The Asia Miner

SEP-OCT 2014

The ASIA Miner - Reporting Important Issues to Mining Companies in the Asia Pacific Region

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78 | ASIA Miner | September/October 2014 Supplier News In recent years, concern has been raised by dragline operators that existing ventilation systems used on dragline machine houses are in- effcient and inadequate at fltering dust from the outside environment. High dust levels within the machinery house have been known to cause problems with commutation and damage to electronics equipment. The longer term dust levels and effectiveness of the fltration systems have never before been measured and reported in any comprehensive or objective way which has led to a range of subjective opinions and beliefs within the mining industry as to which systems provide optimum performance. Funded by ACARP, the Australian coal industry's research program, BMT WBM has carried out a number of studies to address this issue. Bruce Manser, research project leader and engineer at BMT WBM, and Tony Egan, from ACARP, discuss the fndings which have now provided a much more comprehensive understanding of dragline cooling and dust control issues. Both Bruce and Tony also highlight several design concepts involving alternative technologies which were investigated to determine whether or not dramatic improvements in overall dust fltration effciencies could be made possible. DRAGLINE ventilation systems are needed to provide cooling air to both machinery and operator while fltration systems are needed to ensure that that air is clean. Both systems are fundamental to the suc- cessful operation of a dragline. The effectiveness of the systems vary particularly in relation to their basic design and the level of maintenance/ cleaning effort which mines are prepared to undertake. In addition to the requirement to supply clean air, a positive pressure differential must be maintained in the machine house to prevent dust from being drawn back in through the exhaust louvres. BMT WBM was engaged by ACARP to complete three major projects to address these issues – dragline machine house cooling and dust control, dragline machine house dust control, and feld testing of alter- native cartridge technologies. The initial package of work undertaken by BMT WBM focused on how the air fowed through the machine house of a typical dragline, as well as investigating the air velocities around heat generating equipment and the effectiveness of the air in carrying heat away from that equipment. The study involved site work to measure airfows and temperatures, and computational fuid dynamics (CFD) simulations of the air fowing from the ventilation fans situated on the roof of the dragline, into the machine house, over and around gearboxes and the motor generator (MG) sets as well as through the electric motors on swing, hoist and drag. There were two main challenges - ensuring that any dust collection and measurement activities did not have any adverse effects on the draglines or shovels during their operation was paramount, and es- tablishing a simple but robust means of determining the overall dust collection effciency of the fltration system on each machine tested. It was found early on in the study that measuring short term dust con- centrations inside and outside the machine house was a very unreliable way of quantifying the overall dust collection effciency of the fltration system. This particular challenge was overcome in what might be de- scribed as rather a low-tech but very logical way. Firstly, it was decided to measure exactly what the dragline operators were complaining about (the level of dust fallout both inside and outside the machine house) rather than the suspended dust concentrations and then compare the two dust fallout readings. Even implementing that had its challenges, since natural wind gusts outside the machine house and gustiness inside the machine house caused by the ventilation system and windage from the drag and hoist drums tended to make it diffcult to achieve consistent repeatable re- sults under essentially similar situations. To effectively form a windbreak for the dust fallout gauges, large plastic buckets were secured to the dragline at the selected dust fallout sampling locations in such a way as not to become dislodged during normal machine movements. Each dust fallout gauge was a plastic jar which was held in place inside the plastic bucket by means of a fexible foam donut cut to shape. The jar was readily removable and replaceable with a new jar when the time came for the jars to be sent back to the researchers for analysis. An unexpected challenge early on with these 'dust collection stations' was to ensure that they weren't mistaken for regular cleaning buckets and accidentally removed. To counter this, a number of signs were placed around the pails and a lot of adhesive used to prevent the buckets easily fnding legs and walking off. The large number of draglines and the one shovel covered under the study were spread across several mine sites and different operating companies. Also, since these were operational machines, down time was scarce and schedules had to be ftted in with. This meant that a large amount of coordination and fexibility on the part of the research- ers was required during the initial setup of the dust samplers and a very signifcant amount of assistance was subsequently required from key mine staff to regularly collect the jars at the appropriate times and send them back for analysis. This challenge was overcome by liaising regularly with the key mine staff, who, without exception rendered the necessary assistance when and as requested so as to make the proj- ect a success. The key fnding of the program was confrmation of long-held suspi- cions that current systems are not adequately removing very fne dust from the outside air. This leads to dust accumulation within the machine house which subsequently leads to re-entrainment. Personal exposure levels within the machine house for Total Sus- pended Particulate Matter (TSP) at PM10 (particulate matter with less than 10μm diameter), PM2.5 (particulate matter with less than 2.5μm diameter) and PM1.0 (particulate matter with less than 1μm diameter) were found to be well within the occupational limits set by the Australian National Occupational Health and Safety Commission (NOHSC). Howev- er, measured PM10 concentration levels on all machines indicated that they would fairly regularly exceed the more stringent criteria that would normally apply in the wider community. They would exceed, for example, the Queensland Environmental Protection Agency (EPA) and New South Wales Department of Environment, Climate Change and Water (DECCW) criteria for residential receptor locations adjacent to mines. As to which of the two main fltration systems currently used on the draglines - Dynavane or Floseps - performs better, the view is that it was not possible to make a clear statement. This is because of the need to take into account the sensitivity of each system to blockage and its effect on airfow rate into the machine house. However, both systems are susceptible to dramatically reduced fltration performance once blockage occurs. Improving dragline fltration effciencies

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