The PS version, known as Presensitized Offset Plates, was developed to meet the rapid development of lithography. Because the PS version has high resolution, full dot reproduction, rich layers, balanced ink and easy to handle, and high resistance to printing, it has rapidly gained popularity in the printing industry. Judging from the statistical data currently available, the PS version is still the largest consumer and most important plate material. The PS plate manufacturing industry has become one of the most important pillar industries in the printing equipment manufacturing industry.
In the PS plate production process, chemical materials such as hydrochloric acid, sulfuric acid, sodium hydroxide, sodium fluoride, and sodium dihydrogen carbonate are used, and cooling and heating are required. Most of these materials are highly corrosive media, and equipment must be seriously corroded. The materials required for many production facilities must be both corrosion resistant and good heat transfer properties.
Currently, PS plate manufacturers generally use plate heat exchangers whose cost is four to five times higher than that of graphite, such as PS plate electrolysis process 2% hydrochloric acid solution cooler, oxidation process 25% sulfuric acid solution cooler, and sealing process. Fluo-sodium, sodium dihydrogen carbonate solution coolers, although the heat transfer efficiency is good, but easy to block, inconvenient maintenance, cleaning is also frequent, causing great inconvenience to the production of tension; and graphite heat exchanger unit heat transfer area The cost is much lower than the plate heat exchanger, and the thermal conductivity is quite high. It is convenient for installation, cleaning, maintenance and maintenance. It not only shortens the production stop time, but also does not reduce the heat exchange area of ​​the equipment, so it can well replace the titanium alloy plate type. Heat Exchanger.
The following brief introduction to graphite chemical equipment.
Graphite chemical equipment
(a) Impermeable graphite
Impervious graphite is a new type of structural material made from artificial graphite and synthetic resin by impregnation, pressure molding, casting, etc. It differs from all other non-metallic corrosion resistant materials in that it has a high degree of chemical stability. In addition, it also has extremely high thermal conductivity, which greatly expands its application range.
Impermeability graphite is widely used in chemical anticorrosion as corrosion-resistant non-metallic inorganic materials. At present, impermeable graphite has been widely used in the manufacture of various types of heaters, cooling condensers, synthesis furnaces, membrane absorbers, Pipes, fittings, valves, towers and accessories, lining anti-corrosion of pumps and equipment. Its structural performance is as follows:
1. Phenolic impregnated graphite mechanical properties
Volume weight 1.8 to 1.9 G/m3
Compressive strength 58.8 to 68.6 Mpa
Tensile strength 7.8 to 9.8 Mpa
Flexural strength 23.5 to 27.4 Mpa
Resistance to attack strength 2.7 ~ 3.1 KJ/m2
Hardness 25 to 35 Brinell
Thermal conductivity, thermal conductivity 105 to 116 W/m·K
Heat resistance 170 °C
Thermal expansion coefficient 4.4 1/°C×106
2. Mechanical strength impermeability Graphite can be used for various kinds of mechanical processing such as car, planing, sawing and milling. These properties provide good conditions for processing and manufacturing various equipment.
3. Chemically stable impermeable graphite is resistant to most chemical substances except strong oxidizing acids and bases, especially hydrochloric acid, which is resistant to any concentration below the boiling point.
4. Thermal conductivity of impregnated graphite thermal conductivity of 100 to 110 kcal / m · h · °C, impregnated graphite thermal conductivity and copper, aluminum and other similar, usually as a heat exchanger or other heat transfer device is based on the impermeable This feature of graphite.
5. The coefficient of thermal expansion of the heat-stabilized graphite itself is very small, 0.24 x 10-5 1/°C. Although the linear expansion coefficient of the resin is much larger, it is widely confined in the voids after impregnation and solidification, and cannot expand freely, so that the total linear expansion coefficient of the impregnated graphite does not increase much, being 0.4-0.45×10 −5 1/° C. .
(II) Introduction to various equipment
Impervious graphite heat exchange equipment and absorption equipment has excellent corrosion resistance and heat transfer performance. It is widely applied to the treatment of hydrochloric acid, sulfuric acid and other corrosive media for heating, in the heat transfer process of corrosive media. Chemical unit operations such as cooling, condensation, evaporation and absorption. Graphite heat exchange equipment and absorption equipment according to its structure can be divided into tube type, block hole type (circular block hole and rectangular block hole type), spray type, dip type, tube type and other structural forms. Among them, there are a series of designs for column-type and block-hole types, and graphite equipment technical standards have been formulated. The following focuses on the characteristics, classification, application scope, and individual applications of the following tubular, block-hole, and column-tube falling film absorbers.
1. The combined tube-type graphite heat exchanger tube and the tube plate are connected in an elastic sealing structure. The graphite tube can flex freely under the action of temperature difference stress, which can avoid the stress damage caused by the adhesion of the graphite tube and the tube plate under the action of temperature difference stress. High utilization of graphite material, can be made into a large heat transfer area equipment, the unit heat transfer area cost is lower than other structural forms, for a larger amount of heat exchange process; fluid resistance is small, maintenance and repair and cleaning convenient; equipment The allowable pressure is 0.5MPa and the temperature is 150°C. Due to the good interchangeability of equipment components, it can be replaced individually, which greatly extends the service life of the equipment. In the sulfuric acid, hydrochloric acid industry and epichlorohydrin production and other fields have been widely used.
2. Heat exchangers (circular block holes, rectangular block holes) are graphite heat exchangers with material channels, upper and lower graphite heads and their metal covers, and cylindrical steel shells (round holes) or two The main components such as the end cover (block hole type) are composed of gaskets sealed with parts and fastened with long bolts. Block hole heat exchanger has the following characteristics:
1 The structure is strong, and the graphite block is mainly subjected to compressive stress and can fully utilize the characteristics of high compressive strength of graphite materials. Can increase operating pressure, suitable for thermal shock or vibration applications.
2 compact structure, small footprint.
3 adaptable, can be used for heating, cooling, condensation, evaporation, reboiling, absorption, desorption and many other chemical processes.
4 The parts are interchangeable, using the "block type" detachable combination structure, requiring a small number of standard components, can be assembled into a variety of different heat exchange area of ​​equipment, its disassembly, installation, cleaning, repair and transportation, This has great advantages for manufacturing and maintenance.
5 can obtain higher heat transfer coefficient.
For example YXSQ round hole sulfuric acid diluting cooler, the upper part is the mixture of concentrated acid and demineralized water, dilution and distribution, and the middle part and the lower part are cooling parts, and can dilute 98% concentrated sulfuric acid to 50~60%. As a relatively advanced equipment in the current sulfuric acid dilution process, it can dilute the concentration of concentrated sulfuric acid to less than 65% and can be directly cooled after dilution until the required temperature.
3, falling film type graphite absorber is actually a vertical installation of tube or round hole heat exchanger. The heat exchanger tubes (or longitudinal channels on the blocks) correspond to many juxtaposed water-cooled wet-wall columns. Above it, an overflow pipe for distributing the absorbing liquid is provided. The falling film absorber continuously removes dissolved heat during the absorption process, and its heat and mass transfer effect is good. It has significant advantages compared to the adiabatic absorption of packed towers.
The by-produced hydrogen chloride used in the production of epichlorohydrin absorbs water and is hydrochloric acid. It has strong corrosivity and greatly shortens the service life of the metal heat exchanger. Therefore, the production of epichlorohydrin is related to the medium of hydrogen chloride. Heat exchangers are made of highly corrosion-resistant graphite heat exchangers.
Application prospect
With the development of society and advancement of technology, the quality of products has gradually increased. Carbon steel and cast iron have not been able to meet the requirements for the development of modern industrial production and the demand for large-scale production. As a result, some new materials have emerged, such as: Alloy cast iron, stainless steel, titanium, engineering plastics and various anti-corrosion linings have been widely used in production.
Carbon steel equipment for anti-corrosion treatment, most of the use of phenolic, epoxy resin coating, in particular heat transfer equipment through the anti-corrosion heat transfer effect greatly reduced, thereby increasing the heat transfer area, so graphite has become a very suitable material in equipment manufacturing . For example, in the calcium carbide process PVC production process related to HC1 gas or hydrochloric acid, the main equipments are: hydrochloric acid cooler, round block type graphite triple hydrochloric acid synthesis furnace, graphite hydrogen chloride synthesis furnace, round graphite sulfuric acid diluent, mixing Gas cooler, polymerization section preheater and converter vinyl chloride cooler, EDC cooler in the rectification section of ethylene oxide chlorination production, have received good results.
The thermal conductivity of graphite is 480. 7 J / (m · h · °C), while the thermal conductivity of the general alloy is much lower, such as 304 stainless steel is 58. 69 J / (m · h · °C), and therefore the same The graphite thermal resistance of the thickness is smaller than the thermal resistance of stainless steel, and it also has a strong heat transfer capability. Although the thermal resistance of the pipe wall during heat transfer is much lower than the thermal resistance of fluid and dirt, this effect can sometimes not be ignored.
Even the most corrosion-resistant alloys have a corrosion rate of 0.1 mm/a in highly corrosive media such as hydrochloric acid, and the corrosion rate of graphite is almost zero. Therefore, in a highly corrosive environment, the life of a graphite heat exchanger is obviously longer than that of a metal heat exchanger.
Graphite heat exchangers not only effectively exchange heat and reduce energy consumption during production, but also increase the yield of related materials, thereby reducing material consumption. Its use in the production of epichlorohydrin means that the cyclization reaction tower is saved. The steam consumption increases the reaction yield of dichloropropane.
Impervious graphite equipment is widely used in other fields, but its application in PS plate production is still at its infancy. However, as far as actual production is concerned, as long as the working pressure does not exceed 0.6 MPa and the working temperature is lower than 160°C, the medium Corrosive materials can be used impermeable graphite equipment.
Metal heat exchangers often require plugging even under other media conditions. When operating under acidic media, they often need to be replaced. This can cause frequent shutdowns, direct loss of replacement tubes or heat exchangers, and stoppages. The indirect loss cannot be ignored. It can be seen that the graphite heat exchanger not only has a good heat exchange effect, but also has a long service life due to its high corrosion resistance, and prevents the device from being stopped due to frequent plugging or replacement of the heat exchanger. Therefore, the chemical plant really achieves long-term, safe and stable operation, and it is worth further promotion.
Through the above introduction, we believe that with the passage of time and understanding and understanding of graphite equipment is becoming more and more profound, its application prospects will be quite good.
In the PS plate production process, chemical materials such as hydrochloric acid, sulfuric acid, sodium hydroxide, sodium fluoride, and sodium dihydrogen carbonate are used, and cooling and heating are required. Most of these materials are highly corrosive media, and equipment must be seriously corroded. The materials required for many production facilities must be both corrosion resistant and good heat transfer properties.
Currently, PS plate manufacturers generally use plate heat exchangers whose cost is four to five times higher than that of graphite, such as PS plate electrolysis process 2% hydrochloric acid solution cooler, oxidation process 25% sulfuric acid solution cooler, and sealing process. Fluo-sodium, sodium dihydrogen carbonate solution coolers, although the heat transfer efficiency is good, but easy to block, inconvenient maintenance, cleaning is also frequent, causing great inconvenience to the production of tension; and graphite heat exchanger unit heat transfer area The cost is much lower than the plate heat exchanger, and the thermal conductivity is quite high. It is convenient for installation, cleaning, maintenance and maintenance. It not only shortens the production stop time, but also does not reduce the heat exchange area of ​​the equipment, so it can well replace the titanium alloy plate type. Heat Exchanger.
The following brief introduction to graphite chemical equipment.
Graphite chemical equipment
(a) Impermeable graphite
Impervious graphite is a new type of structural material made from artificial graphite and synthetic resin by impregnation, pressure molding, casting, etc. It differs from all other non-metallic corrosion resistant materials in that it has a high degree of chemical stability. In addition, it also has extremely high thermal conductivity, which greatly expands its application range.
Impermeability graphite is widely used in chemical anticorrosion as corrosion-resistant non-metallic inorganic materials. At present, impermeable graphite has been widely used in the manufacture of various types of heaters, cooling condensers, synthesis furnaces, membrane absorbers, Pipes, fittings, valves, towers and accessories, lining anti-corrosion of pumps and equipment. Its structural performance is as follows:
1. Phenolic impregnated graphite mechanical properties
Volume weight 1.8 to 1.9 G/m3
Compressive strength 58.8 to 68.6 Mpa
Tensile strength 7.8 to 9.8 Mpa
Flexural strength 23.5 to 27.4 Mpa
Resistance to attack strength 2.7 ~ 3.1 KJ/m2
Hardness 25 to 35 Brinell
Thermal conductivity, thermal conductivity 105 to 116 W/m·K
Heat resistance 170 °C
Thermal expansion coefficient 4.4 1/°C×106
2. Mechanical strength impermeability Graphite can be used for various kinds of mechanical processing such as car, planing, sawing and milling. These properties provide good conditions for processing and manufacturing various equipment.
3. Chemically stable impermeable graphite is resistant to most chemical substances except strong oxidizing acids and bases, especially hydrochloric acid, which is resistant to any concentration below the boiling point.
4. Thermal conductivity of impregnated graphite thermal conductivity of 100 to 110 kcal / m · h · °C, impregnated graphite thermal conductivity and copper, aluminum and other similar, usually as a heat exchanger or other heat transfer device is based on the impermeable This feature of graphite.
5. The coefficient of thermal expansion of the heat-stabilized graphite itself is very small, 0.24 x 10-5 1/°C. Although the linear expansion coefficient of the resin is much larger, it is widely confined in the voids after impregnation and solidification, and cannot expand freely, so that the total linear expansion coefficient of the impregnated graphite does not increase much, being 0.4-0.45×10 −5 1/° C. .
(II) Introduction to various equipment
Impervious graphite heat exchange equipment and absorption equipment has excellent corrosion resistance and heat transfer performance. It is widely applied to the treatment of hydrochloric acid, sulfuric acid and other corrosive media for heating, in the heat transfer process of corrosive media. Chemical unit operations such as cooling, condensation, evaporation and absorption. Graphite heat exchange equipment and absorption equipment according to its structure can be divided into tube type, block hole type (circular block hole and rectangular block hole type), spray type, dip type, tube type and other structural forms. Among them, there are a series of designs for column-type and block-hole types, and graphite equipment technical standards have been formulated. The following focuses on the characteristics, classification, application scope, and individual applications of the following tubular, block-hole, and column-tube falling film absorbers.
1. The combined tube-type graphite heat exchanger tube and the tube plate are connected in an elastic sealing structure. The graphite tube can flex freely under the action of temperature difference stress, which can avoid the stress damage caused by the adhesion of the graphite tube and the tube plate under the action of temperature difference stress. High utilization of graphite material, can be made into a large heat transfer area equipment, the unit heat transfer area cost is lower than other structural forms, for a larger amount of heat exchange process; fluid resistance is small, maintenance and repair and cleaning convenient; equipment The allowable pressure is 0.5MPa and the temperature is 150°C. Due to the good interchangeability of equipment components, it can be replaced individually, which greatly extends the service life of the equipment. In the sulfuric acid, hydrochloric acid industry and epichlorohydrin production and other fields have been widely used.
2. Heat exchangers (circular block holes, rectangular block holes) are graphite heat exchangers with material channels, upper and lower graphite heads and their metal covers, and cylindrical steel shells (round holes) or two The main components such as the end cover (block hole type) are composed of gaskets sealed with parts and fastened with long bolts. Block hole heat exchanger has the following characteristics:
1 The structure is strong, and the graphite block is mainly subjected to compressive stress and can fully utilize the characteristics of high compressive strength of graphite materials. Can increase operating pressure, suitable for thermal shock or vibration applications.
2 compact structure, small footprint.
3 adaptable, can be used for heating, cooling, condensation, evaporation, reboiling, absorption, desorption and many other chemical processes.
4 The parts are interchangeable, using the "block type" detachable combination structure, requiring a small number of standard components, can be assembled into a variety of different heat exchange area of ​​equipment, its disassembly, installation, cleaning, repair and transportation, This has great advantages for manufacturing and maintenance.
5 can obtain higher heat transfer coefficient.
For example YXSQ round hole sulfuric acid diluting cooler, the upper part is the mixture of concentrated acid and demineralized water, dilution and distribution, and the middle part and the lower part are cooling parts, and can dilute 98% concentrated sulfuric acid to 50~60%. As a relatively advanced equipment in the current sulfuric acid dilution process, it can dilute the concentration of concentrated sulfuric acid to less than 65% and can be directly cooled after dilution until the required temperature.
3, falling film type graphite absorber is actually a vertical installation of tube or round hole heat exchanger. The heat exchanger tubes (or longitudinal channels on the blocks) correspond to many juxtaposed water-cooled wet-wall columns. Above it, an overflow pipe for distributing the absorbing liquid is provided. The falling film absorber continuously removes dissolved heat during the absorption process, and its heat and mass transfer effect is good. It has significant advantages compared to the adiabatic absorption of packed towers.
The by-produced hydrogen chloride used in the production of epichlorohydrin absorbs water and is hydrochloric acid. It has strong corrosivity and greatly shortens the service life of the metal heat exchanger. Therefore, the production of epichlorohydrin is related to the medium of hydrogen chloride. Heat exchangers are made of highly corrosion-resistant graphite heat exchangers.
Application prospect
With the development of society and advancement of technology, the quality of products has gradually increased. Carbon steel and cast iron have not been able to meet the requirements for the development of modern industrial production and the demand for large-scale production. As a result, some new materials have emerged, such as: Alloy cast iron, stainless steel, titanium, engineering plastics and various anti-corrosion linings have been widely used in production.
Carbon steel equipment for anti-corrosion treatment, most of the use of phenolic, epoxy resin coating, in particular heat transfer equipment through the anti-corrosion heat transfer effect greatly reduced, thereby increasing the heat transfer area, so graphite has become a very suitable material in equipment manufacturing . For example, in the calcium carbide process PVC production process related to HC1 gas or hydrochloric acid, the main equipments are: hydrochloric acid cooler, round block type graphite triple hydrochloric acid synthesis furnace, graphite hydrogen chloride synthesis furnace, round graphite sulfuric acid diluent, mixing Gas cooler, polymerization section preheater and converter vinyl chloride cooler, EDC cooler in the rectification section of ethylene oxide chlorination production, have received good results.
The thermal conductivity of graphite is 480. 7 J / (m · h · °C), while the thermal conductivity of the general alloy is much lower, such as 304 stainless steel is 58. 69 J / (m · h · °C), and therefore the same The graphite thermal resistance of the thickness is smaller than the thermal resistance of stainless steel, and it also has a strong heat transfer capability. Although the thermal resistance of the pipe wall during heat transfer is much lower than the thermal resistance of fluid and dirt, this effect can sometimes not be ignored.
Even the most corrosion-resistant alloys have a corrosion rate of 0.1 mm/a in highly corrosive media such as hydrochloric acid, and the corrosion rate of graphite is almost zero. Therefore, in a highly corrosive environment, the life of a graphite heat exchanger is obviously longer than that of a metal heat exchanger.
Graphite heat exchangers not only effectively exchange heat and reduce energy consumption during production, but also increase the yield of related materials, thereby reducing material consumption. Its use in the production of epichlorohydrin means that the cyclization reaction tower is saved. The steam consumption increases the reaction yield of dichloropropane.
Impervious graphite equipment is widely used in other fields, but its application in PS plate production is still at its infancy. However, as far as actual production is concerned, as long as the working pressure does not exceed 0.6 MPa and the working temperature is lower than 160°C, the medium Corrosive materials can be used impermeable graphite equipment.
Metal heat exchangers often require plugging even under other media conditions. When operating under acidic media, they often need to be replaced. This can cause frequent shutdowns, direct loss of replacement tubes or heat exchangers, and stoppages. The indirect loss cannot be ignored. It can be seen that the graphite heat exchanger not only has a good heat exchange effect, but also has a long service life due to its high corrosion resistance, and prevents the device from being stopped due to frequent plugging or replacement of the heat exchanger. Therefore, the chemical plant really achieves long-term, safe and stable operation, and it is worth further promotion.
Through the above introduction, we believe that with the passage of time and understanding and understanding of graphite equipment is becoming more and more profound, its application prospects will be quite good.
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