Lime kilns switch to DeltaV system with no shutdown
(Excerpted from the June 1999 issue of Control
Engineering magazine)
Facing up to four days' shutdown time to replace its process
control system, Carey, Ohio-based National Lime & Stone
Co. found it could install the DeltaV™ automation system for
tighter control of its lime kiln production -- with no downtime.
National Lime & Stone's Carey mill kilns operate 24 hours
a day, seven days a week, processing 20 million tons of limestone
annually for use in products like asphalt, carpet backing,
ready-mix concrete, and other non-organic substances. It takes
at least 12 hours for a cold kiln to regain operating temperature,
so shutting down is avoided.
Each kiln moves limestone through combustion gasses at over
2,000°F, in an effort to reduce residue carbon dioxide
to 1-2% in the shortest possible time. If the kiln is too
hot, limestone sinters into lumps and fuel is wasted. A too-cool
kiln increases cycle time, reducing profits.
To increase production and reduce variability, National Lime
& Stone looked to Emerson Process Management's DeltaV system.
Beginning on a Monday in February 1998, the old system was
removed. With none of the original signal wires tagged, each
pair of wires was tested and leveled, and a lot of unused
wires were removed.
By Wednesday afternoon, all wires had been identified, application
software configured, remote devices working; the system was
powered up, with the controller and operator station on line.
With the kiln kept hot, troubleshooting was easy, and system
tuning was possible. Customer acceptance testing was completed
on Thursday, and by mid-day Saturday, most of the kiln operators
had been trained to navigate the DeltaV system's graphical
displays and to make operational changes.
In the changeover, 15 temperature transmitters to profile
kiln performance and lime quality were added to the original
temperature flow, pressure, amperage, and oxygen transmitters.
Control logic includes a master kiln temperature loop with
adjustable air/fuel ratios to trim combustion air and natural
gas demands. Cross-limiting these ratios ensures safe combustion
control during load changes.
The project came in on time and on budget, providing additional
performance enhancements including:
-System logic that monitors and remembers modes and setpoints
and can restart control logic following power outages.
-Remote diagnostics and engineering via modem from anywhere,
24 hours a day.
-Online data collection and graphing of temperature and speed
variables, which aids in laboratory analysis to better meet
customer specifications.
"We're real tickled with the project," says National
Lime & Stone's project manager Lloyd Kelly, "Putting
in the system is one of the better projects we've had here.
It went real smooth. The operators are real comfortable and
happy with it." Kelley adds, "We recently finished
the update so we feel ready for Y2K." The DeltaV system
has been fully Y2K compliant since the 2.3 and 3.2 releases.
Future enhancement plans at the Carey Mill kilns include
developing fully automatic kiln control to reduce process
variability from manual interventions, and installing a fuzzy
logic controller to stabilize kiln temperatures caused by
raw material variations.
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