Selecting a separation technology from among 20 leading varieties depends upon a chemical’s nature, the number of phases, and the capacity, speed and efficiency required. Distillation - separating substances based on differences in volatilities - is the most widely used separation and purification method. Today, approximately 40,000 distillation towers are operating in U.S. chemical plants.
Level measurement at the bottom of a distillation tower controls the "bottoms" product rate. Poor level control could allow liquid to back up over the stripping trays causing damage and reduced yields. Too low level may cause pump cavitation. In related extraction towers, interface level control provides optimal separation from associated substances.