Originally Dendrobium was going to have access to the Nebo shafts for upcast or downcast ventilation but a change in the mine plan meant this was not an option.

 

Gas emission models produced by gas consulting company GeoGAS and ventilation modelling by Australian Coal Mining Consultants provided gas emission estimates for the three mining areas. In area 1 gas content was determined to be 2-5m3/t CH4 and in area 2, 4-5m3/t. Area 3 is split into two zones by a dyke structure and thus presents a difficult challenge in gas environment. South of the dyke gas is up to 6m3/t CH4 while north of the dyke is 17m3/t of CO2.

 

Modelling indicated that development panels south of the Area 3 dyke would be managed with an 18m 3/s open circuit auxiliary fan with 610mm diameter ducting and no requirement for gas drainage. In the last cut-through of Area 2, prior to the commissioning of Number 2 shaft, gas capture would be required where 55m3/s cannot be delivered. This will potentially occur in TG3 and MG3 prior to the commissioning of the number 2 downcast shaft.

 

Gas capture and/or drainage will be required in Area 3 for gateroad development. The ventilation requirements allow for 50m3/s to be delivered to the last cut through of the Area 3 gate roads.

 

On the longwall ventilation requirements assume a face and a longwall return general body contamination of 0.8% CH4; bleed return general body contamination of 1.5% CH4.

 

It was assumed that a minimum average ventilation velocity of 2m/s is required for the control of airborne dust. Volumes for longwalls 2 to 6 ranged from 37 to 40m/s on the face and 20-30m/s for return quantities.

 

According to BHP Billiton Illawarra manager special projects, Peter Whittall, the design of ventilation systems have traditionally been undertaken with the resultant airflow velocity maximums being 2.5m/s in belt roads, 4m/s in intake airways and 6m/s in return airways. The use of these velocities limited the Dendrobium mine intake quantity to 156m3/s while the Dendrobium Tunnel and Kemira Valley Tunnel are the only intakes to the mine.

 

“In order to mitigate against this limitation, Australian Coal Mining Consultants used maximum velocities as a design basis, which are generally 50% greater than those traditionally used. These are 3.8m/s in belt roads, 6 m/s in intake airways and 9 m/s in return airways,” Whittall said.

 

When the main fan is located at the Number 1 shaft collar, collar duty would vary from 190m3/s at 1.4 kPa to 300 m3/s at 4.5 kPa, requiring 370kW to 1.83 MW motor power capacity. When the main fan is located at the Number 2 shaft collar, collar duty would vary from 190m3/s at 1.8 kPa to 250m3/s at 5.4 kPa, requiring 471 kW to 1.86 MW power.

 

The wide range of duties requires the fans to be able to perform across a wide range over the mine’s life.

 

The fans that have been tendered are twin centrifugal Flakt-Woods fans with Variable Speed Drives (VSD) 850Kw, 690V. The VSD drives allow reduced speeds for lower duties and reduced operating costs.

 

During startup only one fan has been installed because of the low duty point with the second required during extraction of Area 1. The two fans will be installed as stand alone units with their own control systems (interlocked during twin fan operation) to allow easy relocation to the No 2 shaft during the LW 2-3 changeout.

 

For Part 1 of the Dendrobium report Click here