Page 349 - Advanced Mine Ventilation

326 Advanced Mine Ventilation

went bankrupt. This truly exemplifies the benefits of coal mine degasification. The
most valuable commodity that comes out of a coal mine is a healthy coal miner.

20.2 Reduced Cost of Mining by Improved Productivity

Next to the safety of the mine workers the biggest financial benefit of degasification is
the improved productivity. In a highly gassy mine in Virginia, USA, the productivity
improved from 14 tons/man-day to 40 tons/man-day when nearly 70% of the in situ
gas was drained from the coal seam prior to mining and nearly 80% of gas was
captured from the gob areas. The cost of mining was reduced by at least 25%. For
example,
Let us suppose the mine produces 6 million tons of clean coal per year.
Sale price of coal: $150/ton. (It is a metallurgical coal.)
Annual gross: $900 million/year.
Estimated cost of mining: $300 million/year.
Avoided cost by degasification: $75 million/year.
The savings owing to degasification is thus a significant part of the net income.
Sometimes, the revenue from gas alone makes the mines profitable.

20.3 Revenues From Drained Methane

A typical mine produces 5e30 MMCFD gas depending on the thickness of coal seams
and their gas contents. At an assumed price of $5/MCF, the annual gross revenue can
range from $9 million to $54 million. The actual net profit will be less when the cost of
degasification and gas processing are included.
The actual cost of degasification will depend mainly on the gassiness of the coal
seam (see Chapter 13) and the degree of degasification needed for an uninterrupted
coal production. Table 4.1 defines the three categories of coal seams based on their
gas contents. Premining and postmining schemes were discussed in Chapters 15 and
16, respectively.
For all underground longwall mining, a generalized scheme of degasification
depending on the gassiness of the coal seam has been proposed by Thakur and Zach-
wieja [1]. The following assumptions were made

1. The longwall panel is 1000 ft wide and 10,000 ft long.
2. The coal seam has an average thickness of 6 ft.
3. The coal block to be degassed is 1300 ft by 10,000 ft, assuming that the width of chain pillars
is 300 ft.
4. The cost of contract drilling for the in-mine horizontal drilling is $50/ft.
5. The cost of a gob well is $50,000 to $200,000, depending on the depth of the mine and the
size of the borehole.
6. The cost of a well with hydrofracturing is $250,000.