Optimal Operation of an Industrial Smelter Furnace Off-Gas Cleaning System

Off-gas cleaning systems extract and treat hazardous emissions, and ensure that smelter operations are in accordance with environmental and industrial hygiene regulations. To this end, it is paramount that a well designed control structure be incorporated into the system. We first approach the problem by conducting a steady-state analysis based on a nonlinear model of the process, where the objective is to achieve safe, clean, and economic operation. Results reveal that this is accomplished by keeping the temperature in the furnace and in the two louvers at their upper bounds (active constraints). The unconstrained variable is found by applying the self-optimizing control technique, and the results indicate that a small loss is acceptable when one of the manipulated variables is fixed. The bottleneck of the system is identified as the fans' discharge pressures when we allow the feed rate as a degree of freedom. A control structure is then designed to keep pressures in the system well within the negative region such that acceptable dynamic performance in face of known, deterministic disturbance is achieved. Nonlinear dynamic simulations showed that very good dynamic performance is achieved with decentralized PI control schemes for both regulatory and supervisory designs.