Titanium has excellent corrosion resistance and mechanical properties and is widely used in many sectors. Especially in chemical applications, titanium can replace stainless steel as a corrosion-resistant material, which is of great significance for extending the service life of equipment, reducing costs, preventing pollution and improving productivity. In recent years, the range of titanium used in China's chemical industry has been expanding, and the amount has increased year by year, and titanium has become one of the main anti-corrosion materials in chemical equipment. As a kind of corrosion-resistant structural material used in chemical equipment, titanium has become an ideal material in chemical equipment.
Chlor-alkali industry
Chlor-alkali industry is an important basic raw material industry, and its production and development have a great impact on the national economy. This is because the corrosion resistance of titanium to chloride ions is better than that of commonly used stainless steel and other non-ferrous metals. At present, titanium is widely used in chlor-alkali industry to manufacture metal anode electrolyzer, ion membrane electrolyzer, wet chlorine cooler, refined brine preheater, dechlorination tower, chlorine cooling scrubber and so on. The main parts of these equipment used to use non-metallic materials (such as graphite, polyvinyl chloride, etc.), due to the mechanical properties of non-metallic materials, thermal stability and processing performance is not ideal, resulting in heavy equipment, large energy consumption, short life, and affect product quality and pollution of the environment. Therefore, since the 1970s, China has begun to replace graphite electric tanks with metal anode electric tanks and ion film electric tanks, and replace graphite coolers with titanium wet chlorine coolers, and good results have been achieved.
For example: titanium to wet chlorine cooler application. The production of caustic soda by salt electrolysis is to produce a large amount of high temperature wet chlorine gas, the temperature is generally 75~95 degree , and it needs to be cooled and dried before it can be used. The production of chlorine gas from salt electrolysis in China has affected the production and quality of chlorine gas in the past because of unreasonable cooling process or corrosion of cooling equipment, and has seriously polluted the environment. The titanium cooler resistant to high temperature wet chlorine gas corrosion has been put into production, which has changed the production face of chlorine production in chlor-alkali industry. Titanium in the high temperature wet chlorine environment is extremely resistant to corrosion, titanium at room temperature chlorine water, corrosion rate is 0.000565mm/a; In chlorine water at 80 degree , the corrosion rate of titanium is 0.00431mm/a; In the 95% wet chlorine gas, the corrosion rate of titanium at room temperature is 0.00096mm/a. Many chlor-alkali coolers are often used to make wet chlorine gas from titanium, and some have been used for nearly 20 years and are still intact.
Soda ash is one of the most basic chemical raw materials, which is directly related to the development of national economy. In the process of soda ash production, the gas medium is mostly NH3 and CO2, and the liquid medium is mostly the solution of NaCl, NH4Cl, NH4HCO3 and Cl- with high concentration. The carbonization tower tubes, hot mother liquid coolers, coolers, crystallizing external coolers and other main equipment using carbon steel and cast iron materials for carbonation reaction are not corrosion resistant, and the corrosion leakage is serious. Service life is not more than three years. From 1975 to 1977, Tianjin Alkali Plant and Dalian Chemical Industry Company built plants for titanium application demonstration work, carbide tower cooling pipe 63×2mm, titanium plate heat exchanger, titanium external cooler, titanium pump, CO2 turbine compressor rotor, Ti-6Al-4V alloy impeller, etc., the application effect is very good. This has played a model role in the transformation of titanium technology for the whole industry and the construction of three new soda plants with an annual output of 600,000 tons.
For example, the ammonia condenser at the top of the distillation tower of a soda plant uses pure titanium tubes instead of cast iron tubes. Ammonia condenser is a equipment for condensing the ammonia vapor from the distillation tower in the process of soda ash production. It is composed of two cast iron cooling boxes, each box has a diameter of 2.5m and a height of 1.2m. The original box contains 214 cast iron tubes of Φ63×6×2986mm, and the two boxes have 428. Both inside and outside the pipe are anticorrosive with thermosetting phenolic varnish. The medium outside the pipe is NH3, CO2, H2O vapor, and the temperature is about 95 degree . The NH4Cl mother liquor is carried through the pipe to exchange heat with the medium outside the pipe. Under this condition, the cast iron pipe is seriously corroded, and some pipes are corroded and perforated within a year of use, and the corrosion damage is serious in 2 years, and the use is stopped. In order to solve the serious corrosion problem of cast iron pipes in ammonia condenser, all cast iron pipes are replaced with TA2 titanium pipes, Φ60×2×3010mm, and O-shaped rubber rings are used to seal the end of titanium pipes and cast iron panels. This is the first distillation column cooling tube in China's soda ash industry using pure titanium tube. Put into operation for more than two years, the pipe has been pumped for macroscopic inspection, no corrosion phenomenon was found, and the service life is expected to reach more than 20 years, which is 10 times longer than that of cast iron pipe. Due to the corrosion resistance of the titanium pipe, the heat transfer efficiency is maintained well (the cast iron pipe in a three-year overhaul period, the heat transfer efficiency is good in the early stage, poor in the middle stage, and the failure in the later stage), the NH4Cl mother liquor in the pipe is preheated to recover heat, improve the temperature of the mother liquor entering the distillation tower, which can save a lot of steam and has obvious economic benefits.
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