Intro4u2u

Real Life Experience
As you can see, the game has changed. Focusing on dynamic performance
of a process control system by optimizing control valve
performance can have a very positive impact on your O&M
budget and your throughput. Utilizing modern digital equipment
to monitor your valves and establishing a state-of-the-art maintenance
program can further boost your bottom line. We’ll complete
this article by reviewing a few case studies:

A coated-paper machine was having production and quality
problems. A dynamic audit of the process control system identified
stability and control problems in the headbox flow control
system. A faster, more stable valve was installed and new loop tuning
applied; sheet quality went up by an order of magnitude; and
overall production rates improved by 1.4% due to reduced times
to change grades. Bottom-line annual impact: $1.1 million.

A Canadian coal-fired plant was running 19 MWs under its
rated capacity and could not be automatically dispatched because
its ramp rates were too slow. A loop audit found 24 of 35 loops
were suboptimized due to aging and obsolete control valve assemblies.
Corrective action included installation of an upgrade to the
DCS system and the installation of 24 new control valve assemblies
with modern digital positioners. The investment: $900,000.
The payback: $1.4 million a year, primarily due to increased
capacity related to smoother operation of critical loops.

A crude unit had a main feed valve deadband (see Part 1 of
this article) of 6%. This resulted in fluctuations of +/-12 psi to the
de-salter units in the pre-heat train. The setpoint had to be lowered
due to the fluctuations. A faster, more stable valve was installed
with a digital positioner, and fluctuations dropped to +/-1 psi,
allowing the loop’s setpoint to be increased. This higher setpoint
resulted in an increase in flow of 2,000 barrels/day, an increase in
revenue for the plant of $1.9 million a year.

In another crude unit, fired heaters were employed. The fuel
gas valve was found to be unresponsive, and this resulted in fluctuations
in temperature of +/-9° F and an average fuel consumption
of 18.7 MMSCFD. After the valve performance was
optimized, the fuel consumption dropped to 17.5 MMSCFD and
the temperature fluctuations dropped to +/-2° F. The fuel savings
alone amounted to $500,000 a year.

A nuclear plant in the Midwest is looking at a 12% uprate
in power output from its plant, which will greatly improve overall
plant financial performance. A lot of attention was being paid to
the major plant components like the turbines and the steam generators,
but as plant personnel worked on determining the implications
of the power uprate on some of the subsystems within the
bowels of the plant, they began to find a number of critical valves
that were becoming system bottlenecks. The uprate was driving
higher pressures, temperatures, and flows throughout the plant,
and in some cases the old valves could not handle these new operating
conditions. As a result, plant personnel are now drilling
down into their control valve infrastructure to ensure that these
components will not keep them from obtaining operational goals.
By converting to new equipment to handle the more stringent
operating conditions, they are using the occasion to upgrade to
new technologies that will enable them to take advantage of the
operational advantages mentioned earlier in this article. A 12%
uprate in a typical nuclear plant could mean as much as $24 million
in increased annual revenue for the plant.
Conclusion
As you can see from the previous examples, there is gold to be
mined if one takes the proper approach to the care and feeding of
the control valve installed base. New technology makes this
approach easy to adopt and the paybacks are tremendous. Progressive
process companies looking for the next opportunity to
improve performance need look no farther than their plants’ lowly
control valves. Every one is a profit opportunity!