New South Wales longwall mines this year are implementing a range of equipment and management controls to meet new guidelines governing diesel particulate exposure.
Mine action is necessary, with recent statistics obtained by coal services indicating that DPM levels in some NSW underground coal mines currently exceed maximum levels stipulated under the guidelines.
The guidelines were introduced by the NSW Department of Primary Industries on February 2, outlining the monitoring and control of diesel particulates in underground environments (MDG29).
These guidelines were issued via gazettal notice, effectively making the guidelines legislation.
The guidelines call for the periodic testing of both tailpipe and atmospheric (underground) emission levels, with maximum DPM levels stipulated at 0.1mg/m^3, measured as elemental carbon (EC).
To help mines meet these guidelines and the Australian Standard (ASNZS3584), diesel vehicle manufacturers must now provide air volume required over the engine (diesel particulate signature). This is the minimum ventilation quantity required to dilute diesel particulate exhaust emissions to 0.1mg/m^3 EC.
Diesel particulate signatures must now be calculated with and without particulate filters fitted.The guidelines provide an example diesel particulate signature calculation for a 150kW, 7.2 litre engine.
In this instance, the minimum ventilation quantity required to disperse gaseous emissions to statutory limits is found to be 9m^3/s.
In the case of DPM, 28m^3/s of air is required for an unfiltered exhaust.
However, the utilisation of an exhaust particulate filter means that just 4m^3/s of air is required.
With many of the mines operating fans near the top of their curves, increasing ventilation can be prohibitively expensive, especially for older mines that struggle for air.
To increase ventilation rates, new fans are required at a cost of $60,000-100,000 each, new cabling, increased power supply, installation, new or changed brattice doors and panel redesign.
According to Micro Fresh , this type of investment typically runs into the millions of dollars, if not tens of millions.There has also been an increased focus on maintenance to reduce DPM emission levels.
Industry is to establish baseline emission levels for different machines/engines. Emissions are then not to deviate from these by more than 20% for engines that meet/exceed Tier II standards or more than 15% for engines that do not meet Tier II standards.
The guidelines also dictate that atmospheric DPM testing is carried out by NATA-certified laboratories. According to Gary Mace of Coal Services, the addition of regular DPM testing to existing statutory particulate testing was relatively easy and not costly.
Under the guidelines, operators are free to implement whatever control measure they deem appropriate to reduce atmospheric DPM concentrations below 0.1mg/m^3 EC.
These measures include increased ventilation; low emissions engine technology, regular maintenance and exhaust filtration.According to Micro Fresh Filters’ Business Development Manager, Stephen Gledhill, exhaust filtration is currently the only control measure that can feasibly reduce DPM levels in coal mines by more than 90%.
BHP Billiton Illawarra Coal has founded much of the work in this area, utilising Micro Fresh exhaust filters on its underground fleet, which played an integral part in reducing maximum DPM emission levels from 0.6mg/ m^3 in 1993, down to 0.1mg/m^3 in 2001.
In certain instances, profits resulting from productivity improvements associated with using exhaust filtration and having an effective diesel management plan have been shown to far outweigh any associated costs, Gledhill said, quoting “Best Practices in The Australian Coal Mining Industry” Steve Pratt, Chairman of the BHP Billiton Illawarra Coal Diesel Research Group (1991-2003).
Another facet of the guidelines stipulates that consideration should be given to the times when operators are at greatest risk to high emissions and tailor a diesel management plan to minimise this.
It has been identified that underground workers are at greatest health risk to DPM during periods of high use and/or large diesel engine use, for example longwall relocations; areas that are poorly ventilated; areas where older engines operate; and areas where complaints are being made by employees underground.
In anticipation of MDG29, Centennial Coal's Tahmoor diesel fleet manager Steve Thomas recently installed Micro Fresh diesel particulate filters onto the mine's PJ Berriman minecruisers and Sandvik 130 loaders.
According to Thomas, the PJB Minecruisers, which are equipped with new Tier II cross-flow Perkins engine technology, perform exceedingly well with Micro Fresh DA100 filter cartridges.
The combination of low emission engines and the new exhaust filtration technology has resulted in filter change-out periods in excess of four to five days.
Micro Fresh filtration technology has also been incorporated into the exhaust system of the PJB Flitmate, which is one of the worlds highest power underground generator set ever put into an underground coal mine.
The major aim of the Flitmate project was to develop the required equipment utilising every available emission control technology.
This included a Tier II diesel engine with a full authority electronic control system, a catalytic oxidiser, selective catalytic reducer, water-based conditioner and Microfresh exhaust filters.
According to PJB, these combined technologies provide the lowest carbon monoxide, oxides of nitrogen, polycyclic aromatic hydrocarbons, aldehydes and DPM that have ever been achieved with an underground engine.
Tahmoor's larger 130 loaders also perform well with Sandvik engine technology yielding two days between filter change-outs.
According to Thomas, since operating the Tahmoor fleet with Micro Fresh exhaust filtration technology, there has been a marked improvement in the underground environment.
Next on the agenda, Sandvik are to release their C7 Tier III package, which promises to reduce emissions considerably.
Sandvik Engineering manager Phil Nelthorpe, recently indicated that while there would still be a requirement to use exhaust filters on these engines to be in accordance with MDG29 emission levels (without increasing ventilation), filter life should be substantially increased, reducing maintenance costs.
It has been a NSW DPI requirement for some time that canisters for holding disposable DPM filters be incorporated into the exhausts of new underground coal mining diesel machinery.
According to Micro Fresh, numerous original equipment manufacturers and equipment hire groups have recently indicated that further to new vehicles, they intended to retrofit their entire hire fleet with filter canisters to cope with demand for exhaust filtration resulting from MDG29.
Taken from Australian Longwall Magazine, March 07.