Softeners – PPR Water

Hard Water Areas – Hard water is where calcium or magnesium carbonates are dissolved in the water as it passes through the ground on its way to being processed and sent to buildings. Hard water is where the levels of these salts (usually calcium carbonate) is higher than 100 parts per million (ppm), in some regions of the country this can be higher than 300ppm such as London the South East and Yorkshire. Hardness can then be deposited in your water systems forming layers on heat transfer surfaces. This can be easily seen in places like kettles or water heaters. These layers of scale can cause a number of problems

Building up on Heat transfer Surfaces blocking the transfer of heat into water, 1mm of scale can reduce efficiency of heat transfer by 5-8% (depending on the efficiency of a system. If there is 5mm of scale the effect would be 25-40%, this is the amount of extra fuel (gas or electricity) to heat the water to the required temperature. The same is true of chilled systems meaning in hard water areas more energy is required to cool the system down.
Scale build up on heat transfer surfaces will cause differential heating of those surfaces as the scale build up is not uniform, this will lead to different expansion rates, this will lead to cracking of the heat transfer surface and eventual failure. If this is a boiler, heater or calorifier this can be very expensive and even if the plant is replaced the same thing will happen again at some later point.
Build up of scale allows places for bacteria to grow and more importantly the legionella bacteria which can cause legionnaires disease.

How a Softener Works:

Softeners consist of columns that contains Ion exchange media (the blue columns) control heads (on top of the columns) and a brine tank. This piece of equipment treats all the water passing through it to remove hardness preventing it from being deposited in the water systems.

Normal Operation
The softener in the photo (see right) is a Duplex (two columns) during normal operation one will be in service, the other will be regenerating and then waiting to come into service. The head controls this and directs the water to the column in service and also the regeneration of the one not in use.

Technical Discussion
Hardness is caused by Calcium or Magnesium Carbonates (scale) which have low solubility and their solubility is affected by temperature and pH. pH which is higher than 7 (neutral) will reduce the solubility of scale as it rises increasing above pH 8, the difference in solubility between pH 6 and pH 8 is 1000 times!! As temperature rises the solubility of scale decreases this is why kettles in hard water areas get coated in it.

How does scale get into the water? it dissolves in acid conditions as it passes through limestone or chalk rock and then is deposited where the pH is higher or temperature is raised. This means any area where water passes through Limestone or Chalk will have hard water. The Ion exchange resin in the softener has Sodium ions on it Na+ which are more reactive than Calcium or magnesium ions so they replace the, calcium/magnesium ions and sodium carbonates are very soluble so therefore don’t cause a problem. After all the sodium ions have been used up and replaced with calcium ions the softener will then need to regenerate. At this point the water flow will switch over to the second column so there is still soft water. The first column with then regenerate using brine (salt water) which will put new sodium ions back on the media and wash the calcium ions down the drain leaving the column ready to go back in service.

Common Softener Problems
Softeners should be serviced every year and if this is not done properly or as the unit gets older problems can occur. Here is a list of faults that can occur leading to the softener not working properly.Passing Hard Water This can happen for a number of reasons:

No salt in the brine tank – means the calcium salts are not removed and the hardness is left in the water going through the softener. – Fill up brine tank with salt.
Incorrect sizing – this is where a softener has been fitted that is too small for the water going through it or the hardness levels where higher than the unit can cope with. It will soften some of the water but once the media is full of calcium salts then hard water will be passed. If the pipework is too small this can cause cold water storage tanks to empty as the booster set takes water quicker than the softener can provide it. – replace softener with correct size and pipework
Head failure – this can cause a number of issues such as:
1. Water starvation as it is stuck pouring water down the drain
2. Brine tank overflowing due to stuck or broken pistons
3. Motor failure leading to system not regenerating and then passing hard water
Proper servicing will help these issues, parts may need to be replaced and for an old head, the whole head to be replaced.
Media problems- old media that cannot regenerate properly due to age or being poisoned by iron other contamination. Blinding where the media has become stuck due to other substances getting in there and preventing water from flowing. Replace media with new media.