column reactor for Fischer-Tropsch synthesis ..

Since the discovery of Fischer-Tropsch (F-T) synthesis in 1920's, the technology has been successfully developed up to a commercial stage. The earliest reactor type utilized in Fischer-Tropsch synthesis was a fixed bed (ARGE) and in later stages, a circulating fluidized bed (Synthol) which were both commercially used by SASOL (South Africa). The other development in this technology is the "Fixed bed Fluidized bed" reactor which is commercially known as the "Sasol Advanced Synthol Reactor" (SASR).The alternative to the ARGE (fixed bed reactors, used in the recently commissioned Shell Malaysia plant at Bintulu) operating at low temperature is the slurry bed reactor. This type of reactor allows 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. In addition, a number of studies have shown that among the available Fischer-Tropsch technologies, the most cost effective one is the slurry bed process which is directed towards the production of middle distillates.

Fischer–Tropsch Synthesis in Slurry Bubble Column ..

Modeling of the Fischer-Tropsch synthesis in slurry bubble column reactors.
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(2012)Modeling, Scaleup and Optimization of Slurry Bubble Column Reactors for Fischer-Tropsch Synthesis. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

bubble column reactor for Fischer-Tropsch ..

The hydrodynamic and mass transfer parameters of gaseous mixtures of N2 and He, used as surrogate components for CO and H2 respectively, were measured in three Fischer-Tropsch (F-T) liquids in the presence and absence of solid particles (Al2O3, FeOx). The data were obtained in a pilot-scale (0.29 m ID and 3 m high) slurry bubble column reactor (SBCR) within wide ranges of operating conditions covering those of F-T synthesis. The manometric method, the Transient Physical Gas Absorption technique and the Dynamic Gas Disengagement technique were employed to obtain the gas holdup, the volumetric liquid-side mass transfer coefficient and the gas bubbles Sauter mean diameter, respectively. Statistical experimental design was used to investigate the effect of these operating conditions on those parameters. The gas-liquid interfacial area appeared to control the mass transfer behavior of the SBCR operating in the churn-turbulent flow regime.
A user-friendly simulator based on a comprehensive computer model for F-T SBCRs, taking into account the hydrodynamics, kinetics, heat transfer, and mass transfer was developed. Novel hydrodynamic and mass transfer correlations, covering wide ranges of reactor geometry, gas distributor types, and operating conditions were established using our experimental data and those available in the literature; and a new relationship between the axial dispersion of large gas bubbles and their average diameter were developed and included in the reactor model. All reactor partial differential equations, equation parameters along with the pertinent boundary conditions were simultaneously solved numerically using the finite elements method. Different kinetic rate expressions available in the literature for iron and cobalt-based catalysts were included in the simulator which was used to predict the effects of the operating conditions, such as catalyst concentration, pressure, temperature, H2/CO ratio, and superficial gas velocity on the performance of a F-T SBCR. The predictions showed that the performance of the reactor was strongly dependent on the catalyst type and the kinetic rate expression used. The simulator was also used to optimize the reactor geometry and operating conditions in order to produce 10,000 barrels per day of synthetic hydrocarbons.

Modeling of Fischer-Tropsch synthesis in bubble column slurry reactors: numerical analysis.
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These are used for high-temperature Fischer–Tropsch synthesis ..

This research project focuses on the determination of the volumetric liquid-side mass transfer coefficient, (), gas holdup, () and the bubble Sauter mean diameter, () for N2 and He in different F-T cuts (waxes) in the presence and absence of Fischer-Tropsch catalyst (iron and cobalt). The data are obtained 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 is used to determine , the manometric method is used to calculate the gas holdup, and the Dynamic Gas Disengagement (DGD) technique is employed to determine the bubble size and bubble size distribution. The Central Composite Statistical design technique is employed to investigate the effects of the pressure, temperature, catalyst loading, and superficial gas velocity on the reactor behavior. The hydrodynamic and mass transfer parameters to be obtained are empirically and statistically correlated and the resulting correlations can be used for F-T reactors scaleup.

Slurry Reactors for Gas-to-Liquid Processes: A Review

An SBCR operates preferentially in the churn turbulent flow regime for best distribution of catalyst particles as well as minimizing mass and heat transport restrictions. In the churn turbulent flow regime there is a mixture of smaller and larger bubbles that undergo frequent beak-up and coalescence. This mechanism prevents serious film transport restrictions on the catalyst slurry interphase, and with catalyst particles below 200 μm the H2/CO ratio as well as water vapor pressure can be assumed constant over the entire reactor volume. Thus, deactivation should be more easily controlled compared to other reactor configurations. Further details on operation of SBCRs can be found in the book on Fischer-Tropsch technology by Steinberg and Dry [].

Chemical Reaction Engineering - Industrial & …

Reasons for selection of a slurry bubble column reactor for Fischer-Tropsch synthesis include: (1) a comparatively simple construction; (2) high space-time-yield and catalyst efficiencies; (3) high heat transfer coefficients; and (4) isothermal conditions. Continuous catalyst regeneration of a slip stream is a viable option. Challenges include minimizing catalyst particle attrition and efficiently separating catalyst from the products. Efficient liquid and gas back-mixing and a high exit water concentration lead to high selectivity; the high exit water concentration is beneficial in reducing coke deposition. On the other hand reactant concentrations are lower than the average of a fixed-bed reactor resulting in comparatively lower global rates. Single pass conversion is typically in the range of 55–65%, significantly higher than for fixed-bed. Conversion is limited by the feasible height of the reactor, but there is also an upper conversion limit above about 75–80% for which the water-gas-shift activity will lead to possible catalyst oxidation and a steep increase in CO2 yield []. Naturally, extensive recycle of syngas in the FT-section of the plant is necessary to obtain a very high overall CO conversion.