Application of stainless steel in ammonia and fertilizer industry
The pipeline of the downstream part of synthetic ammonia production uses OCr18Ni9 under the service conditions below the dew point, and the inner cylinder of the ammonia synthesis tower uses 0Cr18Ni9.
In the ammonium nitrate production process, the nitric acid preheater, low-pressure neutralization tower, concentrator, prilling tower, and other devices and corresponding pipelines are all made of 0Cr18Ni9 austenitic stainless steel.
Ammonium sulfate is synthesized from sulfuric acid and nitrogen. The by-products in coking production can also be used for sulfur plating. Crystallization tanks and heaters under strict control of acidity and temperature. 00Cr17Ni14Mo2 steel has a good use effect, such as pH3? 35. 00Cr17Ni14Mo2 has achieved satisfactory results under the temperature of 63～66℃ and reduced pressure evaporation. In the impurity-containing ammonium sulfate, in the case of higher temperature, steel grades such as 00Cr18Ni14Mo2Ca2, 0Crl9Nil3Mo3, or 00Cr20Ni25Mo45Cu should be used.
Urea is a high-efficiency fertilizer with an ammonia content of up to 46%. Urea is synthesized from CO2 and ammonia, and the process is high temperature (180~210℃) and high pressure (140-250 atmospheres). In the production process, the intermediate reaction product-carbamate hinges (urea reaming liquid) will strongly corrode stainless steel under high temperature and high pressure.
Under oxygen conditions, due to the passivation of stainless steel, stainless steel is used in urea production equipment. The application becomes possible. At present, in the Sitai high-pressure equipment in the large-scale urea production by carbon dioxide stripping method, namely the synthesis tower, high-pressure condenser, high-pressure scrubber and carbon dioxide stripping tower, except that the distribution pipe of the stripping tower adopts 00Cr25Ni22Mo2N, the others are all made of 00Cr17N -14Mo2 (urea grade) stainless steel manufacturing.
The pelletizing tower uses 0Cr18Ni9 or 0Cr17Ni12Mo2. In recent years, it has been discovered that high-chromium duplex stainless steel has good corrosion resistance in the process environment of carbon dioxide stripping to produce urea. Therefore, Japan has officially adopted 00Cr25Ni7Mo3N to make stripping tower distribution tubes. Stainless Steel Practical Manual Regarding carbamate pump cylinders, fatigue from corrosion, etc., duplex stainless steels 00Cr18Ni5MO3Si2 and 00Cr25Ni7Mo3N have good results. Valves in urea production are made of 0Cr25Ni6Mo3CuN (Ferralium255), which exhibits good corrosion resistance.