Hydrocarbon Processing - April 2021 - 67

Process Control, Instrumentation and Automation
at regular intervals. Maintenance spend is
a large percentage of operating costs in any
process facility or terminal, but it can be
minimized with the right monitoring and
control devices and systems.
The goals of any maintenance program are to maintain equipment without
excessive cost, while maximizing uptime.
Corrective or reactive maintenance costs
are often substantially higher than preventative maintenance costs, so the latter
method is strongly preferred.
According to an ARC Advisory Group
study, the global process industry loses
about $20 B due to unscheduled downtime-around 5% of its annual production.4 Every plant operator can recall
several instances where an emergent maintenance item ended up causing significant
downtime, but many of these incidents
can be avoided with proper care and attention, facilitated by careful device selection.
Proper product design leads to improved maintenance practices related to
tank devices. Some pressure regulators
on the market can be installed 'at-grade,'
meaning they can be set up, checked and
calibrated from the ground. This makes
maintenance much easier, quicker and
safer because technicians can work with
their feet on solid ground. To determine
if this is a possibility, plant personnel must
analyze the specific system and process
conditions for the tank blanketing regulators under consideration, often with assistance from vendors.
To provide remote visibility to control
room personnel, many pressure control
devices available are wireless-ready, and
they can be used to remotely monitor various parameters in the tank or its support
systems. Although each of these devices
could be monitored via traditional wired
means, this is often cost prohibitive due to
the difficulty of installing wired infrastructure from tanks back to the control room.
Wireless devices can be added to tank
vents and regulators to indicate position.
Information collected from such an installation helps determine baseline operation
of regulators and vents, indicates if both
devices are open at the same time (which
should not be the case), shows if a vent
fails to reseat and alerts if an emergency
vent were to open.
Many of these status readings are useful
as leading indicators for whether maintenance or inspections should be scheduled
for later work or must be performed imme-

FIG. 5. Tank blanketing regulators sense tank pressure and provide inert blanketing gas
at a low setpoint to minimize the amount of gas consumed.

diately. With respect to vent monitoring,
wireless devices also help plants compile
an auditable record to present to government regulators regarding emissions.
Regulators in action. Utilizing tank

blanketing regulators as part of a complete
tank pressure control system yields financial benefits due to improved operations
while minimizing risk. Several vendors offer tank walkdowns to provide a review of
tank pressure control devices. Walkdowns
can be as narrow or broad as desired, but
typically include a review of each tank's
physical condition, operability and sizing.
During a tank survey of 40 tanks at a
U.S. Gulf Coast chemical plant, plant personnel needed a focused analysis of the
costs used for nitrogen blanketing, which
were higher than expected. Upon review,
it was found that the setpoints of tank
blanketing regulators and PVRVs were too
close together on several of their tanks.
As a result, the two devices were occasionally open at the same time, thus
venting excess nitrogen into the atmosphere during normal operations. By implementing recommendations to adjust
the setpoints of their devices, as well as
by installing pilot-operated tank blanketing regulators to maintain lower blanketing pressures in the tank, the plant saved
more than $500,000/yr in nitrogen costs
and reduced emissions.

Takeaway. Fixed-roof storage tanks present various challenges to operators, many
of which can be mitigated with a well-designed tank blanketing system. Tanks may
often be overlooked at industrial facilities,
but technology exists in the market to
provide complete pressure control, along
with visibility of tank pressure control
system operation.
Tank blanketing and vapor-recovery
regulators are only a part of a complete
system to control the complex tank ecosystem. These devices-along with vent
valves, hatches, overfill protection device
and others-provide operators with the
reliability they need to properly operate
and maintain these assets, while minimizing risks to personnel, equipment, the environment and the community.
LITERATURE CITED
Complete Literature Cited available online at
www.HydrocarbonProcessing.com.
DAVE MACEDONIA is a Business
Development Director with
Emerson's Automation Solutions
business, covering pressure control
devices and steam equipment. He has
12 yr of experience in the process
industries and has broad subject
matter expertise in industrial fluid and mechanical
systems. Prior to joining Emerson, he was a submarine
officer in the U.S. Navy, with supervisory roles in
operations and maintenance of naval nuclear propulsion
plants. He earned a BS degree in mechanical engineering
from Northwestern University and an MBA from
Carnegie Mellon University's Tepper School of Business.
Hydrocarbon Processing | APRIL 2021

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Hydrocarbon Processing - April 2021

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