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 Below are examples of real-world successes achieved by
variability management consulting engagements in a variety of
processes and industries including:
-
Chemical
-
Food
& Beverage
-
Life
Sciences
-
Pulp
& Paper
-
Refining
These
examples also illustrate that plant limitations may be found
in a variety of causes, requiring expertise in many areas such
as:
-
Process
design
-
Control
strategy
-
Controller
algorithm
-
Controller
tuning
-
Performance
of final control elements (control valves, drives)
-
Performance,
installation, and setup of field transmitters
-
Operating
practices
Chemical
CHALLENGE
·
An industrial gas plant was experiencing problems
with product quality and had several
shutdowns per month. The suction flash cooler level was
cycling strongly and its output to an ammonia valve was
upsetting the refrigeration system.
SOLUTION
·
The
Emerson consultant found problems with the instrumentation,
controller tuning, and maintenance practices. Several
pneumatic controllers
and other instruments
were repaired or
replaced, and six controllers were
retuned using the Lambda tuning method.
RESULTS
·
Shutdowns due to cycling were eliminated.
This significantly increased the plant’s monthly production
and extended the equipment life.
Food & Beverage
CHALLENGE
·
A vitamin manufacturer experienced abnormally long cook cycles in one of their batch reactors. The
operator struggled to keep the temperature on setpoint due to
fluctuating temperature in glycol
supplied to the jacket. The
glycol heat exchanger had steam pressure cycling from 1 to 5
bar around a setpoint of 3 bar.
SOLUTION
·
Within
two hours of arriving at the plant, the Emerson consultant traced
the problem to dead band and sizing of the control valve.
When the controller output reversed direction, a 4% change was
needed to move the valve stem due to a faulty positioner.
Emerson’s local business partner replaced the positioner
that day and replaced the valve trim a few days later.
RESULTS
·
Deadband reduced from 4% to <0.5%.
The total time
to make a batch was reduced by 27% and the operator can
now spend his time on other tasks. The changes have also
resulted in an extended life expectancy for the heating
system.
Life
Sciences
CHALLENGE
·
A
pharmaceutical manufacturer was unable
to hold constant vent pressure in a new centrifuge. The
large pressure cycle affected the weight sensor, so the
reagents and washing agents could not be filled correctly.
This resulted in out-of-specification
product.
SOLUTION
·
An
Emerson consultant found an inappropriate
controller algorithm in the PLC supplied by the turnkey
centrifuge vendor. The consultant worked with the plant
systems engineer to change the PLC algorithm, then applied Lambda tuning to the pressure loop.
RESULTS
·
Vent
pressure cycling was eliminated.
Variations in pressure (shown as “After”) are ±1 bit,
which is the smallest variation theoretically possible. The
customer is now able to make
product to FDA standards and sell it.
Pulp and Paper
CHALLENGE
·
A
paper mill had serious quality problems - basis weight and
moisture consistency did not meet customer specifications.
SOLUTION
·
The
Emerson EnTech Variability Index found variability was much
larger for this paper machine than for comparable machines in
the industry. The Emerson Consultant identified problems with
control valves, control strategies, and controller tuning and
systematically worked with the mill to rectify these problems.
RESULTS
·
Basis weight variability was reduced by 30% for 45-gsm
grade and 50% for the 49-gsm grade. This also gave similar
improvements in the moisture variability. The mill’s major
customers resumed accepting shipments.
Refining
CHALLENGE
·
A
group of distillation columns in a refinery had cycling
in the levels,
flows, temperatures, and product
quality. The plant was forced
to stop feed periodically to recover from disturbances.
SOLUTION
·
The
Emerson consultant analyzed process dynamics of the
debutanizer, depropanizer, and deisobutanizer. The consultant
applied Lambda tuning
to give non-oscillatory response and proper cascade
relationships.
RESULTS
·
Cycling
was eliminated and the loops now responded to changes in
production rate and ambient conditions, keeping product
in specification despite disturbances. The feed runs
without interruption, so the annual production is significantly increased. Opportunities to
implement model predictive control for further improvement in
production, quality, and energy cost reduction were also
identified.
To learn more about Variability Management quantified
business results, please contact us at AAT@EmersonProcess.com
or call +1 (512) 832-3575
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