Hybrid model of an industrial HDPE reactor

An industrial slurry high density polyethylene reactor with one outlet opening for the flow of both gases and slurry is modelled with a discontinuous system of differential algebraic equations. It is shown that the system reaches a state of sliding. Pressure, which is a fast variable, but not concentration, which is a slow variable, should be used as a manipulated variable to control the system. The dynamic characteristics of this system have been validated by plant tests and a laboratory air-water system. The notion of sliding has been extended to index-1 differential algebraic equation systems.