Answers for energy.

POWER-GEN Asia 2011 KLCC,Malaysia, Kuala LumpurSeptember 2729, 2011

Authors:Jan Dirk BeilerSiemens AG, Energy Sector Fossil Power Generation Division

Peter TraunerSiemens AG Energy Sector Service Division

High efficient peak power on demand

www.siemens.com/energy

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3Copyright Siemens AG 2011. All rights reserved.

ContentAbstract 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

4AbstractAs part of our ongoing commitment to meet the changing requirements of customers operating assets, we offer the latest technology helping to enhance customers 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.

IntroductionIn 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 increas-ing. 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 per-mitting and construction, an appropriate alternative is to increase the capacity of the already existing plants with

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 imple-mentation time.

Wet Compression is a system for compressor intercooling. By cooling the media inside the compressor and the con-sequently 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

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 principleUnlike 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.

5for 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 usageWet 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 combina-tion 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.

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 Com-pression) is used which provides less water but a faster ramp up of the water mass flow. Still the initial reaction time of about 1520 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.

The significant power increase of Wet Compression mainly consists of 3 different effects.

Compressor intercoolingDue 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 coolingAlthough 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 increaseThe 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.

Air inlet flow

Water injection

Compressor

Combustion Chamer

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 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 conse-quently 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

6PerformanceWet Compression has influence on different parameters in the gas turbine and combined cycle process. The main influences can be described as follows:

ParameterChange by Wet Compression

Gas turbine power output

Gas turbine efficiency

Gas turbine outlet temperature

Fuel mass flow

Exhaust gas energy

NOx emissions

Combined cycle power output

Combined cycle efficiency

Increase decrease

Fig. 3: Influences of Wet Compression operation

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.

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 Com-pression at an ambient temperature of 30 C as a function of the ambient humidity in comparison to an Evaporative Cooler (exemplary for SGT5-2000E).

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 compres-sor and therefore the basic mass flow increase can be achieved even at 100 % relative humidity.

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.

Reference conditions used: Ambient temperatures 10 50 C Ambient pressure 1013 mbar Relative humidity 60 % Fuel Methane

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Power output at 30 C ambient temperature related to the relative humidity

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7In 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

Fig. 5: Range of power increase at SGT5-2000E depending on ambient temperature

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 30 C Ambient pressure 1,007 mbar Relative humidity 55 % Fuel Fuel gas (LHV = 46,170 kJ/kg)

Fig. 6: Gas turbine power increase measured at SGT5-4000F

The achievable maximum power output with Wet Com-pression 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 limit-ing 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 applica-tion 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.

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8Fig. 7: Gas turbine efficiency increase measured at SGT5-4000F

Operating experiencesSince 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 Compres-sion, erosion and corrosion on the compressor blades and vanes is a predominant topic.

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.

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.

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9ConclusionWet 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 com-parison the standard systems for compressor inlet cooling like Fogging or Evaporative Cooler.

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 useThe 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.

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