Investigation of Fischer-Tropsch synthesis performance and its intrinsic reaction behavior in a bench scale slurry bubble column reactor

A bench scale slurry bubble column reactor (SBCR) with active-Fe based catalyst was developed for the Fischer-Tropsch synthesis (FTS) reaction. Considering the highly exothermic reaction heat generated in the bench scale SBCR, an effective cooling system was devised consisting of a U-type dip tube submerged in the reactor. Also, the physical and chemical properties of the catalyst were controlled so as to achieve high activity for the CO conversion and liquid oil (C₅₊) production. Firstly, the FTS performance of the FeCuK/SiO₂ catalyst in the SBCR under reaction conditions of 265 °C, 2.5 MPa, and H₂/CO = 1 was investigated. The CO conversion and liquid oil (C₅₊) productivity in the reaction were 88.6% and 0.226 g/g_cat-h, respectively, corresponding to a liquid oil (C₅₊) production rate of 0.03 bbl/day. To investigate the FTS reaction behavior in the bench scale SBCR, the effects of the space velocity and superficial velocity of the synthesis gas and reaction temperature were also studied. The liquid oil production rate increased up to 0.057 bbl/day with increasing space velocity from 2.61 to 3.92 SL/h-g_Fe and it was confirmed that the SBCR bench system developed in this research precisely simulated the FTS reaction behavior reported in the small scale slurry reactor.     

浆态床鼓泡反应器中气含率的分布

为了解浆态床鼓泡反应器中气含率的分布规律,在浆态床鼓泡反应器冷模试验装置中,以空气-液体石蜡-氧化铝微球为试验介质对装置内部的气含率进行研究。利用压差法研究了表观气速、浆液固含量等操作条件对反应器床层总体气含率的影响,利用光纤探针法研究了浆态床反应器不同操作条件对局部气含率的影响,总结了反应器内部气含率的分布规律,并由此对工业浆态床鼓泡反应器的设计进行了研究。结果表明:浆态床反应器的总体气含率随表观气速的增大而增大,固体细颗粒的加入能适当降低总体气含率;在反应器底部,分布器对气体的均布作用明显,但表观气速的增大能够弱化分布器的作用;在反应器的中上部气含率不受分布器的影响,沿反应器径向呈现"中间高,边缘低"的分布趋势;在工业费托浆态床中,表观气速不宜低于0.12 m/s,内过滤系统适宜设置于反应器中上部靠近器壁的位置。     

SEBS高黏度溶液气液鼓泡塔的流体力学研究

针对SBS加氢反应器开发与设计,以SEBS-1650己烷溶液为液相,采用差压法和床层塌落法研究了气液鼓泡塔中高黏度溶液的流体力学行为,考察了黏度对低表面张力溶液的气含率、大小气泡气含率、大小气泡上升速度和比表面积等因素的影响。结果表明,随黏度增加,大气泡增多,气含率明显降低,塔内流型处于湍流区;由床层塌落曲线确定鼓泡塔内存在三种类型的气泡：大气泡、小气泡及细小气泡,随黏度增加,小气泡与细小气泡逐渐减少;黏度对大小气泡的上升速度略有影响,比表面积随黏度增加而明显降低。根据实验结果给出了大小气泡气含率与平均气含率的计算公式。     

A statistical approach of heat transfer coefficient analysis in the slurry bubble column

Heat transfer plays an important role in slurry bubble column reactors (SBCRs). Design of heat transfer equipments for SBCRs is a limiting step in sizing and scale up of them. In order to study the convection heat transfer coefficient (CHTC) in industrial SBCRs, a proper column was designed and manufactured in pilot scale with a special convection heat transfer coefficient measurement probe (CHTC MP). In this study, influence of effective parameters such as solid fraction, superficial gas velocity, radial and vertical position of the column was investigated on CHTC. The design of experiments was performed using a full factorial method including 3¹ × 2² × 9¹ = 108 experiments, to determine the main effects, binary and ternary interactions of variables. Study of the curvature functionality of CHTC versus gas velocity and effect of flow regime transition from homogeneous to heterogeneous flow was the other goal of this work. A statistical model including the main variables and their significant binary and ternary interactions was explained for CHTC with a good fitness with experimental data. Interactions of four effective parameters including solid fraction, superficial gas velocity, radial and vertical position of the column was studied for the first time in the SBCRs. A dimensionless correlation for local Stanton number was developed as a function of Pr, Re, Fr, non-dimensional radial position and non-dimensional distance from the sparger. Considering local positions in the correlation is a novel work and this correlation has good agreement with experimental data.     

Catalyst mixing in bubble column slurry reactors

The reported experimental data of Pandit and Joshi (1984) on axial and radial steady-state catalyst concentration in a semibatch bubble column slurry reactor is interpreted by the dispersion model. The elliptic partial differential equation with its associated boundary conditions is solved analytically for catalyst concentration by the method of separation of variables. The proposed model adequately fits the experimental data.     

Survey of heat transfer mechanisms in a slurry bubble column

Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil‐free compressed air, tap water and 35 μm glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time‐averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model.     

Modeling and optimization of industrial Fischer–Tropsch synthesis with the slurry bubble column reactor and iron-based catalyst

To optimize industrial Fischer–Tropsch(FT) synthesis with the slurry bubble column reactor(SBCR) and ironbased catalyst, a comprehensive process model for FT synthesis that includes a detailed SBCR model, gas liquid separation model, simplified CO_2 removal model and tail gas cycle model was developed. An effective iteration algorithm was proposed to solve this process model, and the model was validated by industrial demonstration experiments data(SBCR with 5.8 m diameter and 30 m height), with a maximum relative error b 10% for predicting the SBCR performances. Subsequently, the proposed model was adopted to optimize the industrial SBCR performances simultaneously considering process and reactor parameters variations. The results show that C_(5+) yield increases as catalyst loading increases within 10–70 ton and syngas H_2/CO value decreases within1.3–1.6, but it doesn't increase obviously when the catalyst loading exceeds 45 ton(about 15 wt% concentration).Higher catalyst loading will result in higher difficulty for wax/catalyst separation and higher catalyst cost. Therefore, the catalyst loading(45 ton) is recommended for the industrial demonstration SBCR operation at syngas H_2/CO = 1.3, and the C_(5+) yield is about 402 ton" per day, which has an about 16% increase than the industrial demonstration run result.     

Development of Fe Fischer–Tropsch catalysts for slurry bubble column reactors

The effect of two binder systems — a silica-based system and a silica–kaolin–clay–phosphate-based system — on a doubly promoted Fischer–Tropsch (FT) synthesis iron catalyst (100Fe/5Cu/4.2K) was studied. The catalysts were prepared by coprecipitation, followed by binder addition and spray drying at 270°C in a 1 m diameter, 2 m tall spray dryer. The binder silica content was varied from 0 to 20 wt.%. A catalyst with 12 wt.% binder silica was found to have the highest attrition resistance. The FT activity and selectivity of this catalyst are better than a Ruhrchemie catalyst at 270°C and 1.48 MPa. The addition of precipitated silica or kaolin to catalysts containing 10–12 wt.% binder silica decreases attrition resistance and increases methane selectivity. Based on the experience gained, a catalyst has been successfully spray dried in 500 g quantity. This catalyst showed 95% CO conversion over 125 h of testing at 270°C, 1.48 MPa, and 2 NL/g-cat/h and had less than 4% methane selectivity. Its attrition resistance was one of the highest among the catalysts tested.     

Influence of structured packing on gas holdup in a three-phase bubble column

In this work, the influence of structured packing on gas holdup in gas-liquid-solid dispersions has been studied. The experiments were carried out in an empty column and in column containing structured packing operating under identical conditions. Glass beads and silicon carbide particles were used as the solid material and the volumetric fraction of solids was varied from 0% to around 10%. The liquid viscosity was strongly modified using water, CMC solution and glycerol. The experimental results obtained with both columns were compared with previous results obtained in two-phase bubble columns. The influence of structured packing on the total gas holdup for different superficial gas velocities was found to be similar with and without suspended solids. Therefore, the results obtained in this work were analysed on the basis of correlations derived earlier for gas-liquid dispersions. Excepting the results obtained with glycerol, these correlations can predict the gas holdup of three-phase bubble columns with reasonable accuracy.     

鼓泡塔反应器气液两相流CFD数值模拟

对圆柱形鼓泡塔反应器内的气液两相流动进行了三维瞬态数值模拟,模拟的表观气速范围为0.02～0.30 m•s^-1; 模拟采用了双流体模型,并耦合了气泡界面密度单方程模型预测气泡尺寸,该模型考虑了气泡聚并与破碎对气泡尺寸的影响。液相湍流采用考虑气相影响的修正k-ε模型,两相间的动量传输仅考虑曳力作用。模拟获得了轴向气/液相速度分布、气含率分布、湍流动能分布以及气泡表面面积密度等,对部分模拟结果与实验值进行了定量比较,结果表明模拟结果与实验结果吻合较好。     

Solids exit discontinuity in slurry bubble columns

The exit discontinuity in slurry bubble columns, i.e., the difference in the apparent solids concentration at the very top of the column (C_t) and the concentration in the effluent (C_e), was studied in a 0.3 m ID bubble column, using air as the gas phase, water, a light hydrocarbon oil (Varsol) and trichloroethylene as liquids and glass beads of different sizes and density as solids. The results showed that the drop in solids concentration occurs in a very small layer at the gas/liquid interface. By changing the column exit configuration and removing the gas/liquid interface the exit discontinuity disappeared. The extent of the exit discontinuity depended on the liquid properties and appeared to be related to the foaming tendency of the liquid. In addition, in those systems where the exit discontinuity was significant, it depended on the solids properties and the gas and liquid superficial velocities.     

鼓泡塔中气泡尺寸分布和局部气含率研究

在内径为0.38 m的鼓泡塔中采用双电导探针法对不同通气速率下的气泡尺寸分布和局部气含率进行了实验研究,分析了气泡尺寸的概率密度分布。结果表明:气泡尺寸随轴向高度的增加而增大,随径向距离增加而减小;鼓泡塔中气液流动可分为过渡流域和充分发展流域,在过渡流域气含率随轴向高度增加而增大,在充分发展流域气含率趋于均值,径向局部气含率分布呈抛物线型下降。高气速下气泡尺寸概率密度分布比低气速下宽,且随轴向高度的增加分布变宽。     

Effect of resistance internal on hydrodynamic behaviours and bubble characteristics in a laboratory-scale bubble column

A novel resistance internal is proposed to optimize the flow field and improve the gas–liquid contact in a co-hydrogenation reactor of coal and vacuum residuum. Local gas holdup, local liquid velocity, and characteristics of the bubble were investigated in a scaled-down laboratory model. The quantitative results showed that the resistance internals could reduce the thickness of the liquid reflux layer by a percentage up to 32% and reduce the difference in the local gas holdup at cross-sections of up to 44%. The Sauter mean diameter of the bubble decreased from 20.30 to 16.00 mm, which aroused the increase in bubble surface area by a percentage of up to 71.9%. The resistance internal promoted the breakup of the bubble with multiple mechanisms and provided diversion to fluid. In this work, improvement at multiple scales was realized, and the technical support for industrial application was provided.     

Hydrodynamics of the flow transition from a bubble column to an airlift-loop reactor

The hydrodynamics of an airlift-loop reactor (ALR) and a bubble column (BC) were studied in the same reactor unit. When the liquid circulation in the ALR was impeded gradually in order to obtain a BC mode of operation, there was a transition flow regime inbetween that of the ALR-type flow and the BC-type flow. In the BC the heterogeneous flow was represented by an instationary circulatory flow pattern and characterized by a liquid circulation velocity. The liquid flow in the ALR was represented by a drift-flux model. In the transition flow regime, hydrodynamic calculations based on the plug-flow behavior of an ALR appeared to be valid up to a certain defined value of the total gas-liquid flow rate. To distinguish between BC and ALR flow characteristics, a simple criterion is proposed, qualifying that the distinction between both flow patterns is determined by the superficial liquid velocity and the liquid circulation velocity. If the latter velocity exceeds the superficial liquid velocity a hydrodynamic transition will occur from a uniform ALR type of flow to a heterogeneous BC type of flow. The criterion coincides with an empirical power law function in which the liquid velocity is given as a function of the gas velocity. The values of the power-law coefficients depended on the characteristics of the two-phase flow. The change in value cohered with the onset of a change in the flow pattern.     

Liquid-Solid mass transfer in a slurry bubble column and a gas-liquid-solid three-phase fluidized bed

Mass transfer coefficients between particles and liquids in a slurry bubble column and a three-phase fluidized bed containing small size particles were obtained with two mass transfer systems: (1) K⁺ –Na⁺ ion-exchange in cation-exchange resin bead beds, including anion-exchange resin beads as inert particles; (2) zinc dissolution by HCl in zinc-plated glass bead beds, and in beds of non-plated glass beads. Operating parameters were gas velocity, liquid velocity, particle diameter, and particle concentration. The dependence of mass transfer coefficients on these parameters is discussed from the viewpoint of the energy supplied into the systems. Correlations of the experimental data using dimensionless groups are compared to previous correlations.     

Hydrodynamics of slurry bubble column during dimethyl ether (DME) synthesis: Gas-liquid recirculation model and radioactive tracer studies

Radioactive tracer measurements, using impulse injections of Ar⁴¹, powdered oxide of Mn⁵⁶ and real catalyst particles doped with an oxide of Mn⁵⁶, conducted at the Advance Fuels Development Unit (AFDU) slurry bubble column (BC) reactor during dimethyl ether (DME) synthesis (reactor pressure of 5.27 MPa, reactor temperature of , inlet superficial gas velocity of 17.1 cm/s, and a catalyst loading of 36 wt%) at LaPorte, Texas, are interpreted. The differences in the responses obtained by the catalyst and fine powdered Mn₂O₃ tracer injections are minimal indicating the validity of the pseudo-homogeneous assumption for the liquid plus solid (catalyst) phase mixtures. The gas-liquid recirculation model [Gupta et al., 2001a. Comparison of single- and two-bubble class gas-liquid recirculation models—application to pilot-plant radioactive tracer studies during methanol synthesis. Chemical Engineering Science 56(3), 1117-1125. 2001b. Hydrodynamics of churn turbulent bubble columns: gas-liquid recirculation and mechanistic modeling. Catalysis Today 64(3-4), 253-269], based on a constant bubble size, describing gas-liquid mass transfer superimposed on turbulent mixing of the gas and liquid phases, is used to simulate the gas, liquid and catalyst tracer responses acquired at the AFDU. The model is able to predict the characteristic features of the experimental responses observed for gas, slurry powder and catalyst tracers at different reactor elevations. The fact, that the same model was previously shown capable of predicting both gas and liquid radioactive tracer responses during methanol and Fischer-Tropsch (FT) synthesis, indicates that this model offers a relatively simple tool for assessing mixing and transport in bubble (BCs) for a variety of gas conversion processes and provides a phenomenologically based framework for BC reactor modeling.     

Multicompartment hydrodynamic model for slurry bubble columns

A core-annulus multicompartment two-dimensional two-bubble class model accounting for slurry recirculation and coupled with catalyst transport was developed as a part and parcel of the analysis of the behavior of slurry bubble column reactors at high gas throughputs corresponding to the churn turbulent flow regime. The model analyzed the contributions of bubble-induced turbulence closures, bubble coalescence and breakup phenomena, and catalyst axial distribution as the resultant of sedimentation, advection via liquid-solid slip, per-compartment axial dispersion and core-annulus lateral exchange of catalyst by bubble-induced turbulence. The model was also used to analyze the effects of catalyst loading, gas density and superficial velocity, and column diameter and vessel aspect ratio on the hydrodynamics of slurry bubble column reactors, namely, the per-compartment phase holdups and interstitial velocities, pressure gradient, bubble coalescence and break-up rates, and loci of velocity inversion for the gas and slurry profiles.     

A comparison of triglyceride oil hydrogenation in a downflow bubble column using slurry and fixed bed catalysts

The hydrogenation of the triglyceride oil, soya bean oil, has been studied in the temperature range 130–160 °C and in the pressure range 100–600 kPa using (i) a 5% w/w Pd/C slurry catalyst and (ii) a 3% w/w Pd/Al₂O₃ Raschig ring catalyst in a cocurrent downflow contactor (CDC) reactor. Separate studies of residence time distribution (RTD) were carried out in a modified CDC device in order to determine dispersion numbers and dispersion coefficients. The RTD measurements indicated that the overall flow was a mixture of well‐mixed and plug flow for the unpacked CDC, so that the entry section (0–30 cm from entrance) was perfectly mixed and the remainder of the column (30–130 cm) gave predominantly plug flow behaviour. The introduction of random packing in the form of 13 mm Raschig rings gave rise to increased back mixing in the lower part of the CDC and the overall dispersion number increased due to liquid and gas circulation around the packing elements. Kinetic studies revealed an initial rate reaction order of 1.24–1.26 with respect to hydrogen concentration both in slurry and fixed bed CDC reactors and is interpreted as a combination of a parallel pair of first and second order reactions during the initial stages of reaction. Mass transfer coefficients for gas absorption (k_La) and liquid–solid mass transport (k_s) were determined for both types of reactor. The k_La values lay in the range 1.0–3.33 s⁻¹ and the liquid–solid transport resistances (X_LS) were all <1%, so that the reaction was almost totally surface reaction rate controlled. Apparent energy of activation measurements gave values of E_A = 49 ± 6 kJ mol⁻¹, which is strongly indicative of surface reaction rate control involving the hydrogenation of an olefinic double bond. The selectivity in respect of linolenate (three double bonds) removal and linoleate (two double bonds) retention was high with, for palladium, relatively low trans‐isomer production (<30%). The overall selectivity was slightly, but significantly, better for the fixed bed CDC reactor and this is attributed to the greater degree of plug flow behaviour in the latter, despite the bed causing an increase in dispersion number. However, there is no reaction in the well‐mixed section of the fixed bed CDC reactor as there is in the slurry CDC reactor and this is likely to improve selectivity in a consecutive reaction sequence. © 2000 Society of Chemical Industry     

Modeling the fischer-tropsch reactionin a slurry bubble column reactor

Reactant (CO and H 2 ) concentration and conversion profiles were determined as a function of axial distance for the Fischer-Tropsch reaction in a slurry bubble column reactor. Model equations were developed from the basic concepts, i.e., conservation of mass and momentum, and combined with iron catalyst reaction kinetics as well as mass transfer coefficients, gas, liquid, and solid phase holdup, Henry's Law constants, minimum fluidization velocity, and terminal velocity obtained from empirical correlations. Concentration profiles and conversion were determined for varying key process variables: liquid-phase velocity and rate constant. Results suggest that the reaction is kinetically limited and that conversion is proportional to liquid velocity. Thus, process improvements can be achieved by either maximizing liquid-phase velocity or increasing the rate constant by modifying the catalyst.     

三相淤浆床冷态特性研究——气体—石腊油—催化剂系统

本文研究了气体—石腊油—催化剂三相体系在淤浆床反应器中的流体力学特性,考察了各种因素对气含率和压降的影响,并回归得到如下关联式:ε_g=0.1152u_g~(0.41)c_g~(0.093)ρ~(0.018)。