Coal dust emissions
Air quality has the potential to be impacted by the coal dust emissions from coal mining activities, the transportation of coal from mines to designated ports and the loading operations at the port’s export terminals. Air quality monitoring and reported observations have shown that coal dust is emitted from coal trains during transit and from coal terminal stockpiles. Impacts are generally limited to those locations in close proximity to railways and coal loading terminals.
Potential effects of coal dust
Dust and fine particles (general dust) can be generated in many different ways, particularly in a city where a wide range of domestic, commercial, industrial and transport activities take place. Other sources of general dust include bushfires, strong winds and dust storms. General dust can remain suspended in the air for many days and has the potential to cause a variety of health and amenity effects depending upon the concentration, size of particles and the duration of exposure.
Health effects are mainly associated with exposure to elevated levels of fine particles PM10, particles of less than 10 microns in diameter (one micron equals one-millionth of a metre).
PM10 particles are very small and are invisible to the naked eye. By comparison a human hair is approximately 60 microns (µm) in diameter. PM10 particles can arise from combustion processes (e.g. motor vehicle engines) and mechanical processes (e.g. windblown dust).
Health effects associated with elevated levels of fine particle exposure include coughing, sneezing, wheezing and increased breathlessness. Amenity effects of elevated fine particle dust levels include short-term reduction in visibility (e.g. bushfires, dust storms).
Coal dust generally comprises a small component of total dust present in air near coal mines, railways and coal export terminals. Nevertheless, coal dust emissions can affect amenity, and predominantly comprises coarse dust particles (dustfall) of particle size generally between 50 and 200 microns in diameter. As coal dust is black in colour, it is generally highly visible. It is these dark visible dust particles that can cause nuisance due to soiling of property, surfaces and washing. The fine particle (PM10)composition of coal dust is generally quite low.
Sources of coal dust emissions from coal trains
Prior to coal being loaded on trains, coal is crushed and washed to remove impurities and a high proportion of coal dust and fine particles. Product coal typically comprises lumps of coal the size of a 20-cent piece. Until the recent development of comprehensive coal dust management plans (CDMPs), the main treatment measures to minimise any residual dust emissions has been the use of water. It has normally been a requirement that coal is supplied for transport with a specified coal surface water content (sometimes referred to as the dust extinction measure) to reduce dust emissions.
The main sources of coal dust emissions from coal trains are from:
- wind erosion of the coal surface of loaded wagons during transit
- leakage of coal particles from the doors of loaded wagons
- wind erosion of spilled coal in the rail corridor
- residual coal dust from unloaded wagons and leakage from doors; and
- coal or coal dust deposited on sills and wagon bogies.
Management of coal dust emissions from coal trains
Central and Southern Queensland
In Queensland a comprehensive set of measures to control dust emissions from coal trains has been implemented by Aurizon Limited (formerly QR National) in collaboration with the mining industry and represents best practice in Australia. Aurizon’s Central Queensland coal network is the largest in Queensland and carries 95 per cent of Queensland coal exports.
Aurizon, in conjunction with coal miners, rail haulage operators and coal terminal owners, have developed comprehensive Coal Dust Management Plans for Central Queensland coal network (PDF, 2.66MB) (CQ-CDMP) and South West Queensland coal network (SW-CDMP) to manage and minimise coal dust emissions during rail transport.
Key rail components of the CDMPs include improved loading techniques, load profiling, veneering and sill sweeping. Improved loading techniques such as load profiling and veneering at coal mine loading facilities aims to reduce parasitic load on horizontal surfaces, reduce wagon over-filling and hence coal spillage during transport, and minimise loss due to wind erosion of the coal surface during transport.
Load profiling involves profiling the loaded coal into a garden-bed shape—reducing aerodynamic drag and consequently dust lift-off during transport. Veneering involves the spraying of a bio-degradable binding polymer onto the surface of loaded coal wagons before they leave the mine rail-loading facility, forming a flexible binding layer to the surface of a loaded coal wagon. The degree of dust reduction depends on a number of factors, however wind tunnel testing has indicated a reduction of up to 75 per cent is achievable.
All rail loadouts on the South East Queensland Rail network (by end of 2013) and Central Queensland Rail Network (by mid–2014) have installed veneering systems.
New Queensland coal railways
Since 2012 all proposed new coal railways in Queensland, such as the Surat Basin Railway and Adani’s Galilee Basin Railway, have committed to or been conditioned by the Coordinator-General to develop CDMPs similar to Aurizon’s CQ-CDMP achieving outcomes broadly equivalent to or better than the CQ-CDMP.
Management of coal dust at Queensland coal terminals
Coal terminal operations are environmentally relevant activities and operate under environmental authorities conditioned by the Queensland Government . Each environmental authority impose conditions to manage and mitigate the coal dust emissions produced during operations.
A site-specific CDMP has been developed and implemented at the Port of Brisbane.
Coal dust management measures implemented at coal terminals typically comprise the following:
- The rail unloading station is an enclosed facility which helps to contain dust emissions.
- Exhaust fans create a degree of negative air pressure within the rail unloading facility and extract dust particles from the air and pass them through an air-handling system that redirects coal fines into the hopper while air is filtered and expelled.
- Wagon vibrators are installed at some rail unloading stations to dislodge remnant coal and minimise coal carry-back in coal wagons.
- Regular cleaning of the unloading facility also redirects small coal particles and remnants into the hopper.
- Water sprays at the rail receiving hoppers allow adjustment coal moisture levels as coal is transferred to terminal stockpiles.
- Covered conveyors are used to minimise dust dispersal.
- Belt washing stations clean belts and reduce coal carryback and spillage.
- Water sprays are located at transfer points to dampen coal as it is transported.
In the stockyard
- Water sprays are located around terminal stockyards, and are controlled at some terminals by an automatic system connected to real-time weather monitoring stations. Changes in weather conditions and dust levels initiate automatic responses, but these water sprays can be activated manually if needed.
- Stockpile heights are generally limited in height to make them less susceptible to wind and reduce the likelihood of dust particles becoming airborne.
- Earth mounds and trees are maintained as wind-breaks to reduce the impact of high winds and reduce dust lift-off.
- Vacuum trucks are used to remove dust from sealed roadways and other hard surface areas.
- Training in various techniques to minimise dust emissions is provided to all staff including managers, operational staff and machine operators.
On the wharf
- Covered conveyors are used to transport coal to the wharf and shiploader. Pans below the conveyors prevent spillage into the river/harbour and shields coal stockpiles for wind effect.
- Vacuum trucks are used to remove any coal residue or spillage on the wharf.
- Shiploaders feature a telescopic boom, allowing the coal to be deposited deep inside the hold of each vessel. The boom encompasses an enclosed section that minimises exposure of product coal to wind during ship loading.
- Weather forecasts consisting of three-day and daily forecasts are accessed from the Bureau of Meteorology (BOM) website.
- Continuous BOM observational data is monitored at regional sites to assist operational planning and to complement information available from on-site weather stations.
Dust monitoring and reporting
- Air quality monitoring systems are established both on-site and surrounding coal terminals to provide regular air quality monitoring and reporting to the Queensland Government.