Level Measurement & Control

Level measurement probes for flotation applications

June 2017 Level Measurement & Control

This article aims to introduce the LTM-2 level measurement probes from Instek Control as an alternative to traditional measurement systems employed throughout the flotation industry. The LTM-2 probe was designed and developed in Germany, specifically to meet the challenges of flotation applications. The probe is a 2-wire loop powered instrument constructed from high grade stainless steel, with no moving parts it utilises a form of conductivity called the Electro Potentiometric Effect to determine the pulp/froth interface.

Put to the test in a field trial

In 2016, Booysendal Platinum’s concentrator plant agreed to trial a unit supplied by Redland Engineering, distributors for the LTM-2 in Mpumalanga and Limpopo. The probe was trialled on a column float cell, a cleaner float cell and on a concentrate sump, all applications known to pose difficulties in respect of accurate level measurement when utilising conventional methods.

Prior to the trials, level measurements were achieved by means of a bubbler for the columns, a ball-and-striker plate for the cleaner float cells, and an ultrasonic level sensor on the concentrate sumps. These methods all posed challenges, which could result in production losses through:

Bubblers on column flotation:

• Variations in the air supply to the bubbler tube affected the bubbler level readings.

• Bubbler level readings are sensitive to density changes in the froth and pulp phase.

• Frequent chokes occur on bubbler tubes.

• Calibration on bubbler tubes are labour intensive and need to be carried out regularly.

• False level readings cause instability to down-stream processes as well as unnecessary wear on control valves.

Float balls, striker plates and ultrasonics on flotation cells

• Losses occur due to either the ball and striker plate ‘getting stuck’ or when the float ball detaches from the rod.

Ultrasonics on concentrate sumps

• Froth build-up in the concentrate sumps results in false high level readings which in turn reduces the mass pull in the float cells feeding into them (Floatstar controls the air on the float cells according to the level reading from the concentrate sump). The reduced mass pull decreases the level in the sump, which creates even more froth and the net result is production losses due to low mass pull and unstable operation due to concentrate pumps cavitating.

The LTM-2 probe showed the following advantages when installed in place of the ultrasonic devices:

• No moving parts.

• Not density dependent.

• Not sensitive to froth or product build-up.

• Setup can be achieved in less than 5 minutes.

• The probes are virtually maintenance free.

• The unit accurately measures the pulp/froth interface and provides a stable feedback signal at an optimal update rate without excessive ‘damping’, all of which provides improved process control and stability.

Subsequently, Booysendal Platinum has replaced all bubbler tubes with LTM-2 probes and they will consider phasing in LTM-2 probes in the concentrate sumps on the cleaner circuit with a view to implementing them in the

flotation cells in the future.

For more information contact Raymond Karsten, Instek Control, +27 (0)12 998 6326, info@instek.co.za, www.instekcontrol.com


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