On-line sensors for measuring the total ball and charge level in tumbling mills

Donkor, Sarpong Bismark

On-line sensors for measuring the total ball and charge level in tumbling mills

Master Thesis

2014

Publisher

University of Cape Town

Department

Department of Chemical Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

Tumbling mills are still the mostly used milling device in the mineral processing industry for both coarse and fine grinding applications. A number of factors affect the performance of tumbling mill. One of these factors is volumetric filling which is the volume of charge in the mill expressed as a fraction of the total volume available. The volumetric filling controls the mill throughput, power draw and product size. The common method of measuring volumetric filling is by taking in situ measurements when the mill is stationary. This method is disruptive to production due to the mill downtime involved. The use of on-line sensors for measuring the volumetric filling using acoustic, inductive proximity and conductive sensors are the new technologies attempting to monitor volumetric filling in situ. The methods are non-intrusive and low cost approach for direct monitoring of dynamic volumetric filling conditions in the tumbling mill. The dynamic volumetric filling was assumed to be directly related to static mill filling conditions. In this study, the volumetric filling was calculated from the toe and shoulder angles estimated by the CSIRO monitor (acoustic) and the Magotteaux Sensomag (inductive proximity and conductive) sensors. The CSIRO acoustic sensor was installed on a run-of-mine (RoM) ball mill at Angloplatinum UG2 Concentrator at Rustenburg, South Africa. The toe and shoulder angles were obtained from the surface vibration caused by the impact of the charge on the mill shell. The industrial scale experiments were performed at varied mill feed rate at constant ball load of 28%. In the pilot scale experiments, the Magotteaux ball mill at Frank Concentrator was equipped with a Sensomag sensor for measuring the toe and shoulder angles of the slurry and ball load based on the principle of conductance and induction, respectively. The mill was configured to operate as a RoM ball mill. The experiments were conducted at varying mill speeds (75%-85% critical speed), feed rate (1200-2800kg/hr) and ball loads (15-26%). The static mill filling was determined from physical measurements after crash stopping the mill.

Description

Includes bibliographical references.

Keywords

Chemical Engineering

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Masters

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