Continuous Sodium Hypochlorite Process System

Powell Continuous Sodium Hypochlorite Process System -
General Information

Introduction

The sodium hypochlorite process is a unique process utilizing liquid chlorine and fifty percent caustic. It
will produce high quality bleach at a minimum operating cost and with maximum safety compared to
other existing commercial processes.

The physical plant is constructed with the highest quality components available to insure long service
life with a minimum of maintenance. The plant is equipped with numerous safety devices, which are intended to shut down the plant if a process upset threatens personnel or product quality. The plant is completely automatic, starts up readily on automatic control in a very short time and during operation, and requires only that someone be available to attend it if the alarm sounds.

General Description

The continuous bleach plant is available in two basic designs. If the plant is to manufacture bleach to be marketed, it must utilize heat exchangers to remove the heat of reaction. If the plant is to manufacture low strength bleach such as 50 grams per liter and the bleach will be used in an internal process, no heat exchangers are required. The rate of production for low strength bleach is specified by the customer with a maximum flow rate of 180 gallons per minute. The higher the concentration, the lower the rate of production available, i.e. the maximum flow rate for 160 grams per liter is 150 gallons
per minute. Every plant has the capabilities of making any strength desired up to 200 grams per liter by
the addition of heat exchangers. A modified unit will also use vapor chlorine coming from a chlor-alkali
cell.

The residual caustic can be controlled within very close tolerances. The maximum residual caustic for
a standard plant can be controlled as high as 1% by weight, with higher concentrations of residual
caustic available upon request.

The frame size of either plant is standardized to 7’W x 7’H x 20’L. This standardization enables the
location of the equipment and piping to be basically the same on each plant. The weight of the plant
without heat exchangers is approximately 6 tons (8 tons with heat exchangers).

Advantages of Continuous System

The elimination of a chlorine vaporization system is a major advantage of this process. Since the
continuous system uses liquid chlorine, all the equipment, services, and energy requirements of a
chlorine vaporization system are eliminated.

Another major item that is eliminated is the mechanical refrigeration, which is required when high
strength bleach is normally produced by other methods. Since the continuous system cools the bleach
by using water from a cooling tower (typically 300 to 500 tons) a considerable savings in energy,
equipment and maintenance cost is realized.

Another advantage of the continuous process is that it utilizes 50% caustic, eliminating
the need for costly dilution tanks and production space.

Since this continuous plant is completely automatic, considerable man-hours are saved in comparison
to other bleach operations. One man, including all material, handling, and testing can operate a typical
plant, which will produce 24,000 gallons per 8-hour day of 200 grams per liter sodium hypochlorite.
Major cost savings in raw materials by the continuous process are due to a 98% plus efficiency in the
use of raw materials, in contrast with the 93 – 96% efficiency experienced in batch operations. This
increase in efficiency is from a decrease in the amount of chlorate produced.

The following example will provide you with some insight on the possible savings due to the increase in efficiency: