The PH control in the large-scale MSF plants by using drop structure type decarbonator

Abstract

The pH control by means of decarbonation is well known as the effective method for scale prevention. However, decarbonation and pH control characteristics for the large-scale plants are not so clear. So, we studied scale-up techniques for the module of MSF plants with a capacity of 100,000 m 3/d under the sponsorship of the Ministry of International Trade and Industry in Japan. We studied many decarbonators, i.e, packed tower type, spary tower type, air bubbling type and drop structure type. The packed tower type decarbonator had most reliable performance in these equipments. As the scale-up technique of the packed tower had been completed, we examined the drop structure type decarbonator that was more simple than the others. The apparatus consists of eight step channels, (3m in length, 7m in width and 0.8m in drop distance) At the results of experiments, decarbonation phenomena had been successfully revealed as the mass transfer with chemical reaction of the carbon dioxide. Decarbonation ability depended on acid addition and sea water temperature from the point of equilibrium and drop distance for the structure factor. It became clear for the estimation of decarbonation performance to be able to adapt with mixing model rowing each step channel. On the other hand, it was established for the pH control condition that brine pH could set up in the range from 7.0 to 7.8 by using the method of partial neutralization. Further, during the long time continuous operation using these apparatus, we succeeded in getting the constant performance and preventing the scale deposition.