CFD Simulations of Heat Recovery Steam Generators Including Tube Banks

Abstract

CFD (Computational Fluids Dynamics) simulations of HRSGs (Heat Recovery Steam Generators) can improve and optimize the performance of combined cycle power plants. For example CFD results can help to analyze the effect that different working conditions such as changes in power or fuel quality can have on the uniformity of the flow. A uniform flow is important because the tubes inside the HRSG are more susceptible to corrosion and rupture when the flow distribution is strongly nonuniform. An accurate modeling of the flow and heat transfer characteristics is paramount in order to obtain a realistic representation of the process. However, a big problem in CFD modeling of HRSGs, or any equipment with tube-and-shell heat exchangers, is the different length scales of the equipment, which vary from a few centimeters for the tubes diameter to tens of meters for the HRSG vertical height. The problem is that these different length scales would require a very large computational mesh and consequently a very expensive simulation. To overcome this problem, a common approach in CFD simulations of HRSG has been to model the tube banks following a porous media approach, where the tubes are represented by a volume with a porosity factor which gives the volume fraction of fluid within the porous region. Using this model a pressure drop and the total heat absorbed due to the presence of the solid tubes is calculated. However, due to the recent advances and relatively lower prices of computer equipment it is now possible in a relatively economical way to explicitly include the tube banks in the CFD models of HRSGs. In this study a CFD model of a HRSG is presented where the tube banks are included in the geometric model. Results using this model show the fluid flow and heat transfer between the numerous tubes. A further advantage, in contrast to the porous media model, is that the flow inside the tubes is also modeled which gives a more realistic representation of the phenomena inside the tubes.

Analysis of Fired Equipment within the Framework of Low-Cost Modelling Systems

“…Models with individual HRSG tubes were compared by Galindo-García et al [18] with models that replaced tube bundles with porous layers. In order to decrease the number of cells, Galindo-García et al [18] relied on a non-conformal mesh, with individual parts of HRSG being linked by an interface. Additional shortening of evaluation time brings a steady state simulation.…”

Method for CFD facilitated pressure rise calculation due to deflagration in heat recovery steam generator

“…Time‐dependent simulations are developed as well to study the transient behavior. Most of the HRSG CFD studies have been focusing on looking at the flow patterns, pressure drops, and heat transfer; and not many CFD studies are performed to evaluate the fuel distributions and accumulations in a transient combined cycle shutdown or startup process. It is also noted that a commercial software FLACS is developed specifically for modeling explosion.…”