PROCESS DESIGN OF ROTARY DRYERS FOR OLIVE CAKE

Olive-mill cake is one of the most widespread biomaterials for bioenergy exploitation in Greece. It is a sludge-type material, produced as byproduct from olive-mill extraction process. Its energy content is higher than 15 MJ/kg db and it can be used for direct burning, after drying. The drying process of olive cake is examined in the present paper. Drying kinetics data as well as the related thermophysical properties are obtained experimentally. The appropriate dryer model is proposed, validated and used to design an industrial rotary dryer. Economic analysis of the process is also discussed. A characteristic case study of an industrial rotary dryer for olive cake is included to illustrate the effectiveness of the proposed approach.     

SCALE-UP OF CASCADING ROTARY DRYERS

Until now most of the design methods for cascading rotary dryers have been either empirical or purely theoretical. A theoretical model is presented which simulates the operation of both cocurrent and countercurrent rotary dryers. It relies on pilot plant and bench scale tests to determine the values of parameters which describe respectively the transport of solids through the dryer and the drying rate of the feedstock. A procedure is outlined for using the model to scale up from these pilot-plant and bench-scale tests to full-scale dryers.     

SCALE-UP OF CASCADING ROTARY DRYERS

Abstract

Until now most of the design methods for cascading rotary dryers have been either empirical or purely theoretical. A theoretical model is presented which simulates the operation of both cocurrent and countercurrent rotary dryers. It relies on pilot plant and bench scale tests to determine the values of parameters which describe respectively the transport of solids through the dryer and the drying rate of the feedstock. A procedure is outlined for using the model to scale up from these pilot-plant and bench-scale tests to full-scale dryers.     

RESIDENCE TIMES OF TWO- AND THREE-COMPONENT MIXTURES IN CASCADING ROTARY DRYERS

The residence times of the components of two- and three-component mixtures of fine (195 µm), coarse (1315 µm) and very coarse (5040 µm) sands were measured in a pilot-scale cascading rotary dryer. The effects of mixture composition and air velocity (0-5.4 m s^-1) were determined. With no air flowing through the drum, the residence times of the individual components were almost the same as that of the overall mixture. Increasing the gas velocity caused a large decrease in residence time. In contrast, particle size had very little effect. The spread of residence times increased with air velocity, peaking between 2 and 4 m s^-1; composition had very little effect on the spread. The residence time of the overall mixture could be calculated using the particle transport model of Matchett and Baker if both the modified drag coefficient Φ_d and the particle Reynolds number Re_p were based on the superficial air velocity and the mass-average particle diameter.     

COMPARISON OF RESIDENCE TIME MODELS FOR CASCADING ROTARY DRYERS

ABSTRACT

The predictions of the models of Matchett and Baker (1988) Saeman and Mitchell (1954) and Friedman and Marshall (1949) for the solids residence time in rotary dryers have been compared with both pilot-scale and industrial-scale data. A countercurrent pilot-scale dryer of 0.2m diameter and 2m long has been used with air velocities up to 1.5 ms^?1 to measure the residence times of sorghum grain, The average discrepancy for the solids residence time between the predictions and the experiments that were carried out in the pilot-scale rotary dryer is — 10.4% Compared with the models of Friedman and Marshall (1949) and Saeman and Mitchell (1954) for the pilot-scale data obtained here, the Matchett and Baker model is more satisfactory for predicting the solids residence time in this pilot-scale dryer. It has also been found that the model of Matchett and Baker describes the industrial data of Saeman and Mitchell (1954) than the correlation of Friedman and Marshall (1949).     

AIR-SOLIDS DRAG IN CASCADING ROTARY DRYERS

ABSTRACT

This paper describes the results of theoretical and experimental studies on the effect of air flow on particle transport through cascading rotary dryers. Two possible models are formulated. In the first, the drag coefficient between the air and the solids is calculated on the assumption that the particles can be regarded as isolated spheres. This approach has been employed widely in the literature to estimate particle residence times in rotary dryers. The results yielded coefficients which were 1–2 orders of magntiude greater than those measured experimentally; this demonstrates the inadequacy of this approach. In the second model, the curtains are treated as flat. two-sided plates and the drag coefficient calculated accordingly. The predictions of this model are in much closer accord with the     

AIR-SOLIDS DRAG IN CASCADING ROTARY DRYERS

This paper describes the results of theoretical and experimental studies on the effect of air flow on particle transport through cascading rotary dryers. Two possible models are formulated. In the first, the drag coefficient between the air and the solids is calculated on the assumption that the particles can be regarded as isolated spheres. This approach has been employed widely in the literature to estimate particle residence times in rotary dryers. The results yielded coefficients which were 1-2 orders of magntiude greater than those measured experimentally; this demonstrates the inadequacy of this approach. In the second model, the curtains are treated as flat. two-sided plates and the drag coefficient calculated accordingly. The predictions of this model are in much closer accord with the     

OPTIMUM AIR DRYING STRATEGY FOR DEHUMIDIFIER TIMBER DRYERS

This paper presents an economic model for analyzing the cost behavior of dehumidifier timber drying process. Various costs, including those of air drying, are identified and quantified. Reasonable assumptions are made to simplify the calculation process. For species of both softwoods and hardwoods, the optimum air drying strategies are investigated based on two scenarios of existing commercial dehumifier dryers and well-run high performance dehumidifier dryers. This paper finds that when the timber maximum air drying degrade rate is less than 5%, air drying adds significant value to the operation of dehumidifier dryers. This benefit accelerates with the extent of air drying. With the use of high performance dehumidifier dryers, the importance of air drying tends to decrease. The cost of air drying is very sensitive to both the assumed interest rate and timber maximum air drying degrade rate.     

OPTIMUM AIR DRYING STRATEGY FOR DEHUMIDIFIER TIMBER DRYERS

This paper presents an economic model for analyzing the cost behavior of dehumidifier timber drying process. Various costs, including those of air drying, are identified and quantified. Reasonable assumptions are made to simplify the calculation process. For species of both softwoods and hardwoods, the optimum air drying strategies are investigated based on two scenarios of existing commercial dehumifier dryers and well-run high performance dehumidifier dryers. This paper finds that when the timber maximum air drying degrade rate is less than 5%, air drying adds significant value to the operation of dehumidifier dryers. This benefit accelerates with the extent of air drying. With the use of high performance dehumidifier dryers, the importance of air drying tends to decrease. The cost of air drying is very sensitive to both the assumed interest rate and timber maximum air drying degrade rate.     

OPTIMAL DESIGN OF WELL-MLXED FLUIDIZED BED DRYERS

ABSTRACT

In a recent article, Baker described a novel technique for estimating the energy consumption of well-mixed fluidized bed dryers based on the use of experimental drying curves. An integrated approach to performing sizing and energy consumption calculations for such dryers using this technique is described in the present paper. A computer program, which includes not only the dryer simulator but also a heat recovery module and an exhaust air recycle option, is used to evaluate the viability of different energy-conservation strategies. The effects of operating parameters such as bed temperature, solids loading and air velocity on energy consumption and bed area are also explored. The observed drying kinetics are shown to have a major effect on the optimal design and operation of the dryer.     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure that they can adequately accommodate the contents of the drum. A set of equations has been derived to calculate the solids holdup on angular and extended-circular flights in such dryers. Three examples of the practical use of these equations are presented. These include estimation of the design holdup of the dryer, selection of the number of flights, and exploration of the flight cascade characteristics.     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure....     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure....     

A SIMPLE DYNAMIC MODEL FOR SOLID TRANSPORT IN ROTARY DRYERS

ABSTRACT

The solid particle movement in a rotary drum plays an important role in drying processes. The solid distribution in the drum affects the amount of contact surface between the solid and the gas. The retention time of solids influences the time particles can stay in contact with the gas in order to transfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based control, it must be simple and yet represent dynamics of the system accurately. This paper addresses solid motion modelling and the effects of different variables involved in solid transport phenomena. Sugar drying process is the case study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorporated into a heat and mass transfer model ;o predict solid moisture and temperature for inferential and model-based control purposes. Results of several experiments that have been used to investigate dynamics of the system in terms of solid motion and to validate the model are also presented. The approach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a generalized model.     

A SIMPLE DYNAMIC MODEL FOR SOLID TRANSPORT IN ROTARY DRYERS

The solid particle movement in a rotary drum plays an important role in drying processes. The solid distribution in the drum affects the amount of contact surface between the solid and the gas. The retention time of solids influences the time particles can stay in contact with the gas in order to transfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based control, it must be simple and yet represent dynamics of the system accurately. This paper addresses solid motion modelling and the effects of different variables involved in solid transport phenomena. Sugar drying process is the case study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorporated into a heat and mass transfer model ;o predict solid moisture and temperature for inferential and model-based control purposes. Results of several experiments that have been used to investigate dynamics of the system in terms of solid motion and to validate the model are also presented. The approach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a generalized model.     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure.…     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure.…     

炭素回转窑的工艺设计与计算

通过对各种参数的计算,导出回转窑的长度,内径,煤气量、空气量,并对回转窑的物料平衡和热平衡进行计算,最终计算出烟气量,烟气成分及温度。     

MULTIVARIABLE PROCESS IDENTIFICATION AND CONTROL OF CONTINUOUS FLUIDIZED BED DRYERS

ABSTRACT

Dynamic models that rigorously describe fluidized bed dryers based on the fundamental principles of the process are usually so complex to be employed in control system design. To obtain simple reduced-order models for such systems, a sequence of step changes in the manipulated and load variables is introduced into the rigorous model. The obtained input–output dynamic response data are used for off-line model identification. Different types of linear models are generated, which are shown to be adequately representing the fluidized bed drying dynamics. The derived models are useful to develop model-based control algorithms such as Internal Model Control (IMC) and Model Predictive Control (MPC). Performance and robustness properties of these controllers are analyzed. Simulation results demonstrate a good performance in terms of tracking and load rejection capabilities.     

MULTIVARIABLE PROCESS IDENTIFICATION AND CONTROL OF CONTINUOUS FLUIDIZED BED DRYERS

Dynamic models that rigorously describe fluidized bed dryers based on the fundamental principles of the process are usually so complex to be employed in control system design. To obtain simple reduced-order models for such systems, a sequence of step changes in the manipulated and load variables is introduced into the rigorous model. The obtained input-output dynamic response data are used for off-line model identification. Different types of linear models are generated, which are shown to be adequately representing the fluidized bed drying dynamics. The derived models are useful to develop model-based control algorithms such as Internal Model Control (IMC) and Model Predictive Control (MPC). Performance and robustness properties of these controllers are analyzed. Simulation results demonstrate a good performance in terms of tracking and load rejection capabilities.