Theoretical study of the application of the outlet diffuser of a gas turbine as a steam circuit superheater of a combined gas-steam plant

Abstract

Currently, thermal insulation of GTU output diffusers uses insulation of their inner surface. This is an expensive and complicated technological procedure. For gas turbines as part of CCGT, in order to reduce the cost of insulation and at the same time increase the useful power of the turbine, cooling the diffuser outer surface with a steam stream of a steam circuit can be an alternative way of internal insulation. Steam and gas parameters of a combined cycle plant with a CCGT-450T, as well as the results of experimental and computational studies of the GTU SGT5-3000E gas turbine exhaust channel model were used. The calculations of the efficiency of the surface cooling of the diffuser with the steam coming from the steam circuit were carried out using the analytical method. A scheme of a superheater located on the outer surface of the GTU outlet diffuser operating in a combined cycle is proposed. Analytic evaluation of its effectiveness showed that the surface area of the GTU diffuser of the type SGT5-3000E is sufficient to provide the necessary overheating of low-pressure steam. Installation of such a heat exchanger using the outer surface of the diffuser provides a decrease of the temperature of its outer wall from 537 to 200 оC. The study validity is confirmed by a patent for an invention. It has been established that the use of the outer surface of the GTU outlet diffuser instead of the heat exchange surface of the low pressure superheater of the utilizer boiler can be applied at CCGT unit to reduce heat and hydraulic losses in the diffuser path and in the utilizer boiler path.