Modeling and control studies of a magnetically staged fluidized bed.

摘要

A column which contains a series of three fluidized beds for counter-current contacting of solid particles with a gas stream has been studied. Successful, independent control of solids holdup on each stage has been achieved by manipulating the field of a magnetic distributor-downcomer on each stage. Two methods to manipulate the field were investigated: an "on/off" method versus a continuous adjustment of the DC current used to create the field (the "leaking valve"). A model of the column, which includes pressure fluctuations in each fluidized bed, was used to design a control law based on proportional feedback control with some logic statements to compensate for interactions. Both simulated and actual performances in setpoint and disturbance rejection experiments were obtained with solids consisting of 100 percent iron, 50/50, and 25/75 percent mixtures of iron and sand. In all cases the gas stream was air.;The leaking valve approach was found to be more efficient in terms of average power consumption and in some experiments was found to yield better performances.;This is the first study of the magnetic distributor-downcomer under conditions where there is a net flow of solids through the fluidized bed. This is also the first study of a process where multiple fluidized bed stages are used and interactions are analyzed. The study of the staged fluidized beds when not all the solids are magnetic yielded new results on particle segregation within a bed as well as modifications needed in the control law.