CSIRO Exploration and Mining's Ting Ren and Rao Balusu, together with EnviroCon's Brian Plush, have developed a shearer scrubber system prototype which they are about to trial at BHP Billiton Mitsubishi Alliance's Broadmeadow mine in Queensland's Bowen Basin.

By the end of the ACARP-funded project, the team hopes to provide the longwall sector with a new type of shearer dust scrubber system which will significantly reduce the dust contamination levels generated by the shearer cutting.

Dust exposure on the longwall face remains a major challenge and a sensitive issue for mines. Although significant progress has been achieved, respirable dust exposure on longwall faces is significantly higher than in other mining environments, and the problem of containing dust concentration to acceptable levels continues to be a challenge.

“As the current trend in the industry is to introduce wider longwall faces and operate thick seams, there is an urgent need for detailed investigation of various options and development of appropriate dust control technologies and strategies for high production faces," Ren said.

“As the majority of the dust control techniques have been developed in the USA, UK and other western countries, their applications are more applicable to low to medium coal seam heights up to three metres.

“Dust control in thick coal seams appears to be more problematic, particularly due to the differences in face airflow patterns and potentially higher dust generation and pick-up in thick seams.

“In addition, face spalling ahead of the cutting drum also generates a high proportion of respirable dust in thick seam longwall faces."

CSIRO has already done a large amount of work looking into reducing dust exposure.

Two ACARP-funded projects looked into computational fluid dynamics (CFD) modelling to improve the understanding of dust flow patterns around the longwall shearer and walkway under different operating conditions.

The project also investigated a range of dust control options for reducing operators’ dust exposure levels.

“During these simulation studies, the shearer scrubber system has shown to be capable of significantly modifying the airflow patterns around the maingate cutting drum and reducing dust roll-up towards the walkway area," Ren said.

CSIRO is working with EnviroCon on the current ACARP project to develop and fabricate the shearer scrubber system for the Broadmeadow field trial.

The shearer scrubber system has been developed as a stand-alone module and can be fitted to any shearer onsite.

The scrubber is manufactured from a minimum of 10mm steel for the intake duct up to the face of the ranging arm and then a 16mm plate over the ranging arm. For the fan housing and dust box a 6mm steel will be used as it is protected by the shearer covers.

The knit-mesh panels will be all stainless steel, with a minimum of two in the dust box. All internal spray will be brass.

The team will bolt the intake duct to the inspection cover bolts already existing on the ranging arm by replacing the existing 16mm diameter bolts with ones long enough to hold the duct in place.

The dust box will be bolted to the body of the shearer with negative pressure flexible duct joining the intake duct to the scrubber box and fans. The intake duct will also be bolted to the top of the ranging arm.

The scrubber works by utilising two hydraulically driven fans in parallel to produce up to 10 cubic metres per second of air. This air is drawn through the intake duct fitted to the shearer arm, sucked through a preconditioning fogging chamber to encourage agglomeration and then forced into two knit-mesh panels to remove the dust/water particles from the air. Clean air is then discharged along the face.

No modifications need to be done to the shearer when fitting the scrubber other than the relocation of hardware that may be in the way of the fan housing and exhaust duct.

“We plan to put a priority valve in the main oil feed line to the shear-up, shear-down function with a solenoid valve to switch the flow to the scrubber once shear demand has ceased,” Plush said.

“The scrubber will run until the ranging arm is required to move, at which time the solenoid will switch flow to the arm. Heat generation in the oil will be monitored during the trial to ascertain if a heat exchanger will be required."

The team will install the scrubber at Broadmeadow and commission it before the end of June. Trials will start around mid-July and continue for about a month. Plush said comprehensive gravimetric testing will be performed to quantify performance of the scrubber.

Based on the field trial results, Ren said the design of the dust scrubber may be modified to improve the performance of the system.

“These modifications may include relocation of the scrubber inlet or increasing its area of cross section, and streamlining of the ducting arrangement on the shearer body," he said.

Next, further field studies will be conducted to demonstrate the effectiveness of the system in a thick seam longwall face.

“These studies will evaluate the efficiency of the shearer scrubber system on reducing the operators’ dust exposure levels,” Ren said.

“Detailed respirable dust surveys should be carried out on the longwall face to quantify the effects of the shearer scrubber system on both the dust concentration levels in the walkway and on the operators’ dust exposure levels."

Together with the field trials of the shearer scrubber system, CSIRO is continuing its investigation into the airflow and dust dispersion patterns along the longwall, particularly for respirable dust particles from the chock movements near the maingate and those dust particles escaped from the beam stage loader (BSL).

CSIRO is currently applying for support from ACARP to conduct a study to evaluate the effectiveness and applicability of ultra-fine water mist technology for the suppression of both respirable and inhalable particles in underground coal mines.

The aim of the project is to develop and test a new venturi system based on ultra-fine water mist technology to significantly reduce airborne respirable dust generated on medium and thick seam longwalls, particularly those dust particles from the advancement of maingate chocks and the intake ventilation passing the BSL on to the longwall face.

The system will also be tested near the tailgate chocks to assist the dispersion of methane near the return corner and reduce the total dust make from the longwall.

“It is anticipated results from this investigation would help the introduction and implementation of automatic dust suppression systems in longwall panels that are much effective with more precise spraying, reduced water and electricity consumption, and minimal down time and maintenance," Ren said.