Modeling of Start-Up Behavior of Combined Cycle HRSGs

Abstract

A thorough understanding of boiler performance during start-up is essential in the design and operation of Heat Recovery Steam Generators (HRSGs). It is during this time interval that the boiler may be subjected to maximum thermal and pressure gradients. Repeated exposure to corresponding stresses may lead to the fatigue failure of the material. Despite its importance, not enough work has been done on this topic. The main objective of this research is to analyze the performance characteristics of HRSG during start-up with the help of a mathematical model. The main characteristics of interest are the steam flow, steam pressure, steam temperature and water level in the drum. The behavior of these parameters is studied during start-up at the normal operating conditions at different positions of the diverter damper, the vents and the drains. Since the superheater and evaporator sections are exposed to maximum gas temperatures, only these two sections are considered in the analysis although the given methodology could be applied to include other sections as well. Finally, a practical application of the proposed model is discussed with the help of a numerical example.