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Modeling of Fischer-Tropsch Synthesis Reactor for GTL Process

Al Taha Motahar, Narges Khatoon | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40616 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Khorasheh, Farhad; Taghikhani, Vahid
  7. Abstract:
  8. There is a need from the natural gas and energy industries to seek for an economically attractive way of converting remote gas reserves into transportable products, such as high quality fuels or petrochemicals. A possible way for the conversion of natural gas to middle distillates is based on a three-step process. Firstly, production of syngas from natural gas. Secondly,catalytic conversion of syngas into hydrocarbons, mostly parafins from C5 to C100. (Fischer-Tropsch (F-T) synthesis). Thirdly, hydrocracking of the heavy paraffinic hydrocarbons to middle distillates. The F-T synthesis step is highly exothermic. In order to control the temperature within the reactor, when considering high capacity plants, the bubble column slurry reactor is the preferred choice when compared to a fixed bed reactor, because of the possibility in the slurry type reactor to achieve almost isothermal conditions. This work deals with the simulation of a commercial size slurry bubble column reactor for catalytic conversion of syngas (CO.H2) to liquid hydrocarbons (Fischer±Tropsch synthesis). The reactor was assumed to operate in the heterogeneous or churn-turbulent flow regime and the hydrodynamics of the slurry bubble column was has been studyed. The reactor model was developed adopting two different classes of bubbles: large bubbles (20±70 mm) which rise through the column virtually in plug-flow, and small bubbles (1±10 mm) which are entrained in the slurry phase (liquid.solid catalyst particles). The slurry phase, together with the entrained small bubbles, was considered completely mixed due to the upward motion of the fast-rising large bubbles. The intrinsic kinetic equation for the consumption rate of syngas, chosen in this work, was that proposed by Yates and Satterfield, which is a Langmuir-Hinshelwood type, which can describe hydrodynamic characteristics and reaction behaviors of the FTS take palace on a Cobalt Catalyst, in slurry bubble column reactors. Mass transfer equation was developed for both reactant (H2 and CO). To obtain higher reactor productivity and higher selectivity of intermediate distillates, proper reaction conditions (such as superficial gas velocity, solid concentration, reaction temperature, reaction pressure, and inlet H2/CO ratio, etc.) should be selected. The simulation results provide necessary data for the reactor design and the process scale-up of the FTS. In this work, as a result of simulation, Concentration profile in different phases, superficial gas velocity in order to syngas conversion and gas hold up change along reactor was obtained. With the steady-state simulation results and ASF selecivity model, products distribution in the reactor outlet was described. Simulations were carried out in commercial scale SBC reactors under various conditions as a reperesentative of industrial practice. The influences of the superficial gas velocity and the catalyst concentration on syngas conversion and reactor productivity were discussed (superficial gas velocity = 0.15-0.45 m/s, catalyst concentration = 0.2-0.4). A sensitivity analysis was also performed to study the influence of inter-phase mass transfer and kinetics on the reactor productivity.

  9. Keywords:
  10. Fischer-Tropsch Synthesis ; Modeling ; Gas to Liquid (GTL)Process ; Slurry Bubble Column Reactor

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