GB396256A - Process of and apparatus for the production of bleaching powder - Google Patents

Abstract

Bleaching-powder of low water-content is obtained in an intermittent process by the action of chlorine on lime by first chlorinating under such conditions that no substantial quantity of water is removed and until a moderate chlorine concentration at which the "wet point" is not reached is attained, and then, chlorination being continued, gradually removing water in such measure that the granular character is preserved without impairing the capacity for absorbing chlorine. In the first stage, the temperature is maintained below 40 DEG C., preferably between 25-35 DEG C. In examples, the chlorine concentration of the product of this stage varies from 23-32 per cent. In the second stage, water is removed by the use of a temperature above 45 DEG C., and preferably between 50 - 55 DEG C., with or without reduced pressure. As an alternative to reduced pressure, the water may be carried off by air employed to dilute the chlorine, or if concentrated chlorine is used, a special current of air may be passed through the apparatus. The dilute chlorine or air may be preheated to 35 DEG C. Near the end of the chlorination, the air current is decreased or shut off. When the product contains at least 36 per cent chlorine, it is completely dehydrated as by treatment with air at 45-55 DEG C. In a modification in which a pulverulent product is obtained, a continuous removal of a moderate amount of water in the first stage may be effected under a reduced pressure decreasing from 90-40 mms. mercury, a pressure of 30-50 mms. being maintained in the second stage. A suitable apparatus consists of a water-jacketed iron drum, provided with an axially mounted shaft carrying paddles, the ends of which are provided with spring-pressed scrapers. Chlorine inlets are distributed over the upper side of the shell.