Efficiency fired combined cycle turbines

Gas turbine-based power plants, particularly natural gas-fired cogeneration and combined-cycle faciUties, have proven to be highly rehable, efficient, and environmentally attractive. Advances in machine design, more efficient plant integration, and optimistic forecasts for the availabiUty of affordable natural gas worldwide have boosted the appeal of these systems for both base-load and peaking service. 

A 165-MW-class gas turbine/generator has been introduced by another manufacturer. This machine, also developed by scaling up a proven design, features a simple-cycle efficiency of 37.5% a turbine inlet temperature of 1235°C a pressure ratio of 30 1, up from 16 1 on the previous generation and an output of 165 MW for gas fuel firing under International Standards Organization (ISO) conditions (101 kPa, 15°C (14.7 psia, 59°F)). A combined-cycle facihty based around this machine could achieve efficiencies up to 58% or a heat rate of about 6209 kj/kWh (5885 Btu/kWh). 

At least two manufacturers have developed and installed machines rated to produce more than 210 MW of electricity in the simple-cycle mode. In both cases, the machines were designed and manufactured through cooperative ventures between two or more international gas turbine developers. One 50-Hz unit, first installed as a peaking power faciUty in France, is rated for a gross output of 212 MW and a net simple-cycle efficiency of 34.2% for natural-gas firing. When integrated into an enhanced three-pressure, combined-cycle with reheat, net plant efficiencies in excess of 54% reportedly can be achieved. 

The new marketplace of energy conversion will have many new and novel concepts in combined cycle power plants. Figure 1-1 shows the heat rates of these plants, present and future, and Figure 1-2 shows the efficiencies of the same plants. The plants referenced are the Simple Cycle Gas Turbine (SCGT) with firing temperatures of 2400 °F (1315 °C), Recuperative Gas Turbine (RGT), the Steam Turbine Plant (ST), the Combined Cycle Power Plant (CCPP), and the Advanced Combined Cycle Power Plants (ACCP) such as combined cycle power plants using Advanced Gas Turbine Cycles, and finally the ITybrid Power Plants (HPP). 

Natural gas also has an efficiency advantage in electricity generation. The economic and operational superiority of gas-fired combustion turbines and combined-cycle machines (and prospectively, the superiority of gas-powered fuel cells) relative to coal-and nuclear-powered steam turbines made the combination of natural gas and natural gas turbines the supply favorite of most electric utilities in the 1990s. 

For a modern gas-fired power station in the UK the electrical efficiency is about 45% and for a coal-fired station about 37%. There are combined cycle plants in which the waste heat from the gas turbines is used to produce steam that in turn drives a steam turbine generator. Such combinations, which are... 

Combined-Cycle Power Plant - A power plant that uses two thermodynamic cycles to achieve higher overall system efficiency e.g. the heat from a gas-fired combustion turbine is used to generate steam for heating or to operate a steam turbine to generate additional electricity. 

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