Here is my basic list of top 10 tips for consideration when specifying your new longwall.
10. Keep it simple
All too often we expect a roof support to do too many things. The more jobs it has to do, the more compromised the design. It becomes a jack of all trades and a master of none. Be specific about the height range required. A large height range means a bigger leg angle and therefore less tonnes going into the roof when operating in the lower end.
Specify a realistic transport height of the supports. The smaller the transport height, the more the support design is compromised. At the end of the day, a longwall is a complex integration of many components but keep the specification as simple as possible.
Good examples: West Cliff, Ulan, New Denmark
9. Surface communications
The ability to pipe all equipment data to the surface is an invaluable tool for maintenance and for operational monitoring of the longwall, such as strata control. Surface communications are now so “smart” that live information can be analysed many thousands of miles away. I highly recommend using pressure transducers in all support legs.
Good examples: Beltana, Tahmoor, Crinum
8. Working environment
People still have to work on longwalls and travelling through them many times a day can be hazardous. Ensure a good travel way with good lighting for operator comfort. All longwall equipment should be fitted with dust suppression equipment including the powered supports. Adopt slab-type relay bars in lower seam sections.
Good example: Ulan
7. Structural design
Support designers now have a vast array of technologies as well as experience to produce effective and efficient designs. The biggest problem they face is external interference from over-ambitious audits or just plain bonkers specifications.
All hoses and components should be well protected but easy to access for maintenance and replacement. During the compatibility phase of the project, the practice changeout of all major components should be exercised. I always recommend craftsmen attend compatibility trials, as they will do the job in real life underground.
Good examples: West Cliff, Ulan
5. Web depth and tip to face
The smaller the web depth, the better your roof control and therefore the more tonnes you will produce. In most instances a web depth of 800mm is optimum. Avoid designing equipment for multiple web options. This will complicate side shield design, interchock hose lengths, relay bar design and D/A ram requirements. Tip to face should be as small as practicable, but certainly no more than 450mm before cut.
Shearer initiation and auto-steering systems are no longer science fiction. They are now standard equipment that perform a very good job with excellent consistency. Utilise the automation to full effect, including gate-end automation.
Good examples: Beltana, Broadmeadow
3. Set to yield ratio
For far too long support manufacturers have had it too easy with a set to yield ratio of 75-80%. Remember that set load determines your roof control not yield load. Specify a set to yield ratio of 90% on your longwall supports for improved roof control.
It makes no difference to the support structures, which are rated way beyond yield load anyway. Use the equipment you have to maximum potential.
2. How big?
The big question: how big should the support rating be? The big answer: as big as you can make it. The higher the support density, the better the roof control.
Another question is how wide? Experience is telling us that wider is better. The limiting factor seems to be AFC power, not geotechnical considerations.
Examples: Ulan, Oaky North, Newlands, Moranbah North, Broadmeadow
1. Power pack design and filtration
This is the heart and kidney of anylongwall system. However, unlike our own body parts we can build multipleredundancies into the power pack andfiltration systems.
Most modern longwalls now operate with a standby pump so that there is no risk of working at reduced flows orpressure. Where high-pressure pumps are used, there should also be a backup HP pump. I recommend high-pressure set pumps to ensure 90% set to yield ratios.