LONGWALL OR NOT?
The large majority of coal mines, existing or planned, work with the aim of maximum production at minimum cost and in the majority of cases a correctly designed and well operated longwall installation is the best means of attaining this objective. Few mines are able to operate profitably where the ratio of first to second workings is high.
Nevertheless, there are cases where longwall mining may not be the best option, for example:
- Where the market for the product is limited; longwalls are not generally successful with intermittent operation. Though a longwall could be operated continuously to complete a block and the product stored on surface, it must be remembered that the coal is paid for when it is mined but does not provide income until sold or used. Storage on the surface is also an additional cost and in some cases coal quality deteriorates when stored in air;
- Where the mining lease contains a large number of seam discontinuities (longwall systems generally do not handle discontinuities of any significant size well) or other restrictions on the size of longwall blocks such as lease boundaries or existing workings;
- Where surface or sub-surface structures or landforms prohibit subsidence and restrict mining to first workings only
- Where simply raising the large amount of capital required to invest in a longwall is problematic, at least until some income is available;
- Where the infrastructure available is inadequate to handle high tonnages of coal or to provide adequate supplies; or
- Where the labour force available will be difficult to train to the standard required for successful longwall operations (continuous miner operations tend to be somewhat less demanding).
Considerations such as those listed above can dictate at a very early stage that a particular lease is more suited to being worked by continuous
miner systems and the large cost of a longwall installation cannot be justified. It may be necessary to follow the full planning process to
prove such a decision but the earlier it can be recognised the less the resources which are wasted on planning an installation which will
never occur. Such a mine may never reach the star status of high production longwall mines but may well provide a satisfactory return on
investment and efficient use of a resource. The result of the planning assessment may even be that the lease should not be worked at all.