What are the external water treatment processes?

It is generally agreed that where possible on steam boilers, the principal feedwater treatment should be external to the boiler.

External water treatment processes can be listed as:

1) Reverse osmosis- A process where pure water is forced through a semi-permeable membrane leaving a concentrated solution of impurities, which is rejected to waste.

2) Lime; lime/soda softening- With lime softening, hydrated lime (calcium hydroxide) reacts with calcium and magnesium bicarbonates to form a removable sludge. This reduces the alkaline (temporary) hardness. Lime/soda (soda ash) softening reduces non-alkaline (permanent) hardness by chemical reaction.

3) Ion exchange - Is by far the most widely used method of water treatment for shell boilers producing saturated steam. This module will concentrate on the following processes by which water is treated: Base exchange, Dealkalisation and Demineralisation.