The influence of tube and membrane structure on dynamic instability in furnace wall tubes of a fossil fired once-through boiler in a simulated furnace environment

Abstract

A numerical model was developed to investigate dynamic instability in fossil fired once through boilers and the influence of the dynamics of tube and membrane structure furnace wall tubes on the stability boundary was examined. In order to predict density wave oscillation (DWO), the most common type of dynamic instability, a time domain nonlinear analysis approach was used to give a transient flow field in the tubes. The tubes were divided into one-dimensional finite volumes along their lengths and equations of conservation of mass, momentum and energy were discretized to give algebraic equations. The SIMPLE algorithm was adopted to solve these equations. Analysis of two-dimensional transient conduction across a tube-membrane section of each volume was performed concurrently and the resulting heat transfer between tube inner wall and fluid was included in the source term of the energy equation. After verification with results in available literature, the model was applied to a wall tube section of a 700 MW boiler furnace in subcritical once-through condition. The stability boundaries for three types of tube configuration were predicted, and it was found that the dynamics of tube configuration can have a significant effect on the flow instability in the boiler furnace wall tubes.