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Mine ventilation networks optimized for safety and productivity 89

6.6 Ventilation of longwall faces in coal mines

Longwall sections require considerable more fresh air on the face than continuous
miner operations. Typical longwall panels are ventilated using between 30 and
3
50m /s (70,000–110,000cfm) of fresh air on the face. There are two fundamentally
different ventilation systems in use, bleeder ventilation systems and progressively
sealed gobs. Fig. 6.1 shows a schematic comparison of these ventilation systems.
The bleeder system usually requires multiple, parallel gate roads that can be
maintained open throughout the life of the longwall panel and is ventilated in an
“H” configuration. The progressively sealed layout is known as “U”-type ventilation.

6.6.1 Bleeder ventilation systems
Bleeder systems are systems of exhaust entries surrounding a mined-out area. They
are required in US longwall coal mines as per 30 CFR §75.334(b). The technique
was first developed in conjunction with room-and-pillar mining and was effective
in draining smaller, pillared areas of methane-air mixtures while keeping active faces
supplied with fresh air. Research [5] shows that longwall gobs cave tightly under over-
burden stresses, which reduces the permeability of the gob and limits the ability of
surrounding bleeder systems to effectively drain the methane, especially with today’s
longwall panel geometries that have widths of 300–450m (1000 to 1500ft) and may
be over 6000m (20,000ft) long. Additional research [6–8] using computational fluid
dynamics (CFD) modeling confirms that with bleeder systems, a fringe area with
methane-air-mixtures in explosive concentration may form along the edges of the

Tailgate Unmined Headgate Tailgate Unmined Headgate
coal
coal

Intake
Face Return Face
Seal Seal RR
Regulators
Sealed
gob Gob

Bleeder fan
8
(Not to scale)
Fig. 6.1 Schematic comparison of longwall section ventilation systems: progressively sealed or
U-type (left) and bleeder or H-type (right).