Handbook for Methane Control in Mining - AMMSA

64DESIGNING BLEEDER SYSTEMSAs part of the mine ventilation system, bleeder systems should be addressed in the overall minedesign. Designing a good bleeder system requires consideration of ground control and pillardesign, strata characteristics, contaminant liberation, airflow distribution, and the internal workingsof the bleeder system. When bleeder systems are incorporated into an existing mine ventilationsystem, the capacity of that ventilation system should be considered.There are two basic design classifications for bleeder systems used in U.S. coal mines: wraparoundand flow-through. Although there are many variations, the concept by which they allfunction is the same. 4 A ventilating pressure differential is established from the active workings,across the pillared area, to the bleeder and/or return entries. Sufficient connections are establishedbetween the pillared area and these entries for the airflow to be induced and distributedthrough the pillared area by the applied ventilating pressure differential. Gases in the pillaredarea are diluted and moved away from the active workings by the airflow induced through thepillared area. The applied ventilatingpressure is that pressurewhich actually causes the airflow.The primary differencebetween the two designs is themeans used to maintain thepressure differential across thepillared area.Figure 5–1.—Simplified illustration of a wrap-around bleeder systemfor a longwall panel.Wrap-around system designsrely completely upon ventilationcontrols constructed betweenthe pillared area and bleederentries to establish the ventilatingpressure differential.Numerous ventilation controlslocated close to the pillared areaare often necessary with thisdesign. The additional groundpressures from the pillared areaincrease the susceptibility ofthese ventilation controls todamage. Figure 5–1 is a simplifiedillustration of a wraparoundsystem for a longwallpanel. Flow-through systemsuse solid coal barriers inconjunction with ventilation4 Some unique systems have been developed for ultragassy mines affected by spontaneous combustion. Thesespecial cases are not be covered in this chapter.