Hydrodynamic, Mass Transfer Parameters and Modelling of Slurry Bubble Column and Ebulating Bed Reactors Operating under Fischer-Tropsch Conditions
Laurent Sehabiague1, Mariela Sanoja1, Yannick J. Heintz1, Romain O. Lemoine1, Arsam Behkish1, Rachid Oukaci2, and Badie I. Morsi1. (1) Chemical and Petroleum Engineering, University of Pittsburgh, 1249 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA 15261, (2) Energy Technology Partners, Pittsburgh
Since its discovery in 1920's, Fischer-Tropsch synthesis (FTS) has been carried out in a fixed bed reactor (ARGE), a circulating fluidized bed (Synthol), and a "Fixed Fluidized bed" reactor, which is known as the "Sasol Advanced Synthol Reactor" (SASR). Slurry bubble column reactors (SBCRs) and Ebulating bed reactors (EBRs) for Fischer-Tropsch synthesis were reported to have several advantages over fixed bed reactor technology. For instance, SBCR or EBR enjoys a much higher "online factor" when compared with the ARGE reactor, which operates in short cycles due to catalyst deactivation and the consequence drop of wax yield and quality. Also, recent studies have shown that the SBCR is the most cost effective FTS technologies directed towards the production of middle distillates. The present study focuses on the determination of the equilibrium solubility (C*), volumetric liquid-side mass transfer coefficient, (kLa), gas holdup, (εG) and the bubble Sauter mean diameter, (dS) for N2 and He (surrogates of CO and H2 respectively) in Fischer-Tropsch products (Polyalphaolefins and wax) in the presence and absence of Fischer-Tropsch catalyst (cobalt). The data were obtained in a 4-Liters Zipper-Clave stirred tank reactor and in a pilot-scale slurry bubble column reactor of 0.3-m in diameter and 3-m high, operating under Fischer-Tropsch conditions. The transient physical gas absorption technique was used to determine kLa, the manometric method is used to calculate the gas holdup, and the Dynamic Gas Disengagement (DGD) technique was employed to determine the bubble size and bubble size distribution. The effects of the pressure, temperature, catalyst loading, and superficial gas velocity on the reactor behavior were investigated and an algorithm was developed to predict the hydrodynamics and mass transfer parameters in SBCRs for FTS. This algorithm, along with available reaction kinetics and heat transfer characteristics, was used in a comprehensive computer model in order to predict the effects of reactor geometry and operating conditions, such as reactor diameter, length, superficial gas and slurry velocities, temperature, pressure, syngas composition and catalyst loading on the performance of SBCRs and EBRS operating under FTS conditions. The model was also used to scaleup and optimizes SBCRs and EBRS for FTS with iron and cobalt-based catalysts.