We have discussed about the Demin Plant in the last article, do you remember? Actually softener is a type of demin plant, namely the Strong Acid Cation (SAC) Exchanger. However, the difference is that the resin softener contains a counter ion of Na+ which has a more specific duty to exchange total hardness or total hardness (cations Ca2+ and Mg2+) in the water.
So what is meant by hardness? Hardness is the mineral content or TDS in water in the form of calcium and magnesium ions, usually as carbonate, sulfate, chloride and nitrate salts. If the water contains high hardness content then the water is called hard water and if the hardness content is low then the water is called soft water. Hard water when mixed with soap will be difficult to foam, while soft water will produce a lot of foam.
There are two kinds of hardness:
- Temporary hardness: calcium and magnesium bicarbonate
- Permanent hardness: calcium and magnesium non bicarbonate (sulfate, chloride and nitrate)
It is quite easy to find out the type of hardness, that is, if the water is heated and mixed with soap it is still difficult to foam or the foam is very little, then the water contains permanent hardness.
Total Hardness is the sum of carbonate + noncarbonate hardness. The amount of carbonate and noncarbonate hardness is determined from the water analysis as follows:
- If M-Alkalinity >= Total Hardness then the Hardness is carbonate (temporary)
- If M-Alkalinity < Total Hardness then Carbonate hardness = M-Alkalinity; and Noncarbonate hardness = Total Hardness – M-Alkalinity
Why do we need to eliminate or reduce hardness levels in water? Water with high hardness levels can cause scaling (scale) on the metal surface thereby reducing the metal’s ability to transfer heat. For example, in the use of mild steel boilers, if the water contains high hardness, it will certainly cause the boiler to crust and heat transfer to decrease so that the boiler performance is not optimal. That’s why a softener is needed to convert the hardness into sodium ions.
Then what are the operating conditions for the softener? Resin Softener operates under certain conditions, such as a maximum inlet TDS of 500 mg/l, a typical linear flowrate of 12 m/hour, a bed depth of 750 mm and a service flowrate of 16 BV/hour. The regenerant chemical used is 10% NaCl with a minimum contact time of 25 minutes. Ok so this is our short article this time, we hope you find it useful. Keep learning and see you in the next article.