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.
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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 customers operating assets, we offer the latest technology to help enhance customers operating plant capability and flexibility. One of our modernization products for power enhancement is the Wet Compression upgrade. 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; for example, during summer peaks or grid fluctuations driven by renewable energy sources that increase revenues at high peak load electricity prices. Wet Compression is designed to increase power output by injecting water into the compressor inlet, which intercools the compressor, reduces the compressor inlet temperature, and increases 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. Wet Compression caused a measurable power increase of up to 16 % of the dry gas turbine base load power. Wet Compression provides peak power on demand with a higher efficiency level compared to other stand by generators or simple cycle diesel applications. This reduces or eliminates carbon and nitrogen emissions. In situations where there are high ambient temperatures and increased peak load electricity demand, Wet Compression provides economic benefits. Introduction The need for peak load and reserve capacity is constantly increasing. With the growing amount of regenerative energy generation (wind, solar) being added to power systems worldwide, the requirement for reserve capacity that can be provided on demand is also increasing. In Germany, for example, installed wind-generation capacity accounts for more than 26 GW of installed capacity, and significant additional generation is being provided through new offshore wind parks. The proportion of actual energy contribution from wind generation is typically between 5 % and 10 % of annual energy generation, with generation duration being approximately 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 renewable generation. Gas turbines with fast reaction times are the preferred technology to fulfill this demand. Because new projects usually require lengthy development due to long lead times for site permits and construction, a useful alternative is to increase the capacity of existing plants with power upgrades. Siemens offers Wet Compression as an upgrade that 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 increasing mass flow, the power output of the gas turbine increases significantly. Additional benefits may include an increase in gas turbine efficiency and reduction of NO x -emissions. Wet Compression was developed in 1995 and was redesigned for the SGT5/6-2000E in 2003. In May 2010 the commissioning of the first application on the advanced frame SGT5-4000F was successfully accomplished. Wet Compression description Fig. 1: Wet Compression impressions Using a nozzle rack in the air inlet close to the compressor entrance, demineralized 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 Computational Fluid Dynamics (CFD)-optimized nozzle positioning ensure that small and well distributed water droplets enter 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 for compressor intercooling. The purpose of Wet Compression is to distribute fine water droplets into the compressor where they evaporate gradually. 4
The significant power increase of Wet Compression derives mainly from three different effects. Compressor intercooling Evaporation inside the compressor reduces the work required to compress the cooled air, which in turn reduces compressor power consumption. Inlet cooling Although this is not its main purpose, Wet Compression provides an inlet cooling effect as droplets evaporate on their way into the compressor. Additional air mass flow enters the gas turbine as the inlet air cools down. Turbine power/mass flow increase Turbine power/mass flow increase Increased air mass flow due to inlet cooling Additional air mass flow by reducing the mass flow limitation of the first compressor stages through additional cooling Additional water mass flow Higher fuel flow. Air inlet flow Water injection Fig. 2: Wet Compression principles Compressor Combustion Chamber Turbine Wet Compression operating conditions Wet Compression can 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 subsequent damage while operating at lower temperatures is too high, and therefore prevented by 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 thermal stresses for the gas turbine components at a low level; consequently maximum performance is typically reached after 18 minutes for the SGT5-2000E. Wet Compression can be operated without respect to ambient humidity. Combined operation with an evaporative cooler is also 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 (especially Base Load off Frequency Characteristics (BLOC) and secondary frequency response) Base load increase for simple cycle gas turbines Seasonal operation of Wet Compression to compensate for capacity losses during high ambient temperatures is possible for both dry and humid areas. Operation can even be combined with an evaporative cooler or chiller as long as the compressor inlet temperature stays above 10 C. Using Wet Compression to increase marketable power reserve and to handle occasional peaking is ideal because it has very little effect on the normal operation of the gas turbine. Wet Compression can also be used for grid code support, usually in combination with other measures. For grid code support, a special Wet Compression system called fast Wet Compression is used to provide less water but a faster ramp up of the water mass flow. Although the initial reaction time of about 15 20 seconds is too slow for a primary frequency response, it can easily be used as an additional measure for a BLOC operation or to take over the secondary frequency response. Continuous operation of Wet Compression to increase base load is appropriate for simple cycle gas turbines because doing so improves both power and efficiency. When continuous operation of Wet Compression is carried out for a combined cycle configuration, however, the combined cycle efficiency will be marginally decreased. 5
Performance Wet Compression affects different parameters in the gas turbine and combined cycle process. The primary changes are described in figure 3 below. Parameter Gas turbine power output Gas turbine efficiency Gas turbine outlet temperature Fuel mass flow Exhaust gas energy NO x emissions Combined cycle power output Combined cycle efficiency Change by Wet Compression As mentioned before, Wet Compression has various effects on the performance of the gas turbine. In addition to boosting power, 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 ambient humidity compared to inlet cooling applications such as Evaporative Cooler or Fogging. The following graph shows the achievable power (as a percentage 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 for SGT5-2000E. The power gain of the evaporative cooling is reduced by increasing relative humidity. Although the delta power output of Wet Compression is slightly reduced as well, it remains high because intercooling of the compressor and basic mass flow increase can be achieved even at 100 % relative humidity. Increase decrease Fig. 3: Influences of Wet Compression operation 20 Power output at 30 C ambient temperature related to the relative humidity Delta power output (to Base Load, R.H. 10 %) [%] Power output with Wet Compression (2 %-MVI) 18 16 14 12 10 8 6 4 2 0 10 20 30 40 50 60 70 80 90 100 Power output with Evaporative cooler (85 % Eff.) Base load power, dry 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 switching between a minimum mass flow and a maximum mass flow. The following figure shows 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 6
20 Power increase by Wet Compression [% of base load power] 18 16 14 12 10 8 6 4 Shaft limit reached Maximum mass flow (design) 75 % of design mass flow 50 % of design mass flow Minimum mass flow (start) 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 was successfully completed. The system shows 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 first-time application on the SGT5-4000F. The highest gas turbine delta power of about 16 % was measured at a Wet Compression mass flow of about 10.2 kg/s. In addition, the gas turbine efficiency 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) Delta power output [% of dry base load] 20.0 18.0 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 Start mass flow Measurement points from first time application 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 not validated design reserve Fig. 6: Gas turbine power increase measured at SGT5-4000F Wet Compression mass flow [% of compressor inlet mass flow] The achievable maximum power output with Wet Compression is limited by the maximum design water mass flow (2 % of the compressor inlet mass flow). However, not all sites can reach the full potential of Wet Compression because of site-specific generator or transformer limits, shaft limit, combustion instabilities, or special hardware configurations. For advanced gas turbine frames, the maximum allowed water mass flow must be checked under site-specific conditions to ensure gas turbine operation without limits. Siemens experience with the first application of Wet Compression on the SGT5-4000F revealed that gas turbines with potential combustion system issues (for example, burner clogging and bad fuel distribution) may experience difficulties with Wet Compression mass flows >1 %, because existing issues will be exacerbated by the increased fuel flow in Wet Compression operating mode. 7
2.5000 Measurement points from first time application Delta Efficiency [% of dry base load] 2.0000 1.5000 1.0000 0.5000 0.0000 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. 7: Gas turbine efficiency increase measured at SGT5-4000F Operating experiences Wet Compression was introduced in the SGT5-2000E frame in 2004, and the design has delivered very satisfying results. To minimize risks to the gas turbine hardware, the Wet Compression design, operating regime, and controller reactions are carefully engineered. To ensure safe operation of different gas turbine frames, Wet Compression operation is validated with these additional measurements of the gas turbine reactions. 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 of the compressor blades and vanes are primary concerns. Along with the design of the spray rack, Siemens uses Advanced Compressor Coating (ACC) to minimize the erosion and corrosion. The key is to isolate corrosive products like salts from the blade base material. Although Wet Compression utilizes demineralized water, salt in the air (especially at maritime sites) is left on the blades and vanes after evaporation. The deposits concentrate on the rear part of the suction side, especially in the mid- and rear part of the compressor. Start mass flow Siemens long-term field experience shows the following effects on the compressor blades and vanes: No increased appearance of pitting corrosion. Coating loss on the leading edge and on the pressure side after short operation periods. However, coating stays intact in areas where salt residue was left on the blades and vanes, so the equipment retains most of its 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 thousands of equivalent operating hours of Wet Compression, no compressor blades had to be exchanged during a running maintenance interval. The base material of the blades remained mostly undamaged and their strength was not significantly reduced. There are no noticeable findings concerning the effects of Wet Compression on other gas turbine components. There are no significant findings on the Wet Compression system itself either. A 3-staged filter prevents clogging and damage to the nozzles. So far, no nozzles have been replaced because of damage. not validated design reserve 8
Conclusion 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. Higher power output and low sensitivity to changes in ambient humidity make Wet Compression an attractive alternative to standard systems for compressor inlet cooling, such as Fogging or Evaporative Cooler. The short lead time required to implement Wet Compression also makes it an attractive option for responding to shortterm capacity needs, as opposed to building a new project. In summary, Wet Compression is one of the best solutions available to help operating plants cost-effectively increase their 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. Disclaimer 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, performance 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. 9
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