Gas Turbine Life Extension: A 655 MW Combined Cycle Power Plant User’s Experience

Gujarat Paguthan Energy Corporation Pvt. Ltd. (GPEC) is operating a Combined Cycle Power Plant, located near Paguthan in the state of Gujarat, India. It is a dual fuel 655MW combined cycle power station consisting of three Heavy Duty Industrial Gas Turbines coupled with three Heat Recovery Steam Generators and one Steam Turbine. In a combined cycle plant, Gas Turbine is the single most critical piece of equipment & costliest to maintain. Maintenance cost of GT can be as high as 85% of the total maintenance cost of a combined cycle power station. It therefore becomes important for a plant operator not only to optimise the maintenance cost but also to look for possible extension in the life of the engine. OEM inherently builds in a factor of safety and coupled with the site operating conditions it is a question of how much more can be squeezed out of a component & the engine as a whole. GPEC’s experience of getting life assessment done on 6 numbers of turbine blades and also making an experience based risk assessment of various hot gas path and critical components is discussed in this paper. The life assessment, for a user, has to basically answer two questions: 1) Can the interval between outages of GT be extended? in other words — How long can the GT be run before taking a planned shutdown (Combustion Inspection or Hot Gas Path Inspection or Major Inspection)? 2) Can the component be refurbished and reused? in other words — How long can a component be used before discarding? Decision for life extension is taken on the basis of the design criteria & OEM’s recommendation, operating experience of self & other users and, results of life assessment testing specially of hot gas path components. A risk assessment table is generated which gives a picture of the possibility of engine life extension and in particular the possibility of extension in running hours between outages. GPEC’s experience, from both technical and commercial point of view, with regard to extending running hours beyond standard recommendation & analysing right refurbishment requirements for hot gas path components to further extend the running hours, is put up in this paper.