摘要:

AbstractMacroscopic flow structures of gas‐liquid and gas‐liquid‐solid fluidization systems are studied through flow visualization using a two‐dimensional column under various operating conditions. The gas distributor in the column comprises multiple injectors which are individually regulated to generate desired gas flow rates, bubble injection frequencies, and bubble sizes. Colored bed particles and neutrally buoyant particles as solid and liquid tracers, respectively, are used for flow visualization through video photography. In a gas‐liquid system operated under liquid‐batch conditions, bubble streams injected near both sidewalls are observed to migrate toward bed vertical axis, and vortices appear along the sidewalls when gas velocity exceeds 4–6 mm/s. A considerable amount of liquid descends along the sidewalls in a vortical flow pattern. The gross circulation pattern occurring at high gas velocities is associated closely with induced liquid or liquid‐solid flows resulting from rising bubbles and bubble wakes. When the gross circulation occurs, four flow regions can be distinguished. The formation of and mechanism for gross circulations can be interpreted in part based on two simplified flow conditions involving single bubbles rising in a stationary liquid and single chains of bubbles injected in a batch liquid. The effects of particle size, inlet liquid velocity and gas flow distribution on the macroscopic flow structure ar

ISSN:0001-1541    

DOI:10.1002/aic.690390502

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe flow field inside an orifice flowmeter with a beta ratio of 0.50 operating at a Reynolds number of 91,100 has been studied using a three‐color, 3‐D laser Doppler anemometer system. Mean velocity measurements show large radial velocities leading into the orifice, the fluid separating from the orifice plate at the throat, the presence of a vena contracta farther downstream, flow reattachment to the pipe wall 5.3 pipe radii (R) downstream, the presence of a small upstream recirculation zone, and both a primary and secondary recirculation zone downstream of the orifice plate. The static wall pressure distribution attains a minimum pressure at 1.5 R, which does not coincide with the location of the vena contracta (0.75 R). Distributions of the entire Reynolds stress tensor are presented along with calculated values of turbulence kinetic energy, turbulence kinetic energy production, vorticity, and turbulence induced accelerations. These data are analyzed to interpret the complex turbulent flow fi

ISSN:0001-1541    

DOI:10.1002/aic.690390503

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractWhen the total reactant diffusivities are equal, the time‐average concentration fields which result from turbulently mixing reactants can be measured thermally if the temperature difference between the feed streams is suitably chosen. Each reactant profile is obtained from measurements of the temperature profile in an experiment in which the inlet temperature of that reactant is less than that of the other reactant by an amount equal to the adiabatic reaction temperature change of the measured reactant. The method is demonstrated in a liquid phase confined jet reacto

ISSN:0001-1541    

DOI:10.1002/aic.690390504

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA fundamental study was conducted on the effectiveness of the chemical calcium magnesium acetate (CMA) as a sulfur capture agent during combustion of pulverized coal. It was based on high‐temperature laboratory‐bench experiments with the scope of exploring the use of CMA as a “dry scrubbing” medium for in‐boiler injection. Two methods of CMA introduction in the furnace were considered: dry‐spraying fine powders of the chemical and wet‐spraying aqueous solutions to generate fine aerosols. It considered conditions pertinent to post‐flame in‐boiler injection of CMA to identify optimum temperatures and residence times. In addition to the versatility of the water‐soluble CMA to enable spray drying injection and therefore eliminate grinding costs, there are other attractive features. Mainly, its ability to form highly cenospheric, “popcorn” ‐like, oxide particles on heating to high temperatures. These cenospheres possess thin, porous walls with blowholes that enable penetration of the SO2in the interior of the particle which promotes high sorbent utilization. SO2captures in the order of 90% were achieved with dry‐injection of the chemical at furnace gas temperatures of about 1,000° C, a Ca/S ratio of 2, and particle size of ≈ 50 μm. Moreover, CMA was superior(by over 40%) to either CaCO3or Ca(OH)2in sulfur capture effectiveness per unit mass of calcium. This commercially obtained CMA was even superior to reagent‐grade calcium acetate (by as much as 30%), again per unit mass of calcium. The utilization of CMA and calcium acetate depended on the cenosphere wall thickness, rather than the particle size and, thus, outperformed other sorbents regardless of the size

ISSN:0001-1541    

DOI:10.1002/aic.690390505

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA simple model is proposed for the evaluation of the primary and secondary adsorption and desorption processes for hysteresis‐dependent sorption systems. The model is based on the use of pore blocking interpretation of hysteresis in an interconnected network of pores. The model is simple to use and requires only the primary adsorption and primary desorption isotherms to predict all secondary desorption and adsorption isotherms. A complete set of equilibrium adsorption‐desorption curves covering the hysteresis loop (appearing in the range of relative pressure 0.3–0.7) was measured for water vapor on silica gel at 25° C. The usefulness of the model is supported by its agreement with experimenta

ISSN:0001-1541    

DOI:10.1002/aic.690390506

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA new model‐based controller for profile position control of high‐purity distillation columns is presented. The controller has been developed by incorporating nonlinear wave model into the generic model control framework. An observer based on the nonlinear wave theory is also proposed to determine the profile position. The performance of the nonlinear control scheme has been tested in simulation experiments of high‐purity binary distillation columns. Tight control of profile position, which leads to fast stabilization of product compositions, has been achieved. Since the profile position control alone produces a slight offset from the desired product concentration, the composition/profile position cascade system has been used to remove the offset. The control scheme can handle significant disturbances and model‐plant m

ISSN:0001-1541    

DOI:10.1002/aic.690390507

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractColumn chromatography and electrophoresis are combined in electrochromatography, where an electric potential is applied to a chromatography column in the axial direction. These studies utilized a dextran gel stationary phase and an eluent of low ionic strength, which were chosen to minimize electric current and therefore column heating and undesirable dispersion effects. The gel, with a small ion exchange capacity of several microequivalents per mL, turned out to be more conductive than the eluent and was able to concentrate macromolecules in the presence of combined electric and flow fields. The model presented describes solute retention due to electrically induced concentration polarization of solute on the resin surfaces, as well as electrophoresis in the mobile and stationary phases. The polarization effect explains differences between retention of high‐molecular‐weight solutes with exclusion coefficients of less than 1 and that of a charged low‐molecular‐weight solute, which is hypothesized to pass through the gel matrix in the presence of an electric field and does not experience concentration polarization. It also shows the application of this effect for protein separation in a liquid chromatography system with a superimposed electric po

ISSN:0001-1541    

DOI:10.1002/aic.690390508

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractUsing the equilibrium‐dispersive model of chromatography, we have investigated recycling as a means to improve the recovery yields and possibly the production rates of chromatographic separations. When compared with the optimal values obtained for the conventional single‐cycle regime, our results prove the potential for recycling in preparative chromatography. The analysis performed for the separation of two binary mixtures demonstrates that recycling not only improves the recovery yield but can increase the production rate under certain conditions. Different possibilities of collecting sufficiently separated fractions during recycling are compared. The mathematical model developed can be used effectively for designing optimal recycling strategies in preparative liquid chromatogra

ISSN:0001-1541    

DOI:10.1002/aic.690390509

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA new concept of reliability of estimation of variables is introduced which relates to the estimability of variables in the presence of sensor failures. Based on this concept, a method for optimal location of sensors in a pure flow process is developed. A graph‐theoretic algorithm, SENNET, developed for this purpose, is shown to perform robustly and give globally optimum solutions for realistic processe

ISSN:0001-1541    

DOI:10.1002/aic.690390510

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of inaccessible porosity on the rate of gasification reactions is illustrated under conditions where intraparticle and extraparticle resistances to mass transfer are significant. The mathematical model developed here is based on a mass balance for the reactant fluid in the porous particle, coupled with an appropriate structural model developed for the kinetics‐controlled case (Delikouras and Perlmutter, 1991). It is demonstrated numerically that the effects of inaccessible porosity generally diminish with increased diffusional resistances. In agreement with the prior kineticscontrolled case, it is shown that the effects of inaccessible porosity are more pronounced at lower values of the structural parameter ψ and at greater levels of the inaccessible fracti

ISSN:0001-1541    

DOI:10.1002/aic.690390511

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY