THERE has been a debate in the media about underground coal gasification by the burning of Thar coal.

Thar coal’s product is useful for several purposes, especially for power generation. From the ongoing deliberations it is evident that opponents of this method are many; Dr Samar Mubarakmand is the only one advocating it tooth and nail.

Being a mining engineer myself, I have been following this debate with keen interest.

All coal in Sindh is ‘lignite’, i.e. brown coal, (very young) the first rank in the ladder of coal formation. Therefore, the rocks (mostly clays and sands) over and underlying this lignite are young, weak and friable, thus are not at all self - supporting.

In the case of fire, it will result in hollow spaces by consuming coal underground. The roof of this hollow space consisting of soft, friable clays and sands will not hold for long and will collapse, thus completely filling/choking the space created by the burnt - out coal/lignite.

As huge quantities of coal will have to be burnt to feed the proposed plants, large hollow spaces will be created with no support to hold the roof/upper strata of those spaces, and will collapse filling/ choking these spaces.

Therefore, the fire once started will continue till such time the hollow space is not large enough to cause a fall. This respite may not be more than a few days at a time. The instant it reaches that stage, falls will cause choking and extinguish the fire underground.

The underground coal gasification (UGC) gasification/burning is practicable and effective in stratas which are strong and self - supporting to a great extent.

This only is possible in higher rank coals having strong self - supporting upper and lower strata. Also UGC gasification is preferable in situations where underground mining is not economically feasible due to difficult mining conditions.

Sustaining the coal for large volumes and for longer periods seems to be impossible for reasons enumerated above.

The only viable method of mining Thar coal is by ‘open pit’.

Thar coal seems not at all suitable for underground mining due to their geological formation. Mining lignite coal by underground mining method is wasteful and especially in case of Thar coal it is not at all feasible because of multi - seam deposition.

Also for power generation etc large quantities of coal are required which cannot easily be mined in this way.

SHAHID ALI BAIG Karachi