a 132 ms
2s

& a 2.03 m/s

Fowl e258

dus

H 10 RAM-concentration

3

aos

OU 234 5678 9 10111213 415 161718 19302122 292625
Shield Number

Figure 6, Average RAM-dust concentration levels along the
longwall gallery in SPSS

those at the tailgate operator (shield 13). Immediately
downwind of the head gate drum (shields 11 and 12), the
concentration does not increase. However, it rises steeply
downwind of shield 12, exposing the tailgate operator to the
headgate drum dust. Immediately downwind of the tailgate
operator (shield 13), the concentration increases from the
tailgate drum dust source. However, after shield 16, it
decreases towards the tailgate. Overall, the concentration at
the return station is lowest when compared to that of
tailgate operator (shield 13), 2/3rd downwind of the shearer
(shield 18) and shield 19.

In Figure 6, the average dust concentrations measured by
the RAMs at each shield from shield number 8 to shield

number 23 are shown for the three velocities, These
concentrations are calculated from the RAM plots for each
experiment. The dust profile for the locations, 1/3rd upwind
of the shearer, headgate operator and return location for
different test conditions, were of similar pattern. As the
shearer is between shield 10 and shield 16, it is evident that
the shearer dust contamination of the walkway air starts
between shield 13 and 14 and increases to a maximum
between shields 16 and 17. The effect of increased air
quantity on concentrations is more pronounced downwind
of shield 16. These data indicate that the location of miners
downwind of shield t4 is not advisable.

TPSS results

The TPSS experiments were performed at three air/water
pressures (414 kPa, 552 kPa and 690 kPa) and three face air
velocities (1.52 m/s, 2.03 m/s and 2.54 m/s). The average of
the two gravimetric dust concentration measurements at the
various sampling stations is shown in Figure 7 (left plot).
The pattern shown is similar to that of SPSS results, As in
the case of SPSS, the concentrations at the headgate
Operator and shearer mid-point are quite low whereas those
at the tailgate operator are comparatively very high. As
shown in Figure 8, for a constant pressure, increase in
airflow decreases the dust concentration at the stations. On
the other hand, though pressures higher than 414 kPa lead
to lower concentrations at all stations except at shield 18,
the effect of increasing pressure at a constant airflow on
concentration is not as distinct,

In Figure 7 (right plot), the average dust concentrations

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Figure 7. Average dust concentration levels (left plot) and average RAM-dust concentration levels (right plot)
along the fongwall gallery in TPSS


arithmetic mean of the RAM dust concentrations from the
top, middle and bottom levels. As expected, with increase
in air velocity there is a decrease in the dust concentration
and the relationship is linear. However, the coefficient of
determination of 0.78 (correlation coefficient = 0.88)
indicates that 22 per cent of the variance in the data is not
explained by using the velocity factor alone as the
independent variable. This is an indication of the several
factors other than velocity, which cause variability in dust
measurements during each experiment.

Size distribution of airborne dust

Two experiments were conducted at air velocities 1.68 m/s
and 2.37 m/s in the longwall gallery to determine the
' changes in the size distribution of the airborne dust as it
flowed in the gallery. For this purpose, impactors were set-
up at shields 18, 21 and 24. The impactors were operated
for a period of 60 minutes with a sampling rate of 2 L/min.
During these experiments, dust was released but all sprays
were turned off. Based on the mass of dust on each stage in
the impactor, the concentrations as well as the size
distributions of the airborne dust in gallery were calculated.
The size distribution of the feed dust is shown in Figure 4.
The total weight of the dust collected in the impactor at
shield 18 is lower as compared to those at shields 21 and
24, Ata velocity of 2.37 m/s, airborne dust at shields 18,
and 24 have greater proportion of fines than in the feed
dust. Their distributions also appear to be fairly close.

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2 ‘ mw Shield 24
; 1 Feed Dust
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Particle size iw microns

100
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10
.

i Pe ss
z # aw Shiekt 21
a ° a Shick 4
5 : . Foot Dust

Ait velocity. 1.68 ms

oa

or i ta dow
Purtiche size in microns

Figure 4, Size distribution of coal dust along the longwall gallery
(2.37 ms and 1.68 m/s)

Table I.
Summary of the droplet size and number of droplets

‘Spray |- Pressure [Volume cf | Mass of | Droplet] Numberof
Type kPa _| Water Limin | Water, gfmin | Size um | Oropletsimin
30 sai EG 350 2EE 8
sPss 328 3405 34085, 260, ‘S70E+08
4035 30.74 307425 280 4.866409
EXETE ral 22710 7, TOSE+11
Tess | sagvata 23.84 23045.5 86 T.AtE+10
ELE 28.40 26406. 5, ER0E+10

However, the results at the lower velocity of 1.68 m/s do
not follow this trend, The impactor data at shield 18 shows
a greater proportion of fines than in the feed dust. The
airborne dust size distributions at shields 21 and 24 appear
to be identical, and have fewer fines than at shield 18. The
size distributions also appear to be closer to that of feed
dust. Deposition and agglomeration are two phenomena
affecting changes in the size distributions of the feed dust
and airborne dust. The measurement of the airborne dust
size distribution by impactor may also be a contributing
factor to the differences observed in these results.

Droplet size and number of droplets

The droplet sizes and the total number of droplets at
different pressures in SPSS and TPSS experiments are
shown in Table 1. The droplet size data were provided by
the manufacturer whereas the data on the number of
droplets were calculated using Equation [3]. The data
indicate that a SPSS droplet is comparatively larger than a
TPSS droplet size in all ‘cases, and the number of droplets
in TPSS is about 20 times more than that in SPSS.

SPSS results |

The SPSS experiments were performed at one water
pressure (1035 kPa) and three face air velocities (1.52 m/s,
2.03 m/s and 2.54 m/s). The average of the two gravimetric
dust concentration measurements at the various sampling
stations are shown in Figure 5. The concentration data
obtained from the tailgate station is not used in the
discussion here due to the fact that due to its location. the
airflow at the station is not representative of the airflow in
the face. The patterns of dust concentrations at the three
velocities are similar. As expected, the increased air
velocity in the gallery causes, a decrease in dust
concentration. The concentrations at the headgate operator
(shield 6) and‘shearer mid-point (shield 12) are lower than

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OV 23 AS 67 HF 111213 14 15 1617 18 192024 29.23 2428
Shield Number

Figure 5.A verage dust concentration levels along the longwall
gallery in SPSS


measured by the RAMs at each shield from shield number 8
to shield number 23 aré shown for the three air velocities.
The pattern of dust concentration increase around the
shearer is similar to'that noted-in SPSS. Higher RAM
concentrations in all the eighteen experiments (3 pressures
X 3 air velocities X 2 replicates) was teached at shield 16,
In all cases, these concentrations are higher thin the highest
SPSS ‘concentrations (3 pressures *X *
experiments). ‘The increase in’dist concentration levels
between shield numbers 13 and 18, probably resulted due to
the rollback of dust onto the. walkway. As opposed to the
experiments reported in a ‘continuous miner gallery or a
laboratory set-up!'0.!2, the walkway location in the longwall
gallery is relatively close to the sprays for the dust rollback
to influence the ambient concentration in the walkway, The
decrease in the dust concentration from shield: 19 towards
shield 24 is due to. knockdown, deposition and diffusion of
the dust. ... eee . -

In.the RAM data, the highest concentration for both
TPSS and SPSS. was noted at shield.16. In-SPSS, this
concentration was 27.74. mg/m3 at 2.03 m/s velocity. In
TPSS, the experimental condition at which the highest
concentration observed was 690 kPa pressure and 1.52 m/s
velocity. The highest concentration was 38.61 mg/m3.
RAM samplers have shown to be affected by water sprays
and the smaller droplet size and greater number of droplets
with TPSS may have.moré impact on the RAMs.
Gravimetric results suggest that, in general, dust levels with
TPSS were equal to or less than dust levels with SPSS
(Figures 5 and 7 [left plot]).

Using the RAM data, the rates of change of
concentrations in SPSS and TPSS were calculated for the
following locations and are shown in Table II: (a) the rate
of increase in concentration from shield 14 to shield 16, {b)
the rate of decrease in concentration from shields 16 to 19,
and (c) the rate of decrease in concentration from shields 19
to 23. In TPSS, the average rate of increase of
concentration from shields 14 to 16 is lower with higher
pressures. The average rates of decrease in concentration
between shields 16 and 19, and shields 19 to 23 in TPSS are
also lower at higher pressures. When SPSS results are
compared with TPSS results, it is noted that: there is no
consistent pattern. However, the higher rates of decrease in
concentration in TPSS may be the result of greater
atomization of spray. These results suggest that the
performance of TPSS is better than SPSS downwind of the
shearer.

Water and energy consumption in SPSS and TPSS

The water consumptions at different pressures in both SPSS
and TPSS are shown in Figure 8 (top plot). At all pressures,
the water consumption in SPSS is higher than those in

Table It
Rates of change of concentration in SPSS and TPSS
PSs TPS

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oss

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5
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414. 552 690. 1035

‘Water/Air Pressure. kPa

Power Consumption. kW.

Figure 8: Water consumption (top plot) and power consumption
(bottom plot) in TPSS and SPSS

TPSS. In TPSS, at 690 kPa water and air Pressure, the
water consumption is.26.45. L/min. In the case of SPSS, at
1035 kPa, the water consumption is 39.74 L/min. The
power consumptions in SPSS and TPSS are shown in
Figure 8 (bottom plot). TPSS consumes approximately six
times more power than SPSS at high pressure.

Comparison of SPSS and TPSS results

The highest gravimetric concentration in SPSS and TPSS
experiments was at the 2/3rd downwind station (shield 18).
In SPSS, this concentration was 21.34 mg/m3 at 1.52 m/s
velocity. In TPSS, the experimental conditions at which the
highest concentration observed were 414 kPa pressure and
1.524 m/s velocity. The highest concentration was 21.08
meg/m3.

Conclusions

The dust collection efficiencies of SPSS and TPSS were
studied through experiments in a model longwall gallery.
The experimental design consisted of 2 factors: spray water
and air pressure, and ventilating airflow. Each factor had
three levels. The differing spray characteristics of the
chosen TPSS and SPSS nozzles did not allow a direct
comparison of the two systems.

In the present experimental set-up, the dust rollback into
the walkway may be a factor in the case of TPSS. Other
important observations from this study are.noted. The rate
of decrease in concentration with TPSS is higher than. that
with SPSS. This may be due-to the greater atomization of
the water. Positioning of the personnel upwind of the


Evaluation of two-phase spray system for airborne dust

control in a longwall gallery

B.K. BELLE*, R.V. RAMANII and J.F. COLINETt
*CSIR-Miningtek, Pretoria, South Africa
t Pennsylvania State University, USA
+Pittsburgh Research Laboratory, NIOSH, USA

The increased effectiveness of a two-phase spray system (TPSS) over a single-phase spray system
(SPSS) for dust suppression is reported in several laboratory studies. The dust collection
efficiencies of SPSS and TPSS were studied in a mode! experimental longwall gallery facility at
Pittsburgh Research Laboratory at NIOSH (USA). The experimental design consisted of two
factors: pressure, and airflow. Each factor had three levels. SPSS experiments were conducted at
only one pressure (1035 kPa) which is nearly 1.5 times higher than the highest air and water
pressure for TPSS experiments. The results of the study are presented in this paper.

While it appears that TPSS performed better than SPSS, the data is not sufficiently conclusive
on this aspect. The differing spray characteristics of the chosen TPSS and SPSS nozzles did not
allow a direct comparison of the two systems. In the TPSS arrangement, considerably greater
turbulence in airflow is created around the shearer; it is likely that at feast in the immediate
vicinity of the tailgate drum, there is a roll back of the dust/mhist cloud into the walkway.
Therefore, positioning of the personnel upwind of the tailgate drum is necessary to avoid high
dust exposures, The rate of decrease in concentration with TPSS is higher than that with SPSS.
This may be due to the greater atomization of the water, The test set-up did not allow the study of
conditions when coal is cut from tail to head where the potential for personal exposure is high.
Changes in the experimental design are necessary to overcome some of the reasons expected for

the inconclusive results.

Introduction

The most common method to control the airborne dust in
longwall is through water sprays mounted on the shearer
cutting drums!. Techniques implemented for the control of
shearer-generated dust included high drum water flow
rates, improved cutting techniques*, shearer clearer-type
external water spray systems’, and radio-remote controlé, It
has been suggested that to move air and redirect the dust
away from the operator in a longwall face, the external
spray pressure should be at least 1035 kPa. To suppress
dust before it becomes airborne, drum spray pressure
should be kept below 690 kPa’. Several Jaboratory studies
have shown®-!3 that the dust collection efficiency of TPSS
is greater than that of SPSS. In view of these positive
laboratory results, a study was planned at the model mine
gallery, at the Pittsburgh Research Laboratory.

The model longwall gallery at the Pittsburgh Research
Laboratory consisted of a simulated longwall face, a modei
double-ended ranging drum shearer, and a face ventilation
system capable of generating a wide range of ventilation
rates. The gallery is 37.8 m long and simulates a 2.13 m
high coal face. The model longwall has 24 wooden shields
along the face. The double-drum shearer is 11.9 m long and
0.96 m wide; the diameter of the drums is 1.6 m. The drums
rotate to simulate the effect of rotation on air and dust
behavior. The drum spray nozzles used in this study were
Spraying Systems H-1/4U-0010 and H-1/4U-0015. solid
stream nozzles, The headgate drum had 7 nozzles of the

0010 type and 26 of the 0015 type, while the tailgate drum
had one nozzle of 0010 type and 32 of the 0015 type. Water
is supplied to the shearer with a 450 L/min pump operating
at pressures up to 1380 kPa. One water line supplies the
drum sprays at a pressure of 552 kPa, while another
supplies the sprays mounted on the shearer body and can be
changed to that required for experimental conditions. Each
line is fitted with a flow meter and a pressure gauge. The
drum sprays are fed through a rotary union. The spray
system, mounted on the shearer body (the shearer-clearer
sprays) is designed for exchangeable nozzle configurations.
These were the nozzles that were studied in the SPSS and
TPSS experiments. The shearer body sprays are pointed
toward the drums, and spray over the ranging arm to wet
material within the cutting and loading zones, The gallery is
ventilated by an adjustable vane-axial fan with a maximum
capacity of 14.2 m/s. The maximum face air velocity
attainable is 2.54 m/s.

Experimental design

Two sets of experiments were designed for the study. The
design considered two factors that are readily changeable in
a mining operation. The factors are.(a) spray water and air
pressure and (b) air quantity in the face. Each factor had 3
levels, In the TPSS experiments, the pressures ranged from
414 kPa to 690 kPa, and air velocity ranged from 1.52 m/s
to 2.54 m/s. In the SPSS experiments, the effect of
changing air velocity for a single test pressure of 1035 kPa


tailgate drum is necessary to avoid high dust exposures.
The present set-up did not allow the study of conditions
when coal is cut from tail to head where the potential for
"personal exposure is high. Changes in the experimental
design are necessary to overcome some of the reasons
expected for the inconclusive results. Some suggested areas
are experiments with same nozzle types, same pressure
conditions and higher TPSS pressures. This might have
created a different air flow pattern around the shearer.
While it appears that TPSS performed better than SPSS, the
data is not sufficiently conclusive on this aspect.

Acknowledgements

The authors gratefully acknowledge the support of the
NIOSH for the research reported in this paper. They also
express their appreciation to Robert Jankowski (deceased),
Group Supervisor, and Tom Ozanich, Technical Staff, and
G. Sun, R.Srikanth, S. Sharan and P. Liu, graduate students
in Mining Engineering at the Pennsylvania State University
for their assistance during the design and performance of
the experiments.

References

1, WIRCH, S., and JANKOWSKI, R.A. Shearer-
mounted scrubbers, are they viable and cost-effective?
Proceedings of the 7th US Mine Ventilation
Symposium, Wala, AM. (ed.). Littleton, USA, SME,
1995. pp. 319-325.

2. JANKOWSKI, R.A., and ORGANISCAK, J.A.
Research allays longwall dust. Coal Mining and
Processing, vol. 21, No. 2, 1984. pp. 48-52.

3. LUDLOW, J.E., and JANKOWSKI, R.A. Use lower
shearer drum speeds to achieve deeper coal cutting.
Mining Engineering, vol. 36, No. 3. 1984. pp. 251-
255.

4, WIRCH, S., KELLY, J.S., and JANKOWSKI, R.A.
An expert system for longwall shearer drum design.
Proceedings of Longwall USA, Published by McGraw
Hill Company, 1988. pp. 257-264,

5. JAYARAMAN, N.1., JANKOWSKI, R.A., and
KISSELL, F.N. Improved shearer-clearer system for

double-drum shearers on longwall faces. U.S. Bureau
of Mines, RI 8963, 1985. LE pp.

Bureau of Mines. How to reduce shearer operators’
dust exposure by using remote control. Technology
News, no, 203, 1984,

Bureau of Mines. Selecting water spray pressures for
optimum dust control. Technology News, no. 244.
1986.

JAYARAMAN, N.L., JANKOWSKI, and R.A.,
BABBITT, C.A. High pressure water-powered
scrubbers for continuous miner dust control.
Proceedings of the 4th US Mine Ventilation
Symposium. McPherson, M.J. (ed.). CO, SME, 1989.
pp. 437-441.

WHITEHEAD, K.L., and JAYARAMAN, N.I.
Evaluation of two-phase flow scrubber. Report on
contract S0398000, USBM/SSI Services Inc., 1990.
45pp.

JAYARAMAN, N.I., COLINET, J.F., and
JANKOWSKI, R.A. Evaluation of a two-phase flow
scrubber in a model mine. Proceedings of the 3rd
Symposium on Respirable Dust.’ Robert L. Frantz,
and Raja V. Ramani, (eds). Littleton, CO, SME, 1991.
pp. 223-226.

ALABOYUN, A.R. The effect of surfactant on
suppression of coal dust particles. Master of Science
thesis, Pennsylvania State University, PA, 1989,
pp. 17-38.

HU, Q. Dust removal by surfactant containing water
sprays. Master of Science thesis, The Pennsylvania
State University, PA, 1992. pp. 12-22.

. Belle, B.K. Evaluation of a two-phase spray system

for dust suppression, Master of Science thesis,
Pennsylvania State University, PA, 1996. pp. 75-79.
HAGERS, J. A simple method for determining nozzle
atomization/power efficiency. Spraying Systems Co.,
IL, 1988.

KISSELL, F.N., RUGGIERI, S., and JANKOWSKI,
R.A. How to improve the accuracy of coal mine dust
sampling. American Industrial Hygiene Association
Journal, vol. 47, 1986. pp. 602-606.


was evaluated. In all the test conditions, the drum sprays’
pressure was maintained at 552 kPa. For each test
condition, two experiments were conducted. A total of 24
experiments were performed.

Coal dust and particle size distributions

Bituminous coal dust was used in the experiments as the
feed dust. The size distribution of the feed dust was
obtained through Microtrac Particle Size Analyzer (PSA).
Samples of the feed dust were obtained directly by random
collection of the coal dust from the feeder. For determining
the size distribution of the airborne dust along the gallery,
airborne dust samples were obtained using cascade
impactors.

Dust feeder

Two mini eductors utilized compressed air at 345 kPa to
transport dust through two hoses to the shearer drums, A
pressure gauge and a regulator were installed in the
compressed air supply line to monitor and control the air

feeding the mini eductors. The compressed air entering the ~

mini eductors passed through a venturi like section in the
eductors, which induced the dust feed into the air stream.
Two screw feeders discharged coal dust at rates of 0.0355
kg/min and 0.0545 kg/min through the head gate drum and
tailgate drum respectively. The approximate location of
these dust sources are shield 10 and shield 15, respectively.

Spray nozzles

The nozzle selected for the SPSS experiments was a 3/8
BD-3 hollow-cone hydraulic spray nozzle (Mode! No
747886-2). For the TPSS experiments, the air-atomizing
nozzle used was of the type Model No 1/4J-SU-22.

SPSS and TPSS set-up

The number of sprays in the shearer-body (the shearer-
clearer spray bar system) is 10. The spray bars had been
designed to provide clean water and air for both the
hydraulic and air atomizers. For the TPSS experiments, the
spray manifolds are assembled on a new spray bar, so that
there was the same number of nozzles with nearly the same
spacing between the nozzles as in the SPSS experiments.
High-pressure compressor and water pump were used to
obtain the required air and water pressures for the tests.
Pressure regulators and control valves were used to adjust
and maintain, as far as possible, constant air and water
pressures and the rate of water flow during an experiment.

Figure 1. Schematic view of the model longwall gallery

Sampling plan

The sampling plan is shown in Figure 1. For each test,
gravimetric samples were collected at the 1/3rd upwind of
the shearer (shield 6), headgate operator (shield 8), shearer
mid-point (shield 12), tailgate operator (shield 13), shield
19, 2/3rd downwind of the shearer (shield 18), tailgate
(shield 24) and at the return: Two gravimetric tespirable
dust samplers, operating at 2 L/min, were used to sample
respirable dust concentrations-at each of the sampling
locations. Excepting in the return, the units were suspended
from a hanger in the approximate breathing zone of the
operator. In the return, two samplers were suspended at the
top, middle and bottom locations.

Real-time aerosol monitors (RAM-1), were used to
supplement the gravimetric samplers at selected locations.
RAMs are positioned at 1/3rd upwind of the shearer,
headgate operator, tailgate operator, 2/3rd downwind of the
shearer, shield 19 and at the return. In the return location,
cyclones for RAM-1 were located at approximately 0.51,
1.02, and 1.52 metres from the roof. The cyclone
preseparator for each RAM was suspended between the two
cyclones used for gravimetric sampling and connected to
the RAM with Tygon rubber tubing. Data loggers were
used to record instantaneous dust concentrations. In
addition, the output of the RAMs in the return station was
transmitted to the multi-channel strip chart recorder in the
control room for monitoring during the test.

Sampling time

From the shake-down test, it was observed that after about
10 minutes from the start of the experiment, the dust
concentration in the gallery stabilized. Therefore, the sprays
were turned-on after 10 minutes. Excepting for the samplers
at the intake, and headgate shearer operator position, a
sampling time of 75 minutes from the time the sprays were
turned on, was sufficient for all other sampling locations to
obtain the necessary weight gain on the gravimetric filters.
During the experiment, the sampling packages at the
headgate operator, tailgate operator, and shield 19 position
were moved to the next downwind shield after 15 minutes
of sampling at one shield. The purpose of this method of
sampling was to obtain the dust profile around the shearer
from the RAM charts, and assess the exposure potential of
the shearer operators.

Experimental procedure for TPSS and SPSS

The following procedure was followed for each of the
experiments.

+ Firstly, all the gravimetric samplers, and RAMs fitted
with data loggers were positioned according to the
sampling plan. The water and air supply systems were
checked for the highest and the lowest pressure ranges
which can be attained during the experiment,
Throughout the experiment, water and air pressures and
the airflow were monitored and recorded automatically.
The monitored data are frequently checked both on
instant dials and the strip charts. The RAMs were
turned on,

*Secondly, the fan, the dust injection system, and
shearer drums, were switched on, and sufficient time
(>10 minutes) was allowed for the experimental
conditions to stabilize, The air velocity and the
concentration in the return were monitored in the
control room.

* When the flow conditions stabilized (>10 minutes). the


drum sprays were turned on. The spray system (SPSS
or TPSS) under investigation was aiso turned on after a
lapse of 2 to 3 minutes, and the water and air pressures,
and water flow were increased to the experimental
conditions. Then, the gravimetric samplers were also
turned on, .

+ After sampling for fifteen minutes at a location, the
sampling packages at locations, headgate operator,
tailgate operator, and shield-19 were moved to the
immediately downwind shield.

* After at least 75 minutes, the gravimetric samplers and
the RAMs were switched off. The dust feeder and
shearer drums, and the water and air to the nozzles
were also turned off in that order.

° Finally, the dust samples were removed from the
samples for gravimetric analyses. The data loggers are
Processed to download the data onto a personal
computer and a software package was used to calculate
average dust concentrations for the base and the test
periods,

Data acquisition
Tn each experiment, the following data were collected:

Air velocity in the gallery, water and airflow rate
through the nozzle, and water and air pressures,

* The gravimetric dust samples at specified locations.

* The impactor samples at specified locations,

* Instantaneous concentrations recorded by RAMs at
specified locations.

Data analysis procedure

Concentration and size analysis

Using the data collected above, the following information is
generated: (a) The gravimetric dust concentrations at
different locations along the longwail gallery, (b) The size
distribution of the airborne dust along the longwall gallery,
and (c) The total number of droplets generated in both
SPSS and TPSS at different pressures.

An example of the typical output from the RAM is shown
in Figure 2. This specific chart is for the RAM at shield 19
during the TPSS experiment at 690 kPa pressure and 1.524
mvs air velocity. As the RAM is moved from shield 19 to
shield 23, there is a decrease in the dust concentration. This
may be the result of dust knockdown as well as dust
dilution. The average return concentration for each test was
calculated as the arithmetic average of the individual dust
concentrations for the six return samples.

‘Ar Velocity: 1 524 mis
Preasure: 890 kPa
Spray Type: TPSS.
Shearer Locstian: Sruekia 101018

ie Pend Shield 19 SPruyPenad

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Ya2es0 135280 134280 IESESO 140RSO teIZSO W4.2Red 142280 14aZed
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Figure 2. Typical RAM-1 output from a test along the longwall
gallery

Power consumption

The power consumption calculated here is the cross product
of the volume of fluid flow and the pressure drop across the
nozzle!4, This energy does not include line losses, pump
and motor efficiency. For, the TPSS nozzle, power input to
the nozzle consists of the sum of power supplied for the
water and air. In SPSS, it is only the power supplied by
water. The air power required fora TPSS nozzle is given
by:

HP, = 0.221* SCFM * ((Pa/ 14,7)" — 1) (1)

where SCFM is the air quantity flowing through the nozzle
m3/s, and Pa is the absolute pressure in kPa.
The water power required for a TPSS nozzle is given by:

BP we, = (GPM * PSIG)/IT14.3 [2]

where GPM is the water quantity flowing through the
nozzle in L/min, and PSIG is the gauge water pressure in
kPa,

Number of droplets and droplet size

For the SPSS and TPSS nozzle, the droplet size for the
specified water/air pressures were obtained from the
manufacturer. The number of droplets generated per minute
for a particular set of operating conditions was calculated
using the following equation by Alaboyun!'!.,

M, 6M,

=k (1

Ny =the,
o My” mp,(Rp)

where,
Kz is the constant (value depends on the units used)
Np is the number of droplets generated /minute
M is the mass rate of water flow, g/minute
Mp is the mass of a droplet, g/droplet
Rp is the droplet diameter, um
pu is the liquid density, g/m3.

Results

Several prior investigations have provided data to conclude
that measurements of airborne dust concentrations are
associated with variabilities arising from several
uncontrollable factors!5, In this experimental study,
airborne dust concentration was measured in the return
without turning on the sprays prior to each experiment. The
plot of the average respirable dust concentration at the
return without the sprays on is shown in Figure 3. Here, the
average dyst concentration at the return was calculated as

Respirable dt concentration = 35.79 - #.54° Air velocity
. Correlation coetTicient (1) = 0.88

Dust concentration, mg/a*
8

Air Velocity, ovs

Figure 3. The plot of air velocity vs. average dust concentration in
the return