C. M. Consulting
P.O. Box 407
Odell, Oregon 97044
C. M. CONSULTING
A Division of Cliff Mansfield Incorporated
yields positive results
Take a 5’ drum plant and put it into operation at 6500 feet elevation,
feed it aggregate with 6% moisture and you will soon discover that your
production rate is down around 40 tph. Add a couple of decades of wear and tear
and the production rate can get as low as 20 tph. This is the situation I
discovered at a southern Idaho plant last summer.
The AEDCO plant had been purchased new in the ‘70s by Smith Paving. It
was set-up with a wet scrubber, a two bin cold feed and a bucket elevator
feeding directly into a truck. Over the years the bucket elevator caused the
company some problems so it was replaced with a belt conveyor.
Mike Shurtz, owner of ALmix in Fort Wayne Indiana, called and asked me to
see if I could help Smith Paving get some production out of their facility. I
contacted Edwin Smith in March and traveled to his plant in early April. It was
snowing and cold in the high Rockies, but beautiful and exhilarating at the same
I talked with Mr. Smith, his son Bryant and his grandson Alan. Their goal was to
increase the plant’s production, now at around 25 to 30 tons per hour, to
somewhere near 80. Since the plant was producing less than 20,000 tons per year,
I would be on a budget. What could I do?, they asked.
The plant exhibited several problems that contributed to the low
production. The drum flighting was worn out, the burner safeties and main
controls were inoperative, the main fan was undersize for the altitude and worn
out and the wet scrubber was very inefficient. Additionally, the hot oil heater
controls were archaic at best and the asphalt ratio system had died a long time
ago. I told the Smiths that I felt we cold increase their production to the
levels they wanted and I gave them an estimate which they accepted without
hesitation. Due to the weather and their paving schedule I couldn’t start on the
plant until late May.
A 5’ drum flows approximately 19,500 ACFM (actual cubic feet per minute)
of air at 1,000 feet per minute velocity through the drum. By taking some
readings and measurements I was able to determine that Smith’s drum was only
flowing about 9,000 ACFM of air. There were two causes for the low air flow.
First, was the altitude. At 6,500 feet the factory fan, rated at 20,000 ACFM
when it was new, would only flow about 70% of its capacity. Second, our fan was
worn out so it flowed considerably less than that.
Air is the single most important issue in any asphalt plant. The best
plant on earth will fall flat when it runs out of combustion and drying air. The
main fan on a contemporary asphalt plant supplies 60 to 70% of the air required
by the burner. As that fan wears out it will move less and less air, taking away
from the combustion process and slowly lowering the production capacity of your
With these things in mind I contacted Mike Shurtz at ALmix and purchased a
28,000 ACFM main fan and motor. I also asked him to add an exhaust damper so
that I could control the air through the drum. We installed the fan and built an
oversize knock-out box to help with the increased fines carry-out I felt we
would encounter. We also installed an automatic damper control to optimize air
flow through our drum.
Another major concern was the burner safeties on the Hauck Jet burner,
always an important issue but even more so at this plant since the burner was
natural gas fired. Over the years, as system components had failed some had been
completely eliminated, others just by-passed. The control panel had suffered a
fire and as a result the burner was being positioned by hand, the air to fuel
ratio being guessed at. Ignition of the burner was handled by a propane torch.
My first thought was to overhaul the system, but as I looked around it quickly
became apparent that the costs would be prohibitive. Instead, we installed a new
Hauck SJO 200 Star Jet burner and new controls. We also converted to diesel
since it is a safer fuel in this case.
The flights inside the drum were worn out. To optimize the fuel
consumption we installed a set of high efficiency flights and converted the drum
from a bottom discharge to a side discharge configuration. We also installed a
set of heavy duty rakes at the discharge end of the drum.
We then moved the hot-mix belt to the side and built a 6,000# holding
hopper on the end so that we could have a minute or two to get trucks in
position on the scales. Prior to this installation, the plant operator would
position the trucks tailgate to tailgate and back one under when the other one
got loaded. This was a tedious way to load trucks and required a high level of
coordination between all parties involved. Spills happened occasionally,
requiring the plant to shut down for the cleanup process.
Once these improvements were made it was time to upgrade the asphalt
ratio system. I had just finished upgrading another plant to computerized
controls and, as a result, had a perfectly good set of Ramsey based ratio
controls. I installed these along with a Ramsey 10-201 belt scale and
integrator. We then installed frequency controlled variable speed drives on the
feeders. Lastly, we overhauled the hot oil control system, updating it to
automated controls. We spent a day calibrating everything, then made plans to
pave the first job. Then it began to snow. Time passes slowly when you wait out
a June snowstorm at 6,500 feet in the Rocky Mountains!
Finally, the big day arrived. At 7:00am, with trucks lined up, I lit the
burner and started up at 50 tons per hour. After things warmed up I started
increasing speed. At 100 tons per hour (6% moisture in the rock) I was at 40%
burner and 50% on the damper. At 120 tons per hour I was at 60% burner and 70%
on the damper. The job was finished before I had a chance to experiment any
The next day I was off to another plant for more mischief. The Smiths are
consistently running their plant at 80-100 tons per hour; a 300 to 400% increase
over what they could do prior to our modifications.
For additional information on this subject
or help with any problems encountered
contact Cliff Mansfield,
7:30am to 9:00pm Pacific Standard Time.
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