Study on the effects of scrubber operation on the face ventilation 

A. M. Wala 

University of Kentucky, Lexington, KY, USA 

S. Vytla & G. Huang 

Wright State University, Dayton, OH, USA 

C. D. Taylor 

NIOSH Pittsburgh Research Laboratory, Pittsburgh, PA, USA 

ABSTRACT: For the past four years, the Department of Mining Engineering at the University of Kentucky has 

conducted a validation study of the CFD Fluent code, by comparing its results against mining-related benchmark 

experimental data provided by NIOSH’s Pittsburgh Research Laboratory. This particular study is dedicated to the 

effect of machine-mounted dust scrubbers on the performance of face ventilation systems using extended-cut 

mining with a blowing curtain. 

1 Introduction 

One of the main concerns during coal extraction, when 

room and pillar mining method is used with a continuous 

miner, is the large amount of methane released in the face 

area. In such circumstances, it is necessary that the 

methane concentration be checked and maintained at safe 

levels. There are various ventilation techniques and 

systems that supply air used to dilute and carry-out 

accumulated methane (Goodman el at., 1990) to avoid 

ignition. However, due to the geometry of the face area, 

especially for a box cutting sequence with a blowing 

curtain, a very complicated flow patterns occurs (Wala et 

al., 2003). 

During the earlier studies performed by the authors 

(Wala et al., 2007) in an empty (containing no equipment) 

face area, it was found that in order to maintain the same 

level of methane concentration at the face area, the 

quantity of air needed to ventilate the box cut was 

approximately five time higher than for the slab cut (Wala 

et al., 2007). This is caused by flow separation from the 

wall that results in an unsteady flow behavior, which is 

predominant during the box cutting mining sequence 

(Wala et al., 2005). In this case around 70 to 80% of the 

airflow delivered behind the curtain does not reach the face 

area. Therefore, due to the greater difficulty of ventilating 

the face area during the box cut mining sequence, the 

authors of this paper chose to focus their research on this 

particular scenario. 

As mentioned above, this study was carried out, first to 

validate the Fluent as a CFD simulation tool, and secondly, 

to better understand how the use of a mining machinemounted dust scrubber affects the airflow and methane 

distribution. These scrubbers, which are primarily used for 

dust collection, have been shown to be very useful 

ventilation devices in directing air into the immediate face 

area where ventilation is poor during the box cut mining 

sequence. 

2 Experimental Studies at NIOSH Laboratory 

Two independent studies were conducted at the NIOSH’s 

Pittsburgh Research Laboratory to study the effect of 

scrubbers on airflow and methane distribution at the 

mining face. These tests were a combined effort of NIOSH 

and Department of Mining Engineering at the University of 

Kentucky because of their mutual interests. The results of 

the first test were presented during the 11th U.S./North 

American Mine Ventilation Symposium (Taylor et al., 

2006). The results of the second test, performed by 

NIOSH, have been used for the research study presented in 

this paper. 

2.1 Test Facility 

The testing was conducted in the NIOSH’s Pittsburgh 

Research Laboratory’s Ventilation Test Gallery, shown in 

Figure 1. A part of the “L” shaped building is designated to 

model an underground mining entry, which is 5m (16.5ft) 

wide by 2.2m (7ft) high. The 1.2m (3.5ft) wide by 12.2m 

(40ft) long box was built along the right side of the entry to 

simulate an uncut slab of coal. The resulting entry 

simulated a 4m (13ft) wide box cut. 

The exhaust fan draws approximately 5.9m3

/s 

(12,500cfm) of air through the gallery. A brattice and 

wood curtain constructed 0.6m (2ft) from the left side of 

the entry directed airflow toward the face. The curtain was 

positioned so that setback distances between the curtain 

and the face was 10.7m (35ft). Regulator doors were 

adjusted to provide intake flows behind the curtain of 

either 1.9 or 2.8m3/s (4,000 or 6,000cfm). A full-scale 

wooden model of the continuous miner, was located at the 

center of the entry to simulate a mining machine during the 

box cutting sequence (see Figure 2). The continuous miner 

model includes a simulated scrubber system that consists 

of the following: 
 

Face area

lowing curtain

Continuous 

miner

Regula

doors

- Two inlet openings 0.25m by 0.3m (10 by 14 

inches), one on each side of the mining machine, 

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

drum. 

- An exhaust opening 0.38 by 0.38m (15 by 15 in.) 

at the right rear of the machine chassis. 

- Ducting to provide flow between inlets and 

exhaust openings. 

- An axial fan to move the air from the scrubber 

inlet opening to the exhaust. 

Scrubber airflow is adjusted by inserting a different size of 

the orifice plate into the ducting. Airflow distribution was 

not measured during this test because of a space limitation 

and very complicated 3D flow patterns. 

B tor 

Face area 

Blowing curtain 

Continuous 

miner 

Regulator 

doors 

Figure 1. Ventilation test gallery 

2.2 Methane Measurement 

Methane measurements were made by drawing air samples 

through eight air sampling tubes that were suspended from 

an overhead support system. The ends of the upper four 

tubes were 0.4 (1.3 ft) from the roof while the lower four 

were 0.7 m (2.4 ft) from the roof. By moving the overhead 

support system either toward or away from the face, 

samples were collected for 28 locations at each of the two 

sampling heights. These 28 sampling locations were 

arranged in four columns and seven rows as shown in 

Figure 2. The total number of methane measuring points 

(upper and lower) was 56, see Figure 2. 

To simulate liberation of methane from a mining face 

methane gas was released from a manifold made of four 3-

m (10-ft) long horizontal copper pipes that were located 

0.1 m (4 in) away from the face. The pipes were equally 

spaced horizontally to provide a relatively uniform release 

of gas. Two millimeters (1/16 in) diameter holes were 

drilled 6.5cm (2.5 in) apart on the top and bottom of each 

of the 10-ft long pipes. For the box cut mining sequence 

the methane flow rate into the gallery was regulated to the 

level of 0.0063m3

/s (13.4cfm) to prevent methane 

concentration in face area from exceeding 2.0 percent. 

2.3 Experimental Results 

The contours in Figures 3 and 4 show the distribution of 

the methane concentration in the face area for all four 

scenarios mentioned above. Some general observations can 

be made by looking at Figure 3 and 4: 1). The ratio 

between a maximum methane concentration at the methane 

elevated regions between scenario 1 and 2 is 2.0/0.5 (4.0), 

and 

Figure 2: Sampling locations 

2.4 Testing Scenario 

Methane concentrations readings for the box cut mining 

sequence were taken for the following four scenarios: 

1.	 Scrubber off, intake flow 1.9m3

/s (4,000ft3/min) 

2.	 Scrubber off, intake flow 2.8m3

/s (6,000ft3/min) 

3.	 Scrubber flow 1.9m3/s (4,000ft3

/min), intake flow 

1.9m3

/s (4,000ft3/min) 

4.	 Scrubber flow 1.9m3/s (4,000ft3

/min), intake flow 

2.8m3

/s (6,000ft3/min) 

between scenarios 3 and 4 is 2.6/0.5 (5.5). This means that 

the scrubber improved the ventilation at the face area. 

However, the remaining question is, how much? 2) 

Methane concentration along the intake (left-hand) side, 

between the rib and the miner is lower than on the opposite 

side of the miner. This means that although the majority of 

the intake air does not flow along the rib to the mining 

machine, due to separation from the rib, a small part of the 

intake air from the curtain does flow between the mining 

machine and the rib. This flow pattern varies a little from 

the flow seen during tests in the empty face area 3) 

Although more air is delivered during test scenario 2 

(6,000 cfm) the methane zone is larger and the maximum 

concentration inside this zone is higher than for scenario 1 

with an intake flow of 4.000cfm. These experimental data 

will be compared with the CFD simulation data later in this 

paper. 

3	 Computer Simulation Study 

There are three major steps in any CFD solution process: 

(1) preprocessing (mesh generation), (2) processing (CFD 

simulation and refinement/adaptation of grid), and (3) post 

processing (visualization and analysis of results). 

FLUENT 6.X, commercially available CFD solver 

together with the GAMBIT mesh generator (preprocessor), 

which comes as a package along with Fluent, was used to 

simulate the methane and flow behaviors, for the same 

scenarios used during the laboratory tests. The results of 

these simulations are visualized using the post processing 

capabilities of the Fluent and graphically shown using the 
simulate the methane and flow behaviors, for the same 

scenarios used during the laboratory tests. The results of 

these simulations are visualized using the post processing 

capabilities of the Fluent and graphically shown using the 

Excel plots capability. The results of these simulations 

were tested (compared) against the experimental data for 

CFD code validation. For the validation purposes the CFD 

simulation data were extracted at the same locations as the 

experimental data were collected. 

Based on experiences gained during the previous CFD 

studies using fluent code were applied to simulate the 3-D 

methane concentration along with the air flow 

distributions. 

Figure 3: Methane concentration contour maps for intake 

flow equal 4,000 cfm cases: (left) no scrubber (scenario 

#1), (right) scrubber flow equal 4,000 cfm (scenario #3) 

30 30 

CH4

Ch4 CH4Ch4 

2 0.5 

1.8 0.45 

1.6 0.4
 

20
 1.4 20 0.35 

1.2 0.3 

1 0.25 

0.8 0.2 

0.6 0.15 

0.4 0.1 

0.2 0.05 

0 0 10 10 

0 0 0 10 0 10 

Figure 4: Methane concentration contour maps for intake 

flow being 6,000 cfm cases: (left) no scrubber (scenario 

#2, (right) scrubber flow equal 4,000 cfm (scenario #4) 

30 CH4Ch4 30 

2.6 

2.4 CH4

Ch4 2.2 

2 0.5 

1.8 0.45

0.4
 

20
 

1.6 

1.4 20 0.35

0.3 

1 

1.2 

0.25 

0.8 0.2

0.6 0.15

0.4 0.1

0.05 

0 

0.2 

0 10 10 

0 0 0 10 0 10 

X 

3.1 Pre Processing 

The configuration of the model for the box cutting 

sequence is shown in Figure 5. The geometry includes: (1) 

flow path between the rib and brattice from the Velocity 

Inlet (Air) to the discharge location at the end of the 

blowing curtain; (2) flow through the Interface zone; (3) 

flow in the face area; (4) flow return toward the Outlet and 

(5) Velocity Inlet (Methane). One ventilation arrangements 

for the box cutting mining sequence, with 35 ft setback 

blowing curtain was considered. 

The computational mesh (grid) was generated using the 

GAMBIT 2.1., mesh generator. In the CFD model the 

methane boundary condition at the Velocity Inlet 

(Methane) represents 192 nozzles which bring the methane 

into the face area. These nozzles are evenly distributed on 

the face surface. The most important zone in this study is 

the area between the end of blowing curtain and the face. 

In order to have enough grid resolution in the area of 

importance the entire flow region was divided into two 

zones. First, the zone of the face area and second the 

interface zone. The mesh generation for each zone was 

performed independently. These two zones are connected 

by an interface boundary condition. 

Figure 5: Boundary conditions (box cutting sequence) 

Velocity Inlet 

(Methane) Interface 

Velocity Inlet 

(Air) Fan 

Outflow 

(Outlet) 

The velocity inlet boundary condition was applied at 

the air and methane inlets. The out-flow boundary 

condition was applied at the outlet. All the other surfaces 

are treated as adiabatic walls with no slip boundary 

condition. Table 1, shows the experimental values used to 

calculate the boundary conditions. A correction was 

applied to the flow of methane delivered to the face area 

because the flow-meter (Rotometer) used during the 

NIOSH test was calibrated for airflow. The computational 

mesh of the test box cut configuration is shown in Figure 

6. The mesh with around 1,830,000 cells was accepted 

based on previously performed studies concerning the grid 

independence results. 

Scenario Intake flow 

(cfm) 

Scrubber flow 

(cfm) 

Methane 

(cfm) 

1 4,000 0 13.4 

2 4,000 4,000 13.4 

3 6,000 0 13.4 

4 6,000 4,000 13.4 

Table 1: Data used to calculate the boundary condition 

3.2 Processing 

A 3D steady state, incompressible solution for NavierStokes equations with species transport without chemical 

reactions was performed using Fluent. Fluent solves the 

Reynolds averaged form of Navier- Stokes equations, 
 

 

considering the conservation of mass, momentum, energy 

and species transport. The analysis was performed using 

different turbulence models to identify the model which 

can best predict both the flow and the methane distribution. 

In this study only the analysis results using SST (ShearStress Transport) turbulence model are discussed. Pressure 

velocity coupling of momentum and continuity equations 

is obtained using the SIMPLE algorithm. The outflow 

boundary condition is applied at the outlet. Effect of 

buoyancy is also included by switching on the gravity. 

Further details will be discussed in the results section. 

Figure 6: Computational mesh; top view and side view of 

the mesh 

3.3 Post Processing 

Based on the computer simulations, the methane 

distributions are presented as contour maps and the airflow 

distribution as flow lines (path lines). The results for all 

four scenarios are shown in Figures 7 and 8. In general the 

CFD simulation and experimental study results are similar 

and show that scrubber helps to ventilate the face area by 

bringing more air into the face. 

0 10 0

10

20

30 

20 

10 

0

0 10 

Figure 7(a): Methane concentration contour plots and path 

lines (colored by particle numbers) for intake flow 4,000 

cfm and no scrubber flow, (scenario #1) 

4	 Comparison of Experimental and Simulation 

Results 

In this section, the experimental results (NIOSH) are 

compared with the CFD simulation results. NIOSH’s 

experimental results plotted in Figures 3 and 4 show 

methane concentration contour maps for all four scenarios 

tested in the NIOSH’s ventilation gallery. These results are 

compared to the methane concentration contour maps 

shown in Figures 7 and 8, which were generated using data 

from the CFD simulation. The experimental data and CFD 

results are compared based on the scenarios given in Table 

1. 

Figure 7(b): Methane concentration contour plots and path 

lines (colored by particle numbers) for intake flow 4,000 

cfm and scrubber flow 4,000 cfm, (scenario #3) 

30 

20 

10 

0

0 10 

Figure 8(a): Methane concentration contour plots and path 

lines (colored by particle numbers) for intake flow 6,000 

cfm and no scrubber flow, (scenario #2) 

30 

20 

10 

0

0 10 

Figure 8(b): Methane concentration contour plots and path 

lines (colored by particle numbers) for intake flow 6,000 

cfm and scrubber flow 4,000cfm (scenario #4) 

30 

20 

10 

0

0 10 

Scenario #1: For this scenario the amount of air being 

delivered behind the blowing curtain, for ventilation, is 

4,000cfm and continuous miner’s scrubber is off. Figures 3 

(left part) and 7a show that the maximum methane 

concentration in the methane elevated zone is around 2.0 

percent. The shape and sizes of the methane elevated zones 

for both cases are different. Figure 3 shows that majority of 

air delivered to the face is flowing along the left-hand side 

of the entry, between the entry rib and continuous miner. 

This makes the methane concentration along this path 
 

 

 

 

 

lower. According to the simulation study the limited 

amount of air is reaching the face area because the majority 

of air is separating from wall (rib) and flowing back out of 

the face area. Even though the flow behavior predicted in 

the simulations is different to that of experiments it is 

observed to be consistent with our previous validation 

study (Wala et. al. 2007). This kind of flow behavior 

makes the methane elevated zone bigger and concentration 

higher. To better understand this flow behavior, please see 

the flow path lines plot, as a part of Figure 7a and Figure 

9a. 

0.00 

0.50 

1.00 

1.50 

2.00 

2.50 

1 5 9 13 17 21 25 

Sample Number 

Methane concentration 

Experiment 

Simulation 

Figure 9(a): Methane concentration comparison 4,000 cfm 

intake airflow and no scrubber (scenario #1) 

Scenario #2: For this scenario the amount of air being 

delivered behind the blowing curtain is 6,000cfm and 

continuous miner’s scrubber is off. Figures 4(left) and 8a 

show that the maximum methane concentration in the 

methane elevated zone is around 2.0 percent. The sizes and 

the shape of the methane elevated zones for both cases are 

similar. Figure 4 shows the high methane concentration on 

the left side this can be explained by the fact that majority 

of air delivered to the face behind the curtain is separating 

from wall and flowing back, out of the face area. The rest 

of the intake air is flowing into the face along the righthand side. The experimental data and simulated results are 

similar. The limited amount of air is reaching the face area 

because the majority of air is separating from wall (rib) and 

flowing back, out of the face area. This kind of flow 

behavior makes the methane elevated zone bigger. To 

better understand this flow behavior, please see the flow 

path lines plot, as a part of Figure 8a and Figure 10a. 

Scenario #3: The difference between this scenario and 

scenario #1 is that the continuous miner’s scrubber is on. 

Figures 3 (right) and 7b show that the maximum methane 

concentration in the methane elevated zone is relatively 

low and is around 0.5 percent. This means that scrubbers 

have helped improve the ventilation at the face area. The 

larger amount of air is reaching the face area because of 

4,000cfm scrubber being in operation. This kind of flow 

behavior makes the methane elevated zone smaller. The 

shape and sizes of the methane elevated zones for both 

cases are different. Figure 3, right side, shows that majority 

of air delivered to the face is flowing along the left-hand 

side, between the entry rib and continuous miner. However 

the simulation results show a different picture. Simulation 

results predict an increased airflow towards the face area 

but there still exists a separation and a recirculation region 

resulting in a different methane concentration in the face 

area to that of the experiments. With the lack of velocity 

measurements from experiments for comparison the 

simulation results are inconclusive. To better understand 

the flow behavior for this scenario, please see the flow path 

lines plot, as a part of Figure 7b and Figure 9b. 

Figure 10(a): Methane concentration comparison 6,000 

cfm intake airflow and no scrubber (scenario #2) 

0.00 

0.50 

1.00 

1.50 

2.00 

2.50 

3.00 

1 5 9 13 17 21 25 29 

Sample locations 

Methane Concentration 

Experiment 

Simulation 

Figure 9(b): Methane concentration comparison 4,000 cfm 

intake airflow and scrubber flow is 4,000 cfm (scenario #3) 

-0.20 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

1.40 

1.60 

1 5 9 13 17 21 25 

Sample locations 

Methane Concentration 

Experiment 

Simulation 

Scenario #4: In this scenario the amount of intake air 

delivered at the curtain is 6,000cfm and continuous miner’s 

scrubber is on with flow of 4,000cfm. Figures 4 (right) and 

8b show that the maximum methane concentration in the 

methane elevated zone is around 0.5 percent. This means 

that scrubbers have improved the ventilation at the face 

area. The shape and sizes of the methane elevated zones 

for both cases are different. Figure 3, right-side, shows that 

majority of air delivered to the face is flowing along the 

left-hand-side, between the entry rib and continuous miner. 

However the simulation results show a different picture. 

The same can be said for Scenario #4 as discussed in 

Scenario #3 the simulation results were inconclusive with 

the limited comparison with experimental data. To better 

understand the flow behavior, please see the flow path 

lines plot, as a part of Figure 8b and Figure 10b. 
 

Figure 10(b): Methane concentration comparison 6,000 

cfm intake airflow and scrubber flow 4,000 cfm (scenario 

#4) 

0.00 

0.20 

0.40 

0.60 

0.80 

1.00 

1.20 

1 5 9 13 17 21 25 

Sample location 

Methane Concentration 

Experiment 

Simulation 

5 Conclusions 

•	 Based on these studies there is potential of using 

Fluent CFD code to develop stand-alone mine 

face ventilation system design simulation 

packages. 

•	 Similar type of validation studies for various 

mining scenarios must be performed in the future 

in order to build confidence in the use of CFD as 

a tool for face ventilation analysis and design. 

•	 Such studies had never before been tried to such 

an extent. By conducting these studies, a vast 

amount of knowledge is gained about the face 

mine ventilation process. 

•	 Some differences between the experimental data 

and simulated data were found. The reasons for 

these differences must be determine and proved 

by performing additional tests. 

References 

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“Ventilation schemes permit deep advance,” Coal 

October 

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

2006, “Effect of scrubber on airflow and methane 

patterns at the mining face,” ”, Proceedings: 11th 

U.S./North American Mine Ventilation Symposium, 

University Park, PA, June. 

Wala, M.A., Jacob, Huang, P.G., and Brown, J.T., 2003. 

“A new approach to evaluate mine face ventilation”, 

Mining Engineering, Vol 55, No 3, March. 

Wala, M.A., Jacob, Huang, P.G., and Rangubhotla, L., 

2004. “How scrubbers help ventilate the face during 

deep cut mining with a blowing curtain”, Proceedings: 

10th U.S. Mine Ventilation Symposium, Anchorage, 

AL, May. 

Wala, M.A., Vytla, S., Taylor, C.D., and Huang, P.G., 

2007, “Mine Face ventilation: a comparison of CFD 

results against benchmark experiments for the CFD 

code validation,” Mining Engineering, Vol 59, No 10, 

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