UNITED STATES DEPARTMENT OF THE INTERIOR 
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: 

4 

Krickovic, Stephen 

Methane emission rate studies in a central Pennsylvania 

mine, by Stephen Krickovic and Charles Findlay. [Washington] U.S. Dept. of the Interior, Bureau of Mines [I9711 

9 p. illus., table. (U.S. Bureau of Mines. Report of investigations 7591) 

1. Methane. I. Findlay, Charles, jt. auth. 11. Title. (Series) 

TN23.U7 no. 7591 622.06173 

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

Abstract ................................................................ Introduction.... ........................................................ Acknowledgments ......................................................... Description of the study area........................................... 

Mining method and equipment ............................................. Ventilation .............................................................. Monitoring .............................................................. Reconnaissance.. ................................................... Location of instruments ............................................ Instrumentation..... ............................................... Results ................................................................. Conclusions ............................................................. 

TRATIONS 

1. Location of the study area.......................................... 

2. Location of face and monitoring instruments and ventilation 

arrangement during study .......................................... 3. Air velocities at station A in return airway showing average 

velocity (circled) ................................................ 4. Air velocities at station B in return airway showing average 

velocity (circled) ................................................ 

TABLE 

1. Summary of results................ .................................. 

Page 

1 

1 

2 

2 

2 

5 

5 

5 

5 

6 

7 

9 
METHANE EMISSION RATE STUDIES IN A CENTRAL PENNSYLVANIA MINE 

by 

Stephen Krickovic ' and Charles ~indla~~ 

ABSTRACT 

A methane emission rate study was conducted in 1969 on a longwall section 

of a Lower Kittanning coalbed mine in central Pennsylvania. The longwall face 

was mined with a drum shearer between developed headings on the head end and 

headings on the tail end that were driven with a ripper-type continuous miner 

as needed. The study was conducted over 22 consecutive shifts (7-1/3 days). 

The average methane emission rate from the Lower Kittanning coalbed during mining at the face and developing the headings at the tail end of the face 

was 34 cfm. Caving of the gassy overlying strata as the result of mining at 

the face increased the methane emission to rates ranging from 702 to 1,049 cfm. 

INTRODUCT ION 

Methane is contained under pressure within the micropores, joints, and 

fractures of gassy coalbeds and may be present in adjacent strata at various 

distances above and below the ~oalbed.~ Thus, methane may enter the mine from 

the coalbed, from the strata overlying the coalbed as a result of caving, and 

from the strata underlying the coalbed as a result of floor heaving. 

In mining systems where roof caving is part of the mining cycle, a properly designed and maintained bleeder system usually is satisfactory to remove 

excess methane to reduce the concentration to a safe working level. The gob 

area created by the cave usually is small, and a proper air differential pressure can be applied across the area to bleed off the excess gas to a suitable 

extent. However, in longwall mining, the overlying strata are caved across 

the entire face. Overlying gassy strata, when caved, emit a flow of methane 

which the usual type of bleeder system cannot remove entirely. 

The purpose of this Bureau of Mines study was to determine the characteristics of methane emissions during coal extraction by a longwall mining system. 

Supervisory mining engineer. 

2~ining engineer. 

3~ervik, Joseph. An Investigation of the Behavior and Control of Methane Gas. 

Min. Cong. J., v. 53, July 1967, pp. 52-57. 
Studies of this type are an essential part of the ~ureau's comprehensive 

methane control program.4 

ACKNOWLEDGMENTS 

The cooperation of the mine management is greatly appreciated. 

DESCRIPTION OF THE STUDY AREA 

Figure 1 shows the location of the longwall study area in the Lower 

Kittanning coalbed. The longwall block being mined was 585 feet wide and 

3,000 feet long, and averaged 54 inches thick. At the start of the study, 

1,200 feet of the block had been mined out. 

An area on the easterly side of the longwall block was mined out with a 

ripper-type continuous miner. A 50-foot barrier was left between this area 

and the three entries at the head end of the longwall face. 

MINING METHOD AND EQUIPMENT 

As shown in figure 2, three headings (3 Right) and related breakthroughs 

were developed on 100-foot centers the entire length of the longwall panel on 

the head end, and four headings (4 Left) and related breakthroughs were being 

developed with a ripper-type continuous miner keeping ahead of the face as 

needed on the tail end. Three of the 4 Left headings were driven on 60-foot 

centers; the one farthest from the longwall panel was driven on a 90-foot 

center. 

The coal was mined with a 15-foot-long, bidirectional shearer equipped 

with a single 48-inch-diam, double-spiral vane drum which made a 27-inch-wide 

shear. Approximately 200 tons of coal was produced during one pass of the 

shearer across the face. The vertical position of the drum could be adjusted 

to compensate for undulations in the coalbed. 

Roof was supported with self-advancing hydraulic units, each equipped 

with four, 42-ton-capacity, hydraulically operated steel props mounted on a 

rigid base and topped with shielded-type, steel beams. Two units were connected to be operated jointly as an eight-prop chock. These chocks were 

spaced on 42-inch centers across the entire length of the face. 

An armored flexible face conveyor discharged the extracted coal into a 

short chain conveyor hopper which, in turn, discharged onto a 36-inch belt 

conveyor. 

4~ervik, Joseph. Behavior of Coal-Gas Reservoirs. BuMines Tech. Prog. 

Rept. 10, April 1969, 10 pp. 

Deul, Maurice. Methane Drainage From Coalbeds: A Program of Applied 

Research. Proc. 60th Ann. Meeting of the Rocky Mt. Coal Min. Inst., Estes 

Park, Colo., June 28-July 1, 1964, pp. 54-60. 

Perkins, J. H., and Joseph Cervik. Sorption Investigations of Methane on 

Coal. BuMines Tech. Prog. Rept. 14, May 1969, 6 pp. 
FIGURE 1. - Location of the Study Area. 

VENTILATION 

As shown in figure 2, the study area was ventilated by two air splits-- 

one for the 4 Left and one for the 3 Right headings. All 3 Right headings on 

the head end of the longwall served as intake airways, with a belt conveyor 

for coal transport in the center heading. Approximately 20,000 cfm of air in 

the easterly heading of 3 Right adjacent to the mined-out area could not be 

traced exactly. It ultimately entered the main return airways at the back of 

the longwall area (north end). 

Two of the 4 Left headings were used for intake air, with a belt conveyor 

in one, and the next adjacent heading served as the positive return for the 

development air split and for the longwall face air reaching the tailpiece. 

The intake air volume was 20,000 cfm in the 4 LeLt headings, and was reduced 

to 16,000 cfm near the tailpiece of the longwall conveyor. 

Of the 30,000 cfm of air that entered the longwall face area at the head 

end from 3 Right, approximately 7,000 cfm was measured at the tail end. 

Airflow was hardly perceptible in the breakthroughs at the back end 

(north) of the longwall panel, and bleeding occurred mostly by diffusion to 

the more permeable caved headings immediately adjacent to the caved longwall 

area on both sides. Most of the longwall face air found its way to the same 

two caved headings. 

MONITORING 

Reconnaissance 

After a study area had been selected, Bureau mining engineers and the 

company's ventilation engineer examined the area to note the details of the 

ventilation and haulage arrangements and the condition of particular airways 

to find specific locations for monitoring continuously with recording and 

handheld instruments. 

Location of Instruments 

The continuously recording anemometers and methanometers were installed 

at locations where reasonably uniform air velocities in the cross-sectional 

areas of two return airways were carrying 85 pct of the total volume of air 

ventilating the study area. The locations of instrument stations A and B are 

shown in figure 2. 

A grid system of vertical and horizontal strings was set up to form 

1-foot squares across each of the two return airways. Air velocities in each 

square then were measured with handheld, vane-type anemometers to locate the 

square in which the air velocity most closely approached the average for each 

total cross-sectional area. Figures 3 and 4 show the air velocities in the 

1-foot squares and the average velocity (circled) in the return airways at 

stations A and B. 
Total cross-sectional area = 66 sq ft 

Averageairvelocity =495fpm 

FIGURE 3. - Air Velocities at Station A in Return Airway Show ing Average Velocity (Circled). 

W/['' /'/' ///// 

460 445 400 402 430 460 458 420 460 440 518 345 353 360 400 

545 525 485 500 495 486 475 440 415 435 430 40!3 393 392 385 

RIB 

555 547 525 525 515 500 501 465 465 459 461 

499 471 532 540 516 541 500 499 480 488 492 472 420 446 435 

3 492 495 495 330 378 332 375 

Total cross-sectional area = 83 sq ft 

Average air velocity = 454 fpm 

FIGURE 4. - Air Velocities at Station B in Return Airway Showing Average Velocity (Circled). 

Instrumentation 

The sensing heads of the recording methanometer and anemometer developed 

by the ~ureau~ were installed in the average velocity squares. It was 

~a~cola, J.C., and Joseph Cervik. Development of Recording Methanometers 

and Recording Anemometers for Use in Underground Coal Mines. BuMines 

Tech. Prog. Rept. 15, May 1969, pp. 9-14. 
necessary to supplement the data collected by the recording instruments with 

handheld anemometers and methanometers in the intake ends of air splits in the 

return air regulator east, and in the back end of the study area. 

A methane-monitoring team consisted of a mining engineer and an engineering aid on each shift. The engineer time-studied the longwall shearer to 

record the operating and idle times, feet of mining advance, and production 

per shift; to secure data on all mining, ventilation, and haulage equipment; 

and to observe any unusual conditions relating to the study. 

The engineering aid was responsible for adjusting and replacing instruments, and changing batteries as required. He also took periodic check 

measurements of the air velocities and the methane concentration near the 

"average squares" with handheld instruments to ascertain the accuracy of the 

recording instruments. These check measurements and the time at which each 

was taken during the shift were recorded on the respective instrument charts. 

RESULTS 

Table 1 is a sumnary of data collected during the study. The study 

period comprised 14 operating shifts and eight idle shifts, during which time 

the longwall face was retreated 20 feet; an estimated 1,842 tons of coal was 

produced, and the shearer was in operation 1,457 minutes. 

More specifically, table 1 shows that on November 20, 1969, during 

shift 3, the shearer was operated for 140 minutes, was idle for 340 minutes, 

and produced 180 tons of coal. The 33,400 cfm of air passing station A contained 381 cu ft of methane (1.14 pct); the 34,700 cfm passing station B contained 632 cu ft of methane (1.82 pct); and the 10,200 cfm of air passing 

through the regulator end of the study area contained 36 cu ft of methane 

(0.35 pct) . The 78,300 cfm of air leaving the section, as a whole, contained 

1,049 cu ft of methane for an overall concentration of 1.34 pct. 

Handheld instruments were used to measure the airflow and methane content 

of the ventilating air on the longwall face and at other points. These measurements are not given in table 1 but they showed that-- 

1. Thirty thousand cubic feet of air per minute entered the head end of 

the longwall face, but only 7,000 cfm reached the tail end. 

2. The concentration of methane measured along the entire face during 

operation of the shearer was 0.10 pct. 

3. The concentration of methane in the return air from 4 Left ranged 

from 0.0 to 0.2 pct near the tail end of the face. 

4. Methane was not detected in any intake air. 

5. The 4 Left intake averaged 19,000 cfm, which was reduced by leakage to 

16,000 cfm at the face. 
TABLE 1. - Summary of results 

Regulator east 

Station B 

, Me

Pct 

1.34 

1.34 

1.22 

1.2

1.1

1.1

1.1

1.1

1.0

.9

.9

.8

.8

.8

.8

.9

.9

1.0

1.0

Date, 

1969 

Nov. 20 

Nov. 21 

Nov. 22 

Nov.23 

Nov.24 

Nov. 25 

Nov. 26 

Nov. 27 

Average. 

area 

Air, 

cfm 

10,200 

10,200 

10,200 

10,700 

10,700 

10,700 

10,800 

10,800 

10,800 

12,700 

12,700 

14,700 

14,700 

14,700 

14,300 

14,300 

14,300 

14,000 

12,300 

Station A 

of study Shift 

No. 

3 

1 

2 

3 

1 

2 

3 

1 

2 

1-3 

1-3 

3 

1 

2 

3 

1 

2 

3 

. . . . . . 

Air, 

cfm 

34,700 

34,700 

34,700 

36,000 

36,000 

36,000 

36,700 

36,700 

36,700 

35,300 

35,300 

34,000 

34,000 

34,000 

35,400 

35,400 

35,400 

35,500 

35,400 

Methane 

Pct 

0.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

.35 

Methane 

Pct 

1.82 

1.82 

1.64569 

1.60 

1.44 

1.46 

1.38 

1.34 

1.25459 

1.17413 

1.17413 

1.10 

1.07 

1.04 

1.04 

1.09 

1.16410 

1.20427 

1.29 

Coal 

production, 

tons 

180 

40 

1 

154 

58 

0 

131 

231 

129 

0 

0 

154 

0 

185 

199 

154 

5 9 

167 

117 

Air, 

cfm 

33,400 

33,400 

33,400 

33,300 

33,300 

33,300 

34,000 

34,000 

34,000 

32,700 

32,700 

31,500 

31,500 

31,500 

31,500 

31,500 

31,500 

31,400 

32,700 

Minutes 

Cfm 

36 

36 

36 

37 

37 

37 

38 

38 

38 

44 

44 

51 

51 

51 

50 

50 

50 

49 

43 

I 

Cfm 

632 

631 

576 

517 

526 

508 

494 

375 

364 

354 

368 

386 

458 

Methane 

Pct 

1.14 

1.14 

1.05351 

1.05 

1.05 

1.09 

1.09 

1.16 

1.14387 

1.02334 

1.02334 

.91 

.91 

.95 

.95 

.98 

1.08340 

1.11349 

1.04 

Working 

140 

30 

10 

120 

45 

0 

110 

180 

100 

0 

0 

120 

0 

152 

155 

120 

45 

130 

91 

Cfm 

381 

381 

350 

350 

363 

371 

394 

287 

287 

299 

299 

309 

341 

Idle 

340 

450 

470 

360 

435 

480 

370 

300 

380 

1,440 

1,440 

360 

480 

328 

325 

360 

435 

350 

389 
The efficiency of a longwall mining system is dependent upon the continuity of the operation. Idleness during operating shifts or on idle weekends 

disrupts the normal caving cycle, and the coal in the face becomes more difficult to mine. 

One advantage during idleness is that methane emission from the freshly 

exposed faces and gob is reduced. This is shown in table 1 where, during the 

period November 20 through November 23, the total methane emitted ranged from 

1,049 to 884 cfm, which was reduced to 791 cfrn during the idle shifts on 

November 24 and November 25. 

The emission rate continued to drop during two shifts after operations 

were resumed, but on the next shift (shift 2, November 25) it began to 

increase and continued increasing through the end of the study period. 

Methane released by mining coal at the face was 0.10 pct of the average 

of 18,000 cfrn of air, or 18.0 cfm; the 4 Left headings produced an additional 

16 cfrn of methane for a total of 34.0 cfm. The average daily methane emission 

rate during the entire study was 842 cfrn of methane, of which an average of 

808 cfrn of methane was released from the strata above the coalbed. 

CONCLUSIONS 

The total average methane emitted from caving gassy overlying strata 

during mining was 808 cfm. 

The total volume of ventilating air (table 1) would be more than adequate 

were it not for the large inflows of methane resulting from caving. 

Bleeding of gob gases occurred primarily along the long sides of the longwall panel (1,200 feet had been mined out) and to an unmeasurable extent at 

the back end.