What are all the key processes that need to be controlled?

The key processes need to be identified so the proper control system could be designed. The followings are the main ones.

1. One of the most important process for the chlorine production is the brine making. Some might even call it the bottle neck. To be more specific, the last part of brine making, which was mentioned in the flow diagram few postings ago, is the ion exchange purification. The is the last stage of brine treatment which takes care of the hardness (Ca and Mg) down to 0.02 parts per million (PPM). It is particularly important to keep the hardness just under 0.02 ppm to prolong the life of the electrolyzer cells (membrane part of the cells). In order to satisfy this need, the ion exchange columns need to be regenerated as soon as the resin exhaustion occurs. Think of resins, as elements that substitute Calcium and Magnesium ions with Sodium ions. At some point they run out of Sodium ions (exhaustion) and need to be regenerated. If this regeneration doesn't occur at the right time, the purity of the brine will be compromised. This is why you'd need the right control system to ensure the right sequence of regeneration occur at the right time not too soon since regeneration is costly and not too late in order to avoid brine hardness above the threshold of 0.02 ppm.

2. Controlling temperature of brine and caustic soda at various points of the plant is crucial.

3. Control of input flow of caustic soda and brine to the electrolyzer with respect to the load on the rectifier which is another factor in production efficiency is critical.

4. Addition of water to the exit caustic soda to thin it down from 32% to 28% in order to recirculate back into the system.

5. Last and most important part of the whole system is controlled start up and shut down of electrolyzer in case of failure at any point of the production which involves a multiple number of fail-safe sequence of actions.