HRSGs for Combined Cycle Plants: Design Considerations and Life Consumption Estimation Using Dynamic Software

Today’s Heat Recovery Steam Generators are exposed to more severe operation than just running at a base load. The deregulation of the electric generation industry has resulted in an increase of merchant plants that are required to supply electrical power to the grid as needed and when needed. The plants will be coming on line with minimal notice. This puts a strain on the HRSG and unless properly designed and operated to withstand the quick start-ups and shut downs, the integrity will be compromised. Fast starts result in achieving full load revenues much sooner including the cost of high start-up emission reduction. Basic definition of a fast start is to have about 66% of the plant power available in 30–50 minutes and full plant power available in 60–75 minutes with a hot or warm steam turbine. This paper describes various mechanisms which affect the integrity of the boilers. These include the damage mechanisms, their effect on various parts and how to control them. The causes and the end results of these damage mechanisms are not the same for all components of the boiler. This analysis results in deciding which components need further review of the critical components. Detailed analysis of the critical components under the specified operating conditions can lead the nature and origin of the forces causing adverse impact on the life of the component. Once the failure mechanism is determined, means to eliminate or reduce the impact can be developed. This paper also describes the Life Consumption Estimation software which uses the data directly retrieved from the plant data acquisition system, thus eliminating the tedious task of manual data transmission. Based on the correlations developed by Vogt Power International Inc. (VPI) with the detailed dynamic simulation, Finite Element Analysis and various codes the component consumption is estimated and displayed with the calculated replacement and start-up costs on a continual basis. This gives the plant owners and operators an on line tool to gauge the economic benefits of the aggressive operations in real time.