A water softener is one of the most used equipment in water treatment, it is used in many sectors of the industry and here we will explain how it works, how to calculate the regeneration time, the use of salt, and what it is used for.
To thoroughly discuss the operation of water softening equipment it is necessary to know concepts such as:
Table of Contents
What is called hard water?
When water is referred to as “hard” water it simply means that it contains more minerals than normal water, especially calcium and magnesium minerals. The degree of hardness of a water increases, the more calcium and magnesium there is dissolved.
This is in fact the reason that the soap does not really dissolve in hard water, or that there is a scale on pipes or household equipment.
The water hardness can be measured in grains per gallon (gr/gal) or ppm of CaCO 3 parts per million of calcium carbonate; hardness is usually expressed as the equivalent number of milligrams of calcium carbonate (CaCO 3 ).
To take it to grains of hardness, the ppm of hardness is divided by 17.1
Example: 300 ppm / 17.1ppp per grain hardness = 17.54 grains
Why is the water softener applied?
Hard water causes a high risk of limescale deposits in users’ water systems. Due to the lime deposition, the pipes are blocked and the efficiency of the boilers and tanks is reduced.
The water softener is one of the equipment used in a water bottling plant to prevent reverse osmosis membranes from embedding.
How does Water Softener work?
The hard water (water with a high content of calcium and magnesium) entering the softener through the inlet valve.
It passes through the control valve and into the main tank, where it goes from top to bottom through a resin bed that softens it.
The resin is made of specially made pearls that have been saturated with sodium ions.
Calcium and magnesium are often referred to as “hard minerals”.
Water softeners are specific ion exchangers, which are positively charged. Softeners mostly remove calcium (Ca2 +) and magnesium (Mg2 +) ions.
The softening occurs when hard minerals (calcium and magnesium ions) of water bind to the resin and exchange for sodium, which enters the water in place.
The softened water enters the long central tube, called the riser or dip tube, through the filter basket at the bottom of the tank and rises through the riser.
The water leaves the softener through the control valve to the house network.
When an ion exchanger is applied to soften the water, it will replace the calcium and magnesium ions with other ions, for example, sodium and potassium.
Basically, the exchange process occurs on the surface of a polymeric resin, when the latter is saturated, that is, when all the sodium ions are exchanged for the calcium and magnesium ions present in the feed water, it must be regenerated through of the passage of a mixture formed by sodium chloride (table salt) and water, commonly called «brine».
Softeners are sometimes even applied to remove iron when iron causes the hardness of the water. Softening mechanisms are capable of removing more than five milligrams per liter (5 mg / l) of dissolved iron.
How to know the capacity of a water softener?
The capacity of a softener varies according to the cubic feet of resin and the amount of salt used to regenerate. 1 gallon of water dissolves 3 lb of salt or 1 liter of water dissolves 360 grams of salt. On the other hand, a cubic foot of resin also has a flow of water that is capable of softening:
Normal Flow Per Cubic Foot: 5 GPM
Peak Flow Per Cubic Foot: 7.5 GPM up to 50% additional.
If we consider a peak flow, it is important to think that 100% of the water could not be softened as a normal flow would be. The cationic resin for ion exchange is what allows us to soften the water.
This is done by exchanging calcium/magnesium for sodium as the water passes through the resin.
Once this resin is filled with calcium/magnesium and the sodium is exhausted, the resin must be regenerated with a salt water solution known as brine.
A cubic foot of resin has a capacity of 25,000 grains at 9 pounds of salt, but it can vary if the amount of salt used to regenerate it varies. The estimated capacity of 1 cubic foot of resin to regenerate with:
6 pounds of salt = 20,000 grains Saves salt but regenerates more frequently
9 pounds of salt = 25,000 grains Normally used consumption
12 pounds of salt = 28,000 grains Higher consumption, but fewer regenerations
According to the above and considering 9 pounds of salt we have.
Example of calculation of a water softener:
We have 500 ppm of hardness ≈ 29,240 grains of hardness.
Next, we will take the consumption of normally used salt: 9 pounds ≈ 4.08 Kg.
Finally the feed flow per day: 1000 gpd
Therefore the softener size in feet 3 , taking the resin regeneration every 5 days would be:
(Flow x days of regeneration x hardness in gpd) / Capacity per foot 3 :
(1000 x 5 x 29,240) / 25000 = 5,848 ft 3 .
Now, if we want to calculate the days of regeneration:
For a flow of 1000 gpd and 29,240 gpg = 29240 grains per day.
According to the capacities of the softeners and considering 9 pounds of salt we have:
Considering the size of 5 ft 3, we have:
125,000 grains / 29240 grains per day = 4.27 ≈ 5 days.
When does the water softener resin need to be replaced?
When the water is not soft enough, one should first consider the problems of the salt being used, or try troubleshooting, or malfunctioning of the machinery, or the softening components. When these elements are not the cause of the unsatisfactory water softening, perhaps it is the replacement time of the softening resin or even the entire softening system.
Taking into account the above, softener resins normally last between 20 and 25 years.