Titanium metal has excellent corrosion resistance and mechanical properties, and is widely used in many sectors. Especially in chemical applications, the use of 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 scope of titanium in my country’s chemical industry has been expanding, and the amount of use has increased year by year. Titanium has become one of the main anti-corrosion materials in chemical equipment. As a corrosion-resistant structural material used in chemical plants, titanium has become an ideal material in chemical equipment.
The 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 superior to commonly used stainless steel and other non-ferrous metals. At present, titanium is widely used in the chlor-alkali industry to manufacture metal anode electrolyzers, ion membrane electrolyzers, wet chlorine coolers, refined brine preheaters, dechlorination towers, and chlorine gas cooling scrubbers. Non-metallic materials (such as graphite, polyvinyl chloride, etc.) have been used as the main components of these equipment in the past. Due to the unsatisfactory mechanical properties, thermal stability and processing performance of non-metallic materials, the equipment is cumbersome, consumes large energy, and has a short life , And affect product quality and environmental pollution. Therefore, since the 1970s, my country has begun to replace graphite electric cells with metal anode electric cells and ion-membrane electric cells, and to replace graphite coolers with titanium wet chlorine coolers, all of which have achieved good results.
For example: the application of titanium wet chlorine cooler. The production of caustic soda by salt electrolysis requires the production of a large amount of high-temperature wet chlorine gas. The temperature is generally 75 to 95°C, and it needs to be cooled and dried before it can be used. The production of chlorine gas from salt electrolysis in my country has previously affected the production and quality of chlorine gas due to irrational cooling process or corrosion problems of cooling equipment, and also seriously polluted the environment. Titanium coolers resistant to high temperature, wet chlorine gas corrosion have been put into production, changing the appearance of the production of chlorine in the chlor-alkali industry. Titanium is extremely resistant to corrosion in a high temperature and wet chlorine environment. The corrosion rate of titanium in chlorine water at normal temperature is 0.000565mm/a; in chlorine water at 80°C, the corrosion rate of titanium is 0.00431mm/a; In wet chlorine gas, the corrosion rate of titanium at normal temperature is 0.00096 mm/a. Many chlor-alkali often use titanium wet chlorine gas cooler, and some have been used for nearly 20 years, still intact.
Soda ash is one of the most basic chemical raw materials, and it is directly related to the development of the national economy. During the production of soda ash, the gaseous medium is mostly NH3 and CO2, and the liquid medium is mostly NaCl, NH4Cl, NH4HCO3 and Cl-concentrated solutions. Carbonized tower small tubes and hot mother liquid coolers using carbon steel and cast iron for carbonation , The main equipment such as cooler, crystallization external cooler, etc. are not resistant to corrosion, serious corrosion leakage, and the service life is not more than three years. From 1975 to 1977, Tianjin Alkali Plant and Dalian Chemical Industry Company built a plant to carry out titanium application demonstration work, carbonization tower cooling tube 63×2mm, titanium plate heat exchanger, titanium external cooler, titanium pump, CO2 turbine compressor rotor , Ti-6Al-4V alloy impellers and other applications have been very good, which has played a role in the industry for the transformation of titanium technology and the construction of three new 600,000 tons of soda ash plant.
For example, an ammonia condenser at the top of a distillation tower of a soda ash plant should use pure titanium tubes instead of cast iron tubes. The ammonia condenser is a device for condensing the ammonia gas distilled from the distillation tower during the production of soda ash. It consists of two cast iron cooling boxes, each with a diameter of 2.5m and a height of 1.2m. The original box has Φ63×6 214 × 2986mm cast iron pipes, 428 in two boxes. Both the inside and outside of the pipe are anti-corrosion with thermosetting phenolic varnish. The medium outside the pipe is NH3, CO2, H2O vapor, the temperature is about 95℃. Take the NH4Cl mother liquor inside the tube to exchange heat with the medium outside the tube. Under this condition, the cast iron pipe is severely corroded. Some pipes are corroded and perforated after one year of use. After two years, the pipes have been severely corroded and damaged. In order to solve the serious corrosion problem of the cast iron pipe in the ammonia condenser, all cast iron pipes were replaced with TA2 titanium pipes, the specification was Φ60×2×3010mm, and the titanium pipe ends were sealed with O-type rubber rings. This is the first titanium cooling tower in my country’s soda industry. It has been put into production for more than two years. The tube has been drawn for macro inspection, and no corrosion has been found. The expected service life can reach more than 20 years, which can be 10 times longer than that of cast iron pipes. Due to the corrosion resistance of the titanium tube, the heat transfer efficiency remains good (the cast iron tube has a good heat transfer efficiency in the early stage, poor in the middle stage, and fails in the later period) during the overhaul of 3 years. The NH4Cl mother liquid in the pipe is preheated to recover heat, and the mother liquid enters the distillation tower. Temperature can save a lot of steam, and the economic benefit is obvious.