to claim 4,
In the temperature raising step (S62), the temperature of the PFA impregnation furnace is raised at a rate of 0.5 to 5 ° C per minute and maintained in a vacuum state at a pressure of less than 1 torr,
In the PFA pressing step (S63), the block type graphite heat exchanger PFA impregnation method, characterized in that made to press at a pressure of 5 to 30 bar.

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