POWER July 2017 - 27

ENVIRONMENTAL ISSUES
Table 1. Five retrofits. EPRI studied five plants that retrofitted their electrostatic precipitators
(ESPs). This table provides some details associated with each project. (kacfm = thousands
of actual cubic feet per minute) Source: EPRI
Unit size
(MW
gross)
2 x 1,200
Fuel
Low-sulfur eastern
bituminous coal
2 x 423
550
550
Eastern bituminous
coal and Powder
River Basin coal blend
Coal blend
Eastern bituminous
coal and Powder
River Basin coal blend
112
Eastern bituminous
coal and Powder
River Basin coal blend
Specific
collection
area (ft2/
kacfm)
Retrofit description
262 ESP sectionalized on first two fields and
upgraded with 32 high-frequency power
supplies (HFPSs), upgraded controls,
grounding, and load center.
495 Units retrofitted with 16 HFPSs, upgraded
cables, automatic voltage control
(AVC) boxes, and communications.
445 Units retrofitted with 32 HFPSs, upgraded
communications, cables,
and distribution transformers.
312 Units retrofitted with 32 HFPSs, upgraded
communications, cables,
and distribution transformers. Also
modifications to AVC controls.
266 Units partially sectionalized and
retrofitted with four three-phase power
supplies, decreased rapper density, and
computer and control upgrades.
with existing ESP equipment, such as voltage
controls, rapper controls, and supervisory
controls. Cost, availability, and predicted
reliability may make these power supplies
more attractive than HFPSs.
Case Studies
The most recent EPRI study documented five
case studies of plants retrofitting their ESPs.
The plants involved were of the following
designs:
■ Two 1,200-MW units with one-third of the
ESP sectionalized and retrofitted with a
HFPS.
■ Two 423-MW units retrofitted 100% with
HFPS.
■ One 550-MW unit retrofitted 100% with
HFPS.
■ One 550 MW unit retrofitted 100% with
HFPS.
■ One 112-MW unit sectionalized and retrofitted
with a three-phase low-frequency
power supply.
Some of these case studies also involved
increased electrical sectionalization, which
enhances the collection efficiency of the
various fields across and through the ESP
(Figure 2). The case studies are summarized
in Table 1.
Potentially Improved ESP
Performance
All of the new power supplies (HFPS, threephase
low- and mid-frequency) and other
July 2017 | POWER
Typical
opacity
(%)
2-3
2-3
<10
<10
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equipment described in the EPRI report offer
the potential for improved ESP performance
and should be considered when an existing
precipitator is in need of a performance upgrade
or the existing conventional TR sets
are in need of replacement.
Voltage-current curves generated from
ESP operating data (secondary voltage
versus secondary current) and computer
modeling can be used to predict potential
performance enhancement and the best
new power supply configuration. Exact
performance will depend on the size of the
ESP, the fuel quality, and consequently its
particulate properties. Process conditions,
including the application of sorbents for environmental
control, flue gas and particulate
distribution, and other site-specific conditions,
will affect results.
The new power supplies are not a panacea
for an ESP that is in poor mechanical
condition, but for precipitators that are in
reasonably good mechanical condition, they
offer a viable means for performance enhancement.
For some ESPs, they can be the
difference between a marginally compliant
ESP and a reliably compliant ESP at substantially
less cost than adding collecting
surface area or a polishing unit. ■
-Jose Sanchez (josanche@epri.com)
is technical leader for the Integrated
Environmental Controls Program in EPRI's
Generation Sector, and Tom Keeler
(trkeng@apcnetwork.com) is president
of TRK Engineering Services,
which specializes in ESPs.
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POWER July 2017

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