5. Liquid sulfur dioxide production technology
We have always been committed to the research and development and promotion of acid and environmental protection technologies. The developed zero-discharge wastewater technology, high-temperature cracking and recovery of refractory waste acid, high-arsenic ore treatment and arsenic recovery, and sulfur downstream product production technology have been widely used in the industry. The promotion and application of these technologies have enabled the project device to meet the strict national emission standards and also achieved the goal of energy saving and consumption reduction.
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Sulfur dioxide is an intermediate substance in the production of sulfuric acid and an important chemical raw material. Sulfur dioxide has a strong reduction and bleaching effect. It is used to produce various sulfites, synthetic fibers, detergents, rubber auxiliaries, dyes and other organic substances. It is also used in papermaking, medicine, food and other industrial sectors. In order to facilitate transportation and storage, most of the sulfur dioxide gas is processed into the form of liquid sulfur dioxide for the user. Therefore, liquid sulfur dioxide has become a chemical commodity, which has a long production history at home and abroad, and has formed a certain production capacity. There are many production methods of liquid sulfur dioxide, but it can be roughly divided into two categories: one is to first produce high-concentration sulfur dioxide gas and then liquefy it. There are three main methods for producing high concentrations of sulfur dioxide, namely, absorption, pure oxygen combustion and sulfur trioxide.-Sulfur method; The second is to directly pressurize and freeze the low-concentration sulfur dioxide gas containing a large amount of non-condensable gas, so that the sulfur dioxide is partially condensed, that is, the partial condensation method. At present, the first type of production method is mainly used in China.
1, from the concentration of SO2Preparation of gas
1.1Absorption method
The absorption method is to separate sulfur dioxide from the sulfur dioxide-containing gas with an absorbent, and then obtain a high-concentration sulfur dioxide gas by desorption. The absorption method allows the medium φ(SO2) 0.3-12% gas made of SO2About 100 percent pure sulfur dioxide gas. According to the different absorbents, the absorption method can be divided into ammonia-acid method, sodium citrate method, CANSOLV renewable amine method, LABSORB regeneration method and water absorption method.
1.2Pure oxygen combustion sulfur method
Combustion of sulfur and pure oxygen in sulfur incinerator to produce high concentration of SO2The gas is purified, cooled, dried, compressed and liquefied to produce liquid sulfur dioxide. The advantages of pure oxygen combustion sulfur method are mature technology, simple process, simple operation and management, low water content of the product, and relatively independent production, do not need to rely on sulfuric acid plant. Due to the control conditions of over-sulfur and oxygen depletion in the production, a large amount of sulfur particles are entrained in the gas, which requires an increase in purification processes and equipment, and an additional air separation unit. In addition, when the pressurized method is used to liquefy sulfur dioxide, it is prone to compressor cylinder explosion accidents, so it is suitable for freezing liquefaction, the process has a high power consumption and is suitable for production in areas with low electricity prices. Some domestic without SO2Resource enterprises use this process to produce liquid sulfur dioxide, most of the products for their own use.
1.3Sulfur trioxide-sulfur method
Sulfur trioxide-sulfur method with liquid SO3Or oleum as raw material, react with sulfur to generate SO2. Since the reaction is slightly exothermic under normal operating conditions, the reaction needs to be properly cooled; unreacted SO3The gas continues to react with sulfur in the secondary reactor to remove the remaining SO3. The advantages of this process are high product purity, simple operation and less construction investment. The disadvantage is to use more expensive liquid SO3Or oleum as raw material, the cost of liquid sulfur dioxide basically depends on the liquid SO3Or the price of oleum, thus limiting the application of the process.
2Drying and purification of gas
To SO2The gas is dried on the one hand to protect the compressor from corrosion, and on the other hand to ensure that the moisture content in the liquid sulfur dioxide reaches the specified target. Water content is an important indicator of liquid sulfur dioxide, China's national superior product standards.ѡ(H2O)≤ 0.02%The water content of liquid sulfur dioxide produced by pure oxygen combustion sulfur method in China is very low, generally.ѡ(H2O)are less than 0.01 per cent, while most liquid sulphur dioxide is produced using the ammonia-acid and sodium citrate processes.ѡ(H2O)>0.02%. Therefore, drying is very important to control the moisture index of liquid sulfur dioxide. According to SO2Gas moisture content to determine the process indicators and equipment, high moisture content can be considered to use two drying tower series operation.
3Liquefaction of sulfur dioxide
Pure sulfur dioxide gas is easily liquefied at room temperature, and there are two methods of liquefaction: pressurization and freezing. The pressurization method is to liquefy sulfur dioxide through a compressor at room temperature. The advantages of the pressurization method are simple production process, low power consumption and low production cost, so it is adopted by most enterprises. The freezing method is to liquefy sulfur dioxide with a freezing liquid at atmospheric pressure, and ammonia is generally used as a refrigerant. First, the refined sulfur dioxide is sent to the ammonia evaporator for indirect contact with liquid ammonia from the refrigeration system. Generally, the liquefaction temperature is controlled at about -15 ℃, and the sulfur dioxide is measured and stored after liquefaction. Liquid ammonia is gasified and returned to the refrigeration system. The advantage of the freezing method is that the operating conditions are good and leakage is not easy to occur, but the disadvantage is that the production cost is high and there is a source of liquid ammonia nearby.
4Partial condensation method
Partial condensation method, in which φ(SO2) about 10% of SO2Part of the SO in the gas2Condensed into liquid sulfur dioxide, the condensation rate is generally only 30%-60%, so the uncondensed SO2It needs to be handled by sulfuric acid system or other devices. SO2The gas in the condenser is cooled by indirect heat exchange with evaporating refrigerants (such as fluorinated hydrocarbons), according to SO.2Partial Pressure and Temperature, Part SO2After being condensed, the liquid sulfur dioxide is pumped to the liquid-liquid heat exchanger, condensed by the liquid refrigerant and sent to the pressure storage tank. The technology is mature and suitable for the production of liquid sulfur dioxide with sulfuric acid plant.
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5. Liquid sulfur dioxide production technology
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