METHOD AND APPARATUS FOR STEAM TURBINE START-UP IN COMBINED CYCLE POWER PLANT
Publication Date: 2012-Dec-31
The IP.com Prior Art Database
The present invention relates generally to improving the overall efficiency of combined cycle power plants (CCPPs), and more particularly to improving cycling and start-up capabilities of steam turbines in CCPPs. The CCPP comprises a steam turbine with an electric start-up. The invention provides for improvement of thermal performance and operational flexibility of a CCPP. This invention provides for continuing efficiency improvements on frequently cycling CCPPs while minimizing the capital investment to achieve the efficiency improvements. The CCPP comprises a plant master controller, a gas turbine, a steam turbine, turbine controllers, steam generators, a static starter, a condenser, a heat recovery steam generator, control valves and a pump.
The present invention relates generally to improving the overall efficiency of combined cycle power plants (CCPPs), and more particularly to improving cycling and start-up capabilities of steam turbines in CCPPs.
The increased use of combined cycle power plants (CCPPs) for power generation over the past decade is attributed to the high efficiencies, short execution times and relatively low investment costs. With the ever increasing number of power plants, the price of fuel continues to rise. Further, many power plants initially planned to have base load role have to shift to the load regime of intermediate or load following power plants. The challenge presented due to rise in fuel price and the capacity factor stimulated development of technology that improves plant flexibility, such as frequent cycling and fast start-up capabilities, without compromising plant service life or plant efficiency.
However, equipment wear and tear due to a CCPP on/off and load cycling remains a challenge and is a significant production cost component. For example, every time a CCPP is brought on-line, shutdown, or used for load following, the gas turbines, steam turbines, heat recovery steam generators (HRSGs), steam piping, and auxiliary components go through large thermal and pressure cycles. Further, expansion and contraction of the components of the CCPP leads to thermal and mechanical fatigue damage. Other phenomena, such as corrosion fatigue and water chemistry transients, creep, creep/fatigue interaction, erosion, wear, and vibration also contribute to accelerated life expenditure of critical components. The production cost component due to fast start-up and frequent cycling requires proper unbundling and quantification. One problem is that the production cost component due to fast start-up and frequent cycling is still not well understood or accounted for by most power plant owners.
A similar situation exists in the HRSG when the duct burner is activated or shut off, or when the turbine is dispatched in a load following mode. Subtle changes in temperature occur among the individual tube circuits causing additional thermal/mechanical fatigue cycles. Since HRSG components are densely packed and rigidly supported to optimize the amount of heat recovered from the turbine exhaust, flexing of tube-to-header connections and transfer piping nozzles impose huge stresses on connections, ultimately resulting in cracking and tube failures. In addition, the steaming of water-cooled components and chemical attack of exposed metal beneath internal deposits lead to further damage.
Some CCPPs are better designed for only cycling than others. Specifically, some designs for the CCPPs are either inefficient or the service duty/ramp rates are so severe that the HRSGs experience forced outages within a hundred on/off cycles. Other CCPPs only cycle on a daily basis without major problems, e...