POWER October 2021 - 49

WATER
ness and responsibility that hinges on the
participation of various environmental,
engineering, and operational personnel.
It is also a framework of procedures that
allows operators to avoid uncertainties,
take short-term corrective actions, and
implement adequate long-term management.
Intake operators should consider
the following critical items to ensure reliability
of the cooling water intake system.
How Do I Know When an Intake
Blockage Event Is Imminent? Some intake
blockage events are episodic (such
as massive jellyfish ingress) and, historically,
have been difficult to predict. Other
intake blocking phenomena may result
from years of steady (but unnoticed
or ignored) biological change, primarily
though shifts in species community
and their seasonality in the source waterbody.
Therefore, long-term changes in
the source waterbody should be monitored
and result in modified approaches
to managing potential blockage events.
Short-Term Forecasting. Most approaches
to mitigating the effect of an
intake blockage event are reactive (such
as increasing trash rack raking frequency
or increasing rotational speed on
traveling water screens). By contrast,
forecasting potential
debris
events is proactive.
Current
and
emerging
blockage
monitoring
tools enable close and detailed observation
of biota and materials in the farfield,
mid-field, and near-field, as well
as monitoring in-plant. Integration of
data from combined monitoring tools
allows estimation of the likelihood that
an event will take place and (potentially)
the event magnitude. Such tools may
include traditional sonar, optical or highfrequency
acoustic cameras, meteorological
and oceanographic data buoys,
hydraulic current monitoring, numerical
hydrodynamic modeling, and satellite
and hyperspectral imagery. Data from
these various tools can be integrated and
evaluated online by a dedicated software
platform, though such technologies address
only near-term threats.
Long-Term Monitoring of Environmental
Change. An important component
of intake reliability is preparing for
intake threats that have yet to materialize
due to their slow rate of change. Preparation
for intake blockage events that
may not occur for 10 or 20 years requires
more than maintaining the operability of
intake screening equipment and ensuring
that procedures are in place to manage
intake blockage events when they
occur. It requires that dedicated personOctober
2021 | POWER
1. Schematic example of jellyfish ingress at a cooling water intake structure (CWIS) where various
intake screening components are functioning to reduce the impact on cooling water flow:
far field including a seasonally deployed, coarse barrier net (A), balanced removal at the coarse
trash rack (B) and fine traveling screen stages (C), and finally disposal of the collected debris (D).
Courtesy: Electric Power Research Institute and Info-graphics
nel identify, collect, and analyze relevant
long-term data sets.
Moreover, when data indicate a
change is happening, these observations
should be shared and discussed among
the wider plant operations team. At such
inflection points, decision-makers should
identify modifications (structural and/or
operational) to the intake system in anticipation
of new threats.
Long-term environmental changes
can cause unnoticed ecological shifts
until a tipping point is reached. Whether
the changes are caused by rising seawater
temperatures, shifts in sand/silt
transport/deposition, introduction of invasive
nuisance species (such as zebra
and quagga mussels), or another source,
each may raise new challenges for which
a plant is no longer designed, equipped,
or operated to manage.
What's the Condition of the Intake
Screening Equipment? Major problems
resulting from intake blockage events are
typically caused by equipment failure due
to inadequate preventative maintenance
(PM), postponed corrective maintenance,
or incorrect operational settings. Examples
include out of calibration water differential
level alarms, corrosion of mesh
panels and chains, missing or broken
seals, blocked or misaligned spray-wash
systems, or improper chain alignment.
Such factors may go unnoticed during
the normal operation of the intake and
equipment; however, they become painfully
evident when the equipment is challenged
during a debris event. Inadequate
preventative maintenance thus leads to
a reduced equipment reliability and increased
risk of intake blockage.
Condition assessment of intake
equipment is comprised of making sure
that equipment issues are identified
through observation and that intake operations
personnel keep up with regular
PM and, where required, corrective
www.powermag.com
maintenance. PM tasks depend on the
equipment type and components that
are subject to wear and tear, as well as
water quality conditions.
Observation/Inspections/Walkdowns.
Information collection and trend
analyses are critical to understanding
equipment status and its readiness to handle
debris events. Information is collected
by monitoring through in-plant sensors
and visual observation of equipment/material
integrity. Such information should be
documented and clearly reported to other
station team members for evaluation.
Station team members should actively
review collected information to quickly recognize
suboptimal conditions and respond
with additional appropriate PM or, in some
cases, immediate corrective actions. Assessing
equipment reliability may include:
■ Documenting differences between
design drawings and as-builts (particularly
in cases where the differences
are visually obvious). Current conditions
can vary from as-built because
long-term operation and frequent
maintenance can affect tolerances/
clearances. In addition, repairs may
further alter components from their
original
design
■ Adhering
condition.
Updated
documentation can assist in troubleshooting
intake equipment reliability
questions when issues arise.
to
have
vendor
recommendations
about operation and PM. Often,
vendors
considerable
experience
at other similar plants and their
recommendations are based on operational
experience and equipment
performance data.
■ Encouraging intake operations personnel
to frequently observe and report
potential issues with the intake
equipment and its critical components
before it affects intake availability during
a debris event.
49

http://www.powermag.com

POWER October 2021

Table of Contents for the Digital Edition of POWER October 2021