SELF-TUNING CONTROL OF EGG DRYING IN SPOUTED BED USING THE GPC ALGORITHM

A spouted bed is used to dry many and different materials ranging from granules to pastes and suspensions. This work presents an implementation and tests of an advanced control strategy on a spouted bed dryer. Water was used as the ideal paste for tests. An adaptive control algorithm GPC (Generalized Predictive Control) was implemented. A microcomputer was used to maintain humidity and temperature set points of air in the dryer by manipulating electric power of heat exchanger and paste feed flow rate. Instrumentation was set-up with different sensors, interface and final control elements for operation. Stability and performance analysis of the control strategy was accomplished. A robust stable controller was obtained which had also encouraged us to extend the investigation of this control strategy to the drying of other pastes.     

Drying Of Pastes In Spouted Beds Of Inert Particles: Design Criteria And Modeling

ABSTRACT

The drying of pastelike materials can be performed well in spouted beds (SB) of inert particles. In this work the drying performance of pastes in conical pastes in conical spouted beds is analyzed as a function of column dimensions, fluid flow characteristics and paste properties. imulated data on fluid flow together with the experimental results on drying of different pastelike materials are presented and discussed to provide criteria for the design of a conical spouted bed dryer for suspensions.     

Industrial Trials of Paste Drying in Spouted Beds Under QDMC

Abstract

Spouted bed has been extensively investigated by many authors for years, but the issue of controlling its operation still remains in basic developing stages. The present work consists of the application of an advanced control strategy (QDMC—Quadratic Dynamic Matrix Control) to automate the operation of a large-scale spouted bed dryer. The work on control strategies for spouted bed was motivated by the lack of references on this subject and the encouraging results obtained by Corrêa et al. (Corrêa, N.A.; Freire, J.T.; Corrêa, R.G. Improving operability of spouted beds using a simple optimizing control structure. Brazilian Journal of Chemical Engineering 1999 16 (4), 359–368; Corrêa N.A. Corrêa, R.G.; Freire, J.T. Adaptive control of paste drying in spouted bed using the GPC algorithm. Brazilian Journal of Chemical Engineering 2000 17 (4–7), 639–648; Corrêa, N.A.; Corrêa, R.G.; Freire, J.T. Self-tuning control of egg drying in spouted bed using the GPC algorithm. Drying Technology 2002 20 (4), 813–828.) for a laboratory-scale apparatus. The industrial-scale spouted bed dryer has a height of 4 m and a diameter of 66 cm. The same configuration of data acquisition unit, sensors, and interface developed for the laboratory-scale unit was employed. The dryer is capable of processing up to 20 L/h of pasty material. The powder moisture content (Ys), inferred from measurements of temperature at the exhaustion of the bed bulk, and the powder production rate (Pr), measured on-line by an electronic balance, are the controlled variables. The manipulated variables are: the paste inflow rate (W), regulated by an automatic pump, and the electrical power supply for air heating (P), regulated by a thyristor. The bed pressure drop, the airflow rate, and the information from the environment are monitored by means of an interfaced microcomputer. Experimental runs of drying up to 400 kg/day of an Al₂O₃ 10% aqueous suspension were carried out. The results showed that the QDMC control is robust with respect to the main variables involved and is efficient in maintaining the operation of the bed under the constraints of the system. The major aim concerning the scale-up of spouted bed, which is the determination of the minimum amount of energy required to ensure spout stability, was accomplished by the constrained control strategy.     

EFFECT OF THE PRESENCE OF PASTE IN A CONICAL SPOUTED BED DRYER WITH CONTINUOUS FEEDING

ABSTRACT

The spouted bed with inert particles has been used as a paste dryer, producing a fine powder. Few authors have studied the behavior of the bed in the presence of paste, which is important for the design of this equipment. In this work the spouting pressure drop, the minimum spouting velocity and the paste residual content in the bed were measured as a function of the feed rate. Experiments were carried out with two Newtonian pastes (egg paste and blood), a pseudoplastic one (xanthan gum suspension) and water, used as a referential material. These three types of paste behaved differently in terms of the variation of the spouting pressure drop and the minimum spouting velocity. The paste residual content in the bed was only measured with the egg paste, and in this case it increased very slightly with the feed rate, until the maximum throughput allowed by the system.     

Drying Of Pastes In Spouted Beds Of Inert Particles: Design Criteria And Modeling

The drying of pastelike materials can be performed well in spouted beds (SB) of inert particles. In this work the drying performance of pastes in conical pastes in conical spouted beds is analyzed as a function of column dimensions, fluid flow characteristics and paste properties. imulated data on fluid flow together with the experimental results on drying of different pastelike materials are presented and discussed to provide criteria for the design of a conical spouted bed dryer for suspensions.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

Abstract

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20–25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

A MATHEMATICAL MODEL FOR CONTINUOUS DRYING OF GRAINS IN A SPOUTED BED DRYER

ABSTRACT

A mathematical model for a continuous spouted bed dryer has been presented to predict moisture content, air and grain temperatures as well as energy consumption. To better understand the interactive influence of processes in each region of the spouted bed, solution schemes for the spout and downcomer were treated separately. The behavior of dryer was investigated experimentally and found that the dryer behaved differently from an ideal plug flow. The drying rate as simulated by the model is almost constant during grain movement in the dryer. Absence of airflow in the downcomer leads to a tempering process that takes place in the downcomer while intense heat and mass transfer occurs mainly in the spout due to the high airflow rate there. Furthermore, by considering the predicted grain temperature history as one of the indicators of product quality, one can, in principle, design appropriate successive processes in a continuous spouted bed dryer to minimize product damage.     

EFFECT OF THE PRESENCE OF PASTE IN A CONICAL SPOUTED BED DRYER WITH CONTINUOUS FEEDING

The spouted bed with inert particles has been used as a paste dryer, producing a fine powder. Few authors have studied the behavior of the bed in the presence of paste, which is important for the design of this equipment. In this work the spouting pressure drop, the minimum spouting velocity and the paste residual content in the bed were measured as a function of the feed rate. Experiments were carried out with two Newtonian pastes (egg paste and blood), a pseudoplastic one (xanthan gum suspension) and water, used as a referential material. These three types of paste behaved differently in terms of the variation of the spouting pressure drop and the minimum spouting velocity. The paste residual content in the bed was only measured with the egg paste, and in this case it increased very slightly with the feed rate, until the maximum throughput allowed by the system.     

Drying of Liquid and Pasty Products in a Modified Spouted Bed of Inert Particles

A novel type of a dryer is presented in which finely dispersed liquids or pastes are dried in a modified spouted bed of inert particles. Due to unique configuration of a drying chamber and gas distributors, the dryer combines advantages of the spouted bed, swirling bed, and counter-rotating impinging streams. Correlations and graphs for design calculations are given.     

Control of Spouted Bed Dryers

During the last 8 years, the Drying Center at Universidade Federal de São Carlos has been investigating the control problems of drying process of pasty materials associated with the spouted bed dryer. Starting with structures involving PI controller, we also implemented advanced MPC control techniques and real time optimization (this last one based on simulations only). Different control structures were implemented in a pilot spouted bed dryer where the behavior of the system was tested for water and homogenized chicken eggs. Based on promising results, the perspective is to use an adequate control system in a spouted bed scale‐up.     

SCALE-UP OF SPOUTED BED DRYERS: CRITERIA AND APPLICATIONS

Abstract

The criteria required for reliable scale-up of the aerodynamics of spouted bed dryers of grains are stated and discussed. The dryer modeling role for effective scale-up, design and analyses of such dryers will be outlined. Suggestions are made on how small scale drying and aerodynamic data may be scaled up for spouted bed dryers. Appropriate empirical and semi-empirical correlations are listed. A flowchart is provided for design and analysis of a conventional and a two-dimensional spouted bed dryers.     

Drying of Liquid Feedstocks in a Spout‐Fluid‐Bed with Draft‐Tube Submerged in Inert Solids: Hydrodynamics and Drying Performance

A spout‐fluid bed with draft tube submerged in a bed of polypropylene beads was used for drying maltodextrin solutions. The hydrodynamics of the dryer were studied by determining the annular air flow vertical profile at different spouting velocities, using an additional air flow rate through the annulus equivalent to 0.5 U_mf. The drying performance of the dryer was studied through the determination of several dryer response parameters (product moisture, evaporative capacity and volumetric evaporative capacity). These parameters were compared with those obtained in a conventional spouted bed with inert solids and a spray dryer.     

BEAN DRYING IN FIXED,SPOUTED AND SPOUT-FLUID BEDS: A COMPARISON AND EMPIRICAL MODELING

ABSTRACT

In this work the drying of IAC-Carioca bean was analyzed experimentally in fixed, spouted and spout-fluid beds. A laboratory scale, batch operated apparatus was used. To obtain experimental data, a factorial design technique was used and the influences of the following variables on the process were evaluated: the solids toad, initial grain moisture and drying air temperature. This analysis was done for each dryer by means of drying curves, evolution of grain temperature over time, drying rate and statistical results obtained from factorial design. An energy evaluation was also done and used as a means of comparison between the dryers studied. The three dryers operating under the same conditions showed very similar behavior and the fixed bed dryer showed a performance slightly better. With this work the potential of using spouted bed grain dryerswas confirmed and the possibility of using the spout-fluid bed as a dryer was verified. Two empirical models were proposed and their parameters were correlated with experimental variables. A sensory evaluation was also performed for the purpose of evaluating the effects that the high drying temperatures had on the grain's potential value as food.     

HYDRODYNAMICS AND MASS TRANSFER IN A SPOUTED BED DRYER

ABSTRACT

The disposal of sludge generated by water treatment plants poses major financial and environmental problems. Drying of the sludge is an essential pan of any disposal process which may include incinerating, landfilling or upgrading. In the present study, experiments were carried out to investigate the drying of sludge in a spouted bed and to characterize the hydrodynamics and mass transfer mechanisms. The effect of bed moisture content on the minimum spouting velocity (U_ms) was examined for sludge granules. U_ms was found to increase with increasing the moisture content of the sludge particles. The gas phase mass transfer coefficient in the dryer was determined using porous calcined alumina particles and the results were compared with predictions by correlations available in the literature. The existing correlations gave poor predictions for the mass transfer coefficient. A new correlation for the mass transfer coefficient in a spouted bed dryer was developed based on the experimental results.     

Moisture Prediction During Paste Drying in a Spouted Bed

The objective of this work was to derive and experimentally verify a hybrid CST/neural network model to determine the moisture content of the powders produced during paste drying in a spouted bed and describe the highly coupled heat and the mass transfer. The model was derived from overall energy and mass balances with effective drying kinetics given by a neural network. Simulations were performed in MatLab and drying experiments for model verification were carried out for different pastes in a conical, semi-pilot-scale spouted bed.     

SPOUTED AND SPOUT-FLUIDIZED BEDS FOR GRAM DRYING

The objectives of this work are to analyze the drying performance of conical-cylindrical spouted bed (CSB) dryers for three different grains (rice, corn and wheat), and to compare the drying efficiency of CSB dryers with that of spout-fluid bed (SFB) dryers. A PC-program was developed for: (I) -optimization of the CSB dryer dimensions; (2) -simulation of drying grains in the optimized CSB dryer (including start-up period); and, (3) -analysis of the drying performance in a similar SFB dryer.

The liquid diffusion model is used to describe the falling rate drying period. Semi-empirical correlations available in the literature as well as information obtained in the authors' laboratory for spouted and spout-fluidized beds of grains are used to describe the aerodynamic parameters.

The results are presented in terms of the size of the dryer, energy consumption, air handling requirement, drying characteristics etc for different drying conditions. The drying effeciency in a CSB is compared with that in a similar SFB for different grain feed rates and drying temperatures.     

Real-time monitoring of milk powder moisture content during drying in a spouted bed dryer using a hybrid neural soft sensor

The direct measurement of the moisture content of dried products would be more interesting for process control purposes. However, the most common procedures for such measurement are either slow or expensive for industrial dryers. Alternatively, one might reduce the cost of an effective measurement procedure by using other sensors (which are less expensive and whose response is faster), which can provide information for a physical–mathematical model representing well the drying process. In this context, the objective of this work was the application of a previously developed soft sensor for the online measurement of milk powder produced in a spouted bed dryer. A hybrid neural model was used as part of a soft sensor and coupled to the data acquisition interface. The sensor was capable of estimating milk powder moisture content when the dryer was submitted to disturbances on air inlet temperature and paste inlet flow rate. On the other hand, the model failed to describe paste accumulation within the bed, which is the reason why the soft sensor tended to overestimate moisture content for longer operation times.     

Analysis of the dynamics of paste drying in a spouted bed

Although there are some models available in the literature for paste drying in spouted beds, few of them have focused on transient analysis of dynamical systems. Our objective was to integrate experiments and simulations of a dynamic model to investigate the transient response to disturbances and interruptions in the feed flow during paste drying in a spouted bed with inert particles. The spouted bed consisted of a cylindrical column with 50.0?cm of height and 20.0?cm of diameter. Drying tests were performed at inlet gas temperatures of 70?°C and 100?°C and inlet air flow 30% above the minimum spouting velocity. A 5% w/w suspension of calcium carbonate was used as paste material, and glass spheres of 2.2?mm were used as inert materials. Different patterns of step function changes were tested in the paste feed flow rate. A lumped parameter model was used to predict mass and heat transfer during the drying. Experiments and simulations were in good agreement.     

The Gas-to-Particle Heat Transfer and Hydrodynamics in Spouted Bed Drying of Sawdust

This article presents experimental results for spouted bed drying of sawdust, carried out in a full-scale as well as in a laboratory-scale dryer using air as well as steam as drying media. The aim is to present design parameters for a spouted-bed sawdust dryer that can be used by the industry in designing full-scale dryers. A hydrodynamically stable spouted jet spouted bed was obtained. The heat transfer characteristics of the bed were represented in terms of a volumetric heat transfer coefficient (VHC). When sawdust is dried in a spouted bed, the mean VHC is increasing up to fiber saturation level (20-25% wb) from 40 to 110 W/m³ K. The VHC decreases with the residence time and with an increased static bed height. Gas temperature profiles are also presented for the bottom part of the drying chamber.     

SPOUTED BED DRYING OF SLUDGE FROM METALS FINISHING INDUSTRIES WASTEWATER TREATMENT PLANTS

ABSTRACT

A 0.15 m diameter half cylindrical spouted bed was used to dry a ferric hydroxide - zinc hydroxide sludge with a moisture content of 83.4 % wet basis. Heat for drying was provided by an electrical air preheater. The sludge was fed through an air cooled feeder into the spout and dried product was removed by elutriation; it was captured by a cyclone and baghouse. The mechanisms of drying and the performance of the drier were studied as a function of the operating variables. A glass front panel was used for visual observation of the system to elucidate the drying mechanisms, a stainless steel panel was used at other times.

The study showed that a spouted bed drier could produce a consistent fine powder product with a mechanically simple and reliable design. A cost comparison of a spouted bed with other driers for a typical metals finishing installation shows that the spouted bed is cost competitive with conventional technology.