Turning NGCC Into IGCC: Cycle Retrofitting Issues
The increase in price of natural gas and the need for a cleaner technology to generate electricity has motivated the power industry to move towards Integrated Gasification Combined Cycle (IGCC) plants. The system uses a low heating value fuel such as coal or biomass that is gasified to produce a mixture of hydrogen and carbon monoxide. The potential for efficiency improvement and the decrease in emissions resulting from this process compared to coal-fired power plants are strong evidence to the argument that IGCC technology will be a key player in the future of power generation. In addition to new IGCC plants, and as a result of new emissions regulations, industry is looking at possibilities for retrofitting existing natural gas plants. This paper studies the feasibility of retrofitting existing gas turbines of Natural Gas Combined Cycle (NGCC) power plants to burn syngas, with a focus on the water/steam cycle design limitations and necessary changes. It shows how the gasification island processes can be treated independently and then integrated with the power block to make retrofitting possible. This paper provides a starting point to incorporate the gasification technology to current natural gas plants with minor redesigns.
ADVANCED F CLASS GAS TURBINES CAN BE A RELIABLE CHOICE FOR IGCC APPLICATIONS
With the increase in natural gas fuel prices, customer interest in IGCC plants is growing as an alternative to the traditional coal plants. Future IGCC plants are expected to be more efficient, use less water, produce significantly less emissions, and have the potential to be a lower cost solution to address future CO2 and Hg regulations compared to the direct coal fired steam plants. Since IGCC plants’ availability is a widely documented industry concern, this paper will summarize how the integration of the Siemens SGT6-5000F (formerly W501F) into future 60 Hz IGCC plants will address this issue. Siemens has over 300,000 hours of successful IGCC gas turbine operating experience in the United States and Europe and has supplied a range of products for many of today’s IGCC plants. Currently in the Siemens 60 Hz natural gas based operating fleet, the SGT6-5000F gas turbine has the largest number of operating engines and the most cumulative operating hours. Several advancements to this frame have increased its power and efficiency while decreasing emissions and life cycle costs without impacting reliability. Development programs, including syngas combustion system testing, were initiated to verify the SGT6-5000F readiness for future IGCC applications. This paper addresses the results of the comprehensive development program initiated to allow syngas operation of the SGT6-5000F in IGCC applications while maintaining the gas turbine system’s availability and reliability at levels expected by the industry.
SGT6-5000F (W501F) Engine Enhancements to Improve Operational Flexibility
This paper describes recent changes made to the SGT6-5000F gas turbine (previously named W501F) to enhance its operational flexibility. The engine is designed for a wide range of operating modes, such as peaking, intermediate and continuous duty. The changes incorporated will further enhance its demonstrated record in flexible operation demanded by the current US market conditions of overcapacity and high fuel prices. This paper describes benefits resulting from these changes, as well as verification testing carried out to validate them. The changes focused on engine operation, performance, component mechanical integrity and combustion system improvements. The paper also summarizes the SGT6-5000F field experience over the 15 years since its introduction and outlines planned improvements for the near future. Introduction In the 40 years prior to the SGT6-5000F design, aviation and land-based gas turbines experienced evolutions in performance and design leading to improved mechanical integrity and reliability. During that period our engineers made significant contributions in developing heavyduty gas turbine technologies. Heavy-duty gas turbines remained at 1093°C (2000°F) rotor inlet temperature levels in the decade before the SGT6-5000F introduction. The introduction of F-class firing temperatures (1260°C / 2300°F) represented a step change made possible by advancements in manufacturing, material processing, improved analytical techniques and advanced cooling technology. Significant improvements in thermal performance were achieved simultaneously with gas turbine emissions reductions through dry low NOx technology. The SGT6-5000F heavy-duty gas turbine was designed for both simple cycle and combined cycle (CC) power generation in utility and industrial service. This engine represented the next model in the family of successful W501 gas turbines (see Reference 1). It is an advanced, efficient, low NOx, powerful gas turbine able to operate on all conventional fuels as well as coalderived low Btu gas. The introductory design, in 1990, carried a simple cycle rating of 145 MW of power and 34.1% net thermal efficiency. In CC applications, the introductory net plant efficiency was more than 53% with 200 MW of power. In 2005, 185 SGT6-5000F engines are employed in peaking, intermediate and continuous duty operation. The fleet has amassed more than 2.5 million operating hours and has demonstrated excellent reliability, availability and starting reliability. These units, plus an additional 38 under contract, represent the highest number of any one model of 60 Hz Siemens gas turbines sold. Due to design enhancements, development efforts and technology cross flow from other Siemens’ advanced gas turbines, the simple cycle output has increased from 145 MW to 200 MW and its efficiency from 34.1% to 38%. In one on one CC applications, the net plant output and efficiency are now 293 MW and 57%, respectively. SGT6-5000F gas turbines have demonstrated successful operation on different fuels and in different modes of operation including engines with numerous start cycles and engines with long run times between starts. Due to increases in natural gas prices and the overcapacity in the US electric power market after 2002, conditions shifted such that the nuclear and coal-based plants have become the lowest cost electricity producers. This significantly reduced the number of hours that the deregulated gas turbine-based plants could operate economically. Currently, many gas turbines run in a cyclic duty profile with daily start cycles fulfilling peak power requirements. To further enhance the gas turbine’s operational flexibility, design changes were incorporated to reduce emissions (at full and part load), life cycle costs, and startup/cool down times while simultaneously improving performance and operational reliability. OW2014_A © Siemens AG 2005. All rights reserved. 1 9/6/2005 The focus of this development included operational/control modifications, combustion system enhancements, sealing improvements, tip clearance optimizations, cooling optimizations, hot path hardware durability improvements (especially as related to ability to operate in start-stop and cyclic modes) and exhaust system durability improvements. This effort provides a product that addresses market conditions such as high fuel prices and requirements for cyclic/intermittent operational capability. To take advantage of the low cost and secure U.S. coal supply, the SGT6-5000F has been adapted for incorporation into an integrated gasification combined cycle (IGCC) plant and has been proposed for several new IGCC plants targeted for 2010 operation. Engine Design Features SGT6-5000F design was based on fundamental time-proven design concepts used in earlier models as well as new concepts and technologies incorporated to increase efficiency, reduce emissions and allow reliable operation (see Reference 2). Figure 1 illustrates the engine longitudinal section. To develop a highly reliable gas turbine, reliability/availability/maintainability (RAM) principles were applied to the SGT6-5000F design and development. These principles were focused not only on the gas turbine and its components, but also on auxiliaries and controls, since they have a significant impact on overall plant reliability and availability. The RAM approach involved systematic and iterative evaluations of the design, comparison against design objectives and recommendations for design enhancements, using a full range of tools, such as reliability allocations, modeling and Failure Mode and Effects Analysis (see Reference 3). The current SGT6-5000F fleet average availability has reached world class levels, currently at 95% on a 12 month rolling average basis. Figure 1. SGT6-5000F Longitudinal Section Component and Engine Verification Tests All the new advanced technology, incorporated into SGT6-5000F design, was validated for engine use by extensive rig and fully loaded engine shop tests. This verification test program included rotating blade vibration, combustion system, turbine aerodynamics, cooled turbine component heat transfer, and other shop tests (see References 5-7) The latest improvements OW2014_A © Siemens AG 2005. All rights reserved. 2 9/6/2005 have been fully tested and validated in the 235 MW test bed located at the Siemens factory in Berlin. This test bed which uses a water brake to absorb the full power of the SGT6-5000F engine is a unique facility for the testing of large gas turbines and allows operation of the engine at full power and off frequency to fully map out the mechanical and aerodynamic operating envelope for the engine. Field Experience The measure by which a gas turbine model is judged to be successful is its field operating experience. The specific criteria for success include performance, emissions, mechanical integrity, (as defined by RAM and starting reliability), life cycle costs and operational flexibility. All of the above are important, but in the current competitive and changing market environment, operational flexibility and adaptability to this environment have assumed a much greater importance. To be economically viable, the electricity generating plant must respond quickly, efficiently and reliably to any required changes in operating conditions such as load demand, start-stop operation, and different fuels, etc. The SGT6-5000F has demonstrated over the last 12 years its success in this environment, providing its operators with exceptional service. 185 SGT6-5000F engines are currently operating in peaking, intermediate and base load modes. Figure 2 shows the number of engines plotted versus the year of initial operation. The fleet has amassed more than 2.5 million operating hours (see Figure 3) and demonstrated excellent reliability and availability (see Figure 4). The fleet 12 month rolling average reliability* is currently over 99%, and availability* over 95%, as of May 2005. The lead engine has accumulated more than 94,000 operating hours. The simple cycle output power and efficiency for the latest model is 200 MW and 38%, respectively, and in CC application 293 MW and 57%, respectively . NOx and CO emissions of <9 ppm are available. The SGT6-5000F engine has demonstrated its operational flexibility and excellent performance through a continuous improvement & dedicated product development effort carried out since its introduction.* This data includes the gas turbine, generator, mechanical auxiliaries (lube oil, fuel, etc.), electrical components and control system. 9999 1919 0 25 50 75 100 125 150 175 200 225 250 19 93 19 94 19 95 19 96 19 97 19 98 20 00 20 01 20 02 20 03 20 04 20 05 20 06 20 07 223 SGT6-5000F Units Operating & Under Contract 185 Units Operating Year of Initial Operation N u m be r o f U n i t s 19 93 19 94 19 95 19 96 19 97 19 98 20 00 20 01 20 02 20 03 20 04 20 05 20 06 20 07 Figure 2. SGT6-5000F Engines in Operation OW2014_A © Siemens AG 2005. All rights reserved. -3 9/6/2005 19 97 19 97 O p e ra t in g H o u rs 0 500,000 1,000,000 1,500,000 2,000,000 2,500,000 3,000,000 19 93 19 94 19 95 19 96 19 98 19 99 20 00 20 01 20 02 20 03 20 04 20 05 19 93 19 94 19 95 19 96 19 98 19 99 20 00 20 01 20 02 20 03 20 04 20 05 Figure 3. SGT6-5000F Fleet Cumulative Operating Hours SGT6-5000F 12 Month Rolling Average Availability and Reliability 0 20 40 60 80 100 120 140 160 180