Technology News

From the Bureau of Mines, United States Department of the Interior

Technology news describes tested Gevalopments from Bureau of Mines programs. itis published to encourage the

transfer of this information to the minerais industry and its application in commercial practice. Mention of company
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No. 440, Octaber 1994

Improved Dust Control for Surface Coal Mine
Drills With Rotoclone Collectors

Objective

Improve the dust-control effectivencss of the Rotoclone*
dry-dust collection systems used on surface coal mine
drills.

Approach

Tnject small amounts of water into the Rotocione ex-
haust to mix the dust and water, reducing the levels of re-
spirable and total dust discharged from the Rotoctonc
exhaust,

Background

The U.S. Bureau of Mines ficld tested a method for re-
ducing dust cmissions on small drills, such as Davey, uscd
in surface coal mining. These drills typically use a dust
collection system called a Rotoclone. The Rotoclone, not
a high-efficiency collector of very small dust particles,
discharges significant amounts of visible dust. Typically,
the Rotoclone discharge gocs through a short section of
pipe where it is directed vertically so that prevailing winds
will disperse the dust away from the drilling operation.
However, new Mine Safety and Health Administration reg-
ulations on dust emissions require that no visible dust be
discharged to the atmosphere. Many operations will find
it difficult to mect these new requirements.

"Reference to specific products does not imply endorsement by the
U.S. Bureau of Mines.

How It Works

The Rotoclone discharge port initially must be rotated
so that the discharge is horizontal or downward. Approxi-
matcly 6 meters (20 feel) of cither flexible or rigid plastic
tubing (although not tested, a shorter length may possibly
work as well) with approximately the same diameter as the
discharge port is coupled to the port, This duct is mount-
ed at a downward-sloping angle along the side of the drill
so that the exit remains approximately 0.3 meter (1 foot)
above the ground.

A water tank of approximately 26.4 liter (100-gallon) ca-
pacity is mounted at a location and elevation to gravity
feed a small amount of water into the Rotoclone discharge
port. In practice the drill operator can use a truck fuel
saddle-tank system to supply the required water. It is es-
timated thal 26.4 liters (100 gallons) or less will be suf-
ficient for 8 hours of continuous drilling using the 0.05-
litcr-per-minute (0.2-gallon-per-minute) flow rate for most
Rotoclone systems used on small drills, Because of the
Tow flow rate, the water from the tank can be supplied
through 0.6-ccntimcter (0.25-inch) tubing, A variety of
suitable fittings can be mounted in the metal discharge
port of the Rotoclone. It is recommended that two valves
be used to control the water flow. One valve will be used
as a flow regulator and the second valve will be the on-off
control.

Test Results

Tests were performed on the same drifl bench with and
without the usc of water to evaluate the effectiveness of

This document was prepared by the U.S, Bureau of Mines. Neither the United States Government nor any person acting on behalf of the United
‘States Government assumes any liabiity resulting from the usc of the information contained in this document, or warrants that such use be {ree from

privately owned rights.



the water-trickle system in reducing dust emissions from
the Rotoclone discharge. With the trickle system, dust
sampling conducted approximately 10 feet directly down-
wind of the Rotoclone discharge showed 90 percent reduc-
tion of total airborne dust, 92 percent reduction of re-
spirable dust, and climination of all visible dust emissions.
Analysis of the dust samples showed that the quartz con-
tent of the respirable samples decreased from 21 percent
without using water to 18 percent with the water-trickle
system, Figures 1 and 2 show the cffectiveness of the
trickle system in eliminating visible emissions from the
Rotoclone discharge,

To prevent clogging problems during opcration, it is
critical to not usc too much water. Since the airflow from
the Rotoclone varies widcly, depending on the revolutions
per minute of operation, the amount of water used must
be determined individually for cach application. One sim-
ple guideline is to slowly increase the trickle flow rate until
the visible emissions are significantly reduced. It will be
found that with time {less than approximately 1 hour), as
the duct interior becomes wetted, dust reduction will
improve.

Figure 1.—Visible dust in the exhaust from a coal mine drill.

Also, the downward slope of the discharge duct is im-
portant to allow excess water to drain from the line. Ac-
tual extended operation of the system showed that some
material agglomeration will occur within the first 0.3 meter
(i foot) of duct length during an 8-hour drilling period.
However, this material is easily removed by disconnecting
the duct from the Rotoclone exit. If the duct is connected
with a standard hose clamp, cleaning can be performed in
a few minutes.

For More Information

Additional information can be obtained by contacting
the principal investigator for this research, Steven J. Page,
at the U.S, Burcau of Mines, Pittsburgh Rescarch Center,
P.O. Box 18070, Pittsburgh, PA 15236, or telephone (412)
892-6669. Technology News issues 286, 308, and 338 pro-
vide additional information on techniques to control re-
spirable dust emissions from highwall drills,

SEL eC aanipo “sear
Skene ws

Figure 2.—No visible dust In the exhaust from a drill equipped
with the water-trickle system.

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