Turbine Efficiency

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Turbine Efficiency

Background

Turbines have been the world's energy workhorses for generations, harkening back to primitive devices such as waterwheels (2,000 years ago) and windmills (over 1,000 years old). Today, turbines not only power aircraft and vehicles of all sorts, they are the heart of almost all of the world's electric generating systems.

Power generation from fossil energy relies upon gas turbines and steam turbines, and in combination as combined-cycle units:

		Gas Turbines. A gas turbine is a heat engine that uses high temperature, high-pressure gas as the working fluid to spin the turbine and generate power. Combustion of fuel in air is usually used to produce the needed temperatures and pressures in the turbine, which is why gas turbines are often referred to as “combustion” turbines. To capture the energy, the working fluid is directed by vanes at the base of combustor nozzles to impinge upon specially designed airfoils (turbine blades). The turbine blades, through their curved shapes, redirect the gas stream, which absorbs the momentum of the gas and produces power. A series of turbine blade rows, or stages, is attached to a rotor/shaft assembly. The shaft rotation drives an electric generator and a compressor for the air used in the gas turbine combustor. This process of imparting potential energy to a gas working fluid by adding heat and pressure, and translation of the potential energy to work through interaction of gas and blades, is called a Brayton cycle. In the simple Brayton cycle, the turbine exhaust is typically vented to the atmosphere.
		Steam Turbines. Steam turbines work on the same basic principles as gas turbines, but use steam as the working fluid. This steam is typically generated in an external boiler and fired by an external heat source. The process of imparting heat to pressurized water to produce a high potential energy steam, and translation of the potential energy to work through interaction of steam and blades, is called a Rankine cycle. In the Rankine cycle, the turbine exhaust (steam), now at low temperature and pressure, is condensed and recycled back to a boiler or heat source in a closed loop.
		Combined-Cycle. A combined-cycle integrates Brayton and Rankine cycles. High quality exhaust heat from a gas turbine generates steam in a heat recovery steam generator to power a steam turbine, significantly enhancing efficiency. In utility applications, both turbines produce electricity. The trend in combined-cycle design is to use a single-shaft configuration, whereby the gas and steam turbines are on either side of a common generator to reduce capital cost, operating complexity, and space requirements.

At the U.S. Department of Energy, a Fossil Energy program began in 1992 to break through technical barriers that had essentially capped gas turbine efficiencies. Within eight years, this program produced turbine systems that could operate at temperatures in excess of 2600 degrees F (300 degrees hotter than conventional turbines) and achieve efficiencies above 60 percent, a mark once thought unachievable. At the same time, new combustion techniques were developed to limit the formation of nitrogen oxide (NOx) emissions (the principal air pollutant released by gas turbines). As a result, high-efficiency natural gas turbines continue to be among the cleanest ways to generate electricity from fossil fuels. Further, if the waste heat is captured from these systems for heating or industrial purposes, the overall energy cycle efficiency could approach 80 percent.

The use of gases produced from coal as gas turbine fuel offers an attractive means for efficiently generating electric power from our Nation's most abundant fossil fuel resource. The adaptation of gas turbine technologies to use with fuels produced from coal gasification has been demonstrated under the Clean Coal Technology Program (specifically, the Tampa Electric's Polk Station and the Wabash River Repowering Projects).

The Energy Department's Fossil Energy Program is developing key technologies that will enable advanced turbines to operate cleanly and efficiently when fueled with coal derived synthesis gas and hydrogen fuels. Developing this turbine technology is critical to the creation of near-zero emission power generation technologies. This will assist with the deployment of future plants that may couple production of hydrogen and electricity from coal with sequestration of the carbon dioxide that is produced.

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References, Sources, and Other Useful Data

Federation of Electric Companies of Japan, "Green Handbook Peer Review: Instructions for the Operation & Maintenance Technologies and Efficiency Improvements for the Coal fired Power Plants", (April 2007)
http://www.fepc.or.jp/english/environment/asia-pacific/green_handbook_peer/index.html

This textbook has been prepared by Japanese electric power companies as a contribution to “PGT-06-01: Best Practices for Power Generation” one of the activities undertaken by the ‘Power Generation and Power Distribution Task Force’ in the context of the ASIA-PACIFIC PARTNERSHIP on Clean Development and Climate. The textbook describes important issues associated with maintaining, and enhancing, levels of heat efficiency at a coal-fired thermal power plants, and constitutes a summary of matters of which all technicians working in power generation plants need to be aware. The 482 pages in this manual cover in depth the best practices for thermal power plants for functional and operational control, maintenance and efficiency control, and environmental preservation.

GE Energy, "Heavy Duty Gas Turbines & Combined Cycle"
http://www.gepower.com/prod_serv/products/gas_turbines_cc/en/index.htm

GE offers the widest range of heavy duty gas turbines available, ranging from 26 to 480 megawatts. Within the GE product line are machines for every utility, IPP and industrial application, from pure power generation to cogeneration and district heating.

GE Energy, "H System™ Combined Cycle Gas Turbine"
http://www.gepower.com/prod_serv/products/gas_turbines_cc/en/h_system/index.htm

GE's H System—one of the world's most advanced combined cycle system and the first capable of breaking the 60 percent efficiency barrier—integrates the gas turbine, steam turbine and heat recovery steam generator into a seamless system, optimizing each component's performance. A leading technology for both 50 and 60 Hz applications, the H delivers higher efficiency and output to reduce the cost of electricity of this gas-fired power generation system.

Siemens Power Generation, "Advanced W501G Gas Turbine Plants in U.S. Go Commercial" (03-May-2001)
http://www.thefreelibrary.com/Siemens+Westinghouse+Power+Corporation+Announces
+Advanced+W501G+Gas...-a074017873

Siemens Power Generation is one of the world's leading specialists in planning, construction and upgrades of power plants; development, production and supply of components and systems; comprehensive plant services, I&C solutions and energy management systems; fuel cells, turbines, compressors and full-scope solutions for industrial plants, in particular for the oil & gas business. At a 250-megawatt nominal capacity and with a net efficiency of approximately 58 percent in combined cycle application, Siemens Westinghouse’s W501G is the largest 60-Hz gas turbine in the world and is among the most efficient. The W501G achieves superior performance through advanced technologies developed and validated under the DOE’s ATS program. The W501G is designed to optimize life-cycle costs by balancing capital cost, efficiency and maintenance costs to yield the lowest overall cost of electricity.

U.S. Department of Energy, National Energy Technology Laboratory "Coal and Power Systems: Turbines"
http://www.netl.doe.gov/technologies/coalpower/turbines/index.html

This site explores the Turbine Program of the U.S. Department of Energy's (DOE) Office of Fossil Energy (FE). It provides information about NETL's Turbine Program and its goals, current projects and solicitations, and performance targets of on-going projects.

U.S. Department of Energy, National Energy Technology Laboratory "Turbine Program: Enabling Near-Zero Emission Coal-Based Power Generation" (June 2005)
http://www.netl.doe.gov/technologies/coalpower/turbines/refshelf/brochures/Brochure%209-19-05.pdf

This document delineates today’s U.S. Department of Energy (DOE) Turbine Program being
implemented by the DOE National Energy Technology Laboratory (NETL). The Turbine Program
leverages the knowledge gained in making unprecedented advances in natural gas-fueled turbine
technology under the highly successful, predecessor Advanced Turbine Systems (ATS) Program.
This knowledge will be applied to support DOE efforts to develop and deploy near-zero emission
(including carbon dioxide) coal-based energy plants capable of producing both electricity and hydrogen.

U.S. Department of Energy, Office of Fossil Energy, "How Gas Turbine Power Plants Work"
http://fossil.energy.gov/programs/powersystems/turbines/turbines_howitworks.html

A simple cycle gas turbine can achieve energy conversion efficiencies ranging between 20 and 35 percent. With the higher temperatures achieved in the Energy Department's turbine program, future hydrogen and syngas fired gas turbine combined cycle plants are likely to achieve efficiencies of 60 percent or more. When waste heat is captured from these systems for heating or industrial purposes, the overall energy cycle efficiency could approach 80 percent.

U.S. Department of Energy, Office of Fossil Energy, "The Turbines of Tomorrow"
http://fossil.energy.gov/programs/powersystems/turbines/index.html

The Energy Department's Fossil Energy Program is developing key technologies that will enable advanced turbines to operate cleanly and efficiently when fueled with coal derived synthesis gas and hydrogen fuels. Developing this turbine technology is critical to the creation of near-zero emission power generation technologies. This will assist with the deployment of FutureGen plants, an initiative to equip multiple new clean coal power plants with advanced carbon capture and storage (CCS) technology.

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Website prepared for the Edison Electric Institute and the Electric Power Industry Climate Initiative		Prepared by Twenty-First Strategies, LLC. Copyright © 2009. All rights reserved. Last revised: Dec. 11, 2009.