Fixed-bed Fischer-Tropsch Research Articles

Performance of a multi-tubular Fischer–Tropsch reactor with two catalytic zones of different intrinsic chemical activity

The effect of axial distribution of the intrinsic catalytic activity on the performance of a multi-tubular fixed bed Fischer–Tropsch reactor was investigated.

Effect of mass transfer on the deactivation model and GPLE parameters of Co/γ-Al2O3 catalysts in the Fischer Tropsch synthesis

The activity of catalysts with various sizes was compared in a fixed-bed Fischer–Tropsch reactor under similar operating conditions by determining the deactivation model. Catalyst size had no impact on the type of deactivation model. The smaller catalyst showed a smaller deactivation constant of catalyst (kd) and a lower deactivation rate in the initial stage. The decline in the activities of the catalyst with a mesh size of 40 was lower than the other catalysts, suggesting its higher long-term stability (ass). Larger catalyst sizes led to the fouling of carbon and heavy hydrocarbons, decreasing the specific surface of the catalyst, thus increasing the pore diffusion resistance and further decrementing the catalyst activities.

Experimental and simulation study of the temperature distribution in a bench‐scale fixed bed Fischer–Tropsch reactor

AbstractThe temperature distribution in a bench‐scale fixed bed Fischer–Tropsch reactor using Co‐based catalyst was investigated under conditions of 2 MPa and 458 K at various syngas partial pressures and space velocities. The single‐tube reactor had a diameter of 0.05 m, which is representative of the diameters used in industrial applications. With a special designed temperature measurement, the detailed temperature distribution in a bench‐scale reactor was reported for the first time. The changes of maximum temperature in the bed and hot spot region were discussed at different N2 flow rate and gas hourly space velocity. A 2D pseudo‐homogeneous fixed bed reactor model was developed using ANSYS Fluent. A position‐dependent heat‐transfer coefficient, which considered more accurate in temperature prediction, was applied. The model was validated against both the reaction results and the measured temperatures. The inferred properties within the reactor were analyzed to give insight as to how to increase the reactor production capacity.

Adoption of 3D printed highly conductive periodic open cellular structures as an effective solution to enhance the heat transfer performances of compact Fischer-Tropsch fixed-bed reactors

Heat transfer is universally recognized as a key challenge for the intensification of the Fischer-Tropsch (FT) process in compact fixed-bed reactors. For the first time in the scientific literature we demonstrate experimentally that the adoption of a highly conductive periodic open cellular structure (POCS, 3D-printed in AlSi7Mg0.6 by Selective Laser Melting) packed with catalysts pellets is a promising solution to boost heat exchange in fixed-bed FT reactors. This reactor configuration enabled us to assess the performances of a highly active Co/Pt/Al2O3 catalyst packed into the POCS at process conditions relevant to industrial Fischer-Tropsch operation. Unprecedented performances (CO conversion ≈ 80%) could be thus achieved thanks to an outstanding heat management. In fact, almost flat axial and radial temperature profiles were measured along the catalytic bed even under the most severe process conditions (i.e. high CO conversions corresponding to high volumetric heat duties), demonstrating the effective potential of this reactor concept to manage the strong exothermicity of the FT reaction.The heat transfer of the packed-POCS reactor outperformed both packed-bed and packed-foam reactors, granting smaller radial temperature gradients in the catalytic bed, as well as smaller temperature differences at the reactor wall, with larger volumetric power releases. The strengths of the packed-POCS reactor configuration are its regular geometry, which enhances the effective radial thermal conductivity, and the improved contact between the structure and the reactor wall, which governs the limiting wall heat transfer coefficient.

Effects of process and design parameters on heat management in fixed bed Fischer-Tropsch synthesis reactor

A two-dimensional pseudo-homogeneous model of wall-cooled fixed bed Fischer-Tropsch synthesis (FTS) reactor with Co/Re/γ-Al2O3 catalyst was developed to study the effect of process and design parameters on heat generation and removal characteristics. The influence of liquid-phase formation on heat transport was accounted for by using two-phase correlations. The effect of intraparticle diffusion on heat generation was considered. Detailed numerical simulations were performed to analyze the effect of process and design parameters on the reactor performance in terms of heat management. Results show that thermal behavior of FTS fixed bed reactors is very sensitive and any large disturbances can lead to temperature runaway. Large tube diameters are shown to be particularly unfavorable, with d t >5 cm resulting in axial and radial gradients greater than 20 K and 13 K, respectively. The importance of detailed reactor modeling when designing and optimizing FTS fixed bed reactors is highlighted.

Parametric Study and Multiobjective Optimization of Fixed-Bed Fischer–Tropsch (FT) Reactor: The Improvement of FT Synthesis Product Formation and Synthetic Conversion

A mathematical model of a fixed-bed reactor for Fischer–Tropsch synthesis (FTS) over 37% Co/SiO2 catalyst was developed to investigate the performance of the whole process for products’ selectivity and syngas conversion. The model was capable of calculating the changes of reactant and products’ concentrations, partial pressures, conversion, and selectivity. In a previous study, a series of combined novel FT and water gas shift (WGS) reaction mechanisms (eight elementary FT reaction pathways along with seven WGS kinetics models) were developed in order to calibrate and validate the mathematical model along with reaction kinetics at different experimental conditions. Such mathematical models with reaction networks can be used as a key tool to emphasize the most significant facts of FTS catalysis and chemistry. Integration of the global search optimization algorithm with the developed model was explained for estimation of kinetics parameters. Data analyses were carried out to ensure that the predicted model ...

Fischer-Tropsch route for the conversion of biomass to liquid fuels - Technical and economic analysis

The techno-economics of biomass gasification systems for the production of Fischer-Tropsch (FT) based liquid fuels are analysed by estimating the overall mass and energy conversion of biomass to liquid (BTL) fuel. The investigation of BTL systems for 1000 kg/h biomass gasification system and an expected liquid hydrocarbon output of 1500 tonnes are estimated. The cost analysis, based on the annualized life cycle of the systems, includes a steam-oxygen based biomass gasification plant paired with the FT unit. The gasifier considered in this analysis is the downdraft reactor design, operating on oxygen-steam gasifying medium at an equivalence ratio of 0.1 and a steam-to-biomass ratio in the range of 0.8–1.2 to generate syngas with H2/CO ratio of 2.1:1, ideally suitable for the cobalt based fixed bed FT reactor. The mass and energy balance reveal that for a once-through FT reactor configuration, substantial energy exists in the gas phase, which includes C1-C5 hydrocarbons and unconverted syngas. The study suggests that the product gas be utilized in an IC engine and converted to electricity, for in-house power demands and for the sale of excess electricity to the grid. The analysis indicates a market competitive liquid fuel production with CO conversion greater than 60%, at a cost ranging from INR 35–40/litre (0.5–0.6 USD/litre) alongside electricity as a major co-product in the BTL system. This study examines the economics of building economically affordable and environmentally favourable BTL systems of smaller throughputs with particular reference to India.

Multi-scale modeling of fixed-bed Fischer Tropsch reactor

Abstract A multi-scale pseudo-homogeneous one-dimensional model for the Fischer Tropsch fixed-bed reactor has been developed in this study using a detailed mechanistic kinetic scheme proposed in an earlier study (Todic et al., 2013). The developed model is capable of predicting the concentration and temperature profiles at the micro-(catalyst pores) level as well as the macro-(reactor bed) level for a cobalt-based catalyst (15 wt% Co/Al2O3). The uniqueness of this model is that it tries to combine different levels of complexity (product distribution modeling, particle diffusion and reactor bed modeling) into one single model. The predictability of this model has been validated experimentally using an advanced high-pressure FTS reactor unit over a wide range of testing conditions. It quite accurately predicts experimentally measured CH4 selectivity at different gas hourly space velocities but less accurately predicted CO conversion. On the other hand, a hydrocarbon product distribution has been predicted using a MATLAB® code that was written to estimate the FTS kinetic model’s parameters (Todic et al., 2013) based on the experimental data collected using bench scale FTS fixed-bed reactor. The optimization of this model was done using a Genetic Algorithm (GA). The findings showed excellent predictability of the experimentally measured hydrocarbon product distribution profile of the catalyst, specifically paraffin formation rates which are the main products of the cobalt-based catalyst. This comprehensive model also involved modified thermodynamic equation of state and currently is upgraded to enable a direct comparison of the gas-phase and supercritical solvent-assisted FTS reactions under a variety of conditions using the experimental data reported in a recent study by our team (Kasht et al., 2015).

Increasing ethylene production as a high value hydrocarbon in Fischer-Tropsch (FT) reactor: A concept reactor for combining FT with oxidative coupling of methane

The paper proposes a concept configuration of reactors for coupling OCM and FTS, and presents systematic simulation results. FTS section is a combination of fixed bed and membrane fluidized bed reactor, and feed of the FT reactor is supplied by OCM. The reactor configuration is compared with the consecutive reactors of OCM and one fixed bed FT reactor. Effects of CH4/O2 ratio, percent of N2 in the feed, contact time, and input temperature on the yield of ethylene and valuable hydrocarbons are studied. The results show that compared with one FTS reactor configuration, the dual FTS reactor configuration is more effective and thus gives much higher product yields. Furthermore, a main decrease is observed in the formation of CO2 and CH4.

Effect of feeding nitrogen to a fixed bed Fischer–Tropsch reactor while keeping the partial pressures of reactants the same

The effect of co-feeding nitrogen in Fischer–Tropsch synthesis (FTS) in a fixed bed reactor over a Co/TiO2 catalyst was investigated. The partial pressure of reactants (CO and H2) in the feed to the reactor was kept constant, while the partial pressure of N2 was switched between a low and high value. The low value corresponded to a syngas feed while the high value corresponded to a feed of syngas enriched with N2. A comparison of the results obtained from more than four switches between syngas and syngas enriched with N2 are reported. The results indicate that there was almost no effect on the overall reaction rate, but that there was a significant, positive effect on the product selectivity. A lower selectivity to the undesired light hydrocarbons (especially methane) was observed when co-feeding N2. Such results cannot be explained by classic kinetics alone as the partial pressures of CO and H2 were held constant during the experiment. The laboratory data indicates that the selectivity to the (C5–C19) fraction is particularly enhanced by co-feeding N2 in FTS.

Effects of Particle Size and Shape on the Performance of a Trickle Fixed-Bed Recycle Reactor for Fischer–Tropsch Synthesis

A previously developed one-dimensional reactor model was employed to understand the effects of pellet size and geometry on the performance of a wall-cooled multitubular fixed-bed Fischer–Tropsch reactor for producing hydrocarbons from synthesis gas. The effects of pellet size/shape on catalyst effectiveness, bed void fraction, and overall heat transfer coefficient were studied through a comprehensive parametric study of a reactor with cobalt catalyst. The relative impact of each of these parameters on the overall required amount of catalyst was also determined. The simulations show that the amount of catalyst required to achieve a specified conversion increases with pellet size and shape in the order: trilobes < hollow cylinders < cylinders < spheres. The pressure drop per unit length can be significantly reduced and the catalyst effectiveness increased by using advanced extrudates, i.e., trilobes or hollow cylinders.

Process intensification of tubular reactors: Considerations on catalyst hold-up of structured packings

Several structured packing elements for multiphase tubular fixed bed reactors are compared with regard to catalyst hold-up, heat transfer performance and pressure drop. Structured packings with catalyst coating typically exhibit low pressure drop compared to the conventional randomly dumped packed bed, as well as excellent heat transfer characteristics, but also have considerably less catalyst inventory per reactor volume. A particle-packed structured alternative (packed cross flow structure) exploits the advantages of structured flow, while not sacrificing much in catalyst hold-up (50 v%) compared to a randomly packed bed (65 v%). This alternative retains favorable pressure drop characteristics, which allows the use of reduced catalyst particle size. A numerical analysis of a 1-dimensional reactor model of a fixed bed Fischer–Tropsch process demonstrates that the packed cross flow structure, despite a lower catalyst hold-up than the randomly packed bed, can have a 25% higher C5+ productivity per tube volume than the RPB. The increased productivity results from an increased catalyst effectiveness combined with better temperature control, necessary to keep the catalyst sufficiently selective.

One-dimensional heterogeneous model of a Fischer-Tropsch synthesis reactor with a fixed catalyst bed in the isothermal granules approximation

A one-dimensional heterogeneous model has been developed for a cat6alytic fixed-bed Fischer-Tropsch (FT) synthesis reactor in the isothermal granules approximation. The FT process has been simulated for a laboratory-scale reactor. The effects of the linear gas velocity and of the inner diameter of the reactor on the thermal stability of the process are considered. The size of the reactor is limited by the possibility of a “thermal explosion” occurring in the frontal layer of the catalyst. Raising the linear gas velocity enhances heat transfer, thereby reducing the overheating of the catalyst bed. The synthesis of solid hydrocarbons can be conducted in reactors no larger than 18 mm in diameter. According to calculations, the maximum temperature drop in a 3-, 4-, and 6-m-long reactor is 4.7, 4.2, and 3.6°C, respectively. The corresponding CO conversion is 35.0, 34.4, and 33.9%, respectively. For producing liquid hydrocarbons in a high-performance reactor, it is necessary to decrease its inner diameter to 12 mm. In this case, the maximum temperature drop at a reactor length of 3, 4, and 6 m is 9.6, 8.7, and 7.6°C, and the CO conversion is 78.0, 77.4, and 76.7%, respectively. The mathematical model devised here provides means to estimate the necessary design parameters of the reactor and the appropriate FT synthesis conditions for producing liquid or solid hydrocarbons.

Comparison of CFD results and experimental data in a fixed bed Fischer–Tropsch synthesis reactor

Hydrogenation of carbon monoxide in a fixed bed Fischer–Tropsch reactor has been simulated using computational fluid dynamics. The geometry of fixed bed reactor was modeled using the discrete packing method. The effects of reaction temperature, feed flow rate and H2/CO ratio on CO conversion and product selectivity were investigated. The mass fraction of products was also predicted by using the CFD model at different H2/CO ratios. It was observed that the CO conversion increased with increasing temperature, while decreased with increasing mass flow rate. The selectivity and mass fraction of products also increased with increasing temperature and H2/CO ratio.

Experimental studies and modeling of a fixed bed reactor for Fischer–Tropsch synthesis using biosyngas

The aim of this work was to study the Fischer–Tropsch (FT) synthesis of a model biosyngas (33% H2, 17% CO and 50% N2) in a single tube fixed-bed FT reactor. The FT reactor consisted of a shell and tube with high-pressure boiling water circulating throughout the shell. A spherical unpromoted cobalt catalyst was used with the following reaction conditions: a wall temperature of 473K, a pressure of 20bars and a gas hour space velocity (GHSV) of 37 to 180NmL.gcat−1.h−1. The performance of the FT reactor was also validated by developing a 2D pseudo-homogeneous model that includes transport equations and reaction rate equations. Good agreement between the model predictions and experimental results were obtained. This developed model was extended to predict and quantify the influence of the FT kinetics as well as determine the influence of the tube diameter and the wall temperature. The predicted behaviors for CO and H2 conversion, productivity of hydrocarbons (mainly CH4 and C5+) and fluid temperature along the axis of the reactor have been analyzed.

Role of Palladium in Iron Based Fischer−Tropsch Catalysts Prepared by Flame Spray Pyrolysis

Flame spray pyrolysis (FSP) is a novel technique for the fabrication of nanostructured catalysts with far-reaching options to control structure and composition even in cases where complex composites need to be prepared. In this study, we took advantage of this technique to synthesize highly dispersed pure and Pd-doped iron oxide nanoparticles and investigated them as Fischer−Tropsch (FT) catalysts. By systematically varying the Pd content over a large range from 0.1 to 10 wt %, we were able to directly analyze the influence of the Pd content on activity and selectivity. In addition to catalytic measurements, the structure and composition of the particles were characterized before and after these measurements, using transmission electron microscopy, adsorption measurements, X-ray diffraction, and EXAFS. The comparison revealed on the one hand that small Pd clusters (diameter: 1−2 nm) evolve from initially homogeneously distributed Pd and on the other hand that the iron oxide transforms into iron carbides depending on the Pd content. The presence of Pd influences the particle size in the pristine samples (8−11 nm) resulting in specific surface areas that increase as the Pd content increases. However, after activation and reaction the specific surface areas become similar due to partial agglomeration and sintering. In a fixed bed FT reaction test, enhanced FT activity was observed with increasing Pd content while the selectivity shifts to longer chain hydrocarbons, mainly paraffins. Mechanistic implications regarding the role of Pd for the performance of the catalysts are discussed.

Fischer–Tropsch catalyst testing in a continuous bench-scale coal gasification system

A bench-scale oxygen-blown fluid-bed gasifier was coupled to a modular fixed-bed Fischer–Tropsch (FT) reactor system for testing an FT catalyst under syngas. Various blends of subbituminous coal, torrefied biomass, and untreated biomass were gasified at 22 bar absolute, 800°–860 °C, and 4 kg/h. Syngas exiting the fluid bed passed through a cyclone, candle filter, and sulfur sorbent to reduce fine particulate and H 2S to levels well below 1 ppmv. The syngas was cooled to condense out moisture and volatiles and then reheated to temperatures required for FT synthesis. The clean syngas then flowed into the FT reactor with a 5:1 ratio of recycled FT product gas-to-fresh syngas feed. A 70% overall conversion of CO and H 2 was achieved at 269 °C and 18.9 bar over an iron-based catalyst supported on gamma-alumina pellets.

Fischer-Tropsch Synthesis: Modeling and Performance Study for Fe-HZSM5 Bifunctional Catalyst

A water-cooled fixed bed Fischer-Tropsch reactor packed with Fe-HZSM5 catalyst has been modeled in two dimensions (radial and axial) using the intrinsic reaction rates previously developed at RIPI. The reactor is used for production of high-octane gasoline from synthesis gas. The Fischer-Tropsch synthesis reactor was a shell and tube type with high pressure boiling water circulating on the shell side. By the use of a two-dimensional model, the effects of some important operating parameters such as cooling temperature, H2/CO ratio in syngas and reactor tube diameter on the performance capability of the reactor were investigated. Based on these results, the optimum operating conditions and the tube specification were determined. The model has been used to estimate the optimum operating conditions for the pilot plant to be operated in RIPI.

Heterogeneous modeling for fixed-bed Fischer–Tropsch synthesis: Reactor model and its applications

A comprehensive one-dimensional heterogeneous reactor model is developed to simulate the performance of fixed-bed Fischer–Tropsch reactors for hydrocarbon production. The detailed mechanistic kinetics is combined into the reactor model along with considering the fact that the catalyst pores are filled with liquid wax under realistic conditions. The equilibrium between the gases in the bulk and the wax in the catalyst pores is correlated by using a modified SRK equation of state (MSRK EOS). The model is solved by using Gear method to integrate the reactor model with the embedded pellet model discretized by orthogonal collocation on finite elements. The validity of the reactor model is tested against the measured data from different-scale demonstration processes. Satisfactory agreements between model predictions and experiment results are obtained. Detailed numerical simulations are performed to investigate the effect of major process parameters on the reaction behavior of fixed-bed FTS systems with recycle operation.