POWER November 2014 - 58

GAS POWER
4. Damper remodel. The existing 9E
CTs exhaust through a stack in simple cycle
mode. Converting the units to combined cycle
required removal of the casing elbow and
installation of a new " T " box with a diverter
damper. The first conversion was completed
in only three days. In this photo, the old " T "
section has been pulled from beneath the
stack and will soon be removed from the rails.
The diverter damper section in the foreground
is sitting on the rails, ready to be slid into
place. Courtesy: CMI Energy
large quantities of raw materials long distances
over difficult terrain.
Accessibility is greatly improved in a vertical
HRSG arrangement. There are access
doors strategically located on its casing so that
an inspector can easily reach any location on a
module without scaffolding by standing on the
module's horizontal tubes. Headers are also
accessible from inside the HRSG casing.
The vertical arrangement is also more
forgiving when there is a failure in a specific
tube in a module. Because the drums
are located away from the tube bundles and
return bends are without intermediate headers,
specific tubes can be extracted from a
module and replaced in the field. The serpentine
configuration of the vertical HRSG
has a good track record on cycling operation
because the tube modules have flexible return
bends instead of fixed headers, allowing
free expansion of the tubes, much like a
feedwater heater.
The vertical HRSG is designed for ther5.
Flexible operations. One of the
eight HRSGs is shown with the CT on the
far left, with the diverter damper and bypass
stack shown between the CT and the HRSG.
The diverter damper allows operation of the
CTs in simple cycle mode by bypassing the
CT's exhaust gases before entering the HRSG.
Courtesy: CMI Energy
mal cycling. A HRSG must be purged of
any lingering explosive gases prior to restart.
This means the CT supplies the purge
air by blowing relatively cold air through
the hot HRSG for several minutes prior to
a CT restart. Inside the HRSG, the cold air
quenches the superheater, forming condensate
inside the tubes that drains and thermally
shocks the bottom headers on a horizontal
HRSG. Any accumulated water within the
bottom header must be drained to prevent
any condensate carryover into the superheat
piping that can thermally shock and deform
downstream tubes. In the vertical HRSG,
the superheater outlet header is the single
low point in the system that collects any
condensate formed, preventing condensate
carryover by design. Horizontal HRSGs are
configured with many large drains beneath
the superheater and reheater bottom headers
to prevent condensate carryover.
Conversely, a vertical arrangement consists
of individual modules with a single
inlet and outlet header, with the " jumper
pipes " replaced by shop-welded elbows.
The entire module is then hydro tested
between a single inlet and outlet header
before shipment. Boiler drums sit independently
on the steel superstructure, and field
welding consists only of the inter-module
piping connections and connections to the
boiler drums, significantly simplifying the
erection process. The high level of shop
fabrication of tubes, components, and other
sub-assemblies for EGPS reduced the time
and construction labor required to erect
each HRSG (Figure 3). Prefabrication also
reduces the logistical challenge of moving
58
Phased Conversion
Phase 3 included erecting the HRSG, STs,
and ACCs in the midst of an operating plant,
connecting the HRSGs through a diverter
damper during a short outage, followed by
startup of each power block in combined
cycle mode.
One challenging problem was making the
physical connection of the CT to the HRSG
connection flange prior to HRSG erection on
a very tight schedule. The existing CT stack
structures were reconfigured by replacing the
casing elbow with a new CMI-provided shopprefabricated
" T " box with integral diverter
damper on each of the eight CTs during sequential
CT outages to minimize downtime
(Figure 4). The first CT was completed in
three days; subsequent units were completed
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in only two days each. Each CT was restarted
when its diverter damper was completed, and
the CTs continued to operate in simple cycle
mode during the subsequent erection of the
HRSG (Figure 5). The conversion process
went smoothly because provisions for the
diverter damper conversion were included in
the original stack structural design, minimizing
impact on the existing stack.
The HRSGs installed during Phase 3 are
dual-pressure (high-pressure [HP] and lowpressure
[LP] superheat sections) without
reheat, a common arrangement with the
9E configured in a 4 x 1 power block. The
main steam conditions are 77 bara at 520C
at 50.93 kg/s for the HP and 8.2 bara and
219.9C at 10.96 kg/s for the LP superheat.
The main steam produced by each HRSG in
a power block is fed to a common header
that goes to the ST. A minimum of two CTs
must be in operation to produce sufficient
steam for the ST and for the power block to
remain in service.
Training of the plant staff was also a priority
for the project team. CMI Energy developed
a training program tailored for the
operation and maintenance of the plant's
HRSG system. Two courses were presented,
each five days long.
The KRG's critical need for additional
power accelerated the project schedule after
work on the contract commenced in April
2012. Working closely with ENKA and other
supplier subcontractors, CMI was able to
fast-track its engineering, raw material procurement,
and shop fabrication work, thus
accelerating onsite erection by two months.
Steel erection began in April 2013, the first
hydro test was completed in December 2013,
and first firing took place in January 2014.
MGH has signed contracts with Enka
and CMI to similarly repower its Sulaymaniyah
and Duhouk plants, also located
in the Kurdistan region of Northern Iraq.
Each of the two plants is now in the process
of being repowered from simple cycle
(eight Frame 9E CTs producing 1,000
MW) to combined cycle (1,500 MW) operation.
The Sulaymaniyah project began
construction in July 2013 and is expected
to be complete in early 2016. The Duhouk
project began in October 2013.
Even after completing these three projects,
the potential for repowering simple cycle
CTs in Iraq is enormous-provided security
of the facilities can be ensured. The latest
information indicates there is another 4,000
MW to be captured simply by repowering
existing simple cycle CTs. We will surely see
many new repowering projects on the scale
of EPGS in the coming years. ■
-Dr. Robert Peltier, PE is POWER's
consulting editor.
POWER | November 2014
http://www.powermag.com
POWER November 2014

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