Bureau of Mines Report of Investigations/ 1973 

Bleeder System in Virgin Area 

in a Pittsburgh Coalbed Mine 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Rogers C. B. Morton, Secretary 

BUREAU OF MINES 

Elburt F. Osborn, Director 
This publication has been cataloged as follows: 

Krickovic, Stephen 

Bleeder system in virgin area in a Pittsburgh coalbed mine, 

by Stephen Krickovic, T. D. Moore, Jr., and J. E. Carpetta. 

[Washington] U.S. Bureau of Mines [ 19731 

8 p. illus., tables. (U.S, Bureau of Mines. Report of investigations 7805) 

1. Methane. 2. Mine gases. 3. Mine ventilation. I. U.S. Bureau of Mines. 11. Moore, T. D., jt. auth. 111, Carpetta, John E., 

jt. auth, IV. Title. (Series) 

TN23.U7 no. 7805 622.06173 

U.S. Dept. of the Int. Library 
CONTENTS 

Abstract ................................................................. 1 

Introduction ............................................................. 1 

Description of study area ............................................... 2 

Mining method and equipment .............................................. 3 

Air quantity-pressure and methane concentration surveys .................. 4 

Results .................................................................. 7 

Conclusions .............................................................. 8 

I LLUS TRA . TIONS 

1 . Study area with air. methane. and pressure measuring stations ........ 3 

2 . Air and methane volume and air pressure distributions in study area .. 6 

TABLES 

1 . Details of air and methane volumes and methane concentration 

distributions in the study area .................................... 5 

2 . Summary of air and methane volumes in active sections and in 

bleeders, and pressure differentials in butt headings .............. 7 
BLEEDER SYSTEM IN VIRGIN AREA IN A PITTSBURGH COALBED MINE 

by 

Stephen Krickovic, T. D. Moore, Jr., and J. E. Carpetta 3 

ABSTRACT 

Air quantity-pressure and methane concentration surveys were conducted by 

the Bureau of Mines in accessible portions of an area being pillared in a 

Pittsburgh coalbed mine in West Virginia. These included two mined-out and 

three active butt headings and a bleeder system. The particular mine workings 

were started in virgin coal directly from a set of main headings; the main 

reason for the study was the difficulty usually encountered in adequately 

bleeding the gobs under such conditions. Although the two separate return 

airways in each active butt heading and the North and 1 Left bleeders contained acceptable methane concentrations (0.01 to 0.78 percent in the butts 

and 0.73 to 1.0 percent in the bleeders) with significant total methane 

removal (109 cfm in butts and 631 cfm in bleeders), there were relatively 

large areas in the gobs with possible minimal airflows. This condition 

appears to have developed from lack of systematic regulation of the airflow 

across the gobs and appears to indicate the existence of considerably more 

methane in the probably low flow areas in the gob. 

INTRODUCTION 

While methane exists under pressure in the micropores, joints, and fracture systems of gassy coalbeds, it is also found in the superjacent and subjacent strata. Methane occurs in shales and sandy shales, "rooster" coal, 

porous sandstones,and in rock bedding planes; methane frequently is liberated 

in large quantities during caving in conjunction with extracting pillars. 

Although the in situ gas pressure is important in liberating methane from 

superjacent strata, the magnitude of this pressure is not known as it is in 

coalbeds. Surface degasification boreholes drilled ahead of an approaching 

pillar line or longwall face seldom produce significant quantities of methane 

until caving occurs at and near the borehole. In some, and perhaps, most 

cases, the methane liberated during caving of superjacent strata presents a 

more difficult control problem than does the methane in the coalbed. 

' Supervisory mining engineer. 

"~ining engineer. 3 Mining engineering technician. 
In Section 75.316-2 (g), (h), and (i) of the Mandatory Safety Standards, 

the 1969 Federal Coal Mine Health and Safety ~ct~ states that 

(g) The ventilation pressure differential between the active 

pillar line and the junction of any bleeder connection to the 

bleeder entries of such system should at all times be adequate to 

assure gob gas drainage to the bleeder entries. The pressure differential shall be considered adequate when perceptible airflow exists 

in all open or regulated bleeder connections, as determined with 

chemical smoke or other approved means. 

(h) The methane content of the air current in the bleeder 

split at the point where such split enters any other air split 

should not exceed 2.0 volume percentum. 

(i) When the return air courses from all or part of the 

bleeder entries of a gob area and air other than that used to ventilate the gob area is passing through the return air courses, the 

bleeder connectors between the return air courses and the gob shall 

be considered as bleeder entries and the concentration of methane 

should not exceed 2.0 volume percentum at the intersection of the 

bleeder connectors and the return air courses. 

The aforementioned safety standards can be interpreted to mean that a 

safely accessible and effective bleeder system is a basic requirement, and 

that other techniques used for the removal of methane from gob areas are 

supplementary. This is true even if mined-out butt headings or panels are to 

be sealed. 

The objective of this Bureau of Mines investigation was to determine the 

effectiveness of a bleeder system in conjunction with mining butt headings in 

a virgin area of a coal mine. 

DESCRIPTION OF STUDY AREA 

No bleeder system utilized in the pillaring of butt headings developed in 

virgin coal off a set of main headings can be considered typical because various mining plans are used. The particular study area considered here consisted of two retreating and one mined-out butt headings on one side of a set 

of bleeders (North bleeders) and one mined-out and one retreating butt heading 

on the opposite side of the same bleeders with a set of three bleeder headings 

at the back end (fig. 1). Mining was in a virgin area approximately 3,500 

feet wide and 2,600 feet long; the mouth of North bleeders was 2,900 feet from 

the main intake shaft and 3,600 feet from the main return shaft. Total static 

ventilating pressure developed by the fan was approximately 5.5 inches water 

gage 

*u.s. Code of Federal Regulations. Title 30--Mineral Resources; Chapter I-- 

Bureau of Mines, Department of the Interior; Subchapter 0--Coal Mine Health 

and Safety; Part 75--Mandatory Safety Standards, Underground Coal Mines. 

Federal Register, v. 35, No. 226, Nov. 20, 1970, p. 17905. 
FIGURE 1. - Study area with air, methane, and pressure measuring stations. 

MINING METHOD AND EQUIPMENT 

The two mined-out butt headings (1 Right and 1 Left) were developed in 

sets of four headings on 100-foot centers with the breakthroughs driven on 
approximately 60" angles and on 100-foot centers (similar to the North 

bleeders). Rooms were turned toward the North bleeders at 90' angles from the 

outside headings of 1 Right and 1 Left at the end of each 60" breakthrough. 

Borer-type continuous miners were used to mine a 13-foot width in these butt 

headings, with the recovery ranging from 72 to 75 percent. Ripper-type continuous miners were used to mine a 15-foot width in the active headings 

(2 Right, 3 Right, and 2 Left) with average recovery of 85 percent. Height 

of coal mined was 7 feet. Continuous miners discharged the coal on the mine 

floor from where conventional loaders transferred it into 10-ton-capacity 

shuttle cars for loading into belt feeders that, in turn, discharged the coal 

uniformly onto tail end of belt conveyors. Two shuttle cars serviced each 

miner. 

AIR QUANTITY -PRESSURE AND METHANE CONCENTRATION SURVEYS 

Using a station in the main intake airway opposite the North bleeders as 

the base, air pressure measurements were taken with portable aneroid barometers at the locations shown in figure 1 in 1 West mains and 1 East mains; at 

the entrance and near the working faces in 3 Right, 2 Right, and 2 Left; and 

in return airways of the active butts near the mains. A second barometer 

located at the base was read at 3-minute intervals to obtain the atmospheric 

changes during the survey. With the main mine ventilation system exhausting, 

all measured pressure values are negative with respect to atmospheric pressure. 

It was deemed inadvisable to travel to the back end of the North bleeders 

owing to roof falls and pools of water. Therefore, the negative pressure at 

the back end was calculated by the senior author on the basis of unit resistance developed in many ventilation surveys of 10,000 cfm of air flowing in a 

1,000-foot-long single airway having an effective cross-sectional area of 66 

square feet. Adjustment was made for the larger cross-sectional area in the 

North bleeders heading. Using the measured pressure differential from the 

intake to the return airways at the mouth of the North bleeders (1.02 inches 

water gage) and subtracting the calculated loss to the back end, the authors 

obtained the available negative air pressure at that point. 

All active sections were ventilated with two splits of air. Air volumes 

and methane concentrations were obtained by careful measurement of areas at 

selected locations (fig. 2) and by uniformly traversing each cross -sectional 

area with a hand-held amemometer. Hand-held methanometers were used at all 

air velocity measurement stations except for the North bleeders. Since this 

proved to be a significant location owing to the relatively large volume of 

air and methane concentration, a recording methanometer was installed at station 7 (fig. 1) to operate continuously during the 2-day study. Periodic 

readings were taken at all other stations except for the bleeder volume in 

1 Left (obtained by difference in table 1). Bottle samples were also taken to 

check the accuracy of the hand-held instruments. 
TABLE 1. - Details of air and methane volumes and methane 

concentration distributions in the study area 

Air 

measuring 

stations1 

3 Right: 

13 ..... 14 ..... 15 ..... 16 ..... 17 ..... 

Tota1..'44,900 

2 Right: 

g...... 

9a ..... 10.. .... 11.. .... 12 ...... 

Tota1..,26.800 

1 Right ... 

2 Left: 

1 ....... 

2.. ..... 3....... 

4 ....... 

Total.. 

1 East 

mains at 

1 Left: 

1 Left.. 

5 ....... 

6 ....... 

Total.. 

1 East 

Air split Airflow 

to 

bleeders, 

cfm 

19.500 

23.200 

23,000 

39,900 

317,000 

- 

volume, 

Intake 

- 

18,800 

33,800 

22,300 - 

- 

3,000 

4,900 

18,900 - 

- 

- 

40,900 

20,700 - 

,61.600 

- 

- 

- 

- 

Me 

3~leeder volume in 1 Left = 130,900 - (68,800 + 45,100) = 17,000 cfm. 

Methane in 1 Left bleeder = 665 - (451 + 90) = 124 cfm. 

*~irflow and methane concentration measured at station 7 in North bleeders. 

Remarks 

Flow to bleeder entries. 

- 

Flow to bleeder entries. 

- 

Flow to 1 West mains 

return 1.87 pct and 

56 cfm CH4. 

Flow to North bleeders 

and 1 Left bleeder. 

- 

Flow in 1 Left bleeder 

to 1 East mains return 

0.73 pct and 124 cfm 

CH, . 

Main return. 

Main return. - 

Flow in North bleeders 

445,100 

- 

1 Right 

cfm 

Return 

18,600 - 

- 

- 

6,800 

25,400 

7,100 

- 

- 

- 

13,500 

20.600 - 

12,000 - 

- 

9,700 

21.700 

- 

50,900 

80,000 

130.900 

Intake 

Pct 

- 

0.00 

.05 

.OO 

- 

- 

- 

.OO 

.OO 

.OO 

- 

- 

- 

- 

.OO 

.OO 

- 

- 

- 

- 

- 

- 

thane 

Return 

Pct 

0.14 

- 

- 

- 

.78 

- 

.10 

- 

- 

- 

.01 

- 

- 

.15 

- 

- 

.07 

- 

- 

- 

.38 

- - 

mains at 

North 

bleeders: 

7 ....... 

8 ....... 

Total.. 

1.0 pct 451 cfm CH,. 

Main return. 

Main return. 

and into bleeder entries. 

Cfm 

- 

0 

2 

0 

- 

2 

- 

0 

0 

0 

- 

0 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

Cfm 

26 

- 

- 

- 

53 

79 

7 

- 

- 

- 

1 

8 

- 

18 

- 

- 

6 

24 

- 

361 

304 

665 

- 

.13 

- 

return 

- 

90 

90 

from 

See figure 1. 

2~stimated flow into 1 West mains 

- 

- 

- 

- 

68,800 

68,800 

- 

- 

- 

- 

- 

- 
FIGURE 2. - Air and methane volume and air pressure distributions in study area. 

The survey was started on March 7, 1972, at a time when the mine was idle 

due to a strike that had started on March 2. A repeat survey was run on 

March 8 with one crew mining in 3 Right on the 8 a.m. to 4 p.m. shift. 

Despite the conditions under which the two surveys were run, the data is valid 

for evaluation of the bleeder system. 
RESULTS 

Table 1 shows in detail the measured air volumes with methane concentrations and volumes, and the methane volume and concentration in 1 Left obtained 

by difference in main returns. 

Table 2 shows summaries of air and methane volumes in operating sections 

and in bleeders as well as the pressure differentials across gobs. Data in 

table 2 show that only 25,400 cfrn (6,800 plus 18,600) of air and methane 

returned in 3 Right from a total intake of 44,900 cfm. The remainder 

(19,500 cfm) flowed by a very permeable course with a total pressure differential of about 0.3 inch water gage to the North bleeders. Approximately half 

the difference of 6,200 cfm (26,800 minus 20,600) between the intakes and 

returns in 2 Right found a permeable path near 3 Right to reach the North 

bleeders by a shortcut with estimated 3,000 cfm flowing across 1 Right gob to 

the main returns. Thus the total volume of 22,700 cfm (19,500 plus 3,200) 

reached the North bleeders for the most part by shortcuts. This left a large 

gob area in the back end of 1 Right and 2 Right with little or no airflow. 

TABLE 2. - Summary of air and methane volumes in active sections and in 

bleeders, and pressure differentials in butt headings 

I Total air I Methane volumes in ( Bleeder volume, Pressure 

Location differential, 

3 Right ... 2 Right ... 1 Right.. . 2 Left.. .. 1 Left.. .. North 

bleeders. 

Total.. 

inches 

water gage 

0.32 

.40 

.60 approx. 

.45 

1.18 

lGob flow to bleeders obtained by difference between total intak 

- 

s and returns 

volumes, cfm 

in 3 and 2 Rights and 2 Left and by estimated flow from 1 Right. 

2~ob flow to bleeder entries. 

3 Gob flow in 1 Left as obtained in table 1. 

4~easured volume in the bleeder; represents 19,500 + 3,200 + 22,900 with an 

acceptable error of 500 cfm, compared with measured 45,100 ch in North 

bleeders. 

Intake 

44,900 

26,800 - 

61,600 - 

- 

133,300 

Total methane liberated from gob areas: 

Split returns minus intake methane 111 - 2 = 109 cfm 

1 Left bleeder .............................. 124 cfm 

Return 

25,400 

20,600 - 

21,700 - 

- 

67,700 

return airways, cfm 

1 Right bleeder ............................. 56 cfm 

North bleeders .............................. - 451 cfm 

Total .................................... 740 cfm 

Left split 

53 

1 

- 

6 

- 

- 

60 

ch 

The considerable difference in flows of 39,900 cfm between the intake and 

returns in 2 Left may be ascribed to two permeable paths. The shorter path 

Right split 

26 

7 

- 

18 

- 

- 

5 1 

Total 

119,500 

'3,200 

13,000 " 22,900 

317,000 

445,100 

65,600 

Methane 

- 

- 

56 

- 

124 

451 

631 
was across the gob to the North bleeders with a pressure differential of 

slightly less than 0.45 inch water gage; the longer path was along the right 

edge of 1 Left gob and a short bleeder from this portion of gob to 1 East 

mains with a significant pressure differential of 1.18 inches water gage. The 

flow in the longer path was 17,000 cfm, and the flow in the North bleeders was 

45,000 cfm. Thus, there was little or no gas flow across an appreciable area 

of 1 Left and 2 Left gobs. 

Referring to table 2, 109 ch (2 cfm intake methane subtracted) of methane were removed from the pillared areas in 3 Right, 2 Right, and 2 Left, and 

631 cfm from the portions of the gobs traversed by air, or a total of 740 cfm-- 

1,065,000 cfd. It is not known why the barriers on both sides of North 

bleeders were left solid. 

CONCLUSIONS 

Although a significant volume of methane was removed from the study area 

without recorded violations of the 1969 Act, it is believed that appreciably 

more methane existed in the gobs. The total area mined out in 3 Right, 

2 Right, 1 Right, 1 Left, and 2 Left is approximately equal to slightly more 

than three full butt headings. In a number of Pittsburgh coalbed mines, one 

butt heading similar in dimensions to 1 Right has produced the same quantity 

of gob gases as the total from the study area. While this is not actual proof, 

it is relatively indicative. 

It is always difficult to adequately ventilate and bleed an area mined in 

virgin coal. However, with the bleeder system established in the area, relatively minor additions would have improved the situation significantly. Three 

or four regulated "taps" into the North bleeders from 1 Right and 1 Left would 

have been effective. Also since the two middle North bleeders were arranged 

for intake air, the system could have been continued into the back bleeders, 

with the outside heading placed on regulated intake air. This would have provided a safe approach for maintaining the bleeders in open condition (pumping 

of water and/or cleanup of falls). 

With the bleeder arrangement described,'more effective regulation could 

be provided at the back end. As the gobs become more extensive and less permeable, sliding doors in properly located regulators would be completely 

opened, and total stoppings could perhaps be removed, with additional regulation progressively provided opposite the more permeable gob areas. 

Because the bleeder air contained a maximum of 1 percent methane, it is 

conceivable that the 133,000 ch of air used here would have removed at least 

50 percent more methane without violating the 1969 Act if (1) the bleeder system had been properly arranged and (2) the main fan pressure had been 

increased.