Handbook for Methane Control in Mining - AMMSA

58corner and by 43% at supportNo. 4. These higher air velocitiesreduce the methane concentrationby 60% during the headgatecutout.Figure 4–5.—Walkway curtain at support No. 3 forces air overthe shearer.During the longwall cutting cycle,the walkway curtain need only bein position during the headgatecutout. Since it is not neededfor the remaining 95% of the cuttingcycle, it should be tied up tokeep it out of the way. For theremaining 95% of the cuttingcycle, the modified shearer-cleareris used.The modified shearer-clearer may need to be turned off duringthe headgate cutout. During testing of the combined systems,the high air velocity over the shearer created by the walkwaycurtain overpowered the shearer-clearer sprays and forcedwater mist over the tail-side shearer operator [Cecala andJayaraman 1994].Methane accumulations caused by inadvertent eddy zones. Certain ventilation practices leadto the creation of inadvertent eddy zones. Figures 4–6 and 4–7 illustrate two ventilation mistakesthat can cause an accumulation of methane. Figure 4–6 shows an upwind-pointing venturi spraymounted on the headgate end of a shearer. The venturi spray creates an airflow opposing themain ventilation flowdirection along the face,thus creating an eddy zonewhere methane builds up.Figure 4–6.—Upwind-pointing venturi spray creates eddy zone andmethane buildup.Another type of eddy zoneis shown in Figure 4–7,which depicts an L-shapedwing curtain used by someoperators to control dustduring the headgate cutout.Although convenientto use, it can allow theaccumulation of methane.