Aiming for a goal of over 70 per cent efficiency21 May 1999
The US Department of Energy's Vision 21 looks to the future of the power industry, with a number of very ambitious objectives, building on the ATS Programme, which is nearing completion
As the world approaches the 21st century, the US Department of Energy (DoE) has developed its Vision 21, mapping out its vision for R&D for the new millenium. The programme is intended to integrate emerging concepts for high efficiency power production and pollution controls into a new class of fuel-flexible generation facilities.
Vision 21 builds on the Advanced Turbine Systems (ATS) programme, first launched in 1992, and now near completion.
The initial objective of the ATS programme was to achieve, by 2000, turbines that were:
Two classes of turbine are being developed under the ATS programme. Simple cycle industrial turbines, less than 20 MWe, are being developed for distributed generation, industrial and cogeneration markets. Combined cycle turbines greater than 20 MWe are being developed for large baseload, central station generation markets. However, turbines that are smaller than 3 MWe are not covered by the ATS programme.
ATS turbines are scheduled to enter pre-commercial demonstration by 2000, and commercialisation is expected by 2002.
ATS programme status
Allison Engine Company
Allison Engine Company's research is based on its aircraft gas turbine experience. Increased efficiency for its simple cycle engine is achieved by raising the turbine inlet temperature to 2400°F and the pressure ratio to 30:1. Allison has developed a 'core' ATS engine that will serve multiple applications with an overall cycle efficiency of 41 per cent.
Solar Turbine's research is based on a recuperated cycle, based on its proprietary primary surface recuperator, which has an effectiveness in excess of 90 per cent. Solar's cycle provides 43 per cent efficiency at a turbine inlet temperature of 2200°F and pressure ratio of 9:1. Under the Ceramic Stationary Gas Turbine Programme, Solar is testing a Centaur 50S engine that incorporates monolithic ceramic first stage blades and a ceramic composite combustion liner. Solar's ATS is the Mercury 50, a single-shaft recuperated 5 MWe turbine system.
GE's ATS is the MS7001H (60 Hz)/MS9001H (50 Hz). This is a 400 MWe combined cycle system with efficiency above 60 per cent, achieved by increasing turbine inlet temperature to 2600°F. High temperature tests verified effective cooling of hot turbine components by steam. Air is delivered at 1230 lb/s at a pressure ratio of 23:1.
GE's efforts were focused on compressor, combustor, turbine design validation and manufacturing of hardware.
Good results were obtained from the compressor and stage 1 nozzle cascade tests run during 1998. The 9H compressor tests validated the efficiency, performance and operating characteristics. Similar results are expected for the 7H compressor tests, which will be carried out this year.
Earlier, test results for the stage 1 nozzle of the GE ATS were incorporated into detailed models in order to verify that the nozzle met design expectations. In 1997, full-scale validation of the stage 1 nozzle was achieved at the GE Aircraft Engine test facility in Cincinnati. Actual full-scale prototype, steam-cooled stage 1 nozzle segments were tested under actual operating conditions. Since the heat transfer phase of the testing was successfully completed, the test rig was reconfigured with less instrumentation. Under this new arrangement, low-cycle fatigue analyses are being conducted to simulate field operation. After performing full-scale, no-load 9H ATS engine tests at the GE Greenville turbine plant, similar testing for the 7H ATS is planned during this year.
Casting of the largest advanced single crystal turbine components in the world was completed, which was a critical step towards commercialisation.
The H system gas turbine is likely to be first installed commercially at Baglan Energy Park in Wales.
Siemens Westinghouse introduced the 501G ATS gas turbine, capable of operating at 420 MWe at an efficiency of about 60 per cent. It operates with a turbine inlet temperature of 2750°F, delivering 1200 lb/s of air at a 29:1 pressure ratio. To solve efficiency losses caused by leakage around internal parts, brush and abradable coating seals were developed for stationary sections of the turbine.
To achieve its ATS goals, Siemens Westinghouse is undergoing an extensive technology verification programme in combustion, cooling, aerodynamics, leakage, control, coatings and materials. The 501 ATS piloted ring combustor has demonstrated single-digit NOx emissions under low-pressure tests, and is currently undergoing high-pressure testing.
Siemens Westinghouse plans to validate first-stage turbine vane component design with a series of heat transfer tests on model turbines and on a full hot cascade test rig at the Amold Engineering Development Center, Amold Air Force Base, Tennessee.
During 1998, full-scale compressor testing was completed at the US Navy Base in Philadelphia, with measurements taken for design point performance, blade vibration, guide vane optimisation and map definition.
At Ohio State University, aerodynamic development testing on a 1/3 scale model rig is being conducted. The Siemens Westinghouse brush seal programme continues with long-term performance testing of its new interstage seal designs on a new 501F engine and retrofits into 501D5 engines. A new coating developed for the 501 ATS has accumulated over 20 000 hours in cyclic testing. Work continues in the casting development of hot gas path components with CMSX-4 to enhance turbine performance and reliability.
The first unit has started operation, and to date, has operated successfully.
ABB is participating in the ATS programme under a Phase 2 project. During the past year, ABB has demonstrated that an advanced air-cooling technique can deliver the increase in power output and power plant efficiency required under the programme. ABB also commissioned a turbine test rig to measure aerodynamic and cooling interaction under engine conditions. ABB is pursuing a detailed test programme for Thermal Barrier Coating (TBC) development.
Research to develop advanced alloys for ATS hot gas path components continues. Advanced single crystal alloy developments enable the scale-up of technologies to produce high temperature blades and vanes for aircraft engines. Recent accomplishments have reduced levels of sulphur and defects in production castings of these components. Future emphasis is being placed on the cost-effective manufacturing of these components.
Projects have been initiated so as to develop advanced casting and fabrication methods to increase yield rates to reduce production costs. Successful commercialisation of these new processes is critical to achieving the cost of electricity goals of the ATS programme. Currently, the teams of Howmet-GE-Solar Turbines and GE-PCC Airfoils are participating in the new casting projects.
Under the Thermal Barrier Coatings (TBC) programme, novel coatings, testing methods and a final long-term durability engine test will be performed. Currently, Siemens Westinghouse and Pratt and Whitney are participating in the TBC programme. The DoE believes that there is a need to develop TBC's which have greater durability and life prediction, as well as availability of in-situ repair and monitoring. Researchers are looking for coatings with twice the thickness than are currently being applied, and lifetimes of 30 000 hours.
Technology base development is handled by a collaborative university-industry R&D consortium managed by the South Carolina Institute for Energy Studies. The consortium targets research in combustion, heat transfer, materials, aerodynamics, controls, alternative fuels and advanced cycles. Presently, 95 universities and 8 gas turbine corporations make up the consortium. Fifty one research projects have been completed or are underway.
The Federal Energy Technology Center (FETC) combustion group supports the programme and provides technical evaluation of novel concepts.
Planning for the future: Vision 21
With the ATS programme now coming to a conclusion, the DoE is developing its plans for the next phase, Vision 21.
The programme's objective is to develop a wide suite of technologies that would eliminate concerns associated with the use of fossil fuels while assurring continuing availability of low cost energy. The programme takes account of the financial environment under deregulation. The transformation to a deregulated power industry results in a risk-averse market. Gas turbine vendors will have to make money on servicing units, as competition has forced the profit out of supplying new ones. This makes it difficult to determine real life-cycle costs.
The main goal of the programme is to integrate new concepts for high efficiency power production and pollution controls into a new class of fuel flexible generation facilities. The plan is for Vision 21 plants to greatly reduce energy intensity through dramatic generation efficiency improvements with virtually no environmental impact. For example, DoE has set very ambitious targets of no less than 70-75 per cent efficiency for combined cycle gas turbines and 60 per cent for coal-fired power plants.
Among technologies the DoE believes should be developed are substantial increases in pressure ratio and firing temperature while maintaining low life-cycle costs.
Creation of greenhouse gases would be reduced by high efficiency; after this, carbon emissions could be captured at plant or offset by carbon removal processes elsewhere. The captured carbon could be sequestered or potentially recycled into useful products.
Objectives of Vision 21
The objectives of Vision 21 are as follows:
Develop existing gasification, gas cleanup, combustion turbine, fuel cell and coproduction technology to meet efficiency goals greater than 60 per cent for coal-fired units and 75 per cent for gas-fired units, with near-zero SO2, NOx, and particulate emissions.
Development of advanced materials, components, catalysts and sorbents, computational sciences, and other fundamental technologies that will support integration of modules into the Vision 21 fleet of energy plants.
Ensure specific enabling technologies have been identified, are available, and are market-ready to achieve the benefits of Vision 21.
Vision 21 is intended to bring to the commercial market technologies that will achieve these objectives by the 2010-2015 time frame.
Another element of the programme is directed towards clean and reliable distributed generation systems. The DoE believes that distributed systems will be well suited to applications in areas not served by a grid network. These systems could range from a few hundred kWe to 50 MWe. At the lower end, from 500 kWe to 5 MWe, gas turbines are expected to compete with fuel cells, diesels, and gas engines. The large industrial segment, up to 50 MWe extends into the mid-size domain where new generation designs could serve as a distributed resource for self-generation or cogeneration.
Carbon sequestration is part of of the programme. To substantially reduce total world greenhouse gas emissions, new CO2 sequestration technologies are required. Research targets longer-term solutions, including CO2 recycling, enhanced natural sinks for carbon, and geological sequestration.
Links to other programmes
Vision 21 is seen as a long-range cost-shared industry-driven R&D programme designed to produce public benefits from the present to 2030 and beyond.
Partnerships and linkages are being created with industry, universities, private and public R&D laboratories, and Federal and State agencies. The Vision 21 programme includes enabling technologies, supporting technologies, systems integration and market analysis, and Vision 21 plant design. The final goal is the commercial application of Vision 21 plants.
Significant near-term benefits may be realised during the course of the programme. For example, high efficiency fuel cell/turbine cycles using natural gas would be developed for the distributed power generation market.
There are a number of planned enabling technologies. These include:
High temperature heat exchangers, hot gas clean up, advanced combustion systems and fuel flexible turbines are directly relevant to development of gas turbine technology.
High temperature heat exchangers
A team being led by United Technologies Research Centre is developing a high temperature air furnace (HITAF) for heating turbine air in high performance power systems, a type of indirectly-fired cycle.
The HITAF uses advanced materials and an innovative design that prevents hot heat exchanger tubes from contacting corrosive combustion products.
Advanced hot gas cleanup
Cleaning and conditioning of combustion product gases is crucial to the goal of high efficiency, near-zero emissions, and low cost. Product gases must be cleaned of particulate matter, all sulphur- and nitrogen-containing compounds, and all traces of other hazardous compounds that may affect downstream operations or be emitted into the atmosphere.
Gases must be cleaned at temperatures and pressures close to combustor operating conditions and those of downstream operations. Research activities will focus on:
Advanced combustion systems
The Vision 21 advanced combustion systems are focused on the indirectly fired cycle, because this cycle is fuel flexible and efficient. A key characteristic of the indirectly fired cycle is that combustion products do not contact the turbine, thus avoiding potentially serious corrosion problems that may arise from the use of sulphur-containing fuels.
Fuel flexible turbines
By 2002, advanced materials, combustion systems and cooling techniques will provide highly efficient, clean power from combined cycle gas turbines.
Vision 21 demands these achievements be extended to other fuels, including flue gas from coal and hydrogen. This is being pursued by development of advanced cycle configurations with increased pressure ratios, advanced alloys and ceramic materials, and combustion technology that could advance gas turbines to higher levels of performance at reduced cost.
Vision 21 plant design
The Vision 21 Programme will produce engineering designs for prototype,small commercial, and large commercial plants. The major products of the programme are:
|A Vision 21 fleet for the 21st century
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