The combined-cycle system provides flexibility with features that include:

 High Thermal Efficiency

Combined cycle thermal efficiency is higher than that of other conventional power generation systems

Low Installed Cost 

Combined-cycle equipment is pre-engineered and factory packaged to minimize installation time and cost. All major equipment (gas turbine generator, heat recovery steam generator [HRSG], and steam turbine generator) is shipped to the field as assembled and tested components. Auxiliary equipment, such as condensers, can be shipped factory-tubed and hydro-tested.

      This greatly reduces the inventory of parts that must be managed in the field and minimizes installation cost. Though combined-cycle equipment cost is higher than that for conventional steam plants due to pre-engineering, combined-cycle plant installation costs are significantly lower, resulting from the reduced installation cycle.

Fuel Flexibility 

Combined-cycle plants operate efficiently by burning a wide range of fuels, ranging from clean natural gas and distillate oil fuels to ash bearing crude oil and residual oil fuels.

Operation with coal-derived gas fuels has been applied in many commercial sized, combined-cycle systems (IGCC).

Flexible Duty Cycle 

Combined-cycle systems provide flexibility in operation for both base load and mid-range duty with daily startup.

Gas turbines in multi-shaft, combined-cycle configuration can be started quickly, bringing about two thirds of plant power on-line, typically in less than 60 minutes.

Combined-cycle plants also provide efficient operation at part load, particularly for multiple gas turbine combined-cycle systems. Modulating compressor inlet guide vanes are standard features of many gas turbine models, enabling high efficiency operation at part load through reduction in turbine airflow. This is accomplished at nearly constant turbine exhaust temperature, so that design steam conditions and low stack loss can be maintained to provide excellent part-load efficiency.

Short-Installation Cycle 

Combined cycle plants can be installed and operated in less time than that required for conventional steam plants. Again, this is primarily due to the pre-engineering and packaging of major components in the factory. Phased installation of the plant, when gas turbines are installed and operated in the simple-cycle mode during the steam-cycle equipment installation, enables the user to generate power and revenue in as little as a year from order date. 

High Reliability/Availability 

High reliability operation results from evolutionary design development that improves parts and components, and quality manufacturing programs that offer operational factory testing.

High availability is achieved through development of sound operation and maintenance practices, which reside principally with the user. Manufacturer’s experience and recommendations also contribute to this feature.

Reduced Emissions and Fuel Consumption

Combined cycle plants use less fuel per kWh and produce fewer emissions than conventional thermal plants, thereby reducing the environmental damage caused by electricity production.

Compared with a coal-fired plant installed with the latest clean coal technology, the burning of natural gas in combined cycle plants is much cleaner. Combined cycle plants produce no sulfur and virtually no particulate matter; they reduce nitrous oxide emissions by up to 90 percent and carbon dioxide by 60 percent.