Most hospital boilers are used to supply low temperature hot water systems (LTHW), primarily for space heating. Boilers can also be used to generate steam used both for heating and other duties such as humidification, sterilisation and laundry cleaning.
In each case, closed loop water circuits with minimal evaporation or bleed losses are normally used. There is therefore no need for the blowdown procedures associated with high temperature or pressure boilers, or the associated addition of high volumes of makeup water. This minimises the requirement for sophisticated feedwater and makeup water purification systems, such as reverse osmosis units.
Feedwater will, however, still require a degree of treatment to prevent the build-up of scale, fouling or corrosion in boiler and downstream pipework, as this will lead to a reduction in efficiency, increased energy consumption and high maintenance costs. These problems are caused by naturally occurring mineral salts, such as Calcium and Magnesium, which are dissolved in the water supply. Heating the water causes these salts to precipitate and form scale. The greater the concentration of minerals and salts, the harder the water and the greater the risk of scale and fouling.
The conventional solution is to install a water softener. These devices contain ion exchange resins through which feedwater is pumped under pressure. The resins typically take the form of small spherical beads that are negatively charged with Sodium ions. In simple terms, these attract the positively charged Calcium and Magnesium ions in the water, removing the salts and at the same time releasing Sodium ions to create a feed-stream with a much lower pH; i.e. it has a lower level of alkalinity or is softer.
Water softeners are generally self-contained modular systems, complete with all pipework, manifolds, valves, sensors and control panels, which makes them easy to adapt or scale-up as the needs of each hospital change. Most high throughput systems tend to have twin resin vessels, or a duplex arrangement, where one vessel is in use while the other is being automatically regenerated using a salt solution supplied from a separate brine tank.
Although this technology is relatively simple, it is highly effective, being capable of removing up to 99% of dissolved mineral impurities from a mains water supply, with the ability of reach levels of purity up to 10 MΩ.cm.