Study on direct alcohol/ether fuel synthesis process in bubble column slurry reactor

The recent studies of direct alcohol/ether synthesis process in slurry reactors were reviewed, and the research work in our laboratory was carried out in this paper. a global kinetics model for direct dimethyl ether (DME) synthesis from syngas over a novel Cu-Zn-Al-Zr slurry catalyst was established according to the total of 25 experimental data, and a steady-state one-dimensional mathematical model was further developed in bubble column slurry reactor (BCSR), which was assumed that the bubble phase was plug flow, and the liquid phase was fully mixed flow. The numerical simulations of reactor design of 100000 t/a dimethyl ether pilot plant indicate that higher pressure and lower temperature were favorable to the increase of CO conversion, selectivity of dimethyl ether, product yield and height of slurry bed. The optimal operating conditions for DME synthesis process were obtained: reaction temperature at 240°C, reactor pressure at 5 MPa and reactor diameter of 2.5 m.     

Dynamic Matrix Control of a Bubble‐Column Reactor for Microbial Synthesis Gas Fermentation

A spatiotemporal metabolic model of a representative syngas bubble‐column reactor was applied to design and evaluate dynamic matrix control (DMC) schemes for regulation of the desired by‐product ethanol and the undesired by‐product acetate. This model was used to develop linear step response models for controller design and also served as the process in closed‐loop simulations. A 2 × 2 DMC scheme with manipulation of the liquid and gas feed flows to the column provided a superior performance to proportional integral (PI) control due to slow process dynamics combining the multivariable and constrained nature of the control problem. Ethanol concentration control for large disturbances was further improved by adding the flow of a pure hydrogen stream as a third manipulated variable. The advantages of DMC for syngas bubble‐column reactor control are demonstrated and a design strategy for future industrial applications is provided.     

三相鼓泡淤浆床环氧乙烷合成反应器数学模拟及工程分析

建立了加压三相鼓泡淤浆床环氧乙烷合成反应器的数学模型 ,计入了催化剂颗粒在床层中沉降形成沿床高浓度分布对反应的影响以及由于惰性液相载体部分返混对传递的影响 ,进一步利用经实验验证的上述数学模型模拟不同表观气速、床高、反应器直径 (扣除传热元件截面积 )、进口乙烯摩尔分数等参数对床层中催化剂浓度随床高的分布、出口环氧乙烷摩尔分数、环氧乙烷选择率以及单位质量催化剂环氧乙烷年产量的影响 .通过模拟分析预示了工业三相床环氧乙烷反应器的合理尺寸、表观气速、环氧乙烷选择率以及时空产率 ,为工业化提供必要的设计依据     

MASS TRANSFER AND REACTION IN BUBBLE COLUMN SLURRY REACTOR WITH DRAFT TUBE

Gas-liquid and liquid-solid mass transfer coefficients were obtained in a draft tube bubble column slurry reactor (abbreviated as DTBCSR) from the measurements of gas absorption and ion-exchange, respectively. Oxidation of sulfur dioxide on activated carbon was carried out in the same reactor. The effects of gas flowrates, diameters of draft tube and solid concentrations were investigated. These results were compared with those in a bubble column slurry reactor without draft tube (abbreviated as BCSR). Minimum gas velocities for complete suspension of solid particles in DTBCSR were lower than those in BCSR. Gas-liquid and liquid-solid mass transfer coefficients in DTBCSR were higher than those in BCSR. Both coefficients were almost independent of solid loadings. Reaction rates in DTBCSR were higher than those in BCSR and a stirred slurry reactor (abbreviated as SSR) except for lower gas flow rates and smaller particles.     

Effect of pressure fluctuations on the heat transfer characteristics in a pressurized slurry bubble column

The hydrodynamics and heat transfer characteristics were investigated in a slurry bubble column reactor whose diameter was 0.0508 m (ID) and 1.5 m in height. Effects of gas velocity (0.025–0.1 m/s), pressure (0.1–0.7MPa), solid concentration (0–20 vol%) and liquid viscosity (1.0–38.0 mPa s) on the hydrodynamics and heat transfer characteristics were examined. The pressure difference fluctuations were analyzed by means of attractor trajectories and correlation dimension to characterize the hydrodynamic behavior in the column. The gas holdup increased with increasing gas velocity or pressure, but decreased with increasing solid concentration or liquid viscosity. It was found that the attractor trajectories and correlation dimension of pressure fluctuations were effective tools to describe the hydrodynamic behaviors in the slurry bubble column. The heat transfer coefficient increased with increasing pressure or gas velocity, but decreased with increasing solid concentration or viscosity of slurry phase in the slurry bubble column. The heat transfer coefficient value was well correlated in terms of operating variables and correlation dimension of pressure fluctuations in the slurry bubble column.     

Multiple effects of operating variables on the bubble properties in three-phase slurry bubble columns

Flow properties of gas phase reactants such as size, rising velocity and frequency were investigated in simulated three-phase slurry bubble column reactors. Effects of gas velocity, reactor pressure, liquid viscosity, solid content in the slurry phase and column diameter on the flow properties of a gas reactant were determined. The multiple effects of operating variables on the bubble properties were well visualized by means of contour maps. The effects of operating variables on the flow properties of bubbles changed with changing column diameter of the reactor. The size, rising velocity and frequency of reactant gas bubbles were well correlated in terms of operating variables including column diameter of the reactor. This work was presented at the 7 ^th China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

合成气制二甲醚三相淤浆床反应器的数学模型研究

A mathematical model for a bubble column slurry reactor is presented for dimethyl ether synthesis from syngas. Methanol synthesis from carbon monoxide and carbon dioxide by hydrogenation and the methanol dehydration are considered as independent reactions, in which methanol, dimethyl ether and carbon dioxide are the key components. In this model, the gas phase is considered to be in plug flow and the liquid phase to be in partly back mixing with axial distribution of solid catalyst. The simulation results show that the axial dispersion of solid catalysts, the operational height of the slurry phase in the bubble column slurry reactor, and the reaction results are influenced by the reaction temperature and pressure, which are the basic data for the scale-up of reactor.     

Bubble size fractal dimension,gas holdup,and mass transfer in a bubble column with dual internals

As the scale of residual oil treatment increases and cleaner production improves in China, slurry bubble column reactors face many challenges and opportunities for residual oil hydrogenation technology. The internals development is critical to adapt the long-term stable operation. In this paper, the volumetric mass transfer coefficient, gas holdup and bubble size in a gas–liquid up-flow column are studied with two kinds of internals. The gas holdup and volumetric mass transfer coefficient increase by 120% and 42% when the fractal dimension of bubbles increases from 0.56 to 2.56, respectively. The enhanced mass transfer processing may improve the coke suppression ability in the slurry reactor for residual oil treatment. The results can be useful for the exploration of reacting conditions, scale-up strategies, and oil adaptability. This work is valuable for the design of reactor systems and technological processes.     

Low-temperature methanol synthesis in a circulating slurry bubble reactor

A circulating slurry bubble reactor was developed to synthesise methanol via methyl formate from the gas mixture of carbon monoxide and hydrogen at low temperature. The strategy for designing and scaling up the bubble reactor involved a preliminary understanding of fluid dynamics in a cold model, continuous operations under industrial conditions and a parallel experiment in an autoclave. Per-pass syngas conversion was investigated during 100-h operations. The axial profile of solid catalyst concentration was measured just before the shutdown and the composition of liquid product was analysed after the shutdown. These results show that the circulating slurry bubble column will become a potential reactor for the commercial process of low-temperature methanol synthesis after the catalyst system has been improved.     

A new approach for scale-up of bubble column reactors

The reactor of choice for the Fischer-Tropsch synthesis is a slurry bubble column. One of the few disadvantages of bubble columns is the difficulties associated with their scale-up. The latter is due to complex phases’ interactions and significant back-mixing.     

DME DIRECT SYNTHESIS FROM SYNGAS IN A LARGE-SCALE THREE-PHASE SLURRY BUBBLE COLUMN REACTOR: TRANSIENT MODELING

In this research, a new transient mathematical model based upon tanks-in-series configuration was developed to simulate the direct synthesis of dimethyl ether (DME) from syngas in a commercial-scale slurry bubble column reactor. A comparison between the simulation results and experimental data showed that the applied model might acceptably describe the behavior of the slurry reactor. Furthermore, simulation results in the heterogeneous bubble flow regime indicated that the proposed model with 10 tanks-in-series provided the optimum condition. Utilizing this transient model and considering catalyst deactivation, the effect of operating conditions on DME productivity and CO conversion were investigated. In addition, the dynamic behavior of the reactor was studied after implementing a step change in the reactor's coolant fluid temperature.     

Mass Transfer Characteristics of Syngas Components in Slurry System at Industrial Conditions

The gas‐liquid mass transfer behavior of syngas components, H₂ and CO, has been studied in a three‐phase bubble column reactor at industrial conditions. The influences of the main operating conditions, such as temperature, pressure, superficial gas velocity and solid concentration, have been studied systematically. The volumetric liquid‐side mass transfer coefficient k_La is obtained by measuring the dissolution rate of H₂ and CO. The gas holdup and the bubble size distribution in the reactor are measured by an optical fiber technique, the specific gas‐liquid interfacial area aand the liquid‐side mass transfer coefficient k_L are calculated based on the experimental measurements. Empirical correlations are proposed to predict k_L and a values for H₂ and CO in liquid paraffin/solid particles slurry bubble column reactors.     

CFD modeling of slurry bubble column reactors for Fisher-Tropsch synthesis

Industrial bubble column reactors for Fischer-Tropsch (FT) synthesis include complex hydrodynamic, chemical and thermal interaction of three material phases: a population of gas bubbles of different sizes, a liquid phase and solid catalyst particles suspended in the liquid. In this paper, a CFD model of FT reactors has been developed, including variable gas bubble size, effects of the catalyst present in the liquid phase and chemical reactions, with the objective of predicting quantitative reactor performance information useful for design purposes. The model is based on a Eulerian multifluid formulation and includes two phases: liquid-catalyst slurry and syngas bubbles. The bubble size distribution is predicted using a Population Balance (PB) model. Experimentally observed strong influence of the catalyst particles concentration on the bubble size distribution is taken into account by including a catalyst particle induced modification of the turbulent dissipation rate in the liquid. A simple scaling modification to the dissipation rate is proposed to model this influence in the PB model. Additional mass conservation equations are introduced for chemical species associated with the gas and liquid phases. Heterogeneous and homogeneous reaction rates representing simplified FT synthesis are taken from the literature and incorporated in the model.Hydrodynamic effects have been validated against experimental results for laboratory scale bubble columns, including the influence of catalyst particles. Good agreement was observed on bubble size distribution and gas holdup for bubble columns operating in the bubble and churn turbulence regimes. Finally, the complete model including chemical species transport was applied to an industrial scale bubble column. Resulting hydrocarbon production rates were compared to predictions made by previously published one-dimensional semi-empirical models. As confirmed by the comparisons with available data, the modeling methodology proposed in this work represents the physics of FT reactors consistently, since the influence of chemical reactions, catalyst particles, bubble coalescence and breakup on the key bubble-fluid drag force and interfacial area effects are accounted for. However, heat transfer effects have not yet been considered. Inclusion of heat transfer should be the final step in the creation of a comprehensive FT CFD simulation methodology. A significant conclusion from the modeling results is that a highly localized FT reaction rate appears next to the gas injection region when the syngas flow rate is low. As the FT reaction is exothermal, it may lead to a highly concentrated heat release in the liquid. From the design perspective, the introduction of appropriate heat removal devices may be required.     

费托合成鼓泡浆态床反应器气体添加模拟研究

采用建立数学模型的方法在鼓泡浆态床反应器体系中讨论了气体添加对费托合成反应行为的影响。先采用惰性气体添加的方法找到最适合鼓泡塔反应器体系的气体添加模拟方法,在最优方法中,随气体添加相应改变总压和扩散高度以保持合成气分压和空速不变。采用该方法讨论了二氧化碳和烯烃对反应行为的影响。结果表明,随二氧化碳添加量的增加,合成气转化率降低,二氧化碳的添加使得总烯烷摩尔比增加,二氧化碳添加主要通过水煤气变换反应影响费托合成行为;烯烃添加将抑制小于其碳数的烃类的生成,促进大于其碳数的烃类的生成。     

浆态床合成气制二甲醚反应器数学模拟

建立了包括液相返混和催化剂颗粒沉降的合成气一步法制二甲醚浆态床反应器的数学模型,模拟计算了空速、原料气组成、反应温度、反应压力等反应条件对反应的影响。计算结果表明,CO转化率和二甲醚的选择性随温度增加、压力增大而提高,在一定温度、压力条件下,CO转化率随空速增大而减小,合成气含有一定量的CO2有利于CO转化率增加。     

Mass transfer in sparged and stirred reactors: influence of carbon particles and electrolyte

Mass transfer in multiphase systems is one of the most studied topics in chemical engineering. However, in three-phase systems containing small particles, the mechanisms playing a role in the increased rate of mass transfer compared to two-phase systems without particles, are still not clear. Therefore, mass transfer measurements were carried out in a 2D slurry bubble column reactor , a stirred tank reactor with a flat gas-liquid interface, and in a stirred tank reactor with a gas inducing impeller. The rate of mass transfer in these reactors was investigated with various concentrations of active carbon particles (average particle size of ), with electrolyte (sodium gluconate), and with combinations of these. In the bubble column, high-speed video recordings were captured from which the bubble size distribution and the specific bubble area were determined. In this way, the specific mass transfer area a_gl was determined separately from the mass transfer coefficient k_l. Mechanisms proposed in literature to describe mass transfer and mass transfer enhancement in stirred tank reactors and bubble columns are compared. It is shown that the increased rates of mass transfer in the 2D bubble column and in the stirred tank reactor with the gas inducing impeller are completely caused by an increased gas-liquid interfacial area upon addition of carbon particles and electrolyte. It is suggested that an increased level of turbulence at the gas-liquid interface caused by carbon particles accounts for a smaller effective boundary layer thickness and an enhancement of mass transfer in the flat gas-liquid surface stirred tank reactor. However, for the carbon particles used in this study, it is rather unlikely that mass transfer enhancement takes place due to the well-known shuttle or grazing effect.     

Bubbly flow with particle attachment and detachment – A multi-phase CFD study

The available computational fluid dynamics (CFD) models for multi-phase bubble column ignore the effects of attached particles on the dynamics of the bubbles. Bubbles become heavier with the attachment of solid particles which has significant impact on their buoyancy, and hence their flow dynamics. The present paper endeavours to simulate multi-phase slurry bubble column accounting for the effect of bubble–particle aggregate density on the flow dynamics in a multi-phase slurry bubble column. A CFD model was developed and validated against air–paraffin oil data at ambient conditions to understand the hydrodynamics of a three-phase slurry bubble column.     

Dehydration of ortho-boric acid in a three-phase bubble column reactor operating at low pressure

This study investigates the applicability of the bubble column as a reactor to perform the dehydration of ortho-boric acid efficiently and economically. The effects of operating conditions such as reaction time, temperature, gas flow rate, particle size and solid content in the slurry phase on the fractional conversion of the reaction have been determined, and the performance of the three-phase bubble column reactor operating at low pressure (92 kPa) has been discussed. It can be noted from this study that the reaction time has been reduced and the particle size and solid content which are required in the slurry phase for favourable fractional conversion have been increased in the bubble column reactor in comparison with those in the continuous stirred tank reactor. The reaction could be described by means of a fluid–solid heterogeneous reaction model.