A heat recovery steam generator (HRSG) produces steam by recovering waste heat from gas turbine exhaust and is a key component for improving the efficiency of combined-cycle power generation systems. Flow-accelerated corrosion (FAC) causes localized wall thinning in HRSG evaporator tubes. Although FAC is generally associated with low-pressure evaporators, it can also occur in intermediate-pressure (IP) evaporators depending on local flow and evaporation characteristics. This study numerically investigated the effects of flue-gas-side flow control structures on FAC-related heat loads and evaporation characteristics in the IP evaporator of a commercial 530 MWe combined-cycle power plant. Computational fluid dynamics simulations were performed for a reference configuration and three modified configurations involving different arrangements of baffle boxes and seal plates. Flue gas flow and heat transfer were analyzed to determine the heat transfer rate of individual tubes, while a separate single-phase water flow analysis was used to obtain the feedwater distribution and calculate the outlet quality and velocity. In the reference configuration, flow concentration near the baffle boxes and seal plates increased the heat load of specific downstream tubes. The maximum outlet quality and velocity were 0.676 and 1.36 m/s, respectively, and these locations corresponded to major FAC wall-thinning locations observed in the actual HRSG. Removing only the seal plates reduced the flow concentration near the side walls and decreased the high outlet quality of the adjacent tubes. Removing both the side baffle boxes and seal plates increased the flow along the side walls, resulting in concentrated heat loads and higher outlet quality and velocity in the adjacent tubes. In contrast, adjusting the baffle box geometry to the staggered tube arrangement reduced flow concentration near both the side and central baffle boxes and most effectively alleviated the high tube outlet quality and velocity at the major FAC wall-thinning locations. These results demonstrate that appropriate modification of the flue-gas flow control structures can improve the heat-load and evaporation distributions in IP evaporator tubes and thereby mitigate the flow and evaporation conditions associated with FAC.
 

Heat recovery steam generator,Flow-accelerated corrosion,Intermediate-pressure evaporator,Computational fluid dynamics (CFD),Heat transfer