1 

EFFECTS OF WATER SPRAYS USED WITH A MACHINE-MOUNTED SCRUBBER ON FACE METHANE 

CONCENTRATIONS 

C. D. Taylor and J. A. Zimmer 

Natl Inst for Occuptnl Sfty and Health

Pittsburgh, PA, USA 

ABSTRACT 

This study was conducted to determine the effects 

of a machine-mounted scrubber and water sprays on 

face methane levels. Testing was conducted in the 

NIOSH ventilation test gallery which was designed to 

simulate a full-scale mine entry. In the test entry, a 

model mining machine, equipped with water sprays 

and a simulated dust scrubber, was located at the 

face of a 20-ft box cut. Blowing ventilation was 

provided using a curtain with a 40-ft setback 

distance. Methane released from a pipe manifold 

located inby the mining machine was monitored at 

six locations that were 1 ft outby the pipe manifold. 

Tests were first conducted to evaluate the effects of 

using sprays and scrubber separately on face 

methane levels. Additional tests were conducted to 

determine how a scrubber used with various water 

spray systems would affect face methane levels. 

The use of either sprays or scrubber reduced face 

methane levels significantly. The combined use of 

sprays with the scrubber further reduced face 

methane levels a small amount. Primarily the sprays 

affected methane levels by changing airflow 

distribution close to the face. 

INTRODUCTION 

To have effective face ventilation, the intake air 

delivered to the end of the tubing or brattice must 

reach the face. Studies have shown that often only 

a small fraction of the intake air exiting the end of 

the curtain or tube actually reaches the face 

(Thimons, 1999). The amount of air reaching the 

face usually decreases the greater the tubing or 

curtain setback distance. Research conducted 

concurrently with the development of extended cut 

mining methods demonstrated that machinemounted water sprays and scrubbers could be used 

to help direct additional intake air to the mining face 

when setback distances exceeded 20 ft (Volkwein, 

1985). 

Although designed primarily for dust control, 

machine-mounted water sprays and scrubbers play 

an important role in increasing the amount of intake 

air that reaches an extended cut mining face. A 

water spray moves air like a small fan. When used 

with exhaust ventilation, groups of sprays directed 

30° toward the return side of the entry create airflow 

patterns that help clear methane from the face. 

On sections with blowing ventilation, the large 

quantities of air moved by machine-mounted dust 

scrubbers affect face airflow patterns. Tests using 

scrubbers with both blowing and exhausting 

ventilation show that operation of a scrubber always 

reduces face methane concentrations unless the 

scrubber exhaust flow interferes with the movement 

of the intake air toward the face (Taylor, 1996). 

Most exhaust ventilation sections use sprays but 

no scrubbers. Sprays with a scrubber are used 

together on most sections that have blowing 

ventilation. Past research to evaluate the effects of 

scrubber use on face methane levels has been 

conducted with operating spray systems. Using a 

scrubber and sprays together reduced face methane 

levels for a range of setback distances, and scrubber 

and intake flows (Taylor, 1996). Another study 

showed that water spray systems, regardless of 

design, improved methane control when used with 

scrubbers. However, ventilation improved most 

when the spray system was directed toward the 

return side of the face (Volkwein and Wellman, 

1989). 

The current research is a continuation of earlier 

studies to evaluate how the combined use of 

scrubbers and water sprays affect face methane 

levels while using blowing ventilation. Tests were 

conducted for a range of operating conditions that 

included multiple drum heights and the use of side 

and underboom sprays. 
 

TEST FACILITY 

Gallery 

Testing was conducted in the NIOSH Pittsburgh 

Research Laboratory’s Ventilation Test Gallery. One 

side of the “L” shaped building is designed to model 

an underground mining entry which is 16.5 ft wide by 

7 ft high (Figure 1). An exhaust fan draws 

approximately 12,500 cfm of air into the gallery. For 

these tests a brattice and wood curtain, constructed 

2 ft from the left side of the entry directed 7,500 cfm 

of intake air toward the face. Curtain setback 

distance for all tests was 40 ft. The return air was 

pulled from the gallery behind a brattice and wood 

wall built along the right side of the entry. A 4-ft wide 

by 20-ft long box was built along the right side of the 

face to simulate an uncut slab of coal. A box cut, 

rather than a slab cut configuration, was selected 

because changes in methane levels inby the cutting 

head are easier to detect in the more confined area 

of the box cut. 

Figure 1. Ventilation test gallery. 

Mining Machine 

A full-scale model mining machine was located at 

the center of the 12.5 ft wide box cut face (Figure 2). 

During testing the cutting head rotated at 40 rpm 

and the center of the drum was positioned 

approximately 20, 40 and 60 in. above the floor 

(Figure 3). These locations are referred to as the 

“down,” “middle,” and “up” drum heights. The mining 

machine was equipped with a simulated dust 

scrubber. A fan mounted in the machine drew air 

into two 10 by 14 in. scrubber inlets located below 

and just behind the machine boom (Figure 4 ). An 

orifice plate was placed in the scrubber duct to limit 

flow to approximately 7,000 cfm for all tests where 

the scrubber was operating. Air from the scrubber 

was exhausted through a 15 by 15 in. opening at the 

right rear of the machine and directed straight back 

the entry toward the return. The water spray system 

included manifolds located on the top, side and 

under the boom (Figure 5). 

Figure 2. Model mining machine at face of box cut. 

Figure 3. Drum test heights. 

Figure 4. Scrubber location on model mining machine. 
 

Figure 5. Spray locations on model mining machine. 

Water Spray Systems 

Top spray manifold: Ten BD-3 hollow jet nozzles 

were mounted approximately 12 in. apart in each of 

two 10-ft long plastic pipes located on top of the 

miner boom. The sprays in one pipe were directed 

straight toward the face. In the other pipe they were 

directed 30° to the right. All spray nozzles were 

approximately 30 in. from the face. 

Side spray manifold: Four Vee-jet nozzles were 

positioned 6 in apart in a 28-in. plastic pipe that was 

mounted vertically on the left side of the mining 

machine. The flat spray nozzles were aligned so 

that the spray pattern was vertical and directed 

toward the face. 

Underboom spray manifold: Four BD-3 hollow jet 

nozzles were positioned 6 in. apart in a 28-in. plastic 

pipe that was attached to the underside of the 

cutting boom. The nozzles were mounted in swivel 

fittings that allowed them to be directed toward the 

face or angled to the right. 

Water flow and pressure: The water pressure 

provided by a centrifugal pump was measured at a 

gauge mounted near the front of the model mining 

machine. Flows and pressures varied depending on 

the number of operating sprays. For all tests using 

water sprays, pressures were maintained between 

110 and 130 psi and the flow was allowed to vary 

depending on the number of sprays operating. 

Pressure at the gauge was adjusted by redirecting 

part of the water flow at the pump. 

METHANE RELEASE AND INSTRUMENTATION 

Methane gas was released into the gallery through 

four horizontal copper pipes that were drilled on top 

and bottom with 1/16 in. diameter holes (Figure 6). 

The pipes were equally spaced horizontally, and 

located 4 in. away from the face to provide a 

relatively uniform release of gas. 

Methane was released at a flow rate of 

approximately 45 cfm. For some tests, however, the 

gas flow was reduced to prevent concentrations in 

the gallery from exceeding 2 pct. Methane gas 

concentrations were measured at the six locations 

shown on Figure 6. 

• Locations 1, 2, and 3 are 1ft from the roof 

and face, evenly spaced across the face 

• Locations 4, 5, and 6 are 1ft from the face 

and 4 ft below locations 1, 2 and 3. 

A vacuum pump was used to draw an air sample at 

0.5 lpm from each of the six sampling locations. 

Each air sample was drawn through 30 ft of 1/4 in. 

plastic tubing and passed over an individual catalytic 

heat of combustion type sensor head. 

Figure 6. Gas release and sampling locations at the model 

face. 

TEST PROCEDURE 

After setting up the operating conditions (spray 

configuration, scrubber and intake flow, and cutting 

head height) for each test, gas was injected through 

the manifold for five minutes to allow time for the gas 

and air to mix and reach a relatively steady state in 

the gallery. After allowing time for mixing, data was 

collected for an additional five minutes. 

Concentration data from each methanometer was 

down-loaded to a personal computer via a 

Metrabyte1

 A/D conversion board for the entire ten 

minute test. Lab Tech software was used to 

organize and store the data, and an computer 

spreadsheet was used to calculate the average 

methane concentrations for each of the six sampling 

locations. Tests were repeated once and the results 

averaged. 

An “overall” average concentration was calculated 

for all six sampling locations, and group average 

concentrations were calculated for samples on the 

 1

Reference to specific manufacturers does not imply 

endorsement by NIOSH. 
 

“left” (locations 1 and 4), “center” (locations 2 and 5) 

and “right” (locations 3 and 6) of the face. The 

effectiveness of the face ventilation provided by the 

different spray and scrubber systems was 

determined by comparing average methane 

concentrations. 

RESULTS 

Methane concentrations measured with only the 

scrubber or sprays operating were compared to 

concentrations during tests with neither operating. 

Only the top-mounted 30° sprays were used for 

these tests. The scrubber was operated at 7,000 

cfm. Due to a mechanical problem during this series 

of tests, data was obtained only with the drum at the 

middle and down heights. Figure 7 shows that the 

use of the scrubber or water sprays reduced 

methane concentrations at the left, center and right 

side of the face. Overall average reductions due to 

the use of the scrubber or sprays were 70 and 56 

pct respectively. 

Figure 7. Effect of drum height on methane levels using 

top mounted sprays at three face areas. 

Additional tests were conducted using the scrubber 

and either the 30° or straight top sprays. Data was 

obtained with the drum at three heights. Figure 8 

shows average concentration data obtained with the 

drum at all three heights for the left, center and right 

face sampling locations. At each location, methane 

concentrations were slightly higher when using the 

straight sprays. Overall average face concentrations 

with the straight sprays were about 14 pct higher 

than with the 30° sprays. 

Drum height also had an effect on methane 

concentrations when either top spray system was 

used with the scrubber. Figure 9 shows the 

combined average for all six face location 

concentrations calculated for the straight and 30° 

spray systems at each drum height. With the drum 

up, average face methane concentrations with the 

two top water sprays systems were about 30 pct 

higher than when the drum was down. Average 

face concentrations were lowest when the drum was 

at the middle height. 

Figure 8. Comparison of methane reduction with top 

mounted sprays at three face areas. 

Figure 9. Effect of drum heights on methane levels using 

top mounted sprays. 

Remaining tests were conducted only with the 

drum up and the top water sprays (either straight or 

30°) and scrubber operating. Scrubber and intake 

flow were maintained at 7,000 cfm. Using 

underboom sprays with the nozzles directed straight 

toward the face, and top 30° sprays, methane levels 

increased 42 pct on the left side of the face (Figure 

10). Methane levels on the right side of the face 

increased 66 pct when the side sprays were used 

with the top straight sprays (Figure 11). 

Combining use of the underboom and side sprays 

with the top 30° sprays reduced left side methane 

concentrations 39 pct (Figure 12). Right side 

concentrations were reduced 50 pct when the 

underboom and side sprays were used with the top 

straight sprays. 

For the tests conducted with the underboom 

sprays, the spray nozzles were directed straight 

toward the face. With the drum up and the 30° top 

sprays operating, tests were conducted with the 

underboom sprays angled approximately 45° to the 

right. Figure 13 shows a comparison between face 

concentrations measured with underboom straight 
 

and underboom angled sprays. With the underboom 

sprays angled 45°, the average face concentration 

on the left side of the face was reduced 60 pct. 

Figure 10. Using underboom sprays with the top sprays. 

Figure 11. Using side sprays with the top sprays. 

Figure 12. Combined use of underboom and side sprays 

with top sprays. 

DISCUSSION AND CONCLUSION 

Methane concentrations at the face were reduced 

significantly when either water sprays or the 

scrubber were turned on. Baseline airflow patterns 

were drawn for face ventilation provided only by the 

blowing curtain (7,000 cfm) set at a 40-ft setback 

distance. Using smoke tubes airflow patterns were 

drawn for the baseline condition, and ventilation with 

either the scrubber or sprays operating (Figure 14). 

Ventilation with only the blowing curtain created a 

“figure 8” flow pattern that moved from the return to 

the intake side of the face. Operation of the 

scrubber or water sprays reversed the direction of 

the face airflow resulting in movement from the 

intake to the return side of the face. Based on 

observations of the smoke flow, more intake air 

reached the face with only the scrubber operating, 

and the flow patterns were straighter and better 

defined. Establishing a face airflow that moves from 

the intake to return side of the entry is an important 

factor in reducing face methane levels. 

Figure 13. Comparing the effects of straight and angled 

underboom sprays. 

The turbulence created by operating the scrubber 

and sprays together made it difficult to accurately 

determine face airflow direction. However, when the 

sprays and scrubber were used together intake air 

moved up the curtain side of the entry and back the 

return side of the entry. It is likely, therefore, that 

using top sprays and the scrubber together results in 

face airflow that moves from the intake to the return 

side of the face. Top sprays angled 30° toward the 

return side of the face created a spray pattern that 

interfered less with face air flow pattern than the top 

straight sprays. This resulted in lower face methane 

levels. 

Water sprays have a greater effect on face airflow 

patterns when exhaust ventilation is used because 

the face air velocities are generally lower than with 

blowing ventilation. When sprays are used with 

blowing face ventilation and a scrubber, the water 

sprays influence air flow primarily within 3 or 4 ft of 

the face. Although they can have a significant effect 

on re-distributing the gas at the face, the sprays 

have less effect on moving methane out of the face 

area. 

Cutting drum height affected methane levels. For 

the conditions tested, which included a uniform 

release of methane at the face, methane levels were 
 

highest when the drum was up. When the drum is 

up most of the water impacts the roof and the spray 

has less of an effect on face airflow. Most tests 

were conducted with the drum up because 

concentrations were higher. Methane levels were 

lowest when the drum was at the middle height. 

With the drum at the middle the sprays move more 

air. 

When used with top 30° sprays, underboom 

sprays, which are primarily used for dust control, 

created air flow turbulence that interfered with airflow 

movement across the face. The result was that face 

methane levels increased on the left side of the face. 

Adding side sprays improved airflow across the face 

and reduced methane levels. Angling the 

underboom sprays toward the return side of the 

entry also helped to reduce turbulence and reduced 

methane levels. 

The conditions tested were designed to simulate 

face ventilation during mining of a box cut using 

blowing ventilation. Methane concentrations 

measured in an operating mine will vary depending 

on the actual operating conditions and the methane 

liberation rate in the face area. The results obtained 

provide guidelines for selection and use of water 

spray systems for use in improving face airflow and 

reducing methane concentrations at the face. 

The guidelines are designed to reduce methane in 

the face area using water sprays and scrubbers, but 

will not necessarily reduce dust generated at the 

face by the mining operation. Water sprays increase 

turbulent airflow at the face that can improve dilution 

of methane with available intake air. Turbulent flow 

can increase dust levels if it creates excessive dust 

rollback. In some situations the use of a particular 

water spray system can reduce the collection 

efficiency of scrubbers by causing the dust to bypass 

the scrubber inlets. Studies to evaluate the effect of 

water sprays on dust and water for the same range 

of operating conditions are planned. 

Figure 14. Face airflow patterns for (A) no water sprays or 

scrubber, (B) scrubber only, and (C) water sprays only. 

REFERENCES 

Taylor, C.D., Rider, J. and Thimons, E.D. 1996, 

“Changes in Face Methane Concentrations Using 

High Capacity Scrubbers with Exhausting and 

Blowing Ventilation," Proceedings of the SME 

Annual Meeting, Preprint 96-167, Phoenix, AZ, 

March 11-14, 5 pp. 

Thimons, E. D., Taylor, C. D., and Zimmer, J. A., 

1999, “Ventilating the Box Cut of a Two-Pass 40 ft 

Extended Cut,” Journal of the Mine Ventilation 

Society of South Africa, Vol. 52, No.3, July/Sept., 

108-115 pp. 

Volkwein, J. C., Ruggieri, S. K., McGlothlin, C. and 

Kissell, F.N., 1985, “Exhaust Ventilation of Deep 

Cuts Using a Continuous-Mining Machine,” Bureau 

of Mines Report of Investigation No. 8992, 16 pp. 

Volkwein, J. C., Thimons, E.D., and Hallfinger, 

G.,1985, “Extended Advance of Continuous Miner 

Successfully Ventilated With a Scrubber in a Blowing 

Section,” 2nd US Mine Ventilation Symposium, Reno, 

NV, Sept 23-25, pp. 741. 

Volkwein J C., and Wellman, T.S., 1989, “Impact of 

Water Sprays on Scrubber Ventilation 

Effectiveness,” Bureau of Mines Report of 

Investigation No. 9259, 12 pp.