Effect of lifter shape and operating parameters on the flow of materials in a pilot rotary kiln: Part II. Experimental hold-up and mean residence time modeling

TLDR: In this article, the effects of the kiln slope, rotational speed, mass flow rate of materials, and exit dam height on the hold-up and the mean residence time (MRT) were determined from the residence time distribution measurements.

About: This article is published in Powder Technology.The article was published on 2015-01-01 and is currently open access. It has received 38 citations till now. The article focuses on the topics: Rotary kiln & Kiln.

Figures

Fig. 3: Comparison of experimental MRT and time of passage of solid particles. Solid lines are ±20% margins.

Table 2: Physical properties of materials

Fig. 2: In uence of operating parameters (N, S, Ṁ and exit dam height) on the hold-up volume fraction for the ow of sand and broken rice, when the kiln is equipped with either straight or rectangular lifters.

Fig. 4: In uence of operating parameters (N, S, Ṁ and exit dam height) on the MRT for the ow of sand and broken rice, when the kiln is equipped with either straight or rectangular lifters.

Fig. 8: Comparison of experimental MRT from a) Sai et al. [18] and b) Chatterjee et al. [2] with predicted values from Eq.13 using the 3 sets of parameters as given in Table 4. Solid lines are ±20% margins.

Fig. 6: Comparison of experimental MRT from Debacq [16] with predicted values from Eq.13 using the 3 sets of parameters as given in Table 4. Solid lines are ±20% margins.

Frequently asked questions

Q1. What have the authors contributed in "Effect of lifter shape and operating parameters on the flow of materials in a pilot rotary kiln: part ii. experimental hold-up and mean residence time modeling" ?

The MRT was determined from the residence time distribution measurements as detailed in Part I of this work. The correlation not only gave good agreements with the experimental data from the present study, but also demonstrated good predictive performances when applied to published experimental data of other kilns from the literature ; the model is applicable for kilns which are inclined, equipped or not with lifters, and tted or not with a dam at the outlet end. Furthermore, two shapes of lifters were used to determine the in uence of lifters geometry: straight lifters ( SL ) and rectangular lifters ( RL ) were compared. 

Q2. What future works have the authors mentioned in the paper "Effect of lifter shape and operating parameters on the flow of materials in a pilot rotary kiln: part ii. experimental hold-up and mean residence time modeling" ?

Therefore, possible directions for further work could be ( i ) to extend the validity of the model to other types of bed motion with adequate set of parameters, ( ii ) to enrich the experimental data matrix with results from the use of new types of solid materials for a better con dence in the set of parameters determined. 

Q3. What is the purpose of this model?

The main purpose of this model is to come up with a prediction of the MRT of solid particles de ned as a function of operating parameters, namely the kiln rotational speed, the kiln slope, the mass ow rate and the exit dam height, as well as the kiln design and the bulk materials properties. 

Q4. What is the definition of rotary kilns?

Rotary kilns are gas-solid reactors widely used in mineral process applications and other processes applied to speci c granular materials. 

Q5. What are the parameters that are dependent on the materials properties?

The angle of repose and the (inverse of) Hausner ratio are strongly dependent on the materials properties; for this reason, when determining the parameters with either sand or broken rice experimental data, γ and ζ were xed to the values obtained from the whole experimental data matrix . 

Q6. Why have there been studies aimed at predicting the ow of solids in rotary?

Due to their extensive use in industry, there have been several studies intending to model the solids transport through the kiln cylinder, usually equipped with lifters. 

Q7. What is the purpose of this paper?

This paper is concerned with the study of the e ects of usual operating conditions, shape of lifters, and type of materials on the mean residence time of solids particles as well as on the kiln hold-up. 

Q8. What is the earliest equation for the calculation of the time of passage of particles in rotary?

One of the earliest equations was developed by Sullivan et al. [1] for the calculation of the time of passage of particles in rotary kilns which do not have lifters, as follows:τ = 1.77L√ θSDN × factor (1)where θ is the angle of repose, S is the kiln slope, N is the rotational speed, L and D respectively the length and internal diameter of the kiln, factor is a parameter accounting for the operating conditions, it is unity for a simple kiln without obstructions or constrictions. 

Q9. What could be the directions for further work?

possible directions for further work could be (i) to extend the validity of the model to other types of bed motion with adequate set of parameters, (ii) to enrich the experimental data matrix with results from the use of new types of solid materials for a better con dence in the set of parameters determined. 

Q10. What is the explanation for the poor results of the model?

These latter poor results of the model can be attributed to (i) the di culties in extrapolating to kilns of rotational speed lower than 2 rpm, leading most of time to small Froude numbers characteristic of beds in slipping motion [19], or perhaps (ii) the wide range of variation of the e ective exit open diameter achieved by Chatterjee et al. [2] even if the results obtained in the case of Sai et al. [18] experiments were quite acceptable. 

Q11. What are the parameters missing from the kiln model?

some parameters were missing such as the exit dam height, which does not appear in the list of parameters, though its e ect has been studied in their experimental matrix. 

Q12. What are the parameters used to predict the hold-up and the MRT of the solids?

The e ects of operating parameters, namely, the rotational speed, the kiln slope, the mass ow rate, the exit dam height, the type of materials and shape of lifters, on the hold-up and mean residence time have been investigated.