Boilers and cooling towers share two major water related problems: deposits and corrosion. As steam is generated by a boiler or water evaporating from a cooling tower, dissolved minerals are left behind, increasing the concentration of these minerals. Additional minerals are introduced via the water added to makeup the water lost to steam/evaporation. Eventually, the minerals reach a level (or cycle) of concentration that will cause either loss of efficiency due to scale or damage from corrosion. This level can be determined by the Ryznar or Langlier indices and correlated to a conductivity or TDS range. Most people recognize problems associated with corrosion. Effects from scale deposits, however, are equally important. For example, as little as 1/8` of scale can reduce the efficiency of a boiler by 18% or a cooling tower heat exchanger by 40%!
By Myron L Company based in Carlsbad, CALIFORNIA (USA).
In ongoing operation, the substances suspended in the boiler water are concentrated. In order to avoid the negative consequences (foaming, deposits) of excessive salt content in the boiler water, specified limit values must not be exceeded. With the aid of a desalination control valve, boiler water with concentrated content is constantly removed and replaced with clean water. If the limit values are exceeded, the conductivity limitation ensures prompt switching off of the burner(s). Foreign substances that have sunk to the bottom of the boiler are removed by briefly opening a drainage valve.
Discontinuous control is used mainly in smaller steam boilers with low output since the temperature fluctuations in the boiler are fairly great as a result of irregular refilling with water. Continuous control, on the other hand, permits still more economical steam generation with high quality.
Depending on the regulations, a steam boiler must be equipped with one or more direct and/ or indirect level gauges. With direct level gauges, the liquid level can be seen directly through a glass or mica window. The use of a transparent level gauge with background illumination gives operating staff a clear separation between the water and steam zones even when viewed at a relatively long distance. Bicolour level gauges (black and white or green and red) are very suitable for camera transmission to the measuring station because of their special design and the intense LED illumination. With indirect level gauges, the water level is transmitted by a magnetic system to a display panel on the outside of a pipe.
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