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02.04.2018 Modelling in fluidized bed dehydrogenation processes

The experts of Katalizator JSC have developed software for modelling fluidized bed hydrodynamics in dehydrogenation process, which allows quickly solving practical tasks of our customers. The software is unique in that it is based on a mathematical model that takes into account the catalyst circulation in the fluidized bed and models the dynamic distribution of the catalyst along the apparatuses heights.

In industrial paraffin dehydrogenation apparatuses, the hydrodynamic calculations are complicated due to the presence of distribution grids and constant circulation of a microspherical catalyst. Mathematical models applied in commercial software that can be used for CFD[1] modelling often apply a model that does not allow for the catalyst circulation and, therefore, distorts the calculation, which may lead to design defects.

Unlike mathematical models where the fluidized bed exists under static conditions, the software developed by Katalizator JSC uses a model that is adjusted for the catalyst circulation and enables calculations and optimisation of both the fractional composition separately for each dehydrogenation unit and the design of sectioning grids, with allowance for the raw material feed rate, temperatures, and thermal expansions of internal structures. Based on the data from temperature and pressure sensors, the radial temperature distribution can be modelled, which enables predicting cases when inhomogeneous gas and catalyst displacement develops, i.e. bypassing. This effect is clearly noticeable in modelling when temperatures inhomogeneities are arranged vertically, as shown in figure. It can be seen that the raw material flow moves mainly along the left side of a dehydrogenation reactor, and a hot catalyst flows from the distributor largely down along the right and rear parts of the apparatus, thus delivering heat from the regenerator.

Regular audit along with modelling enables predicting and reducing the risk of such situations and also timely developing corrective measures to decrease the effect of bypassing and inverted mixing, which in turn increases production of isobutylene.

Modelling of fluidized bed hydrodynamics in dehydrogenation processes is an integral part of operational excellence. Currently, the Chemical Engineering Department of Katalizator JSC employs almost all methods for designing and optimising dehydrogenation reactors, which have been implemented in industrial production. We are always ready to provide prompt assistance to the enterprises in solving their challenges and keep further improving our methods for the consumers' benefit.

Author: Aleksey Kreiker

Editors: Galina Yastrebova, Roman Artemev, Anastasiya Tarasenko

[1] Computational fluid dynamics