LONGWALL COAL MINING
Addressing ventilation air methane
Fugitive emissions from coal mining are significant , accounting for some 8.9 % of greenhouse gas emissions ( Scope 1 ) in New South Wales , Australia , in 2018-2019 , according to government data .
Most of these emissions are from underground coal mines in the form of ventilation air methane ( VAM ), a gas that is challenging for the coal industry to mitigate or use as an energy source because the air volume is large , and the methane resource is dilute and variable in concentration .
Australia ’ s CSIRO has been looking to address this issue having , in recent years , come up with a suite of technologies that aim to mitigate methane emissions by either destroying or enriching VAM from coal mines and using it to generate electricity .
The VAMMIT mitigation unit is a compact flow reversal reactor with a newly structured regenerative bed to destroy methane in a cost-effective manner , CSIRO Lead Scientist and Technology Inventor , Shi Su , explains . The second technology is a “ capture and enrichment ” unit , called VAMCAP , which collects and separates the methane from the ventilated air using carbon composites . The third technology , VAMCAT , uses a catalytic combustion gas turbine to create electricity from an otherwise waste product .
It is the first technology – VAMMIT – that South32 is running with as part of a circa-A $ 20 million ($ 13.7 million ) project that has received funding from the New South Wales Government .
This will see South32 design and construct a full-scale next generation VAMMIT unit able to demonstrate CSIRO ’ s technology . This follows previous successful trials of smaller-scale VAM technology from CSIRO at the Appin coal mine in southern NSW .
VAMMIT technology works by oxidising almost all the methane (> 99 %) in a combustion chamber heated to approximately 1,000 ° C . At this temperature , the methane is converted to water and carbon dioxide , which has a significantly lower Global Warming Potential than methane . A key feature of the technology is its ability to be self-sustaining as it doesn ’ t need additional energy to maintain the temperature in the combustion chamber .
A South32 spokesperson explained : “ Over the last few years , South32 has been supporting a number of studies and trials with Australia ’ s national science agency CSIRO to increase the effectiveness of methane capture at low concentrations in ventilation air in a safe manner . The latest of these is a four-year , commercial scale trial of CSIRO ’ s VAMMIT abatement technology at Appin commencing in 2022 , with support from the NSW Government .”
If deemed successful , this technology will expand the toolkit of safe and commercially feasible abatement technology in underground coal mines , suited to Australian conditions and requirements , according to South32 .
It will also help the mining company in its pursuit of achieving net zero greenhouse gas emissions by 2050 . This comes alongside a medium-term target to halve its operational greenhouse gas emissions ( Scope 1 and 2 ) by 2035 .
While South32 has not gone on record about how much methane it could abate with this technology , IM understands the two units being tested at Appin have the potential to abate around an estimated 30,000 t / y of the gas .
The next obvious step after such a trial would be to integrate the VAMMIT technology with the VAMCAT technology to create electricity from what would otherwise be considered a waste product .
CSIRO and South32 have previously collaborated on trials of smallerscale ventilation air methane technology at the Appin coal mine in southern NSW ( one trial unit pictured here ) solutions specifically built for different commodities and mining methods . It is 100 % script-free and made up of pre-defined logic , which , when combined with the knowledge of mining engineers , automatically determines what is practically possible to achieve across one or many mining operations , the company says .
Because of the disparate systems of existing software platforms , it has been hard to consider gas drainage at the same time as the mine ’ s production schedule , according to David Batkin , RPM ’ s Head of Product Strategy .
“ The gas drainage functionality of UGCS provides a step change in scheduling gassy underground coal mines ,” he said . “ The solution tightly integrates the drainage activities into both the mine design and the scheduling processes . It makes gas drainage a key consideration every time the schedule is updated .”
The solution , developed with some of Australia ’ s largest underground coal miners , allows the user to directly include factors that influence drainage times – like gas content and permeability – into the in-situ model . When users design a series of longwall panels , gas drainage stubs can be inserted automatically , along with the associated patterns that will be drilled from them . These drill pattern envelopes adjust dynamically based on the longwall dimensions and gateroad properties , but users are can also refine these in the model .
The rigs used to perform the gas drainage drilling are treated as independent resources and scheduled in the same way as continuous miners and longwalls . Rules govern when the drill sites become available and , once drilled , the schedule starts tracking drainage status as soon as each pattern has been drilled .
Mitigation strategies for gas drainage
challenges are typically required several years in advance if they are to be effective , RPM says .
As a result , a range of tools have been provided to analyse these challenges and communicate when they need to be implemented . Animations highlight the status of drill sites so it ’ s clear when they are available for drilling , when they are drilled and when they are being drained . The drainage status of all development is also displayed , and warnings are generated automatically whenever mining is impacted by incomplete drainage .
Batkin stated the solution has been designed to make it as practical as possible for mines with gas drainage challenges .
“ This solution has been produced in collaboration with underground miners who face these challenges day in and day out ,” he said . “ They have helped us take a very practical approach to the problem .”
IM
18 International Mining | AUGUST 2022