Effects of Steam Reheat in Advanced Steam Injected Gas Turbine Cycles

Steam injection is a well-known principle for increasing gas turbine efficiency by taking advantage of the relatively high gas turbine exhaust temperatures. Unfortunately, performance is not sufficiently improved compared with alternative bottoming cycles. However, previously investigated supplements to the STIG-principle — such as sequential combustion and consideration of a back pressure steam turbine — led to a remarkable increase in efficiency. The cycle presented in this paper includes a further improvement: The steam, which exits from the back pressure steam turbine at a rather low temperature, is no longer led directly into the combustion chamber. Instead, it reenters the boiler to be further superheated. This modification yields additional improvement of the thermal efficiency due to a significant reduction of fuel consumption. Taking into account the simpler design compared with combined-cycle power plants, the described type of an advanced STIG-cycle (A-STIG) could represent an interesting alternative regarding peak and medium load power plants.