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| Soda ash | ||
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Technology Out of the total production, 70-80% of soda ash is produced through the conversion of common salt. The balance 20-30% is obtained as naturally occurring soda ash deposits. There are three processes currently used to process soda ash
Standard Solvay Process The Solvay process is the often-called ammonia process. Brine (saltwater) solution is reacted with ammonia to form ammoniated brine, which is then passed over carbonators to react with carbondioxide to form sodium bicarbonate slurry. This slurry is then passed to a centrifuge section where crystals of soda bicarbonate are collected and passed through steam tube drier to form soda ash. Mixing limestone and coke in vertical shaft kilns obtain carbon dioxide. The milk of lime and steam from the mother liquor containing ammonium chloride and sodium chloride recovers ammonia. The major drawbacks are: Low utilization of raw salt and the requirement of good quality limestone and coke Large effluent facilities for the treatment of the by-products. Modified Solvay process The main raw material in this process is common salt. This process does away with the use of limestone in the previous process. Ammonia and carbon dioxide are supplied from outside. In this process the lime kiln and the ammonia recovery sections are replaced with ammonium chloride section where ammonium chloride is crystallized and recovered. The end products are ammonium chloride and soda ash. This process has major advantages of better salt utilization and low effluent generation. These plants are located proximal to the fertilizer plants. The major drawbacks of this process are the availability of refined salts and the production of ammonium chloride, which finds very little usage today. Dry Liming Process The basic advantage is the perfect steam balance and reduction in the raw material inputs resulting in substantial savings in energy. The consumption of steam and lime is very less as compared to other processes. The mother liquor (the remains after sodium bicarbonate have been removed) is fed to the pre-limer. The lime from the vertical shaft kiln is crushed and passed to the pre-limer unit directly instead of making slurry. The heat of hydration of the lime and the chemical reaction raise the liquor to boiling temperature. The steam drives out the ammonia and carbon dioxide from the solution.
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