By Joseph Cervik, Albert Sainato, 

and Eugene Baker 

UNITED STATES DEPARTMENT OF THE INTERIOR 
UNITED STATES DEPARTMENT OF THE INTERIOR 

William P. Clark, Secretary 

BUREAU OF MINES 

Robert C. Horton, Director 
Library of Congress Cataloging in Publication Data: 

Cervi k, Joseph 

Water infusion. 

(Report of investigations / United States Department of the Interior, 

Bureau of Mines ; 8838) 

Bibliography: p. 13-14. 

Supt. of Docs. no.: 1 28.23:8838. 

1. Coal mines and mining-Dust control-Water infusion. I. Sainato, 

Albert. 11. Baker, Eugene. 111. Title. IV. Series: Report of investigations (Unitzd States. Bureau of Mines) ; 8838. 

TN 312.C47 1983 622'.8 83-600307 
CONTENTS 

Page 

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

Introduction ................................................................... 2 

Acknowledgment .............................................................. 3 

Water infusion process ......................................................... 3 

Drilling ..................................................................... 3 

Hole packing ................................................................. 4 

Water infusion ............................................................... 6 

Case study ..................................................................... 7 

Cost effectiveness ............................................................. 9 

Interaction of face air velocity and water infusion ............................ 11 

Summary and conclusions ........................................................ 12 

References .................................................................... 13 

ILLUSTRATIONS 

1 . European methods of water infusion ......................................... 2 

2 . Pajari surveying tool and protective case .................................. 4 

3 . Sealed water infusion hole ................................................. 5 

4 . Bureau packer .............................................................. 5 

5 . Shapes of infused zones .............................................m...... 6 

6 . Test longwall panel ........................................................ 7 

7 . Air velocity correction ................................................... 9 

8 . Effect of ventilation on shearer operator's dust exposure .................. 11 

9 . Effect of moisture content of coal on dust ................................. 12 

TABLES 

1 . Effects of infusion on dust generation ............................... 8 

2 . Working time distribution of shearer ....................................... 10 

3 . Unidirectional versus bidirectional mining of longwall ..................... 10 

4 . Economic summary (mining of one longwall) .................................. 10 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

angs t rom 

centimeter 

foot 

cubic foot 

foot per minute 

gallon 

gallon per minute 

gallon per ton 

inch 

kilopascal 

mg/m3 milligram per cubic 

meter 

mg/m3 *t- milligram per cubic 

meter per metric ton 

mg/m3 ton- milligram per cubic 

meter per short ton 

m/s meter per second 

minlshift minute per shift 

mm millimeter 

Pet percent 

pound per square inch 

gage 

liter r Pm revolution per minute 

liter per cubic meter t metric ton 

liter per minute ton/min ton per minute 

meter wt pct weight percent 

cubic meter 
WATER INFUSION-AN EFFECTIVE AND ECONOMICAL LONGWALL DUST CONTROL 

By Joseph Cervik, Albert Sainato, and Eugene ~aker~ 

ABSTRACT 

In Europe, water infusion is used widely to reduce generation of respirable dust during mining. Its use in the United States is limited to 

a few plow operations in the Pocahontas No. 3 Coalbed. This Bureau of 

Mines report describes the technology for infusing water into a longwall panel and reports the results of a recent demonstration in the 

Lower Sunnyside Coalbed that achieved dust reductions averaging 58 pct. 

Because water infusion increases moisture content of the coalbed, face 

air velocities in excess of 500 ft/min (2.5 m/s) are possible, further 

diluting dust levels before dust entrainment occurs. An economic analysis shows a 23-pct reduction in operating costs when coal production 

is increased by changing from unidirectional mining to bidirectional 

mining with water infusion. 

- 

l supervisory geophysicist. 

2~ining engineering technician. 

3~hysical scientist. 

Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
prevention technique is water infusion, 

which covers 89 pct of the coal produced 

(2). In Belgium, water infusion for dust 

suppression has been practiced for over 

20 years (13). Belgian experience indicates a of water equivalent to 1 

pct of net tonnage, or 2.4 gallton (13 L1 

m3) of coal, reduces the respirable dust 

particles produced during mining by 

B - Infusion from advance roads 

65 pct. 

In China, the Fushun and Chong Qing 

Coal Research Institutes conducted water 

infusion experiments in about 10 coalfields between 1953 and 1974, according 

to Lide Xu, Fushun Coal Research Institute. Generally, resulting dust reductions during mining ranged from 30 to 50 

pct; coalbed moisture content was increased from a preinfusion level of 1.0 

wt pct to 2.0 wt pct after infusion. 

4~nderlined numbers in parentheses re- C-Infusion from entry in roof strata 

f er to items in the list of references 

at the end of this report. FIGURE 1. - European methods of water infusion. 
infu 

coal 

is s 

the 

ion 

face 

igh t 

ace, 

can only be applied from the 

(fig. lA). Because hole length 

ly greater than daily advance of 

a large number of holes must be 

drilled and infused along the longwall 

face. Thus, if the daily advance is 10 

ft (3.3 m), hole length is about 11 ft 

(3.4 m) and distance between holes averages 19 ft (5.8 m). If panel width is 

550 ft (168 m), about 29 holes are necessary to infuse the face of the panel. 

This procedure is repeated daily. During 

the drilling and infusion cycles, no coal 

can be extracted from the panel. Production delays occur if the drilling and infusion cycles are not completed in one 

shift. In some cases, holes are drilled 

to depths of 40 ft (12 m) (deep infusion). The spacing between holes averages 70 ft (21 m); on a 550-ft (168-m) 

face, about eight holes are required. 

Although deep infusion requires fewer 

holes, more time is needed to infuse a 

larger volume of coal. 

If gate roads are driven ahead of the 

advancing face, holes are drilled and 

infused from these roads (fig. 1B). In 

this way, water infusion can be carried 

out without affecting mining operations at the face. In France, advancing 

longwalls are infused from the advance 

gate roads and complemented by infusion 

into the longwall face (5). - 

In some cases, an entry is driven into 

the roof strata and water infusion holes 

are drilled downward from this entry into 

the mined coalbed (fig. lC). Water infusion is carried out for up to a year before coal extraction and is discontinued 

when the coal face approaches the infusion hole. 

In spite of the operational difficulties of incorporating drilling and infusion cycles on an advancing longwall 

and not withstanding production delays, 

water infusion for dust control is a 

widespread practice in Europe. In the 

United States, all longwalls are retreating faces, and drilling and infusing the 

longwall present no operational difficulties or production delays; however, very 

few U.S. longwalls are infused as a means 

of dust control. This report briefly describes the technology for infusing a retreating longwall panel, gives results 

of a recent infusion experiment, and 

discusses the interaction of water infusion and face ventilation, and cost 

effectiveness. 

ACKNOWLEDGMENT 

The cooperation of the management No. 1 Mine, Sunnyside, UT, is greatly 

of Kaiser Steel Corp.'s Sunnyside appreciated. 

WATER INFUSION PROCESS 

The water infusion process involves 

three distinct operations: (1) hole 

drilling, (2) hole packing, and (3) water 

infusion. Each must be successfully completed to ensure that the infused panel 

is saturated with water. 

DRILLING 

Three-in (7.6-cm) diameter holes are 

drilled from the rib side of the panel 

to a depth about 25 ft (8 m) beyond the 

centerline of the panel. For example, 

on a 550-ft (168-m) panel, the infusion 

hole is drilled to a depth of about 300 

these short holes is described elsewhere 

(2, 1). 

The hole should be surveyed periodically during drilling to determine bit inclination in the vertical plane and to 

make necessary changes in drilling parameters to ensure that the hole trajectory 

remains within the coalbed and reaches 

beyond the centerline of the panel. Hole 

surveying can be conducted with an inexpensive instrument such as a Pajari borehole surveying tool5 (fig. 2). The 

5~eference to specific equipnent does 

ft (91 m). The equipment for drilling not imply endorsement by the Bureau. 
HOLE PACKING 

To ensure that the longwall panel is 

saturated with water from rib to rib during the infusion phase, water must enter 

the coalbed from a small segment of the 

hole near the centerline of the panel. 

The segment of hole from the collar to 

about 25 ft (8 m) away from the centerline of the panel must be sealed. In 

this way, water is infused into the panel 

from a 50-ft (15-m) segment of hole 

across the centerline of the panel 

(fig. 3). 

Holes can be sealed with hydraulic 

packers, but the cost to effectively seal 

250 ft (76 m) of hole is about $50,000. 

The packers are retrievable and reusable, 

but installation is time consuming and 

laborious. If the hole deforms during 

the infusion cycle, the packers are 

locked in place and lost. 

The Bureau has developed an alternate 

hole sealing method which is less costly 

psig (1,380 kPa), forcing the 10mil 

(0.025-mm) tube against the wall of the 

hole to form a good seal. The ends of 

the packer are protected with 1-ft (30.5- 

cm) lengths of rubber hose. Pressurizing 

the cement in the packer does not produce 

any stress in the 10-mi.l (0.025-mm) polyurethane tube because it is wider than 

the hole. Stress does exist near the 

ends of the packer, and the short pieces 

of rubber hose prevent the 10-mil (0.025- 

mm) tube from overexpanding and rupturing. The packer can be constructed in 

lengths of a few feet to over 250 ft (76 

m), and the material cost to seal a 250- 

ft (76-m) hole is about $250. 

Sealing a hole for water infusion is a 

very important step. If the hole is not 

sealed properly, water will short-circuit 

along the hole instead of penetrating the 

coalbed from the back part of the hole. 

The Bureau packer filled with pressurized 

cement ensures that the hole is sealed 

along its entire length and that water 

enters the coalbed from the back 50 ft 

(15 m) of the hole. 
FIGURE 4. - Bureau packer. 
p

cleat direction is parallel to the long 

axis of the longwall (fig. 5B). In the 

latter case, a much larger volume of coal 

A- C~rcular ~nfus~on zone 

nnooo cl LI nnno nun 

B- El lhpt~cal ~nfus~on zone 

FIGURE 5. - Shapes of infused zones. 

where r = half-width of panel, ft (m) 

and h = coalbed thickness, ft (m). 

Because fracture porosity is assumed 

to be 1.0 pct, the fracture volume within the infused zone is 2,375h ft3 (221h 

m3), or 17,760 gal (221,000 L) per unit 

thickness of coalbed. Thus, for a 7-ft 

(2.1-m) coalbed, at least 124,300 gal 

(464,100 L) of water is required. If 

the infused zone is elliptical, a much 

larger quantity of water will be required 

(fig. 5B). 

During the infusion phase, the ribs on 

both sides of the panel are inspected periodically for water seeps to determine 

the extent of water migration through the 

panel. Seeps may be difficult to find 

because mining-induced fractures parallel 
to the ribs of the panel prevent water places along the ribs, or it nay be obfrom migrating to the entry. Consequent- served seeping from the panel near the 

ly, water may not be observed a t a l l floor. 

CASE STUDY 

The following example illustrates procedures and gives results of the effects 

of water infusion on dust generation during retreat longwall mining in the Lower 

Sunnyside Coalbed. 

Panel width was 550 ft (168 m), and 

coal height was 7 ft (2.1 m). No surfactant was used in the infused water. A 

3-in (7.6-cm) diameter hole was drilled 

to a depth of 300 ft (91 m) and sealed 

with a Bureau packer (fig. 3) to 235 ft 

(72 m), leaving 65 ft (20 m) of open hole 

for infusion of water into the coalbed 

(fig. 6). During the day shift, water 

was forced into the coalbed with a pump 

at a rate of 27 gallmin (102 L/min) at 

600 psig (4,130 kPa). On the other two 

shifts , the mine water supply line was 

connected to the hole. Water flow rates 

and pressure were 13 gal/min (49 L/min) 

and 315 psig (2,170 kPa), respectively. 

The calculated quantity of water required to saturate the panel was 124,300 

gal (464,100 L), based on a circular 

infusion zone and 1.0-pct fracture porosity. The actual quantity of water infused over a 10-day period was 208,000 

gal (787,300 L). Water seeps were observed along both ribs of the panel up 

to 550 ft (168 m) on both sides of the 

water infusion hole. Thus, water migrated faster by a factor of about 2 

along the long axis of the longwall (approximate face cleat direction) than 

towards the ribs of the panel, indicating 

an elliptical infused zone. 

Four dust sampling surveys were conducted to determine the effects of water 

infusion on dust generation during mining. Each sampling period was 6 to 8 

days. The first survey was conducted before water was infused into the panel, 

to establish a base dust level for comparison with dust levels in the infused 

zone. The following surveys were conducted in the infused zone: (1) when 

the panel face was 400 ft (122 m) to the 

IUI n Ire 

~ronn~u~uonun~~onrunnn!rnnnr

LIP uu u 

Face location Face location Face location 

infused zone infused zone infused zone 

lor 

I lnf usion hole 

300 ft 

 ace location 

base dust study 

FIGURE 6. - Test longwall panel. 
right of the infusion hole (test l), 

(2) when the face passed through the vicinity of the infusion hole (test 2), and 

(3) when the face was about 600 ft (183 

m) to the left of the infusion hole (test 

3) (fig. 6). 

Dust measurements were made with MSA 

Monitore model G personal dust samplers. 

mining are summarized in table 1. Line 1 

shows the average Mining Research Establishment (MRE) dust concentration for the 

noninfused zone and the three surveys in 

the infused zone. The measured dust levels are affected by variations in air velocity near the tail end of the longwall 

(line 2) and by coal production (line 3), 

which increased by a factor of about 3 

A set of four instruments was hung from a between the first and last survey. To 

shield directly over the chain conveyor correct for variations in air velocity 

and approximately 100 ft (30 mj upstream and coal produc~iuu, dust concentrations 

from the tailgate entry. Intake air was 

also monitored with a set of four instruments, and those dust levels were subtracted from the dust levels at the tailgate station. Because the velocity of 

the ventilating air varied from 93 to 

400 ft/min (0.5 to 2.0 m/s) and the tonnage of mined coal varied from 630 to 

3,940 tons (572 to 3,574 t)6 between sampling shifts, all dust measurements were 

divided by tonnage of coal mined during 

the sampling shift and then corrected to 

an air velocity of 300 ft/min (1.5 m/s). 

Data for the air velocity correction were 

generated by the Mine Safety and Health 

Administration (MSHA) from a 1978 survey 

of all longwall sections for compliance 

with respirable dust standards (14) (fig. 

7). This survey showed that dust levels 

during mining tended to be less on longwalls where air velocities at the tail 

end of the longwall were higher. However, where air velocities were above 500 

were normalized to an average air velocity of 300 ftlmin (1.5 m/s) and then 

divided by tonnage mined during the sampling shift. Line 4 shows the corrected 

dust concentrations. In noninfused coal, 

dust concentrations averaged 0.0045 mg/ 

m3ton1 (0.0050 mg/m3*t-I) of mined 

coal, compared with 0.0016 to 0.0024 mg/ 

moton-' (0.0018 to 0.0026 mg/m3*t-I) in 

the infused zone. Thus, water infusion 

reduced the generation of respirable dust 

during mining by 47 to 64 pct (line 5). 

Average dust reduction was 58 pct. 

Because of day-to-day variations in 

dust levels and variations between dust 

sampling periods, the dust data were analyzed statistically using the t test to 

determine if the differences between the 

average dust levels in noninfused and infused coal (line 4) are significant (8). 

The t test involves setting up the Xypothesis that no difference exists beft/min (2.5 m/s), dust levels increased tween average dust levels in infused and 

because of dust entrainment. noninfused coal. A t value is computed 

for the experimental data and then comThe effects of water infusion on respi- pared with a theoretical t value for a 

rable dust generation during longwall given probability level. If the computed 

- t is greater than the theoretical t for a 

61 t (metric ton) = 2,205 lb. given probability level, the conclusion 

TABLE 1. - Effects of infusion on dust generation 

Effect 

Average MRE conc. ........... .mg/m3. . Average air velocity ........ ft/min.. 

Production ........... ...tons/shift .. Corrected MRE conc, 

per ton.. .................. .mg/m3.. 

Dust reduction .................p ct., 

Average water use ..............g al.. 

Average water use ..........g al/ton.. 

NAp Not applicable. 

Noninfused 

zone 

5.2 

190 

8 30 

0.0045 

NAP 

10,200 

12.3 

Infused zone 

Test 1 

2.3 

340 

1,010 

0.0024 

47 

9,500 

9.4 

Test 2 

2.4 

350 

1,420 

0.0017 

62 

10,500 

7 .4 

Test 3 

4.8 

240 

2,680 

0.0016 

64 

14,700 

5.5 
VELOCITY, TAIL END OF LONGWALL FACE, ft/min 

FIGURE 7. - Air velocity correction. 

is that differences are significant. A 

computed t less than the theoretical t 

implies that the differences are not 

significant . 

The average dust level of each test in 

infused coal was compared to the average 

dust level in noninfused coal. The calculated t values were in each case greater than the theoretical t value at the 

1-pct probability level. Thus, the probability that no differences exist between 

dust levels in noninfused and infused 

coal is only 1 pct or less. Stated in 

another way, the probability is 99 pct or 

greater that water infusion suppresses 

dust generation during mining. 

shift during the study is shown in line 

6. No changes were made to the shearer's 

spray system during the study. Line 7 

shows that the water consumed by the 

spray sys tem gradually decreased from 

12.3 gallton (65.8 ~/m~) of mined coal 

during the first survey to 5.5 gallton 

(29.4 ~/m~) during the last survey. One 

would expect dust concentrations to increase, but the three surveys in the infused zone (line 4) show that dust concentrations generally decreased. These 

data suggest that increasing the water 

consumption of the spray system above 5.5 

gallton (29.4 ~/m~) of mined coal in the 

Lower Sunnyside Coalbed would not be effective in suppressing respirable dust 

during mining. 

The average quantity of water used by 

the spray system of the shearer each 

COST EFFECTIVENESS 

According to a 1978 MSHA survey (12) 70 the generation of respirable dust during 

pct of longwall mining operations employ- mining by as much as 64 pct, should reing a double-drum shearer were not in duce the high-risk occupational exposure 

compliance with the 2.0-mg/m3 dust stan- well below the 2. 0-mg/m3 standard. Thus, 

dard, and the average high-risk occupa- production could be increased without extional exposure (shearer operator) was ceeding the 2.0-mg/m3 standard. 

2.6 mg/m3. Water infusion, which reduces 
Time and motion studies on double-drum 

shearers employing unidirectional mining 

show that the actual working time of the 

shearer averages 180 min/shift. This can 

be divided further into cutting, cleaning, and turnaround times (table 2) (6). 

Coal cutting is primarily in one direction, with the return pass used to clean 

up. Thus, if bidirectional mining is introduced, an additional 35 min/shift is 

panel where 1,500 tons of coal are produced per shift by unidirectional mining. 

With bidirectional mining, cutting time 

increases from 117 to 152 min/shift, and 

consequently coal production increases to 

1,950 tons per shift. The same 5,000-ft 

(1,524-m) panel can then be mined in 210 

days, or 63 days less than with unidirectional mining. 

available for coal cutting and increasing An economic analysis of costs associproduct ion. ated with mining of one longwall panel is 

shown in table 4 (9). Capital costs are 

TABLE 2. - Working time dis- higher for bidirectional shearing because 

tribution of shearer the costs of drilling and infusion equipment are included. A water infusion test 

Time, on a retreating longwall in the Lower 

Operation min/shif t Sunnvside Coalbed indicated that one infusion hole will saturate over 800 ft 

Cutting ............. 117 (244 m) of the panel. Consequently, six 

Cleaning... ......... 35 holes spaced 800 ft (244 m) apart are 

Turnaround.......... 28 required to saturate a 5,000-ft (1,524-111) 

panel. The labor requirement for drillTable 3 shows that 273 working days are ing and infusing a 5,000-ft (1,524-m) 

required to mine a 5,000-ft (1,524-m) longwall is 120 man-days, which increases 

TABLE 3. - Unidirectional versus bidirectional mining 

of longwall 

TABLE 4. - Economic summary (mining of one longwall) 

Longwall dimensions......ft.. 

Tons per panel ............... Cutting time ...... min/shift.. 

Cleaning time... ..min/shift.. 

Production. ...... tons/shift.. 

Production ......... tons/min. . Shifts per day ............... Run of mine.. ..... .tons/day.. 

Reject ..................p ct.. 

Clean coal.. ....... tons/day .. Clean coal ....... tons/panel.. 

Mining time ...... days/panel.. 

Unidirectional 

mining 

5,000 x 550 x 7 

818,100 

117 

35 

1,500 

12.8 

2 

3,000 

15 

2,550 

696,000 

273 

Capital cost1.. ....................... Production...........tons clean coal.. 

Operating cost1 ....................... Operating cost per ton of clean coal.. 

Capital cost per ton of clean coal.... 

Bidirectional 

mining 

5,000 x 550 x 7 

818,100 

152 

0 

1,950 

12.8 

2 

3,900 

15 

3,310 

696,000 

2 10 

'costs updated to 1981. 

Unidirectional 

mining 

(273 days) 

$6,370,000 

696,000 

$3,157,000 

$4.54 

$9.15 

Bidirectional mining 

with water infusion 

(210 days) 

$6,407,000 

696,000 

$2,428,000 

$3.49 

$9.21 
operating costs. However, this increase preceding analysis was conducted for a 

is counterbalanced by the decrease in longwall production of 1,500 tons per 

operating costs, because 63 fewer days shift. A similar analysis for a longwall 

(1,386 fewer man-days) are required to production of 800 tons per shift also 

mine the panel with bidirectional mining shows a 23-pct reduction in operating 

(table 3) and operating costs per ton of costs when bidirectional mining with 

clean coal decrease from $4.54 to $3.49, water infusion is employed. 

a reduction of 23 pct (table 4). The 

INTERACTION OF FACE AIR VELOCITY AND WATER INFUSION 

The principal means for diluting and 

removing respirable dust on longwall mining operations in the United States is 

face ventilating air. The average face 

air velocity measured at the midpoint of 

the face on double-drum shearers in the 

United States is 285 ft/min (1.4 m/s). 

Experience indicates a higher face air 

velocity of approximately 450 to 500 ft/ 

min (2.3 to 2.5 m/s) (fig. 8) (12) is required to minimize the shearer operator's 

respirable dust exposure. In addition to 

the dilution effect, higher air velocities tend to keep airborne dust nearer 

the face, again reducing the operator's 

respirable dust exposure. 

Studies in the Federal Republic of Germany indicate similar results (fig. 9). 

The optimum face air velocity is about 

450 to 500 ft/min (2.3 to 2.5 m/s) when 

the moisture content of the coal is 3 to 

4 wt pct (12). Air velocities exceeding 

500 ft/min(2.5 m/s) result in increased 

dust concentrations, becausc thc dust entrainment effect is greater than the dilution effect. However, when the moisture content of the coal is 5 to 8 wt 

pct, velocities up to about 900 ft/min 

(4.5 m/s) are possible before dust entrainment occurs. 

Infusion of water into a longwall panel 

is the only known method of increasing 

the moisture content of coal before mining. Analyses of coal samples taken from 

a longwall face in the Lower Sunnyside 

Coalbed showed that the average in situ 

moisture content of the coal is 3.7 wt 

pct. After infusion of water into the 

AVERAGE FACE AIR VELOCITY, ft/min 

FIGURE 8. - Effect of ventilation on shearer operatoras dust exposure. 
AVERAGE FACE AIR VELOCITY, ft/min 

FIGURE 9. - Effect of moisture content of coal on dust. 

panel, the moisture content of coal Sam- dust entrainment effect begins to operples taken from the face had increased ate. These higher air velocities, in adto 5.0 wt pct. Thus, if the German stud- dition to reducing airborne dust levels 

ies apply to the Lower Sunnyside Coalbed, by dilution, prevent the dust from "boilface air velocities in excess of 500 ft/ ing back" over the shearer operator. 

min (2.5 m/s) are possible before the 

SUMMARY AND CONCLUSIONS 

Water infusion is an effective and economical method of reducing the generation 

of respirable dust on longwalls. Dust 

reductions averaging 58 pct were demonstrated in the Lower Sunnyside Coalbed. 

This large reduction was due to the addition of only 1.7 gallton (9.1 ~/rn~) of 

coal; in contrast, the spray system of 

the mining machine utilizes more than 5.5 

gallton (29.4 ~/m~) of mined coal. 

Seventy percent of double-drum shearer 

operations are not in compliance with 

the 2.0-mg/m3 dust standard. The average 

exposure of the shearer operator is 2.6 

mg/m3; this can be reduced by water infusion well below the 2.0-mg/m3 standard. 

Thus, coal production can be increased by 

changing from unidirectional to bidirectional mining with water infusion, without exceeding the 2.0-mg/m3 standard. 

Increases in capital and operating costs 

associated with water infusion are insignificant compared to the 23-pct savings 

in operating costs caused by increased 

coal production. 
Because water infusion increases the 

moisture content of the coalbed, ventilation velocities in excess of 500 ft/min 

(2.5 m/s) reduce dust levels further by 

dilution and prevent generated dust from 

"boiling back" over the shearer operator. 

German studies show velocities up to 900 

ft/min (4.5 m/s) are possible before dust 

entrainment occurs when moisture content 

of the coalbed is increased. 

The technology for infusion of water 

into retreating longwall panels has been 

developed. Drilling equipment is available commercially, and procedures and 

materials for effectively sealing water 

infusion holes are available. A Bureaudesigned packer reduces the cost of sealing one hole from $50,000 to $250. 

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