1) Sodium Hypochlorite Bleach Preparation Control System

The flow sheet in Fig. B-3 shows the process for its manufacture. Dilute caustic (NaOH) is continuously prepared, to a set concentration (15% solution), by water dilution of a 50% caustic solution and stored in an intermediate tank. From this tank, the solution is pumped to the hypochlorite reactor. Chlorine gas is introduced into the reactor for the reaction.

A. Design the control system to accomplish the following:

1. Control the level in the dilution tank.

2. Control the level in the bleach liquor storage tank.

3. Control the ratio of excess NaOH to available Cl, in the outlet stream from the hypochlorite reactor.

B. Specify the action of valves and controllers. Briefly discuss your design.

C. For safety reasons, when the flow of caustic solution from the dilute caustic tank to the reactor fails, the flow of chlorine must be stopped immediately. Design this scheme and explain it.