Mean residence time and hold-up of solids in rotary kilns

Axial transport and residence time of MSW in rotary kilns: Part I. Experimental

Experiments were conducted in a rotary kiln containing ilmenite particles to study the residence time distribution (RTD) of low-density particles, holdup, and bed depth profile. The variables include feed rate of solids, slope and rotational speed of the kiln, type and size of the tracer, and dam height. Correlations are presented for mean residence time, dispersion number, holdup, and steady-state throughput of solids in terms of the process variables. A simple method is proposed to estimate the dam height that gives rise to a flat profile of solids bed along the length of the kiln.

Residence time distribution and material flow studies in a rotary kiln

On a mene des experiences dans un four rotatif a l'echelle pilote avec des particules de charbon et de coke en vue d'etudier le temps de sejour, la distribution du temps de sejour, le profil de profondeur du lit et le temps passe a la surface du lit. L'influence du coefficient de remplissage sur le temps de sejour a ete etudiee avec une profondeur de lit uniforme dans le four. Des mesures de la distribution du temps de sejour et du profil de profondeur du lit ont ete effectuees dans un four sans constriction finale, a differente vitesses de rotation et a differents apports en solides. On a mesure la fraction du temps de sejour correspondant au passage des particules a la surface du lit en photographiant le mouvement d'une particule coloree. Differentes equations ont ete testees pour representer les resultats experimentaux. L'equation de Kramers et Croockewit (1952) et celle de Ronco (1965) se sont revelees adequates pour calculer les temps de sejours moyens, tandis que seule la premiere a pu representer correctement le profil de profondeur du lit. On propose une equation qui s'est averee suffisamment precise pour predire la fraction du temps de sejour dans la couche superieure du lit

Experimental study of residence time, particle movement and bed depth profile in rotary kilns

This paper reports the results of an experimental and theoretical study to investigate the transient response of the granular flow through a laboratory scale inclined rotating cylinder to large step changes in one of three variables: (i) mass feed rate, (ii) rotation speed or (iii) axis inclination. Experimental measurements are reported for a range of operating conditions, sizes of step and a number of cylinder geometries. A mechanistic model for the transient response is derived based on a published steady state model. The dynamic model parameters are the cylinder radius, length, discharge dam height, axis inclination and rotation speed, the granular feed rate, and the bulk density and dynamic angle of repose of the granular material. The model has no adjustable parameters, making it useful for scale-up. The model takes the form of a non-linear partial differential equation, equivalent to a one dimensional unsteady diffusion equation with variable coefficients, and solution has been obtained numerically. Good agreement is found between the model and experiment both in the range of cases considered in the current study, and also for published experimental work, for which the cylinder size and granular material properties differ substantially from those of this work.

The Transient Response of Granular Flows in an Inclined Rotating Cylinder

The present work identifies the basic features of burden movement in a rotary kiln The cold model study was conducted with iron ore as the feed material to determine the influence of length to diameter ratio (L/D) of a rotary kiln on the filling degree, hold-up, and residence time of the charge An empirical equation correlating different operating variables has been derived on the basis of the experimental results The influence of individual parameters under different conditions on the residence time and back spillage has also been evaluated

Flow of materials in rotary kilns used for sponge iron manufacture: Part II. Effect of kiln geometry

Looking forward to the need of developing coal-based sponge iron technology in India, a country having no significant resources of either coking coal or natural gas, the Research and Development Division of the Tata Iron and Steel Company Limited (TISCO) set up a rotary kiln based direct reduction pilot plant in 1975. In this pilot plant, a totally indigenous technology for production of sponge iron has been developed in which non-coking coal is essentially used as the reductant. For easy scaling up of the TISCO Direct Reduction (TDR) process to units of 300 to 400 tpd capacity, it was thought necessary to explore some of the fundamental aspects of material flow in a rotary kiln. This was carried out by studying the flow of materials in room temperature models. The work was divided into two parts: first, a study of the influence of several operating parameters,viz., rotational speed, inclination of the kiln, effect of circular dams at the feed and the exit ends of the kiln,etc., and second, an investigation of the extent of segregation of a mixture of solids in a rotating kiln. The highlights of the experimental results dealing mainly with the effect of various kiln operating variables on the filling degree profile of the charge in the kiln are presented.

Flow of materials in rotary kilns used for sponge iron manufacture: Part I. Effect of some operational variables

The formation of accretions or ’rings’ in rotary kilns used for the manufacture of directly reduced iron (sponge iron) affects the residence time of the charge, kiln hold-up, and the kiln output to a great extent. In this part of the work, the effect of ring formation was simulated at room temperature in a scaled-down model of a rotary kiln by inserting conical dams in the shape of frustrums of cones through the feed end of the kiln. The influence of such conical dams on various operating parameters was evaluated.

Flow of materials in rotary kilns used for sponge iron manufacture: Part III. Effect of ring formation within the kiln

Procede TDR (Tisco Direct Reduction) avec reducteur solide, experimente en installation-pilote. Determination experimentale des profils de temperature des gaz et de la charge, ainsi que degre de reduction en bon accord avec un modele mathematique simplifie

Amit Chatterjee

Papers

Flow of materials in rotary kilns used for sponge iron manufacture: Part II. Effect of kiln geometry

Flow of materials in rotary kilns used for sponge iron manufacture: Part I. Effect of some operational variables

Flow of materials in rotary kilns used for sponge iron manufacture: Part III. Effect of ring formation within the kiln

A mathematical model of direct reduction of iron oxides in rotary kilns using the TDR process