Scheme of chemical water preparation
for steam boilers
 
PREPARATION OF FEEDER WATER

For steam boilers the difference between the produced steam and the return condensate must be replaced with feeder water. Feeder water must be prepared in such a way that does not cause formation of sediments, deposits or corrosion. The method of feeder water preparation depends on the type of boiler, working pressure, the quantity and quality of return condensate.

To prevent formation of sediments and deposits we must remove some substances from the feeder water, which could form deposits. This can be done by means of ion exchange (softening or demineralisation) or with membrane separation (reverse osmosis).

To protect system material against corrosion we supply corrosion inhibitors into the feeder water and we regulate pH. Only the right concentration of such substances in the system water enables efficient corrosion prevention. In the system with stable water quality, under supposition that the quality of raw water is relatively stable, inhibitors can be supplied proportional to the feeder water flow. In other cases we must control the level of inhibitors regularly and adjust (add) their quantity if needed.

Corrosion dynamics can be ascertained and estimated with measurement of weight loss on corrosion coupons. These must be embedded into the circulation subject to the appropriate standards.

Chemicals for boiler water treatment normally contain hardness stabilizers and dispersants. Hardness stabilizers are substances, which prevent that eventual rest of hardness after ion exchange or in any other process of water treatment would be released in the form of deposits. Dispersants have a cleansing effect. They remove deposits which occur as a consequence of local and short-term excess of solubility of dissolved substances due to a local temperature increase or due to short-term failures in the process of water preparation.

In case of smaller boiler systems we normally dose a multifunctional chemical which contains all needed components to protect the system.
FEEDER WATER TREATMENT
The first and the biggest problem in the system is corrosion.

At the inlet into the water supply tank water is normally thermally degasified. Additionally we need to add chemical binders of oxygen. In a larger systems dosing of such chemicals is normally carried out if or when needed, based on the prior feeder water analysis. When selecting a binder of oxygen we need to pay attention to the steam purpose.

The second and not minor problem is the quality of reverse condensate. In order to cut costs of feeder water, we pay attention to the proportion of reverse condensate to be as high as possible, to be of adequate quality and clean.