with factory-installed CDPF’s. These LHD’s were
equipped with two CDPF’s, one for each exhaust manifold.

These LHD’s are primarily used for loading trucks.
The duty cycle is the same as for the 3.8-m> (5-yd?)
LHD’s, except that a truck can be loaded with three cycles,
providing even more time for the CDPF to cool down
between trucks.

The backpressure alarms on both LHD’s are no long-
er functional, because of missing wires and tubing, but
during the time that they were operational they indi-
cated regeneration problems and/or consistently high
backpressure.

The duty cycle of these LHD’s is sufficient to initiate
regeneration, but probably insufficient to sustain regenera-
tion, This results in a gradual buildup of exhaust back-
pressure, necessitating removal of the CDPF for pressure
washing. This reinforces the need to have temperature
traces of a multishift duration performed on equipment
before installing the CDPF. Ordering factory-installed
CDPF’s solves the problem of locating the CDPF’s on the
vehicle, but might create a problem if the duty cycle of the
vehicle is insufficient to sustain regeneration.

The two CDPF installations had accumulated 8,337 h
of use as of December 31, 1992. The CDPF’s, backpres-
sure alarms, and factory installation for the two LHD’s
cost $19,970. The LHD operating costs for 1992 were
$70.56/h. Since the purchase of these LHD’s, the CDPF’s
have accounted for 3.6 pet of the operating cost per hour.

Trucks, 23.6 mt (26 t)

The mine has five 23.6-mt (26-t) trucks with Caterpillar
3406 prechambered, turbocharged, and aftercooled engines
that are equipped with CDPF’s. The duty cycle of these
trucks is probably adequate for the use of CDPF’s, but
these CDPF’s are more susceptible to damage from opera-
tion and the mine environment. The trucks spend a signif-
icant portion of time operating under high-engine-load
conditions such as being driven fully loaded up a 15-pet
ramp. Temperature traces performed by the CDPF manu-
facturer indicated periods of time with exhaust tempera-

. tures above 400° C. However, full shift temperature traces
were not recorded, so it is possible that regeneration is
incomplete.

Regeneration problems and/or ceramic substrate dam-
age are strongly suspected. Black exhaust smoke is fre-
quently observed, the CDPF’s have required pressure
washing, and none of the backpressure alarms are func-
tional. The CDPF’s installed in these trucks are prone
to damage due to impact against the mine rib. When a
CDPF is hit, the substrate is frequently crushed at the
point of impact, which affects filtration efficiency. Fig-
ures 5 through 7 show the damage sustained by a CDPF
in use on a 23.6-mt (26-t) truck and by a CDPF that was
removed from service.

A total of 13 CDPF’s were used, or are presently in
use, on these trucks at a capital cost of $106,123, including

the cost of the backpressure alarms, which amounts to
about 3 pet of the total. These trucks have accumulated
a total of 41,135 h with an average filtration cost of
$2.58/h. The average operating cost of the trucks during
1991 was $80.13/h. CDPF’s account for 3.2 pct of the
operating cost for these trucks.

co eee

ee eee
eet


UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

°c
cm

gal

hp

Hz

in HO
kPa

kw

L

Ibeft
Ib-ft/min
a
mg/sm?

min

degree Celsius
centimeter

gallon

hour

horsepower

hertz

inch

inch of water
kilopascal

kilowatt

liter

pound foot

pound foot per minute
cubic meter

milligram per standard cubic meter

minute

pm
mt

mt/d
Nem
Nem/min
pet

ppm

rpm

t/d
wt pet
yP
$/h

$/mt

micrometer

metric ton

metric ton per day
newton meter
newton meter per minute
percent

part per million
revolution per minute
ton

ton per day

weight percent

cubic yard

dollar per hour
dollar per metric ton

dollar per ton



can be removed by blowing out with compressed air, steam
cleaning with or without nonphosphate detergent, or bak-
ing in an oven. Backpressure alarms require frequent
maintenance to remain operational. Equipment operators
and mechanics must be adequately trained in their use and
maintenance. Improved backpressure alarms need to be
developed specifically for mine vehicles.

5. Periodically inspect the CDPF, gauges, and alarms.
The inlet and outlet faces of the CDPF should be in-
spected periodically because DPM buildup on the inlet
face can indicate a regeneration problem. Inspection can
be done each time the vehicle is brought into the shop for
preventive maintenance. Backpressure gauges and alarms

should also be checked at this time. If cracking or melting
of the ceramic is observed on the inlet or outlet face, the
collection efficiency of the CDPF has diminished. While
it may still be capable of filtering particulate, considera-
tion should be given to replacing the CDPF. The time at
which the CDF is replaced is dependent upon a number of
factors, including the amount of substrate damage, the
appearance of smoke, and the cost of replacement.

6. Educate operators and mechanics. Vehicle opera-
tors and mechanics should be instructed in how a CDPF
works, how to determine if it is becoming plugged, what to
do if it does become plugged, and the need for operational
backpressure alarms.

REFERENCES

1. Howitt, J. S, and M. R. Montierth. Cellular Ceramic Diesel
Particulate Filter. SAE Tech. Pap. Ser. 810114, 1984, 9 pp.

2. Bagley, S. T., K. J. Baumgard, L. Gratz, K. L. Bickel, and W. F.
Watts, Jr. Effects of a Catalyzed Diesel Particle Filter on the Chemical
and Biological Character of Emissions From a Diesel Engine Used in
‘Underground Mines. SAE Tech. Pap. Ser. 911840, 1991, 12 pp.

3. Howitt, J. S,, W. T. Elliot, J. P. Morgan., and E.D. Dainty. Appli-
cation of a Ceramic Wall Flow Filter to Underground Diesel Emissions
Reduction. SAE Tech. Pap. Ser. 830181, 1983, 9 pp.

4, Stawsky, A, A. Lawson, H. Vergeer, B. Manicom, and
W. Drummond. Control of Diesel Exhaust Emissions in Underground
Coal Mines (contract H0199021). BuMines OFR 47-87, 1987, 401 pp
NTIS PB 88-133673.

5. Enga, B. E., and E, D. Dainty. Off-Highway Applications of Ce-
ramic Filters, SAE Tech. Pap. Ser. 890398, 1989, 8 pp.

6. Engler, B, E. Koberstein, and H. Vélker. Catalytically Acti-
vated Diese! Particulate Traps—New Development and Applications,
SAE Tech. Pap. Ser. 860007, 1986, 9 pp.

7. Baumgard, K. J., and K. L. Bickel. Development and Effective-
ness of Ceramic Diesel Particle Filters. Paper in Diesels in Under-
ground Mines: Measurement and Control of Particulate Emissions.
BuMines IC 9141, 1987, pp. 94-102.

8. Kulkarn, N. S. Cellular Ceramic Products Help Curb Diesel En-
gine Emissions. Automot. Eng,, v. 100, No. 1, 1992, pp. 21-25.

9. Gulati, S. T., J. L. Summers, D. G. Linden, and K. I. Mitchell.
Impact of Washcoat Formulation on Properties and Performance of
Cordierite Ceramic Converters. SAE Tech. Pap. Ser. 912370, 1991, 8 pp.

10. Corning Glass Works (Corning, NY). Product brochure for Corn-
it sel Filters. 1986, 3 pp.
1e Control Systems, Ltd. (Newmarket, Ontario, Canada).
PILP Final Report. Prep. for Nat. Res. Counc. Can. NRC Arrang. CA.
910-5-0956/965, Feb. 1990, 145 pp.

12. McKinnon, D. L., K. G. Wheeland, and K. Gavel. Diesel Particu-
late Filter Underground Trial at Brunswick Mining and Smelting’s
No. 12 Mine. SAE Tech. Pap. Ser. 891846, 1989, 10 pp.

13. Sherwood, D. L., D. L. McKinnon, and W. J. von Hagn. Evalua-
tion of a Wall Flow Diesel Filter After > 4000 Hours of Use on an
Underground Mining Vehicle. SAE Tech. Pap. Ser. 912336, 1991, 6 pp.

14, Anderson, C. F,, J. D. Gage, M. J. Vogel, and N. D. Lange. U.S.
Bureau of Mines’ Diesel Emission Research Laboratory. Paper in Die-
sels in Underground Mines: Measurement and Control of Particulate
Emissions. BuMines IC 9324, 1992, pp. 91-102.

15. Johnson, J. H., E. O. Rhinebold, and D. H. Carlson. The En-
gineering Control of Diesel Pollutants in Underground Mining. SAE
Tech. Pap. Ser. 810684, 1981, 46 pp.

16. Sims, G. S. Durability Characteristics of Palladium Catalysts.
SAE Tech. Pap. Ser. 912369, 1991, 10 pp.

17. Niura, Y., K. Ohkubo, and K. Yagi. Study on Catalytic Regenera-
tion of Ceramic Diesel Particulate Filter. SAE Tech. Pap. Ser. 860290,
1986, 9 pp.

18, Henk, M. G., W. B. Williamson, and R. G. Silver. Diesel Catalysts
for Low Particulate and Low Sulfate Emissions. SAE Tech. Pap. Ser.
920368, 1992, 10 pp.

19. Baumgard, K. J., and D. B. Kittelson. The Influence of a Ceramic
Particle Trap on the Size Distribution of Diesel Particulate. SAE Tech.
Pap. Ser. 850009, 1985, 12 pp.

20. Gulati, S.T., and I. D. Helfinstine. High Temperature Fatigue
in Ceramic Wall-Flow Diesel Filters. SAE Tech. Pap. Ser. 850010, 1985,
7 pp.

21. Engine Control Systems, Ltd. (Newmarket, Ontario, Canada).
Product Brochure for ECS Purifilters. 1988, 1 pp.

22, Engine Control Systems, Ltd. (Newmarket, Ontario, Canada).
Private communication, 1991; available upon request from J. J. Baz-
Dresch, Asamera Minerals (U.S.), Inc. Wenatchee, WA.

23, Pattas, K. N., A.M. Stamatelos, and J. C. Constantinidis, Exhaust
‘Temperature Response of Trap Oxidizer Systems. SAE Tech. Pap. Ser.
900323, 1990, 9 pp.



LABORATORY RESULTS

REGENERATION TEMPERATURE

The regeneration temperature of the CDPF increased
from 405° C after 839 h to 450° C after 2,881 h. Possible
explanations for this temperature increase are (1) DPM
and ash buildup covered much of the active portion of the
catalyst, reducing catalyst effectiveness by masking sites
for catalytic activity, and (2) catalyst performance was
affected by poisoning, sintering, or some other cause (16).
One study of three base-metal CDPF’s has shown that the
regeneration temperature increased by 20° to 50° C after
thermal aging using a diesel fuel burner for regeneration
a).

GASEOUS EMISSIONS

The CDPF, depending on the engine mode, reduced
CO emissions (table 2) from 21.3 to 648 pet after 839 h,

from 14.3 to 57.5 pet after 1,584 h, and from 2.9 to
42.1 pet after 2,881 h of in-mine service. A 14.9-pct
increase in CO emissions was observed at mode 6 after
2,881 h. The CDPF regenerates at mode 6, and the
amount of CO emitted depends on the particulate loading
and rate of regeneration (7).

The CDPF was also effective at reducing HC emissions
(table 2), with reductions of 5.4 to 89.7 pct after 839 h,
23.1 to 76.5 pet after 1,584 h, and 39.4 to 83.2 pet after
2,881 h. Similar CO and HC reductions with increasing
temperature were observed by Bagley (2) in a study of a
CDPF using a platinum-based catalyst.

A wide range of CO and HC removal efficiency is ex-
pected over the six steady-state modes because removal
efficiency is primarily dependent upon CDPF temperature
for catalyst activation (2).

Table 2.—Effect of CDPF on CO and HC emissions at different temperatures, over time

CO concen- HC concen-
Time of Mode tration, ppm tration, ppm Reduction in CO Reduction in HC. CDPF temper-
operation, h Without With jour 7 emissions, pet emissions, pot ature, °C
COPF _CDPF CDPF _CDPF
839 «0... 1 57.2 45.0 25.7 24.3 21.3 5.4 235.0
2 660 © 28.8 43.4 153 59.4 647 334.0
3 203.3 73.8 39.4 63 63.7 84.0 537.0
4 O14 46.0 59.4 28.6 49.5 51.9 294.0
5 1045 368 68.2 15.2 64.8, 77.7 405.0
6 1243 637 64.2 66 48.8 29.7 877.0
Mean 1077487 50.1 16.1 513 62.2 397.0
STD 52.9 17.3 16.5 o1 16.2 31.0 136.3
1,584 1 453 38.8 45.1 347 143 23.1 256.0
2 64.41 39.3 54.2 25.0 38.7 53.9 344.0
3 290.7 152.4 a7 4 13.6 476 713 547.0
4 827 50.6 648 38.7 38.8 40.3 293.0
5 93.6 45.5 74.0 25.9 51.4 65.0 400.0
6 195.7 83.2 63.0 148 875 76.5 576.0
Mean 1287 683 58.1 25.5 41.4 55.0 402.7
sTO 951 44.4 4 102 15.4 203 132.6
2,881 ..... 1 60.8 448 66.3 36.0 26.3 45.7 243.0
2 719416 78.5 20.3 42.4 626 342.0
3 410.6 398.8 78.2 21.0 29 73.1 568.0
4 982 708 78.2 474 27.9 39.4 292.0
5 1119673 88.4 32.9 39.9 627 396.0
6 135.7 156.0 87.0 146 149 83.2 568.0
Mean 148.2 © 129.9 79.4 30.2 20.7 61.4 401.5
STD 131.4 138.2 79 115 22.3 16.4 138.7,

STD Standard deviation.


INTRODUCTION

DESIGN AND OPERATION OF CDPF’s

CDPP’s are used to filter DPM from diesel exhaust.
The CDPF has a catalyst-coated, porous, ceramic substrate
enclosed in a steel housing with longitudinal channels (1).
In the inlet end, every other channel is plugged with
ceramic material, while the adjacent channel is plugged at
the outlet end (fig. 1). The exhaust gas enters a channel
and is forced to pass through the porous channel walls
where filtering takes place. The exhaust exits through
adjacent channels. CDPF’s remove 63 to 95 pct of the
DPM from exhaust (2-4), They are used on nonpermis-
sible mine production vehicles that have exhaust tem-
peratures exceeding 400° C for at least 25 pet of the duty
cycle. These engines operate frequently at high power,
eg, engines on vehicles that climb a ramp many times
each shift.

The CDPF is installed in the exhaust stream as close to
the engine as possible. As DPM collects within and on the
porous walls of the ceramic, the backpressure on the en-
gine increases. When the correct conditions are achieved
in the CDPF, the DPM burns and the backpressure de-
creases. This self-cleaning process is called regeneration.
Typically, complete regeneration occurs when the temper-
ature in the CDPF exceeds 400° C for approximately 15 to
20 min (5-6).

If the CDPF reaches regeneration temperature fre-
quently during a vehicle’s duty cycle, the engine back-
pressure will remain within acceptable limits. However, if
the vehicle’s duty cycle or operating condition of the
engine changes such that regeneration does not occur, or
occurs less frequently, the CDPF may become overloaded
with DPM. If the DPM burns too quickly, and there is in-
sufficient exhaust gas flow to dissipate the heat, thermal
stress may crack the CDPF or excessive heat may melt the
ceramic substrate. This is referred to as an "uncontrolled
regeneration." A laboratory investigation of uncontrolled

._ regeneration (7) showed exhaust temperatures can exceed
925° C and CO emissions can exceed 5,000 ppm. This
study concluded that as long as the engine backpressure
remained below the engine manufacturer’s recommended
limit, uncontrolled regeneration was unlikely to occur.
The frequency of occurrence of uncontrolled regeneration
in mining applications is not known,

The primary reason to apply a catalyst to the ceramic
substrate is to lower the regeneration temperature, but
some catalysts also reduce CO and gaseous HC emissions.
The catalyst is applied on a washcoat, the composition of
which varies by manufacturer. The washcoat improves

performance by increasing the surface area of the sub-
strate and improves catalyst binding (8). The strength of
the substrate may also be enhanced by the washcoat (9).
The catalyst formulations are proprietary. They are either
base metal or noble metal, and new formulations are cur-
rently under development for heavy-duty diesel engines.
One study of a CDPF on a mining engine tested over a
transient engine cycle reported a decrease in CO emissions
of 79 pet and HC emissions of 59 pet (2). A fuel contain-
ing less than 0.05 pct sulfur should be used with a CDPF
to minimize the formation of sulfate particulates.

The objectives of this report are to present results from
the U.S. Bureau of Mines’ evaluation of a CDPF used at
the Cannon Mine, to describe the mine’s experience and
cost analysis of the CDPF’s, and to make recommenda-
tions for the use of CDPF’s. This work was done as part
of a USBM program to improve the health of the Nation’s
miners.

CANNON MINE—A FILTER USER AND TEST SITE

The Cannon Mine of Asamera Minerals is a 1,294-mt/d
(1,427-t/d) underground gold mine located on the outskirts
of the city of Wenatchee, WA. Declining ore reserves
have recently forced a drop to 967 mt/d (1,065 t/d).
Wenatchee lies on the eastern slope of the Cascade
Mountains midway between Seattle and Spokane.

In September 1987, the Cannon Mine became the first
US, mine to install a CDPF, and the mine has continued
to use CDPF’s to reduce DPM emissions from under-
ground diesel equipment. Currently, the mine has CDPF’s
installed on one roof-bolting jumbo, one road grader, five
23.6-mt (26-t) trucks, two 3.8-m? (5-yd*) load-haul-dumps
(LHD’s), two 4.6-m? (6-yd®) LHD’s, and one 6.1-m? (8-y°)
LHD. CDPF’s were tried, unsuccessfully, on a diesel farm
tractor used for personal transportation.

In 1990, Asamera Minerals and the USBM entered into
a cooperative agreement to study the durability and
performance of a CDPF, over time. The CDPF was in-
stalled on a 3.8-m? (5-yd*) LHD powered by a Deutz®
F10L413 FW engine rated at 172.3 kW (231 hp) at 38.3 Hz
(2,300 rpm). The duty cycle of this LHD is similar to
other LHD’s in many trackless underground mines using
truck haulage. The LHD often loads trucks rather than
tramming to the ore pass. When loading a truck, the
LHD makes four passes in the muck pile, then either idles
while waiting for another truck or shuts down while the
operator drives the truck to the ore pass. When loading
in this location is completed, the LHD is driven to a new

‘Italic numbers in parentheses refer to items in the list of references
at the end of this report.

SReference to specific products does not imply endorsement by the
USS. Bureau of Mines.


EVALUATION OF CATALYZED DIESEL PARTICULATE FILTERS
USED IN AN UNDERGROUND METAL MINE

By John J. Baz-Dresch,' Kenneth L. Bickel,? and Winthrop F. Watts, Jr.

ABSTRACT

Catalyzed diesel particulate filters (CDPF’s) reduce the concentration of diesel particulate matter
(DPM) and may reduce the emissions of carbon monoxide (CO) and hydrocarbons (HC) in diesel
exhaust. Asamera Minerals’ Cannon Mine first installed CDPF’s in 1987, and currently has 12 diesel-
powered vehicles equipped with CDPF’s.

The Cannon Mine and the U.S. Bureau of Mines collaborated to evaluate the durability and
performance of a CDPF. One of the CDPF’s used at the mine was periodically evaluated in the
USBM’s diesel emissions laboratory after 839, 1,584, and 2,881 h of in-mine service. The objectives of
this report are to present results from the USBM’s evaluation of this CDPF, to describe the Cannon
Mine’s experience and cost analysis of using CDPF’s, and to make recommendations for the future use
of CDPP’s.

CDPF’s improve air quality at the Cannon Mine, but they frequently become plugged and are subject
to excessive mechanical shocks and stress, shortening their useful life. Mine records indicate that
CDPF’s account for 0.8 to 4.9 pct of the vehicles’ operating cost at the mine. CDPF life to date has
ranged from 1,671 h to more than 5,992 h. Laboratory tests of the CDPF determined that DPM
removal efficiency decreased and regeneration temperature increased over time,

Mining engineer, Asamera Minerals (U.S.), Inc., Wenatchee, WA.
2Mining engineer, Twin Cities Research Center, U.S. Bureau of Mines, Minneapolis, MN.
3Industrial hygienist, Twin Cities Research Center.


LABORATORY TEST PROCEDURE

The CDPF was evaluated in the USBM’s diesel re-
search laboratory (14) after 839, 1,584, and 2,881 h of in-
mine service over a period of 21 months. The test proce-
dure was designed to determine the CDPF’s particulate
collection efficiency, its effect on CO and HC emissions,
and its regeneration temperature. Regeneration tempera-
ture is defined as the temperature at which the amount of
DPM being collected equals the amount being regener-
ated, as measured by the change in pressure across the
CDPF. Engine baseline emissions and emissions with the
CDPF were collected each time the CDPF was evaluated.
No attempt was made to duplicate the exhaust flow condi-
tions the CDPF experienced in the mine.

Testing was conducted using a Caterpillar 3304 pre-
chambered, naturally aspirated engine rated at 74.6 kW
(100 hp) at 36.7 Hz (2,200 rpm) with a peak torque of
380 Nem (280 Ib- ft) at 20 Hz (1,200 rpm). This engine is
smaller than the 172.3-kW (231-hp) engine used at the
mine, with a lower exhaust flow. The CDPF has a lower
space velocity when used on the Caterpillar engine.
This probably resulted in higher DPM collection efficien-
cies and enhanced CO and HC removal. A low-sulfur fuel
(0.03 to 0.04 wt pct) was used for all tests.

The CDPF was prepared for laboratory evaluation by
placing one 0.16-cm (0.63-in) diameter k-type thermo-
couple 2.5 cm (1.0 in) into the center of the substrate face
on both the inlet and outlet ends to measure temperatures
(fig. 2). The thermocouples were installed through ther-
mocouple fittings welded to the canister.

Pressure ports were installed at the inlet and outlet of
the canister to monitor the pressure drop across the
CDPF. The difference in pressure between the inlet and
outlet of the CDPF is an indication of how much particu-
late is trapped. When the CDPF is regenerating, the pres-
sure drop decreases.

‘Thermocouples:

Filtered
exhaust
gas out

Exhaust
gas in

‘CDPF pressure drop:

Stainless steel housing

Figure 2.—Location of thermocouples and pressure ports on
CoPF.

Upon arrival at the USBM, the CDPF was examined
visually for physical damage and for evidence of plugging.
If plugging was suspected, the CDPF was installed in the
laboratory and the engine backpressure was measured. If
the backpressure exceeded the manufacturer’s recommend-
ed maximum, it was removed and blown out with com-
pressed air to remove as much DPM as possible. This
reduced the potential for an uncontrolled regeneration.
Testing proceeded only when engine backpressure was less
than 7.5 kPa (30 in H,O).

DPM COLLECTION EFFICIENCY
AND EMISSIONS SAMPLING

The CDPF collection efficiency was evaluated at the six
steady-state modes described in table 1. These modes
were selected because they represent operating modes an
LHD might experience in a mine (15) and because they
have a wide range of exhaust temperatures, including
modes 3 and 6 where the CDPF should regenerate.

Table 1.—Six steady-state engine conditions

Mode ‘Speed Load,

Hz tpm pet

T. 20 1,200 50
2. 20 1,200 75
3. 20 1,200 100
4. 30 1,800 50
5. 30 1,800 75
6. 30 1,800 100

During the collection efficiency tests, DPM samples
were obtained with and without the CDPF installed. One
to three samples were obtained at each mode. Sampling
times were 15 to 30 min without the CDPF installed, and
60 min with the CDPF installed. CO and HC emissions
were measured as described by others (14).

REGENERATION TEMPERATURE TESTING

The regeneration temperature was determined using an
engine ramp test procedure. The engine was operated at a
constant speed of 30 Hz (1,800 rpm) and the load was in-
creased from 27.1 Nem (20 Ib+ft) to 339 Nem (250 Ibe ft)
at a rate of 1.02 Nem/min (0.75 lb- ft/min). The CDPF
temperature increased slowly, from about 170° to 520° C.
The pressure drop across the CDPF was monitored to de-
termine the regeneration temperature. The ramp test dif-
fers from the steady-state tests used to determine col-
lection efficiency because the exhaust temperature slowly
increases with load, allowing the regeneration temperature
to be determined, as opposed to remaining constant for
each steady-state mode test.


9478

Evaluation of Catalyzed Diesel Particulate
Filters Used in an Underground Metal Mine

By John J. Baz-Dresch, Kenneth L. Bickel,
and Winthrop F. Watts, Jr.

UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF MINES



CANNON MINE’S EXPERIENCE WITH CDPF’S

CLEANING OF CDPF’S

Cleaning of plugged CDPF’s with a water-pressure
washer without detergent is a common practice at the
Cannon Mine, because not all the CDPF’s regenerate
properly. It is not known exactly how cleaning affects
filtration efficiency and catalyst performance, but it is
suspected that using a pressure washer to clean CDPF’s
may be detrimental to the ceramic substrate. Water may
cause dynamic fatigue by accumulating in cracks in the
ceramic substrate and expanding as the CDPF heats up.
This causes further cracking of the ceramic material, which
will eventually degrade performance (20).

On average, it takes a mechanic approximately 1 h to
remove, clean, and reinstall a CDPF. The estimated cost
for cleaning a CDPF is $24.50, assuming $18.15/h for the
mechanic and 35 pet for fringe benefits.

Other reported methods that are used to clean plugged
filters include oven baking, compressed air cleaning, and
water-pressure washing with nonphosphate detergent (21).
Oven baking simulates what actually happens on the vehi-
cle but requires a large oven with vents. The manufac-
turer’s recommendations should be followed in each case.

BACKPRESSURE ALARMS

Backpressure alarms were installed on all vehicles
equipped with CDPF’s at the Cannon Mine to indicate to
the equipment operator when the CDPF requires regen-
eration, When the exhaust backpressure alarm activates,
it is necessary, as discussed earlier, to raise the engine’s
exhaust temperature to initiate regeneration.

The backpressure alarms installed on Asamera’s equip-
ment consist of a “black box" with a red light that is
mounted in the engine compartment. The unit (fig. 3) is
connected to the inlet of the CDPF with a metal tube. A
red light is also installed on the dashboard in the op-
erator’s compartment that glows when the backpressure
exceeds a preset value, indicating the CDPF requires

regeneration.

Only 2 of the original 12 backpressure alarms are cur-
rently operational. Production equipment is not removed
from service to repair a backpressure alarm, and frequent-
ly pressure tubes and wires are not reattached after engine
repairs are completed. Production and maintenance per-
sonnel, both staff and hourly, must be aware of the pur-
pose of these alarms and trained to maintain them. Oper-
ators must ensure that regeneration occurs frequently to
avoid damage to the CDPF, in order to protect the mine’s
large investment in CDPF’s.

Fatigue-induced breaks and leaks in the metal tube
and fittings of the backpressure alarm are reported by
Asamera’s maintenance personnel to be at least partly
responsible for backpressure alarm failure. These leaks

are caused by engine vibration and stresses developed
from operating a machine in a harsh mine environment.

New backpressure alarms, which take advantage of
improved technology to improve durability and per-
formance, need to be developed. One such system com-
bines sensors to monitor backpressure with thermocouples
to monitor exhaust temperature on the inlet and exit of
the CDPF. Digital readouts in the operator’s cab display
current conditions, and indicator lights flash when the
exhaust temperature and/or backpressure exceeds accept-
able limits. This type of monitoring system is advanta-
geous because it provides information when the CDPF is
undergoing regeneration, but it is more costly. The mon-
itoring system must be made to withstand the mine envi-
ronment and be simple to maintain.

CDPF USAGE AT CANNON MINE

This section describes, in detail, the Cannon Mine’s
experience with CDPF’s on specific machines. The re-
ported engine hours are based upon the hour meters on
the respective engines. Vehicle operating costs include
operating and maintenance labor, fringe benefits, wear and
repair parts, consumable repair items, tires, and fuel, but
do not include bonus, sales tax, or amortized capital costs.
These costs are derived from the detailed cost records
kept by the mine.

Load-Haul-Dumps, 6.1 m? (8 yd?)

The first installation of a CDPF in a U.S. underground
mine was in September 1987, on a 6.1-m° (8-yd*) LHD,
which is powered by a 201-kW (270-hp) Caterpillar 3306
prechambered, turbocharged, aftercooled engine (fig. 4).
Prior to CDPF installation, the filter manufacturer per-
formed a temperature trace of the engine’s exhaust. The
exhaust temperature was well over the 400° C required for
regeneration of the CDPF. The manufacturer stated that
an exhaust temperature of 400° C must be sustained for
25 pet of the unit’s duty cycle for the CDPF to properly
regenerate (22). Based on this information, the mine
installed the CDPF on the LHD, but the exhaust tempera-
ture was not measured with the CDPF in place to ensure
that the manufacturer’s recommended requirements were
met,

The CDPF immediately improved mine air quality
by reducing the black smoke emitted from the tailpipe.
However, the ceramic substrate of the CDPF broke apart
after 2,960 h of use and the CDPF was replaced. The re-
placement CDPF now has 3,483 h of use. The total time
that this LHD has been equipped with a CDPF providing
exhaust filtration is 6,443 h as of June 30, 1992.

Black smoke is now being emitted from the tailpipe,
indicating that the replacement CDPF has reduced


DPM COLLECTION EFFICIENCY

The DPM collection efficiency of the CDPF after 839 h,
as described in table 3, ranged from 85.5 to 94.5 pet at
modes 1 to 5. At mode 6, where the CDPF regenerates,
its DPM collection efficiency was 48.1 pet. The lower col-
lection efficiency at mode 6 may be due to the release of
sulfate (18). Particles can be driven off the CDPF during
regeneration when oxidation and breakup of the collected
DPM occur, leading to lower collection efficiencies (19).

The collection efficiency of the CDPF after 1,584 h de-
creased at five of the six engine modes by at least 15 pct
when compared with the testing at 839 h. The collection
efficiency ranged from 81.9 pet at mode 5 to 41.2 pet at
mode 3. The collection efficiency after 2,881 h ranged
from 82.2 pet at mode 2 to 28.5 pet at mode 3. When
compared with collection efficiency data after 1,584 h, a
decrease in collection efficiency of 15 pet or more oc-
curred at modes 3 and 4, Problems that occurred during
the filter weighing procedure prevented obtaining an
accurate measure of collection efficiency at mode 6.

The lowest collection efficiencies were at modes 3 and
6, where regeneration occurs, probably due to the release
of sulfur stored during testing at lower exhaust tempera-
tures, which is released as particulate matter.

No damage could be seen on the inlet or outlet faces
of the ceramic substrate after 2,881 h, but internal damage
is suspected because of the lower collection efficiency.
The damage could have occurred because of mechanical
shock and vibration, cracking or melting of the ceramic
due to uncontrolled regeneration, or a cracked substrate,
resulting from repeated thermal stresses during repeated
regeneration,

Table 3. - CDPF particulate collection efficiency

DPM concentra-
Time of Mode .mg/sm? CDF collection
operation, hy Without With efficiency, pet
CDPF CDP
889 see 1 214 3.0 85.5
2 24.0 24 912
3 137.7, 17.7 87.1
4 447 32 92.7
5 34.5 19 945
6 403 209 48.1
Mean 50.4 84 83.2
STD 43.7 87 17.5
1,584... 1 24.6 96 60.9
2 23.1 9.0 608
3 1439 «84.6 412
4 426 9.9 768
5 38.0 69 819
6 632 314 50.3
Mean 559 25.2 62.0
sTD 455 30.5 15.4
2,881 .......4. 1 43.1 9.0 79.1
2 43.2 7 82.2
3 164.1 117.3 28.5
4 40.3 16.3 59.6
5 28.6 64 78.4
6 NAp NAP NAD
Mean 639 31.3 65.5
sTD 56.4 48.2 22.6

STD Standard deviation.

SUMMARY OF LABORATORY RESULTS

1. The regeneration temperature of the CDPF in-
creased from 405° to 450° C after 839 and 2,881 h of oper-
ation, respectively. .

. 2, The CDPF reduced CO emissions by 21.3 to 64.8 pet
and HC emissions by 5.4 to 89.7 pct after 839 h, depending
on the engine mode, The CDPF was still effective at low-
ering CO and HC emissions after 1,584 h and 2,881 h, al-
though its CO conversion efficiency was reduced consider-
ably at modes 3 and 6, when the CDPF was regenerating.
In most instances the emissions reductions were within
20 pet of the reductions measured after 839 h.

3, The collection efficiency of the CDPF decreased
when measured after 1,584 h of operation, and again after
2,881 h, suggesting damage to the substrate. Its collection
efficiency after 2,881 h showed a wide range from 82.2 to
28.5 pet.

4. A CDPF can lower DPM concentrations in exhaust.
Depending on the type of catalyst used, it can also reduce
emissions of CO and HC. Its performance, however, will
change with use. This change could be due to physical
damage to the ceramic or to a change in the catalyst that
affects performance.


Stainless steel
canister

Figure 1—Schematic of CDPF.

location. Temperature traces of the LHD’s exhaust ob-
tained prior to installation of the CDPF indicate that
exhaust temperatures periodically exceed 400° C and are
sufficient to initiate regeneration. However, concerns now
exist that the exhaust temperature may not be sustained
long enough to allow sufficient regeneration.

The CDPF replaced the LHD’s catalytic converter and
muffler and was installed on the right side of the LHD
next to the engine compartment just after the point where
the right and left exhaust manifolds merge. The exhaust
pipe from the left side of the engine runs behind the
engine, merges with the exhaust from the right side of the
engine, and then enters the CDPF. This does allow the
exhaust from the left side to cool before entering the
CDPF.

The CDPF had a ceramic substrate composed of Corn-
ing, Inc.’s EX-66 cordierite material, which has a mean
pore size of 35 ym and 15.5 cells per square centimeter
(100 cells per square inch) and an advertised, uncatalyzed
collection efficiency of 65 to 70 pet (10). The ceramic
substrate was 38.1 cm (15 in) in length, had a diameter of
38.1 cm (15 in), and was mounted in a steel canister. The
application of the washcoat and catalyst increased the
collection efficiency by decreasing porosity and promoting
oxidation of the soluble organic fraction of the trapped
particulate.

The CDPF was removed from the LHD and tested in
the USBM’s diesel emissions laboratory after 839, 1,584,
and 2,881 h of in-mine service. The objective of the
laboratory investigation was to determine whether the
regeneration temperature, collection efficiency, and CO
and HC removal efficiency changed with use.

PREVIOUS IN-MINE EVALUATIONS OF CDPF’s

Previous evaluations of CDPF’s used in underground
mines have shown mixed results. A study of 18 CDPF’s in
Canadian mines reported that 8 were removed after an
average of 1,704 h of operation because of failure to
regenerate, physical deterioration, production of unusual
odors, or other reasons. The remaining 10 CDPF’s were
still operable and had accumulated an average of 1,984 h
of operation, with 1 CDPF operating for over 4,000 h at
the time of the report (11). However, similar problems of
inadequate regeneration, which led to plugging of CDPF’s,
and unusual odors that concerned some vehicle operators
were also reported for the filters that remained in service.

As a result of a trial of uncatalyzed diesel particulate
filters (DPF’s) and CDPF’s on LHD’s, front-end loaders,
and bulldozers at a Canadian mine, it was concluded
that DPF’s and CDPF’s can be used successfully under-
ground. DPF’s and CDPP’ are said to decrease vehicle
maintenance costs (12) by reducing the frequency of
vehicle removal from service because of exhaust smoke.
However, this may lead to higher engine maintenance
costs over the long term, because maintenance personnel
frequently use smoke characteristics as an indicator of
engine problems.

Another study (J3) reported that an uncatalyzed DPF
operated for about 5,000 h on an LHD in an underground
mine. When the DPF was removed and analyzed, no
cracking or melting of the substrate was observed. Ash
accumulation was apparent because the baseline backpres-
sure had increased from 2.5 to 4.0 kPa (10 to 16 in H,0).


CONTENTS

Abstract .
Introduction . . .
Design and operation of CDPF’s .....
Cannon Mine—a filter user and test site .
Previous in-mine evaluations of CDPF’s
Laboratory test procedure .............005
DPM collection efficiency and emissions sampling .
Regeneration temperature testing .
Laboratory results
Regeneration temperature .
Gaseous emissions
DPM collection efficiency ..
Summary of laboratory results . .
Cannon Mine’s experience with CDPF’s .
Cleaning of CDPF’s
Backpressure alarms
CDPF usage at Cannon Mine .
Load-haul-dumps, 6.1 m?
Load-haul-dumps, 3.8 m?
Load-haul-dumps, 4.6 m?
Trucks, 23.6 mt . .
Road grader ...
Roof-bolting jumbo .
Tractor
Estimated cost of using low-sulfur diesel fuel .
Summary of Cannon Mine’s experience with CDPF’s -
Recommendations .
References ........ seeeees

ILLUSTRATIONS

Schematic of CDPF ...... .
Location of thermocouples and pressure ports on CDPF .
Mounted backpressure alarm . .

Load-haul-dump, 6.1 m?...
Truck, 23.6 mt, with dent in CDPF .
CDPF with damage to inlet end .
CDPF with damage to exhaust end .
Road grader with CDPF .....
Roof-bolting jumbo with CDPF .

PRENAKEYNE

Six steady-state engine conditions
Effect of CDPF on CO and HC emissions at different temperatures, over time
CDPF particulate collection efficiency .... .

CDPF operating costs at Cannon Mine ...

fener


Road Grader

A CDPF was installed in April 1989 on a road grader
(fig. 8) powered by a 93-kW (125-hp) Caterpillar 3304
engine at a cost of $4,545 including the backpressure
alarm. The CDPF failed in June 1992, after 1,671 h of
use, although the backpressure alarm remained intact and
appeared operational. For that period the cost of opera-
tion was $2.72/h. The road grader’s operating cost for
1991 was $55.50/h, which included the cost of the CDPF.
The cost of the CDPF represents 4.9 pct of the road
grader’s operating cost.

This CDPF showed a gradual decline in filtration ef-
ficiency, as increasing amounts of black smoke were ob-
served in the exhaust stream. Several times the CDPF was
removed from the road grader and pressure washed with
water to remove some portion of the collected DPM and
to reduce backpressure. After cleaning, visual observations
suggested that the CDPF appeared to trap more of the
DPM, but eventually the backpressure built up to unac-
ceptable levels and further cleaning was required. At the
time of the last cleaning, light could be seen through the
CDPF and it was considered to have failed.

Figure 7.-CDPF with damage to exhaust end.

Figure 8.—Fload grader with CDPF.


listed at 469,754 mt (517,669 t), diesel fuel amounted to
acost of $0.335/mt ($0.304/t) mined, or $0.362/mt
($0.328/t) after taxes. If it is assumed that low-sulfur die-
sel fuel will cost an additional 5 pct, diesel fuel costs will
rise to $165,292, or $178,350 with a 7.9-pct sales tax. This
yields a diesel fuel cost of $0.352/mt or $0.380/mt

($0.319/t or $0.345/t) after taxes. This is an increase in
mine production costs of $0.017/mt ($0.015/t) before taxes
or $0.018/mt ($0.017/t) after taxes. It is highly unlikely
that the increase in diesel fuel cost is offset by savings in
prolonged CDPF life; however, mine air quality is im-
proved by the minimization of sulfate aerosol formation.

SUMMARY OF CANNON MINE’S EXPERIENCE WITH CDPF’S

CDPF’s on diesel engines will, in the right application,
do a good job of removing much of the DPM. However,
the Cannon Mine’s experience with CDPF’s has shown
that CDPF’s are costly and frequently require cleaning,
that backpressure alarms fail frequently, and that proper
vehicle screening prior to CDPF installation is critical if
these problems are to be minimized.

The miners, support personnel, and staff of the Cannon
Mine feel that CDPF’s have improved air quality. When
a CDPF is working properly, the cloud of black smoke
usually so noticeable with a diesel engine is absent or
nearly absent. However, these improvements in air quality
are costly. Table 4 summarizes the costs of using CDPF’s
at the Cannon Mine. Some installations of CDPF’s at
Asamera were inappropriate because of engine compart-
ment limitations, insufficient exhaust temperature to
ensure regeneration, or inadequate protection from the
rigors of the mine environment. Merely obtaining an ex-
haust temperature trace prior to installing a CDPF is not

necessarily adequate to ensure that the exhaust tempera-
ture is sufficiently hot for long enough periods of time to
properly regenerate the filter. A detailed examination of
the machine’s duty cycle using an onboard data logger is
the best way to ensure proper application of the CDPF.

Table 4.—CDPF operating costs at Cannon Mine

Vehicle Cost, $/h Operating
costs, pet
6.1-m? LHD . 2.43 29
3.8-m? LHD! 1.82 16
3.8-m? LHD? . 1.45 18
4.6-m* LHD? ..... 2.39 3.6
23.6-mt truck? .. . 2.58 3.2
Roof grader . . 272 49
Roof bolter . . 76 3

THD Load-haul-dump.
‘Evaluated in mine.

Evaluated in USBM laboratory.
3average operating costs are shown.

RECOMMENDATIONS

CDPP’s are best suited for vehicles with consistently
heavy duty cycles that produce exhaust temperatures ad-
equate for regeneration. The ability of the catalyst to
lower the temperature at which regeneration occurs will
degrade with time, hindering regeneration. This results
in DPM buildup in the CDPF that can lead to plugging of
the filter and decreasing filtration efficiency. The fol-
lowing recommendations are made to help ensure proper
CDPF operation.

1. Use low-sulfur fuel. A fucl sulfur level of 0.05 wt
pet or below is recommended. This will limit the produc-
tion of sulfate and lower the risk of catalyst poisoning by
sulfur.

2. Perform vehicle screening. The exhaust temperature
of each candidate vehicle should be measured over several
days of use. A rule of thumb is that the CDPF tempera-
ture should exceed 400° C for at least 25 pet of its duty
cycle. The duration of the periods the CDPF is above
400° C and peak temperatures of the CDPF are also fac-
tors to be considered. The portion of the time the CDPF

must exceed 400° C to achieve proper regeneration may
vary with the catalyst used in the filter. The exhaust
temperature should be measured where the CDPF will be
installed. On a V-type engine, where two CDPF’s are rec-
ommended, the temperature of cach exhaust bank should
be determined. If the vehicle’s duty cycle changes, or if
there is a change in engine condition, the exhaust temper-
ature should be remeasured to ensure that the CDPF will
regenerate adequately.

3. Minimize loss of exhaust heat and backpressure.
The CDPF should be installed as close to the exhaust
manifold as possible. Consideration should be given to
insulating the exhaust line to the CDPF, especially if
exhaust temperatures are marginal for regeneration (23).
The number of pipe bends and length of exhaust pipe
should be kept to a minimum to reduce backpressure.

4, Monitor backpressure. A backpressure gauge should
be installed in the operator’s cab. When the backpressure
becomes excessive (exceeding 30 kPa (40 in H,O) for most
engines) the CDPF should be regenerated by operating the
vehicle at a high-load condition. If necessary, the DPM


Library of Congress Cataloging in Publication Data:

Baz-Dresch, John J.
Evaluation of catalyzed diesel particulate filters used in an underground metal mine
/ by John J. Baz-Dresch, Kenneth L. Bickel, and Winthrop F. Watts, Jr.
p. cm. — (Report of investigations; 9478)
Includes bibliographical references (p. 13).
Supt. of Docs. no.: 128.22:199
1. Diesel motor exhaust gas—Purification. 2. Air filters—Testing. I. Bickel, Ken-

neth L. II. Watts, W. F. (Winthrop F.). II. Title. IV. Series: Report of investi-
gations (United States. Bureau of Mines); 9478.

TN23.U43 [TN305] 622 s—de20 [622.82] 93-5103 CIP



Report of Investigations 9478

Evaluation of Catalyzed Diesel Particulate
Filters Used in an Underground Metal Mine

By John J. Baz-Dresch, Kenneth L. Bickel,
and Winthrop F. Watts, Jr.

UNITED STATES DEPARTMENT OF THE INTERIOR
Bruce Babbitt, Secretary

BUREAU OF MINES


Aer aareenietheneantgssse
rr :

coe

Seestchsusan gas

Figure 4.—Load-haul-dump, 6.1 m? (8 yd).

filtration efficiency. Both CDPF’s were removed and
cleaned on several occasions, because the filters were
plugged because of incomplete regeneration. The back-
pressure alarm is no longer operational on this LHD.
The total cost of the two CDPF’s, one backpressure
alarm, and one site visit by the filter manufacturer to
obtain an exhaust temperature trace and to provide
installation assistance was $15,626. The 1991 operating
costs for this unit, including the cost of the CDPF, were
$83.84/h. This gives a cost for exhaust filtration of
$2.43/h for the 6,443 h or 2.9 pet of hourly operating cost.

Load-Haul-Dumps, 3.8 m? (5 yd?)

A CDPF was installed in the first quarter of 1990 on a
3.8-m? (5-yd?) LHD powered by a 172-kW (231-hp) Deutz
F10L413W engine. Because of the exhaust system design
of this LHD discussed previously, the optimal installation
would have had two small CDPF’s on this LHD rather
than one large CDPF. Each CDPF would serve one ex-
haust manifold, rather than a single large CDPF serving
both exhaust manifolds. However, it was impossible to
retrofit this machine with two CDPF’s because of limi-
tations posed by the engine compartment.

This LHD is primarily used for loading trucks, Four
passes are made to fill a truck, after which time the LHD
is either idled until another truck arrives or is shut down
while the LHD operator drives the truck to the dump
point, allowing the CDPF to cool down between loading
cycles. This duty cycle has a peak exhaust temperature
that is sufficient to initiate regeneration, but is probably
too short to sustain regeneration long enough to prevent
a gradual buildup in exhaust backpressure.

Three months after a single CDPF was installed, the
filter broke apart at the center body-end-cone joint. The
CDPF was returned to the manufacturer for inspection
and was replaced. It is probable that the CDPF broke
because of stress imparted by normal engine movement,
since the CDPF was mounted rigidly without any flexible
exhaust pipe to isolate it from engine vibration. A new
CDPF was installed with a flexible exhaust pipe, but it also
broke in the same area. This CDPF was repaired and
reinstalled, and there have been no further problems with
breakage of the filter housing.

The CDPF and backpressure alarm cost $8,466. The
CDPF has operated for 4,653 h at a cost of $1.82/h.
Operating costs for this LHD during 1991 were $114.83/h
and filtration cost accounts for 1.6 pct of the LHD’s
operating cost. This CDPF also required pressure washing
on several occasions.

The CDPF evaluated in the USBM’s laboratory was
mounted on a 3.8-m? (5-yd°) LHD, which was powered by
an air-cooled, prechambered, Deutz F10L413 FW engine,
rated at 172.3 kW (231 hp) at 38.3 Hz (2,300 rpm). The
CDPF was installed during July 1990, at a cost of $4,175,
and was used for a total of 2,881 h. The CDPF was not
reinstalled after 2,881 h because the laboratory evaluation
showed a decrease in filtration efficiency and an increase
in regeneration temperature. The estimated cost to
operate this scoop during the 1991 calendar year was
$81.95/h, which included the $1.45/h cost of the CDPF.
This represents almost 1.8 pct of the operating cost of this
LHD.

Load-Haul-Dumps, 4.6 m? (6 yd*)

Two new 4.6-m} (6-yd?) LHD’s equipped with Deutz
F10L413 FW, 172-kW (231-hp) engines were purchased


Roof-Bolting Jumbo

A diesel-hydraulic roof-bolting jumbo (fig. 9) powered
by a 61-kW (82-hp) Deutz F6L912W engine was equipped
with a CDPF in October 1988. The unit’s diesel engine
provides power both to move the unit from location to lo-
cation and to operate the hydraulic systems that power the
drilling and bolting functions. The jumbo installs roof
bolts throughout the mine, but stays in a given location for
anywhere from a few hours to several days, with the diesel
engine running under heavy load for a large portion of the
shift. This duty cycle is ideal for a CDPF, because the
high exhaust temperatures promote regeneration and me-
chanical stresses are limited when the jumbo is not
moving.

This CDPF has accumulated 5,992 h of use as of
June 30, 1992, and the backpressure alarm on the roof
bolter remains functional. The CDPF and backpressure
alarm cost $4,345, The bolting jumbo’s operating costs
for 1991 were $92.35/h, which included the CDPF cost,
but not the cost of the roof bolts. The CDPF accounts for
08 pet of the drill’s operating cost per hour over the life
of the filter to date.

This CDPF has failed to regenerate properly on several
occasions and has required pressure washing. The condi-
tion of the ceramic substrate is unknown, but it appears to
be providing some exhaust smoke reduction.

Tractor

A 34-kW (45-hp) farm tractor, used for personal trans-
portation by the underground mine foremen, was equipped
with a CDPF. The duty cycle included driving up and
down ramps and over level ground and periods of idling.
The temperature trace performed on the tractor engine
prior to installation of the CDPF showed that the exhaust
temperature was well in excess of the 400° C required to
initiate filter regeneration. High temperatures were ap-
parently not maintained for a sufficient duration, however,
because the CDPF failed to regenerate properly, leading
to the buildup of excessive backpressure and stalling of the
engine. This CDPF was removed from service after about
2weceks and this installation of a CDPF was judged a com-
plete failure. No backpressure alarm was used in this
installation.

ESTIMATED COST OF USING
LOW-SULFUR DIESEL FUEL

Low-sulfur diesel fuel is recommended for use with
CDPF’s because the formation of sulfate particles is
reduced and there is less chance for catalyst poisoning
(18). During 1991, the Cannon Mine purchased 850,246 L
(223,749 gal) of diesel fuel at a cost of $157,421, or
$169,857 with 7.9-pet sales tax. With 1991 production

Figure 9.—Roof-bolting jumbo with CDPF.