Pure Titanium Tube and Ti-6Al-4V Alloy Impeller Products Used in Soda Industry
The pure titanium tube was used instead of cast iron tube in ammonia condenser at the top of distillation tower in a soda plant. Ammonia condenser is the equipment which condenses the ammonia gas from distillation tower in 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. There are 214 original Φ63×6×2986mm cast iron tubes in the box, and 428 in two boxes. The inside and outside of the tube are protected by a thermosetting novolac. The medium outside the tube is NH3, CO2, H2O vapor, and the temperature is about 95 °C. The NH4Cl mother liquor is taken in the tube to exchange heat with the external medium. Under this condition, the cast iron pipe is seriously corroded. Some pipes are corroded and perforated in one year, and the corrosion has been seriously damaged in 2 years and is stopped. In order to solve the serious corrosion problem of the cast iron pipe in the ammonia condenser, the cast iron pipe is completely replaced by the TA2 titanium pipe, the specification is Φ60×2×3010mm, and the pipe end of the titanium pipe and the cast iron plate are sealed by the O-ring. This is the cooling tube of the first distillation tower of China's soda ash industry using pure titanium tube. It has been put into production for more than two years. It has been subjected to macro inspections and no corrosion has been found. The service life is expected to be more than 20 years, which is 10 times longer than that of cast iron pipes. Due to the corrosion resistance of the titanium tube, the heat transfer efficiency is kept good (the heat transfer efficiency of the cast iron pipe is good in the early stage of 3 years, the medium-term difference is bad, and the later stage is invalid). The NH4Cl mother liquor in the titanium tube preheats the heat to increase the temperature of the mother liquor entering the distillation column, which can save a lot of steam and has obvious economic benefits.
▲ Dalian Chemical Industry Company's alkali plant has an annual output of 720,000 tons of soda ash, which is produced by ammonia-alkali method and combined alkali method. Since the late 1970s, in order to change the backwardness of equipment, some major equipment has been gradually updated with titanium and tantalum equipment. After 1983, the application range of titanium materials was further expanded. The application situation is briefly described below.
2.1 Replace the cast iron pipe in the ammonia condenser with a titanium tube The ammonia condenser is a device for condensing ammonia gas distilled from the distillation column during the production of soda ash. It consists of two cooling boxes with 214 pieces of φ63mm*6mm*2986mm cast iron pipes. Both inside and outside of the tube are treated with thermosetting novolac. The external medium is NH3, CO2, H2O steam, the temperature is about 95 °C, and the medium NH4Cl is used to exchange heat with the external medium. Under this condition, the cast iron pipe is seriously corroded. Some pipes are corroded and perforated after one year of use. In two years, the corrosion has been seriously damaged. When the distillation tower was overhauled for 3 years, the cast iron pipes in the ammonia condenser were all replaced.
In 1977, the Dalian Chemical Industry Company's alkali plant was included in the scientific research project to solve the serious corrosion problem of the cast iron pipe in the ammonia condenser. The TA2 pipe with the specification of φ60mm*2mm*3010mm was ordered from Baoji Nonferrous Metals Processing Factory and installed in 1979. This is the first titanium tube equipment of the plant, and it is also the first pure titanium tube used in China's soda ash industrial distillation tower. In December 1979, it was put into production and it has been used for 14 years. No corrosion leaks have been found so far, and the effect is good. According to the pipe inspection and appraisal in September 1982 (commissioned for 2 years and 10 months), the service life is expected to be more than 20 years.
Due to the corrosion resistance of the titanium tube, the heat transfer efficiency is kept good (the heat transfer efficiency of the cast iron pipe is good in the early stage, medium-term difference, and late failure). The NH4Cl mother liquor in the titanium tube preheats the heat to increase the temperature of the mother liquor entering the distillation column, which can save a lot of steam and has obvious economic benefits (see Table 1).
Table 1 Comparison of economic benefits between titanium tube and cast iron tube
|Project||Titanium tube||Cast iron pipe|
|equipment cost||180000 RMB||24000 RMB|
|Service life||Expected for 20 years||2years|
|Annual depreciation||9000 RMB||12000|
|Annual savings||3000 RMB||0|
|Annual production capacity||14.6 million t||14.6 million t|
|Saving steam throughout the year||4.38million t||2.17million t|
|Steam unit price||RMB 7/t||RMB 7/t|
|Saving value throughout the year||306600 RMB||153300 RMB|
|Annual income||153300 RMB||0|
|Total annual income||156300 RMB||0|