IMPACT OF UNBALANCED INTAKE AND SCRUBBER FLOWS 

ON FACE METHANE CONCENTRATIONS 

Charles D. Taylor, James P. Rider, and Edward D. Thimons 

Pittsburgh Research Center, Pittsburgh, Pennsylvania 

ABSTRACT 

Research was conducted to investigate how ventilation of a 

mining face is affected when scrubber flow is greater or less than 

intake flow. Tests were conducted in a full-scale surface test gallery built to simulate a mining entry with a continuous mining machine at the face. Methane gas was released at constant flow at 

the mining face. Gas measurements taken at six locations near 

the face were used to evaluate how well the face was being ventilated. Increasing scrubber flow resulted in lower methane levels 

even when scrubber flow was much greater than intake flow. 

INTRODUCTION 

Cutting depths for continuous mining machines are getting 

deeper. More than half of the operating continuous miner sections 

have received approvals to cut deeper than 6.1 m (20 ft). A ventilation research program at the NlOSH Pittsburgh Research Center has been dedicated to looking at those factors that affect the 

ventilation of extended cuts. The goal is to provide methods for 

maintaining ventilation effectiveness for a variety of operating 

conditions including increased set back distances. 

Flooded bed scrubbers are widely used on mining machines to 

reduce airborne dust levels during cutting. Research by Volkwein 

(1986) and Gillies (1982) has shown that operation of scrubbers 

also help reduce face methane levels by increasing face airflow. 

Research conducted by Taylor (1996) and others at the Pittsburgh 

Research Center has further documented the role that machinemounted scrubbers play, especially during the mining of extended 

cuts. The earlier research at the Pittsburgh Research Center 

showed that operation of the scrubber resulted in reduced face 

methane levels as long as: 

the scrubber exhaust didn't interfere with intake airflow, and, 

intake and scrubber flow were equal. 

Common practice in most mines that use scrubbers is to maintain scrubber and intake airflows within 0.5 M3/s (1000 cfm). This 

practice is based on the assumptions that: 

When intake flow is greater than scrubber flow, dust concentrations increase due to decreased dust collector inlet efficiency. 

When intake flow is less than scrubber flow, methane concentrations increase due to increased scrubber recirculation. 

To conform to underground practice, intake and scrubber flows 

were kept equal during earlier research tests conducted at the 

Pittsburgh Research Center. The objective of the current research 

is to determine how face methane levels are affected by unbalanced scrubber and intake flows. All combinations of three intake 

and three scrubber flows were tested. With these conditions it was 

possible to test the assumption that when intake flow is less than 

scrubber flow higher methane levels result. 

DESCRIPTION OF TEST GALLERY 

Testing was conducted in the Pittsburgh Research Center's 

Methane Test Gallery. One side of the "L" shaped building (figure 

1) is designed to model an underground mining face entry which 

has dimensions, 4.7 m (16.5 ft) wide by 2 m (7 ft) high by 37 m 

(1 20 ft) long. The return air from the face exits the entry behind a 

brattice and wood wall located on the right side of the entry. 

Figure 1. Methane test gallery. 

Mining Machine 

A full-scale model mining machine with water sprays, and dust 

scrubber system (figure 2), was located at the center of the face. 

Panels made of brattice and wood 0.9 m x 0.9 m (3 ft x 3 ft) were 

constructed on each side of the cutting head to simulate blocks of 

uncut coal. The center line of the cutting head was 1.2 m (4 ft) 

from the floor. 

Eleven hollow cone (BD-3) water sprays were mounted on top 

of the boom and directed 10 degrees to the right. Three additional 

hollow cone sprays were mounted at the left front of the miner 

chassis. Two of these sprays were directed to the right and one 

toward the left corner of the face. Water pressure and flow were 

kept constant 827 kPa and 83.3 Ipm (1 20 psi and 22 gpm) for all 

tests. 

The scrubber system (figure 2) consisted of: 

inlets on each side of the mining machine, approximately 3.7 

m (12 ft) from the mining face, 
Back scrubbsr 

in~sth p3.7m1 

Figure 2. Model mining machine (plan view). 

an exhaust at the right rear of the machine chassis, and 

two fans with attached ducting to move the air from the inlets 

to the exhaust. Scrubber flows were 2.8, 4.7 and 6.6 m3/s 

(6000,10000 and 14000 cf m). 

Both fans were needed to obtain scrubber flows of 6.6 and 

4.7 m3/s (1 4000 and 10000 cfm), and only one fan was used for 

tests when scrubber flow was 2.8 m3/s (6000 cfm). Orifice plates 

were positioned in the scrubber ducting to adjust the flow. Scrubber flow was measured about 1.5 m (5 A) downstream from each 

fan using a pitot tube and magnehelic gauge (10 point traverse). 

Face Ventilation 

The scrubber was tested with a blowing brattice face ventilation system. Fresh air was directed to the face with brattice cloth 

attached to a wood frame constructed 0.9 m (3 ft) from the left 

side of the entry. The area behind the brattice was 1.9 m2 (21 ft2). 

Tests were conducted for brattice setback distances of 7.6 and 

10.7 m (25 and 35 ft). 

A regulator door in the intake brattice was opened or closed to 

vary brattice airflow during testing. Traverses were made with a 

vane anemometer, at the end of the blowing brattice, to measure 

the average intake air velocity. 

Methane Tracer Gas System 

Methane was released through four perforated horizontal pipes 

located 0.5 m (18 in) outby the face. For all tests, the methane 

flow rate was set at 0.5 m3/min (17.5 cfm) using a rotameter. As 

a check on methane release rate, a methanometer in the return 

continuously monitored methane concentration. 

Methane concentrations were measured at the six locations 

shown on figure 3. Locations 1, 2, and 3 were 0.3 m (1 ft) outby 

the gas manifold and 0.3 m (1 ft) from the roof. Locations 4,5, and 

6 were at the top front of the mining boom, approximately 1.2 m 

(4 ft) from the face and 1.2 m (4 A) from the roof. 

Plastic tubing was extended from the rear of the mining machine to each of the six sampling locations. A vacuum pump was 

used to draw an air sample from each location and direct it over 

a separate methanometer sensor head. Each sensor was attached to a Bacharach methane monitor. [~eference to specific products does not imply endorsement by the NlOSH Pittsburgh Research Center.] For 

the duration of each test, data from each methanometer was 

down-loaded every two-seconds to a personal computer via a 

Metrabyte AID conversion board. For each location sampled, the 

average methane concentration for the 5 minute sampling period 

was calculated using Lotus 1-2-3. 

Before each test, the desired operating conditions (intake airflow, scrubber airflow, and setback distance) were configured, 

@ Sampling locotion 

Figure 3. Methane sampling locations. 

and methane flow into the gallery was initiated. To allow time for 

the gas to mix and concentrations to stabilize, methane flow into 

the gallery was begun 5 minutes prior to collecting data. After allowing time to attain steady state air flow conditions, data was 

collected for 5 minutes at each of the sampling locations. 

RESULTS 

The average methane concentration was calculated for the six 

face locations. A summary of the average methane concentrations for the six sampling locations and the corresponding operating conditions are given in Table 1. Each test was repeated 

once. The average difference between concentrations for the replicated tests was statistically insignificant (95% confidence interval). The average methane concentration for all tests conducted 

at the 7.6 m (25 ft) setback distance and the average methane 

concentration for all tests conducted at the 10.7 m (35 ft) setback 

distance were equal (0.17 pct). Therefore, during further analyses, the data from both setback distances was combined. 

Table 1. Intake Scrubber Setback Methane 

Intake Scrubber Setback Methane 

Flow, Flow, Distance, Conc., 

cfm cfm ft PCt 

6000 6000 25 .21 

6000 6000 35 .18 

6000 10000 25 .19 

6000 10000 35 .15 

6000 14000 25 .13 

6000 14000 35 .ll 

10000 6000 25 .22 

10000 6000 35 .24 

10000 10000 25 .2 1 

10000 10000 35 .21 

10000 14000 25 .18 

10000 14000 35 .18 

14000 6000 25 .14 

14000 6000 35 .18 

14000 10000 25 .12 

14000 10000 35 .15 

14000 14000 25 .12 

14000 14000 35 .13 
2.8 4.7 6.6 

INTAKE FLOW. rn3/s 

Figure 4. Effect of scrubber flow on methane concentration 

XCY 

II17] 0 mJ/s WbbC, 

a 2 8 m3/s scrubber 

4.7 21s scrubber 

6.6 m3//r sccrbbbcr 

Figure 5. Variation in intake velocity with scrubber flow. 

For each intake flow, an increase in scrubber flow reduced the 

average face methane concentrations (see figure 4). An analysis 

of variance (ANOVA) showed that the decreases in methane concentration due to scrubber flows were significant at the 95% confidence level. Methane levels did not increase when scrubber 

flows exceeded intake flows. 

Intake airflow velocities were measured at the end of the blowing brattice with and without the scrubber operating for each of the 

three intake flows. The data given in figure 5 shows that: 

Intake air velocities increased when the scrubber was operating. 

In most cases increasing the scrubber flow increased the intake air velocity. Scrubber flow had the greatest effect on intake velocity at the 2.8 m3/s (6000 cfm) intake flow and the 

least effect when intake flow was 6.6 m3/s (14000 cfm). 

SUMMARY AND DISCUSSION 

The purpose of this research was to examine the effects of 

unbalanced scrubber and intake flow on average face methane 

concentrations. Scrubber and intake airflows were varied from 2.8 

to 6.6 m3/s (6000 to 14000 cfm) for brattice setback distances of 

7.6 and 10.7 m (25 and 35 ft). The effectiveness of each ventilaScrubber, 3.3 m3/s No scrubber 

A KEY B 

- Airflow C Turbvlance 

FACE AIRFLOW PATTERNS 

Figure 6. Face flow patterns with scrubber on (A) and off (6). 

tion system was based on the measurements of average face 

methane concentration. The assumption that methane levels will 

increase when intake flow is less than scrubber flow is incorrect. 

Operation of machine-mounted dust scrubbers promotes better dilution of face liberated methane by increasing airflow turbulence at the front of the mining machine. Face airflow patterns and 

intake velocities were studied to find why use of the scrubber results in lower face methane levels. 

Air flow patterns, shown in figure 6, were drawn with the aid of 

smoke tubes. The smoke was released approximately 0.9 m (3 ft) 

below the roof of the entry, and the flow patterns represent air 

movement at that level. The mining machine was at the face and 

the brattice setback distance was 12.2 m (40 ft). Typical flow patterns are shown with the scrubber on (6A) and the scrubber off 

(6B). 

Flow patterns changed inby and outby the scrubber exhaust 

due to scrubber operation. With the scrubber operating, intake 

flow moved directly up the left side of the entry, and, from left to 

right across the face. Without the scrubber operating, intake airflow moved toward the off-side corner of the entry, and, from right 

to left across the face, creating a "Figure Eight." The "Figure 

Eight" flow pattern is associated with less efficient ventilation of 

the face and consequently higher methane levels. 

Face airflow patterns also show that, with or without the scrubber operating, some of the air exhausted from the face travels 

back toward the face (figure 6). Recirculation occurs whether 

scrubber flow is greater than or equal to the intake flow. It can be 

assumed that the quantity of recirculated air increases with increasing scrubber flow. Determining how much air recirculates to 

the face for different combinations of scrubber and intake flow is 
beyond the scope of this paper. [~n experimental technique for estimating the amount of air recirculated by a scrubber is described by Goodman 

(1983).] 

During earlier research (Taylor), one test was designed so that 

the scrubber exhaust was aimed directly against the intake flow. 

The scrubber exhaust interfered with intake flow toward the face 

and methane concentrations increased. To reduce interference 

between scrubber and intake flow, the scrubber exhaust and intake brattice or tubing should always be placed on opposite sides 

of the entry. 

This study provides information on the performance of a blowing ventilation system used with a machine-mounted dust scrubber. The impact of the test parameters would have to be evaluated by a mine operator for mine-specific conditions. These tests 

do not consider the effects of changes in scrubber and intake 

flows on airborne dust levels, and, therefore, should not be 

used alone to develop a ventilation system for effective dust control. 

REFERENCES 

Gillies, A.D.S., 1982, "Studies in Improvements to Coal Face Ventilation with Mining Machine-Mounted Dust Scrubber Systems," SME-AIME Annual Meeting, Preprint No. 82-24, 13 pp. 

Goodman, G.V.R. and Taylor, C.D., 1993, "A Technique for 

Evaluating Scrubber Recirculation During Deep Cut Mining," 

6th US Mine Ventilation Symposium, pp. 19-24. 

Luxner, J.V., 1969, "Face Ventilation in Underground Bituminous 

Coal Mines," Bureau of Mines RI 7223, 16 pp. 

Taylor, C.D., Rider, J.P., 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. 

Volkwein. J.C. and Thimons E.D., 1986, "Extended Advance of 

Continuous Miner Successfully Ventilated With a Scrubber in 

a Blowing Section," SME Fall Meeting, SME Preprint 86-308, 

4 PP.