Prevention of calcium carbonate scale using electrolyzed water

Abstract

A novel technique for suppressing formation of calcium carbonate scale has been proposed utilizing the forming reaction of bicarbonate ion from carbonate ion by addition of acid created by water electrolysis in an ionic solution. A series of experiments were carried out to examine the effects of acid electrolyzed water on prevention of calcium carbonate scale formation. Firstly, the effects of temperature and flow rate on the precipitation of calcium carbonate were investigated conducting an experiment using a millimeter-sized channel in which the wall temperature can be varied from 20 to 100 °C. It was found that the temperature is crucial for formation of the calcium carbonate scale. Moreover, it was found that formation of calcium carbonate scale can be suppressed keeping its pH level 6.9 or below, by adding acid electrolyzed water to the ionic solution, such that carbonate ions completely turn into bicarbonate ions. In order to evaluate the usefulness of the proposed method for prevention of scale formation, the heat-exchange efficiency was measured by running a plate type heat exchanger. Its heat transfer performance, namely, the total of heat transfer, heat transfer coefficient and fouling thermal resistance, can be maintained without deterioration by supplying the acid electrolyzed water into the ionic solution. Furthermore, the proposed method can substantially reduce environmental burden as compared with conventional ways, since the acid electrolyzed water can be neutralized after all by mixing it with the alkaline electrolyzed water. This study indicates that the proposed method is quite useful for suppression of the calcium carbonate scale.