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SPECIAL ISSUE: OUTAGE
HANDBOOK
POWER AUGMENTATION
To fog or not to fog:
What is the answer?
V
irtually everyone directly
involved in the design, operation, and maintenance of gasturbine-based powerplants
is well aware of the adverse effects
high ambient temperatures and dirty
rotating blades and stationary vanes
have on compressor performance
and power production capability.
Cooling inlet air. The most efficient
way to maximize output and revenue during the warm months, when
power prices typically are highest,
is by cooling ambient air before it
enters the compressor. Recall that
gas-turbine (GT) output is directly
proportional to the air mass flow
rate. But, since the volumetric flow
rate is relatively fixed, the mass flow
of the turbine decreases as ambient
temperature increases—warmer air
being less dense.
Evaporative coolers, historically
the most popular of the technology alternatives for GT inlet cooling,
reduce temperature by evaporation
of water that cascades over a wetted honeycomb media as air passes
through the media. Wetted
media can cool the inlet air
to within a few degrees of
the ambient wet-bulb temperature.
Fogging has become a
popular evaporative technology over the last decade
and now there are well over
1000 systems installed on
GTs worldwide. They saturate GT inlet air by spraying
very fine droplets of water
into the air stream. Fogging
systems are capable of cooling the inlet air to the wetbulb temperature, so they’re
more effective than wetted
media.
Chillers can cool the inlet
air to temperatures much
lower than those possible
with evaporative systems.
Mechanical (electric) and
absorption (steam) chill-
ers can maintain any desired inlet
air temperature down to about 42F,
independent of ambient wet-bulb
temperature. But they have significantly higher capital and operating
costs than evaporative technologies.
Negative impacts of compressor
fouling include reduced compressor
air flow, pressure ratio, and efficiency, which cause a “rematching” of the
turbine and compressor and a drop in
power output and thermal efficiency.
At least one expert estimates that
fouling is responsible for 70% to 85%
of the total performance loss experienced by GTs during operation. Output losses of between 2% (favorable
conditions) and 15% to 20% (adverse
conditions) have been attributed to
fouling. To learn more, access www.
combinedcyclejournal.com/archives.
html, click Fall 2004, click “Gain a
competitive edge with a better understanding of GT compressor fouling,
washing” on the cover.
The two primary methods for
maintaining GT compressors at high
efficiency are offline and online wash-
Learned at
Next meeting: Apr 19-23, 2009
Birmingham (Ala) Sheraton
Details at www.ctotf.org
COMBINED CYCLE JOURNAL, Third Quarter 2008
ing. Goals of the former are to clean
a dirty compressor and restore power
and efficiency to virtually “new and
clean” values. Objectives of online
washing are to keep the compressor
clean, thereby extending the period
between shutdowns required for
offline cleaning and retaining desired
power output and efficiency.
Important to glean from the foregoing is that injection of water into the
inlet air stream and/or directly into
the compressor are industry best
practices critical to achieving plant
pro forma performance and powerproduction goals. While all OEMs are
concerned with what goes into their
GTs, compressors for the 7F series of
engines manufactured by GE Energy, Atlanta, may be more sensitive
than at least some others to impingement by water droplets associated
with evaporative cooling and online
washing.
This conclusion by the editors is
drawn from user comments regarding operating restrictions imposed on
customers by several of the OEM’s
technical information letters (TILs), most recently
TIL 1603. Users have told
the editors that this letter, released in mid 2008,
strongly suggests that customers comply with its operating guidelines to mitigate
erosion of blades in the first
stage of the compressor—
so-called R-zero (R0).
Owners with OEM service
agreements presumably
would jeopardize their contracts if they didn’t implement the 1603 directives.
Those not bound by GE
agreements might decide to
do otherwise, but could run
afoul of insurance carriers
that believe OEM guidelines should be followed.
Several owner/operators
told the editors that the
OEM’s TIL recommends
105
POWER AUGMENTATION
SPECIAL ISSUE: OUTAGE
HANDBOOK
Users, consultants share fogging views, experiences
A
fter listening to Thomas Mee at
the CTOTF’s Fall Turbine Forum
in Tucson, the editors contacted
several users and consultants regarding their views and experiences with
fogging—most specifically, its impact
on compressor-blade erosion. The
effort to provide more balanced coverage of the on-going industry debate
did not achieve the level of success
envisioned. Calls were initiated during
the busy outage season and, understandably, many were not returned.
Below are “sound bites” from conversations with the editors and e-mail
replies to specific questions.
Economic justification for fogging. A
cross section of the industry offered
the following:
n Expect fogging to increase power
output by 7% to 8% given 20 deg
F of cooling. One user’s calculations was based on ambient conditions of 95F dry bulb, 75F wet bulb.
n Heat rate may improve by as much
as a few percent; exact number
depends on cycle arrangement
and site conditions. The heat-rate
improvement on a combined-cycle
plant is negligible.
n Double-digit NOx emissions
reductions are possible on some
engines under certain conditions.
n Lower capital cost than other traditional inlet-air cooling options.
One user put the total installed
cost per “fogging kilowatt” at
about $70 for 7EAs and $80 for
earlier GTs—certainly inexpensive
peak power. All systems were retrofitted.
n Another user’s calculations
showed the annual owning/operating cost of a fogging system for
a 7FA was $200,000 per annum
less than that for a media-type
evap cooler. Reasons include
efficiency and output losses
associated with the pressure drop
across the wetted media. This is
true even when one considers the
higher cost of the demineralized
water required for fogging.
Comments specific to the 7FA fogging debate:
n We fog several 7FAs. Knowing
there are serious consequences to
wet R0s, we are cautious and diligent about monitoring. We expect
some erosion and consequently
follow the guidelines of TIL 1603
very closely. We also fog 7EAs but
don’t have the same level of concern regarding erosion damage to
them that we have for the 7FAs.
n The OEM should develop more
106
n
n
n
n
specific and quantitative bladedeterioration criteria than the 8-mil
erosion limit that it has specified.
Once the 8-mil limit is reached,
you have to operate dry. Our experience indicates you will erode 8
mils quickly when conducting regular online water washes. I believe
washing has a far greater impact
on erosion than fogging.
Anything that damages the leading
edge of a compressor blade reduces its fatigue resistance and that
blade will crack sooner than one not
so damaged. But the root cause of
R0 cracking is blade harmonics—
period. My experience indicates the
OEM’s fogging system is a maintenance nightmare and it is linked to
leading-edge erosion.
We do offline water washes
only, no online washing (multiple
responses).
Plant’s 7241 7FA with a flared
compressor and enhanced P-cut
blades operates in base-load combined-cycle service. It is fogged
about 1500 hr/yr. The enhanced
P-cuts, which replaced original
non-P-cut blades, have a service
history spanning more than 16,000
hours and have been inspected six
times. Blades have noticeable erosion but the OEM does not require
dental molds on airfoils of this
design.
The original fogging system
was installed downstream of the
inlet bleed-heat header and just
upstream of the trash screen
and inlet duct elbow, above the
compressor inlet. It was replaced
nearly four years ago with a more
robust system having nearly twice
the number of spray nozzles and
relocated to just behind the inlet
filters. The new array’s 0.006-in.
orifice nozzles replaced 0.008-in.
nozzles.
Online washing is done every
other day when temperature is
above 50F; offline washing is a
semi-annual event. Goal when
the fog system is in service: 90%
relative humidity as determined
by Vaisala Inc instrumentation at
the compressor inlet. Fogging is
initiated automatically when ambient temperature reaches 62F. A
nozzle monitoring system warns
when low pressure or high flow
is indicated. Plant periodically
experiences filter plugging and the
affected filters are replaced when
this occurs.
Cracked R0 blades have been
n
n
n
n
n
n
found on a significant percentage
of units inspected in the last nine
months of 2008. Industry scuttlebutt is that the OEM will be issuing (no date known) a technical
information letter recommending
initial-inspection and reinspection guidelines as well as a recommended inspection interval.
Online wash five minutes daily. No
other information provided.
Dovetail cracks found on R0
blades of one GT in a 2 × 1 configuration after only 1600 hours
of operation and 132 starts.
No water ever was used in the
machine at this plant, which is
located well inland (no “ring of
fire” effects).
Cracking found on R0 blades of
7FAs located more than 25 miles
from the coast. These units sit
across the fence from another
OEM’s GTs which are problemfree.
Plant was commissioned with
standard R0 blades. They were
replaced a year later with P-cuts to
mitigate the risk of blade liberation
resulting from leading-edge erosion and/or FOD. In less than three
years, the P-cuts were refitted with
standard blades to mitigate risk
from P-cut cracking. Plant then
stopped fogging to prevent the
possibility of blade erosion; units
never had been washed online.
Despite the precautions, a crack
was found in one of the pristine
blades two years later.
We have done only one offline
wash on this unit, never an online
wash. No other information provided.
Our 7FA Model 7221 (unflared
compressor) in base-load combined-cycle service was fogged
approximately 1500 hr/yr for about
nine years. Fogging stopped when
P-cut blades were removed and
replaced with non-P-cut airfoils.
The original R0 blades had more
than 12 mils of erosion after about
six years of fogging service when
replaced with P-cuts. Approximately three years later the P-cuts were
removed. The OEM UT-inspected
the blades and errantly condemned
them for cracking that could not be
confirmed off the engine.
Online washing is done every
other day when temperature is
above 50F; offline washing is a
semi-annual event. Fogging array
with nearly 900 nozzles is located
just behind the inlet filters; silencer,
COMBINED CYCLE JOURNAL, Third Quarter 2008
inlet bleed-heat header, and trash
screen are downstream of the
nozzle array.
Years of fogging experience on
several dozen 7EAs and earlier
engines allowed a major user to offer
others in the industry the following
observations:
n Fogging is an inexpensive but very
effective way of boosting power
output in warm weather.
n O&M effort generally is low-level
and low-cost.
n Zinc deposits on inlet guide vanes
(IGVs) and other compressor parts
were caused by high-purity fog
water washing off the galvanizing
from inlet silencers.
n Accelerated corrosion of non-stainless inlet ductwork and plenums
was experienced, driving replacement with stainless steel parts.
n More rapid corrosion of IGVs
caused binding and pivot-shaft
breakage on old units.
n Sufficient inlet-duct and plenum
drainage is very important.
n Proper winterization is necessary
to avoid freeze damage to spray
nozzles and headers.
n Seal debris from high-pressure
fogging pumps can plug nozzles.
n Biological fouling of nozzles will
occur if fogging systems remain
unused and full of water for several
weeks.
n Dental molds taken at the request
of the OEM revealed negligible
erosion after years of summertime
fogging use during peak periods.
Total fogging hours numbered less
than 1000 on any machine.
Final notes:
n Positive results with both fogging and wet compression have
been profiled at meetings of the
Western Turbine Users, which
focus on GE aeros. In fact, at the
2007 meeting one user presenter
suggested upgrading to a fogging system if you have difficulty
maintaining evap-cooler efficiency
(access www.combinedcyclejournal.com/archives.html, click
2Q/2007, click “Western Turbine
Users” on the cover and scroll to
subhead “Keep compressor inlet
cool, clean to ensure top performance” on p 28.
n Noteworthy, perhaps, is that while
one OEM is striving to keep water
out of its compressors, another is
responding to customer interest by
promoting wet compression in its
large frames. For details, access
www.combinedcyclejournal.com/
archives.html, click 2Q/2008, click
“D5-D5A Users” on issue cover.
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Improves heat rate.
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Changing the way the world boosts power
time limits for online washing that
depend on the design of R0 blades
installed. Recall that the OEM has
changed the design of its blades several times since the first F-class unit
went into operation.
TIL 1603 also is said to present
intervals for so-called “dental-mold”
impressions of the leading edges of
R0 blades to determine if erosion is
within what the OEM considers safe
limits. If it is not, repairs may be
required to mitigate cracking risk.
A concern of several users who
spoke with the editors was that the
recommended intervals between
inspections for erosion were of rela-
COMBINED CYCLE JOURNAL, Third Quarter 2008
tively short duration (in some cases,
100 hours of “wet” operation or less).
Wet operating hours are defined
as hours of operation with fogging,
water wash, or with an evaporative cooler that has water droplets
stripped off because of improper
design/operation. As for the expenses
associated with inspection (staff
and outage time, lab costs, etc), who
pays? A rhetorical question: the
owner, of course. Is the expense budgeted? Doubtful.
A few plant personnel also
expressed concerns about a level
playing field. They said the inspection interval associated with a non107
POWER AUGMENTATION
SPECIAL ISSUE: OUTAGE
OEM evaporative cooling system
was five times that of the interval
suggested for the OEM’s offering. At
least one user considered that unfair;
he believes his third-party vendor’s
evaporative system is superior to the
OEM’s. While a statistically valid
and objective survey on the subject
is virtually impossible to conduct, it
is possible to visually quantify the
amount of water in droplet form
being ingested by the compressor
during fogging operation.
Someone else said that the inspection intervals for the online washing
system provided with his 7FA were
less than 50 hours and the washing
duration was limited to only a few
minutes daily. However, if he could
get the owner to buy the OEM’s latest
washing system, the inspection interval would go up about 20-fold and the
daily wash cycle could return to what
this user considered “normal.”
That’s probably not going to happen. With the current state of the
economy, it’s not unusual to hear
that capital budgets have been frozen
and also that maintenance intervals
are being extended. Short-staffed
and under-funded, some plant managers say they no longer afford to
do online water washes, just offline
washes a couple of times annually.
There are obvious fuel and capacity penalties associated with that
operating philosophy in most areas of
the country. But perhaps those costs
are charged to “a different budget.”
For example, if the plant is “regulated,” the fuel-cost increase attributed to a dirty compressor might be a
“pass-through” to the customer.
There’s a strong connection between
compressor fouling and the effectiveness of inlet-air filtration. In some
locations, it may make sense to consider the installation of HEPA filters
ahead of the compressor if elimination of online washing is a goal. Experience at several plants with Mitsubishi F- and G-class engines has
been positive. The editors have not
been able to identify anyone with GE
machines doing this yet. If you are,
please write [email protected].
Owner/operators also should not
overlook the potential value of coatings on compressor blades. Titanium
nitride and other formulations show
promise in protecting against solidparticle impact damage as well as liquid-droplet erosion (access www.combinedcyclejournal.com/archives.html,
click 2Q/2008, click WTUI on issue
cover and scroll to “Advancements in
compressor coatings” on p 52). Keep in
mind that an OEM service agreement
may preclude the use of coatings—at
least those not offered by GE.
108
HANDBOOK
Erosion concerns in GE F frames may
just disappear with the planned
introduction of the OEM’s new compressor rotor in spring 2009. However, cost undoubtedly will be an issue.
A third-party alternative, also
expected in the spring, is said to offer
redesigned airfoils to accommodate
as much online washing and inlet-air
evaporative cooling as users might
want to use. This would be a far-lesscostly alternative, but it undoubtedly
would violate the terms of the OEM’s
service agreements. Plus, this solution would require your insurer’s
approval.
benefits. Judging from a few user
comments, Mee met expectations.
He can talk endlessly, or so it seems,
about the physics of water droplet
behavior in GT systems. One reason
is the company’s history of research
on the subject. A “summary” of this
work is presented in three comprehensive papers published as part
of the “Proceedings of ASME Turbo
Expo 2002.”
Mee’s message was that fog droplets don’t directly cause erosion.
While compressor suctioning of unatomized, flowing, and pooling water is
potentially conducive to problematic
wear and tear of R0 blades, proper
design of fog and drain systems can
CTOTF looks for
prevent damage from these sources.
answers
He began with a brief discussion
The roiling controversy over whether of factors critical to the design of
evaporative inlet cooling systems an effective fogging system. Dropand/or online washing systems can let size is of primary importance
be held accountable for R0 blade because small droplets evaporate
erosion—and if one or both
quickly. Those too large to
can, to what degree—was
evaporate in less than two
the motivation for inviting
seconds—the approximate
Thomas Mee III, chairman
time it takes air passing
and CEO, Mee Industries Inc,
through the inlet filters to
Monrovia, Calif, to address
reach the compressor—will
delegates to the CTOTF 2008
either fall out on the duct
Fall Turbine Forum on fogfloor or enter the compresging technology.
sor.
Mee participated in the
The majority of existing
group’s GE Roundtable in
fogging systems use either
Mee
mid September, focusing on
impaction-pin (Fig 1) or
optimizing fog evaporation and min- swirl-jet nozzles. “Both nozzles create
imizing compressor water ingress. an expanding conical spray plume,”
Dominion Energy’s Larry Rose, Mee told the group, “which gets provice chairman of the roundtable, gressively thinner as it moves away
moderated the session. Previously, from the orifice.” Eventually, turbumembers of the Combustion Turbine lence created by the interaction of
Operations Task Force had heard the high-velocity water jet with the
from a representative of Gas Tur- surrounding air causes the plume to
bine Efficiency, Orlando, Fla, on the break apart. Surface tension causes
technology of online washing (access
Impaction pin
Orifice diameter,
www.combinedcyclejournal.com/
150 microns
archives.html, click 2Q/2006, click
“CTOTF” on issue cover and scroll
to p 56).
Type-316
stainless
By way of background, Mee Indussteel
tries has supplied nearly 750 fogging
Replaceable
systems for GTs worldwide (81 for
internal filter
O-ring seal
GE F frames) and it claims global
captures
market leadership in this sector.
particles
down to 40
Many Mee systems have more than
microns
10 years of experience; also, a significant percentage were designed
for wet compression—so-called high
fogging (access www.combinedcyclejournal.com/archives.html, click
spring 2004, click “Recent experience
indicates wet compression meets
Stainless steel water
expectations when done correctly” on
distribution tube
issue cover).
The challenge for any moderator of 1. Most fogging systems use either
an electric-power industry meeting is the impaction-pin (shown) or swirl-jet
to keep supplier presenters focused nozzle. Both create an expanding
on the technology and to resist the conical spray plume, but the former is
temptation to discuss features and said to produce droplets of smaller size
COMBINED CYCLE JOURNAL, Third Quarter 2008
SPECIAL ISSUE: OUTAGE
the water particles to adopt a spherical shape.
Impaction-pin nozzles form a
20-micron
droplet
Strand of hair,
100 microns
2. Impaction-pin nozzles produce a
fog with 90% of the droplets 20
microns or smaller, Thomas Mee told
CTOTF attendees in explaining the
capabilities of his company’s product
HANDBOOK
conical plume by impacting the
high-velocity water jet from an open
orifice against the small pin shown
in the illustration. Research by Mee
Industries indicated that impactionpin nozzles produce smaller droplets
than swirl-jet nozzles when compared on a level playing field—that
is, the same flow rate, pressure, etc.
Specifically, Mee Industries’
impaction-pin nozzles are designed
to produce a fog in which 90% of the
droplets are 20 microns or smaller.
To put this in perspective, consider
that the average human hair is 100
microns in diameter (Fig 2).
Size really does matter. Mee took a
POWER AUGMENTATION
few minutes to discuss the physical
nature of water droplets. “Droplets
are spheres,” he said, “and thinking
of them only in terms of diameter can
be very misleading.” When someone
speaks of a 30-micron droplet that
seems very small, he continued, but
it has nearly three-and-a-half times
the mass of a 20-micron droplet and
falls out of the air stream twice as
fast (Fig 3).
Laboratory tests conducted by Mee
Industries determined that 20-micron droplets were “table stakes” in
the design of a fog system for the sensitive 7F frame (Figs 4 and 5). Mee
said this was confirmed in the field.
30-micron droplet
■ 3.4 times more mass and force
of impact than a 20-micron
droplet
■ 33% less surface area per
unit volume
■ Rate of fall is twice as fast
■ Twice the potential for
fallout from centrifuging
60-micron droplet
■ 27 times more mass and force
of impact than a 20-micron
droplet
■ 66% less surface area per unit
volume
■ Rate of fall is nine times faster
■ Nine times the potential for
fallout from centrifuging
20-micron
droplet
3. Droplets are spheres and thinking of them only in terms 4. Smaller droplets produced by impaction-pin nozzles
create a smoke-like white plume
of diameter can be very misleading
COMBINED CYCLE JOURNAL, Third Quarter 2008
109
SPECIAL ISSUE: OUTAGE
80
24
60
Air temperature
18
40
12
Drop
let d
20
0
0
0.5
iame
1
1.5
Time, sec
ter
6
0
2
5. Chaker diagram illustrates how
quickly 20-micron droplets evaporate
on a dry summer day
In Fig 4, note that the small droplets
produced by impaction-pin nozzles
create a smoke-like white plume
that spreads to a diameter of about
12 inches only about a foot from the
spray nozzle.
A comparison photo shown to
attendees revealed that the larger
droplets from swirl-jet nozzles produced a plume with a defined edge
and a spray that is less opaque.
Another important fact: Measurements taken during the lab tests
show that droplets cease to coalesce
inside the spray plume less than a
foot from the nozzle—in fully humidified air. This means that it’s important to measure droplet size far
enough from the nozzle orifice to get
the true size of droplets produced by
that nozzle.
Location, location, location. Fundamentals reviewed, Mee explained
why he believes the 7F series of
machines is seeing more water at
the compressor inlet than necessary.
Fig 6 shows that the OEM’s recommended location for fog nozzles in
its F frames generally does not allow
sufficient time for droplet evaporation and can lead to flowing water at
the compressor inlet.
Referring back to Fig 5, note that
droplet diameter after one second of
evaporation time is about five times
Consider relocating
trash screen
HANDBOOK
Recommended nozzle location allows droplet
residence time of more than two seconds
OEM’s nozzle location allows
droplet residence time of less
than one second
6. OEM’s recommended location for
fog nozzles in its F frames generally
does not allow sufficient time for
droplet evaporation and can lead to
flowing water at the compressor inlet
7. Fog-nozzle manifold immediately
downstream of the air inlet filters
allows about two seconds for droplet
evaporation in a typical 7FA
larger than after two seconds. It follows, Mee continued, the more time
you allow for evaporation the less
likely it is for an R0 blade to experience erosion on the leading edge.
He suggested locating the nozzle
array immediately downstream of the
air filters (Fig 7). This would allow
about two seconds for evaporation—
twice the time available than when
following the OEM’s guidelines for
fog-nozzle location. Mee mentioned
that his company’s first fog system
for an F-series machine was designed
s
30
ity
mid
Relative hu
3 ft/
Relative humidity, %
100
Diameter, microns/Air temperature, C
POWER AUGMENTATION
ec
6 ft/sec
11
ft/sec
13 ft/sec
Flowing water on
the duct wall is
sucked over the
inlet scroll
Install more fog nozzles
in this high-velocity area
of the inlet duct
8. The large variation in
air velocity across the
inlet duct must be
considered when designWater flowing down
the rear wall accumulates ing a fogging system.
on the inlet cone and can More nozzles are needed
be sucked into the
in areas of high velocity,
compressor
fewer where the velocity is
relatively low (above)
Air flow prevents
pooled water from
draining away
9. Improper design of the
fogging system results in
flowing water at the
compressor inlet and a
greater likelihood of
erosion damage to
first-stage blades (left)
Wall gutters and drains
(details in Fig 12)
FRONT VIEW
Gutter around
inlet (details
in Fig 11)
Floor gutters
and drains
False floor allows
water to drain away
Perforated plate and drain
10. A proper system for removing flowing water minimizes the
probability of erosion damage
110
Expansion
Duct wall joint
Stainless steel
gutter
Compressor inlet
TOP VIEW
11. Small gutter installed around the compressor
inlet prevents suctioning of water over the bellmouth.
Details provided here are patent-protected
COMBINED CYCLE JOURNAL, Third Quarter 2008
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this way. After fogging well over 1000 water at the inlet can be avoided by
Locating spray nozzles as close
hours annually for nearly 10 years, setting the fog system control param- to the air filters as practical and
the operator reported relatively little eter so the system always slightly designing the nozzle array to accomblade erosion attributable to fogging.
“under-fogs.” This can dramatically modate the velocity profile across the
Mee paused to discuss the impor- reduce the amount of water at the ductwork are critical to success, for
tance of proper nozzle manifold design compressor inlet.
sure. But proper design and arrangein preventing water accumulation
Mee then showed attendees where ment of gutters and drains also are
at the compressor inlet. He showed to look for flowing water during oper- necessary to provide the contingency
a CFD (computational fluid dynam- ation (Fig 9):
to accommodate varying operating
ics) plot at the filter wall of a typical n On ductwork walls; be sure it is conditions.
7FA to illustrate the large variation
not being sucked over the inlet
Fig 10 shows where Mee recomin velocity across the ductwork (Fig
scroll.
mended gutters and drains to mini8). The message: Air velocity must be n On the rear wall; be sure it is not mize the probability of free water
considered by designers in the placeaccumulating on the inlet cone gaining access to the compressor.
ment of nozzles to avoid localized
and being sucked into the com- Also note the recommendation for
over-saturation. Translation: More
pressor.
moving the trash screen further
nozzles are required in high velocity n On the floor; be sure pooled water upstream than the OEM’s traditional
areas than in low-velocity regions of
is not being sucked into the com- placement—this to prevent condenthe ductwork.
pressor.
sation of fog and the formation of
However, no matter how
large droplets close to the
tight the design, the inletcompressor inlet.
Cover prevents
high-velocity air from
air system is dynamic and
Fig 11 shows details of
scooping water out of
sensitive to changes in
the small gutter Mee Indusstainless steel gutter
air temperature, humidtries installs around the
ity, wind direction and
compressor inlet to prevent
velocity, GT load, etc. This
suctioning of water over
Compressor inlet
makes it impossible to
the bellmouth; Fig 12 the
“tune” the system to maindetails of wall gutters and
tain the ideal 100% saturadrains. Mee mentioned the
Wall gutter is located
tion condition at the comcompany has a patent that
above expansion joint to
pressor inlet throughout a
covers methods for removprevent water from becoming
given production run.
ing flowing and pooling
airborne as it flows over
Windows at the bellmouth
water from the inlet ducts
expansion joint
for visual inspection of
so it cannot be suctioned
pooling or running water 12. Wall gutters and drains are important for preventing
into the compressor as unare a good idea. Flowing water ingestion into the compressor
atomized water. ccj
COMBINED CYCLE JOURNAL, Third Quarter 2008
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