Residence Time Distribution Of Particles Research Articles

Hydrodynamic characteristics of cyclone reactors

Recently, cyclones have been used as chemical reactors for example for coal combustion and gasification. In order to provide information needed for cyclone reactor design, the effects of air inlet velocity (6 ∼ 17 m/s), particle (coal-char and glass beads) size (141 ∼ 211 μm), solid loading (0.0 ∼ 0.189 kg/m 3) and geometric ratio of cylinder to cone height (1.8 ∼ 5.0) on the hydrodynamic characteristics such as pressure drop, collection efficiency and residence time distribution of solid particles have been determined in three different cyclones. Pressure drop increases with gas inlet velocity and decreases with solid loading. Collection efficiency increases with gas inlet velocity up to 1.7 times the saltation velocity, and thereafter decreases with increasing gas inlet velocity. Solid residence time distribution is broadened with increasing gas inlet velocity and the geometry ratio, but narrows with increasing particle size. Average residence time of solids increases with inlet gas velocity but decreases with particle size. Average solid residence time in cyclones is correlated with the relevant dimensionless parameters.

単一水平回転円すい型容器による閉回路造粒操作 製品特性に及ぼす循還比の影響

In order to investigate the effect of the circulating load ratio CL on the properties of granule products in a closed-circuit granulation system, the relationship between CL and the residence time distribution of particles passing through a closed-circuit process was discussed with a few assumptions.Furthermore, the open- and closed-circuit granulation experiments were carried out in a single horizontal rotating conical vessel with a rotary lifter. CaCO3-powder and water were used as powder and binder, respectively. The results are summarized as follows.(1) It is expected that the uniform size and spherical products can be obtained by a closed-circuit granulation process having an effective separating system, although the theoretical consideration showed that the large CL makes the residence time distribution of particles wide in the process.(2) It was experimentally confirmed that more spherical, more uniform size and harder products were obtained in the closed-circuit granulation than that in the open-circuit granulation under the optimum circulating load ratio, CL<1.3 which satisfies the optimum separating condition in the present granulator, which has the functions of both granulation and separation.

Measuring and modelling residence time distribution of low density solids in a fluidized bed reactor of sand particles

An experimental study was carried out to estimate the residence time distribution of low density particles injected into a fluidized bed reactor containing sand particles. Tracer experiments were performed at room temperature, using a pilot plant pyrolysis reactor. A novel technique was used to detect and measure the flow of solid tracer particles having different physical characteristics entering and leaving the fluid bed. The experimental results demonstrated that the degree of particle entrainment was a function of the fluidizing gas velocity, the particle size and the particle density. Solid mixing, segregation and entrainment were also studied as functions of physical and operating parameters. Various models were tested to characterize the non-ideal solids flow patterns within the fluid bed. A circulation model appeared to give a good description of the physical mechanism involved and to provide the best agreement with the experimental results.

Optimal performance of a shape classifier for binary mixtures of granular materials

A rotating cylinder with a row of blades was proposed in the previous paper for the shape classification of granular materials. As one of the subsequent studies, this paper deals with the optimal performance of the shape classifier for binary mixtures of spherical and non-spherical particles. The residence time distribution of particles and Newton's separation efficiency of the classifier are obtained from the multi-staged cascade model for the mixture flow. The operating conditions for establishing the optimal performance of the classifier are also explained.

Residence time distribution of suspended solid particles in multi-stage bubble column.

Methode de calcul de la distribution des temps de sejour basee sur un modele de sedimentation-diffusion avec ecoulement en retour entre etages. Discussion des resultats de calcul de la distribution des temps de sejour et du coefficient de diffusion longitudinale des particules

COMPARISON OF COAL LIQUEFACTION IN BATCH AND CONTINUOUS REACTORS

ABSTRACT Liquefaction of Akabira coal with a sufficient amount of tetralin was conducted in a 27 cm3 batch reactor and two types of continuous reactors - a 5000 cm3stirred tank reactor and a 800 cm3 tube reactor. These reactors were mainly operated at 673°K and 5.4 MPa. The batch reactor was heated at different rates from 4°K/nrin to 150°K/min to examine the effects of the heating rate on the conversion of coal to benzene solubles. Conversions in the continuous reactors were measured together with the residence time distributions of coal particles. In the batch reactor, change of the conversion with time differed appreciably depending on the heating rate even when other operating variables were the same. With increasing heating rate the conversion during heating period decreased while the apparent reaction rate constants increased. Using the kinetic data together with the observed residence time distribution of the coal particles, the conversion in the continuous reactor was predicted. From a comparison b...

A Comparison of Coal Liquefaction Characteristics in a Continuous Stirred Tank Reactor with that in a Batch Micro-Atoclave

Liquefaction of Auefaction of Akabira coal by sufficient amount of tetralin was conducted in both a 5, 000 cm3 continuous stirred tank reactor and a 27 cm3 batch microautoclave reactor at 673 K and 5.4 MPa. The batch reactor was operated with different heating rates ranging from 4 K/min to 150 K/min so that the effects of the heating rate on the conversion of coal to benzene solubles could be evaluated. The residence time distribution of coal particles in the continuous reactor was also measured at room temperature.In the batch reactor, change of the conversion with time differed appreciably depending on the heating rate even if other operating variables were same. With increasing heating rates the conversion during the heating period decreased while the conversion level attained at the final stage of the reaction increased. Using the kinetic data together with the observed residence time distribution of the coal particles, the conversions in the continuous reactor were predicted. From a comparison between the predicted and observed conversions it was concluded that conversion in a continuous reactor can be predicted on the basis of kinetic data obtained in a batch reactor with the same heating rate as in the continuous one.

Solid particle mixing in a continously operated fluidized bed reactor

In a bench-scale fluidized bed reactor, 20cm in dia., residence time distribution of solid particles ( d p , = 137μm) were measured by the radionuclide technique ( 24Na 2C0 3) in the absence and in the presence of the chemical reaction 2NaHCO 3→Na 2C0 3+C0 2+H 2O. The residence time distributions were evaluated by a backflow cascade model by nonlinear optimization. The radial and logitudinal concentration profile of NaHCO 3 in the emulsion phase of the reactor were measured during steady-state operation. The solid is well-mixed. The connection of the measured bubble properties with the longitudinal solid dispersion coefficient and the use of the Haines-King-Woodburn model allow

Axial Dispersion of Sedimented Colloids

Abstract After an ensemble of identical particles has had time to settle along the y-axis to their equilibrium distribution in a field of potential energy %oS(y) by gravity, but prevented from adsorbing by double-layer repulsion, their dispersion by Poiseuille flow between two horizontal plates is predicted. The residence-time distribution of particles is obtained in terms of ⊘(y). For chromatographic peaks with long retention times, equations are obtained relating the elution volume and dispersion coefficient to ⊘(y)- From such data, two pieces of information regarding ⊘(y) can be deduced: the location of the minimum, ym, and ⊘ (ym). However, at the opposite extreme of very short retention times, a major portion of the profile ⊘(y) can be deduced from a single chromatogram. Such an experiment might provide the first measurement of long-range forces between a colloid particle and a flat plate.

Studies on Residence Time Distribution of Particles in Rotary Dryers and Coolers

It is found that the residence time of particles flowing through rotary dryers and coolers under the conditions of no air flow and air flow can be expressed by the logarithmic normal distribution, and also that the median of residence time is approximately equal to the apparent mean residence time.As the empirical equation for the latter had been obtained by the authors, the empirical equations concerning the geometric standard deviation, which is the other parameter in the distribution function, are studied in this paper. As a result, Eq. (8) and Eq. (10), respectively, are obtained as the empirical equations of the geometric standard deviation under no air flow and air flow. These equations approximately correlate the experimental results within the accuracy of ±20%. It is also found from the both equations that the geometric standard deviation under air flow is large in comparison with that under no air flow.

The effect of particle residence time distribution on heat transfer in fluidised bed heat exchangers

The effect of particle residence time distribution on heat transfer in fluidised bed heat exchangers

RESIDENCE TIME DISTRIBUTION OF PARTICLES WITHIN PNEUMATIC ESCALATOR

A new device, the pneumatic escalator, for conveying solids pneumatically was examined from the viewpoint of solids mixing or residence time distribution of particles within a continuous gas-solid contacting apparatus. According to experimental results by tracer technique, the residence time of particles passing through the device could be adjusted by operational variables like solids feed rate, air velocity and inclination angle of the device in addition to material properties of particles and dimensions of the device. Among them, air velocity was found to be effective in controlling the shape of the distribution curve and the mean residence time of particles. The distribution function of residence time was mathematically expressed by applying a complete-mixing model to solids within a cell of the device and a binomial distribution model to solids bypassing flow through the cells. Thus, an appropriate distribution curve of residence time required in each case of gas-solid contact operation can be simulated by changing the operational conditions as well as the dimensions of the pneu-escalator.

回転炉内の粒子軸方向混合と滞留時間分布

回転炉内の粒子軸方向混合と滞留時間分布

On the Residence Time Distribution of Particles in a Rotary Dryer (Continuation)

“On the Residence Time Distribution of Particles in a Rotary Dryer with no Air Flow” had been already reported by authors. In this paper, both effects of the falling time of particles and the rotational speed of a rotary dryer were considered in addition to the previous report.The following theoretical equation was obtained.Tj=L/NSddj′(n/j) [1/(1+Nntj′/60j)] (1+0.033Ga1/3)(no air flow)When taking account of air flow, the following theoretical equation was derived by analizing the effect of air flow in addition to the foregoing effects.Tj=L/NSddj′(n/j) [1/(1+Nntj′/60j)] ±1/1-30/4Re3/2(ρa/ρm)Sd-1G1-1+0.033Ga1/3 (air flow)It was verified that the experimental values by pulse response method coincided fairly well with the calculated results.

Residence Time of Particles in Continuous Fludized Bed with Elutriation of Fines

The residence time distribution of particles in the continuous fluidized bed with elutriation of fines was studied experimentally and compared with that developed from the simple mixing model.It is found that the values of constant fines concentration in beds obtained in the previous work are important for the mixing in beds and the zone below elutriation surface height may be mixed parfectly but the all system of fluidized bed with elutriation of fines is not regarded as a perfect mixing system.

The effect of particle size distribution on the performance of a phosphate flotation process

A 25 cu ft flotation cell was operated continuously to produce an apatite-rich concentrate. The experimental results reported in this paper attempt to elucidate the role of the particle size distribution upon the performance of the cell. The particle size distribution influences performance through its effect on the particle residence time distribution and on the rate of impaction, adherence and detachment of particles and bubbles. A model is developed which is capable of predicting a fractional recovery of apatite in any particular particle size range.

On the Residence Time Distribution of Particles in a Rotary Dryer without Air Flow

On the Residence Time Distribution of Particles in a Rotary Dryer without Air Flow

Multistage column reactors. IX. Residence time distribution of liquid and solid particles in a stirred flow system

Multistage column reactors. IX. Residence time distribution of liquid and solid particles in a stirred flow system

Residence time distribution of solid particles in the lower zone of apparatus with a moving bed of free-flowing material

Residence time distribution of solid particles in the lower zone of apparatus with a moving bed of free-flowing material

Coupled energy and multicomponent mass transfer in dispersions and suspensions with residence time and size distributions

AbstractAn analytical solution for the transport equation is presented for the case of coupled energy and multicomponent mass transfer in an ensemble of spherical drops, bubbles or solid particles. The solution is used to evaluate the total interfacial transfer rates in a population with particle size and residence time distributions. Using matrix notation and appropriate transformations, the partial differential equations are solved for each phase by using an integral operator whose kernel is the residence time distribution for the flow system. The method of attack is illustrated by solving the transport equations for fine dispersions or suspensions with high hold‐up values and presence of adventitious surface active agents.