Titanium metal has excellent corrosion resistance and mechanical properties, is widely used in many departments. Especially in chemical applications, titanium can replace stainless steel as a corrosion resistant material, which has a very important significance in extending the service life of equipment, reducing costs, preventing pollution and improving productivity. In recent years, the scope of titanium used in chemical [SCALE STEEL]industry in China is constantly expanding, the amount of titanium is increasing year by year, titanium has become one of the main anti-corrosion materials in chemical equipment. Titanium, as a kind of corrosion-resistant structural material used in chemical equipment, has become an ideal material in chemical equipment.
Chlor-alkali industry is an important basic raw material industry, its production and development have a great impact on the national economy. This is because titanium has better corrosion resistance to chloride ions than commonly used stainless steel and other non-ferrous metals. At present, titanium is widely used in the chlor-alkali industry to manufacture metal anode electrolytic cell, ion membrane electrolytic cell, wet chlorine cooler, refined brine preheater, dechlorination tower, chlorine cooling washing tower and so on. In the past, non-metallic materials (such as graphite and polyvinyl chloride) were mostly used for the main parts of these equipment. Due to the unsatisfactory[SCALE STEEL] mechanical properties, thermal stability and processing performance of non-metallic materials, the equipment was bulky, consuming large energy and having short service life, and affected product quality and polluted the environment. Therefore, since the 1970s, metal anode and ion membrane electrolytes have been used to replace graphite electrolytes, and titanium wet chlorine cooler has been used to replace graphite cooler, and good results have been achieved.
For example: the application of titanium wet chlorine cooler. Salt electrolysis production of caustic soda is to produce a large amount of high temperature wet chlorine gas, the temperature is generally 75~95℃, need to be cooled and dried before use. The production of chlorine gas from salt electrolysis in China has affected the output and quality of chlorine gas in the past because of unreasonable cooling process or corrosion of cooling equipment, and seriously polluted the environment. Titanium [SCALE STEEL]coolers resistant to high temperature wet chlorine corrosion were put into production, which changed the production face of chlorine in chlor-alkali industry. Titanium is very resistant to corrosion in the environment of high temperature and wet chlorine. The corrosion rate of titanium in chlorine water at room temperature is 0.000565mm/a. In chlorine water at 80℃, the corrosion rate of titanium is 0.00431mm/a. In 95% wet chlorine, the corrosion rate of titanium at room temperature is 0.00096mm/a. Many chlor-alkali coolers, often made of titanium wet chlorine, have been in use for nearly 20 years and are still in good condition.
Soda Ash Industry
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 production, the gas medium is mostly NH3 and CO2, and the liquid medium is mostly NaCl, NH4Cl, NH4HCO3 and Cl- solution with high concentration. The main equipment [SCALE STEEL]such as carbonation tower tubs made of carbon steel and cast iron for carbonation reaction, hot mother liquor cooler, cooler and crystallizing outer cooler are not corrosion resistant and have serious corrosion leakage. Service life is not more than three years. From 1975 to 1977, Tianjin Alkali Plant and Dalian Chemical Industry Company set up factories and carried out demonstration work of titanium application. The cooling pipe of carbide tower 63×2mm, titanium plate heat exchanger, titanium external cooler, titanium pump, ROTOR of CO2 turbine compressor, Ti-6Al-4V alloy impeller and so on had good application effect. This for the whole industry with titanium technology transformation and the new three annual output of 600 thousand [SCALE STEEL]tons of pure alkali plant played a model role.
For example: the ammonia condenser at the top of distillation tower in a pure alkali plant uses pure titanium tube instead of cast iron tube. Ammonia condenser is the equipment for condense ammonia gas from distillation tower in the process of soda 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 with a diameter of 63×6×2986mm, a total of 428. The tube is anticorrosive with thermosetting phenolic varnish inside and outside. The medium outside the tube is NH3, CO2, H2O vapor, and the temperature is about 95℃. NH4Cl mother liquor is carried out in the tube for heat exchange with the medium outside the tube. Under this condition, the cast iron pipe corroded seriously, some of the pipe corroded and perforated in one year, and corroded and damaged seriously in two years, so it stopped using. In order to solve the serious corrosion problem of cast iron pipes in ammonia condenser, all cast iron pipes were replaced with TA2 titanium pipes, with specifications of φ 60×2×3010mm. The titanium pipe ends and cast iron plates were [SCALE STEEL]sealed with O-type rubber rings. This is the first distillation tower in China's soda industry using pure titanium tube cooling. It has been put into production and used for more than two years. No corrosion phenomenon was found when the pipe was pulled out for macroscopic inspection. It is expected to have a service life of more than 20 years, 10 times longer than the cast iron pipe. Due to the corrosion resistance of titanium tubes, the heat transfer efficiency remains good (cast iron tubes have good heat transfer efficiency in the early stage, poor in the middle stage and failure in the late stage during a three-year overhaul). The NH4Cl mother liquor in tubes is preheated to recover heat and improves the temperature of mother liquor entering the distillation tower, which can save a lot of steam and bring obvious economic [SCALE STEEL]benefits.
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