Ahead of the April issue discussion on latest technologies in base metals recovery, at this year’s SME annual meeting in Salt Lake City in February, Dynamic simulation of processing high-arsenic copper concentrates in a fluidised bed roaster, was presented by A. Rajoria et al of Andritz. They present a dynamic process model for predicting the fluidised bed roasting of copper concentrates with high arsenic content. “Mass and energy balances were performed based on roasting mechanism derived from thermodynamic data of species. The reaction rate data, obtained from pilot plant studies on major reactions, were used in tuning the kinetic parameters of the model.
“IDEAS, a dynamic simulation package, is used in setting up the roaster plant model. The effect of process parameters such as concentrate feed rate, concentrate composition, airflow and cooling water rate on the temperature and conversion of roasting reactions are analysed. The plant model captures the highly transient conditions occurring during the plant start-up, shutdown and other process perturbations.”
The paper presents the application of this model in constructing a virtual plant environment for validating the operating procedures and operator training.
Roasting is a suitable pretreatment for the removal of high levels of impurities such as arsenic (As), antimony (Sb) and bismuth (Bi) from copper concentrate prior to smelting under oxidised condition. The process includes a fluidised bed roaster where most of the sulphide is oxidised to SO2, and the arsenic, along with the other impurities, is volatilised into the gas stream. The partially desulphurised calcine from the roaster is cooled and fed to the smelter to recover the metal. The average temperature of the fluidised bed should be maintained at 700°C to allow maximum arsenic volatilisation.
The process model built using IDEAS has various applications. It can be used for:
Validating Operating Procedures: The virtual plant environment created can be of great help to understand and validate the operating procedures for start-up as well as shutdown. This can also be very useful to diagnose emergency faults in real time. In this case of the roaster, a cold-start operating procedure was validated with the use of IDEAS.
Testing What-If Scenarios: The process model can be useful to test the behaviour of a particular unit operation under certain conditions, and subsequently, its effect on the operating parameters. In thi study, four typical industrial scenarios were tested (change in concentrate feed flow rate, airflow rate, cooling water rate, and concentrate feed composition), and their effects were shown on the temperature profile of the fluidised bed and arsenic volatilisation.
Control Logic Verification: The process model can communicate with the control system, i.e., either Distributed Control System (DCS) and/or Programmable Logic Controller (PLC), and hence can be used for logic and control loop verification.
Operator Training: As the process model is connected to the actual plant control system, it can be used for training. The operators, with the use of real control screens, (or Human Machine Interface – HMI) can not only operate the plant but can also be trained to understand the process and equipment interactions.
