APPENDIX - FLUID POWER EQUATIONS

(@ standard barometric pressure and air density, from Bise,
1986; Hartman, 1961)

P,
POWER RATIO = —#*
P vestation

Tf wer Equatic

8.33 H, Q,
“ar 33,000

Where: Pye = hydraulic power, horsepower
H, — = static gage pressure near nozzles, feet of
H,0 (velocity pressure negligible below 8
feet per sec of water velocity in pipe)
Q, = water quantity, gallon per minute

P,,{for 100 =) = 1.542 p, (7°28 - 1)

Where: P,, = compressed air power, horsepower
r = p/p, compression ratio
P; = absolute compressor intake pressure, psi
P; = absolute compressor discharge pressure, psi

_ 52H, 9,

Prentitation 33,000

Where: Prewiusion= Ventilation power, horsepower

H, = ventilation pressure of test section, inches
of HO
2, = air quantity, cubic feet per minute

Aggie (for entry airflow) = Hyg, (entry friction loss)

2
a -KLOV

itkinson Equation)
‘oss 52a. 4 »

Where: H,,, = energy loss due to friction, inches of H,O

K = mine airway friction factor, used 60 x 10°°
for a straight, slightly obstructed
sedimentary airway

L = airway length, feet

ca) = airway perimeter, feet

v air velocity, feet per minute

A = airway area, square feet

y)
Han (F035

Where: Hreyciy = Kinetic energy of ventilation, inches of H,O
v = air velocity, feet per minute



195 Parcent confidence Intervals for Factor Means

A,

et REE a EE ORAL
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rey 4

2

4p 4

z |

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z 2r

ES

wa

MESH POROSITY, pct

{No maun=100 pct porosity!

Figure 2, Experimental mean plots of walkway dust
concentrations versus mesh porosity and downstream
distance.

5 100 T T ,
Ey
x Key
g 60 % Porosity
8 —— 84 pct
= -—- 52 pet
mw 607 nem 30 pet
ti
Z 4oF 4
=
E
z 20r 4
5
os
a — L
° 100 200
LOCATION, m

Figure 3. Downstream air-splitting efficiency
relationships for the mesh barriers tested.

Longwall Field Study
One longwall field study was conducted using

Mesh Type B as the air-splitting barrier, This mesh type
was preferred by the longwall operator as a functional
compromise between worker visibility and dust control
efficiency. A continuous roll of fire-retardant polyester
mesh fabric of type B was obtained for this underground
study. Four samples of this mesh were subjected to a
Flammability Test (ASTM E-162, 1996) and were
classified as a low-risk fire hazard (“Class A”) under the
flame spread classification system.

The longwall operation extracted a 3.7- to 4.3-m-
thick, high-volatile bituminous coal seam along a 225-m-
wide mining face. Methane emission at this mine was
historically low, reducing the potential for methane

accumulation hazards along the face during the mesh air-
splitting tests. This longwall operation used a
unidirectional cutting sequence, with a radio remote-
controlled shearer cutting in the head-to-tail direction and
cleaning up in the tail-to-head direction. Radio remote-
contro! operation of the shearer from the worker walkway
was crucial for operation with the mesh barrier. The
supports were advanced on the tail-to-head cleanup pass.
The mesh was continuously hung along a 140-m
section of the face, from longwall supports 4 through 95,
to separate the worker walkway from the extraction face
(see Figure 4). The mesh was hung from the canopy of
each support by rods bolted to the underside of the face
lighting fixtures. Surgical latex tubing was attached
between the rods on the shields for continuous hanging of
the mesh. Additional mesh material was folded on the
tubing between the supports to accommodate support
movement. Cap lamps were mounted on the shearer and
directed toward the cutting drums to improve the shearer
operators’ visibility of the mining activities through the
mesh. However, the shearer operators still experienced
poor visibility through the mesh, requiring more
background lighting than that provided by the cap lamps.

Figure 4, Mesh barrier hung from longwall supports (from
Organiscak and Leon, 1993).

Respirable dust sampling was conducted in the
worker walkway for several shifts with and without the
mesh barrier to evaluate its dust control efficiency.
Respirable dust sampling was conducted with the same
personal gravimetric dust samplers used in the laboratory
study. Four personal dust samplers were worn by
research personnel; two samplers were operated during
the head-to-tail cut pass and two samplers were operated
during the tail-to-head cleanup pass. Research personnel
followed the coal extraction process at mobile sampling
positions 15 m outby (upstream), 30 m inby
(downstream), and 60 m inby the shearing machine.

Vane anemometer measurements were also made over the
face conveyor and in the worker walkway (both sides of
mesh) along the longwall face. Two shifts of control data
were collected with the mesh; three shifts of baseline data
were collected without the mesh. The average face air
velocities between the mesh tests and baseline tests were
very similar at 1.56 m/sec and 1.57 m/sec, respectively,
making these underground control test conditions
comparable.


Table V. Two-level factorial design of air-atomized spray barrier system.

TRIAL AIR VELOCITY SPRAY OPERATING PARAMETERS,
Code Velocity Code ‘Compressed Air Water
m/sec
Pressure Quantity Pressure Quantity
kPa m/min kPa Umin
1 Low 0.9 Low 207 1.2 138 5.2
2 High 2.0 Low 207 1.2 138 5.2
3 Low 0.9 High 483 29 414 14.7
4 High 2.0 High 483 29 414 14,7
5 Medium 14 Medium 345 2.0 276 10.8

Experimental Results

ANOVA analysis was conducted on these
experimental data to examine the significance of the air-
atomized stage spray barrier system to split entry airflow.
The dust reduction efficiency for each test was the
dependent variable. The independent variables were the
downstream sampling distance, spray operating pressure,
and air velocity. Initial ANOVA results indicated that
these independent variables had confounding effects on
dust reduction. These confounding effects were due to
inconsistent dust control efficiencies measured between
the test conditions at the various downstream sampling
locations. Figure 8 shows the average dust reduction
efficiencies measured along the entry for each test
condition. This graph shows that the staged spray barrier
system performed better at the low and medium air
velocities than at the higher velocity up to the 30.5 m
downstream location. Farther downstream of the 30.5 m
location the performance was marginal and inconsistent
between test conditions. It also seemed that this air-
atomized spray system had a limited performance range
similar to that of the water spray system.

The performance range of this air-atomized
staged spray barrier system was also analyzed by the
relative fluid power ratio between the spray nozzles and
yentilation airflow. Spray-to-ventilation power ratios
were determined for each test condition. Compressed air,
water, and ventilation flow equations used to determine
power usage can be found in the appendix (Bise, 1986;

Hartman, 1961). ANOVA analysis of the dust control
efficiencies with respect to the power ratio and
downstream distance from the dust source was conducted;
results are shown in Table VI, These results show that the
downstream distance had the largest effect on dust
reduction efficiencies provided by the staged spray barrier
system. Although the power ratio effect showed
significance at the 95% confidence level, its overall effect
was small in comparison to the other experimental
variations,

Interactions between the power ratios and the
downstream distances on dust control efficiency can be
seen in Figure 9. The dust control efficiency and power
ratio relationship noticeably vary for the different
downstream sampling locations. The dust efficiency
increases with the power ratio at the 15.2-m location. At
the 30.5-m location, the optimum efficiency occurs in the
middle of the test conditions, similar to the water spray
tests at the 30.5-m location. Further downstream, the dust
control efficiencies become negligible with inconclusive
power ratio relationships. Due to the marginal
downstream performance of the staged spray barrier
system in the laboratory, underground testing of this
system was not pursued.



(see Figure 6). Each spray manifold had three equally
spaced nozzle locations, oriented parallel to the belt
barrier, and was placed on the dust generation side of the
mock spill plate and belt barriers. The preliminary air-
splitting tests examined several spray nozzle sizes, spray
manifold layouts, and spray operating pressures at several
air velocities (see Table IV). A Cat Pump with an
adjustable pressure regulator was used to provide
different water spray pressures. Air velocities in the entry
were controlled by changing the mine’s fan speed (three-
speed fan).

Transveant
‘mesh

BD ousy ation

Plan View

Figure 5. Underground support movement displacement
of mesh (from Organiscak and Leon, 1993).

Dust sampling was conducted 30.5 m
downstream of a Vibra Screw SCR-20 dust feeder on the
opposing entry side of this dust source (walkway side).
Three pairs of personal samplers were equally spaced
from the top height of the mock spill plate (barrier) to the
roof in the center portion of the walkway side of the entry.
Half of these vertically spaced dust sampler pairs were
used to measure ARD concentrations with the sprays
operating; the other half were used to measure ARD
concentrations without the sprays operating. The baseline
and spray sampling segments of a test were 20 min each.
A RAM-1 was also at this sampling location for real-time
examination of dust levels, recorded on a strip chart
recorder upstream of the dust feeder. Dust testing was
supplemented with visual smoke tests to identify airflow
disruptions during this preliminary phase of development.

Figure 6. Walkway side view of staged spray layout.

The preliminary staged spray barrier layout tests
conducted are shown in Table IV. Most of this testing
was completed at manifold spacings of 7.6 m, water
pressures of 689 and 1,379 kPa, and air velocities of about
1.4 nvsec. The ARD results reported are averages of two
tests for each condition, except for the 15.2-m manifold
spacing for which only one test was conducted at each
condition. The very first tests conducted with the
H1/4VV2504 flat fan spray nozzles, mounted 38 mm.
away from the conveyor belt, showed poor dust control
efficiency. Two nozzles used in each manifold provided
slight increases or virtually no change in walkway ARD
levels. Visual smoke examination of these initial staged
spray barrier tests showed that operating the two sprays
(sprays A and B) above the spill plate barrier allowed the
airflow below these sprays to lag and swirl over the spill
plate barrier. Placing one of the sprays below the spill
plate barrier (sprays A and C) reduced this visual airflow
lag; operating all three nozzles (sprays A, B, and C)
showed some improvement in the walkway ARD levels.
Smoke testing also showed that orienting the staged spray
barrier system more than at a slight angle (~5°) with the
primary ventilation increased eddy currents and airflow
migration across the entry.

The most noticeable improvements in ARD
walkway levels were achieved when the spray nozzles
were moved farther away from the belt barrier. Two
H1/4VV2504 spray nozzles seemed to provide the best
dust reductions at the same water pressures when these
nozzles were moved 102 mm from the belt barrier. A
water pressure reduction with the two nozzles showed a
notable reduction in dust control efficiency. When the
larger H1/4VV2506 nozzles were used, entry air velocity
had to be increased to achieve similar results to the
smaller nozzles operating at lower air velocities.
Increasing the manifold spacing from 7.6 m to 15.2 m
with these larger nozzles at the higher air velocity
noticeably diminished dust control performance. From
these test results seemed that optimum performance of a
staged spray barrier system occurred in a limited range of
spray manifold and air velocity parameters.

The performance range of the staged spray
barrier system was examined by the relative fluid power
ratio between the spray nozzles and ventilation airflow.
Sprays move air through momentum transfer of the
kinetic energy of the spray droplets discharged into the


Fic id
The longwall dust data were analyzed for
statistical significance by the T-test statistic; results are
shown in Table III. The T-test hypothesis for the mean
dust concentration difference between test conditions was
equal to zero, with the alternative hypothesis being a
lower dust concentration for the mesh test condition.
Statistical significance was determined for each sampling
position by the one-tailed T-statistic. A significant result
for this hypothesis testing is at the 95% confidence level
or 5% significance level.

The longwall field study verified that significant
walkway dust reductions can be achieved downstream of
the shearer when the mesh barrier is maintained parallel

to the ventilation airflow. The test results show that the
mesh barrier significantly reduced the walkway dust
concentrations by 53% and 45% at 30 m and 60 m inby
(downstream) the shearer, respectively, during the head-
to-tail cut pass. No significant dust reductions at these
inby locations were observed for the tail-to-head cleanup
pass. The key difference between these shearing
directions was the support movement activities for the
tail-to-head cleanup pass. Support movement during this
pass formed an irregular step in the mesh barrier, altering
face airflow movement through the mesh into the worker
walkway (see Figure 5). Therefore, mesh barrier
continuity along the longwall face is a key aspect for
controlling dust downstream of the shearer.

Table III. Longwall mesh test results.

SAMPLE LOCATION MESH BASELINE TONE-TAILED | SIGNIFICANCE
AROUND SHEARER Ne» 2 shifts Ne 3 shifts T-STATISTIC | LEVEL
Average Variance Average Variance
mg/m? mg/m’
15 mOUTBY
Head-to-Tail Pass 1.04 0.12 1.37 0.02 + 1559 0.108
Tail-to-Head Pass 1.28 0.63 1.36 0.02 + 0.178 0.435
30 m INBY
Head-to-Tail Pass 1.45 0.24 3.09 0.07 + 4,989 0.008
Tail-to-Head Pass 5.48 0.57 5.47 0.43 0.008 0.503
60 m INBY
Head-to-Tail Pass 1.95 0.12 3.52 0.07 + 5.902 0.005
Tail-to-Head Pass 5.96 0.12 5.38 3.40 0.421 0.649

TH; (Mesh Average - Baseline Average)» 0
H,: (Mesh Average - Baseline Average) < 0

STAGED SPRAY BARRIER SYSTEM

A staged spray barrier system along the longwall
face was also designed for creating two separate splits of
air downstream of the shearer. The objective of this
study was to develop and test a much simpler and more
functional air-induced spray system compared to past
support-mounted spray systems. This spray system
involved mounting several flat fan spray nozzles
vertically onto a physical barrier (conveyor belting) and
spacing these barriers at equal distances with the
airstream. Preliminary testing was conducted for several
water spray nozzle arrangements and barrier distances. A
two-phase air-atomized staged spray barrier system was
further tested at various spray and ventilation operating
parameters. The tests were conducted in NIOSH’s Safety

Research Coal Mine at the Pittsburgh Research
Laboratory (PRL).

Preliminary Staged Spray Barrier System Development

Preliminary tests were conducted with water
sprays mounted on physical barriers to separate entry
airflow for a 30.5-m distance in the Safety Research Coal
Mine at PRL. A 122-m-long, 0.9-m-high barrier was
constructed out of lumber and brattice cloth to simulate a
longwall face conveyor spill plate. This barrier was
positioned approximately along the center of a 3.0-m-
wide straight section of entry. For the initial spray layout
tests, four water spray manifolds were vertically mounted
on 1.2-m by 1.2 m pieces of conveyor belting and were
hung above and nearly parallel (* 5° orientation with the
airflow) to the mock spill plate barrier on 7.6-m centers



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SPRAY / VENTILATION POWER RATIO

Figure 7. Preliminary water spray-to-ventilation power
ratio relationship with air-splitting efficiency.

Although the initial design of a staged spray
barrier system was shown to be relatively effective in
controlling dust along a short section of entry, the water
quantity needed for operating a larger system along a
longwall face would most likely be impractical. During
these preliminary tests, between 27.0 and 40.4 L/min of
water was required to notably control dust along a 30.5 m
section of entry. Longwall operations with face lengths
typically greater than 180 m would require substantial
quantities of water to operate a staged spray barrier
system along the face. Spacing the spray barriers at the
greater distances reduces water consumption, but also
reduces control efficiency. Several tests conducted with
water spray barriers spaced at 15,2 m showed marginal
dust control efficiency. To reduce the water consumption
of the staged spray barrier concept, further laboratory
experimentation was conducted with two-phase air-
atomized nozzles to investigate their capabilities for air-
splitting. These tests also examined dust control
effectiveness at greater distances from the dust source.

Two-Phase. Atomized Experiments

The staged spray barrier system laboratory
testing was continued with two-phase air-atomized
nozzles over a longer entry distance. For these tests eight
more spray manifold/conveyor belt barrier units were
placed over the mock spill plate on 7.6-m centers along
the test section entry from 30.5 to 91.5 m downstream of
the dust source. The best spray layout identified from the
preliminary water sprays tests was used for these air-
atomized spray nozzle tests. This spray nozzle layout was
the flat fan nozzle positioned above and below the mock
spill plate (spray locations A and C), located 102 mm
away from the conveyor belt barrier (see Figure 6 and
Table IV).

Spraying Systems’ 1/4JSUN23 flat fan air-
atomizing nozzles were tested at various operating
pressures and entry air velocities. A two-level factorial
design of the experiments was followed. The
experimental design and operating factors are shown in

Table V. These nozzles were operated at compressed air
and water pressures within the manufacturer’s
recommended range. The quantities of water used by
these air-atomized spray nozzles were substantially
reduced for a staged spray barrier coverage of 91.5 m
entry length as compared to water sprays. However,
compressed air is also required to operate these air-
atomized spray nozzles.

Dust sampling was conducted at 15.2, 30.5, 61,
and 91.5 m downstream of a Vibra Screw SCR-20 dust
feeder on the opposing entry side of this dust source
(walkway side). Three pairs of personal samplers were
equally spaced from the top height of the mock spill plate
(barrier) to the roof in the center portion of the walkway
side of the entry. Half of these vertically spaced dust
sampler pairs were used to measure ARD concentrations
with the sprays operating; the other half were used to
measure ARD concentrations without the sprays
operating. The baseline and spray sampling segments of a
test were 30 min each. The experiments were randomly
conducted; each test condition (trial) was repeated six
times. Half of these trials were performed with the sprays
operating at the end of the test; the other half, with the
sprays operating at the beginning of the test. A RAM-1
was also at the 30.5-m sampling location for real-time
examination of dust levels, recorded on a strip chart
recorder upstream of the dust feeder. One personal dust
sampler was also located upstream of the test entry
section to ensure that a good quality of ventilation air was
used for each test. Thirty valid tests were completed for
the various test conditions.


INVESTIGATION OF LONGWALL FACE VENTILATION
AIR-SPLITTING METHODS FOR IMPROVED DUST CONTROL

J. A. Organiscak

NIOSH

Pittsburgh, PA

ABSTRACT

Two types of airflow splitting methods for
improving longwall dust control were investigated by
NIOSH's Pittsburgh Research Laboratory. These
methods included a translucent mesh barrier and a staged
spray barrier system to confine the shearer-generated dust
to the coal extraction side of the longwall face while
maintaining a cleaner split of airflow on the opposing
worker walkway side of the longwall face. The
translucent mesh barrier was shown to provide notable
dust control effectiveness up to 60 m downstream of the
shearer in both the laboratory experiments and a longwall
field evaluation, provided the mesh barrier remains
relatively parallel to the airflow. The staged spray barrier
system showed marginal dust control effectiveness in the
laboratory and subsequently was not field tested.

INTRODUCTION

Ventilation is a key element in controlling
airborne respirable dust (ARD) generated at longwall
mining operations. Ventilation is primarily used for
diluting and removing ARD generated from coal
extraction at the mining face. Prior studies have shown
that an indirect relationship exists between the amount of
ventilation and dust concentrations measured at the
longwall face (Haney et al. 1993; and McClelland et al.,
1987). However, there are both practical and economic
limits to the air quantity that can be delivered by the mine
ventilation system to the longwall face.

A significant portion of a mine’s fan(s) capacity
is lost or short-circuited in the ventilation system before it
reaches the mining face. Air leakage from the intake to
the return air courses usually occurs through the
ventilation control devices constructed throughout the
mine. These include stoppings, doors, overcasts, etc.
between the intake and return entries of the mine. These
control devices leak because of stress-induced entry
deformation, physical deterioration with time, and/or
construction quality. Mine ventilation systems are
considered to be efficient if they can deliver 50% of its
fan(s) quantity to the working face(s) (Bise, 1986). Mine

ventilation also has economical limitations placed on it
because the power used to deliver a unit quantity of air
increases by a cubic relationship with quantity.

Although ventilation is one of the most
important elements of longwall dust control, additional
control methods are needed to assist with the reduction of
high dust concentrations in localized areas of the mining
face, The single largest longwall dust source is the
shearing machine cutting coal along the entire longwall
mining face (Colinet et al., 1997; Jankowski et al., 1991;
and Jankowski and Organiscak, 1983). The worker
walkway on the gob side of the longwall face becomes
contaminated with dust adjacent to and downstream of the
shearer (Ruggieri et al., 1983). Employees working in
these areas adjacent to and downstream of the shearer are
commonly exposed to the highest dust concentrations at
the mining face.

Research has been conducted to reduce the dust
contamination of the worker walkway near and
downstream of the shearing machine. Concepts that were
studied included shearer-mounted water spray air movers,
physical barriers mounted on the shearer, ventilation
curtains mounted along the face, and support-mounted
compressed air spray movers. The shearer-clearer water
spray system was one of the most successful
developments of these dust control concepts and is used
by more than 80% of the U.S. longwall operators (Haney,
1995). This shearer-mounted external spray system uses
10 external hollow cone nozzles directed with the
ventilation airflow over the shearer body and has physical
barriers mounted between the cutting drums and worker
walkway from splitter arms attached to the machine, This
system confines the shearer dust to the mining face away
from the shearer operators and has been shown to provide
up to 50% reduction in dust (Ruggieri et al., 1983;
Jayaraman et al., 1985). However, the air-splitting
effectiveness of the shearer-clearer diminishes
downstream of the shearer, especially at the highest water
spray pressure tested (1,724 kPa).

Several ventilation curtain concepts have been
found to be either ineffective or impractical for air-
splitting at longwall operations. One concept was to
increase the air velocity over the shearer and face



the spray nozzles and ventilation airflow. The staged
spray barrier system was observed to have a limited
effective operating range for both water and air-atomized
spray nozzles up to 30.5 m downstream of the dust
source. During the more extensive air-atomized nozzle
experiments, the dust control efficiency of the staged
spray barrier system was shown to be negligible beyond
30.5 m downstream of the dust source. The air-atomized
nozzles tested significantly reduced the water
consumption, but required a compressed air supply to
operate the nozzles. Key results from this staged spray
barrier research are that the spray power expended must
be relatively matched to the ventilation power being used
and the downstream dust control effectiveness beyond
30.5 m is insignificant.

The mesh barrier seemed to be the most robust
air-splitting method as compared to the staged spray
barrier system. The mesh barrier showed significant dust
reductions at the farthest downstream distance from the
dust source, while operating over a wide range of air
velocities. The staged spray barrier system showed a
limited range of dust control with respect to spray
parameters, ventilation parameters, and downstream
distance from the dust source. The spray-to-ventilation
power ratio indicates that the spray system would need to
be significantly enhanced to control dust on longwalls
operating at higher air velocities than those tested. The
enhancements required would likely be more closely
spaced spray manifolds operated at higher nozzle
operating parameters.

Although the mesh barrier seems to be the most
promising air-splitting method for longwall dust control,
several operational design obstacles need to be overcome
for successful integration of this control method into the
mining system. The mesh barrier needs low fabric
porosity and parallel continuity with airflow to be an
effective longwall dust control method. Low fabric
porosity would impede worker visibility through the mesh
barrier, requiring abundant background lighting on the
coal extraction side of the mesh barrier. The lighting
requirements may be accomplished either by placing a
lighting system on the shearing machine or adding to the
existing walkway lighting system used on the supports.
Improving the mesh continuity to face airflow would
involve removing severe anomalies caused by operational
displacements in the mesh. This may be accomplished by
hanging the mesh barrier from a supporting framework
either affixed to the face conveyor spill plate or anchored
periodically among the shield supports. Finally, some
additional methane monitoring along the longwall face
areas (extraction face and walkway, especially at the
longwall gate ends) in gassier coal seams is advisable to
ensure that the mesh barrier does not increase methane
accumulations along the face.

ACKNOWLEDGMENTS

Research on the staged spray barrier system
would not have been possible without the assistance of
several of my colleagues at NIOSH’s Pittsburgh Research
Laboratory (PRL). The author would like to express his
appreciation to Thomas Mal, Engineering Technician, for
his assistance with the setup, preparation, and execution
of these experiments. The author would also like to thank
Paul Stefko, Sam Angelo, and Jack Teatino at PRL’s
Safety Research Coal Mine for their help with the
construction of the test section and mine facility support
services during these experiments.

REFERENCES

ASTM, 1996, “ASTM E162-94--Standard Test Method
for Surface Flammability of Materials Using a Radiant
Heat Energy Source,” Annual book of ASTM standards:
Vol. 04.07, American Society for Testing and Materials,
Conshohocken, PA, pp. 487-497.

Babbitt, C. and S. Ruggieri, 1990, “Evaluate Fundamental
Approaches to Longwall Dust Control Subprogram E -
Longwall Application of Ventilation Curtains,” USBM
Contract Final Report (Contract No. J0318097, Foster-
Miller, inc.), USBM OFR 31E-90, NTIS DE90-015501,

54 pp.

Bise, C. J., 1986, “Mining Engineering Analysis,” Pub.
SME, Inc., Littleton, CO., 153 pp.

Colinet, J. F., E. R. Spencer, and R. A. Jankowski, 1997,
“Status of Dust Control Technology on U. S. Longwalls,”
Proceedings of the 6" international Mine Ventilation
Congress, May 17-22, Pittsburgh, PA, Pub. SME, Inc.,
Littleton, CO, pp. 345-351.

Haney, R. A., R. S. Ondrey, and K. G. Fields, 1993,
“Influence of Airflow and Production on Longwall Dust
Control,” Proceedings of the 6" U. S. Mine Ventilation
Symposium, Salt Lake City, Utah, June 21-23, Pub. SME,
Inc., Littleton, CO, pp. 43-49.

Haney, R. A., 1995, “Trends in Implementation of
Longwall Dust Controls,” Proceedings of the 7" U.S.
Mine Ventilation Symposium, Lexington, KY, June 5-7,
Pub. SME, Inc., Littleton, CO, pp. 311-317.

Hartman, H. L., 1961, “Mine Ventilation and Air
Conditioning,” John Wiley & Sons, New York, 398 pp.

Jankowski, R. A., and J. A. Organiscak, and N. I.
Jayaraman, 1991, “Dust Sources and Controls for High
Tonnage Longwall Faces,” Presented at the 120° SME
Annual Meeting, Salt Lake City, UT, February 22-26.

Jankowski, R. A., and J. A. Organiscak, 1983, “Dust
Sources and Controls on the Six U. S. Longwalls Having


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Figure 8. Downstream air-splitting efficiency of air-
atomized sprays.

‘95 Percent confidence intervals for Foctor Means

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SPRAY /VENTILATION POWER RATIO

Figure 9. Mean plots of air-splitting efficiency versus
spray-to-ventilation power ratio and downstream distance

Table VI. ANOVA analysis of air-atomized staged spray barrier experiments

VARIATION SOURCE SUM OF DEGREES OF | MEAN F-RATIO SIGNIFICANCE
SQUARES FREEDOM SQUARE LEVEL

MAIN EFFECTS

Downstream Distance 44,672.54 3 14,890.84. 82.21 0.000
Power Ratio 1,809.04 4 452.26 2.50 0.048
INTERACTIONS

Distance-Power 8,890.71 12 740.89 4.09 0.000
RESIDUAL 18,112.32 100 181.12

CONCLUSIONS material of 84%. One underground field study verified

Two types of longwall air-splitting methods were
examined for their dust control performance. These
methods included a translucent mesh barrier and a staged
spray barrier system to contain the shearer-generated dust
along the coal extraction side of the mining face,
providing a cleaner split of airflow on the opposing
worker walkway side of the mining face. The most
effective air-splitting method was the translucent mesh
barrier. Both laboratory and underground tests showed
that the mesh barrier was quite effective in containing the
dust to one side of the entry, provided it was kept
relatively parallel to the airflow. Significant dust
reductions were achieved in the laboratory up to 61 m
downstream of the dust source with two mesh fabrics
having material porosities of 52% and 30%. Negligible
dust reductions were observed for a more porous mesh

that the 52% porous mesh provided significant dust
reductions at a longwall operation. Dust concentrations
were reduced by 53% and 45% at 30 and 60 m inby the
shearer, respectively, when the mesh was maintained
relatively parallel to the airflow. During support
movement the mesh fabric was notably misaligned at the
advancing support, negating any dust control effect.
Thus, the key factors for controlling dust downstream of
the shearer with the translucent mesh barrier are porosity
and continuity.

The staged spray barrier system showed
marginal dust control effectiveness in the laboratory. The
nozzle layout for the staged spray barrier system was
developed during preliminary water spray dust control
tests. Performance of the spray system was analyzed with
respect to the relative fluid power ratio expended between


surrounding environment. Fluid energy applied by these
sprays on airflow through a test section of entry can be
reasonably determined by using the Bernoulli equation for
steady-state flow processes with irreversible losses
determined by the Darcy-Weisbach equation. Time
usage of this fluid energy is the power expended by each
system (spray and ventilation). Mine applicable water,
compressed air, and ventilation fluid flow equations are
shown in the appendix and can be also found in (Bise,
1986; Hartman, 1961). Mine entry friction factors are
also found in these references, and a straight, moderately
obstructed sedimentary mine airway friction factor (K *
60 x10" °) was used for all of the ventilation power
determinations. Spray-to-ventilation power ratios were

determined for the more effective tests of sprays located
102 mm from the belt barrier, with the barriers spaced
equally at 7.6 m.

Figure 7 shows the spray-to-ventilation power
ratio results for the two nozzle types operated at various
water pressures and air velocities. The power ratio
variations for the same nozzle type and arrangement were
accomplished by altering the water pressure or air
velocity. Optimum dust control seemed to be achieved
with a spray-to-ventilation power ratio between 15 and 30
for these preliminary water spray tests. Dust control
efficiency decreased below or above this power ratio
range.

Table IV. Preliminary staged spray design testing.

TEST MANIFOLD SPRAY WATER WATER AIR CHANGE IN
SPACING LAYOUT PRES FLOW VELOCITY ARD LEVELS
m kPa Umin m/sec %.
HI/4VV2504 AB 1,379 27.0 13 5% Increase
Nozzles
38 mm Away from 16
Belt
A,C 1,379 27.0 1.4 3% Increase
A,B,C 1,379 40.4 1.4 24% Decrease
HI/4VV2504 689 19.1 14 13% Decrease
Nozzles A.C
102 mm Away 76
from Belt
1,379 27.0 14 46% Decrease
A,B,C 1,379 40.4 1S 32% Decrease
689 28.8 15 30% Decrease
HU/4VV2506
Nozzles 76 AC
102 mm Away
from Belt
1,379 39.4 14 30% Decrease
1,379 39.4 2.0 44% Decrease
1,379 19.7 2.0 13% Decrease
15.2 A,C
2,068 24.2 2.0 13% Decrease

A key observation was that similar dust control
efficiencies were achieved for three smaller H1/4VV2504
nozzles per spray manifold compared to two larger
H1/4VV2506 nozzles per spray manifold, delivering
nearly the same power ratio. This was accomplished at

the same water pressure and nearly the same water flow
rate for these nozzle types (see Table IV). Using a larger
spray nozzle reduces the likelihood of orifice plugging
from particulate matter in the water supply.



Table II]. ANOVA analysis of mesh experiments.

VARIATION SOURCE SUM OF DEGREES OF | MEAN F-RATIO SIGNIFICANCE
SQUARES FREEDOM SQUARE LEVEL

COVARIATE

Entry Dust Concentration 277.43 1 277.43 1000.00 0.000

MAIN EFFECTS

Downstream Distance 195.18 4 48.80 332.21 0.000

Barrier Porosity 175.54 3 58.51 398.36 0.000

Air Velocity 5.10 3 1.70 11.58 0.000

INTERACTIONS

Distance-Porosity 17.60 13 1.35 9.22 0.000

Distance-Velocity 6.49 13 0.50 3.40 0.001

Porosity-Velocity 12.47 9 1.39 9.44 0.000

RESIDUAL 28.64 195 0.15

All of the independent and covariate variables
significantly impacted the dust concentrations on the off-
feeder side (walkway) of the entry. The two independent
variables with the largest effect were the barrier porosity
and downstream distance from the dust source (see Table
Tl and Figure 2), Figure 2 shows that the walkway dust
concentration directly increases with the downstream
distance from the dust source. This figure also shows that
a lower mesh porosity significantly reduces the walkway
dust concentrations and increases the downwind distance
for comparable dust concentrations. Because the dust
feed was adjusted for air quantity to maintain similar dust
concentrations during each test, the air velocity had the
least effect on the dust concentrations on the off-feeder
side of the entry (see Table II).

The relative dust control efficiency of each mesh
type was also examined for its practical application on
longwall operations. Dust control efficiencies for each
mesh at the various downstream locations were
determined as the percent change in walkway dust
concentrations with respect to the baseline tests, without
the mesh barrier. The average walkway dust
concentrations at each downstream sampling location for
the mesh tests were first adjusted or normalized by a
factor that equated the average entry dust concentrations
at each location (both sides of the entry) of the mesh tests
to the baseline tests. These adjusted or normalized
walkway dust concentrations were then used to determine
the percent dust reductions achieved over the baseline
tests.

Dust control efficiencies of each mesh type with
respect to downstream sampling location are shown in
Figure 3. Each dust efficiency curve in Figure 3
represents an average for all of the air velocities tested.
Mesh dust control efficiencies were indirectly related to
both porosity and downstream distance. Mesh C, which
had a 1.6-mm mesh opening size and 30% fabric porosity,
reduced dust levels by 79% and 55% at the 30.5-m and
61-m downstream sampling locations, respectively. Mesh
B, which had a 3.2-mm mesh opening size and 52% fabric
porosity, reduced dust levels by 58% and 36% at the 30.5-
m and 61-m downstream sampling locations, respectively.
Mesh A, which had 6.4-mm mesh opening size and 84%
fabric porosity, showed little improvement over the
baseline conditions for all of the downstream sampling
locations. These results indicate that mesh fabrics for
longwall application need a porosity of about 50% or
lower for efficient dust control. However, as the mesh
porosity or hole size is decreased, visibility through the
mesh fabric is reduced.



roof to the floor in the middle of the test entry (1.2 m
from the entry wall and the brattice wall). Baseline tests
were also conducted without any mesh to measure the
natural dust migration across the test section entry. Air
velocity down the test section was controlled by a brattice
curtain regulator positioned across the beginning of the
adjacent parallel air split, opposite the test section.
Baseline and mesh testing experiments were conducted
under four different air velocities of 1, 2, 3, and 4.1 m/sec,
repeated three times under each test condition. Absolute
random sampling of the test conditions was impractical,
because mesh replacement was very labor-intensive.
However, a moderate mix of the test conditions was
achieved by testing different air velocities for each type of
mesh, changed out several times throughout the total

experimental period.

TIN) \

Figure 1, Lake Lynn experimental setup (from Organiscak
and Leon, 1993).

Airborne respirable dust (ARD) sampling was
conducted on each side of the test section entry at
distances of 30.5, 61, 91.5, 122, and 152.5 m downstream
of the dust source for each test condition. Three
gravimetric ARD personal dust samplers and one Real-
Time Aerosol Monitor (RAM-1)' were located at each
sampling location. The personal dust samplers used a
Dorr-Oliver 10-mm nylon cyclone classifier operated at 2
L/min. The three personal samplers at each sampling
location were spaced at uniform distances between the
roof and floor. The average ARD concentrations of the
three personal samplers for each sampling location were
used in the data analysis. The RAM-1 samplers were
‘only used to ensure uniform dust concentrations during
each test. A sampling station was also located upstream
of the test entry section to ensure that a good quality of
ventilation air was used for each test.

Airborne dust was generated on the mine wall
side of the entry with a Vibra Screw SCR-20 feeder
supplying Keystone Filler and Mfg. Co.'s Mineral Black
#325BA dust into a compressed air dispersion system.
The dispersion system discharged dust at equal distances
from the roof and floor on the mine wall side of the entry.
The dust feed rate was adjusted for air quantity to
maintain a similar dust concentration for each test so that
the effect of air velocity on air-splitting could be more
clearly studied. Test duration was 65 min. A total of 48
valid tests were conducted for the various mesh
configurations at different air velocities.

Experimental Results

ANOVA analysis was conducted on the
experimental raw data to examine the significance of the
controlling factors on mesh barrier air-splitting. The
dependent variable was the dust concentration on the off-
feeder side of the entry. The independent variables were
the downstream sampling distance, the barrier porosity,
and the entry air velocity. The average dust concentration
across the entry (for both sides) at each downstream
sampling distance was used as the covariate for the
dependent variable. The numerical results from this
analysis are shown in Table II. The graphical results are
shown in Figure 2.

* Mention of any company name or product does

not constitute endorsement by the National Institute
for Occupational Safety and Health.


conveyor by placing brattice curtains across the workers
walkway to decrease longwall entry area (Babbitt et al.,
1990). Various curtain spacings (4.6, 7.6, and 12.2 m)
arranged at perpendicular and 45° orientations with the
airflow were studied in a full-scale longwall ventilation
gallery with a tracer gas. Although the curtains increased
face air velocity, the eddy air currents produced
downstream of these curtains allowed contaminated face
air to be drawn into and linger in the walkway. The best
walkway conditions were the baseline tests without any
curtains. Another more effective ventilation curtain
concept studied in the full-scale longwall gallery was an
extended face conveyor spill plate (curtain barrier)
between the face area and worker walkway (Babbitt et al.,
1990). Laboratory tests showed that a fully extended face
conveyor spill plate or curtain to the roof improved the air
quality in the worker walkway downstream of the shearer.
However, this type of barrier would impede worker
visibility of the extraction face and would not be practical
for longwall operations.

Accompressed air spray movement system
mounted on longwall supports was another air-splitting
dust control concept studied in a full-scale longwall
gallery. Four compressed air sprays were mounted on
every longwall support location, Two sprays were
directed from the support canopy 45° downward with the
airflow toward the face conveyor, and two sprays were
directed from the worker walkway 45° with the airflow
toward the face. Eighty nozzles were placed on a 30.5-m
section of face area comprising about 20 supports.

Tracer gas testing showed that the compressed spray air
system provided greater than 60% reduction in tracer gas
levels measured in the worker walkway next to the
shearer at air velocities of 1.0 and 1.5 m/sec. At higher
air velocities of 2.0 and 2.8 m/sec, the system’s
performance diminished to about 50%. Although this
compressed air system displayed good performance, it
required a 183-kW, high-capacity compressed air supply
for the 59.5 m/min delivered along the 30.5-m section of
the longwall gallery, diminishing its practicality for
underground use.

Because the extended spill plate barrier and
support-mounted directional spray system concepts
showed promise for effective longwall dust control,
additional full-scale laboratory tests were conducted on
more practical engineering control applications of these
ventilation concepts. A translucent mesh barrier was
examined to provide a compromise between airflow
containment and visual transparency. A staged spray
barrier method was also studied to provide air-splitting
with a less complex spray system. Both of these air-
splitting methods were studied at NIOSH’s Pittsburgh
Research Laboratory for potential longwall mining
application. This report describes the research into their
design parameters and related dust control effectiveness.

TRANSLUCENT MESH BARRIER

A translucent mesh barrier placed along the
longwall face was devised to create two separate splits of
airflow between the extraction face and worker walkway
while providing some worker visibility through the
barrier. Specific details of the investigation into this
longwall dust control method have been published
(Organiscak and Leon, 1993) and will be summarized in
part in this report. This investigation encompassed
experimental studies at NIOSH’s Lake Lynn Laboratory
and one field study at an operating longwall. A more
rigorous statistical analysis of the laboratory and field
data was recently conducted and is included as part of this
report.

Lake Lynn Laboratory Experiments

Experiments were conducted at Lake Lynn
Laboratory to study the key dust control parameters
involved in the application of the translucent mesh
partition, These key factors included the downstream
distance from the dust source, mesh porosity, and air
velocity. The air-splitting abilities of three polyester
mesh-type fabrics compared with baseline conditions of
no mesh were studied at four air velocities along a narrow
183-m test entry section of the Lake Lynn Experimental
Mine. The characteristics of these polyester mesh fabrics
were notably different and are shown in Table I. The
mesh types tested ranged from the most porous fabric of
84% open area to a tighter fabric of 30% open area. The
weight and strength of the mesh fabrics shown in the table
were indirectly related to the open area of the fabric.

Table I. Characteristics of mesh types studied in the
laboratory (from Organiscak and Leon, 1993).

MESH TYPE A B Cc
Fabric Material Polyester | Polyester | Polyester
Opening Size,mm | 6.4 32 16
Mesh Count, 14x20 [18x35 [3.1x39
holes/cm?

Mesh Porosity, % 84 52 30
Thickness, mm 0.05 0.10 0.13
Weight, g/m” 159 214 365
Ball Burst, kPa 1,380 2,070 3,790

Figure 1 shows the experimental layout of the
mine entry test section. The test entry section was
narrowed from 5.5 to 2.4 m by constructing a 183-m
wood-framed brattice curtain wall 2.4 m from one side of
the entry wall to simulate a realistic cross-sectional area
of an average U.S. longwall face. A 152-m-long
continuous section of each mesh fabric was hung from the



the Most Difficulty Complying with Dust Standards,”
USBM Information Circular (IC 8957), 19 pp.
Jayaraman, N. I.,R. A. Jankowski, and F. N. Kissell,
1985, “Improved Shearer-Clearer System for Double-
Drum Shearers on Longwall Faces,” USBM Report of
Investigation (RI 8963), 11 pp.

McClelland, J. J., C. Babbitt, and R, A. Jankowski, 1987,
“Optimizing Face Ventilation and Shearer Water
Consumption to Reduce Longwall Dust Levels,”
Proceedings of the 3 Mine Ventilation Symposium,
October, 12-14, University Park, PA, Pub. SME, Inc.,
Littleton, CO, pp. 553-557.

Organiscak, J. A. and M. H. Leon, 1993, “Translucent
Face Partition for Longwall Dust Control,” Proceedings
of the 6 U.S, Mine Ventilation Symposium, Salt Lake
City, UT, June 21-23, Pub. SME, Inc., Littleton, CO, pp.
557-562.

Ruggieri, S. K., T. L. Muldoon, W. Schroeder, C. Babbitt,
and S. Rajan, 1983, “Optimize Water Sprays for Dust
Control on Longwall Shearer Faces,” USBM Contract
Final Report (Contract No. J0308019, Foster-Miller,
Inc.), USBM OFR 42A-86, NTIS PB86-205408, 156 pp.