Softener design for hard water

Softener Operation 

Thumb rules of designing a Softener

Step 1 – To Select resin quantity (ltrs) for a particular hardness (ppm) for a particular output (m3) per regeneration per hour based on regeneration level 160 gm/ltr, ion exchange capacity = 55, TDS limit = 1500 ppm

Resin Quty. = Load (ppm as CaCO3) * Flow * time

                                 Ex. Capacity

For example

    Load = Hardness = 100 ppm as CaCO3

    Flow = 5M3/hr

     Time = (Service Cycle) = 12 hrs.

     Ex. Capacity =60 gm as CaCO3

Resin Quanitity = 100 * 5 * 12

                              60

         =    100 litres

Note :

1. Na/Tc and TDS and correction factor should be applied.
2. Actual Resin Quantity = 60* correction due Na/Tc factor * Correction due to TH factor = 60 * 0.96 * 0.97 = 56 (approximately)

Hence Ion Exchange load for designing a softener is 56. These calculations are based on Ion Exchange resin and will varry from manufacturer to manufacturer resin.

Step 2 – To select vessel model for a selected resin quantity, approx. flow rates based on linear velocity min = 8 m3/m2/hr and max = 25 m3/m2/hr, and freeboard 5-100 %,

Important points on Softener

·                     Linear velocity should not be less than 8m3/m2/hr and should not be more than 25m3/m2/hr.

·                     Regeneration level, hardness leakage desired and correction factors can be found from resin supplier graph Tables.

Ion Exchange Materials: Properties and Applications