UNITED STATES DEPARTMENT OF THE INTERIOR 
Report of Investigations 7849 

Methane and Dust Controls 

for Longwalls: 

Pocahontas No. 3 Coalbed, Grundy, Va. 

By Abdurrahman Cetinbas, R. P. Vinson, Joseph Cervik, 
This publication has been cataloged as follows : 

4 

Cetinbas, Abdurrahman 

Methane and dust controls for longwalls: Pocahontas no. 3 

coalbed, Grundy , Va., by Abdurrahman Cetinbas [and others. 

Washington] U.S. Bureau of Mines 119741 

16 p, illus,, tables, (UuS.. Bureau of Mines, Report of investigations 7849) 

Based on work done in cooperation with the Island Creek Coal 

Company, 

l4 Methane, 2, Coal mines and mining-Dust control, 3, Mine 

dusts, 1- U.S.. Bureau of Mines, 11, Indian Creek Coal Co, 111. 

Title, (Series) 

TN23.U7 no. 7849 622.06173 

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

Page 

Abstract ................................................................ Introduction ............................................................ Acknowledgments ......................................................... Characteristics of the Pocahontas No . 3 coalbed ......................... The methane problem in longwalls ........................................ Development of a hole packing and infusion technique .................... Monitoring instruments and procedures ................................... Methane ............................................................ Dust ............................................................... Results and discussion .................................................. Methane ............................................................ Dust ............................................................... Conclusions ............................................................. 

ILLUSTRATIONS 

Gas pressure in Pocahontas No . 3 coalbed ........................... 3 

Adsorbed gas versus gas pressure in Pocahontas No . 3 coalbed ....... 3 

Map of Beatrice mine showing test site ............................. 5 

Locations of monitoring stations ................................... 6 

Schematic of washer-pipe assembly used for water infusion of a 

longwall panel ................................................... 7 

Combined anemometermethanometer instrument package ................ 8 

Methane concentration and air velocity recordings .................. 9 

Face advance near borehole A1 ...................................... 11 

Total dust histograms; borehole A1 ................................. 13 

Respirable dust histograms; borehole A1 ............................ 13 

Face advance in area of boreholes A3 and A4 ........................ 15 

Total dust histograms; boreholes A3 and A4 ......................... 15 

Respirable dust histograms; boreholes A3 and A4 .................... 15 

TABLES 

1 . Baseline dust survey ............................................... 2 . Fire nozzle test ................................................... 3 . Dust survey; borehole A1 ........................................... 4 . Water infusion data ................................................ 5 . Percent of dust reduction; borehole A1 ............................. 6 . Dust survey; borehole A2 ........................................... 7 . Dust survey; boreholes A3 and A4 ................................... 8 . Percent of dust reduction; boreholes A3 and A4 ..................... 
METHANE AND DUST CONTROLS FOR LONGWALLS: POCAHONTAS 

NO. 3 COALBED, GRUNDY, VA. 

by 

Abdurrahman Cetinbas, R. P. Vinson,2 Joseph Cervi k,3 and M. G. Zabetakis4 

ABSTRACT 

The periphery of longwall panels in the Pocahontas No. 3 coalbed is characterized by a zone of reduced permeability that inhibits the natural drainage 

of methane. A residual gas pressure of 105 psig was measured after 1 year in 

an isolated block of coal measuring 340 by 1,100 feet. The buildup of gas 

pressure within such large blocks causes methane problems during plowing opera tions . However, natural drainage holes drilled during development have been 

found to reduce the gas content of the coal in this coalbed by over 90 percent 

The effect of water infusion on dust during plowing operations was investigated using existing methane drainage holes. These holes were cleaned of 

debris and a pipe was grouted into the hole for water infusion of the panel. 

Both total and respirable dust levels were reduced by 40 to 79 percent. Water 

infusion of the panel proved more effective than did the use of a plow-mounted 

spray sys tem. 

INTRODUCTION 

Water infusion of longwall faces to suppress dust is a common practice in 

European mines. Approximately 13 percent of all such faces in Great ~ritain~ 

and over 50 percent of those in Germany6 are being infused. In the United 

States, the longwall mining method7 accounted for about 1.4 percent of the 

coal produced during 1971 (3 percent of underground production). Serious dust 

problems were encountered with some of the installations because of rapid face 

advance rates, and the friable nature of the coal, and the large air volumes 

introduced to the confined area of the face. 

 inin in^ engineer. 

"physicist. 

supervisory geophysicist . 4~upervisory research chemist . 5~regson, H. Deep Hole Infusion in the Kent Coal Field. Colliery Guard., 

v. 212, No. 5482, May 13, 1966, pp. 599-609 

6~chlick, D. P. Respirable Dust Control in the Mines of West Germany. 

BuMines IC 8490, 1970, 16 pp. 7 schlick, D. P. Longwall Mining. Coal Age, v. 77, No. 7, July 1972, 

pp. 138-141. 
ÿ or ton8 found the European technique of drilling 30-foo t infusion holes 

spaced 30 feet across the face could not be adopted in water infusing longwall 

faces in the Eagle coalbed at Carbon Fuel Co. No. 20 mine at Carbon, W. Va., 

because rapid face advance rates of 30 to 40 feet per day precluded incorporating the drilling and infusion phases into the mining cycle. Consequently, 

holes up to 200 feet in length were drilled from the sides of the panel 

parallel to the face. These were used to infuse 5 to 15 gallons of water per 

minute at pressures between 200 and 600 psi. The results of this work 

indicated this is an effective and economical means of controlling airborne 

dust created by mining operations on a longwall face .g The water improved the 

visibility along the face, increased the cutting rate of the plow, and aided 

greatly in controlling float dust in the return airways and along the belt 

conveyor used to transport the coal. 

The present study in the Pocahontas No. 3 coalbed was designed to yield 

quantitative data on the effects of water infusion on methane and respirable 

and total dust. In addition, consideration was given to the incorporation of 

the infus ion technique into the longwall operation. 

ACKNOWLEDGMENTS 

The cooperation of Island Creek Coal Co. , Cleveland, Ohio, during the 

course of this study is greatly appreciated. The authors thank Luther Preston, 

superintendent, and William Delomas, mine foreman, Beatrice mine, for their 

ass is tance and cooperation in conducting the work described in this report. 

We acknowledge the assistance of W. H. Sutherland, Coal Mine Health and Safety 

District 5, in collecting dust samples and T. C. Ruppel, Pittsburgh Energy 

Research Center, for supplying the sorption curves for the Pocahontas No. 3 

coalbed. 

CHARACTERISTICS OF THE POCAHONTAS NO. 3 COALBED 

The Pocahontas No. 3 coalbed is a highly fractured, friable, and dusty 

coalbed. Fracture spacing is of the order of 114 inch. Depth of cover of the 

coalbed in the study area varied from about 1,300 feet at valley floors to 

2,500 feet in mountainous areas. The gas pressure within the coalbed is high; 

figure 1 is a plot of the pressure measured at various depths from the coal 

face. These measurements were made in a section developing into virgin coal. 

The virgin gas or reservoir pressure of the coalbed was found to be about 660 

psig; this corresponds to a hydrostatic head of about 1,550 feet. 

Normally, during development mining, the face is advanced in 20-foot 

increments. At the end of each advance, a steep pressure gradient is es tab10 lished which results in an increase gas flow. Figure 2 shows the quantity 

8~orton, H. C. Try Water Infusion. Coal Min. and Processing, v. 4, No. 8 

August 1967, pp. 48-50, 64-65. " ~hilli~s, Claude E. Water Infusion of Longwall and Conventional Faces, Na t . Safety Council Trans. , 57th Cong. , v. 7, 1969, pp. 23-26. 

10 Cervik, Joseph. An Investigation of the Behavior and Control of Methane 

Gas. Min. Cong. J., v. 53, No. 7, July 1967, pp. 52-57. 
of methane adsorbed in moist 

Pocahontas No. 3 coal as a 

function of gas pressure; at 

660 psi, the coal contains 

about 560 (STP) cubic feet 

of methane per ton of coal, 

In addition, about 21 cubic 

feet of gas per ton at 

standard conditions is contained in the fractures, 

assuming a fracture porosity 

of 2 percent. Therefore, in 

virgin coal no more than 

approximately 3.6 percent of 

the total methane content of 

the coalbed exists in the 

I I I I I I I a J fracture system as a corn- 0 20 40 60 80 100 120 I4O pressed gas; 96.4 percent DEPTH, ft exists in the matrix as 

FIGURE 1. - Gas pressure in Pocahontas No. 3 coalbed. adsorbed gas. A1 though 3.6 

percent is a relatively 

600 I I I I 1 I I _ small amount of methane, this compressed gas is the 

gas that causes ventilation 

500 - - problems initially during 

mining; flow through fracC tures is a very rapid mode - 

Pocahontas NO. 3 coalbed: of gas transport as compared 

W moisture content 1.22 to 4.4806, 

temperature 68°F with diffusion through the z - solid coal. 

Mine openings in the - Pocahontas No. 3 coalbed at 

depths ranging from 1,300 to 

2,500 feet are characterized - 

by a broken, stress-relieved 

zone about 10 feet deep 

I followed by a highly 0 loo 2* 300 400 500 600 700 800 stressed zone from about 10 

GAS PRESSURE. psi to 50 feet. Drilling horiFIGURE 2. - Adsorbed gas versus gas pressure in zontal holes through the 

Pocahontas No. 3 coalbed. highly stressed zone is difficult. The holes may cave 

because of the friable 

nature of the coalbed; often 

the holes stress relieve and cause the bit and drill pipe to bind. 
THE METHANE PROBLEM IN WNGWALLS 

The highly stressed zones around mine openings in the Pocahontas No. 3 

coalbed also exist around large pillars and longwall panels. The flow of gas 

through such zones is slowed by the reduced permeability. A horizontal hole 

drilled into an isolated block of coal measuring 340 by 1,100 feet yielded 

a gas pressure measurement of 105 psig, despite the fact that this block had 

been isolated for more than 1 year. A similar problem was encountered when 

the longwall mining method was first used in this coalbed. The flow of 

methane from a 273- by 3,800-foot panel posed a severe problem during plowing 

operations, commonly causing downtime of 2 to 4 hours per shift. This 

problem was solved by drilling horizontal holes into the panel from the 

ventilation returns on 100-foot centers. However, considerable difficulty 

was experienced in drilling through the highly stressed zone surrounding 

the panel. For this reason the technique was altered to permit the drilling 

to take place during development of the panel. This procedure is currently 

used in longwall mining this coalbed. Hole depths vary from about 75 to 220 

feet and the holes generally are drilled from both sides of the panel using 

an auger with 2-112-inch bit. 

DEVELOPMENT OF A HOLE PACKING AND INFUSION TECHNIQUE 

The present study was conducted on a longwall panel 450 feet wide and 

approximately 3,400 feet long. The panel had been retreated about 900 feet. 

Figure 3 shows the study area (test site) in relation to the development of 

the mine; figure 4 shows this same area on a larger scale. 
Scale, feet 

FIGURE 3. - Map of Beatrice mine showing test site. 
To effectively infuse 

water into an isolated block 

of coal such as a longwall 

panel requires proper packing of the hole along most 

of its length. Best results 

are obtained when water is 

infused from the back of the 

hole. This procedure prevents premature breakthrough 

of the water along the 

l ibWhbk
holes. Initial attempts were made to ream the existing 2-112-inch-diameter 

holes to 3 inches so that 2-518-inch-diameter inflatable packers could be used 

for infusion. These holes collapsed as drilling progressed and this approach 

was abandoned. Attempts then were made to drill new 3-inch-diameter holes; the 

coal around the holes stress relieved and collapsed. The use of inflatable 

packers was abandoned and a grouting procedure was developed using the existing 2-112-inch-diameter methane drainage holes. Because the methane drainage 

holes generally were filled with debris, they were first cleaned by water 

flushing using the mine's 750-psig water supply. Next, a washer-pipe assembly 

(fig. 5) was centered in the hole and grouted in place. An expanding-type 

grout was used, consisting of a blend of 50 percent class A portland cement 

and 50 percent gypsum cement by volume. Salt is added to the slurry to extend 

pumping time and improve bonding characteristics. An organic chemical dispersant such as CFR-~~~ is added to reduce frictional flow pressures and slow down 
Dust was 

sampled at five 

different periods 

during this study. 

All dust samplers 

were operated only 

at the sampling 

locations . The 

length of time a 

dus t sampler was 

in operation was 

the time used in 
panel traveled with the plow and, consequently, the concentration of methane increased. The average speed of 

the plow was 100 fpm (feet per minute) and themeasured 

air velocities in the vicinity of the plow ranged from 

400 to 500 fpm. The troughs on the methane curve were 

obtained when the plow traveled toward the maingate 

when the relative velocity was greatest so the concentrations of methane are lowest. 

Examination of figure 7 shows that the methane 

measured in the immediate return comes from the longwall panel. About 2 to 3 hours after plowing ceased, 

the methane concentration in the air dropped to about 

0.05 percent methane--the level of methane in the 

intake air. There appeared to be no methane coming 

from the gob in this area. 

Taking an average methane concentration of 0.5 

percent during plowing operations, an average air 

velocity of 200 fpm, and a cross-section~l area of 

90 square feet at the measurement point, the volume 

flow of methane from the panel would be 90 cfm (cubic 

feet per minute). During a 6-hour plowing time about 

2,000 tons of coal was mined. For this mining period, 

methane was liberated at a rate of 16.2 cubic feet 

per ton of coal. 

The back-and-forth movement of the plow during 

mining influences the ventilation current as shown in 

the air velocity recording in figure 7. Note the fluctuations in air velocity during plowing operations compared to the variations after the plow is stopped. 

Also, the envelope of the air velocity recording has 

peaks and troughs that correlate with the peaks and 

troughs of the methane recording. When the plow is 

traveling toward the tailgate, air velocity increases, 

and during this time interval the methane concentration reaches its peak also. 

Water infusion has no appreciable effect on methane emission while mining the panel. However, only a 

relatively small volume of the panel was infused near 

the maingate. To reduce methane flows further would 

require the emplacement of a waterbank the width of 

the panel. Figure 7 shows that there is some methane ~'v~&~T~oME+H9\N~~ bleed-of f from the panel after plowing stopped. The 

100 fpm P ct fact that methane concentration maximums did not 

exceed 0.8 percent during plowing demonstrates the 

effectiveness of the drainage holes drilled into the 

FIGURE 7, - Methane con- panel during development as a methane control measure. 

centration and 

- Dust 

air velocity 

record ings. Before the infusion tests were conducted various 

dust control measures were used. During mining, the 
face was sprayed continuously at approximately 90 points,using nozzles mounted 

on spillplates. Water sprays also were used at the inby transfer point (face 

conveyor to stage loader) and at the entry and exit of the coal breaker. A 

wetting agent was metered into the mine's water supply to increase the dustsuppression ability of the water. The outby transfer point (stage loader to 

conveyor belt) was covered with a hook constructed of angle iron and plastic 

sheet to contain the airborne dust at this location. These dust controls were 

in use during the first four sampling periods. During the fifth and finaldust 

survey additional dust controlswereusedand these will be discussedin context. 

The first survey was a base study to determine the dust concentrations at 

the various sampling stations prior to infusion. Dust samples were taken on 

the day shift for 4 consecutive days (table 1.) With this information, an 

average dust concentration was established for each sampling station. 

TABLE 1. - Baseline dust survey 

I Dus t concentration. / 

Intake : 

Mar. 8... 

Mar. 9. .. Mar. 10 ... Mar. 11 ... Average 

Loca t ion 

and date 

Total ' a lent 1 - tons 

respirable 

Maingate : 

Mar. 8.. . 45.4 

Mar. 9.. . 59.1 

Mar. 10 ... 60.8 

mn /m3 ' coal I MRE equiv- production,. 

Mar. 11. .. Average 

Tailgate: 

Mar. 8... 

Mar. 9.. . Mar. 0.. 

'Rock dust voided samples. 

66.1 

57.9 

(l) 

129.8 

88.5 

Mar. 11 ... Average 

Because Pocahontas No. 3 coal is highly friable and not very wettable, 

the dust-suppression effectiveness of water was questionable. To answer this 

question, a one-shift study was made which involved spraying the first 100 

feet of face with three equally-spaced fire nozzles. These nozzles were 

manually operated and used only when the plow was within spray range. Thus 

a high volume of water was concentrated at the plow where the concentration 

of dust was greatest. While the face was being sprayed in this manner, 

dust was being sampled at three locations--all within the first 100 feet of 

face. A significant reduction in dust levels resulted (table 2). 

10.2 

9.6 

.I 

119.2 

,112.5 

2,376 

2,104 

13.9 

12.3 

2,376 

2,104 
TABLE 2. - Fire nozzle test 

Maingate.. 

Downface : 

70 feet. 

75 feet. 

Reduct ion from 

base average, 

percent 

Dust concentration, mg/m3 

Total 

3 1 

44 

3 7 

Total 

40.0 

32.2 

36.3 

MRE equivalent 

respirable 

27 

5 8 

5 3 

MRE equivalent 

respirable 

7.0 

4.0 

4.5 
TABLE 3. - Dust survey; borehole A1 

I Dust concentration, 1 

Location 

and date 

Intake : 

Mar. 28 ... Mar. 30 ... Mar. 31. .. Apr. 3.. . Apr. 4... 

Mainga te : 

Mar. 28 ... Mar. 30 ... Mar. 31. .. Apr. 3. .. Apr. 4... 

Ta ilga te : 

Mar. 28 ... Mar. 30 ... Mar. 31. .. Apr. 3... 

- 1 MRE equiv- production, 

To ta 1 alent 

res irable 

Apr. 4...) 53.9 1 6.6 1 1,900 

'NO samples taken. 

"part-time work. 

Table 4. - Water infusion data 

Borehole 

Water ) Amount of 

A1 

Depth, water 

feet 

220 

The normalized concentrations (mg/m3/ton of coal) taken when the face was 

10 feet from the infusion hole compared with the baseline survey shows a 

Grouted 

part, 

gpm 

18.2 

pronounced reduction in airborne dust (table 5.) This reduction was greatest 

at the maingate locations that collected dust produced mainly from the infused 

portion of the face. 4 

Water 

pressure, 

average 

feet 

85 

ga 1 lons 

4,368 

TABLE 5. - Percent of dust reduction; 

borehole ~1' 

ps ig 

709 

Location 1 Dust reduced, percent 

Tailgate.. ..... ( 47 1 40 

ma ace: 10 feet from hole Al. 

Maingate. ...... Total 

69 

MRE equivalent respirable 

79 
Maingate 

March -1- April I - 

TIME, days 

FIGURE 9. - Total dust histograms; borehole Al. 

- 

- 

- 

- 

- 

- 

TIME, days 

IIII1'1 

Tailgate 

..... 

..... ..... 

..... ..... 

.......... 

..... ..... 

..... ..... 

..... 

0.014 

3 

n' < .012- rn 

J 

a 

8 ,lob 

March - April T 

..... 

..... ..... 

28 129 11.~'131 

March - 

1111111 

Maingate 

The next dust survey 

took place as the face 

approached the second 

infused hole A2. This hole 

was 220 feet deep, grouted 

to 145 feet, and infused 

vith 5,800 gallons of water 

(table 4). Dust was sampled 

on three shifts. Samplers 

were placed at intake, mainga te , and tai lga te sampling 

s tat ions. During sampling 

intervals, hazardous roof 

conditions s lowed production to about one-fourth 

normal. For this reason, 

it was not possible to 

ascertain whether the low 

dust levels were due 

entirely to low production 

or in part to water infusion. 

1 i 2 '3 I 4 

April - 

The samples collected during 

this period do show that at 

low product ion rates the 

dust concentration 

approaches a constant level 

all along the face (table 6.) 

A final dust survey 

(table 7) was made as the 

face receded from an area 

infused through two holes -- 

A3 and A4 (table 4). The 

first hole, A3, was 120 feet 

deep, grouted to 40 feet, 

and infused with 1,000 gallons of water. Hole A4 was 

located 20 feet outby A3 and 

was infused with 4,500 gallons. This hole was 80 feet 

deep and grouted to 50 feet. 

A schematic of the face area 

during the sampling cycle is 

shown in figure 11. As the 

FIGURE 10. - Respirable dust histograms; borehole Al. face receded from the 

infused zone, the his tograms 

(figs. 12-13) show that the 

dust concentration increased. This same trend also may be seen in the total 

dust tailgate samples, with one exception (table 7). On the third day of Sampling, the measured total dust at the tailgate, when normalized, was lower 

than that at the maingate and 100-foot downface locations. There was no 
apparent reason for this low measurement (other than the possibility of a 

malfunction in the sampler). 

TABLE 6. - Dust survey; borehole A2 

TABLE 7. - Dust survey; boreholes A3 and A4 

I Dust concentration, 

Location 

and date 

Intake : 

May 3.. . . . May 4.. . .. May 5.. . . . Average 

Maingate: 

May 3..... 

May 4..... 

May 5.. . .. Average 

Tailgate : 

May 3..... 

May 4..... 

May 5.. . . . Average 

Location 

and date 

Total a lent 

Coa 1 

production, 

tons 

42 5 

625 

53 9 

530 

425 

62 5 

53 9 

530 

42 5 

625 

539 

530 

Remarks 

Bad roof 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Dus t concentration, 

m /m3 

July 18. . . July 19.. . July 20.. . 

To ta 1 

4.1 

4.8 

4.5 

4.5 

16.4 

18.7 

18.6 

17.9 

18.7 

18.0 

18.3 

18.3 

Intake : 

Ma inga te : 

July 18 ... July 19. . . July 20.. . Downface 100 

feet : 

July 18 ... July 19.. . July 20 ... Tailgate: 

July 18. . . July 19.. . July 20. . . 'part-time w 

- zE equivalent 

respirable 

0.6 

.4 

.5 

.5 

1.8 

2.2 

2.0 

2.0 

2.1 

1.7 

2.1 

2.0 

respirable 

"~ault~ resp 

)rk. 

.rable samplers. 

Coa 1 

production, 

tons 

of infusion was measurable, as shown by the histograms. A comparison was 

made between the normalized dust concentrations taken on the first sampling 

day of this period and the baseline normalized concentrations. The results 

are found in table 8. 

TABLE 8. - Percent of dust reduction; 

boreholes A3 and A4 

A comparison of tables 8 and 5 shows that dust concentration decline at 

the maingate was approximately the same in both surveys. At the tailgate, 

however, the comparison shows a slightly greater decline in airborne dust 

during the last survey. At this location, table 8 shows an additional reduction of 15 percent for respirable dust and an additional 24 percent for total 

dust over that in table 5. The most interesting finding here was that water 

infusion alone was more effective in suppressing dust than all the other dust 

controls noted above. 

- - - - - 

~oca t ion 

Maingate ....... Tailgate ....... 

The Pocahontas No. 3 coalbed is highly fractured and friable and apparently the bulk of the dust observed during mining is inherent to the coalbed. 

If the dust in the fracture system can be wetted before the coal is mined dust 

can be controlled to, acceptable levels. Water infusion is an effective dust 

suppressant in the Pocahontas No. 3 coalbed because only a small fraction of 

the dust is generated by breaking blocks of solid coal. 

CONCLUSIONS 

Incons is tent measurement. 

- - - - 

Dust reduced, percent 

Water infusion of longwall panels in the Pocahontas No. 3 coa lbed is an 

effective and efficient means of suppressing total and respirable dust. 

Although the spray system on the plow does suppress airborne dust, it is not 

as effective as water infusion. The bulk of dust observed during mining is 

inherent to the coalbed and wetting this dust before mining prevents it from 

becoming airborne. The effectiveness of water infusion can be increased by 

infusing the panel from both sides. 

Total 

78 

62 

Because less than one-half of the panel near the maingate was infused, 

methane liberation from the longwall face was not affected. The determination 

of the effect of water infusion on methane requires the whole face to be 

infused. The levels of methane observed during plowing operations indicate 

that methane drainage holes drilled into the panel on development are effect ive in predra ining me thane. 

MRE equivalent respirable 

68 

1