Caustic soda (sodium hydroxide) is a soluble strong base. Soda (sodium carbonate) is actually a salt. Because it is hydrolyzed in water to make the solution alkaline, and then because it has some similar properties with caustic soda, it is parallel to caustic soda, and is called "two alkali" in industry. Caustic soda and soda ash are all soluble in water and strong alkaline, which can provide Na+ ions. These properties make them widely used in soap making, textile, printing and dyeing, bleaching, paper making, refined petroleum, metallurgy and other chemical industries. Common soap is a sodium salt of high fatty acids, which is usually made by saponification of oil with slightly excessive caustic soda. If you use fatty acids as raw materials, you can use soda ash instead of caustic soda to make soap. In printing and dyeing and textile industry, too much lye must be used to remove grease from cotton and wool. The production of artificial fibers also needs caustic soda or soda ash. For example, the viscose fiber should be first used in 18 ~ 20% caustic soda solution (or soda solution) to impregnate the cellulose and make it a alkali cellulose. Then the alkali cellulose is dried and crushed, and then the sulfonate is dissolved in the dilute alkaline solution, and the viscose liquid is obtained. After filtering and vacuuming, it can be used for spinning. The refined oil also needs to be used with caustic soda. In order to remove colloids in petroleum fractions, concentrated sulfuric acid in petroleum fractions is generally used to remove colloids from acid residues. After pickling, the oil also contains acid impurities such as phenol and naphthenic acid, as well as excess sulphuric acid. It must be washed with caustic soda solution and then washed to get refined petroleum products. In the paper industry, the first chemical method to deal with the raw materials containing cellulose (such as wood) and chemicals cooking into pulp. Alkaline pulping is used to remove lignin, carbohydrates and resins from raw materials, such as lignin, carbohydrates and resins, by using caustic soda or soda solution to neutralize the organic acids in the raw material, so that the cellulose is separated. In metallurgical industry, it is often necessary to convert the effective components of the ore into soluble sodium salt in order to remove the insoluble impurities. Therefore, it is often necessary to add soda (it is also a flux), and sometimes also with caustic soda. For example, in the smelting process of aluminum, the preparation of cryolite and the treatment of bauxite need soda ash and caustic soda. When the tungsten is smelted, it is also first to roast the concentrate and soda into soluble sodium tungstate, and then by acid analysis, dehydration, reduction and other processes, the powder like tungsten is made. In chemical industry, caustic soda is used for making sodium and electrolyzing water. The production of many inorganic salts, especially the preparation of some sodium salts (such as borax, sodium silicate, sodium phosphate, sodium dichromate, sodium sulfite, etc.), should be used in caustic soda or soda ash. Synthetic dyes, drugs and organic intermediates should also be used in caustic soda or soda ash. The caustic soda production process is a flaky caustic soda, which is an alias of sodium hydroxide. Sodium hydroxide is called industrial alkali, caustic soda and caustic alkali in industry, and can be divided into liquid alkali, tablet base, solid alkali and granular alkali according to the existing form. Among them, caustic soda, solid base and granular alkali are the three forms of solid sodium hydroxide. In the following chart, the caustic soda caustic soda is in turn: 1. lye is concentrated from 32% to 61%, and this stage is carried out in the falling film evaporator. The heating source is medium pressure steam and two steam and evaporates in vacuum. 2.61% alkaline solution is then reduced by the falling film thickener, and the molten salt is used as the heat carrier. The alkali solution is condensed into molten alkali under the atmospheric pressure, and then the flake solid base (the legendary molten salt method) is made by the flake alkali machine. The ionic membrane caustic soda with a mass fraction of 32% is concentrated to 47% by the first effect evaporator (vacuum, two steam). After the alkali pump and the steam condensate of the second effect evaporator, the caustic soda is heated by the steam condensate of the second effect evaporator. The second effect evaporator is further concentrated to 61%, and the alkali pump is pumped into the final concentrator by the alkali pump, and is heated to 98% to 99% by the molten salt, and then made into a slice by a soda machine. Solid caustic soda. The 1 MPa saturated steam from the power plant enters the first effect evaporator. The condensate and I effect alkali heat transfer into the circulating pool. As a supplement of soft water, the two steam produced by the second effect and the two steam produced by the final concentration are entered into the first effect evaporator as the heat source, and the 32% alkaline solution evaporates. The molten salt of 415~430 C is sent into the molten salt furnace by the molten salt pump and heated to the final thickener after heating. As a source of heat, the alkali evaporates to 98% ~ 99%, and is finally returned to the molten salt tank and recycled. The molten salt furnace system is a closed cycle heating system. The molten salt is heated up by heating the inner and outer coils of the ignition head above the furnace to heat the molten salt. The molten salt circulates in the system through the pump, and the decomposition and deterioration of the molten salt is reduced to the maximum extent because of isolation from the outside. The following points should be paid attention to when molten salt is first heated in production. (1) The melting point of molten salt is about 143 C. All molten salt pipelines should have steam tracing. It is better to use electric tracing at the same time to prevent molten salt from solidifying in pipelines. (2) during the heating process of the molten salt, the heat of the molten salt valve should be carefully checked. When the molten salt is circulating in the whole system, it is particularly noted that the small circulation reflux valve can not be shut down and must be turned round to prevent the death of the molten salt valve.