Abstract
For the water quality control of marine boiler, it is very important to investigate the effects of sea water mixing on the conditions of boiler water quality such as pH, concentrations of phosphoric ion PO43-, chloric ion Cl-, and electric conductivity EC. At first, the paper investigates theoretically the change of pH, that is molarity of hydroxyl [OH-], PO43- concentration and EC due to mixing of sea water into boiler water by the consideration of the chemical reactions between scale components and phosphate/alkali type of water treatment chemicals. According to this investigation, the paper proposes a method of automatic water quality control. Secondly the paper carries out an experimental study by the use of an actual boiler in order to confirm the validity of the above theoretical investigation. The experiment reveals the followings; (1) There is some difference between the theoretical estimation and the measurement result regarding the change of pH, PO43- concentration and EC due to sea water mixing. It is found, however, the difference has a certain regular trend being related with the mixing rate of sea water. (2) The PO43- concentration can be arranged corresponding to the addition rate of some blended type of phosphate/alkali treatment chemicals even when Cl- concentration is high, provided that hardness components do not exist. (3) When the pH is kept around 11.0, there are good correlations between concentration of [OH-] and concentrations of P-Alkalinity, M-Alkalinity and PO43-, and also between EC and Cl-. Using adequately these correlations, therefore, there would be a possibility of automatic control of boiler water quality.
