Effect of Scrubber Operation on Airflow and Methane Patterns at the 

Mining Face 

C.D. Taylor, J. E. Chilton, E. Hall, and R.J. Timko 

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA, USA 

ABSTRACT: The National Institute for Occupational Safety and Health (NIOSH) has conducted research to 

determine the influence of mining machine-mounted scrubbers on airflows and methane concentrations at the 

face when blowing ventilation systems are used. Tests were conducted in a full-scale ventilation gallery with 

a model mining machine that simulated airflow created by a dust scrubber. During the tests, ultrasonic anemometers were used to measure airflow speed and direction at several locations near the face. For the same 

test conditions, methane was released from the face and gas concentrations were measured at 21 locations 

above the machine using fixed point methanometers. Changes in airflow speed and direction are correlated 

with scrubber airflow and the measured methane distribution above the mining machine. The research results 

showed that operation of machine-mounted scrubbers improved face ventilation when blowing ventilation is 

used by increasing both the intake flow and the quantity of air reaching the face. 

1 INTRODUCTION 

Effective face ventilation requires that the intake 

air delivered to the end of the tubing or brattice 

must reach the face. For cuts deeper than 6.1 m (20 

ft), as little as 5 pct of the air delivered to the end 

of the curtain reaches the face (Thimons 1999). 

The amount of air delivered generally decreases as 

the curtain setback distance increases. Flooded bed 

scrubbers are widely used on continuous miners to 

reduced airborne dust levels during cutting. Previous research by Volkwein (1986), Gillies (1982), 

and Taylor (1996, 1997) showed that scrubber operation increases the quantity of air reaching the 

face. The increased airflow can result in lower 

methane levels. However, the mechanisms 

whereby scrubber operation increases face airflows 

are not clearly understood. 

The objective of the current work is to use a 

full-scale model of a mining machine at a simulated mining face to examine how scrubber use affects face airflow and methane concentrations. Ultrasonic anemometers were used to measure 

airflow near the face with and without a scrubber 

operating. Changes in methane concentrations resulting from use of the scrubber were determined 

by releasing methane at the face and measuring the 

methane concentrations above the machine. 

2 TEST PROCEDURES 

2.1 Gallery and mining machine 

Testing was conducted in NIOSH’s Pittsburgh Research Laboratory, Ventilation Test Gallery. One 

side of the “L shaped building” is designed to 

model an underground mining entry, which is 5 m 

(16.5 ft) wide by 2.1 m (7 ft) high (Fig. 1). A 1.2 m 

(3.5 ft) wide by 12.2 m (40 ft) long box was built 

along the right side of the face to simulate an uncut 

slab of coal. The resulting entry simulated a 4 m 

(13 ft) wide box cut. 

A brattice and wood curtain constructed 0.6 m 

(2 ft ) from the left side of the entry directed airflow toward the face for the scrubber evaluation 

tests. The curtain set back distance for all the tests 

was 10.5 m (35 ft). The intake flow quantity was 

calculated by multiplying the velocity times 1.3 m2 

(14 ft

2

), the cross-sectional area of the airflow 

pathway behind the curtain. Regulator door openings were adjusted to deliver the desired flows of 

1.9 or 2.8 m3/s (4000 or 6000 ft3/min) to the end of 

the curtain. 
Figure 1. NIOSH ventilation test gallery. 

A full-scale model continuous miner was located at the center of the entry to simulate a mining 

machine at a box-cut face (Fig. 2). The continuous 

miner model includes a simulated scrubber system 

that consists of the following: 

- Two inlet openings 25 by 36 cm (10 by 14 in), 

 one on each side of the mining machine, and 

2.7 m (9 ft) from the front edge of the cutting 

 drum. 

- An exhaust opening 38 by 38 cm (15 by 15 in) at 

the right rear of the machine chassis. Louvers 

over the exhaust opening direct the airflow away 

 from the face. 

- Ducting to provide flow between the inlets and

 exhaust openings. 

- An axial fan to move the air from the scrubber 

inlet openings to the exhaust. 

Figure 2. Continuous miner model used in ventilation gallery.

Scrubber airflow is adjusted by inserting orifice 

plates with different size openings into the ducting, 

just upstream of the fan. 

2.2 Airflow Measurement 

Two, three-axis anemometers ( Windmaster) and 

one, single-axis anemometer (Solent), manufactured by Gill Instruments Ltd. Great Britain (Disclaimer: Mention of any company or product does 

not imply endorsement by NIOSH), were used to 

make the airflow measurements. Both instruments 

measure velocities of 0.01 m/s (2 ft/min) and 

greater. Airflow measurements were made at seven 

locations as marked in Fig. 3. The single-axis instrument measures flow in the direction in which 

the instrument is oriented. An arrow on top of the 

instrument indicates the direction of the flow 

measurement. Behind the curtain, the single-axis 

anemometer was aligned with the airflow that is 

directed toward the face. 

Figure 3. Ventilation gallery airflow sampling locations. 

The three- axis instruments were used to measure flow velocity between the curtain and the face 

where flow direction frequently changes. The instruments were positioned vertically so the flow 

velocity measurements were made only in a plane 

parallel to the top and bottom of the entry (Fig. 4). 

The vector components in this horizontal plane, 

measured by the anemometer, were used to calculate flow in the horizontal plane in the direction of 

the flow. Although the three-axis instrument also 

measures flow in the vertical direction, velocities 

were only calculated for the airflow in a horizontal 

plane. 
 

 

To simplify the comparison of velocities measured between the curtain and the face, measurements with the three-axis anemometers were calculated to give flow velocities either perpendicular or 

parallel to the face. Specifically, velocities perpendicular to the face were determined for locations 3-6. By convention, if the airflow was toward the face it was positive, and away from the 

face it was negative (Fig. 4). Velocities parallel to 

the face were determined for locations 1 and 2. 

The sign for flow parallel to the face was positive 

to the right and negative to the left. 

Figure 4. Ve rtically mounted three-axis anemometer sensor 

head. 

The three-axis sensor heads at locations 1 and 2 

were positioned 61 cm (2 f t) from the roof and at 

locations 3-6 the sensor heads were 30 cm (1 ft) 

from the roof. The sensor head for the one-axis instrument (location 7) was located at the center 

point behind the curtain. 

All anemometers were programmed to record 

average airflow data once a second. A software 

program (ANEMVENT 2003) written by NIOSH 

recorded the three-axis instruments data, and H yper Terminal software (Hilgraeve, Inc.) was used 

to record data from the single-axis instrument. 

Data was transferred to EXCEL spreadsheets for 

analysis. The average velocities were calculated 

for the duration of each test (2 to 3 minutes). 

2.3 Methane Measurements 

To evaluate the distribution of methane concentrations over the mining machine, natural gas (approximately 96 pct methane) was released into the 

gallery through four connected horizontal 3.7 m 

(12 ft) long by 3.8 cm (11⁄2 in) diameter copper 

pipes. Holes were drilled 2 mm (0.06 in) in diameter and 6.3 cm (21⁄2) apart on top and bottom of 

each pipe. The four pipes were equally-spaced vertically, and located 0.1 m (4 in.) away from the 

face to provide a relatively uniform release of gas. 

Methane concentrations were measured at 21 

locations above the mining machine (Fig. 5). All 

21 locations were 43 cm (17 in) from the roof. A 

vacuum pump pulled air samples through plastic 

tubing from each of the sampling locations to one 

of 15 heat-of-combustion methane sensors. Fifteen 

locations (1-15) were monitored simultaneously. 

Tests were then repeated to obtain data for locations 16-21. 

Figure 5. Ventilation gallery methane sampling locations 

above mining machine. 

To allow the methane and air to mix thoroughly, methane was released into the gallery for 5 

minutes before making gas measurements. A constant flow rate [approximately 0.01 m3

/s (21 

ft3

/min)] was monitored and maintained by passing 

the gas through a rotameter. For some tests, however, the gas flow was reduced to prevent concentrations in the gallery from exceeding 2.5 pct. For 

the reduced flow tests, methane concentrations 

were adjusted by using the ratio of the flows. After 

mixing, methane concentrations were measured for 

the next 5 minutes. The concentrations were recorded once every second. Data was downloaded 

to a computer via an analog-to-digital conversion 

board using commercial data acquisition software. 

Average concentrations were then calculated for 

each sampling location. 
2.4 Test Conditions 

Airflow and methane readings were taken for the 

following six operating conditions: 

- Scrubber off, intake flow 1.9 m3

/s (4000 ft3/min) 

- Scrubber off, intake flow 2.8 m3/s (6000 ft3/min) 

- Scrubber flow 1.9 m3

/s (4000 ft3/min), 

intake flow 2.8 m3/s (6000 ft3/min) 

- Scrubber flow 1.9 m3/s (4000 ft3/min), 

intake flow 1.9 m3

/s (4000 ft3/min) 

- Scrubber flow 2.8 m3/s (6000 ft3/min), 

intake flow 2.8 m3/s (6000 ft3/min) 

- Scrubber flow 2.8 m3

/s (6000 ft3/min), 

intake flow 1.9 m3/s (4000 ft3/min) 

Tests were repeated for each of the six test conditions, and the results averaged for each set of conditions. 

3 RESULTS AND DISCUSSION 

3.1 Airflow Measurement Results 

As described above, airflow velocities were calculated for flows moving either parallel or perpendicular to the face. The velocities of the airflow as 

it moved parallel to the face (locations 1 and 2) are 

shown in Figures 6-7. W ith the scrubber operating 

the velocities varied from 0.07 to 0.18 m/s (15 to 

35 ft/m in). Without the scrubber, velocities were 

practically zero. In most cases velocities increased 

when the intake airflow volume was increased. 

Figure 6. Airflow parallel to face (Location 1). 

Figure 7. Airflow parallel to face (Location 2). 

With no scrubber, the air moved toward the face 

on the right side of the machine and away from the 

face on the left side of the machine. With the 

scrubber operating, airflow directions were reversed on each side of the machine. Although directions were reversed, the flow velocities were 

similar on the right side of the machine, with and 

without the scrubber operating. Increasing the 

scrubber flow decreased airflow velocities moving 

toward the left side of the face. 

Figure 8. Airflow perpendicular to face (Location 3). 

Figure 9. Airflow perpendicular to the face (Location 4). 

Figures 10 and 11 show the airflow velocities 

measured at locations 3 and 5-7 along the left side 

of the entry. These locations correspond to distances of 1.5 m (5 ft), 4.6 m (15 ft), 6.1 m (20 ft), 

and 10.7 (35 ft) from the face. Airflow velocities 

decreased as air moved away from the curtain. 

With the scrubber off, velocities 4.6 m (15 ft) from 

the face had decreased to practically zero. Increasing either the intake or scrubber airflows increased 

air velocities, except at sampling location 3, which 

was 5 feet from the face. At this location, the flow 

velocity is reduced because a portion of the air 

moving toward the face is drawn into the scrubber 

inlet, which is just outby location 3. 
 

Figure 10. Left side airflow perpendicular to face (4000 

3 ft /min intake). 

Figure 11. Left side airflow perpendicular to face (6000 

ft3

/min intake). 

 

Flow velocities at the end of the curtain increased when the scrubber was turned on. A test 

was conducted to evaluate the source of the increased flow. Two of the three regulator doors 

were closed and the third left completely open 

(Fig. 1). An outside door was opened enough to 

adjust intake flows to either 1.9 m3/s (4000 

ft3

/min) or 2.8 m3/s (6000 ft3/min) behind the 

blowing curtain. 

For each intake flow, the airflow velocity was 

measured at the end of the curtain and at the regulator door opening with the scrubber operating. 

The air quantities were determined by multiplying 

the measured velocities by either the area behind 

the curtain or the area of the regulator opening. 

The same airflow measurements were made at the 

end of the curtain and at the regulator door opening, but with the scrubber operating with the following conditions: 

- Scrubber flow 1.9 m3

/s (4000 ft3/min), 

intake flow 2.8 m3

/s (6000 ft3/min) 

- Scrubber flow 2.8 m3

/s (6000 ft3/min), 

intake flow 1.9 m3

/s (4000 ft3/min) 

In each case with the scrubber operating, the

airflow behind the curtain increased and the flow

at the regulator door decreased (Fig.12). The flow 

quantity measured at the end of the curtain was 24 

to 51 percent greater than the flow quantity measured at the regulator door. The additional airflow at 

the end of the curtain could be due either to additional intake airflow diverted from the flow at the 

regulator doors, or air leaking from the return to 

the intake side of the blowing brattice. 

Figure 12. Airflow changes measured behind the curtain and 

at the regulator door due to scrubber use. 

3.2 Methane Measurement Results 

Methane concentrations measured above the mining machine are shown in Figures 13 and 14 for 

1.9 m3/s (4000 ft3/min) and 2.8 m3/s (6000 ft3/min) 

intake airflows. The distribution of the methane 

over the mining machine indicates airflow patterns 

that are distinctly different for the various intake 

and scrubber flow combinations. The methane 

concentrations measured over the mining machine 

were higher closer to the face where the gas was 

released, and lower on the left side of the machine 

where the curtain was located. The highest concentrations generally occurred in the corner of the face 

opposite the blowing curtain. Operation of the 

scrubber reduced methane levels at most of the 

sampling locations. 

Figure 13. Methane concentrations above mining machine 

(4000 ft3

/min intake flow). 
 

Figure 14. Methane concentrations above mining machine 

(6000 ft3

/min intake flow). 

The methane sampling locations (Fig. 5) were 

arranged in seven rows with three locations in each 

row. The methane concentrations were averaged 

for each of the seven rows of samples to evaluate 

how concentrations varied with distance from the 

face. The averages for each row were plotted versus the distance from the face (Figs. 15-16). For 

example, rows 1 and 7 correspond to distances of 

0.6 m (2 ft) and 7.9 m (26 ft), respectively, from 

the face. With or without the scrubber operating, 

methane concentrations generally decreased as 

sampling distance from the face increased. The 

concentrations decreased faster when the scrubber 

was on, and intake airflow was higher (i.e. 6000 

cfm). 

Figure 15. Methane concentrations with distance from face 

(4000 ft3

/min intake). 

Figure 16. Methane concentration with distance from face 

(6000 ft3

/min intake). 

Methane released from the pipe manifold simulated methane liberation at the mining face. Some

of the gas liberated at the face will pass through 

the scrubber and be exhausted in the direction of 

the entry return. Part of the gas from the scrubber 

exhaust, however, can move back toward the face 

and over the machine. A test was conducted to 

determine how methane from the scrubber exhaust 

would affect methane levels over the machine. A 

3.8-cm (11⁄2 in) inner diameter hose was placed in 

the scrubber ducting, just upstream of the scrubber 

outlet, to inject methane into the scrubber airflow 

(Fig. 2). The maximum possible methane flow 

[0.016 m3/s (34 ft3/min)] was used to obtain a 

minimum gas concentration in the ventilation airflow needed for detection using the methane monitors. Test conditions included: 

- Intake flow of 2.8 m3

/sec (6000 ft3/min) and 

a scrubber flow of 1.9 m3/sec (4000 ft3/min), and 

- Intake flow of 1.9 m3/sec (4000 ft3/min) and 

a scrubber flow of 2.8 m3

/sec (6000 ft3/min). 

After allowing time for the gas and air to mix, 

methane concentrations were measured at methane 

sampling locations 16 to 21 (Fig. 5). Methane 

from the scrubber exhaust was present above the 

machine for both test conditions. Higher concentrations were measured when scrubber flow was 

greater than the intake airflow (Fig. 17). 

Figure 17. Methane from scrubber exhaust. 
4 CONCLUSIONS 

Scrubber operation increased the airflow velocity 

behind the blowing curtain and at all sampling locations along the intake side of the entry. Consequently, airflow volumes reaching the face were 

greater when the scrubber was on. Scrubber operation also affected flow direction. With the scrubber 

on, air drawn into the scrubber reduced flow velocities at sampling locations inby the inlets, espe -

cially when the intake airflow was 1.9 m3

/s (4000 

ft3

/min). However, airflows inby the inlets were 

still higher and methane concentrations were lower 

than when the scrubber was off. With no scrubber 

operating, air moved from right to left across the 

face and reversed when the scrubber was on. 

Changes in airflow velocities and direction due 

to scrubber operation affected methane concentrations measured above the mining machine. Methane concentrations generally were lower at most 

sampling locations when the scrubber was turned 

on. Methane concentrations were reduced the most 

on the left side of the face where air velocities 

were highest. Regardless of whether the scrubber 

was operating or not, methane concentrations decreased as distance from the face increased. The 

concentrations decreased more quickly when the 

scrubber was operating and the intake airflow was 

1.9 m3

/sec (4000 ft3/min). 

 Methane levels closest to the face (locations 

1-3) were also affected by airflow direction. Concentrations were higher with the scrubber off because the right to left flow interfered with the 

movement of air to the return side of the entry. 

With the scrubber on, velocities decreased as the 

air moved from left to right across the face. The direction of the flow and the reduction in velocity resulted in higher methane concentrations at the right 

corner of the face. 

Because the scrubber operation increased airflow behind the curtain, more air was directed toward the face. This study showed that part of this 

air was intake air drawn up behind the curtain. The 

remainder of the increase in intake airflow most 

likely came from return air that was drawn through 

openings in the blowing curtain. 

Test results showed that methane in the scrubber exhaust can move back over the mining machine. More methane passed back over the machine when the scrubber flow was greater than the 

intake airflow. For the conditions tested, any gas 

from the scrubber exhaust would have had only a 

small effect on methane levels at the face. Moreover, the increase in intake airflow reaching the 

face due to scrubber operation would have further 

reduced methane gas from the scrubber exhaust. 

5 DISCLAIMER 

The findings and conclusions in this report are 

those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. 

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Taylor, C .D., Rider, J .P. & Thimons, E. D. 1 997. Impact of 

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