Application of Titanium in Xiangyu Salt Mine (1)

Hunan Xiangyu Salt Mine

The designed production capacity of Xiangyu Salt Mine is 300,000 tons of refined salt and 30,000 tons of thenardite . March 1977 began, the use of titanium materials produced salt, mention nitrate salt slurry pipelines and equipment, and the official use in the production, not only to extend the service life of equipment, reducing equipment for repair times, lower production costs, but also improves the The production conditions have improved the quality of salt and nitrate and achieved remarkable economic benefits.
Titanium application
The Xiangyu Salt Mine is a sodium sulfate type salt mine, and the raw material brine for production is mainly composed of sodium chloride and sodium sulfate (see Table 1).
The average composition of brine in Xiangyu Salt Mine in 1982 is shown in the following table.

In addition to the production of vacuum salts, in order to ensure the salt quality, it is necessary to extract thenardite. Due to the limitations of the original design, the original design did not consider the anti-corrosion problem from the material. Therefore, most of the main equipment and process piping for hydrochloric acid production use carbon steel. After the official production in January 1972, the corrosion problem in the first year was not outstanding. As time passed, the heating chamber of the evaporation can, the ammonia evaporator, the heat exchanger and the salt slurry pipeline were due to the sodium chloride and sulfuric acid in the raw material brine. Corrosion of salt and scouring and abrasion of crystalline salt particles showed obvious leakage and leakage, and the equipment integrity rate decreased, which affected normal production and was even forced to stop production. At that time, according to the experience of the brother factory mine, the cathodic protection experiment was also carried out, but the effect was not obvious, and the equipment corrosion problem could not be solved. As a result, the salt production decreased by 3.11% in 73 years compared with 72 years, and decreased by 22.06% in 73 years compared with 73 years. The output is only over 60,000 tons. Although many measures have been taken in the future, the phenomenon of running and dripping has increased. The equipment is covered with salt scale, and some pumps and pipes are wrapped in sacks to prevent leakage. At that time, people described salt production as: "Linhai Xueyuan, dry sore, hole, filial wear, filial piety in the mountains." The production conditions are so bad, the output is not going up, and the quality is not up to the requirement. At the end of 74, the salt mine used 1Crl8Ni9Ti stainless steel as the slurry pipe, pre-cooler and ammonia evaporator tube, and the heating chamber and the flower board were all made of steel. steel. March 75 began to replace the heating chamber tubes, plates, copper tube heating chamber has not only to convert all finished, just put on only half of the pitch tube stainless steel salt and corrosion perforation, and the rest of the site instead of stainless steel, corrosion effect is not ideal. Later learned from the study tour report, foreign equipment and technology pipeline vacuum salt use more Monel alloy, which is characterized by good corrosion resistance, continuous production, no monthly inspection. The Salt Mine Party Committee believes that in order to make salt production from passive to active, we must start with the choice of materials to solve the problem of equipment corrosion. In March of the 75th, the salt mine leader went to the Ministry of Light Industry for a report. At the seminar, the comrades of the Salt Bureau of the Food Bureau introduced the experience of the promotion of titanium materials for the metallurgical department of the Ministry of Metallurgy, and suggested research and trial. In mid-September, the Salt Mine established a Titanium Leading Group, developed a work plan, and collected relevant technical information. The Ministry of Metallurgy listed the Xiangyu Salt Mine as a key unit for the promotion of the use of titanium in the vacuum salt industry, and sent a letter to the Guangzhou Nonferrous Metals Research Institute of the Ministry of Metallurgy, asking them to help them technically. On this basis, the salt mine proposed an ordering plan for 50 tons of titanium materials, and signed an order contract with Baoji Nonferrous Metals Processing Factory for titanium pipes, titanium plates and titanium castings . It has created better material and technical conditions for the trial work of titanium.
At the beginning of 1977, the salt mine established a special production team for the production of titanium equipment. After joint efforts, it has produced 5 sets of titanium ammonia evaporators, 4 precoolers, 6 preheaters, and 4 titanium refrigerating pumps. There are hundreds of titanium elbows and titanium flanges, and 440 meters of titanium salt slurry tubes with different diameters are installed. They are put into production and operation. From March to July, titanium materials are officially produced in salt and nitrate production. Promoted.
According to the data report and the report on the study abroad, stainless steel 316L and Monel alloy are mainly used as corrosion-resistant materials in foreign vacuum salt production equipment, and the effect is good. The United States, Japan, and Western European countries also use industrial pure titanium to manufacture a variety of seawater desalination equipment, various heat exchangers resistant to chloride solution corrosion. Because titanium has extremely high corrosion resistance in various concentrations of chloride solution, titanium equipment achieves better technical and economic benefits with less material, light weight and high efficiency.
In order to solve the corrosion problem of equipment, in recent years, some salt mines in China have also used B10 and B30 copper- nickel alloys as heating chamber pipes, which have achieved good results. However, due to the lack of copper and nickel resources in China, there are still some difficulties in applying such materials in large quantities. To this end, we must find new and ideal corrosion-resistant materials that are more suitable for China's resource conditions.
Nitrate salt mentioned in the production process, complicated working conditions, the brine composition of the medium in the medium as a main etching, contained mainly sodium chloride salt, and also containing sodium sulfate, calcium sulfate, magnesium sulfate; Brine The concentration in the evaporation tank is in a state of conservation, and is diluted in the top water washing tank; the temperature in the first effect tank can reach 139 ° C, and the temperature of the old halogen drops to 2-4 ° C in the freezing and withdrawing of the tank, In the pipeline, the slurry and the slurry flow at different speeds. Therefore, the materials sought must meet the requirements of the above working conditions.
According to the application of industrial pure titanium research at home and abroad for more than ten years, titanium is an ideal material to meet the above requirements in salt nitrate production because:
1. Laboratory and production practices have proved that titanium is almost not corroded in various concentrations of sodium chloride solution in the range of not higher than 140 ° C, which is much higher than stainless steel 316L and copper-nickel alloy. Corrosion resistance.
2. Titanium also has high corrosion resistance in high flow medium (including sodium chloride). Because titanium has the ability to quickly repair its protective oxide film, titanium has excellent corrosion resistance.
3. The corrosion resistance of titanium in sodium sulfate solution and ammonia gas and ammonia water is also good. The corrosion rate is less than 0.13mm/year under various temperatures and concentrations.
4. Industrial pure titanium is not sensitive to contact corrosion, pitting corrosion, intergranular corrosion, stress corrosion, etc.
5. Titanium has poor wettability due to surface oxide film, smooth surface and no corrosion, so the surface is not easy to scale, better than other metals. Although the thermal conductivity of titanium is similar to that of stainless steel (thermal conductivity is 14 kcal/square, hour, °C), titanium has good corrosion resistance, and can choose a thinner tube wall. The surface is not easy to scale, and usually does not hinder heat transfer. The membranous fouling material, so the heat transfer efficiency of titanium is very high. Foreign experiments have shown that the heat transfer coefficient of titanium is close to that of naval brass and is suitable for heat exchanger materials.
In September of the same year, the Xiangyu Salt Mine passed more than 20 pieces of titanium test piece, which were hung on the evaporation tank, the circulation pump, the slurry pump outlet, the circulation pump outlet, the ammonia evaporator, the niobium pump outlet, etc. During the production and operation of the month, there is no trace of corrosion on the test piece, and the surface is bright. It proves that the performance of industrial pure titanium is good under the production conditions of specific brine composition, concentration, temperature and pressure of mine.

    ●    Used in hydraulic system.