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

ABSTRACT

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

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.     

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

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.     

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.     

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.     

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.     

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.     

COMPARISON AMONG PI, DMC, QDMC, AND GPC ALGORITHMS IN THE CONTROL OF THE SPOUTED BED DRYER

This article presents comparative analysis between the classical PI (proportional-integral control) and MPC (model predictive control) techniques for a drying process on spouted beds. The on-line experimental setups were carried out in a laboratory-scale plant of a spouted bed dryer. The main objective was to optimize the plant operation by searching for the best control structure to be used in future scale enlargement. The major drawbacks encountered in this kind of system were high interactivity among variables, a malfunction as a result of calculated variables out of the operational window, and modeling mismatch. Despite the robustness of the operational PI, the control actions of this strategy did not overcome the variable interactions. The DMC (dynamic matrix control) and the QDMC (quadratic dynamic matrix control) algorithms performed satisfactorily over the major drawbacks. Special attention was given to the latter algorithm due to its ability to hold the variables under constrained oscillations. However, the best results were found for the adaptive GPC (generalized predictive control) algorithm whose actions prevailed over the modeling mismatch due to the strong nonlinear behavior intrinsic to the process. The main goal of the present work is to describe a procedure that can be standardized for other types of dryers and different scales. This is especially the case for the adaptive GPC, whose control structure is independent of the dryer nature and scale and whose implementation does not require previous identification procedures (self-tuning) and/or structural changes.     

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.     

COMPARISON AMONG PI,DMC, QDMC,AND GPC ALGORITHMS IN THE CONTROL OF THE SPOUTED BED DRYER

This article presents comparative analysis between the classical PI (proportional-integral control) and MPC (model predictive control) techniques for a drying process on spouted beds. The on-line experimental setups were carried out in a laboratory-scale plant of a spouted bed dryer. The main objective was to optimize the plant operation by searching for the best control structure to be used in future scale enlargement. The major drawbacks encountered in this kind of system were high interactivity among variables, a malfunction as a result of calculated variables out of the operational window, and modeling mismatch. Despite the robustness of the operational PI, the control actions of this strategy did not overcome the variable interactions. The DMC (dynamic matrix control) and the QDMC (quadratic dynamic matrix control) algorithms performed satisfactorily over the major drawbacks. Special attention was given to the latter algorithm due to its ability to hold the variables under constrained oscillations. However, the best results were found for the adaptive GPC (generalized predictive control) algorithm whose actions prevailed over the modeling mismatch due to the strong nonlinear behavior intrinsic to the process. The main goal of the present work is to describe a procedure that can be standardized for other types of dryers and different scales. This is especially the case for the adaptive GPC, whose control structure is independent of the dryer nature and scale and whose implementation does not require previous identification procedures (self-tuning) and/or structural changes.     

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.     

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.     

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

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.     

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.     

Drying of industrial sludge waste in a conical spouted bed dryer. Effect of air temperature and air velocity

To determine the performance of a conical spouted bed dryer for the drying of sludge waste, an experimental study of drying in a spouted bed regime was performed under different experimental conditions. The drying performance was determined based on the time evolution of solid moisture content, and the influence of operating conditions (inlet air temperature, air flow rate, and bed mass) on the drying rate of sludge waste in spouted beds of a conical geometry was analyzed.     

Paste Residence Time in a Spouted Bed Dryer. I: The Stimulus-Response Methodology

The stimulus response methodology was evaluated in an experimental study conducted to measure NaCl solution residence time distributions in a spouted bed dryer of inert particles. The influence of tracer volume, concentration, and injection mode upon the measured mean residence time and residence time distribution was determined following experimental design techniques. The injection mode showed no significant effect on residence times, whereas tracer volume and concentration had significant effects at the levels of 1 and 5%, respectively, under the conditions chosen initially. The steepest ascent and factorial design methods were applied to determine the range in parameters for optimum stimulus response. The procedure repeated for a polymeric paste showed similar results. However, the results also showed that care must be exercised when using the stimulus response technique and the optimum injection conditions must be determined. The procedure presented in this study may be adopted in future investigations of paste residence time distributions in spouted bed dryers of inert bodies.