Optimal Control of Continuous Infrared Dryers

In this work, the optimal control policies of radiant temperature versus dryer length are determined for the continuous, steady-state operation of infrared dryers. The optimal control objective is to minimize the product humidity subject to a mathematical model of infrared dryers as well as a set of process inequality constraints. A robust optimal control method based on genetic algorithms is applied. Multiple air injections are also considered. The optimal results show considerable reduction in product humidity. Comparisons with corresponding base cases (using maximum possible uniform radiant temperatures) indicate improvements greater than 50% with the application of optimal control policies.     

THERMAL CONTACT CONDUCTANCE OF A COATED PAPER/METAL INTERFACE

A better understanding of the parameters associated with heating of the coated paper during drying process would permit a more accurate design and control of the process to achieve an improved coated paper quality and printability. Following the application of the coating, the coated paper passes through non-contact dryers (i.e. infrared dryers and impinging hot air dryers). When the coating has coalesced, further drying is achieved with steam-heated, contact dryers. One parameter affecting the heat transfer from a metallic dryer drum to the coated paper is the thermal contact conductance at the interface between the coated paper and the drum. In this paper, the thermal contact conductance of a coated paper/metal interface is determined and compared to that of the uncoated paper. Two types of base stock and one type of coating are considered. The thermal contact conductance values are given as a function of the applied interface pressure.     

THERMAL CONTACT CONDUCTANCE OF A COATED PAPER/METAL INTERFACE

A better understanding of the parameters associated with heating of the coated paper during drying process would permit a more accurate design and control of the process to achieve an improved coated paper quality and printability. Following the application of the coating, the coated paper passes through non-contact dryers (i.e. infrared dryers and impinging hot air dryers). When the coating has coalesced, further drying is achieved with steam-heated, contact dryers. One parameter affecting the heat transfer from a metallic dryer drum to the coated paper is the thermal contact conductance at the interface between the coated paper and the drum. In this paper, the thermal contact conductance of a coated paper/metal interface is determined and compared to that of the uncoated paper. Two types of base stock and one type of coating are considered. The thermal contact conductance values are given as a function of the applied interface pressure.     

A Diffusion Model for a Drum Dryer Subjected to Conduction, Convection, and Radiant Heat Input

Drum dryers are commonly used for production of a flaky dry powder from thick suspensions. This article presents results of a simple diffusion-based model to predict the drying performance of a pilot-scale twin-drum dryer. Numerical results are compared with experimental data obtained for a biological sludge whose initial moisture content varied from 1.0 to 2.3 kg/kg db. The agreement of model predictions with the pilot-scale experimental data is favorable. Effects of film thickness, drum rotational speed, external air flow velocity, and its humidity are examined parametrically. Sludge film thickness is identified as the most critical operating parameter to control the final moisture content and productivity of the dryer. The validated model is used to predict performance of a drum dryer subjected to heat input by convection and radiation along with conduction through the drum wall. It is shown that dryer output can be enhanced significantly by increasing the film thickness and applying radiant heating in the initial period of drying. A simple mathematical model of this type can be used for the purpose of design and analysis as well as scale-up of industrial drum dryers based on simple laboratory-scale experiments.     

Dynamics And Assessment of Some Control Strategies of a Simulated Industrial Rotary Dryer

Rotary dryers are widely used for the continuous drying of minerals and chemicals on a large scale. Hot gases are passed parallel to the flowing solid to achieve the desired product moisture content. Because these dryers are energy intensive, it is mandatory to operate them as efficiently as possible to respond to economic pressures. Using a dynamic rotary dryer simulator for mineral concentrate, five control strategies are evaluated and compared. Two control strategies are based on PI controllers and the others use neural network models. Results clearly show that a feedforward action, in conjunction with a PI controller or incorporated within the structure of a neural network model, led to the best performances provided an accurate measurement of the feed moisture content is available.     

高抗热震性红外辐射涂料的实验研究

针对红外辐射涂料在不同基体表面上应用时出现的涂层易脱落问题 ,采用正交实验设计对不同配方的过渡金属氧化物系红外辐射涂料进行了涂层高温抗热震性实验研究。优化配方制得的红外辐射涂料既适用于 1Cr18Ni9Ti金属基体又适用于耐火材料基体 ;与国外相关产品相比 ,其抗热震性能更佳。     

MODELING AND MEASUREMENTS OF INFRARED DRYERS FOR COATED PAPER

We have developed models to determine the radiative heat transfer of infrared dryers. Using the models, the efficiencies of several IR constructions are calculated. The radiation properties of all parts of the IR dryer are measured with an IT-IR spectrometer using integrating sphere techniques. With these models and measured results, the total efficiencies of several dryer constructions are calculated for: an electric dryer with a pambolic mirror, an elecmc dryer with a flat ceramic mirror, and a gas-fired dryer. The effect of a back reflector on these dryers is also calculated. The efficiencies of all these dryers are compared to each other.     

EFFECTS OF HEATING METHODS ON VACUUM FREEZE DRYING

The heat and mass transfer during freeze drying of raw beef by different heating methods is studied theoretically and experimentally. The difference between radiant heating and microwave heating in freeze drying process has been analyzed. The results obtained are important for the selection of the heating methods in practical freeze dryers.     

On-Farm Drying and Storage Systems

ABSTRACT

Rotary dryers are widely used for the continuous drying of minerals and chemicals on a large scale. Hot gases are passed parallel to the flowing solid to achieve the desired product moisture content. Because these dryers are energy intensive, it is mandatory to operate them as efficiently as possible to respond to economic pressures. Using a dynamic rotary dryer simulator for mineral concentrate, five control strategies are evaluated and compared. Two control strategies are based on PI controllers and the others use neural network models. Results clearly show that a feedforward action, in conjunction with a PI controller or incorporated within the structure of a neural network model, led to the best performances provided an accurate measurement of the feed moisture content is available.     

MODELING AND MEASUREMENTS OF INFRARED DRYERS FOR COATED PAPER

We have developed models to determine the radiative heat transfer of infrared dryers. Using the models, the efficiencies of several IR constructions are calculated. The radiation properties of all parts of the IR dryer are measured with an IT-IR spectrometer using integrating sphere techniques. With these models and measured results, the total efficiencies of several dryer constructions are calculated for: an electric dryer with a pambolic mirror, an elecmc dryer with a flat ceramic mirror, and a gas-fired dryer. The effect of a back reflector on these dryers is also calculated. The efficiencies of all these dryers are compared to each other.     

DEVELOPMENT OF A SUPERVISORY CONTROL STRATEGY FOR THE OPTIMAL OPERATION OF GRAIN DRYERS

In spite of the importance and especially high energy demands of grain dryers, relatively few studies have been carried out to discover the optimal conditions for their operation. High performance operation can only be achieved if an adequate operating strategy is developed. For its implementation, a reliable control structure is required, and some of the limitations of the conventional control strategies normally used in dryers are observed. These strategies are SISO; the control normally used presents low performance and the disturbance is characterized by several amplitudes and frequencies. A possible way to minimize this difficulty consists of defining the multilevel structure such that each level acts at a given amplitude and frequency. In order to implement this multilevel structure, an optimization problem was developed to function as a supervisory control and a predictive algorithm (DMC) was used for servo or regulatory control. The proposed DMC algorithm presented satisfactory results for the load rejection and set-point variation, only when a small disturbance was applied. For a larger disturbance an optimization procedure was necessary. The routine efficiently maintained the optimal operational conditions of the dryer and could be used in the supervisory control of the system.     

Measurement Techniques to Monitor and Control Fluidization Quality in Fluidized Bed Dryers: A Review

Fluidized bed dryers (FBD) are commonly employed in many industries to dry particulate solids. FBDs provide good solids mixing, high rates of heat and mass transfer, and relative ease of material handling. For efficient operation, it is important to be able to monitor and control the fluidization regime, particle size distribution (PSD), moisture content, and bulk density as well as product chemical properties. This review provides an overview of the trends in the application of different experimental techniques to monitor and control the hydrodynamic conditions of FBDs which influence the particle physiochemical properties. This review covers a wide range of measurement techniques, including infrared moisture sensor (IR), near infrared (NIR) spectroscopy, analysis of pressure fluctuations, optical imaging techniques, acoustic emission (AE), electrical capacitance tomography (ECT), spatial filter velocimetry (SFV), Raman spectroscopy, focused beam reflectance measurement (FBRM), microwave resonance technology (MRT), triboelectric probes, positron emission particle tracking (PEPT), and some novel techniques for monitoring and control of FBDs. The present review summarizes the use of the diverse techniques and outlines their merits and limitations. Prospects for future research in this area are also identified. The measurement techniques can be used for research, development, and operation of fluidized bed equipment used in non-drying applications as well.     

EFFECTS OF HEATING METHODS ON VACUUM FREEZE DRYING

ABSTRACT

The heat and mass transfer during freeze drying of raw beef by different heating methods is studied theoretically and experimentally. The difference between radiant heating and microwave heating in freeze drying process has been analyzed. The results obtained are important for the selection of the heating methods in practical freeze dryers.     

微波法制备过氧化尿素

以工业级尿素和双氧水为原料,在微波辐射条件下合成过氧化尿素,考察了过氧化氢与尿素的物质的量比、微波辐射时间、微波功率、稳定剂品种以及稳定剂的用量对产品含氧量、收率和稳定性的影响,得出了最佳的反应条件。实验结果表明,当微波功率200W、过氧化氢与尿素的物质的量比1．4：1、反应时间120s、用0．3％NaH2PO4作稳定剂时,产品过氧化尿素的收率可达56．84％,产品中过氧化氢尿素的活性氧物质的量分数达16．93％。     

DEVELOPMENT OF A SUPERVISORY CONTROL STRATEGY FOR THE OPTIMAL OPERATION OF GRAIN DRYERS

ABSTRACT

In spite of the importance and especially high energy demands of grain dryers, relatively few studies have been carried out to discover the optimal conditions for their operation. High performance operation can only be achieved if an adequate operating strategy is developed. For its implementation, a reliable control structure is required, and some of the limitations of the conventional control strategies normally used in dryers are observed. These strategies are SISO; the control normally used presents low performance and the disturbance is characterized by several amplitudes and frequencies. A possible way to minimize this difficulty consists of defining the multilevel structure such that each level acts at a given amplitude and frequency. In order to implement this multilevel structure, an optimization problem was developed to function as a supervisory control and a predictive algorithm (DMC) was used for servo or regulatory control. The proposed DMC algorithm presented satisfactory results for the load rejection and set-point variation, only when a small disturbance was applied. For a larger disturbance an optimization procedure was necessary. The routine efficiently maintained the optimal operational conditions of the dryer and could be used in the supervisory control of the system.     

Solids transport in mixed-flow dryers

Mixed-flow dryers are broadly used in worldwide agriculture for the drying of grain, corn and rice but are also applied in industry. Although this drying process is well established, there is still a need to optimize the dryer apparatus. Unfavorable design can cause uneven mass flow and air flow distributions, broad residence time distributions and, hence, inhomogeneous drying histories of the particles resulting in non-uniform drying. The transport of solids in mixed-flow dryers has not yet been sufficiently considered and investigated. Therefore, the objective of this study is to derive basic equations on particle flow in mixed-flow dryers which are practically operated in the interrupted flow regime and equipped with discharge gates. The function of the discharge gate, the discharge characteristic and the solids mass flow rate were studied by varying the discharge and standstill times, respectively. The experiments were conducted at a semi-technical dryer test station with a transparent acrylic glass front wall using wheat as bed material. The fundamentals developed serve as a basis for further theoretical and experimental investigations. The future goal is to improve apparatus design and process control so as to homogenize the drying process, to increase energy efficiency and to save product quality.     

Online measurement and control of solids moisture in fluidised bed dryers

Currently, two main methods are used to take online measurement of the solids moisture in fluidised bed dryers, namely microwave resonance and near infrared spectroscopy. In this paper, a new online approach to solids moisture measurement of batch fluidised bed dryers by electrical capacitance tomography (ECT) is presented for the first time. Based on online measurement of solids moisture, it is possible to implement feedback control and process optimisation of batch fluidised bed drying processes, aiming to increase the operation efficiency and to improve product quality. A twin-plane ECT sensor with eight electrodes in each plane is mounted in the bottom of a glass fluidisation chamber. From the adjacent electrode pairs, the water content of the solids is estimated based on the correlation between the moisture content and the permittivity value. To reduce measurement error, the effect of temperature on moisture measurement is compensated. The fluidisation velocity is estimated by a semi-empirical function based on the measured water content. The acquired information is sent to a controller to adjust the air flow rate of the fluidised bed dryer. To validate the moisture measurement by ECT, a mathematical model has been developed, based on the measured temperature and relative humidity of the outlet air. The Landweber iteration method is applied to reconstruct images. The averaged solids concentration along the radial direction at different fluidisation conditions is given and compared with results by the linear back-projection (LBP) method. Results from batch drying processes with online measurement and feedback control are given and compared with no feedback control. To compare the operation efficiency, the thermal efficiency is considered and the results show the possibility of online control and optimisation of the fluidised bed drying processes, based on online measurement of solids moisture by ECT. Some challenges and future work are discussed.     

SIMULATION AND OPTIMIZATION OF CROSS FLOW GRAIN DRYERS

Abstract

In this paper simulation and optimization study on Beidahuang 5HT-15 cross flow grain dryer is presented. The p. d. e. model is employed to establish the simulation program, and the backward difference method and the predictor-corrector integration are used in the thin layer drying process estimation. The optimal analysis is conducted in a 9-dimensional domain and the specific energy consumption is taken as the main target as a weighted sum of heat and mechanical energy according to the factor of cost while the less-important features of performance are put into the target function as penalty factors. The complex polygon method is used in the optimization program. By running the optimization program, a group of optimal policies about the operation of 5HT- 15 dryer have been proposed. Possible improvement and renovation of the cross flow dryers, both in structure and in performance, have also been approached in the simulation and optimization study.     

SIMULATION AND OPTIMIZATION OF CROSS FLOW GRAIN DRYERS

In this paper simulation and optimization study on Beidahuang 5HT-15 cross flow grain dryer is presented. The p. d. e. model is employed to establish the simulation program, and the backward difference method and the predictor-corrector integration are used in the thin layer drying process estimation. The optimal analysis is conducted in a 9-dimensional domain and the specific energy consumption is taken as the main target as a weighted sum of heat and mechanical energy according to the factor of cost while the less-important features of performance are put into the target function as penalty factors. The complex polygon method is used in the optimization program. By running the optimization program, a group of optimal policies about the operation of 5HT- 15 dryer have been proposed. Possible improvement and renovation of the cross flow dryers, both in structure and in performance, have also been approached in the simulation and optimization study.     

Optimal grade transition and selection of closed-loop controllers in a gas-phase olefin polymerization fluidized bed reactor

To satisfy the diverse product quality specifications required by the broad range of polyolefin applications, polymerization plants are forced to operate under frequent grade transition policies. Commonly, the optimal solution to this problem is based on the minimization of a suitable objective function defined in terms of the changeover time, product quality specifications, process safety constraints and the amount of off-spec polymer, using dynamic optimization methods. However, considering the great impact that a given control structure configuration can have on the process operability and product quality optimization, the time optimal grade transition problem needs to be solved in parallel with the optimal selection of the closed-loop control pairings between the controlled and manipulated variables. In the present study, a mixed integer dynamic optimization approach is applied to a catalytic gas-phase ethylene-1-butene copolymerization fluidized bed reactor (FBR) to calculate both the “best” closed-loop control configuration and the time optimal grade transition policies. The gPROMS/gOPT computational tools for modelling and dynamic optimization, and the GAMS/CPLEX MILP solver are employed for the solution of the combined optimization problem. Simulation results are presented showing the significant quality and economic benefits that can be achieved through the application of the proposed integrated approach to the optimal grade transition problem for a gas-phase polyolefin FBR.