Power to Fuels: Dynamic Modeling of a Slurry Bubble Column Reactor in Lab-Scale for Fischer Tropsch Synthesis under Variable Load of Synthesis Gas (original) (raw)
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Progress Towards Modeling of Fischer Tropsch Synthesis in a Slurry Bubble Column Reactor
2010
The Hybrid Energy Systems Testing (HYTEST) Laboratory is being established at the Idaho National Laboratory to develop and test hybrid energy systems with the principal objective to safeguard U.S. Energy Security by reducing dependence on foreign petroleum. A central component of the HYTEST is the slurry bubble column reactor (SBCR) in which the gas-to-liquid reactions will be performed to synthesize transportation fuels using the Fischer Tropsch (FT) process. SBCRs are cylindrical vessels in which gaseous reactants (for example, synthesis gas or syngas) is sparged into a slurry of liquid reaction products and finely dispersed catalyst particles. The catalyst particles are suspended in the slurry by the rising gas bubbles and serve to promote the chemical reaction that converts syngas to a spectrum of longer chain hydrocarbon products, which can be upgraded to gasoline, diesel or jet fuel. These SBCRs operate in the churn-turbulent flow regime which is characterized by complex hydro...
Modeling of the Fischer–Tropsch synthesis in slurry bubble column reactors
Chemical Engineering and Processing: Process Intensification, 2008
A multicomponent mathematical model is developed for a large-scale slurry bubble column reactor operating in the heterogeneous flow regime for the Fischer-Tropsch synthesis (FTS). In the heterogeneous flow regime, the gas phase is modeled using a two-bubble class hydrodynamics model. The reactor model takes into account the detailed kinetics model of the FTS and water gas shift reaction, which can describe hydrodynamic characteristics and reaction behaviors of the FTS in slurry bubble column reactors. Superficial gas velocity decreases along the reactor height due to the gas volume contraction. With the FTS reaction being strengthened, the extent of the gas volume contraction becomes more severe. The values of gas volume contraction factor from model simulation are between −0.53 and −0.65. 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 H 2 /CO ratio, etc.) should be selected. The simulation results provide necessary data for the reactor design and the process scale-up of the FTS.
CFD modeling of slurry bubble column reactors for Fisher–Tropsch synthesis
Chemical Engineering Science, 2009
Industrial bubble column reactor for Fischer-Tropsch (FT) synthesis includes complex hydrodynamic, chemical and thermal interaction of three material phases: population of bubbles of different sizes, liquid and catalyst particles suspended in liquid. To simulate FT bubble column, a Computational Fluid Dynamics model is described here. The model is based on Eulerian multifluid formulation and accounts for the following important phenomena. Turbulence is modeled by ε − k model. Bubble size distribution is predicted by the Population Balance (PB) method. Experimentally observed influence of catalyst particle concentration on bubble size distribution is theorized to be linked to catalyst particle induced modification of turbulent dissipation rate. A simple scaling modification to dissipation rate is proposed to model this influence. Additional mass conservation equations are introduced for chemical species associated with phases. Heterogeneous and homogeneous reaction rates representing simplified FT synthesis are taken from literature and incorporated in the model.
Comparative Analysis of Models for Fischer-Tropsch Synthesis in Slurry Reactors
IJSER, 2019
Two approaches identified in literature for modeling slurry bubble column reactors for Fischer-Tropsch synthesis is presented and compared in this work. The first approach, Uniform Bubble Model (UBM) assumes the gas bubbles moving up the reactor are of uniform sizes, while the second model termed Large-Small Bubble model (LSBM) takes cognizance of the presence of large and small bubbles. It is assumed that both the gas and liquid phases are axially dispersed. Reaction and hydrodynamic parameters are estimated and the sets of equations obtained are solved using MATLAB pdepe solver for hydrogen gas conversion. Results obtained for a typical industrial scale reactor (30m long, 8m in diameter, gas entering at 0.35m/s and 35 vol% catalyst load) indicates that the models (UBM and LSBM) can adequately predict the reactor's performance for gas conversion. The UBM predictions were persistently greater than the LSBM values. Different equations for gas holdup were incorporated in the models and compared for various reactor constraints. The results revealed that the disparity in the models prediction may be related to the method used in deriving the gas holdup value. The results also showed that taller reactors, higher catalyst loadings and lower gas velocity leads to improved conversion.
A user-friendly simulator based on a comprehensive computer model for slurry bubble column reactors (SBCRs) for Fischer-Tropsch (F-T) synthesis, taking into account the hydrodynamics, kinetics, heat transfer, and mass transfer was developed. The hydrodynamic and mass transfer data obtained in our laboratories under typical F-T conditions along with those available in the literature were correlated using Back Propagation Neural Network and empirical correlations with high confidence levels. The data used covered wide ranges of reactor geometry, gas distributor, and operating conditions. All reactor partial differential equations, equation parameters and boundary conditions were simultaneously solved numerically.
Mathematical Modeling of Fischer-Tropsch Synthesis in an Industrial Slurry Bubble Column
International Journal of Chemical Reactor Engineering, 2009
The increase in society's need for fuels and decrease in crude oil resources are important reasons to make more interest for both academic and industry in converting gas to liquids. Fischer-Tropsch synthesis is one of the most attractive methods of Gas-to-Liquids (GTL) processes and the reactor in which, this reaction occurs, is the heart of this process. This work deals with modeling of a commercial size slurry bubble column reactor by two different models, i.e. single bubble class model (SBCM) and double bubble class model (DBCM). The reactor is assumed to work in a churn-turbulent flow regime and the reaction kinetic is a Langmuir-Hinshelwood type. Cobalt-based catalyst is used for this study as it plays an important role in preparing heavy cuts and the higher yield of the liquid products. Parameter sensitivity analysis was carried out for different conditions such as catalyst concentration, superficial gas velocity, H2 over CO ratio, and column diameter. The results of the S...
2008
This paper describes the development of a computational multiphase fluid dynamics (CMFD) model of the Fischer Tropsch (FT) process in a Slurry Bubble Column Reactor (SBCR). The CMFD model is fundamentally based which allows it to be applied to different industrial processes and reactor geometries. The NPHASE CMFD solver [1] is used as the robust computational platform. Results from the CMFD model include gas distribution, species concentration profiles, and local temperatures within the SBCR. This type of model can provide valuable information for process design, operations and troubleshooting of FT plants. An ensemble-averaged, turbulent, multi-fluid solution algorithm for the multiphase, reacting flow with heat transfer was employed. Mechanistic models applicable to churn turbulent flow have been developed to provide a fundamentally based closure set for the equations. In this four-field model formulation, two of the fields are used to track the gas phase (i.e., small spherical an...
Chemical Engineering Journal, 2011
The Hybrid Energy Systems Testing (HYTEST) Laboratory at the Idaho National Laboratory was established to develop and test hybrid energy systems with the principal objective of reducing dependence on imported fossil fuels. A central component of the HYTEST is the slurry bubble column reactor (SBCR) in which the gas-to-liquid reactions are performed to synthesize transportation fuels using the Fischer Tropsch (FT) process. These SBCRs operate in the churn-turbulent flow regime, which is characterized by complex hydrodynamics, coupled with reacting flow chemistry and heat transfer. Results Our team is developing a research tool to aid in understanding the physicochemical processes occurring in the SBCR. A robust methodology to couple reaction kinetics and mass transfer into a four-field model (consisting of the bulk liquid, small bubbles, large bubbles and solid catalyst particles) consisting of thirteen species, which are CO reactant, H 2 reactant, hydrocarbon product, and H 2 O product in small bubbles, large bubbles, and the bulk fluid plus catalyst is outlined. Mechanistic submodels for interfacial momentum transfer in the churn-turbulent flow regime are incorporated, along with bubble breakup/coalescence and two-phase turbulence submodels. The absorption and kinetic models, specifically changes in species concentrations, have been incorporated into the mass continuity equation. The reaction rate is based on the macrokinetic model for a cobalt catalyst developed by Yates and Satterfield. The model includes heat generation produced by the exothermic chemical reaction, as well as heat removal from a constant temperature heat exchanger. A property method approach is employed to incorporate vapor-liquid equilibrium (VLE) in a robust manner. Physical and thermodynamic properties as functions of changes in both pressure and temperature are obtained from VLE calculations performed external to the CMFD solver. The novelty of this approach is in its simplicity, as well as its accuracy over a specified temperature and pressure range.