Biological and Chemical Reactor Control Opportunities

Biological and chemical process performance is largely determined by reactor performance. The stage for product quality and process efficiency and capacity is set by reaction yield and selectivity. The burden and difficulty for downstream separation and purification processes is minimized by better reactor control. In this tutorial the factors affecting reactor performance are described with examples. For chemical reactors, the general effect on reaction rate of temperature and the concentration of reactant and recycle is described. For biological reactions the effect of pH, temperature, dissolved oxygen, byproduct, substrate, and inhibitor concentration on cell growth rate and product formation rate is discussed. Basic control strategies are discussed for chemical reactions based on liquid and gas phases and for biological reactions based on cell type. Considerations for polymerization reactions are briefly outlined. The relative advantages of cooling and heating control system designs are summarized. Simple translations of variables or additions to the basic control strategies are offered for optimizing production rate. Fed-batch profile opportunities are outlined for chemical and biological reactors for faster and more repeatable batches. The dynamics of reactor response are categorized into three general types. The effect of application dynamics such as process response, controller tuning, noise, and automation system response on the ability of reactor control systems to reach setpoint quickly and reject disturbances is explored. An enhanced PID algorithm developed for wireless measurement and control is explained and the algorithm’s ability to eliminate oscillations from backlash-stiction, large update or sample times, split range discontinuities, and valve position control interactions is discussed. The use of dynamic reset limiting and directional velocity limits for preventing oscillations and safety instrumentation system activation is noted.