Characterisation of gas flow behaviour in longwall goafs, presented by Rao Balusu, CSIRO

- Outlined the behaviour of gas – air in goaf areas

- The influence of discontinuities

- The authors used tracer gases to map the flows of gas in the goaf area

- Then utilised three-dimensional computational fluid dynamics to model the field data

With the computer model, analysis could then be made as to the most efficient way the gate roads could be ventilated to control:

1. Egress of goaf gases onto the face, mid-point or tailgate

2. Restrict the ingress of oxygen to minimise spontaneous combustion

3. Determine the most effective point or points to inject inertisation gases to restrict the development of spontaneous combustion

Oxygen concentrations with dyke at 300m behind + “CAN’s” in TG

This paper shows the advancement and direction that ventilation predictive modelling can take and its utilisation can allow mine managers to be proactive in dealing with goaf gas and spontaneous combustion rather than reactive to face gas outs and incipient heatings.

Evermine as a stopping sealant agent, presented by Duncan Chalmers, UNSW.

- Part of an ACARP investigation into a rib reinforcement product

- Its elastic properties suggested promise to provide a flexible sealant for stoppings

- Lab tests showed that it could withstand a 28kPa pressure before rupture

- On rupturing a crack developed to allow the escape of air. The material acted in similar fashion to a pressure relief valve

- One field trial of a test stopping in a coal mine was conducted to test its effectiveness and the results were presented

- The stopping was subjected to three explosions generated by concussion charges of Dynagexâ

- Significant movements were produced in the stopping without the stopping failing

- At the end of the trial the stopping had significant leakage paths that could be repaired

- The main failure of this stopping was due to the method of fixing the battens to the stud props

- Even though the field trial indicated that the use of flexible membranes could be effective, further work would need to be done to prove this. One example does not prove that it is universal

Progress in ventilation. presented by John Rowland, president ventilation officer’s society of Australasia.

- This was a position paper outlining the advances that had been made technically, and looked at the role and effectiveness of ventilation officers in NSW

- Many mines have part-time ventilation officers (VO’s) and some have appointed significant numbers to take advantage of the sunset clause in the legislation

- The author suggested there appeared to be a lack of appreciation for the significance that a ventilation officer can play in the economic operation of the mine. To illustrate this he utilised a case study, showing that by paying proper attention to ventilation issues a mine could save in excess of $100,000pa due to improved efficiency of the ventilation system - it allowed the fan to be slowed while still providing the desired face quantities.

Ventilation management issues associated with increased longwall block dimensions, presented by Roy Moreby. (See edited version of this paper on ILN).

- This paper could be subtitled, “just because you can draw it, doesn’t mean we can operate it!”

- It is essential that the consequential increase in ventilation and associated gas management requirements are adequately addressed at the design stage otherwise these will constrain and restrict the economic gains that could otherwise be achieved

- “By extrapolation of the operational data it is apparent that simply scaling up existing circuit geometry will not be appropriate in many cases”

- The author suggests that by simply increasing block dimensions in all but benign situations would not be appropriate to exceed 3-4km

- If longer block lengths are to be achieved and effectively managed then there must be a review of existing prescribed limits. These would preclude the development of long blocks before compliance is unachievable

- Additionally, the pressures that would need to be generated to overcome the frictional resistance of the gateroads would give rise to a greater risk of spontaneous combustion and place significant strain on ventilation devices

Workshop Discussion

- Jason Wagstaffe delivered a short presentation of the shaft boring technique currently being undertaken at Wyee colliery and outlined the difficulties involved in conducting such a process if access is restricted.

- The afternoon discussion centred around ventilation awareness and training

- Suggestions ranged from having more case studies to raise the level of awareness to suggesting that it was still a reactive science - miners only respond to ventilation issues when they run out of air, are gassed out or there is a fan failure: “No air – ventilation becomes important”. It was suggested that it was like the dentist – you don’t visit unless the pain is too great

- The question was asked: Is the reaction due to a lack of comfort with ventilation flow, and in similar fashion the lack of comfort due to understanding of electricity?

- On a positive note, the need for more short seminars was suggested as a way that the “good news” stories can be told, and the stuff ups can be openly discussed so that we can learn from our mistakes.

* Duncan Chalmers is senior lecturer at School of Mining Engineering, University of New South Wales. He is involved with setting up and running the ventilation officers courses currently on offer through the university.