The main chemical feed to a chloralkali plant is salt, which must be dissolved in water to form a brine solution. However, to obtain long term performance from the cell it is necessary to produce a brine with very low impurity levels. Calcium, magnesium and sulphate are the major impurities which occur naturally in the raw salt and must be controlled during plant operation. The brine preparation section of the chlor-alkali plant consists of five process functions. These are:
• Salt dissolving,
• Primary brine treatment,
• Filtration brine
• Ion exchange, deionized brine storage
Primary Brine Treatment
In the first step of brine preparation, raw salt (sodium chloride) is dissolved in a mixture of warm water to produce a saturated brine solution. The saturated brine solution is then pumped to the primary brine treatment system where most of the calcium and magnesium (dissolved impurities) are removed by chemical precipitation. Soda ash (sodium carbonate) and sodium hydroxide are added to the brine in the primary treatment section and react with the calcium and magnesium to form insoluble solid precipitates.
Filtration of Brine
Twin Filter offers pre coat filters for this application in combination with a polishing filter. Filter aids are used to obtain long filtration cycles and the best filtration results. A polishing filter is used as a safety filter.
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