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1: Preface The PS version is a pre-coated photosensitive version (Presensitized Offset The abbreviation of Plates. Chinese means pre-coated photosensitive plate. It was developed to adapt to the rapid development of lithographic printing. Because the PS version itself has the characteristics of high resolution, full dot reproduction, rich layers, easy to control the ink balance, and high printing resistance, it has been rapidly popularized in the printing industry. Judging from the current statistics, the PS plate is still the largest consumption and the most important lithographic plate. The PS plate manufacturing industry has become one of the extremely important pillar industries of the current printing equipment manufacturing industry. Chemical raw materials such as hydrochloric acid, sulfuric acid, sodium hydroxide, sodium fluoride, sodium dihydrogen carbonate, etc. are used in the PS plate production process, and cooling and heating are required. Most of these raw materials are highly corrosive media. The equipment must be seriously corroded. It is necessary to require that the materials of many production equipment must be corrosion-resistant and have good heat transfer properties. At present, PS plate manufacturers generally use high-cost titanium alloy plate heat exchangers. For example, PS plate electrolysis process 2% hydrochloric acid solution cooler, oxidation process 25% sulfuric acid solution cooler, sealing process sodium fluoride, sodium dihydrogen carbonate and other solution coolers. Although the heat transfer efficiency is good, it is easy to block, maintenance is inconvenient, and cleaning is frequent. It causes great inconvenience to tight production, and the cost of graphite heat exchanger per unit heat exchange area* * Lower than the plate heat exchanger. And the thermal conductivity is quite high. It is also convenient to install, clean, repair and maintain. It shortens the downtime and does not reduce the heat exchange area of the equipment. Therefore, it can be a good substitute for the titanium alloy plate heat exchanger. Let’s briefly introduce the graphite chemical equipment. 2: Characteristics of chemical equipment and introduction to various equipment (1) Impermeable graphite Impermeable graphite is a new structural material made of artificial graphite and synthetic resin through dipping, pressing, casting and other methods. The difference between it and all other non-metallic corrosion-resistant materials is that in addition to its high chemical stability, it also has extremely high thermal conductivity. Therefore * * has greatly expanded its application scope. - As a corrosion-resistant non-metallic inorganic material, impermeable graphite is widely used in chemical anti-corrosion. At present, impermeable graphite has been successfully 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, etc. Its structural properties are as follows: - 1. Mechanical properties of phenolic impregnated graphite Bulk weight 1.8-1.9 G/m3 Compressive strength 58.8-68.6 Mpa Tensile strength 7.8-9.8 Mpa Bending strength 23.5-27.4 Mpa Impact strength 2.7-3.1 KJ/㎡ Hardness 25-35 Brinell thermal conductivity. Thermal conductivity 105-116 W/m·K Heat resistance 170 ℃ Thermal expansion coefficient 4.4 1/℃×106 2. Mechanically strong and impermeable graphite can be used for various mechanical processing, such as turning, planing, sawing, milling, etc. These properties provide good conditions for processing and manufacturing various equipment. 3. Chemically stable, impermeable graphite is resistant to corrosion to most chemicals except strongly oxidizing acids and alkalis, especially hydrochloric acid. It is resistant to any concentration below the boiling point. 4. The thermal conductivity of impregnated graphite is 100-110 kcal/m·hour·℃. The thermal conductivity of impregnated graphite is similar to that of copper, aluminum, etc. It is usually used as a heat exchanger or other heat transfer equipment based on this characteristic of impermeable graphite. 5. The thermal expansion coefficient of thermally stable graphite itself is very small. It is 0.24×10-5 1/℃. Although the linear expansion coefficient of the resin is much larger, after impregnation and curing, it is widely constrained in the gaps and cannot expand freely. As a result, the total linear expansion coefficient of impregnated graphite does not increase much, which is 0.4-0.45×10-5 1/℃. (2) Introduction to various equipment. Impermeable graphite heat exchange equipment and absorption equipment have excellent corrosion resistance and heat transfer performance. They are used in the heat transfer process of corrosive media. In order to save stainless steel and precious non-ferrous metal materials, graphite heat exchangers are widely used to handle corrosive media such as hydrochloric acid, sulfuric acid, etc. for heating, cooling, and condensation. . Chemical unit operations such as evaporation and absorption. Graphite heat exchange equipment and absorption equipment can be divided into tube type, block hole type (round block hole type and rectangular block hole type), spray type, impregnation type, sleeve type and other structural forms according to their structural forms. Among them, the tube type and block hole type have a series of designs. And technical standards for graphite equipment have been formulated. .The following focuses on the characteristics, classification, scope of application and individual applications of tube-type, block-hole type and tube-type falling film absorbers. 1. Combined tube-type graphite heat exchanger tubes and tube sheets are connected with an elastic sealing structure. The graphite tubes can expand and contract freely under the action of temperature difference stress. This avoids the adhesion of the graphite tubes and the tube sheet due to temperature difference stress. The stress damage caused by the action. The utilization rate of graphite material is high. It can be made into equipment with larger heat transfer area. It is used for heat exchange processes with large processing capacity and has small fluid resistance. It is easy to maintain and clean, and the cost per unit heat exchange area is lower than other structural forms. Because the interchangeability of each equipment component is good, it can be replaced individually. In this way * * Extends the service life of the equipment. 2. Block-hole graphite heat exchangers (round block holes, rectangular block holes) are several graphite heat exchangers with material channels. The main components include upper and lower graphite heads and their metal cover plates, as well as cylindrical steel shells (round block holes) or side covers at both ends (rectangular block hole type). It consists of parts. The parts are sealed with gaskets and fastened with long bolts. The block hole heat exchanger has the following characteristics: ① The structure is solid. The graphite block mainly bears compressive stress. It can make full use of the high compressive strength of graphite material. It can improve operation Pressure. Suitable for occasions with thermal shock or vibration. ② Compact structure. Small footprint. ③ Strong adaptability. Can be used for heating, cooling, condensation, evaporation, reboiling, absorption, desorption and many other chemical processes. ④ Good interchangeability of parts. Adopt The "building block" detachable combined structure requires a small number of standard components and can be assembled into various equipment with different heat exchange areas. It is easy to disassemble, install, clean, inspect and transport. This has great advantages for manufacturing and maintenance.⑤ A higher heat transfer coefficient can be obtained. YXSQ round hole type sulfuric acid dilution cooler. The upper part is the mixing, dilution and distribution part of concentrated acid and desalted water. The middle and lower parts are the cooling part. It can dilute 98% concentrated sulfuric acid to 50~60%. As a more advanced equipment in the current sulfuric acid dilution process, it can dilute the concentration of concentrated sulfuric acid to less than 65%. And it can be cooled directly after dilution until the required temperature. 3. Falling film graphite absorber is actually A vertically installed tube type or round block hole type heat exchanger. The tube tubes (or longitudinal holes on the block) of the heat exchanger are equivalent to many parallel water-cooled wet wall towers. Above them are provided overflow tubes for distributing the absorption liquid. The falling film absorber absorbs During the process, the heat of dissolution is continuously removed. The heat and mass transfer effect is good. It has significant advantages compared with the adiabatic absorption of the packed tower. The by-product hydrogen chloride in the production of epichlorohydrin becomes hydrochloric acid after being absorbed with water, which is highly corrosive. * * The service life of the metal heat exchanger is shortened. Therefore, the heat exchangers related to the hydrogen chloride medium in epichlorohydrin production use very corrosion-resistant graphite heat exchangers. 3. Application prospects With the development of society and the advancement of technology, product quality is also gradually improving. Carbon steel and cast iron can no longer meet the growing requirements of modern industrial production and the needs of large-scale production. Then some new materials have emerged, such as: alloy cast iron, stainless steel, titanium, engineering plastics and various anti-corrosion linings, etc., which have been widely used in production. The anti-corrosion treatment of carbon steel equipment. Most use phenolic and epoxy resin coatings. Especially heat exchange equipment has anti-corrosion heat transfer effects. * * Decrease, thereby increasing the heat exchange area. Therefore graphite has become a very suitable material in equipment manufacturing. For example, it is used in processes related to HC1 gas or hydrochloric acid in the production of calcium carbide PVC. The main equipment includes: hydrochloric acid cooler. Round graphite three-in-one hydrochloric acid synthesis furnace. Graphite hydrogen chloride synthesis furnace, round graphite sulfuric acid diluter, mixed gas cryogenic cooler, polymerization section preheater and converter vinyl chloride cooler, EDC cooler in the distillation section of ethylene oxychlorination production, etc. have all received good use results. The thermal conductivity of graphite is 480. 7 J / (m·h·℃), while the thermal conductivity of general alloys is much lower, such as 304 stainless steel is 58. 69 J / (m·h·℃) , therefore the thermal resistance of graphite with the same thickness is smaller than that of stainless steel, and the heat transfer capacity is also stronger. Although the thermal resistance of the tube wall during the heat transfer process is much smaller than the thermal resistance of fluid and dirt, this effect cannot sometimes be ignored. Even the most corrosion-resistant alloy has a corrosion rate of 0.1 mm/a in highly corrosive media such as hydrochloric acid, while the corrosion rate of graphite is almost 0. Therefore, in highly corrosive environments, the life of graphite heat exchangers is obviously longer than that of metal heat exchangers. 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 not only saves the steam consumption of the cyclization reaction tower, but also increases the reaction yield of dichloropropane. Impermeable graphite equipment is used in other fields Although it has been widely used in the field, its application in PS plate production is only in its infancy. As far as actual production is concerned, as long as the working pressure does not exceed 0.6MPa and the working temperature is lower than 160°C, impermeable graphite equipment can be used if the medium contains corrosive substances. Metal heat exchangers can be used even under other medium conditions. Leakage often needs to be plugged. When running under acidic medium conditions, it needs to be replaced frequently, which will cause frequent shutdowns. The direct losses caused by replacing tubes or heat exchangers and the indirect losses caused by shutdowns are not negligible. It can be seen that graphite heat exchangers not only have good heat exchange effects, but also have a high degree of corrosion resistance and long service life. , and prevent equipment shutdown caused by frequent plugging or replacement of heat exchangers, so that chemical equipment can truly achieve long-term, safe and stable operation, so it is worthy of further promotion. Through the above introduction, we believe that as time goes by and the understanding of graphite equipment becomes more and more profound, its application prospects will be quite good.