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1.
iquid phase RTD curves were investigated in classical fixed and fluidized bed regimes with high density particles. The effect
of liquid velocity was studied on bed hydrodynamics. Using an impulse tracer injection technique in a column of 5 cm inner
diameter and 1.2 m height, liquid RTD, mean residence time (MRT), axial dispersion coefficient (ADC) and vessel dispersion
number (N
D
) were determined. ADC increases with liquid superficial velocity. It varied from 4.63 to 20.7 cm2/s for the particle Reynolds number of 43 to 279, respectively. The experimental results show that the hight density particles
cause less ADC than the low density particles at an identical Reynolds number. 相似文献
2.
Uk Yeong Kim Sung Mo Son Suk Hwan Kang Yong Kang Sang Done Kim 《Korean Journal of Chemical Engineering》2007,24(5):892-896
Residence time distribution (RTD) of exhaust gas in a wet scrubbing system was investigated for application to the removal
of SO
x
, NO
x
or dust included in exhaust gas. The mixing of gas phase in the wet scrubbing system was also examined by considering the
axial dispersion coefficient of gas phase. Effects of gas amount (velocity), liquid amount (velocity) and solid floating materials
on the residence time distribution (RTD) and axial dispersion coefficient of exhaust gas were discussed. The addition of solid
floating materials could change the RTD and thus dispersion of exhaust gas in the scrubbing system. The mean residence time
and axial dispersion coefficient of exhaust gas were well correlated in terms of operating variables. 相似文献
3.
Krishna Deo Prasad Nigam Anil Kumar Saroha Arunabha Kundu Harish Jagat Pant 《加拿大化工杂志》2001,79(6):860-865
The 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. 相似文献
4.
This paper presents physical, chemical and mechanical characteristics of metakaolins obtained from an industrial flash calciner, in order to compare their properties with standard industrial metakaolin produced in a rotary kiln calciner. Three kaolins, with three levels of purity, were calcined by these two different methods to give six different metakaolins for the study. The results showed that the method of calcination did not affect the chemical composition of the metakaolins formed but did influence their physical properties and performance as a supplementary cementitious material when blended with Portland cement, and in geopolymer synthesis. Flash metakaolins have a lower water demand than rotary metakaolins, which can be explained by the morphological properties of the flash metakaolin, induced by the calcination process. Traditional rotary-calcined metakaolins tend to be angular layered particles, whereas flash metakaolins contain spherical particles. Mechanical test results showed that the two methods of calcination can lead to metakaolins with equivalent performance in the synthesis of construction materials. 相似文献
5.
Axial and lateral mixing of fine particles in a binary-solid riser have been investigated using a phosphor tracer method. The measured bimodal residence time distribution (RTD) demonstrated two types of axial dispersions of the fines: the dispersion of discrete particles and that of clusters. A proposed one-dimensional, bimodal dispersion model describes the bimodal RTDs very well. The axial Peclet number of the fines is not sensitive to the fraction of coarse particles, gas velocity and solids circulation rate. Lateral solids dispersion was determined by measuring the solids RTD at different radii using a point source tracer injection. A two-dimensional dispersion model describes the measured RTDs satisfactorily. Lateral solids mixing decreased as coarse particles were added into the riser. Correlations of the axial and lateral Peclet numbers obtained fit the experimental data well. 相似文献
6.
Measuring the residence time distribution in a twin screw extruder with the use of NIR‐spectroscopy
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The mean residence time (MRT) and the residence time distribution (RTD) of polypropylene in a twin‐screw extruder was determined directly in‐line with the help of near infrared (NIR) spectroscopy and the use of an UV‐absorber as tracer. Different experiment alignments such as screw speed, mass throughput, back pressure as well as tracer content and their influence on MRT and RTD have been investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39919. 相似文献
7.
Experimental results on the influence of the discharge plate geometry on the dimensionless residence time distribution (RTD) for material transport in a continuous rotary drum are described. The RTD obtained by a stimulus-response technique for the different discharge plates can be described well by the axial dispersed flow model. Based on the characteristic Peclet number of the flow regime, material flow tended more towards the plug flow condition at an intermediate size discharge opening. Calculation of the axial dispersion coefficient in each case revealed that the open-ended drum behaved more like an ideal mixer. The implication of these results on the design of continuous rotary devices is discussed. 相似文献
8.
The mixing in two-phase gas-liquid and three-phase gas-liquid-solid system (turbulent bed contactor) is evaluated through residence time distribution (RTD) studies in terms of Peclet number. RTD experiments are conducted for various gas and liquid velocities, and number of stages for two- and three-phase systems. Since the mean residence time is very short in both the systems, a mixed flow tank with exponential decay RTD is used in series. After deconvolution, the RTD of the system is obtained. The experimental RTD curves are satisfactorily compared with the axial dispersion model and Peclet numbers are evaluated for all the experiments. The axial dispersion coefficients are calculated from Peclet numbers. With this study, it is thought that liquid phase mixing may be controlled by changing the quantity of solid particles in the bed. 相似文献
9.
Synthesis of peroxypropionic and peroxyacetic acids from hydrogen peroxide and their carboxylic acids was carried out in a continuous fixed-bed reactor, demonstrating the concept of green process technology: biodegradable chemicals are made with the aid of heterogeneous catalysts. This reactor was constructed with several sampling locations along its length, allowing a better kinetic investigation. A profound study of the mean residence time distribution (RTD) was performed to analyze the behavior of the flow pattern at different liquid flow rates and catalyst loadings by using step and impulse methods with different tracer molecules. It was found that impulse experiments with HCl as a tracer is the most reliable method to study the RTD, because of this tracer does not interact with the catalyst. Based on the RTD study, it was demonstrated that the temperature (in the range 30–60 °C) and the catalyst distribution inside the reactor do not affect the flow pattern, but the ratio of the catalyst mass-to-liquid ratio affects the mean residence time and the liquid dispersion. Furthermore, it was shown that the presence of an axial dispersion is negligible when the average particle diameter is <1.38 mm, e.g., Péclet number exceeds 100. The kinetic study was carried out at different mean residence times (from 10 to 55 min), at different wet catalyst loadings (from 25 to 49 g) and reactor temperatures (from 30 to 60 °C). Mathematical models comprising kinetic and dispersion parameters were developed to compare the estimated parameters obtained from the continuous fixed-bed reactor with the ones obtained from a batch reactor. 相似文献
10.
A.E.R. Bruce 《Chemical engineering science》2003,58(15):3453-3463
Axial mixing of the liquid phase in turbulent bed contactor (TBC) is studied through residence time distribution (RTD) experiments over a large range of variables such as flow rate of gas and liquid phases, static bed heights, diameter and density of particles and number of stages in presence of downcomer using air water system. Since all the liquid exits only through the downcomer, it enables the correct estimation of exit concentration of the tracer. The experimental RTD curves are satisfactorily compared with the axial dispersion model. The Peclet numbers evaluated by axial dispersion model and the Peclet numbers reported in the literature are used to propose a unified correlation in terms of operating and geometric parameters. Correlation is also developed for predicting the axial dispersion coefficient. It was observed in the present study that almost plug flow conditions can be achieved in multistage TBC. 相似文献
11.
The reduction of the NOx content in in-line-calciner-type kiln systems can be made by optimization of the primary firing in the rotary kiln and of the secondary firing in the calciner. Because the optimization of calciner offers greater opportunities the mathematical modeling of this reactor is very important. A heterogeneous, dynamic mathematical model for an in-line low-NOx calciner based on non-isothermal diffusion-reaction models for char combustion and limestone calcination has been developed. The importance of the rate at which preheated combustion air was mixed into the main flow was particularly studied. The results of the simulations indicate that the external heat and mass transfer to the char particles is not limiting. Internal diffusion of O2, CO, NO and CO2 is important especially in the reducing zone and the first part of the oxidizing zone of the calciner and the internal heat transport limitation is significant for the endothermic limestone calcination. The rate at which preheated combustion air is mixed into the main flow directly influences the coal combustion rate, and thereby through the rate of heat release from combustion, it also influences the calcination rate and the temperature profile. The mixing rate has some influence on the CO concentration profile and an important influence on the overall degree of fuel-N to NO conversion. 相似文献
12.
Xingjun Wang Xianhui Hu Lishun Hu Guangsuo Yu Fuchen Wang 《Frontiers of Chemical Engineering in China》2010,4(3):353-359
Based on some experimental investigations of liquid phase residence time distribution (RTD) in an impinging stream reactor,
a two-dimensional plug-flow dispersion model for predicting the liquid phase RTD in the reactor was proposed. The calculation
results of the model can be in good agreement with the experimental RTD under different operating conditions. The axial liquid
dispersion coefficient increases monotonously with the increasing liquid flux, but is almost independent of gas flux. As the
liquid flux and the gas flux increase, the liquid dispersion coefficient of center-to-wall decreases. The axial liquid dispersion
coefficient is much larger than that of center-to-wall, which indicates that the liquid RTD is dominated mainly by axial liquid
dispersion in the impinging stream reactor. 相似文献
13.
14.
Xingjun WANG Xianhui HU Lishun HU Guangsuo YU Fuchen WANG 《Frontiers of Chemical Science and Engineering》2010,4(3):353
Based on some experimental investigations of liquid phase residence time distribution (RTD) in an impinging stream reactor, a two-dimensional plug-flow dispersion model for predicting the liquid phase RTD in the reactor was proposed. The calculation results of the model can be in good agreement with the experimental RTD under different operating conditions. The axial liquid dispersion coefficient increases monotonously with the increasing liquid flux, but is almost independent of gas flux. As the liquid flux and the gas flux increase, the liquid dispersion coefficient of center-to-wall decreases. The axial liquid dispersion coefficient is much larger than that of center-to-wall, which indicates that the liquid RTD is dominated mainly by axial liquid dispersion in the impinging stream reactor. 相似文献
15.
16.
Gas phase axial dispersion characteristics were determined in a molten salt oxidation reactor (air-molten sodium carbonate
salt two phase system). The effects of the gas velocity (0.05–0.22 m/s) and molten salt bed temperature (870–970 °C) on the
gas phase axial dispersion coefficient were studied. The amount of axial gas-phase dispersion was experimentally evaluated
by means of residence time distribution (RTD) experiments using an inert gas tracer (CO). The experimentally determined RTD
curves were interpreted by using the axial dispersions model, which proved to be a suitable means of describing the axial
mixing in the gas phase. The results indicated that the axial dispersion coefficients exhibited an asymptotic value with increasing
gas velocity due to the plug-flow like behavior in the higher gas velocity. Temperature had positive effects on the gas phase
dispersion. The effect of the temperature on the dispersion intensity was interpreted in terms of the liquid circulation velocity
using the drift-flux model. 相似文献
17.
18.
Hong Il Cho Chan-Hwa Chung Gui Young Han Gui Ryong Ahn Jong Su Kong 《Korean Journal of Chemical Engineering》2000,17(3):292-298
Gas mixing behavior was investigated in a residence time distribution experiment in a bubbling fluidized bed of 0.07 m ID
and 0.80 m high. Linear low density polyethylene (LLDPE) particles having a mean diameter of 772 Μm and a particle size range
of 200-1,500 Μm were employed as the bed material. The stimulus-response technique with CO2 as a tracer gas was performed for the RTD study. The effects of gas velocity, aspect ratio (H0/D) and scale-up on the axial gas dispersion were determined from the unsteady-state dispersion model, and the residence time
distributions of gas in the fluidized bed were compared with the ideal reactors. It was found that axial dispersion depends
on the gas velocity and aspect ratio of the bed. The dimensionless dispersion coefficient was correlated with Reynolds number
and aspect ratio. 相似文献
19.
In this paper, a solids transport model for flighted rotary dryers is presented. Emphasis is placed on combining statistical and mechanistic modelling efforts to create a physically motivated compartment model involving pairs of perfectly mixed tank reactors linked in a series arrangement. Here, each tank pair, or cell, aims to physically describe a finite slice of a case study industrial rotary sugar dryer, and is hence governed primarily by flight geometry and dryer operational variables such as rotational speed and dryer inclination. Solids flow paths are structured to properly represent the different modes of transport in the rotary dryer, and values of transport coefficients are based on calculated rates of rotational and axial flows. A solids dispersion variable is used to correlate the model residence time distribution (RTD) prediction with available data from a tracer study conducted during industrial operation of a full-scale raw sugar dryer. RTD results from the model show intuitive responses to variations in solids feed rate, rotational speed and drum inclination. 相似文献
20.
The hydrodynamic characteristics of propeller-induced toroidal flow in a loop reactor were investigated by performing an RTD analysis. The experimental determination of circulation time allows the calculation of the mean axial velocity with respect to the rotational speed of the impeller. RTD measurements are interpreted with the aid of the dispersion plug flow model, and it is shown that axial dispersion is relatively weak in the torus reactor. The mixing time was also determined experimentally and related to the circulation time. A direct relationship between mixing time and axial dispersion coefficient has been established, leading to a correlation for the mixing time in a torus reactor. 相似文献