POWER February 2020 - 29

CONNECTED PLANT
Increasing Automation
for Fossil Energy Plants
An Electric Power Research Institute study has developed a systematic process
for introducing sequence automation to fossil power plants. Researchers are
now exploring its implementation in case studies.
Steven Seachman
A
s large-scale fossil power plants
are increasingly required to operate
flexibly, control and automation
systems are becoming more important in
operational planning. Automation of these
plants using existing tools in distributed
control system (DCS) toolkits can lead
to many benefits. In particular, sequence
automation can help reduce startup fuel
costs, enable operational efficiency improvements,
and preserve plant equipment
through decreased stress and wear
during startup and shutdown operations.
If plants are to realize these benefits,
however, they need to understand how
best to apply the tools for their site-specific
conditions. To address this need, the
Electric Power Research Institute (EPRI)
recently initiated a project to develop a
systematic process for automation implementation
to assess plant factors that
define their readiness to apply effective
sequence automation functions and to
explore the issues that arise through case
study assessments.
The first phase of the project documents
the potential benefits of power
plant sequence automation and provides
a systematic approach to determining
the specific goals for automation, based
on the identified benefits sought by the
plant owner, the general requirements
for sequence automation based on the
identified goals, and the design philosophies
employed to implement sequence
automation. Researchers also developed
a " readiness index " value that compares
the implementation effort for each option.
The first phase is described in a new report
titled Increasing Automation for Fossil
Energy Plants: Options, Approaches
and Practices (3002016326). The second
phase will implement automation as case
studies and report on the outcomes.
Sequence Automation
The term automation has different meanings
depending on the context and application.
In the context of process control
February 2020 | POWER
applied in large-scale utility power generation,
automation-in the form of continuous
feedback control-is considered
essential to control the many fast, interactive
processes involved.
Less common, however, is the implementation
of sequence automation for
starting and stopping the plant and equipment.
Where the term automation is used
to describe the latter, it is generally for
self-contained subsystems, such as compressed
air systems, oil skids, or auxiliarysteam
package boilers, or for a turbine
plant. In these cases, the sequence automation
design is generally provided by
the manufacturer as part of the equipment
supply, as an integrated design that includes
requirements for sensors, automated
final elements, and protection systems.
In contrast, the extent of sequence automation
of boilers and auxiliary plants, and
the integration of boiler/turbine sequence
controls, vary greatly, not only with plant
age, but also across utilities and individual
stations. The reasons for relatively low levels
of sequence automation overall in largescale
power generation plants, particularly
in the U.S., may be because the requirements
were not included in the original
plant design, perhaps because of a design
criterion for baseload operation or because
of the planned operator attendance regime.
For installed plants, the benefits associated
with sequence automation may not have
been apparent or operationally relevant in
the past, and so the cost-effectiveness of
implementation on installed plants and systems
may have been doubtful.
Several factors have arisen that have
brought interest in wider power plant sequence
automation to prominence. These
factors include:
■ Cost pressures to reduce start times
for economic dispatch and fuel cost
minimization.
■ Flexible, wider-load operations requiring
routine scheduling of equipment,
such as pulverizers and feed pumps,
giving rise to associated process disturwww.powermag.com
■
Minimization
bances, delays, and operational risks.
of additional damage
and maintenance costs resulting from
flexible operations.
■ Aging workforce and loss of operational
expertise.
The generic
functional
architecture
and signal paths for a control and automation
system, as typically implemented
for a large-scale power plant, are shown
in Figure 1. Automatic functions are typically
implemented in the modulating or
continuous controls, drive controls (that
is, controls associated with switchgear,
solenoids, and actuators), and protection
systems to carry out actions that would
otherwise be required to be carried out
by an operator or operators. These functions
are automated to:
■ Provide continuous monitoring of process
variables and timely control actions
to the final elements so that the plant
operates as designed and required.
■ Reduce operator workload and enable
complex plants to be operated with
1. This schematic shows a generic functional
architecture and signal paths for a typical
power plant control and automation system.
Lines depict control system (Ctl. Sys.) inputs
and outputs, operator (op.) commands, and
various sequence (seq.) status and logic connections.
Source: Electric Power Research
Institute (EPRI)
29
http://www.powermag.com
POWER February 2020

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