Installation/Relocation
The initial installation of a set of longwall
equipment and subsequent relocations, which involve recovery, transport and
installation operations, are major logistical operations and require detailed
planning in advance and close supervision during the exercise. The planning
should start prior to development as cut-throughs need to be located at
particular spacings around longwall start and finish points to assist recovery
and installation operations. It can also be advantageous to mine additional
access points (often referred to as "chutes") along a face start line and at the recovery or
finish line, where
these are practical. The extra access points can assist in reducing the
installation and recovery time.
Some mines adopt the practice of pre-driving a
longwall recovery roadway and mining the longwall face into this roadway to
finish. This procedure has the advantage of eliminating the need for the
"bolt-up cycle" (a very slow process) while approaching the finish point to
secure the roof where the supports are to be removed. This would already be
done in the pre-driven roadway. The big risk with this procedure is a massive
failure of the narrowing pillar of coal as the face approaches the pre-driven
roadway; such a failure would make the face recovery very difficult and
possibly hazardous. Only a few mines are sufficiently confident of the
stability of this narrowing pillar to accept the risk.
Most mines hire additional labour and equipment for
the installation, recovery and relocation work as it is difficult to justify
the cost of retaining these resources for use during a period of around four
weeks (depending on the size of the wall and distance to be travelled), maybe
once a year (depending on longwall block lengths and production rates).
Further, much of the equipment is specialized (eg special vehicles to transport
supports and the shearer) and would otherwise remain idle for much of the time.
The opportunity is usually taken during most longwall
changeouts (i.e. relocations) to bring key components of the longwall (e.g.
shearer, AFC drives, possibly supports) to the surface for overhaul, repair or
replacement. Again, much of the overhaul and repair work is outsourced to OEM's
and external workshops.
The need for non-mine resources makes forecasting and
scheduling important as such resources are frequently in heavy demand and have
to be reserved well in advance. Workshop space and resources for equipment
overhaul and repair must also be available to ensure the equipment can be
turned around and sent back without delaying recommencement of the longwall.
In most cases, equipment has to be recovered and
re-installed in a particular order which places additional constraints on the
process.
Some mines are fortunate enough to be able to carry
some extra items of longwall gear and are able to install this on the new face
in advance of the completion of the previous wall. This takes a lot of the
pressure off the relocation process, but the extent to which extra gear can be
purchased depends on a cost/benefit analysis for that particular mine. The
ability to share equipment between a number of mines in a group can also be a
great advantage in this regard, but this would limit the degree to which
equipment can be tailored to the needs of individual mines.
Because of the number of items of equipment, much of
it heavy and bulky, it is important that transport routes underground are
planned in detail and these routes are cleaned and prepared in advance of the
move. It is ideal if one-way routes can be arranged to avoid having to shunt
large equipment to enable other vehicles or equipment to pass.
Storage areas must be allocated to place equipment which
may be recovered early then re-installed late in the process and to place
equipment when installation proceeds slower than the recovery process. It may
be necessary to prepare storage areas on the surface as well, particularly if
major overhaul or repair is required for supports.
The whole process has to be integrated with other mine
operations which in most cases need to continue with minimal disruption.
Apart from the planning, the change process generally
starts when the face is 10-15m from the finish line. At around this point it is
necessary to start installing support in the roof at the face so that stable
roof can be maintained as longwall supports are removed. This will usually
involve installation of roof bolts, possibly with steel roof straps or mesh, or
a strong, flexible, plastic mesh. In lower height seams it is also common to
cut extra height on the face over the final 10-15m to facilitate support and
recovery operations.
At the final two shears extension pieces are attached
to the chock/AFC connections to allow the AFC to be pushed over while leaving
the chocks back. This is necessary to gain sufficient width ahead of the chocks
to allow chocks to be withdrawn across the face line.
Once production is completed, removal of gate road
equipment can commence while the coal face is supported, often with rib bolts
and mesh (which may be a continuation of the plastic roof mesh used). Sprayed
grout has also been used to support the coal face.
An aspect of relocation which does not always receive
the attention it should is ventilation. If, as is normal, recovery and
re-installation operations occur at the same time, then effectively the mine
has an additional panel to ventilate during this period. The ventilation
required at the old face to deal with gas may reduce as the gas make will reduce
when production ceases, however the use of a number of high powered diesel
equipment may require just as much or even more ventilation . Often it is not
possible to set-up the long term ventilation circuit properly because access
needs may prevent construction of control devices - time and resources may
therefore be required to complete the ventilation changes after completion of
the relocation and before production can recommence.
The process of recovery, transport and re-installation
will vary from mine to mine or even within mines depending on mining
conditions, distances equipment has to be transported, the amount of
equipment to be sent to surface, resources available and at times personal
preference.
The Longwall 20 to Longwall 21 Changeover Recovery Manual is an example of a plan used for one relocation
at one mine which is reasonably typical. Other mines may have particular
problems, a different transport system or other factors giving rise to
variations, but in general the processes will be similar. The additional height
available in thicker seams makes some aspects easier, but the equipment to be
moved is typically heavier and bulkier.
