Abstract
Modern high-pressure boilers with high feedwater make-up requirements frequently demand reduction of dissolved silica. A new magnesia process for silica removal has been developed, combining flexibility, simplicity, and economy. It can be applied to any type of water at any temperature; it can be carried out in conjunction with the usual precipitation water-softening process; and the increase in operating cost is very small.
These results are accomplished by a new method of combining a number of principles embodied in this process. Extensive investigations were conducted to determine the influence of each of various factors on the final result, and data are presented on the effects of the following: Form of magnesium used (whether precipitated ionic Mg or undissolved Mg compound), temperature, sludge-magnesium concentration, and agitation for sludge-water contact. The principles of increasing the Mg++ content, when required, by means of a novel sludge recycling process with a magnesium dissolver are described. A method of using cheap dolomitic lime as a low-cost source of magnesium is also presented.
The process lends itself advantageously to a modified Spaulding precipitator type of construction at either low or high temperature, to be followed by suitable treatment with carbonaceous-ion exchangers, when required, for complete removal of residual hardness and reduction of alkalinity to any predetermined figure.
