Chemical Engineering Science 60 (2005) 7121 – 7130 www.elsevier.com/locate/ces The influence of distributed reactant injection along the height of a fluidized bed reactor Fahad Al-Sherehy, John R. Grace ∗ , Alaa-Eldin M. Adris Department of Chemical and Biological Engineering, University of British Columbia, 2216 Main Mall, Vancouver, Canada V6T 1Z4 Received 30 January 2005; received in revised form 29 May 2005; accepted 27 June 2005 Available online 15 August 2005 Abstract A two-phase model is used to simulate spreading the introduction of reactant feed along the height of a fluidized bed reactor for oxidative dehydrogenation of ethane to ethylene. The reactor model is used to predict the reactor performance for different ethane-to- oxygen molar feed ratios, with premixed and non-premixed feed. The proposed model is used to simulate the premixed feed (without secondary injection), and for distributed feed with secondary injection at one, three and five injection levels above the primary distributor. Predictions from the model are shown to compare favourably with experimental data from an industrial pilot reactor of diameter 97mm. A case study is then employed to explore a wider range of conditions than is possible experimentally. Oxidant distribution is shown to be beneficial in expanding the range of reactant compositions beyond those normally allowed by safety constraints. Distributing the feed over a number of levels improves the reactor performance, especially in reducing the selectivities of undesired by-products. Feeding gas at several levels is generally more promising than introducing feed at a single secondary injection level.  2005 Elsevier Ltd. All rights reserved. Keywords: Fluidization; Jets; Hydrodynamics; Multiphase reactors; Dehydrogenation; Reaction engineering 1. Introduction Many chemical processes involve consecutive reactions with the intermediate being the desired product. One possi- bility to improve the selectivity is to separate the intermedi- ate product from the reaction mixture. Another is to alter the concentration profile by distributed addition of one of the reactants. The latter is not always helpful in improving re- actor performance. The main factors justifying reactant dis- tribution depend on the type of reaction (e.g. parallel/series, reversible vs. irreversible, etc.) and the degree of mixing within the reactor. Several industrial processes have implemented reac- tant distribution along the reactor height. For example, to lower NO x emissions, secondary air is usually added in ∗ Corresponding author. Tel.: +1 604 822 3121; fax: +1 604 822 6003. E-mail address: jgrace@chml.ubc.ca (J.R. Grace). 0009-2509/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2005.06.031 circulating fluidized bed combustors, sometimes also with tertiary air. Staged addition has also been used in bubbling bed combustion (e.g. Bramer, 1995). A similar concept has been implemented in the Sohio process for the produc- tion of acrylonitrile where air enters through the grid and a propylene–ammonia mixture is fed through a sparger lo- cated some distance above the grid (Yates et al., 1987). An- other example is in the partial oxidation of butane to maleic anhydride in a circulating fluidized bed in which catalyst is oxidized in one chamber and reacted with butane in an- other to avoid direct contact of the hydrocarbon with oxygen (Contractor and Sleight, 1988). A second important motivation for distributed-addition of reactant is to maintain the composition of the gaseous mixture outside the explosion limits. The ethane-to-ethylene reaction is typical of this type of reaction. In the oxidative dehydrogenation of ethane, the desired reaction for ethylene production competes with reactions that produce acetic acid and carbon oxides. Stoichiometric relations for the four main