An EKF observer to estimate semi-autogenous grinding mill hold-ups

Abstract

A non-linear observer model of a semi-autogenous grinding mill is developed. The observer model distinguishes between the volumetric hold-up of water, solids, and the grinding media in the mill. Solids refer to all ore small enough to discharge through the end-discharge grate, and grinding media refers to the rocks and steel balls. The rocks are all ore too large to discharge from the mill. The observer model uses the accumulation rate of solids and the mill's discharge rate as parameters. It is shown that with mill discharge flow-rate, discharge density, and volumetric hold-up measurements, the model states and parameters are linearly observable. Although instrumentation at the mill discharge is not yet included in industrial circuits because of space restrictions, this study motivates the benefits to be gained from including such instrumentation. An extended Kalman filter is applied in simulation to estimate the model states and parameters from data generated by a semi-autogenous mill simulation model from literature. Results indicate that if sufficiently accurate measurements are available, especially at the discharge of the mill, it is possible to reliably estimate grinding media, solids and water hold-ups within the mill. Such an observer can be used as part of an advanced process control strategy.

A Dynamic Model for a Class of Semi-Autogenous Mill Systems

“…where u w is the input rate of water [t/s], c w is the water discharge rate accompanying with the pulp [t/s]. The outflow rates of water and granules are described in detail [10]. They can be shown as…”

“…However, there is no sensor to measure the particle size in the SAG mill and the influence of rotation speed on the crushing rate is not considered. In [10], a class of SAG mill model was proposed in consideration of the influence of steel ball. Due to lacking of mining instrument and meter to measure the corresponding discharge, this method is not applicable.…”

Hybrid non-linear model predictive control of a run-of-mine ore grinding mill circuit

“…Although various state estimators have been investigated for grinding mills [31,41,42,43], it remains a challenge to estimate mill hold-ups [17,44]. In the aforementioned state estimators the states could be estimated with an average state error of less than 2%.…”

Estudo Comparativo Entre Controladores Pid E MPC Aplicados a Moinhos De Bolas Para Beneficiamento De Minério

“…O número de medições disponíveis em tempo real é geralmente muito menor do que o tamanho do vetor de estado a ser medido. Portanto, as ferramentas periféricas do circuito de controle, soft sensors, tornam-se tão importantes quanto o próprio controlador [20]. O controle utilizando MPC também permite combinações que tornam o controlador mais adaptado ao processo ou ainda melhorando seu desempenho.…”