Page 166 - Advanced Mine Ventilation

146 Advanced Mine Ventilation

significantly reduced dust generation. It is feasible to modify the shearer and install a
high-pressure pump in it to accomplish it. The feed water needs to be very clean.

10.4.2 Water Sprays
Well-designed water sprays are the next best way to control dust on longwall faces. A
minimum of 100 gpm at 100 psi is recommended [11]. Ideally, there should be a spray
behind each cutting bit, but in general, the larger the number of sprays, the better the
dust control. The location of spray is also important. When they are arranged in a
manner that directs the dust cloud away from the operator and holds it against the
coal face, it can reduce the inhaled respirable dust by 30%e50%. Fig. 10.6 shows a
typical layout that is called the shearer-clearer spray system. It is commonly used
on all US longwall mining faces.

10.4.3 Scrubbers on Longwall Shearer
Although highly desirable, no successful design has been developed yet owing to
height limitations. Efforts to design a longwall scrubber should continue.

10.4.4 Ventilation Air
Longwall ventilation air quantity is more often dictated by gas emissions on the face. It
is generally more than adequate to dilute dust concentrations at the operator’s station
below statutory limits. Federal law requires a velocity of air at 400 ft/min at the tail
2
0
gate. Assuming a cross section of the longwall face at 65 ft (10 wide 6.5 high),
0
the minimum ventilation air required is 26,000 CFM. Except for a mildly gassy
coal seam, it is totally inadequate. Actual ventilation air quantity ranges from
35,000 to 70,000 CFM depending on the gassiness of the coal seam and degree of
degasification achieved [12].

Fig. 10.6 The shearer-clearer system on a longwall face.