PRODUCT QUALITY MULTI-OBJECTIVE DRYER DESIGN

ABSTRACT

Design of conveyor-belt dryers constitutes a mathematical programming problem involving the evaluation of appropriate structural and operational process variables so that total annual plant cost involved is optimized. The increasing need for dehydrated products of the highest quality, imposes the development of new criteria that, together with cost, determine the design rules for drying processes. Quality of dehydrated products is a complex resultant of properties characterizing the final products, where the most important one is color. Color is determined as a three-parameter resultant, whose values for products undergone drying should deviate from the corresponding ones of natural products, as little as possible. In this case, product quality dryer design is a complex multi-objective optimization problem, involving the color deviation vector as an objective function and as constraints the ones deriving from the process mathematical model. The mathematical model of the dryer was developed and the fundamental color deterioration laws were determined for the drying process. Non-preference multi-criteria optimization methods were used and the Pareto-optimal set of efficient solutions was evaluated. An example covering the drying of sliced potato was included to demonstrate the performance of the design procedure, as well as the effectiveness of the proposed approach.     

PRODUCT QUALITY MULTI-OBJECTIVE OPTIMIZATION OF FLUIDIZED BED DRYERS

Design of fluidized bed dryers constitutes a mathematical programming problem involving the evaluation of appropriate structural and operational process variables so that total annual plant cost involved is optimized. The increasing need for dehydrated products of the highest quality, imposes the development of new criteria that, together with cost, determine the design rules for drying processes. Quality of dehydrated products is a complex resultant of properties characterizing the final products, where the most important one is color. Color is determined as a three-parameter resultant, whose values for products undergone drying should deviate from the corresponding ones of natural products, as little as possible. In this case, product quality dryer design is a complex multi-objective optimization problem, involving the color deviation vector as an objective function and as constraints the ones deriving from the process mathematical model. The mathematical model of the dryer was developed and the fundamental color deterioration laws were determined for the drying process. Non-preference multi-criteria optimization methods were used and the Pareto-optimal set of efficient solutions was evaluated. An example covering the drying of sliced potato was included to demonstrate the performance of the design procedure, as well as the effectiveness of the proposed approach.     

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 AND PERFORMANCE OF CONTINUOUS WELL-MIXED FLUIDIZED BED DRYERS - AN ANALYTICAL APPROACH

Abstract

In a previous study, a unified approach to the calculation of the size and energy consumption of well-mixed fluidized bed dryers was developed. A computer code was written and a parametric study undertaken to determine the effects of the principal operating variables. The results were shown to depend on the form of the drying kinetics. The present paper describes the formulation of an analytical model of a well-mixed fluidized bed dryer, which applies for materials that exhibit linear falling-rate drying. These materials are typified by small hygroscopic particles, which are frequently dried in such equipment. Equations are presented that enable the drying time, specific energy consumption, heater duty and bed area to be calculated. The predictions of these equations agreed well with previously published experimental findings and with the results of computer simulations for a typical solid (ion exchange resin) exhibiting the required drying characteristics.     

PREDICTING THE ENERGY CONSUMPTION OF CONTINUOUS WELL-MIXED FLUIDIZED BED DRYERS FROM DRYING KINETIC DATA

ABSTRACT

Previous work has shown that it is possible to predict the size of a continuous welt-mixed fluidized bed dryer from batch drying curve measurements. This approach has been extended in the present study to include energy consumption calculations. A computer code was written to simulate the performance of the dryer and to determine its specific energy consumption E_s. Starting in this case with an isothermal bed batch drying curve, the program first calculates the mean solids residence time required under specified operating conditions. Mass and energy balances are then used to calculate the heat duty and E_s. The bed temperature was found to have a significant effect on specific energy consumption in all cases. However, the influences of air flowrate and humidity, and of solids loading, were shown to depend on the solids drying characteristics.     

THE DESIGN AND PERFORMANCE OF CONTINUOUS WELL-MIXED FLUIDIZED BED DRYERS - AN ANALYTICAL APPROACH

In a previous study, a unified approach to the calculation of the size and energy consumption of well-mixed fluidized bed dryers was developed. A computer code was written and a parametric study undertaken to determine the effects of the principal operating variables. The results were shown to depend on the form of the drying kinetics. The present paper describes the formulation of an analytical model of a well-mixed fluidized bed dryer, which applies for materials that exhibit linear falling-rate drying. These materials are typified by small hygroscopic particles, which are frequently dried in such equipment. Equations are presented that enable the drying time, specific energy consumption, heater duty and bed area to be calculated. The predictions of these equations agreed well with previously published experimental findings and with the results of computer simulations for a typical solid (ion exchange resin) exhibiting the required drying characteristics.     

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.     

DYNAMIC ANALYSIS OF CONTINUOUS WELL-MIXED FLUIDIZED/SPOUTED BED DRYERS

A diffusion-based mathematical model is presented for the prediction of the dynamics of drying in continuous well-mixed fluidized/spouted beds. Numerical techniques are used to solve the model equations. The outlet solids moisture content, the outlet air humidity and solids temperature are predicted as a function of time for the falling rate drying period. The model is helpful in describing the drying process during the startup periods and in studying open loop behavior of drying process. The model is also useful in designing control system for fluidized/spouted bed dryers.     

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.     

动态模拟优化尿素产品质量控制

运用动态模拟对尿素装置蒸发系统非正常工况进行分析,找出尿素产品质量参数的变化规律和影响因素,提出操作上的优化措施。     

OPTIMIZATION OF HETEROGENEOUS CATALYTIC PROCESSES IN FLUIDIZED BED

A number of large-scale chemical processes is carried out in fluidized-bed reactors (FBR). Optimization of processes in FBR is thus of great importance both for the increase of efficiency of the existing plants and for the design of new ones. Selection of optimal conditions for exothermic processes should recognize conditions for heat removal and multiplicity and stability of stationary states rather than just the reaction kinetics and fluidized bed hydrodynamics. Mathematically this problem is rather cumbersome. A process in FUR is described by the boundary problem for differential equations while statement of an optimization problem requires some additional limitations to be imposed on concentrations at the input and output of the reactor, on temperature, design parameters etc. One should take special notice of the limitation on the process stability which (owing to great reverse thermal agitation) is much more important in FBRs than in packed-bed reactors.     

OPTIMIZATION OF HETEROGENEOUS CATALYTIC PROCESSES IN FLUIDIZED BED

A number of large-scale chemical processes is carried out in fluidized-bed reactors (FBR). Optimization of processes in FBR is thus of great importance both for the increase of efficiency of the existing plants and for the design of new ones. Selection of optimal conditions for exothermic processes should recognize conditions for heat removal and multiplicity and stability of stationary states rather than just the reaction kinetics and fluidized bed hydrodynamics. Mathematically this problem is rather cumbersome. A process in FUR is described by the boundary problem for differential equations while statement of an optimization problem requires some additional limitations to be imposed on concentrations at the input and output of the reactor, on temperature, design parameters etc. One should take special notice of the limitation on the process stability which (owing to great reverse thermal agitation) is much more important in FBRs than in packed-bed reactors.     

THERMOCOMPRESSOR DESIGN FOR EFFICIENT ENERGY RECOVERY OF PAPER PRODUCTION PLANT DRYERS

Abstract

The operational performance of a paper production plant can be significantly improved by appropriate process interventions. This paper deals with energy aspects of the most important section of such a plant, the paper drying section. A significant intervention that would lower the operational cost of the drying process is proposed. It refers to the recompression of low pressure steam leaving the dryers by means of a thermocompressor that would utilize high pressure steam coming from the plant burners. The mathematical model of the thermocompressor is evaluated and its design procedure is formulated as a mathematical programming problem involving appropriate objective function and constraints.     

循环流化床燃烧数学模型

介绍了有关文献中循环流化床燃烧的数学模型。按照各模型所使用的流体动力学模型的差异,将它们分成了不同的类别。同时也简要介绍了几种目前应用于循环流化就数学模型的气固两相流数值模拟方法。在评述各模型的优缺点和分析目前所存在问题的基础上,初步提出了进一步发展的方向。     

增压流化床燃煤锅炉数学模型

以某 6 0t·h^-1增压流化床锅炉为对象 ,建立了动态数学模型 .模型采用了分小室和分段结合的离散化方法 ,以反映沿炉膛高度方向上温度的分布特性 ;通过描述密相床内不同相区间的气体交换现象 ,使得模型能够模拟氧气通过气泡短路通过密相床的现象 ;以动态固体质量平衡、氧质量平衡、碳质量平衡和总体能量平衡为主体建立动态数学模型 .模型稳态计算结果与实际电厂的运行数据对比 ,表明模型具有一定的定量准确性 .文中最后对快排床料的动态过程进行了仿真和分析 ,结果表明所建模型可以模拟“快加快排”这种增压流化床特有的变负荷方式 ,也较为本质地反映了增压流化床的燃烧机制     

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.     

流化床气化炉的数学模拟

以文献为基础，简要介绍了文献中的流化床气化炉的数学模型，将其分为热力学平衡模型和速率模型；重点分析了速率模型，根据所用流体力学模型不同将其分为全混模型、两相模型、鼓泡床模型和气泡汇集模型。最后针对现状提出了流化床气化炉数学模型的发展方向。     

三相流态化结晶系统的数学模型

<正>要实现工业结晶过程新工艺和设备的开发以及过程操作的优化,就必须建立涉及结晶过程特性并反映结晶器流动、混合和传递规律及其相互作用关系的结晶器总体数学模型。过去几十年中已有许多研究者进行了这方面的探索,提出了各种各样的模型。特别是70年代初由Randolph和Larson提出的粒数衡算模型,将产品的粒度分布与结晶器的结构参数和操作参数联系起来,成为结晶器设计、放大和优化从经验上升到科学的重要标志。 针对不同结晶系统提出的多种数学模型中,最具典型代表性的数学模型是由Mullin等提     

考虑动力学的反应路径多目标优化方法

提出了一种考虑动力学影响和环境约束的反应路径综合方法. 引入平衡温距的概念来估计反应的动力学属性.可从多种备选物质之中找到生产某种指定产品的较好的反应路径和相应的原料.根据原子平衡方程综合反应路径,建立模糊规则来评价反应的平衡温距,并求解带有模糊参数的多目标机会约束规划模型,得到一系列经济、环境上均优化可行的反应路径.用合成氨联产尿素的实例对该方法进行了说明.     

三段串联绝热轴向氨合成塔的模拟计算和设计优化

提出三段轴向氨合成反应器的数学模型和设计优化方法,对三段轴向氨合成反应器进行模拟计算。同时计算了操作压力分别为１５７８,１５０,１００,７．５ＭＰａ时,在三段串联绝热轴向反应器中满足日产１０００ｔ氨所需的最少催化剂用量。