Improvements in chemical processes are regularly achieved as a result of the introduction of new internal geometries within reactors. Conventionally, fixed bed reactor models use an overly simple description of hydrodynamics, based on a “piston”-type reactor configuration. This description demonstrates limitations when seeking to model certain specific technologies and their impact on process performance.
Coupling complex hydrodynamics with kinetic models that are themselves complex makes their incorporation in CFD codes difficult and generates prohibitive calculation times. For reactor simulation requirements, it was therefore necessary to develop a methodology for obtaining sufficiently representative modeling of hydrodynamics, and which is compatible with the use of complex kinetic models. To achieve this, a rigorous approach was used to obtain a one-dimensional representation of the impact of hydrodynamics on the basis of 3D CFD simulations. To construct these one-dimensional models taking into account hydrodynamics, the internal age distribution transport theorya inside the reactor has been used.
For example, a Euler-Euler two-phase model was used to model a fixed-bed reactor (figure), subject to poor liquid distribution due to partial blocking of
a distributor tray(1). In order to assess the impact of this problem on reaction performance in the case of hydrotreatment, chemical species transport simulations were performed. Ultimately, the 1D multi-output piston-dispersion model provides excellent performance prediction, equivalent to complex 3D simulations of the reactor.
a - Which consists in calculating the average age of the molecules at every point of the reactor
(1) M. Fourati, F. Augier, Y. Haroun, Canadian Journal of Chemical Engineering, Vol. 95, No 2, 2017, pp. 222-230.
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