Sophisticated computer simulation has revolutionised the design and control of distillation processes. Despite this, statistics has shown that the number of column malfunctions is rising. It is believed that there is a good amount of art in preventing and trouble-shooting column operational problems. Unlike principal knowledge which can be described in equations and implemented in computer programs, the knowledge for trouble-shooting is often ill-structured. This paper describes the application of Bayesian graphical models for representation of this type of knowledge and for developing trouble-shooting systems.