Water Softeners
Copyright © 2007
Water from most sources contains some hardness - which is calcium and magnesium that is picked up by rainwater as it filters down through the earth. Hard water is just as undesirable in boilers as it is in air-conditioning systems, cooling towers, refrigerating plants and other industrial equipment that uses hot water.
This
is because some of the magnesium and calcium in the water reverts to
it’s solid state and changes to hard scale which can bake onto hot
surfaces. In a boiler or steam generator, scale formation can cause
reduced heat transfer, thermal stress, deposit corrosion and blockages.
SCALE PREVENTION
To prevent scale in a Clayton Steam Generator a dedicated water softener can be supplied as part of the steam raising plant. The principle behind the operation of a water softener is simple. The calcium and magnesium ions in the water are replaced with sodium ions and - since sodium does not precipitate out in the steam generator - the problems associated with hard water are eliminated. The sodium in a water softener is provided by salt which is dissolved in a brine tank to replenish the softener when required.
SOFTENER OPERATION
The heart of a water softener is a cylinder filled with small plastic beads (resin). As the incoming hard water passes over the beads the calcium and magnesium ions, which have a natural positive charge, are attracted to the beads which have a negative charge. The calcium and magnesium ions displace the sodium on the beads and the result is soft water at the outlet of the cylinder.
After a period of time - which depends on how hard the water is - the resin becomes saturated with calcium and magnesium and this must be removed and replaced with fresh salt. This is done by a regeneration cycle.
REGENERATION CYCLE
To regenerate a water softener the cylinder is first backwashed to flush out dirt and to expand and loosen the resin. A large volume of a strong salt solution from the brine tank is then passed over the resin to drive off and replace the calcium and magnesium. Finally the cylinder is given a slow rinse and then a fast rinse to remove any excess salt.
A water softener can be regenerated manually by the operator or it can be fitted with an automatic regeneration system which starts the cycle after a fixed length of time or when a pre-determined amount of water has been treated.
SOFTENER TYPES
Since the water softener will be out of action during the regeneration cycle, a single cylinder softener (simplex) must be sized so that it’s daily operation will coincide with the operating time of the steam generator.
It the steam generator operates continuously, a twin cylinder (duplex) softener is needed so that the water treatment will continue in the second cylinder while regeneration is taking place in the first.
A water softener consists of one or more resin tanks, a controller to instigate and sequence the regeneration cycle, a valve arrangement to direct flow during normal operation and regeneration and a brine tank where salt is dissolved as necessary.
SIZING A WATER SOFTENER
The size of water softener required depends on the hardness of the water being treated and on the daily operating time. Our engineers will be pleased to advise on softener sizing. Where the water hardness figure is not available, a standard unit based on normal conditions can be offered and this should be checked once the actual water hardness is known.