Page 271 - Advanced Mine Ventilation

248 Advanced Mine Ventilation

1500 ft wide and 15,000 ft long containing nearly 5 to 7 million tons of raw coal.
Such large longwall panels offer many benefits as follows:
• Improved safety and reduced injury rate
• Improved recovery of in situ coal reserve
• Improved productivity and reduced cost/ton
On the other hand, large longwall panels cause some concerns, such as follows:
• Ventilation and methane control
• Respirable dust control
• Increased likelihood of geological anomalies, e.g., faults, washouts, etc.
These problems become more serious when the gas content of coal seams increases
with the increase in mining depths. Costs of mine ventilation and coal seam degasifi-
cation go up, and it becomes necessary to optimize the two processes to keep the mine
environment safe and the combined cost at the minimum. Drilling process for degas-
ification can also locate any geological anomalies in the panel prior to mining and
helps in respirable dust control as discussed earlier.
The optimized plan for mine degasification and ventilation with added benefitof
coal seam exploration can be summarized as follows:
1. Recover as much coal bed methane (CBM) as possible prior to mining and postmining to
minimize ventilation requirements.
2. Optimize longwall panel sizes and the size of the district depending on the gas content of the
coal seams to keep the combined cost of degasification and ventilation down.
3. Plan mine ventilation to maximize ventilation efficiency measured as the ratio of air horse-
power delivered to face to the total air horsepower created at the fans.
4. Seal all mined out areas with approved design of stoppings and recover as much CBM as
possible without making the atmosphere in the sealed area explosive.
5. Measure coal seam thickness while drilling and locate geological anomalies if any.
6. Gather all produced gases and market them after processing to defray the cost of degasifica-
tion and ventilation.

15.1 Coal Seam Reservoir Parameters

In addition to the reservoir properties discussed in Chapter 14, the following parame-
ters are the most important for planning a successful mine degasification.

15.1.1 Degree of Gassiness

It is safe to assume that all coal seams are gassy. They only vary in their degree of
gassiness, i.e., gas contained per ton of coal. For planning, all coal seams can be clas-
sified as shown in Table 15.1.
The depth of a coal seam is only a rough indication of its gas content. Direct mea-
surement of gas contents is highly recommended. The technique for direct measure-
ment of gas contents was discussed in Chapter 14.