are they worth their salt?
by Jim Ticcioni
Brine reclamation systems help cut costs.
Industrial process water is consumed in such vast quantities, that in sheer tonnage and bulk it far outshadows all other materials used. For example, it requires over 250 tons of water to make one ton of steel.
The Softening Process
One widely used process for softening residential and industrial process water is sodium cation exchange. This process involves the passing of hard water through a bed of synthetic resin enriched with sodium ions. The treated water is free of calcium and magnesium and now contains an increased level of sodium due to the exchange properties of the resin.
In the U.S. alone, it is estimated that the amount of water now used per day in industrial plants reaches a total of 230 billion gallons. The source of this supply may be surface waters from rivers’ lakes and streams, or ground water from deep wells and springs.
Whatever the source, all natural water supplies, either in their raw state or after treatment by a municipality, contain dissolved mineral matter. The most abundant are the bicarbonates, sulfates and chlorides of calcium, magnesium and sodium.
The hardness of water is due to its calcium and magnesium content. The term hardness was originally applied to waters that were hard to wash in, referring to the soapwasting properties of hard water.
Hard water can also cause scale formation in steam boilers and water heating systems, reducing thermal conductivity of the heat exchange surfaces and resulting in premature hardware failure and loss of efficiency.
When the sodium in the resin bed is diminished, it is said to be exhausted. The chemical energy needed to regenerate the resin is found in common salt, sodium chloride (NaCI).
In round figures, the so-called theoretical salt requirement for regeneration is 0.17 pound for 1,000 grains of hardness removed during the softening run. It is necessary, though, to use an excess of salt in order to accomplish the regeneration. The actual salt used will vary between 0.4 and 0.5 pounds per 1,000 grains of hardness removal.
This relationship, also expressed as 1 pound of salt per 2,000 grains of hardness removal, is frequently used to establish the regeneration efficiency of a water softener.
The amount of salt required to produce soft water can be calculated by using the above relationship when both the water hardness and the desired gallons of softened water are known. The following equation shows that 1,000 pounds of salt would be needed to produce 100,000 gallons of soft water from raw water containing 20 grains of hardness:
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Since salt is consumed to produce soft water, its cost often prompts customers to ask if their water softeners are worth their salt.
The Price Is Right
Salt costs vary throughout the country due to transportation costs. Typical prices ranging from 4 cents to 8 cents per pound delivered to the softener would result in a $40 to $80 cost per 100,000 gallons of soft water at a 20 grain raw water hardness level. Salt-saving techniques using lower dosages (0.25 to 0.3 pounds per 1,000 grains removal) have been tried, but not without:
- A 30 percent reduction in softener capacity
- Increased water usage due to more frequent regenerations
- Reduction in softened water quality.
Another infrequently used saltsaving technique has been gaining popularity due to innovations in process controls. Brine reclamation reuses the brine discharged to sewer during a previous regeneration for a subsequent regeneration.
While not a new concept, this method can now be performed at relatively low cost because expensive storage tanks and forwarding pumps have been eliminated. Floor space has also been significantly reduced due to fewer components.
Brine reclamation can be provided as a retrofit for existing softener installations or be integrated into a new system at a cost increase of less than 15 percent.
Adding brine reclamation to a water softener will immediately reduce salt consumption by 25 percent, improving the operating efficiency to 1 pound of salt per 2,660 grains hardness removal. The payback from saved salt and operating costs can offset the added equipment investment in less than one year. Compared to the earlier example, the cost of softened water would drop to $30 to $60 per 100,000 gallons.
Beyond the savings, however, is the issue of water quality and quantity delivered with reclaimed
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to a water softener will immediately reduce salt consumption by 25 percent. |
brine. The reclamation method capturing a select portion of dilute water brine, then resaturating it ultimately produces brine strength and brine volumes identical to those in systems using 100 percent virgin brine.
Since the water softener resin cannot distinguish the difference in brine quality, the problems with other salt-saving techniques don’t occur with brine reclamation: There is 100 percent softener capacity, identical regeneration schedules are possible and there is no loss in treated water quality.
Mr. Jim Ticcioni is director of engineering at Marlo, Inc., Racine WI. This article originally appeared in The Analist and Water Technology. Above article was provided by Mike Bunz of Summit Engineering and Sales Ltd. For further information Mike can be reached at 403-250-9780.
First published February 1997
