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Development of stainless steel in chemical fertilizer industry
The common inorganic fertilizers in the fertilizer industry include the phosphate fertilizer, potash fertilizer and nitrogenous fertilizer. Class-I ammonium phosphate in nitrogen fertilizer is produced by the action of phosphorylated ammonia and phosphoric acid with sulfuric acid. The leading enterprise in urea production is Stamicarbon (now a subsidiary of Maire Tecnimont), which has been working with Uhde and Sandvik to develop new production processes.
Fertilizer production is mainly concentrated in Argentina, Brazil, China, India and other Asia-Pacific countries, the Middle East and Russia. Not surprisingly, these countries are experiencing rapid economic growth and some are experiencing soaring food prices. This is illustrated by the scale of investment. In addition, IFFCO plans to invest USD 1.2 billion to USD 1.3 billion in India for expansion in the next three years.
Development of Stainless Steel in Chemical Fertilizer Industry
This paper summarizes the development of stainless steel used in fertilizer production. The austenitic stainless steel AL 904LTM produced by Allegheny Ludlum Stainless Steel Company has good corrosion resistance and is suitable for general fertilizer production, especially for the production of sulfuric acid and other reducing acids. AL 904LTM is used in fertilizer production and other process applications.
Application of Stainless Steel in Sulphuric Acid
300 series austenitic stainless steels, especially 304, 316 and 310, are commonly used in sulphuric acid production. Other steels used in the production of strong sulphuric acid include dual-phase stainless steel ZERONN100 and 2507, austenitic steel Saramett, Sandvik SXTM and ZeCorr, all of which are heat-resistant and acid-resistant.
Application of Stainless Steel in Phosphoric Acid
When dealing with low concentration of phosphoric acid, 304 was used, and 316 and 317 with better corrosion resistance were used when dealing with high concentration of phosphoric acid. Sulzer provides corrosion-resistant and wear-resistant pumps manufactured by 654 SMO for phosphoric acid production. Dual-phase UNS 32520/UR52N+ has been successfully used in agitators. Due to its superior mechanical properties, it is comparable to N08904 (904L).
Application of Stainless Steel in Ammonia
In the ammonia production process, most of the processes are moderately corrosive, so 300 and 400 series stainless steel are generally used. These steels are used in the manufacture of reformers, CO2 removal devices, ammonia synthesis, impeller machinery, cooling devices and condensers. During the synthesis of ammonia, corrosive ammonium carbamate is produced, so steel grades with better corrosion resistance, such as ASTM 430, UNSS44625 and UNS S44626, are needed. In order to resist chloride corrosion, duplex stainless steel is used in heat exchanger. The economical duplex stainless steel LDX 2101 produced by Outokumpu Company can be used in pipelines and tanks. The duplex steel has good mechanical properties, can reduce the wall thickness of materials used, save material and manufacturing costs, and its corrosion resistance (pitting corrosion and stress corrosion cracking) is better than the standard 300 series stainless steel.
Application of Stainless Steel in Urea
In recent years, the standard steel used in urea production equipment is improved 316L, that is 316L MOD or 316L Urea. The more corrosive area is stainless steel with higher alloy content. Urea 25/22/2 (25Cr, 22Ni, 2Mo) is an improved 310L austenitic stainless steel with low carbon, low silicon and high nitrogen content.
In urea production, corrosion is affected not only by carbamate level, but also by ammonia/CO2 ratio and oxygen content. Lack of oxygen can cause corrosion of stainless steel, so low oxygen content resistant steels such as Urea 25/22/2 are used. Sandvik 2RE69TM is an improved Urea 25/22/2 model, which can be used in areas where conditions are harsh in urea production process. The pipeline of the stripper of the Indian Farmer Chemical Fertilizer Co-operation (IFFCO) in Kalol's urea plant is made of this material. The pressure and temperature in the stripper are high. The pipeline has been used for more than 25 years. Another kind of dual-phase steel can be used to manufacture urea production equipment, which is DP28WTM produced by Sumitomo Metal Industry and Ocean Engineering Company. The dual-phase steel has high chromium content and low nickel content, so it has good re-passivation performance, and is very resistant to stress corrosion cracking and corrosion of carbamate solution and chloride solution.
Sandvik and Stamicarbon have developed an advanced dual phase steel SafurexTM for anaerobic environment in modern urea plants. By using dual-phase steel SafurexTM and Stamicarbon to simplify the urea production process, blowers, hydrogen converters, high-pressure scrubbers and high-pressure ammonia ejectors were removed.
In the process of urea production, ammonia stripper (NH3) is usually made of titanium. However, in order to prevent the erosion of titanium, it is necessary to add a layer of titanium. In order to solve this problem, Snamprogetti (a subsidiary company of Saipem) and ATI Wahchang developed OmegabondTM advanced pipeline, in which zirconium was bonded to titanium by solid-state bonding technology. The Gulf Petrochemical Company (GPIC) first adopted this pipeline on large equipment in Bahrain (which was put into operation in 2009), and then two other companies adopted this pipeline.
Food is the basic demand of human beings, while the dependence on artificial fertilizers continues to increase, which is the existing market for stainless steel. However, it is far from enough to supply products and wait for customers to place orders on their doors. Only by close cooperation between steel producers and users can a win-win situation be achieved. These collaborations provide a model for our future, not only in the field of fertilizer production, but also in the field of processing and manufacturing.