Plantwide control of an SO2 abatement plant

Abstract

This study focused on an SO2 abatement plant for a platinum group metal (PGM) smelting electric furnace. A systematic approach, using a simulated model of the plant, was followed to investigate plantwide control measures and thereby refine the plant's control philosophy. A steady-state model of a Wet gas Sulfuric Acid plant was developed using Aspen HYSYS software. The model was converted to a dynamic model to enable the evaluation of interactions within the process. This dynamic model was used while implementing a top-down, bottom-up plantwide control procedure. The results produced a control structure by which the first converter’s inlet temperature controls the final SO2 concentration. The feed gas heater’s (second heater in the system) outlet temperature is controlled by varying the steam flow rate, which is used as a means of disturbance rejection.

Furthermore, using a dynamic model to implement a systematic plantwide control procedure eliminates the need to develop complex mathematical models while providing the opportunity to continuously validate the decisions made and selected manipulated and controlled variable pairings. Additional benefits of using a dynamic simulation model to implement a plantwide control model are:

• It provides a link between steady-state optimisation and process control. • Self-optimising control is considered. • Improved understanding of the process and interactions in the process. • Provides a base model with the possibility to apply the solution to similar plants with minimal adjustment. • The opportunity of implementing dynamic matric control or model predictive control models to live plants (software dependent). • Constant consideration of the control and operation of the plant as well as the overall (plantwide) control objective.