In this tutorial we will get to know another more efficient type of power plant using natural gas as a fuel.
7. Combined Cycle Gas Turbine (CCGT)
When flue gases leave a gas turbine, temperatures are partly still as high as 500 °C. The energy contained in those flue gases is being used in combined cycle gas turbine plants (CCGT-plants), the currently most efficient technology for generating electricity with fossil fuels. In such a power plant a gas turbine is coupled with a steam power process.
One or more gas turbines produce electricity via the combustion of gas or mineral oils. The hot flue gases are then directed into a steam generator. In the steam generator water circulates through a system of tubes, absorbs the heat of the flue gases and evaporates. The steam is then driving a steam turbine, which is also connected to a generator and produces electricity. Using a condenser and a pump, the steam power process is closed.
If natural gas or oil is used in the steam generating process, such a power plant is also called combi-block. In order to achieve the highest possible efficiency, primary energy should be utilized most effectively. The combustion of further fuel during the steam generating process should however be avoided, because it leads to a loss in efficiency.
A CCGT-plant that is optimized for its efficiency, two-thirds of the power capacity should be provided by the gas turbine and one-third by the steam power process.
Such a power plant is able to achieve efficiencies of up to 60 % for electricity only.
Application of CCGT-plants
Due to the higher complexity of a CCGT facility and the more sluggish steam power process, a CCGT-plant suits the production of base and medium load.
Profitability of CCGT-plants compared to coal-fired power plants is however reduced due to high fuel costs for natural gas and low CO2 – prices.
An even more efficient utilization of energy carriers can be achieved with a combined-heat-and-power (CHP) plant. This will however be elaborated on in next week’s tutorial.
