Water Softening Systems
Hardness of water is measured as the concentration of the dissolved mineral salts of calcium and magnesium, and can be further categorised as temporary (carbonate hardness) and permanent (non-carbonate hardness). When water containing these hardness salts is heated, the salts become less soluble, and precipitate (unlike many other dissolved minerals which actually become more soluble as water is heated).
The precipitated hardness results in troublesome deposits, which may cause many problems. The inconvenience and problems caused by calcium are well known, and are evident in all aspects of daily life (industry, commerce, hotels, home etc.). For example:
- In steam and hot water boilers
- In cooling towers and humidification systems
- Water heaters, dishwashers and glass washers
- Coffee and espresso machines
- In mixer taps, faucets, pumps, thermostatic valves etc.
- Showerheads, bathroom surfaces, basins, toilets
The presence of hardness interferes with the efficiency of most washing processes, such as for textiles and glassware, where the final rinsed quality is critical. Also, hard water can lead to scale formation, which can be undesirable and costly in many manufacturing processes.
In an age where fuel consumption and carbon dioxide emissions are so crucial, it is shocking to discover that buildings may be burning 30 or 40% excess energy, simply due to an accumulation of lime scale in their water systems. Rough scale deposits in pipework increases the frictional losses of water passing through the system, and the narrowing of waterways forces booster sets to work harder.
These accumulative costs may result in complete failure of a system, causing considerable inconvenience to the operator. Losses experienced by hotels and care homes, for example, can be very damaging both to finances and reputation. Building Regulations Part L states that provision should be made to treat water feeding water heaters and hot water circulation systems, in areas where the total hardness exceeds 200ppm.
To add to the list of issues caused by lime scale in buildings, biological problems can also arise if scale is allowed to deposit in waterways. Lime scale provides a habitat in which bacteria can proliferate, particularly in lower velocity areas such as calorifiers or thermostatic mixing valves. For this reason, the Health and Safety Executive publish in their guidance document, HSG274 P2: The control of Legionella Bacteria in Hot and Cold Water Systems, that softening of water should be considered to avoid the formation of scale in hard water areas.
Ion Exchange Softening
The most effective method of industrial water softening solutions (removing the hardness salts Calcium and Magnesium) is by the process of ion exchange – ions are electrically charged species of the minerals dissolved in water. The water is passed through a synthetic resin, which absorbs the Calcium and Magnesium ions by exchanging them for sodium ions. When the resin is exhausted, it needs to be regenerated. The resin is recharged with sodium ions by rinsing with a brine solution (sodium chloride). The hardness ions previously removed are flushed to drain during the regeneration process.