www.siemens.com/energy
High efficient
peak power on demand
POWER-GEN Asia 2011 – KLCC,
Malaysia, Kuala Lumpur
September 27–29, 2011
Authors:
Jan Dirk Beiler
Siemens AG,
Energy Sector – Fossil Power Generation Division
Peter Trauner
Siemens AG
Energy Sector – Service Division
Answers for energy.
2
Content
Abstract
4
Introduction
4
Wet Compression description
4
Different fields of usage
5
Performance
6
Operating experiences
8
Conclusion
9
Permission for use
9
Disclaimer
9
Copyright © Siemens AG 2011. All rights reserved.
3
Abstract
As part of our ongoing commitment to meet the changing
requirements of customer’s operating assets, we offer the
latest technology helping to enhance customer’s operating
plant capability and flexibility. One of our modernization
products for power enhancement is Wet Compression.
Wet Compression is a reliable and proven method of
injecting water into the gas turbine inlet. Wet Compression
is perfectly suited for upgrading peak load gas turbines.
Providing peak power enables electricity producers to
react to increased grid power demand, i.e. during summer
peaks or grid fluctuations driven by renewable energy
sources leading to increases in customer revenues at high
peak load electricity prices. Wet Compression is designed
to increase the power output by injecting water into the
compressor inlet, hence inter-cooling the compressor,
reducing the compressor inlet temperature and increasing
mass flow throughout the gas turbine.
More than 45 Wet Compression systems have been
installed and operated on SGT5-2000E, SGT6-2000E and
SGT6-3000E gas turbines. Wet Compression has also been
successfully tested in the Berlin (Germany) plant test bed
on a SGT6-4000F. The first application on the advanced
frame type SGT5-4000F was commissioned in May 2010.
A power increase due to Wet Compression of up to 16 %
of the dry gas turbine base load power could be measured.
Wet Compression provides peak power on demand with
a higher efficiency level compared to other “stand by”
generators or simple cycle diesel applications, consequently
carbon and nitrogen emissions can be reduced or avoided.
The mutual occurrence of high ambient temperatures
and increased peak load electricity demand make Wet
Compression economically more beneficial and valuable.
power upgrades. Wet Compression is an upgrade offered
by Siemens which combines a large increase of the power
capacity with reasonable investment costs and fast implementation time.
Wet Compression is a system for compressor intercooling.
By cooling the media inside the compressor and the consequently increasing mass flow, the power output of the
gas turbine increases significantly. In addition to the power
increase, additional positive effects like an increase in the
gas turbine efficiency and a potential reduction of the
NOx-emissions could be achieved.
Wet Compression has been developed in 1995 and was
re-designed for the SGT5/6-2000E in 2003; in May 2010
the commissioning of the first application on the advanced
frame SGT5-4000F has been successfully accomplished.
Wet Compression
description
Introduction
In recent years the need for peak load and reserve capacity
is increasing constantly. With an increasing amount of
regenerative energy generation (wind, solar) being added
to power systems worldwide, the requirement for reserve
capacity which can be provided on demand is also increasing. In Germany for example installed wind generation
capacity accounts for more than 26 GW installed capacity
and significant additional generation is being added
through new offshore wind parks. The proportion of actual
energy contribution in Germany from wind generation is
typically between 5 % to 10 % of annual energy generation
with generation duration being approx. 18 % on an annual
hourly basis. Clearly, reserve peaking capacity needs to be
available at short notice when called upon by the power
system to support such renewable generation. Gas turbines
with fast reaction times are the preferred technology to
fulfill this demand. As new projects usually require long
development periods due to long lead times for site permitting and construction, an appropriate alternative is
to increase the capacity of the already existing plants with
4
Fig. 1: Wet Compression impressions
With a nozzle rack in the air inlet close to the compressor
entrance, deminerilized water is injected in the compressor
air inlet flow. A frequency driven high pressure pump
provides the water for the nozzle rack. This high pressure
pump and a Computational Fluid Dynamics (CFD) optimized
nozzle positioning ensure small and well distributed water
droplets entering the compressor section.
Wet Compression principle
Unlike common systems for compressor inlet cooling like
Fogging or Evaporative Cooler, Wet Compression not only
cools down the compressor inlet temperature but is used
as a compressor intercooling system. Therefore the main
target of Wet Compression is to get fine water droplets
well distributed into the compressor where they evaporate
gradually.
The significant power increase of Wet Compression mainly
consists of 3 different effects.
Compressor intercooling
Due to the evaporation inside the compressor the
necessary work for the compression of the cooled
air and therefore the compressor power consumption
is reduced.
Inlet cooling
Although this is not the main target Wet Compression
still achieves an inlet cooling effect as droplets evaporate
on their way into the compressor. With cooling down the
inlet air additional air mass flow enters the gas turbine.
Turbine power/mass flow increase
The turbine power output is increased by following
factors:
■ Increased air mass flow due to inlet cooling,
■ Additional water mass flow,
■ Additional air mass flow by reducing the mass flow
limitation of the first compressor stages by additional
cooling and
■ Higher fuel flow.
for the gas turbine components at a low level; consequently
the maximum performance is reached after nominally
18 minutes for the SGT5-2000E.
Wet Compression can be operated without respect to
ambient humidity; even the combined operation with
an evaporative cooler would be possible.
Different fields
of usage
Wet Compression can be used for different purposes,
the most common and commercially attractive ones are:
■ Seasonal operation (summer peak operation)
■ Reserve power and occasional peaking
■ Grid support (esp. BLOC and secondary frequency
response)
■ Base Load increase for simple cycle gas turbines
Seasonal operation of Wet Compression to compensate
capacity losses during high ambient temperature conditions
is possible for both dry and humid areas. Even a combination with an evaporative cooler or chiller is possible as
long as the compressor inlet temperature stays above 10 °C.
The Wet Compression installation as an increase of the
marketable power reserve and occasional peaking is ideal
as the influence on the normal operation of the gas turbine
is very low.
Air inlet flow
Water
injection
Combustion Chamer
Compressor
Turbine
Fig. 2: Wet Compression principles
Wet Compression operating conditions
Wet Compression could be used as a flexible peak load
system with easily adjustable power output. Only a few
preconditions for Wet Compression are necessary for safe
operation.
Wet Compression could also be used for grid code support,
usually in a combination with other measures. For grid code
support a special Wet Compression system (Fast Wet Compression) is used which provides less water but a faster
ramp up of the water mass flow. Still the initial reaction
time of about 15–20 sec. is to slow for a primary frequency
response but could easily be used as additional measure for
a BLOC operation or to take over the secondary frequency
response.
A continuous operation of Wet Compression as an increased
base load feature is appropriate for simple cycle gas turbines
as both power and efficiency increase compared to base
load without Wet Compression. When continuous operation
of Wet Compression is carried out for a combined cycle
configuration it necessary to consider that he combined
cycle efficiency will be marginally decreased.
Wet Compression can be operated at compressor inlet
temperatures >10 °C. The risk of ice formation on the
compressor blades and consequential damages while
operating at lower temperatures is too high and consequently prevented in the DCS control settings.
Wet Compression is started from base load with an initial
mass flow of 2 or 2.5 kg/s which is also the minimum mass
flow. Up to the maximum mass flow Wet Compression can
be adjusted in a stepless manner. The gradients for the
water mass flow increase are limited to keep thermostresses
5
Performance
Wet Compression has influence on different parameters
in the gas turbine and combined cycle process. The main
influences can be described as follows:
As mentioned before, Wet Compression has various effects
on the performance of the gas turbine. Beside the power
boost the gas turbine efficiency increases, too. The delta
performance can be adjusted smoothly by changing the
Wet Compression water mass flow.
Change by
Wet Compression
Parameter
Wet Compression is only slightly influenced by the ambient
humidity compared to inlet cooling applications like an
evaporative cooler or fogging. The following graph shows
the achievable power (% of base load power) for Wet Compression at an ambient temperature of 30 °C as a function
of the ambient humidity in comparison to an Evaporative
Cooler (exemplary for SGT5-2000E).
Gas turbine power output
Gas turbine efficiency
Gas turbine outlet temperature
Fuel mass flow
The power gain of the evaporative cooling is reduced with
an increasing relative humidity. Although the delta power
output of Wet Compression is slightly reduced as well, it
remains on a high level as the intercooling of the compressor and therefore the basic mass flow increase can be
achieved even at 100 % relative humidity.
Exhaust gas energy
NOx – emissions
Combined cycle power output
Combined cycle efficiency
Increase
decrease
Fig. 3: Influences of Wet Compression operation
Power output at 30 °C ambient temperature related to the relative humidity
Delta power output (to Base Load, R.H. 10 %) [%]
20
Power output
18
with Wet Compr
ession (2 %-MVI
)
16
14
12
10
Pow
8
er ou
tput
with
6
Evap
orati
ve co
oler
4
(85 %
Eff.)
2
Base load power, dry
0
10
20
30
40
50
60
Relative humidity [%]
70
80
90
Fig. 4: Comparison of Wet Compression power output with an Evaporative Cooler at a variation of relative humidity
The additional gas turbine power output generated by
Wet Compression can be variegated by changing the Wet
Compression mass flow between a minimum mass flow
and a maximum mass flow. The following figure shows
exemplary the operation range for a SGT5-2000E without
site specific limitations.
6
Reference conditions used:
Ambient temperatures
■ Ambient pressure
■ Relative humidity
■ Fuel
■
10 – 50 °C
1013 mbar
60 %
Methane
100
20
Power increase by Wet Compression
[% of base load power]
18
16
14
12
Sh
af
t
lim
it
r
c
ea
he
Maximum
d
mass flow
75 % of desig
n mass flow
50 % of design ma
10
(design)
ss flow
8
Minimum mass
6
flow (start)
4
2
0
10
15
20
25
30
35
40
45
50
Ambient temperature [°C]
Fig. 5: Range of power increase at SGT5-2000E depending on ambient temperature
In May 2010 the first commissioning of Wet Compression
on the advanced frame SGT5-4000F has been successfully
completed. The system shows a similar potential as on the
SGT5-2000E. The next two diagrams show the gas turbine
performance increase related to the Wet Compression water
mass flow as measured during the successful first time
application at the SGT5-4000F gas turbine. The highest gas
turbine delta power of about 16 % has been measured at a
Wet Compression mass flow of about 10.2 kg/s. Additionally
the gas turbine efficiency has been increased by about 2 %.
Measurement conditions:
Ambient temperature
■ Ambient pressure
■ Relative humidity
■ Fuel
■
30 °C
1,007 mbar
55 %
Fuel gas (LHV = 46,170 kJ/kg)
20.0
not validated design reserve
16.0
14.0
12.0
10.0
8.0
6.0
Start mass flow
Delta power output [% of dry base load]
Measurement points from first time application
18.0
4.0
2.0
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Wet Compression mass flow [% of compressor inlet mass flow]
Fig. 6: Gas turbine power increase measured at SGT5-4000F
The achievable maximum power output with Wet Compression is limited by a maximum design water mass flow
(2 % of the compressor inlet mass flow) however, not all
sites can reach the full potential of Wet Compression due
to site specific limitations such as generator/transformer
limits, shaft limit, combustion instabilities or special limiting hardware configurations. For the advanced gas turbine
frames, the maximum allowed water mass flow has to be
checked at site specific condition to ensure limitation free
gas turbine operation. Experiences on the first time application revealed that gas turbines with potential combustion
system issues (burner clogging, bad fuel distribution) may
experience difficulties with higher Wet Compression mass
flows (>1 %) as the already existing issue will be exasperated
with increased fuel flow in Wet Compression operating
mode.
7
2.5000
not validated design reserve
2.0000
1.5000
1.0000
Start mass flow
Delta Efficiency [% of dry base load]
Measurement points from first time application
0.5000
0.0000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Wet Compression mass flow [% of compressor inlet mass flow]
1.8
2.0
Fig. 7: Gas turbine efficiency increase measured at SGT5-4000F
Operating
experiences
Since 2004 Wet Compression is introduced in the
SGT5-2000E frame and the chosen design shows highly
satisfying results.
To minimize the risks to the gas turbine hardware the
Wet Compression design, operating regime and controller
reactions are carefully engineered. For the different gas
turbine frames the Wet Compression operation is validated
with additional measurements of the gas turbine reactions
to ensure a safe operation.
■
■
■
CFD optimized nozzle positioning to equalize droplet,
steam and temperature distribution at the compressor
Validated operational concepts, for example specific
load gradients to ensure low thermal stresses
Full integration of Wet Compression into the gas turbine
control system logic to ensure optimized gas turbine
operation in Wet Compression operational mode
As water penetrates the compressor during Wet Compression, erosion and corrosion on the compressor blades and
vanes is a predominant topic.
Our long term field experiences show following influences
on the compressor blades and vanes.
■ No tendency to increased appearance of pitting
corrosion.
■ Coating loss on the leading edge and on the pressure
side after short operation periods, but coating stays
intact in the areas where salt residuals are left on the
blades and vanes and therefore keep on fulfilling its
major functionality.
■ The leading edge gets rougher (needle structure)
as droplets wash out some of the base material.
No significant shortening of the blade width by
erosion could be recognized.
After many thousands equivalent operating hours of
successful Wet Compression operation, no compressor
blades had to be exchanged during a running maintenance
interval as the base material of the blades remained mostly
unharmed and the strength has not been significantly
reduced.
There are no noticeable findings on other gas turbine
components related to Wet Compression operation. The
Wet Compression system itself has not shown significant
findings either. A 3-staged filter concept saves the nozzles
against clogging and damages, so far no nozzle has to be
replaced because of damages.
Beside the design of the spray rack, Siemens uses the
Advanced Compressor Coating (ACC) to minimize the
influence. The main target is to isolate corrosive products
like salts from the blade base material. Although Wet
Compression utilizes deminerilized water, salts are taken
out of the air (esp. maritime sites) to be left on the blades
and vanes after the evaporation. The deposits concentrate
on the rear part of the suction side, especially in the mid
and rear part of the compressor.
8
Conclusion
Disclaimer
Wet Compression is a proven technology to increase the
capacity of the gas turbine for peak load operation or to
recover performance deficits in summer time. The higher
power output and the low sensitivity to changes in ambient
humidity make Wet Compression very attractive in comparison the standard systems for compressor inlet cooling
like Fogging or Evaporative Cooler.
This document contains forward-looking statements and
information – that is, statements related to future, not past,
events. These statements may be identified either orally
or in writing by words as “expects”, “anticipates”, “intends”,
“plans”, “believes”, “seeks”, “estimates”, “will” or words of
similar meaning. Such statements are based on our current
expectations and certain assumptions, and are, therefore,
subject to certain risks and uncertainties. A variety of
factors, many of which are beyond Siemens’ control, affect
its operations, performance, business strategy and results
and could cause the actual results, per formance or achievements of Siemens worldwide to be materially different
from any future results, performance or achievements
that may be expressed or implied by such forward-looking
statements. For us, particular uncertainties arise, among
others, from changes in general economic and business
conditions, changes in currency exchange rates and interest
rates, introduction of competing products or technologies
by other companies, lack of acceptance of new products
or services by customers targeted by Siemens worldwide,
changes in business strategy and various other factors.
More detailed information about certain of these factors
is contained in Siemens’ filings with the SEC, which are
available on the Siemens website, www.siemens.com and
on the SEC’s website, www.sec.gov. Should one or more
of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary
materially from those described in the relevant forwardlooking statement as anticipated, believed, estimated,
expected, intended, planned or projected. Siemens does
not intend or assume any obligation to update or revise
these forward-looking statements in light of developments
which differ from those anticipated. Trademarks mentioned
in this document are the property of Siemens AG, its
affiliates or their respective owners.
Short lead times for the realization of the Wet Compression
upgrade compared to new build projects enable also the
response on short term capacity needs.
Summarized, the upgrade with Wet Compression is one
of the best solutions for the increasing “power on demand”
capacity.
Permission for use
The content of this paper is copyrighted by Siemens and
is licensed to PennWell for publication and distribution
only. Any inquiries regarding permission to use the content
of this paper, in whole or in part, for any purpose must be
addressed to Siemens directly.
9
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