Batch ED Controller
Batch electrodialysis (ED) desalination, which relies on diluate recirculation to produce a desired product, is often conducted at constant voltage. I showed that constant-voltage operation under-utilizes membrane area because the applied current is much lower than the maximum current achievable early in a batch cycle. I hypothesized that designing a controlled to maximize the average ratio of applied to limiting current during a batch cycle can increase the rate of salt removal from a fixed membrane area. To demonstrate, I designed such a controller and used it to raise the production rate by up to 37%, relative to constant-voltage operation.
I additionally derived and validated an analytical prediction of the batch completion time under this type of operation. Supported by experiments, the prediction indicates that time-variant voltage-control can provide the greatest increase in production rate at high feed-to-product concentration ratios and low flow velocities. This work will assist designers and operators seeking to size, evaluate, and maximize the production performance of new and existing batch ED processes.
Concept, Modeling, Controller Design, and Experimentation