Published in June 2009 Australian Longwall Magazine

CSIRO Exploration and Mining’s Dr Ting Ren and Dr Rao Balusu, together with EnviroCon’s Brian Plush, have developed a new shearer scrubber system. The system was recently installed and successfully trialled on a longwall shearer at BHP Billiton’s Broadmeadow mine, with tests showing that the scrubber cuts respirable dust levels by more than half.

The successful fitting and operation of the scrubber at Broadmeadow sees the end of the ACARP-funded joint venture project between CSIRO and EnviroCon, with the project being deemed a major success by researchers and mine personnel.

The scrubber is a modular designed system consisting of an intake hood directed into the intake ventilation, a hydraulic driven fan sucking the air into an impact filtration system and a discharge duct forcing the clean air under the shearer body towards the face.

The system’s design incorporates some of the major findings from computational fluid dynamics modelling, such as the minimum capacity of the scrubber, its inlet and discharge position, and the use of water spray as an

“air curtain”.

A series of sprays are incorporated into the sides of the intake hood to create the first agglomeration impact point for the dust-water mixture prior to impact filtration removal. It also provides a positive pressure resistance to create an air curtain to stop dust entering the walkway and secondly, to entrain airborne dust out of the walkway.

The combination of the spray pressure, flow and design results in additional collection and dust behaviour modification.

An important feature of the system is the inclusion of sprays inside the intake hood as a second point of agglomeration. These sprays are finer than the hood sprays and are designed to create as small a water particle as possible to enhance dust-water bonding, with the fine mixture being drawn directly into the system for scrubbing through the filter.

The installed fan is an approved glass polyamide blade with antistatic and fire-resistant properties. The fan is driven by a bent axis hydraulic motor.

The motor is driven from the unused cowl circuit and functioned via the shearer remote to turn on or off independently of any other function.

Initial observations of the scrubber operating confirmed a significant reduction in the amount of shearer-generated dust entering the walkway. This was evident in both the maingate to tailgate floor cut and the tailgate to maingate roof cut.

“The operation of the scrubber significantly modified the airflow pattern around the shearer body close to the walkway by reducing the air velocity magnitude at some points down to 1m/s, and the water sprays mounted on the scrubber inlet are working as an air curtain to stop the dust escaping towards the walkway and helping dust capture by the scrubber,” CSIRO senior researcher Dr Ren observed during underground trials.

“The impact of the scrubber on longwall coal dust can be clearly observed when you are standing next to the shearer during the cutting cycle.”

Broadmeadow longwall mechanical engineer Mick Burgess also saw a marked improvement.

“The objective of the project was to reduce the dust exposure levels of our longwall operators in their normal working environment,” he said.

“It was evident from the initial operation that dust was being drawn from the walkways into the scrubber unit and reducing the visible dust significantly. We are now in the process of quantifying the reduction in dust exposure to confirm our initial observations.”

Burgess said the greatest challenge faced during the project was getting operators to take ownership of the scrubber system.

“The new system was a change to the usual approach of using water sprays; hence, the operators were initially sceptical on how effective the system would be,” he said.

The scrubber system was installed during a scheduled 10-hour maintenance shift. This was followed by on-shift training for each crew to ensure they were aware of what the new scrubber system was capable of achieving and to provide them the competency in its operation.

“Initial resistance quickly disappeared as the operators became more confident in its ability to reduce dust and this has led to further improvement suggestions from the operators themselves,” Burgess said.

“We view the current scrubber system as a work in progress and will continue to make further improvements. Eventually we would like to see the operation and cleaning of the scrubber fully integrated into our shear automation system.

“The scrubber system is simple to operate, easily maintained and would be valued by all longwall operators.”

EnviroCon senior consultant Brian Plush said during the system’s development, major mining operational issues had to be considered to get a successful result.

“The most pressing problem was to design a system that would actually stay on the shearer,” Plush said.

“With traditional mining issues such as slabbing, roof falls and AFC choking, scrubber design had to be robust enough to withstand these impacts, compact enough to minimise impact effects and also light enough not to affect shearer arm functions and speed.”

On top of this, Broadmeadow had an additional problem of face flipper bars not retracting and colliding with the scrubber on the tailgate to maingate cut. This destroyed several designs prior to the successful design of the final scrubber unit.

Plush said this problem would be overcome by resetting collision parameters in the software to make them less sensitive.

The final part of the project is to quantify dust behaviour modifications against benchmark dust data collected in previous projects.

Real-time dust collection analysis was conducted in May over four shear cycles, during day and night shifts, by Gillies Wu Mining Technology. The first test showed a 56% reduction in average dust concentration (from 1.59 to 0.7mg/cu.m) in the shearer operator position with the scrubber turned on.

A second test showed a 51% reduction (from 1.54 to 0.79mg/cu.m). In the position four chocks outbye of the operator position, average dust concentrations were reduced by 49% (from 1.59 to 0.77mg/cu.m) in the first test and 43% (from 1.35 to 0.77mg/cu.m) in the second.