Prescribed process

The pharmaceutical industry represents a different set of challenges for process control than the bulk chemicals and plastics sectors. Instead of gargantuan plants where large reactors make tonnes upon tonnes of relatively low-value products on a continuous basis, a pharmaceutical plant is smaller, with products produced in batches. But while each batch may only be a couple of hundred or even tens of kilos, the complex chemicals produced, active ingredients for drugs, are likely to be extremely valuable.

For the process-control engineer, this is a tricky prospect. In a continuous reactor, the conditions — temperature, pressure, concentration and so on — must be kept constant, so the task of the control system is to keep everything within certain set-points. But in a batch reaction, the system never reaches this steady state: everything continually changes. Moreover, a pharmaceutical plant has to be flexible; day to day, a single reactor may produce a range of different products.