Application of industrial pure titanium in chemical industry

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 has a very important significance in extending the service life of equipment, reducing costs, preventing pollution and improving productivity. In recent years, the range of titanium used in chemical industry has been expanding continuously and the dosage has been increasing year by year. 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, its production and development have a great impact on national economy. This is because titanium's corrosion resistance to chloride ions is better than that of common stainless steel and other non-ferrous metals. At present, titanium is widely used in the chlor-alkali industry to manufacture metal anode electrolyzer, ion-membrane electrolyzer, wet chlorine cooler, refined brine preheater, dechlorination tower, chlorine cooling scrubber tower and so on. The main parts of these equipment used to use non-metallic materials (such as graphite, polyvinyl chloride, etc.). Due to the unsatisfactory mechanical properties, thermal stability and processing performance of non-metallic materials, the equipment is bulky, large energy consumption, short service life, and affects product quality and environmental pollution. Therefore, since the 70's, our country has been replacing graphite electric tanks with metal anode electric tanks and ion-film electric tanks, and replacing graphite cooler with wet chlorine cooler made of titanium. Good results have been achieved.

For example: titanium wet chlorine cooler application. The production of caustic soda by salt electrolysis is to produce a lot 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 table salt electrolysis in China has affected the production and quality of chlorine gas and polluted the environment seriously in the past because of unreasonable cooling technology or corrosion of cooling equipment. Titanium cooler resistant to high temperature wet chlorine corrosion has been put into production, which has changed the production face of chlorine production in chlor-alkali industry. Titanium in high temperature wet chlorine environment is extremely corrosion resistant, titanium at room temperature in chlorine water, corrosion rate is 0.000565mm/a; In chlorine water at 80℃, 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 often used titanium wet chlorine cooler, some have been used for nearly 20 years, 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 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 higher concentration. The carbonation tower tube, the hot mother liquid cooler, the cooler, the crystallized external cooler and other main equipment made of carbon steel and cast iron for carbonation reaction are not corrosion resistant, and the corrosion leakage is serious. The service life shall not exceed three years. The cooling pipe of carbonization tower, titanium plate heat exchanger, titanium external cooler, titanium pump, CO2 turbine compressor rotor, Ti-6Al-4V alloy impeller and so on were applied effectively. This has played a model role for the whole industry to use titanium technology transformation and the construction of three new pure soda plants with an annual output of 600,000 tons.
For example, pure titanium tubes should be used instead of cast iron tubes in the ammonia condenser at the top of the distillation tower in a soda plant. Ammonia condenser is a equipment for condensing ammonia gas from distillation tower in the process of soda ash production. It is composed of two cast iron cooling boxes, each with a diameter of 2.5m and a height of 1.2m. The original boxes contain 214 cast iron tubular tubes with a diameter of 63×6×2986mm, and the two boxes have 428 in total. Both inside and outside the tube are anticorrosive with thermosetting phenolic varnish. The medium outside the tube is NH3, CO2 and H2O vapor, and the temperature is about 95℃. The NH4Cl mother liquor is carried through the pipe and heat is exchanged with the medium outside the pipe. Under this condition, the cast iron pipe corrosion is serious, one year after use, some pipes corroded and perforated, two years after serious corrosion damage, stop use. 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, the size of which is 60×2×3010mm. The end of the titanium pipes and cast iron panels are sealed with O-shaped rubber rings. This is the first distillation tower cooling tube in Chinese soda industry using pure titanium tube. It has been put into operation for more than two years, and no corrosion was found in the macro-inspection of the pipe. 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 tube, the heat transfer efficiency is maintained well (cast iron pipe in a three year overhaul period, its heat transfer efficiency is good in the early stage, poor in the middle stage, and will fail in the late stage), the NH4Cl mother liquid in the tube is preheated to recover heat, improve the temperature of the mother liquid into the distillation tower, can save a lot of steam, economic benefits are obvious.