Investigation into the effect of simulating a 3D cylindrical fluidized bed reactor on a 2D plane

2D planar simulations of 3D cylindrical fluidized bed reactors are routinely carried out in order to reduce computational costs. The error involved in this simplification is largely unknown, however, and this study was therefore conducted to quantify this error over a wide range of reactor operating conditions. 2D and 3D simulations were carried out over a wide range of flow conditions in the bubbling fluidization regime by changing the fluidization velocity, bed mass, reaction temperature and particle size. Detailed comparisons revealed that 2D simulations qualitatively behaved similarly to 3D simulations, but over-predicted reactor performance (measured by the degree of conversion achieved) by about 45% on average. Large systematic variations of this error were also observed with changes in all four independent variables investigated. These large errors were due to two primary factors; incorrect predictions of the gas residence time by misrepresentations of the bed expansion and incorrect predictions of the mass transfer by misrepresentations of bubble formation and the splash zone at the top of the expanded bed. The mass transfer error was found to be most influential and was also confirmed as the most important factor to be correctly predicted by CFD simulations. 3D predictions of the mass transfer resistance were further analyzed to identify the particle size as a very influential variable through which the mass transfer characteristics in fluidized bed reactors can be influenced.

Comparisons of the reactor performance returned by 3D cylindrical and 2D planar simulations of a bubbling fluidized bed reactor yielded systematic differences across the parameter space. This is a clear indication that computationally affordable 2D planar simulations of 3D cylindrical fluidized bed reactors can result in significant modelling errors. 2D simulations are therefore recommended only for initial screening studies.Figure optionsDownload as PowerPoint slideHighlights
► 2D planar simulations of 3D cylindrical geometries are often carried out.
► The effects of this simplification were found to be large.
► Reactor performance was about 45% better when simulated in 2D.
► Large systematic differences were also observed across the parameter space.
► 2D simulations should therefore be used with great caution.