554

G. V.R. GOODMAN

TABLE II
Effects of added side sprays at left rear corner and right rear corner sampling locations
Left rear corner Right rear corner
Machine position:
Setback Number of Standard error Confidence interval Number of Standard error Confidence interval*
(m) samples (mg/m?) (mg/m) samples (mg/m?) (mg/m?)

Sump cut: 6.1 6 0.38 1.41 + 1.068 6 0.51 1.19 + 1,42°
Sump cut: 21.2 6 0.30 0.51 £0.83 5 0.32 —0.50 + 1.02
Slab cut: 6.1 6 0.26 —0.03 + 0.72 6 0.15 —0.06 + 0.42
Slab cut: 12.2 6 0.36 0.48 + 1.00 6 0.32 0.26 + 0.89

495 percent confidence interval for difference in mean dust levels. Negative values indicate a reduction in dust levels at that sampling location

due to added sprays.
® Confidence interval is statistically significant at 95 percent.
Confidence interval is statistically significant at 90 percent.

(p-value = 0.08). Changes in dust levels at the left and right rear
corners with the mining machine in the slab cut were not signif-
icant (p-value > 0.20). However, return dust levels did decrease
significantly in the return with use of the additional side sprays
at the 6.1-meter setback distance.

At the larger 12.2-meter ventilation setback distance, the re-
sults were somewhat confounding. Dust levels did not decrease
significantly at the left and right rear corners of the mining ma-
chine (p-values > 0.20), indicating that the additional side sprays
were not as effective at the larger setback distance. This is con-
firmed by the return dust levels which showed only a weak effect
in the slab cut with use of the additional side sprays (p-value =
0.08). No effect was seen with the mining machine in the sump
cut (p-value > 0.20).

Due to cost considerations, silica analyses were conducted
only on selected filters. To avoid small sample sizes that could
have led to questionable results, silica samples from sump
and slab cut tests were combined according to side spray use and
setback distance. For example, all left and right scrubber inlet
samples taken without the side sprays in use and with a6.1-meter
setback distance were considered as a single sample set. The sil-
ica levels of these samples were then compared to those scrubber
inlet samples taken with the sprays in use and with a 6.1-meter

setback distance. Similar comparisons were made for all under-
boom samples taken at a 12.2-meter setback distance. All silica
samples taken at the left rear and right rear corner locations of the
mining machine were combined to form a general machine sam-
ple set and analyzed ina similar manner. The return samples were
combined by ventilation setback distance and side spray use.

Combining samples in this manner eliminated any analysis
of silica dust variation due to mining machine location, that is,
sump cut or slab cut. However, the previous analysis showed
that the effectiveness of the side sprays was most influenced by
ventilation setback distance.

Hypothesis testing and two-tailed t-tests were again used to
assess the significance of the difference in mean silica dust levels
measured with and without the added sprays. A 95 percent level
of confidence was assigned to this evaluation.

The results of the silica analyses are shown in Table IV and
show that silica percentages were essentially unchanged with
the use of the additional side sprays. With the exception of the
return samples at a 12.2-meter ventilation setback distance, all
other silica levels were not significantly affected by these sprays
(p-value > 0.20). This apparent lack of impact on silica dust
levels is not surprising. Previous work showed that capture of
the smaller, denser silica particles increased directly with water

TABLE Ill
Effects of added side sprays at the return sampling location
Return
Machine position:
Setback Number of Standarderror Confidence interval

(m) samples (mg/m?) (mg/m?)
Sump cut: 6.1 6 0.13 —0.62 + 0.368
Sump cut: 12.2 6 0.10 —0.08 + 0.28
Slab cut: 6.1 5 0.06 0.49 + 0.198
Slab cut: 12.2 5 0.20 0.52 + 0.64°

495 percent confidence interval for difference in mean dust levels. Negative values
indicate a reduction in dust levels at that sampling location due to added sprays.

5Confidence interval is statistically significant at 95 percent.

Confidence interval is statistically significant at 90 percent,


USING WATER SPRAYS TO IMPROVE PERFORMANCE

SUMMARY

Additional water sprays were placed along the left and right
sides of a continuous mining machine to improve suppression
and capture of the underboom dust cloud. A full-scale mock-
up of a continuous mining machine was positioned in either
the sump cut or slab cut with ventilation setback distances of
6.1 meters or 12.2 meters. The test results revealed that the side
sprays not only improved suppression of the underboom dust
cloud, but also pushed this cloud toward the right scrubber inlet.
At the smaller 6.1-meter ventilation setback distance, there was
sufficient airflow along the right side of the cutting boom to
keep the dust cloud from flowing out of the underboom area.
Consequently, scrubber capture of this dust may have increased.
At the larger 12.2-meter setback distance, the airflow dissipated
along the right side of the cutting boom and dust flowed out from
the cutting boom. This led to increased downwind dust levels.

These sprays were then installed on a continuous mining ma-
chine at an underground operation. Although sampling could
not be conducted at the scrubber inlets or in the return, dust con-
centrations measured on the machine and at the mining machine
operator did decrease with the use of these sprays, Further anal-
ysis showed that these sprays were more effective at the smaller

559

2. Jayaraman, N.1.; Colinet, J.F.; Jankowski, R.A.: Recent Basic Re-
search on Dust Removal for Coal Mine Applications. Proceed-
ings, Fifth Intemational Mine Ventilation Congress, Johannesburg,
pp. 395-405. (October 1992).

Jayaraman, N.L.; Jankowski, R.A.; Whitehead, K.L.: Optimizing
Continuous Miner Scrubbers for Dust Control in High Coal Seams.
Proceedings, Society for Mining, Metallurgy, and Exploration An-
nual Meeting, pp. 193-205. Phoenix (1992).

Mineral Resources. Code of Federal Regulations Title 30, Parts 70
and 75. (July 1998),

. Mine Safety and Health Administration: Standard Method No.
P-7, Infrared Determination of Respirable Quartz in Respirable
Coal Mine Dust, Internal Document, U.S. Department of Labor,
Washington, D.C. (1989).

Tomb, T.F; Treaftis, H.N.; Mundell, R.L.; Parobeck, P.S.: Compar-
ison of Respirable Dust Concentrations Measured with MRE and
Modified Personal Gravimetric Sampling Equipment, RI7772. US
Bureau of Mines, Pittsburgh, PA (1973).

. Jayaraman, N.L; Jankowski, R.A.: Atomization of Water Sprays
for Quartz Dust Control. Appl Ind Hyg 3(12):327-331 (1998).
USS. Energy Information Agency: Coal Industry Annual—1997,
DOE/EIA-0584(97). Department of Energy, Office of Coal, Nu-
clear, Electric, and Alternate Fuels, Washington, D.C. (Dec.
1998),

»

ba

wa

a

~

cd

setback distances, a finding confirmed by laboratory testing. 9. Colinet, J.F;; Jankowski, R.A.: Dust Control Considerations for
Deep-Cut Mining When Utilizing Exhaust Ventilation and a Scrub-
ber, Report of Investigations 9615. U.S. Bureau of Mines, Pitts-
REFERENCES burgh, PA (1996).

1, O’Green, J.: Using Scrubbers to Comply with Dust Standards in 10. Jayaraman, N.L.; Schroeder, W.E.; Kissell, F.N.: Studies of Dust
High Output Continuous Miner Sections, Preprint Number 90-102, Knockdown by Water Sprays Using a Full-Scale Model Mine
Society for Mining, Metallurgy, and Exploration Annual Meeting, Entry. Transactions Society of Mining Engineering 278:1875—
Salt Lake City (Feb. 1990). 1882.

APPENDIX 1
Experimental data collected
Canta Scrubber inlet dust levels Machine dust levels R a
‘in m2 ‘me/m? eturn dust
Machine setback (mem) (mel) levels
position (m) Left inlet Right inlet Leftrearcorner Right rear corner (mg/m*)
Side sprays off
Sump 61 13,.95+3.41  7.28+4.31 3.74 + 3.32 3.05 £9.16 1.9140.27
Sump 12.2 23.2243.28 15.80 + 1.32 1.24 + 0.84 1.24 0.54 1.03 £ 0.22
Slab 61 17.704142 6344159  2.45+0.50 2.27 £0.45 1.79 £0.10
Slab 12.2 19.5842.31 5.514206 2.3340.40 1.15 +£0.55 1.73 + 2.70
Side sprays on
Sump 61 11.0342.26 7.7249.88  2.3340.73 1.86 + 0.54 1.31 40.27
Sump 12.2 16.9245.19 14.4743.08 1.75 £0.99 0.74 + 1.07 0.95 + 0.35
Slab 6.1 15894647 9,9640.57 2.61+0.84 2.21 40.55 1.30 £0.09
Slab 12.2 14.4143.03 13.3545.26 2.81+0.79 1.41 + 1.24 1.2+0.60

Note: 95 percent confidence intervals shown.


556

Return sampling location

Exhaust fan

G. V.R, GOODMAN

/ Side sprays \

= oe
Z
‘Rear corner / /

\ sampling
locations 1

- Curtain

Dump location for
conveyor bet

Ventilation
controls,

Intake sampling location

aii
<Continuous mining machine
operator sampling location

ad

FIGURE 5
Testing arrangement—field study.

with a flooded-bed dust scrubber. The scrubber, rated at 4.4 m?/s
(9300 cfm), discharged on the left side of the machine.

This mining machine used a spray system composed of 45
hollow cone sprays positioned above, below, and along the sides
of the cutting boom, in the throat and along the frame of the
machine (Figure 6). Due to the large volume of water used at this
operation, it was decided to place two side sprays each on the left
and right sides of the continuous mining machine to confine the
dust cloud under the boom. These sprays were located roughly
1.2 meters (48 inches) from the scrubber inlet (5.2 meters from
the cutting bits) and 1.3 meters (52 inches) off the bottom.

Each set of sprays was mounted in a 20-cm (8-inch) block
constructed from 6.4 cm (2-1/2-inch) steel stock. On each block,
two spray orifices were machined approximately 15.2 cm
(G inches) apart. Due to restrictions on nozzle size at this op-
eration, bigger water sprays were used in this phase of the study.
Spraying Systems Company nozzles H3/8U-5010 rated at 6.0
Ipm/nozzle (1.6 gpm/nozzle) at 689.5 kPa (100 psi) were se-
lected. Spray pressure was 689.5 kPa (100 psi) with and without
the use of these additional sprays.

Two entries (underground passages used for haulage, venti-
lation, or equipment movement) were developed on this section.

The rightmost was the intake airway that supplied fresh air to
the miners. The leftmost entry served a dual purpose. It was
not only the return entry, carrying dusty air away from the mine
workers, but was also the belt entry, containing the belt conveyor
that carried the coal away from the continuous mining machine.
These entries were approximately 6.1 meters wide by 2.7 meters
high (20 feet by 9 feet).3

Dust sampling instrumentation consisted of one RAM instan-
taneous dust monitor and two gravimetric samplers positioned
together at the left rear and right rear corners of the continu-
ous mining machine. Samples were also taken at the continuous
mining machine operator. A RAM monitor was not used at this
location. The two gravimetric samplers were not worn by the op-
erator, but were worn by a researcher who stayed within several
feet of this individual. The operator typically stood away from
the continuous mining machine on the left side of the entry. The
gravimetric dust concentrations at each of these sampling loca-
tions were calculated using the average of the two gravimetric

3A nine-foot seam height encountered in this field work is higher than typ-
ically found in domestic underground coal mining operations. The national
average seam height for current operations lies between five and six feet.®?


USING WATER SPRAYS TO IMPROVE PERFORMANCE,

555

TABLE IV
Effects of added side sprays on silica dust levels
Underboom Rear of machine Return
Setback Number of Confidence Numberof Confidence Number of Confidence
distance samples interval samples interval samples interval*
6.1-meter setback 8 0.10 + 0.49 8 —0.32 + 1.10 4 —0.35 + 2.40
12.2-meter setback 8 —0.42 + 0.74 8 0.82 + 2.10 4 1.104 0.438

495 percent confidence interval for difference in mean silica levels. Negative values indicate a reduction in dust levels at that

sampling location due to added sprays.

Confidence interval is statistically significant at 95 percent.

droplet speed and indirectly with water droplet size.” In that
testing, spray pressures of 17.2 Mpa (2500 psi) were used to
generate the high droplet speed and the lower droplet size. The
testing described in this work used much lower water pressures.
Hence, the added water sprays would have had little significant
effect on silica dust levels.

Field study data collected by NIOSH personnel suggested that
60 percent of the total cut time was spent in the sump cut, and the
remaining 40 percent was spent in the slab cut.) This 60:40 ratio
was used to weight the average sump and slab cut dust levels in
Appendix 1 to define impacts of the side sprays at the two setback
distances tested (Figure 4). For both 6.1-meter and 12.2-meter
setback distances, the side sprays reduced average dust levels at
the left scrubber inlet and increased levels at the right scrubber
inlet. These sprays also produced larger reductions of rear corner
and return dust levels at the 6.1-meter setback distance than at
the larger 12.2-meter distance.

The previous data showed that these added water sprays likely
induced airflow to move the dust cloud from the left scrubber
inlet toward the right scrubber inlet. With nothing to restrain
the dust, it could have continued to flow past the right inlet and

could have flowed from under the cutting boom. This would
have led to dust rollback and increased dust levels downwind of
the continuous mining machine. At the smaller setback distance
of 6.1 meters, air from the intake curtain was sufficient to keep
dust from flowing out the right side of the cutting boom. At the
larger setback distance of 12.2 meter, the intake curtain flow
dissipated while traveling toward the cutting head. This flow
was inadequate to limit the amount of dust flowing from under
the cutting boom. Consequently, dust rollback levels increased
and could have led to the higher dust levels measured around
the mining machine.

FIELD EVALUATION OF SIDE SPRAYS

These side sprays were evaluated at an underground mining
operation to further assess their ability to control dust exposures.
Face ventilation was provided by an exhaust tube hung along
the left side of the entry. Tubing quantity changed with the entry
and varied from 5.3 m*/s to 6.5 m/s (11,300 to 13,700 cfm).
To increase the cross-sectional area of the exhaust ventilation, a
curtain was hung around the mouth of the tube (Figure 5). Face
equipment consisted of a continuous mining machine equipped

"% 25 8 T T T T T
= Key
20 ~y
é 6r £3} Sprays off 7
G 15 r Q Sprays on
G 10
g 5
(=) ° i
6.1m 2.2m 6.1m 12.2m 6.1m "2.2m 6.1m 12.2m
r—Left inlet: Right inlet r-Left corner Right corner: Return—>

SAMPLING LOCATION

FIGURE 4
Side spray impact on average dust levels at different curtain setback distances—laboratory study.


558

the rear corners of the mining machine, small sample sizes did
not allow analyses of statistical significance.

The effect of the sprays was more pronounced at the ma-
chine operator's sampling location where dust concentrations
decreased from 2.64 mg/m? to 1.87 mg/m}, By limiting dust
levels at the rear corners of the mining machine, the sprays of-
fered increased protection of the machine operator from the high
dust levels generated during the mining process.

The data in Table V also reveal that silica dust levels decreased
with the use of the side sprays. Due to the limited data set, it is
unclear whether the reduction was caused directly by the side
sprays or by a localized geological change in the silica content
of the surrounding rock. Operating at 700 kPa (100 psi), these
sprays would have greater ability to control finer-sized silica
particles than sprays operating at, say, 350 kPa. Table V also
shows that the distribution of silica dust levels across the rear
of the continuous mining machine was essentially constant. The
added sprays did not change this condition, although silica dust
levels did decrease. Silica levels also decreased at the machine
operator's sampling location. As with respirable dust levels, sil-
ica dust levels at the machine operator’s location were tied to
silica levels measured at the rear corners of the mining machine.

Of particular interest in this study was the effect of the added
Sprays on measured dust levels at various ventilation setback
distances. This required the measurement of dust levels for dis-
crete time periods corresponding to certain ventilation setback
distances. The RAM monitors provided such a time-based record
of dust levels at the left rear and right rear sampling locations.
The ratio of average gravimetric concentration to average RAM
dust level at each location provided a means to extract equiva-
lent dust concentrations for these time periods. Multiplying this
ratio by the average RAM reading for the time period in question
gave a weighted gravimetric response for that period.

Time study data showed that the average curtain setback
distance was roughly 9.1 meters (30 feet). Thus, the analysis

G.V.R. GOODMAN

"—E 60 7
os
w £ 50 Key 4
by 40 EES! Sprays off 4
6 Ww 30 4
ae
24 20 4
dab 10 4
« .
3 ol tlds
s9.1m >9.1m s91m >9.1m
Left rear corner Right rear corner—>4

SAMPLING LOCATION

FIGURE 7
Side spray impact on average dust levels at different curtain
setback distances—field study.

compared dust levels at setback distances less than or equal to
9.1 meters to those at setback distances greater than 9.1 meters.
Appendix 2 gives the RAM-adjusted data collected during un-
derground testing and shows that tonnages varied for each of the
curtain setback distances. Hence, all dust levels were normalized
to an average tonnage of 410 tons.

Figure 7 shows that setback distance affected side spray ef-
fectiveness. The side sprays decreased dust levels at the left and
right rear sampling locations for setback distances less than or
equal to 9.1 meters. For example, dust levels at the left rear
comer decreased from over 50 mg/m? without the side sprays
to nearly 10 mg/m? with the sprays. At the right rear comer,
dust levels decreased from over 25 mg/m} to 6 mg/m? with the
side sprays in operation. For setback distances greater than 9.1
meters, use of these sprays actually led to slight increases or,
at the least, insignificant changes in dust levels. This suggests
that, as verified by full-scale laboratory testing, the side sprays
are more effective in controlling dust rollback at smaller setback
distances than at larger setback distances.

TABLE V
Gravimetric analysis of field data
Average dust Average silica
Sampling Number of Sample time concentration dust percentage
locations samples (minutes) (standard deviation mg/m*) (standard deviation) (%)
Side sprays off
Left rear corner 2 321 9.74 (2.38) 20.0 (4.38)
Right rear corner 2 321 4.58 (0.16) 23.2 (2.26)
Machine operator 2 103 2.64 (0.02) 6.28
Side sprays on
Left rear corner 2 338 8.00 (0.89) 9.44
Right rear corner 2 340 4.40 (0.01) 12.5 (0.28)
Machine operator 2 120 1.86 (0.43) 07

“Due to low weight gains, two machine operator dust samples composited (combined) into a single sample for silica

analysis.

"Only one sample analyzed for silica at left rear comer location, Sample dropped at analysis laboratory.


Using Water Sprays to Improve Performance

of a Flooded-Bed Dust Scrubber

Gerrit V. R. Goodman

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health,

Pittsburgh, Pennsylvania

Supplemental water sprays were placed along the sides
of a continuous mining machine to improve suppression and
confinement of the dust cloud under the cutting boom to re-
duce downwind dust levels. Using a full-scale mock-up of a
continuous mining machine, preliminary work showed that
these side sprays improved suppression of the dust cloud and
redistributed this cloud under the cutting head. This led to
reductions in dust levels around the machine and in down-
wind airways for some positions of the mining machine. This
testing also showed that side spray effectiveness was influ-
enced by the distance from the fresh air ventilation device to
the cutting surface, termed the ventilation setback distance.
These sprays produced larger reductions in machine and re-
turn dust levels at smaller setback distances than at larger
setback distances. These side sprays then were installed in
similar locations on a mining machine at an underground
coal mine operation to evaluate their effectiveness for im-
proving suppression and capture of dust by the flooded-bed
dust scrubber. Although sampling could not be conducted
successfully in the return, sampling around the mining ma-
chine and at the machine operator showed that dust levels
decreased with use of these sprays. Further analysis showed
that these sprays were most effective at the smaller setback
distances, a result confirmed by full-scale laboratory testing,

Keywords Occupational Health, Dust Sampling, Coal Mining, Con-
tinuous Mining, Control Technology

The increased use of flooded-bed dust scrubbers on contin-
uous mining machines generally has been responsible for de-
creased worker exposures to respirable dusts.” Much work in
government, industry, and academia has been conducted to as-
sess the effectiveness of scrubber-based ventilation schemes un-
der a variety of mining conditions.?)

This article is not subject to U.S. copyright laws.

550

One measure of scrubber performance is related to the capture
of dust or the amount of dust that finds its way into the scrubber
inlets and then to the scrubber filter. Scrubber capture depends
upon many factors such as scrubber capacity, face ventilation
method (method used to direct fresh air to areas where coal is
being cut, i.e., either blowing or exhausting curtain or tubing),
face ventilation capacity (30 CFR 75.325 specifies that at least
1.42 m?/sec [3000 cfm] be supplied to each working face where
coal is being cut),“) ventilation setback distance (distance from
the end of the ventilation curtain or tubing to deepest penetration
of the face), and machine location. During coal extraction, re-
ductions in scrubber capture often lead to increased levels of dust
rollback (dust not captured or suppressed that flows downwind
to other workers).

Scrubber capture was affected by placing water sprays outby
(a direction away from the cutting face area) the scrubber inlets
on the left and right sides of the continuous mining machine.
Sprays placed outby the scrubber inlets were placed between
the inlets and the rear of the mining machine. These side sprays
induced additional airflow along the sides of the machine to
improve containment of the dust cloud under the cutting boom.

This article documents experimental work to examine the ef-
fectiveness of these side sprays for improving capture of dust
by the flooded-bed scrubber. Assessments are given for two po-
sitions of the continuous mining machine and for various venti-
lation setback distances. The underground application of these
sprays also is discussed.

EXPERIMENTAL DESIGN

This work was conducted in a surface test gallery at the Pitts-
burgh Research Laboratory of the National Institute for Occu-
pational Safety and Health (NIOSH). This test facility simulated
acut 12,2 meters (40 feet) deep, 5.5 (18 feet) meters wide, and
roughly 2.1 meters (7 feet) high. Testing was conducted using
a mock-up of a continuous mining machine equipped with a
flooded-bed dust scrubber. The flooded-bed scrubber consisted
of a standard 40-layer filter screen, water sprays, wave plate
mist eliminator, and fan. The scrubber was rated at 2.64 m*/s


G. V.R. GOODMAN

APPENDIX 2
RAM-adjusted dust levels from underground testing (mg/m?)

Ventilation setback

distance (m) Left rear corner Right rear corner Tonnage
Side sprays off

<9.1m 19.5 6.0 160

>9.1m 13.7 3.1 480
Side sprays on

<9.1m 13.9 5.0 570

>9.1m 14.0 47 ~ 410



USING WATER SPRAYS TO IMPROVE PERFORMANCE

dust levels, Selected filters were shipped to an independent lab-
oratory for silica analysis using the P-7 method.

Sampling also was conducted in the return airway (leftmost
airway) roughly 15.2 meters (50 feet) downwind from the
exhaust fan. Preliminary data from the return sampling site
showed dust levels higher than those measured at other locations.
This was later determined to be caused by rock dusting in the re-
turn airway. Rock dust is routinely applied during mining to coat
underground coal mine surfaces with a layer of inert material,
typically limestone dust. Unfortunately, this material contains a
respirable fraction that makes it difficult to discriminate between
the mass deposited by mining and the mass deposited by rock
dusting. For this reason, return dust levels were not used in this
analysis. Also, underboom sampling could not be conducted due
to harsh conditions found near the cutting head. Finally, intake
dust levels were monitored during the study. These levels ranged
from 0.66 mg/m? to 0.74 mg/m? (average = 0.70 mg/m*) during
the study.

Due to equipment breakdowns and major production delays,
only one shift of exposure data was gathered with the side sprays
operating and one shift without these sprays operating. Over
320 minutes of sample time was accumulated for each of the
shifts, the remainder of the time taken for travel in and out of
the mine and for lunch, Dust concentrations were not adjusted

557

for equipment downtime because the sampling pumps could not
be safely reached to shut them off. The pumps near the mining
machine operator, being worn by a researcher, were shut off
during equipment moves and downtimes. For this reason, sample
times for the machine operator were much less (Table V).

The gravimetric samplers at the left and right rear corners of
the continuous mining machine and near the mining machine
operator were initially analyzed. However, tonnages were not
consistent during the study, because 980 tons were produced
with the additional sprays operating and 640 tons without these
sprays. All gravimetric dust levels were consequently normal-
ized to an average production of 810 tons.

At times, gravimetric dust levels showed considerable varia-
tion between adjacent samplers. Due to this and the small sample
sizes, it was difficult to define meaningful confidence intervals
for assessing the effects of the additional side sprays. Hence,
standard deviations are shown for the collected data (Table V).

Table V shows several trends. One, dust gravimetric dust lev-
els were much higher on the left corner of the mining machine
than on the right corner. This is not surprising given that venti-
lation flows from the right side toward the exhaust tube on the
left side. The standard deviations are also higher on the left side,
likely a result of the increased turbulence on that side of the min-
ing machine. Although the side sprays did reduce dust levels at

10 underboom pan

4 boom-end sprays
(each side)

TOP
15 upper boom
sprays. 4 boom-end sprays
(each side)
‘Scrubber inlet
SIDE

sprays

2 side sprays

4 body sprays

Scrubber
inlets

2 side sprays.

4 body sprays

10 underboom pan
sprays

FIGURE 6
Spray configuration—field testing.


USING WATER SPRAYS TO IMPROVE PERFORMANCE

ventilation setback distance, is 6.1 meters, The machine contin-
ues mining the sump cut for another 6.1 meters for a total distance
of 12.2 meters. The ventilation setback distance is now 12.2 me-
ters. The machine then backs out and moves to the left side and
removes the remaining coal block. This is termed a slab cut be-
cause solid coal is present on one side of the cutting head. Curtain
setback distances vary again from 6.1 meters to 12.2 meters.

‘Tests were conducted with and without the side sprays in
operation. The continuous mining machine was positioned in
the sump cut or in the slab cut with curtain setback distances of
6.1 meters or 12.2 meters. Each test ran for 50 minutes to provide
measurable dust quantities for all samples. All tests were repli-
cated. Concentrations for each test run were calculated using
the average of the concentrations for each set of two samplers.
Concentrations for each series of test conditions were calculated
using the average concentrations for each of the tests comprising
that set of conditions.

ANALYSIS OF LABORATORY DATA

Appendix 1 shows average dust levels and standard deviations
calculated for sump and slab cut positions of the continuous
mining machine, 6.1 meter and 12.2 meter ventilation setback
distances, and use of the side sprays. This data shows that the
highest dust levels were measured in the’vicinity of the left and
right scrubber inlets. This was expected due to the suction action
provided by the scrubber fan and the rotation of the cutting drum
which forced dust-laden air toward the scrubber inlets.

The impact of the side sprays was assessed by comparing
the mean dust level at each sampling location without the side
sprays in operation (for each combination of mining machine
position and setback distance) to the mean dust level measured
with these sprays in operation (similar position and setback dis-
tance). Hypothesis testing was then used to assess the signifi-
cance of the difference between these mean dust levels. With the
null hypothesis being no difference in mean dust levels, t-tests
were used to accept or reject this assumption. Two tails were
specified to account for any increase or decrease in dust levels
with the added sprays. Subsequent analyses constructed 95 per-
cent confidence intervals for the difference in mean dust levels.

553

An interval containing zero stated that the difference between
the two mean dust levels was not statistically significant at this
level of confidence.

Table I shows the effects of the side sprays at the left and
right scrubber inlets for various curtain setback distances and
machine positions. With the machine in the sump cut, the supple-
mental sprays generally reduced underboom dust levels. These
reductions were statistically significant when measured at the
left scrubber inlet, possibly a result of improved suppression
provided by the additional sprays on that side. The added sprays
had little significance on dust levels at the right inlet at either
the 6.1-meter setback distance (p-value > 0.20) or 12.2-meter
setback distance (p-value = 0.10).

With the mining machine in the slab cut, however, the side
sprays increased dust levels at the right inlet and decreased dust
levels at the left inlet. All changes were statistically significant,
with the exception of the left inlet sample at the 6.1-meter set-
back distance (p-value = 0.18). The increases measured at the
right inlet, however, indicate more dust in the vicinity of this inlet
which, in turn, could lead to improved capture of the underboom
dust cloud at the right scrubber inlet.

‘Two possible mechanisms could account for the impacts of
the additional side sprays on dust levels measured near the scrub-
ber inlets. One, these sprays improved suppression of the air-
borne dust in the underboom region by placing more water on
the dust cloud. This could have led to the decreases measured at
the left inlet. Two, the unbalanced arrangement of sprays could
have pushed the dust cloud from the left inlet toward the right
inlet. The ability of water sprays to suppress airborne dust and
induce airflow movement is well documented in the literature
and one or more of these mechanisms could have resulted in the
change in dust levels measured during this testing.

The data in Tables II and III show that the side sprays did
not have a consistent effect on dust levels measured at the left
and right rear corners of the mining machine and in the return.
Significant results were found with the mining machine in the
sump cut and a 6.1-meter ventilation setback distance. The re-
duction at the left rear corner and in the return was significant at
the 95 percent confidence level, while the reduction at the right
rear corner was significant at the 90 percent confidence level

TABLE
Effects of added side sprays at the left scrubber and right scrubber inlet sampling locations
Left scrubber inlet Right scrubber inlet
Machine position:
Setback Number of Standard error Confidence interval Number of Standard error Confidence interval*
(m) samples (mg/m*) (mg/m?) samples (mg/m?) (mg/m?)
Sump cut: 6.1 5 071 -2.92 + 2.268 4 0.85 0.44 + 3.66
Sump cut: 12.2 6 1.42 —6.30 + 3.958 6 0.78 =1.3342.17
Slab cut: 6.1 5 1.19 -2.13 £3.78 6 0.32 3.62 + 0.898
Slab cut: 12.2 6 0.88 —5.84 + 2.458 6 1.59 7,84 + 4.428

495 percent confidence interval for difference in mean dust levels. Negative values indicate a reduction in dust levels at that sampling location

due to added sprays.
8 Confidence interval is statistically significant at 95 percent.


552

‘9 underboom pan

3 boom-end sprays sprays

(each side)

1 side spray

TOP 3 scrubber inlets
15 upper boom 10 underboom 2 Side sprays
sprays
sprays
3 boom-end sprays
(each side)
Scrubber inlet
SIDE
10
vnmertooTM 9 underboom pan
sprays
FIGURE 2

Spray configuration—laboratory study.

For this testing, two samplers were placed under the miner
boom at the left or off-curtain side scrubber inlet and the right
or curtain side scrubber inlet (Figure 1). These instruments
were hung roughly 13 cm (5 inches) beneath each inlet. The
scrubber inlet samples served as relative measures of scrubber
capture, where higher dust levels measured at these locations
corresponded to increased dust flow into the scrubber and thus
increased capture of dust.

Two samplers also were placed on the left and right rear cor-
ners of the mining machine. Dust concentrations measured at
these two locations reflected dust rollback levels. For instance,
lower dust levels at the rear corners reflected an increased cap-
ture of dust by the scrubber. Finally, a set of two gravimetric
samplers was placed in the return airway to monitor downwind
dust levels.

A RAM (Realtime Aerosol Monitor, GCA Corp., Bedford,
Massachusetts) dust monitor also was placed in the return to
monitor pre-test or baseline conditions. Prior to each test, dust
was injected at the cutting head for 10 minutes with the cutting
head rotating and only the blowing curtain ventilation in opera-
tion. During this baseline period, the dust cloud was allowed to
stabilize before operating the scrubber and water sprays. A ratio
was then calculated by dividing the average RAM baseline read-
ing for a series of tests (similar setback distance, similar mining

obtained by multiplying the respirable dust concentration measured with an
approved sampling device by the factor 1.38.

G. V.R. GOODMAN

Coal
block

6.1-m setback 12.2-m setback
end of sump cut end of sump cut
6.1-m setback 12.2-m setback
end of slab cut end of slab cut

FIGURE 3
Positions of mining machine and ventilation
curtain—laboratory study.

machine position, similar side spray usage) into the RAM base-
line reading for that test being normalized. This ratio was used to
adjust the average gravimetric concentrations for any variations
in dust feed.

In underground coal mining, a continuous mining machine re-
moves coal in blocks. Although removal or extraction sequences
can differ between mining operations, the following sequence
was used for this testing (Figure 3). The sequence begins with
the mining machine cutting on the right side for a distance of
6.1 meters, This initial cut is termed a sump cut because solid
coal is present on both sides of the cutting head. The distance
from the end of the ventilation curtain to the cutting head, or the


USING WATER SPRAYS TO IMPROVE PERFORMANCE

S51

Gallery exhaust fan

Gallery intake '

Intake curtain

|
Return seein

Intake airflow —|

Right rear corner
sampling location

Right underboom
sampling location

location

Left underboom
sampling location

Left rear corner
sampling location

‘Scrubber exhaust

FIGURE 1
Testing arrangement—laboratory study.

(5600 cfm). Dust drawn by a vane-axial fan through three in-
lets under the cutting boom impacted on a wetted stainless steel
screen. The moisture-laden air continued through the screen and
across a mist eliminator to remove the water. The air then ex-
hausted on the left side of the machine frame.

Air from the main gallery fan was drawn through a series of
curtains to mimic a blowing curtain ventilation scheme. Airflow,
as measured at the mouth of the blowing curtain, ranged from
2.78 m?/s to 3.02 m3/s (5900 cfm to 6400 cfm). This curtain was
positioned on the right side of the test gallery (Figure 1).

The continuous mining machine used a conventional face
spray system consisting of 40 hollow-cone sprays positioned
above, below, and along the sides of the cutting boom. Tests
also were run with additional sprays positioned on the left and
right sides of the continuous mining machine, roughly 61 cm
(24 inches) from the left and right side scrubber inlets. These
sprays were angled outward 30 degrees from the body of the min-
ing machine (Figure 2). These sprays were the flat-fan variety,
instead of hollow-coned or full-coned, to place more water from.
each spray along the body of the machine rather than impacting
on the sides of the machine. Spraying System Company nozzles
H3/8U-4010 rated at 3.78 Ipm at 344.7 kPa (one gpm at 50 psi)
were used during testing. Due to the parameters available for this
testing, an unbalanced arrangement of sprays was discovered to
be best for controlling dust under the boom. Consequently, two
sprays were placed on the left side of the machine and one was

used on the right side. A water pressure of 344.7 kPa (50 psi),
measured at the spray manifolds, was maintained for all tests.
Water flow to the miner was approximately 125 lpm without the
side sprays in use and 136 Ipm with these side sprays in use.

For this testing, a mix of silica dust in coal dust was used.
Samples of this silica-coal feed dust were sent to an independent
laboratory for P-7 silica analysis that showed that the mix aver-
aged 13.0 + 0.7 percent silica. This dust was introduced into
the gallery at the miner cutting head via a compressed air/eductor
system. One hose discharged on the left side of the cutting drum
while the other discharged on the right side of the drum. The
cutting head was rotated at 50 revolutions per minute to insure
adequate mixing of the dust with the ventilation airflow.

For dust sampling, constant flow pumps pulled dust-laden air
through 10-mm nylon cyclone separators at a rate of 2 liters/min
to deposit the respirable mass onto preweighed 37-mm filters.
All filters were subsequently weighed and dust levels calcu-
lated. These levels were not corrected to MRE (Mining Research
Establishment) equivalents.” Selected filters sent to an indepen-
dent laboratory for silica analysis using the P-7 method.

130 CFR 74.3 gives the specifications for approved dust sampling units
in underground coal mining; 30 CFR 70.205 requires that approved sampling
devices operate at a flow rate of 2.0 liters/minute,

230 CFR 70.206 requires that respirable dust concentrations measured
with an approved sampling device be converted to an equivalent concentration
‘measured with an MRE device. Currently, MRE equivalent concentrations are