Fuzzy logic control of a floating level in a refinery tank

This paper presents the development of a fuzzy logic controller that maintains a floating level in a tank on top of the atmospheric distillation unit of a refinery plant. This particular level regulation does not need any fixed setpoint as it is only required for the level to be kept between a minimal and a maximal bounds. The important constraint to take into account is to minimize the action range in order to stabilize the feed flow at the output of the tank. Besides, the system has to anticipate properly the different disturbances that can occur in the distillation unit. The development of the fuzzy logic controller is described. The membership functions and the rulebase are first initialized in order to obtain a fuzzy logic system that is equivalent to the algorithmic controller. Some particular rules are then modified according to the expert knowledge and the particular specifications required. Finally, an adaptation of the rulebase is done to take into account an evolving context in order to reject smoothly important disturbances by anticipation