Vale’s Carborough mine, located 20km east of Moranbah in Queensland's Bowen Basin, was developed from a box cut using three entries, one for men and materials, one for the conveyor and one return portal.

Before starting the project, the three drifts being driven to the coal seam were each ventilated by a Flaktwoods 27cu.m/s, 50-kilowatt fan purchased for the task.

Main fans MF01 and MF02 were a pair of Flaktwoods 1965s salvaged from sister mine Integra (formerly Glennies Creek) in NSW and overhauled.

While the fans were adequate for the original plan of two bord and pillar sections, the operation required four development units for gate road and panel development to prepare for longwall production in 2009.

The longwall equipment is undergoing surface commissioning this month.

Carborough had to upgrade the mine’s fans prior to additional fans MF03 and MF04 being installed on the upcast return shaft. The upgrade was part of the life-of-mine plan for the ventilation circuit, which now had to support a longwall operation.

The existing equipment and ventilation simply couldn’t cope with the planned expansion. After ducting flow testing by Flaktwoods with assistance from Dallas Mining Services’ John Rowland, the existing fan installation proved to have unacceptable shock losses and a pressure drop of around 500 pascals in the adaptor ducting.

According to Carborough ventilation officer Owen Morgan and Vale Group mining engineer Martin Watkinson in a paper presented this year at the Coal Operators’ Conference, the upgrade required elimination of the ducting shock losses by replacement, an increase in the size of the motors from 250kW to 280kW and the installation of new gearboxes with a ratio of 2.5:1.

This would give a projected impeller speed of 595rpm and capacity of 245cu.m/s, an increase from the existing ratio of 311:1 and speed of 473rpm supplying flows of only 175cu.m/s to the mine.

With the necessity of upgrading the ventilation apparent, mine management went to look for a suitable temporary fan installation to maintain the mine ventilation and prevent a shutdown over the three-day upgrade. Temporary ventilation was essential as the mine was driving longwall access roads with typical in situ gas content over 5cu.m/t.

Three mothballed Flaktwoods fans were identified as suitable equipment for the temporary solution as these fans had been previously used in the same configuration by the ventilation officer to ventilate the pit bottom development during the installation of MF01 and MF02.

“It was decided to simply bolt the three Flaktwoods fans in parallel in a steel shipping container. The shipping container was then adapted to fit the mine using mesh and brattice at the conveyor portal,” Morgan and Watkinson said.

The fans were monitored for vibration and pressure, and full predictive ventilation modelling was done using Ventsim software.

To get ready for the changeover the team prepared temporary stoppings and installed brattice rolls ready for deployment and removal. A working procedure was also established to sequence events during changeover.

“Maintaining the mine ventilation enabled the tailgate to complete its panel extension, the installation of the maingate conveyor belt in preparation for panel production and the continuation of inseam methane drainage operations,” Morgan and Watkinson pointed out.

Ventilation changes during changeover meant the mine return roadways connected to the conveyor drift became the temporary return drift, while all other ventilation circuitry remained the same, meaning only minor changes were required to maintain the gas monitoring system.

Maximum methane found during temporary ventilation was 1.2% in the tailgate return and as predicted by the Ventsim model and calculation of methane makes.

While the mine performed as the team predicted, there was some trouble during the changeover.

“One hiccup in the system was realised when a loader that was being used to install a Quickseal at 60 cut through shut down in the return with a methane trip on an NERZ monitor. The problem arose when the crew installing the Quickseal dropped the sheet to the ground and the ventilation was travelling from further inbye carrying general body concentrations of 1.2% CH4

“The ventilation officer was present in the east mains panel at the time and steps were taken to recover the loader using a temporary ventilation change.”

To recover the loader, the tailgate panel was closed off to increase the quantities to the east mains return and therefore reduce the general body concentrations in the return where the loader was located to below 1%.

While the solution worked, the time taken to recover the loader meant when the tailgate ventilation was restored, enough time had passed for methane to reach an NERZ boundary sensor. This tripped underground power and the temporary fan installation that was being powered from a 1000-volt tramming outlet on the main fan substation.

While there were only 20 minutes without ventilation, the delay came in repowering the mine.

“The whole loader recovery, that had only interrupted the tailgate ventilation for a period of 15 minutes, caused nearly two hours delay to the power in the panels,” Morgan and Watkinson said.

With the hiccup over, Carborough was able to go on to successfully change the ventilation without interrupting the workings of the mine. Ventilation capacity was lifted to 245cu.m/s capacity and the mine was able to operate with five working panels during October last year.

Morgan and Watkinson said they took away several lessons from the experience.

“Mine ventilation planning needs to cater for possible increases in ventilation requirements during the life of the mine, catering for possible additional requirements by having contingency in the available quantities/pressure available.

“Although this is mostly not the case with budget constraints, mine plans are a live document and need to be flexible, along with ever-changing market and business requirements.

“Detailed planning and dedicated supervision enabled the upgrade to be completed with minimum interference to mine operations and no hazardous accumulations of methane to occur.”