Influences of top clearance and liquid throughput on the performances of an external loop airlift slurry reactor integrated mixing and separation

A new developed external loop airlift slurry reactor, which was integrated with gas–liquid–solid three-phase mixing, mass transfer, and liquid–solid separation simultaneously, was deemed to be a promising slurry reactor due to its prominent advantages such as achieving continuous separation of clear liquid from slurry and cyclic utilization of solid particles without any extra energy, energy-saving, and intrinsic safety design. The principal operating parameters, including gas separator volume, handling capacity, and superficial gas velocity, are systematically investigated here to promote the capabilities of mixing, mass transfer, and yield in the pilot external loop airlift slurry reactor. The influences of top clearance and throughput of the clear liquid on flow regime and gas holdup in the riser, liquid circulating velocity, and volumetric mass transfer coefficient with a typical high solid holdup and free of particles are examined experimentally. It was found that increasing the gas separator volume could promote the liquid circulating velocity by about 14.0% at most. Increasing the handling capacity of the clear liquid from 0.9 m3·h-1 to 3.0 m3·h-1 not only could increase the output without any adverse consequences, but also could enhance the liquid circulating velocity as much as 97.3%. Typical operating conditions investigated here can provide some necessary data and guidelines for this new external loop airlift slurry reactor to upgrade its performances.

Experimental and Numerical Study of Gas-Liquid Flow in a Sectionalized External-Loop Airlift Reactor

The external loop airlift reactor(ELALR)is widely used for gasliquid reactions.It’s advantage of good heat and mass transfer rates compared to conventional bubble column reactors.In the case of fermentation application where a medium is highly viscous and coalescing in nature,internal in riser helps in the improvement of the interfacial area as well as in the reduction of liquidphase back mixing.The computational fluid dynamic(CFD)as a tool is used to design and scaleup of sectionalized external loop airlift reactor.The present work deals with computational fluid dynamics(CFD)techniques and experimental measurement of a gas holdup,liquid circulation velocity,liquid axial velocity,Sauter mean bubble diameter over a broad range of superficial gas velocity 0.0024≤UG≤0.0168 m s 1.The correlation has been made for bubble size distribution with specific power consumption for different plate configurations.The effects of an internal on different mass transfer models have been completed to assess their suitability.The predicted local mass transfer coefficient has been found higher in the sectionalized external loop airlift reactor than the conventional ELALR.

Modeling of Continuous Cross-flow Microfiltration Process in an Airlift External-loop Slurry Reactor

New modified combination mathematical models including the pores blocking models and the cake layer models were developed to describe the continuous cross-flow microfiltration in an airlift external loop slurry reactor. The pores blocking models were created based on the standard blocking law and the intermediate blocking law, and then the cake layer models were developed based on the hydrodynamic theory in which the calculation method of porosity of cake layer was newly corrected. The Air-Water-FCC equilibrium catalysts cold model experiment was used to verify the relevant models.Results showed that the calculated values fitted well with experimental data with a relative error of less than 10%.

Removal of Real Textile Dyes by Electrocoagulation/Electroflotation in a Pilot External-Loop Airlift Reactor

This paper studied the efficiency of electrocoagulation/electroflotation in removing colour from real textile wastewater by using aluminum and iron electrodes in an innovative pilot external-loop airlift reactor of 150 L. The reactor was designed to operate in batch and continuous modes. The real effluent contained 90% of disperse dye and 10% of reactive dye. A complete flotation of pollutants with acceptable mixing was achieved in this reactor using only the overall liquid recirculation induced by H2 microbubbles. The treatment of these discharges was easier using electrodes of iron rather than aluminum. The optimal initial pH was 10 for both aluminum and iron electrodes. By using iron electrodes, the maximum decolourisation efficiency and COD reduction efficiency reached respectively 96% and 65% for 90 minutes of treatment. Similarly, by using aluminum electrodes, the maximum decolourisation efficiency reached 90%, COD reduction reached 51% for 120 minutes of treatment. In the case of an initial pH slightly different to 10, the required time to reach 90% ranged from double to triple.

Computational fluid dynamics simulation of hydrodynamics in the riser of an external loop airlift reactor

Local hydrodynamics in the riser of an external loop airlift reactor （EL-ALR） are identified and the performances of three drag models are evaluated in computational fluid dynamics simulation. The simulation results show that the Schiller-Naumann drag model underestimated the local gas holdup at lower superficial gas velocity whereas the Tomiyama drag model overestimated that at higher superficial gas velocity. By contrast, the dual-bubble-size （DBS）-local drag model gave more reasonable radial and axial distri-butions of gas holdup in all cases. The reason is that the DBS-local drag model gave correct values of the lumped parameter, i,e., the ratio of the drag coefficient to bubble diameter, for varying operating conditions and radial positions. This ratio is reasonably expected to decrease with increasing superficial gas velocity and be smaller in the center and larger near the wall. Only the DBS-local drag model correctly reproduced these trends. The radial profiles of the axial velocity of the liquid and gas predicted by the DBS-local model also agreed well with experimental data.

Hydrodynamics and Mass Transfer in a Modified Three-phase Airlift Loop Reactor

A modified internal-loop airlif reactor （MIALR） with a continuous slurry phase was studied to investigate the local hydrodynamic characteristics, including gas holdup, bubble size, bubble rise velocity and local mass transfer properties. Based on the analysis of geometrical construction and fluid properties of gas and slurry, MIALR was divided into six flow regions. In these flow regions, the local hydrodynamic characteristics were investigated over a wide range of operating variables. Furthermore, a new method was developed to measure the dissolved oxygen concentration. The volumetric mass-transfer coefficient in six flow regions was also calculated for comparison.

HYDRODYNAMIC STUDIES ON LOOP REACTORS (Ⅱ) AIRLIFT LOOP REACTORS

Hydrodynamics of airlift loop reactors was studied in detail experimentally andtheoretically.An internal airlift loop reactor was designed and set up for this study.An instru-mentation system based on the electrochemical method was adapted to measure local gas holdup andliquid velocity.A two-dimensional two-fluid model based on the first principles was established andimplemented to model the flow in airlift loop reactors.A corrected turbulent model was incorporatedin the simulation.The shear rate,shear stress and energy dissipation are evaluated from the flowfield.The numerically predicted results and experimental data obtained from this work as well as thesereported in literature are analyzed and compared.

Structure optimization of gas-liquid combined loop reactor using a CFD-PBE coupled model

Flow characteristics, such as flow pattern, gas holdup, and bubble size distribution, in an internal loop reactor with external liquid circulation, are simulated to investigate the influence of reactor internals by using the computational fluid dynamics （CFD）-population balance equations （PBE） coupled model. Numerical results reveal that introducing a downcomer tube and a draft tube can help to improve the mass and heat transfer of the reactor through enhanced liquid circulation, increased gas holdup and reduced bubble diameter. The hydrodynamic behavior in the internal loop reactor with external liquid circulation can be managed effectively by adjusting the diameter and axial position of the draft tube.

HYDRODYNAMIC STUDIES ON LOOP REACTORS (Ⅰ) LIQUID JET LOOP REACTORS

Understanding of hydrodynamics in liquid jet loop reactors is a prerequisite step for the fur-ther study of multi-phase flow in loop reactors.A hydrodynamic simulation for liquid jet loop reac-tors is developed from the first principles of transport phenomena in this paper.The turbulence istaken into account by using the standard k-ε model.This approach is used to study the influence ofconfiguration and viscosity on the hydrodynamics.The results are in very reasonable coincidence to ex-perimental data in literature.

SIMULATION OF EFFECTS OF REACTIVE IMPURITIES ON PROPYLENE POLYMERIZATION IN LOOP REACTORS THROUGH GENERATION FUNCTION TECHNIQUE

The estimation of the amount of reactive impurities in a loop reactor is of strategic importance to the propylene polymerization industry. It is essential to investigate the level of impurities in order to develop reliable monitoring and control strategies. This paper described one approach based on generation function technique with the following two steps. First, a new mechanism for propylene polymerization was proposed by considering the effects of the reactive impurities in the material on the propylene polymerization. Second, a series of equations of population balance for the propylene polymerization in loop reactors were established based on the proposed mechanism. Accordingly, the equations were transformed into the mathematic matrix through the generation function technique to investigate the effects of the reactive impurities on the propylene polymerization. Significant effects of the reactive impurities were analyzed through computational simulation. The results show that the concentration of active centre on catalysts and the polymerization conversion both decrease with the increase of the initial concentration of any reactive impurity; hydrogen concentration decreases with the increase of the initial concentration of ethylene or butylenes, whereas, it increases with the increase of the initial concentration of propadiene; the simulated weight average molecular weight and the molecular weight distribution index of polymer resins both increase with the increase of the initial concentration of ethylene or butylenes. They decrease with the increase of the initial concentration of propadiene.

Treatment of methanol wastewater in external circulation anaerobic reactor with different inoculums

In order to guide the inoculums selection for the anaerobic treatment of methanol wastewater in the engineering application,two 7 L bench-scale external circulation (EC) anaerobic reactors were operated to investigate the inoculums of anaerobic granular sludge and anaerobic digested sludge,focusing on the efficiency and process stability.The effect of impact concentration and temperature on the performance was studied.The results demonstrated that anaerobic granular sludge as the inoculums could complete the start-up more rapidly than the anaerobic digested sludge,and above 90% COD removal were achieved at the organic loading rate of 10 to 15 kgCOD/(m3·d).The effect of impact COD on the methanogenic activity of sludge was weak and the removal efficiencies recovered gradually in the two reactors.The COD removal efficiencies reduced swiftly to 50%-60% due to the impact temperature.The results indicated that the complex bacterial groups in anaerobic digested sludge benefited to enhance the reactor's capacity for withstanding the temperature shock at some extent.

CFD Simulation of Scale Influence on the Hydrodynamics of an Internal Loop Airlift Reactor

In this work, the overall gas hold-up in the riser and down-comer of three internal airlift reactors with a working volume of 10.5, 32 and 200 l at the range of temperatures 18℃ - 21℃, under atmospheric pressure was simulated using Com-putational Fluid Dynamics (CFD). The range of superficial gas velocity was 0.5 - 3 cm/s. The three reactors geometrically were similar to each other. CFD simulation and experimental data showed that the gas hold-up in the riser and down-comer increased by increasing the reactor scale. It was concluded that the simulated data were in good agreement with the experimental ones obtained from the literature.

FRACTAL STUDIES IN A SELF-ASPIRATED REVERSED FLOW JET LOOP REACTOR

1 INTRODUCTIONSelf-aspirated reversed flow jet loop reactors,characterized by a well defined flow pat-tern,well better dispersing effects,relatively low power consumption and a high masstransfer coefficient,are widely used in chemical engineering,especially in biochemicalengineering.The characteristics of such reactors are highly random or stochastic due tothe influence of a variety of phenomena such as jetting and bubbling of the

STUDY OF DOWNFLOW LIQUID JET LOOP REACTOR

1 INTRODUCTIONLiquid jet loop reactor(JLR)may be upflow(U-JLR)or downflow reactors(D-JLR)in design.The major differences between the two are the location of the nozzle andthe direction of the fluid flow.A large number of investigations on U-JLR havebeen published,but D-JLR with nozzles positioned on the top portion of the reac-tor was not much studied until recently.Up to now,only a few experimentalstudies on the hydrodynamics and mass transfer of D-JLR have been carried out[1-4].

FLOW AND DIFFUSION IN SELF-ASPIRATED REVERSE FLOW JET LOOP REACTOR

1 INTRODUCTIONGas and liquid distributions in a self-aspirated reverse flow jet loop reactor dependchiefly on the aspiration and the breakup against gas phase by the liquid nozzle aswell as the redistribution in the draft tube.It has also been noted that effective diffu-sion or backmixing in the reactor has great influence on the flow and mass transferrates.In this case,accurate descriptions about the fluid flow and diffusion conditions inthe reactor are most necessary for effective amplification of them.

IMPROVING SOLIDS SUSPENSION USING DEFLECTING BAFFLES IN GASLIFT LOOP REACTORS

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Simultaneous production and utilization of methanol for methyl formate synthesis in a looped heat exchanger reactor configuration

In this investigation, a novel thermally coupled reactor （TCR） containing methyl formate （MF） production in the endothermic side and methanol synthesis in the exothermic side has been investigated. The interesting feature of this TCR is that productive methanol in the exothermic side could be recycled and used as feed of endothermic side for MF synthesis. Other important advantages of the proposed system are high production rates of hydrogen and MF. The configuration consists of two thermally coupled concentric tubular reactors. In these coupled reactors, autothermal system is obtained within the reactor. A steady-state heterogeneous model is used for simulation of the coupled reactor. The proposed model has been utilized to compare the performance of TCR with the conventional methanol reactor （CMR）. Noticeable enhancement can be obtained in the performance of the reactors. The influence of operational parameters is studied on reactor performance. The results show that coupling of these reactions could be feasible and beneficial. Experimental proof-of-concept is required to validate the operation of the novel reactor.

Hydrodynamic Instability Analysis of the Axial Flow Pump in an Ethylene Polymerization Loop Reactor

The hydrodynamic instability of the axial flow pump in a loop reactor has long been a troubling issue to be solved in the polyethylene industry due to the lack of a better mechanismic understanding.Generally,the instability of an axial flow pump can be reflected by the fluctuation of the pump head.In this study,the transient computational fluid dynamics(CFD)simulation is adopted to study the hydrodynamic instability of the axial flow pump used in an ethylene polymerization loop reactor.The results show that the pump head under single liquid phase nearly remains constant while the pump head under slurry phase fluctuates due to the variation of solid volume fraction distribution in the pump.Besides,under the combined effect of the maximum solid volume fraction difference in the pump and the turbulence intensity of the liquid phase,the fluctuation of the pump head under slurry phase increases when the solid volume fraction in the loop reactor increases from 0.10 to 0.29,and the fluctuation decreases,when the solid volume fraction increases from 0.29 to 0.35.Furthermore,there is a negative correlation between the pump head and the solid volume fraction in the pump;with the increase of solid volume fraction in the loop reactor,and the correlation coefficient increases as well.Moreover,a‘spiral particulate band’phenomenon is formed in the ascending leg caused by three mechanisms,viz.:the segregation of particles in all bends,the dispersion of particles by the secondary flow in the ascending leg,and the rotational movement of particles in the pump.

Determination of External Mass Transfer Model for Hydrolysis of Jatropha Oil Using Immobilized Lipase in Recirculated Packed-Bed Reactor

In this study, a simple and effective technique for establishing an external mass transfer model in a recirculated packed-bed batch reactor (RPBBR) with an immobilized lipase enzyme and Jatropha oil system is presented. The external mass transfer effect can be represented with a model in the form of Colburn factor JD = K Re-(1–n). The value of K and n were derived from experimental data at different mass flow rates.The experiment shows an average increment of 1.51% FFA for calcium alginate and 1.62% FFA for carrageenan after the hydrolysis took place. Based on different biopolymer material used in immobilized beads, JD = 1.674 Re-0.4 for calcium alginate and JD = 1.881 Re-0.3 for k-carrageenan were found to be adequate to predict the experimental data for external mass transfer in the reactor in the Reynolds number range of 0.2 to 1.2. The purposed model can be used for the design of industrial bioreactor and scale up. Besides, the external mass transfer coefficients for the hydrolysis of Jatropha oil reaction and the entrapment efficiency for the two biopolymer materials used were also investigated.

Regeneration of waste SCR catalyst by air lift loop reactor

A solution of 0.1 mol/L to 1.0 mol/L H2SO4 can dissolve alkali metals and alkaline earth metals which weaken an active site of SCR catalyst. The waste catalyst washed with 0.5 mol/L H2SO4 regained the best catalytic activity. When a concentration of the sulfuric acid is less than 0.5 mol/L, sufficient cleaning effects cannot be obtained. In contrast, when the concentration is greater than 1.0 mol/L, the active components, vanadium and tungsten are undesirably eluted. The total BET surface of the catalyst regenerated by air lift loop reactor showed almost the same as that of fresh catalyst due to the removal of insoluble compounds which may be penetrated into pores of catalyst. The addition of a solution of 0.075 mol/L ammonium vanadate (NH4VO3) and 0.075 mol/L ammonium paratungstate (5(NH4)2O·12WO3 ·5H2O) to 0.1 mol/L H2SO4 significantly increases the activity of the waste catalyst.