GB871224A - Process for the cooling of alkali metal hydroxide solutions - Google Patents

Abstract

Alkali metal hydroxide solutions are cooled by contact with a positive electrically charged heat transfer surface for removal of heat from the solution. The electrically charged surface is formed by connecting the negative terminal of a direct current supply of 1 to 10 volts and 1 to 70 amperes to an electrode immersed in the solution and connecting the other positive terminal to the heat transfer surface. The current density employed in the process is from 0.05 to 2.0 amperes/sq.ft. of heat transfer surface. Alkali metal hydroxide solutions, e.g. sodium hydroxide, containing from 25-75% wt. of alkali metal hydroxide and which may also contain other salts, e.g. NaCl, NaHCO3 or Na2SO4 in proportion of at least 1% wt. usually 5 to 25% wt. are cooled from temperatures of 150-250 DEG F. to 70-100 DEG F. by contact with the heat transfer surface which may be the surface of a coil containing circulating coolant and made of nickel or nickel alloy to prevent corrosion. The use of a plurality of series connected coolers is also referred to in which solutions are cooled by a counter-current stream of water passing through the series connected cooling coils of the coolers. Each cooler of the series preferably contains a charged heat transfer plate but use is also made of a series of coolers in which only the first one or few coolers has a charged surface. In an example, an alkali metal hydroxide solution at 200-250 DEG F. is cooled by passage through a plurality of series connected coolers in which the first or first and second coolers only contain charged heat transfer surfaces and in which the solution is cooled to about 170 DEG C., the uncharged heat transfer surfaces of the remaining coolers reducing the temperature finally to 70 to 100 DEG F.