Control of the ledge thickness in high-temperature metallurgical reactors using a virtual sensor

Abstract

A non-intrusive inverse heat transfer procedure for predicting the time-varying thickness of the phase change ledge on the inside surface of the walls of a high-temperature metallurgical reactor is presented. A Kalman filter, based on a state-space representation of the reactor, is coupled with a recursive least-square estimator in order to estimate online the position of the phase front. The data are collected by a heat flux sensor located inside or outside of the reactor wall. The inverse method, used here as a virtual sensor, is coupled to a classic proportional-integral controller in order to control the ledge thickness by regulating the air cooling applied on the outside surface of the reactor wall. The virtual sensor and the control strategy are thoroughly tested for typical phase change conditions that prevail inside industrial facilities. Results show that a virtual sensor that relies on a heat flux sensor embedded inside the reactor wall provides more accurate and stable information, but at a price of a more complicated installation. In that case, it is shown that the discrepancy between the exact and the estimated ledge thicknesses remains smaller than 3% at all times, and that the control strategy ensures a null steady-state tracking error, a maximum tracking error less than 10%, no overshoot and no significant time lag. © 2012 Copyright Taylor and Francis Group, LLC.