Mean Residence Time Of Liquid Research Articles

Liquid mean residence time (MRT) in rotating packed bed (RPB) by empirical correlation and residence time distribution (RTD) method using computational fluid dynamics (CFD) simulation

Rotating packed bed (RPB) belongs to a HIGee technology, a process intensification device that can provide better mass transfer rate due to the generation of hyper-gravity under the influence of centrifugal force. While determining the efficiency of the RPB, the MRT of the liquid plays a vital role. The MRT of the RPB is very small and can be tuned in accordance with the mass transfer rate of the solvent to achieve the required outlet concentration of the absorbed gas. There exist two methods, i.e., empirical correlation and the residence time distribution (RTD) method. The applicability of both methods still needs to be investigated for better prediction of MRT in RPB. The current study compares the MRT of the two of the most widely employed techniques, i.e., MRT by empirical correlation and the RTD approach using the Computational Fluid Dynamics (CFD). The difference between the MRT by both methods lies between 30-38%. The results show that the RTD better predicts the MRT in the RPB as compared to the Burns empirical correlation.

Prospect of open-cell solid foams for floating-platform multiphase reactor applications – Maldistribution susceptibility and hydrodynamic behavior

Open-cell solid foams are tested for the first time as prospective structured packings in floating columns to evaluate their potential for offshore multiphase reactor applications. Using a hexapod ship motion simulator and low-intrusive wire-mesh sensors, the effect of floating vessel motions on the hydrodynamic behavior of SiSiC foam packed beds operated with concurrent descending gas-liquid flow was comprehensively investigated. The response of gas-liquid distribution, overall bed pressure drop, and liquid axial dispersion to column tilts as well as translational and rotational motions was acquired and compared to their corresponding stationary (onshore) analog configuration. Maldistribution sensitivity and susceptibility of solid-foam packed beds subject to ship tilts and accelerations were interpreted in terms of fluid uniformity factor. Moreover, a stimulus-response tracer pulse technique and a macro-mixing model were used to estimate the liquid mean residence time and Péclet number. Similar to random packings, fluid maldistribution was found to prevail in solid-foam beds with deviations from uniformity greater for rotational than for translational perturbations. Vessel tilts and oscillations adversely affect open-cell foam bed hydrodynamic performance yielding transient gas-liquid segregated flow regimes, oscillations of pressure drop and uniformity factor, as well as notable deviation from liquid plug flow.

Decolorization of Reactive Orange 16 in Rotating Drum Biological Contactor

A laboratory scale Rotating Drum Biological Contactor (RDBC; drum length×diameter: 255×130mm) filled by randomly arranged particulate carriers with mycelium of the white rot fungus Irpex lacteus was tested for Reactive Orange 16 (RO16) decolorization. Five mycelium carriers were pre-screened for fungus immobilization and the dye degradation in static cultures. The best mycelium growth was observed with the straw, wooden shavings and polyether foam cylinders. Considerable dye adsorption (up to 30%) was observed with natural carriers; very low adsorption was observed with carrier particles made of plastics. Natural mycelium carriers with attached I. lacteus yielded the highest RO16 decolorization efficiency (50–90%). The straw, wooden shavings and polyether foam particles were tested in the RDBC in batch dye degradation experiments and the straw was also tested in continuous experiments. The straw yielded the fastest and stable dye decolorization in the subsequent batches. With the straw, wooden shavings and polyether foam particles RO16 decolorization higher than 90% was achieved within 48h in batch experiments and better than 80% decolorization was attained at liquid mean residence time of 33.3h in continuous experiments. Dye degradation rate of 3.5–4.0gm−3h−1 was achieved in the batch RDBC and the rate of 1.1–1.5gm−3h−1 in the continuously operated reactor.

Hydrodynamics and mass transfer in a tubular reactor containing foam packings for intensification of G-L-S catalytic reactions in co-current up-flow configuration

Stainless steel open-cell solid foams of various linear pore densities (20, 40, 60PPI) are wash-coated with a commercial catalyst and are evaluated as internals for G-L-S reactions in co-current up-flow configuration. Hydrodynamics parameters such as liquid mean residence time, axial dispersion and pressure drop have been determined for an air/water system with superficial velocities between 0.8mm/s and 25mm/s for liquid and between 100 and 900mm/s for gas. A generic piston-dispersion model represents well the liquid hydrodynamics and is used to estimate axial Péclet number and mean residence time for this phase. The Péclet number appears to increase with liquid velocity and foam linear pore density (5<Pe<60 for 20PPI, 10<Pe<140 for 40PPI and 60<Pe<200 for 60PPI). Determined liquid holdups (0.4<ɛL<0.8) are always higher than those encountered in conventional up-flow fixed beds under comparable flow conditions. Liquid superficial velocity and foam linear pore density appear to be the most influent parameters while the gas superficial velocity possesses a less pronounced impact. Pressure drop measurements may indicate the existence of two different flow regimes (bubbly and pulsed regime) and globally the total pressure drop remains low in the experimental domain tested with a maximum value of 0.2bar/m, comparable to literature data. The overall external mass transfer efficiency was determined through the gas/liquid/solid catalytic reaction of α-methylstyrene (AMS) hydrogenation and is compared to theoretical values obtained through correlations for conventional up-flow fixed beds. Very high mass transfer coefficients, in the range of 0.2–0.9s−1 were obtained at low Re numbers, which is one order of magnitude higher than in up-flow fixed beds. A set of correlations is derived for the calculation of the gas/liquid and liquid/solid contributions to external mass transfer and allows explaining the unique bell-shaped Re dependence displayed by the overall mass transfer coefficient.

Hydrodynamics of a Laboratory Scale Rotating Biological Contactor and Its Application for Decolorization of Textile Dyes by White Rot Fungus Irpex Lacteus

Textile industries produce huge amounts of colored wastewaters contaminated with various textile dyes. These waters represent serious environmental problem as common wastewater treatment procedures are not efficient to degrade the dyes. Therefore, new ways of textile wastewater treatment are looked for in order to tackle this environmental problem. An application of the white rot fungus Irpex lacteus, that is known to degrade many recalcitrant pollutants, seems to be one of possible options for the waste water decolorization. A laboratory scale Rotating Biological Contactor was constructed to perform the decolorization tests. The reactor vas equipped with 12 flat circular discs (o = 0.13 m, ?? = 0.01 m) mounted on a common shaft. The discs were made of the Filtren TM30 reticulated polyether foam. Volume of the liquid in the reactor was 1.5 dm3. Residence time distributions of the liquid phase in the reactor were measured to obtain hydrodynamic characteristics. The measurements were carried out at various liquid volumetric flow rates and at different rotational speeds of the discs uncovered with the biomass. The measured data were used to determine the liquid mean residence time and parameters of the gamma distribution model and of the model of the stirred tanks in series with the back-flow. The residence time distributions were also measured after 36 days of the reactor operation, i.e., with the discs covered with the Irpex lacteus mycelium biofilm. The flow behavior of the reactor without the fungus was close to the ideally stirred reactor behavior. The presence of the biomass in the reactor brought about deviations from the ideal mixing. Continuous decolorization experiments with the textile dye Remazol Brilliant Blue R and with a sample of an industrial textile waste water were performed. In the course of the experiments, activities of the enzymes involved in the dye decolorization, i.e., laccase, manganese-dependent peroxidase and lignin peroxidase were determined in the outlet stream of the reactor. The inlet and outlet concentrations of glucose were also measured. The results of the decolorization experiments will be presented and mutually compared and effects of hydrodynamic parameters on decolorization will be discussed.

Characterization and evaluation of a macroporous adsorbent for possible use in the expanded bed adsorption of flavonoids from Ginkgo biloba L.

The suitability of the use of macroporous adsorbent Amberlite XAD7HP in expanded bed adsorption processes for the isolation of flavonoids from crude extracts of Ginkgo biloba L. has been assessed. The expansion and hydrodynamic properties of expanded beds were investigated and analyzed. The bed expansion as a function of operational fluid velocity was measured and correlated with the Richardson–Zaki equation. Theoretical predictions of the correlation parameters (the terminal settling velocity u t and exponent n) were improved by modifying equations in the literature. Residence time distributions (RTDs) were studied using acetone as a tracer. Three measures of liquid phase dispersion (the height equivalent of theoretical plate, Bodenstein number and axial distribution coefficient) were investigated and compared to values previously obtained with commercial EBA adsorbents developed for protein purification. A suitable bed expansion ratio was found to be 1.25 times the settled bed height, which occurred at a corresponding flow velocity of 183 cm/h. For an initial settled bed height of 42 cm, the mean residence time of liquid in the expanded bed was around 28 min. Under these flow conditions, the axial mixing coefficient D ax was 7.54 × 10 −6 m 2/s and the Bodenstein number was 28; the number of theoretical plates ( N) was 19 and the height equivalent of a theoretical plate (HETP) was 2.77 cm. Rutin trihydrate was used as a model flavonoid for the characterization of the adsorption properties of Amberlite XAD7HP. Adsorption was observed to reach equilibrium within 3 h with 70% of the adsorption capacity being achieved within 30 min. The estimated maximum equilibrium adsorption capacity for rutin was estimated to be 43.0 mg/(g resin) when the results were fitted to Langmuir isotherms. The adsorption performance was not seriously impaired by the physical presence of G. biloba leaf powders. Assessment of the kinetics of the adsorption of rutin revealed that the rate constant for adsorption was only reduced by 15% in the presence of leaf powders at a concentration of 50 mg/mL. The results demonstrated that Amberlite XAD7HP should be suitable for expanded bed adsorption of flavonoids from crude extracts of G. biloba L.

Radioisotope tracer study in trickle bed reactors

AbstractThe residence time distribution (RTD) of liquid phase in trickle bed reactors has been measured for air‐water system using radioisotope tracer technique. Experiments were carried out in a glass column of internal diameter of 0.152 m packed with glass beads and actual catalyst particles of two different shapes. From the measured RTD curves, mean residence time of liquid was calculated and used to estimate liquid holdup. The axial dispersion model was used to simulate the experimental data and estimate mixing index, ie. Peclet number. The effect of liquid and gas flow rates on total liquid holdup and Peclet number has been investigated. Results of the study indicated that shape of the packing has significant effect on holdup and axial dispersion. Bodenstein number has been correlated to Reynolds number, Galileo number, shape and size of the packing.

Hydrodynamic characteristics of cocurrent upflow and downflow of gas and liquid in a fixed bed reactor

The residence time distribution (RTD) of a bench-scale multiphase reactor has been investigated in the present study using air as a gaseous phase and water as a liquid phase. Two different sizes (1.1 and 0.3 mm) of silicon carbide were used as diluent for the catalyst bed. In the entire study, equal volumes of catalyst and diluent were used in the bed. The ranges of air and water velocities were kept at such levels as to simulate the liquid hourly space velocities and hydrogen/oil ratios of typical bench-scale hydroprocessing units. The experiments were conducted in both upflow and downflow modes of operation in the reactor. The two modes of operation showed wide differences in RTD when a larger size of diluent was used. However, the differences in RTD in both the modes of operation were eliminated by using a smaller size of diluent. The effect of gas and liquid velocities on different hydrodynamic parameters such as bed Peclet number of liquid, mean residence time of liquid and operating liquid holdup were also investigated for these two levels of diluent size.

A MODEL FOR THE MASS TRANSFER COEFFICIENT IN ROTATING PACKED BED

Based on the locus of ink on the well-rotating disc, a model for the mean residence time of liquid in a rotating packed bed, t = ϕ′ ϵ (ctg(α2/2) − ctg (α1/2))ωu), is proposed. Model predictions agreed with the reported data with relative error within ±15%. A modified surface renewal model based on Danckwerts, is used. For evaluation of the mass transfer coefficient, prediction of surface renewal frequency 5 is assumed as S =ϕω(ϕis a model parameter), and effective contact time t is determined by the residence time model. Model predictions for kL agreed well with the experimental data with relative error within ±14%

00/00709 Effect of gas holdup and liquid mean residence time on coal liquefaction

00/00709 Effect of gas holdup and liquid mean residence time on coal liquefaction

Modelling the flow of liquid in continuous dialyzer

The paper deals with the modelling of the flow of liquid in a compartment of continuous dialyzer. Two simple models, the dispersion model and tanks-in-series model, were used. Their parameters Peclet number, the mean residence time of liquid in dialyzer compartment, the number of tanks and the mean residence time of liquid in each tank were determined from a nonideal step input of a tracer and its response. It has been found that in the range of the Reynolds number from 0.44 to 3.64, the Peclet number and the number of tanks are in the range from about 200 to 320 and from 100 to 310, respectively. Both these parameters and the mean residence time of liquid in the compartment of dialyzer and in each tank decrease with the increasing Reynolds number. Furthermore, it has been proved that the values of the mean residence time of liquid in the compartment of dialyzer calculated from the dispersion model agree well with those calculated from the tanks-in-series model. The obtained values of the Peclet number and the number of tanks indicate that the flow in the dialyzer does not significantly differ from the plug flow.

Mass Transfer in Liquid in Apparatus with Mobile Packing. Application of Model of Cascade of Ideal Mixers

The paper deals with the determination of parameters of a cascade of ideal mixers (i.e. their number and mean residence time of liquid in each member) in modelling the liquid flow on a plate with mobile packing. The number of cascade members has been found practically independent of the gas and liquid velocities and the static bed heights in the gas velocity range from 1.0 to 3.5 m s-1, liquid velocity range from 5.36 . 10-3 to 12.5 . 10-3 m s-1, and the range of static bed height from 21 . 10-3 to 47 . 10-3 m. The mean residence time is increased with increasing static bed height and is decreased with increasing velocities of both gas and liquid. The calculated parameters of the model of flow of liquid and the experimental data on desorption of CO2 from water by a stream of air have been used to calculate the values of mass transfer coefficient in liquid which have been compared with those obtained from the dispersion model. The both approaches have been found to give practically identical results.

Modelling of Flow of a Liquid in Apparatus with Mobile Packing: Dispersion Model

The paper deals with determination of parameters of a dispersion model used for describing the flow of liquid on a plate with mobile packing in the region of gas velocities up to 1.5 m s-1. The parameters of the model - the diffusion Peclet number and mean residence time of liquid - were determined from the nonideal input impulse of tracer concentration and its response by the method of numerical integration of differential equation with subsequent optimization of parameters. The results of measurements are presented graphically and in the form of criterion equations.

Mean Residence Time of Liquid in Trickling Filter

Pilot plant research studies aimed at broadening the basic knowledge relative to the performance of trickling filters were initiated. Here in are presented the results of initial hydraulic studies in which the mean residence time was determined for tap water applied to columns packed with spherical media under conditions of varying hydraulic loading rates, media size and depth.