Relating gas turbine performance to combined cycle efficiency

Abstract: The gas turbine has been around for over a century, providing power for a variety of applications. The efficiency, i.e. the amount of power produced per kilogram of fuel provided, has increased steadily over the years and is today greater than 44 percent in a state of the art gas turbine. For electricity production the efficiency can be increased further by combining the gas turbine with a steam turbine. The energy in the hot exhaust gases can be used to boil water into steam, which can then be used to drive a steam turbine producing additional electricity. In a combined cycle the efficiency can reach 63-64 percent with current technology. These power plants are expensive to operate primarily due to the fuel prices, which heavily drives the need for even higher efficiency. This is why companies operating older power plants often consider upgrading their components. When an upgrade is considered there is often an information gap between the OEM (original equipment manufacturer) and the buyer, in this case the plant owner. If the plant is not delivered as a turnkey by a single OEM, parts and components are purchased from different OEMs specialized on the specific equipment, leading to a situation where the OEM have limited knowledge about the environment in which their equipment operates. Commonly the solution to this is to create models and apply extensive heat and work balance equations to calculate the impact on the plant following an upgrade of a component. This is a time consuming and complicated task which also makes it unnecessarily expensive since an expert has to be involved to perform the calculations. In this report a method of predicting the combined cycle efficiency change is presented. It is a compact formulation which has the potential to speed up the process considerably. This could provide a tool for the OEM to quickly be able to provide an answer to the customer, regarding the potential efficiency increase.