At present, the main applications of graphite equipment include: graphite heat exchangers, graphite condensers, lined graphite reactors, lined graphite reaction tanks, concentration tanks, reaction towers, packed towers and phosphoric acid extraction tanks, granulation towers and other high-temperature reaction equipment, transmission Anti-corrosion equipment for thermal equipment, condensation equipment and anti-corrosion lining. Graphite has good chemical stability. This article discusses the application of graphite in the field of corrosion protection from the application of graphite in water towers, heat exchangers and synthesis furnaces.

1 Overview

In many areas of the national economy, such as chemical industry, medicine, metallurgy, textiles, national defense, electronics, environmental protection, etc., due to the strong corrosiveness of the medium, the equipment should not only be corrosion resistant, but also have good heat transfer performance. According to relevant data, the direct and indirect losses caused by equipment corrosion in China's chemical industry are about 130 billion yuan, which is even much higher than this figure [1]. How to avoid the corrosion of equipment by strong corrosive media, thereby reducing equipment investment and maintenance costs, and improving production efficiency and profit is a problem that every chemical enterprise needs to solve forever. Especially in the chlor-alkali industry, phosphoric acid and fluorine chemical industry, high-temperature reaction equipment and heat transfer equipment, most conventional materials cannot be used. If the wrong materials are selected, the equipment will be damaged, which will cause huge losses to the enterprise. How to choose high-quality anti-corrosion materials is the key to ensuring normal production. Phosphoric acid, hydrofluoric acid and fluorine-containing media have very good corrosion properties at high temperatures [2]. Stainless steel, aluminum, magnesium, copper and most other alloys except steel are severely corroded by phosphoric acid and should not be used. Non-metal silicate materials (such as ceramics, glass and enamel) have good phosphoric acid corrosion resistance at all concentrations and temperatures. However, due to the sweat in raw materials such as fluoride, chloride and sulfuric acid, it cannot resist the corrosion of hydrofluoric acid, hydrogen fluoride and other fluorine-containing media, especially in the wet-process phosphoric acid industry. Therefore, it is impossible to use various plastics (such as polyethylene, polyvinyl chloride, polystyrene) and rubber materials (such as natural rubber, butyl rubber, and fluorine rubber) that are resistant to phosphoric acid and hydrofluoric acid. However, most of the endurance temperatures are relatively low, lower than 65°C, which cannot meet the needs of high-temperature reaction and storage equipment. Fluorine rubber has good corrosion resistance at high temperatures, but its price is too high, and it is usually used in aerospace. Military industry and other industries are rarely used in large-area conventional chemical equipment [3] Graphite is a typical brittle material, it has good corrosion resistance and thermal conductivity, small linear coefficient, good heat resistance, Good processing performance, wear resistance, light weight, temperature rise but strength will not decrease. It is not easy to scale on the surface of the pressed graphite parts, which can ensure the purity of the product. The disadvantages are low mechanical strength, small elastic deformation, brittleness, poor impact resistance and low tensile strength [4]. Graphite equipment is basically thick-walled equipment, which usually does not occur before the compressive strength of the material reaches the limit of instability failure, and is usually used for cylindrical strength failure. Graphite equipment is mainly used for normal pressure and low pressure operation, and the use temperature is not too high. The design pressure of graphite equipment does not exceed 2.4 MPa, and the design temperature is -60~400℃. The material of graphite equipment is usually impregnated impermeable graphite. Graphite materials are mainly used in heat exchangers, towers, filters, reactors, absorbers and other equipment. In the design of graphite equipment, the compressive strength of graphite materials should be fully utilized to make the graphite components bear compressive stress, avoiding or reducing tensile stress and bending stress. The channel direction of the heat exchanger must be consistent with the direction of heat conduction caused by graphite anisotropy. As heating equipment, when resin-impregnated graphite, pressed graphite and its binder are used in combination with metal materials or other materials, the bonding structure should be miniaturized. At the same time, the bonding structure of the main graphite parts of the equipment should be avoided.