A THRESHOLD-ACCEPTING METAHEURISTIC METHOD FOR SCHEDULING THE OPERATIONS OF DEHYDRATION PLANTS

ABSTRACT

Dehydration plants are broadly characterized by a multi-product nature chiefly attributed to the utilization of different raw materials to be processed sequentially so that demand constraints are met. Processing of raw materials is implemented through a series of preprocessing operations that together with drying constitute the production procedure of a pre-specified programme. The core of the manufacturing system that a typical dehydration plant involves, is scheduling of operations so that demand is fulfilled within a pre-determined time horizon imposed by production planning. The typical scheduling operation that dehydration plants involve can be formulated as a general job shop scheduling problem. The aim of this study is to describe a new metaheuristic method for solving the job shop scheduling problem of dehydration plants, termed as the Backtracking Adaptive Threshold Accepting (BATA) method. Our effort focuses on developing an innovative method, which produces reliable and high quality solutions, requiring reasonable computing effort. The main innovation of this method, towards a typical threshold accepting algorithm, is that during the optimization process the value of the threshold is not only lowered, but also raised or backtracked according to how effective a local search is. BATA is described in detail while a characteristic job shop scheduling case study for dehydration plant operations is presented.     

AN EFFICIENT META-HEURISTIC ALGORITHM FOR ROUTING PRODUCT COLLECTING VEHICLES OF DEHYDRATION PLANTS. I. ALGORITHM DEVELOPMENT

Dehydration plants are characterized by a multi-product nature chiefly attributed to the utilization of different raw materials to be processed in parallel so that demand constraints are met. The Just-In-Time production planning policy of these plants require the collection of raw materials to be dehydrated shortly before the actual processing, immediately after harvesting. One of the most important aspects in collection of plant fresh products, is routing of collecting vehicles, so that total collection time is minimized. The aim of this study is to describe a new stochastic search meta-heuristic algorithm for solving the Vehicle Routing Problem (VRP), termed as the Backtracking Adaptive Threshold Accepting (BATA) algorithm. Our effort focuses on developing an innovative method, which produces reliable and high quality solutions, requiring reasonable computing effort. The main innovation of the algorithm, toward a typical threshold accepting algorithm, is that during the optimization process the value of the threshold is not only lowered, but also raised or backtracked according to how effective a local search is. This adaptation of the value of the threshold, plays an important role in finding high quality routing solutions. BATA is described in detail while its performance and characteristic case studies are presented by Tarantilis and Kiranoudis (2000).     

AN EFFICIENT META-HEURISTIC ALGORITHM FOR ROUTING PRODUCT COLLECTING VEHICLES OF DEHYDRATION PLANTS. I. ALGORITHM DEVELOPMENT

Dehydration plants are characterized by a multi-product nature chiefly attributed to the utilization of different raw materials to be processed in parallel so that demand constraints are met. The Just-In-Time production planning policy of these plants require the collection of raw materials to be dehydrated shortly before the actual processing, immediately after harvesting. One of the most important aspects in collection of plant fresh products, is routing of collecting vehicles, so that total collection time is minimized. The aim of this study is to describe a new stochastic search meta-heuristic algorithm for solving the Vehicle Routing Problem (VRP), termed as the Backtracking Adaptive Threshold Accepting (BATA) algorithm. Our effort focuses on developing an innovative method, which produces reliable and high quality solutions, requiring reasonable computing effort. The main innovation of the algorithm, toward a typical threshold accepting algorithm, is that during the optimization process the value of the threshold is not only lowered, but also raised or backtracked according to how effective a local search is. This adaptation of the value of the threshold, plays an important role in finding high quality routing solutions. BATA is described in detail while its performance and characteristic case studies are presented by Tarantilis and Kiranoudis (2000).     

A COMBINED MILP AND LOGIC-BASED APPROACH TO THE SYNTHESIS OF OPERATING PROCEDURES FOR BATCH PLANTS

Synthesizing a set of operating procedures for the safe and efficient transient operation of chemical plants is a difficult problem owing to the enormous number of possible combinations of actions in a typical plant. In most current industrial plant design practice, there are no formal methods for systematically transforming process specifications into operating procedures for the plant operators and into sequence control instructions for the control computers. There is much scope for a formalized computer-based procedure synthesis methodology to assist the design engineer/plant operator with both the formulation and assessment of procedures off-line and, eventually, with the on-line problem of procedure synthesis in response to unexpected situations

A recently developed approach for operating procedure synthesis for multipurpose batch plants is considered. The modelling formalism used includes the separate definition of process operations, as State Task Networks, and of physical plant, at the level of detail of a piping and instrumentation diagram. In this paper, a subgoaling procedure is developed using the State Task Network representation which decomposes the procedure synthesis goals into simpler subgoals by means of an efficient Mixed Integer Linear Programming (MILP) technique. Detailed control sequences are then generated for each subgoal using a set of rules and algorithms specific for each type of subgoal. The procedure sequences thus generated are validated by simulation on a plant model with checking of physical and operational constraints at each new plant state. We have found that this hierarchical approach to the procedure synthesis problem greatly reduces the problem complexity

The usefulness of the general approach and of the subgoaling procedure in particular are demonstrated through a multiproduct batch plant example.     

新的多产品间歇生产调度的MILP模型

提出了一种新的多产品厂间歇调度问题的连续时间混合整数线性规划 (MILP)模型,该模型的整数变量体系不依赖于时间块(或者事件点)的概念,并且利用了变量物理概念上的对称互补性,使得与传统的建模方法相比不仅整数变量的数目减少了一半以上,而且建模思想、建模理论都有了新的改进.通过对一个算例的考察证实了新模型可以快速地求得全局最优解.     

MASS-TRANSFER FLOW IN A PARALLEL-PLATE CHANNEL WITH PERMEABLE BARRIERS INSERTED FOR COUNTERCURRENT MULTI-PASS OPERATIONS

The mass-transfer flow of a multi-pass counterflow laminar mass exchanger by inserting three permeable barriers with external refluxes was investigated theoretically, and the mathematical formulation was developed as well. With the use of an orthogonal expansion technique and the eigenfunction expanding in power series, the analytical solutions were obtained for finding the outlet concentration and mass transfer efficiency. The influences of the design parameters, the channel thickness ratio (β) and barrier characteristics (γ), and the operating parameters, the mass-transfer Graetz number (Gz _m ) and recycle ratio (R), are examined. Theoretical predictions of the new multi-pass operations are compared with those in the single- (without the permeable barrier inserted) and double-pass operations under the same working dimensions and represented graphically. The results show that the influences of the recycle ratio and channel thickness ratio in the present device with external refluxes are dominant in low and high mass-transfer Graetz number regions, respectively. Therefore, an optimal economic feasibility of multi-pass mass exchangers was found when the recycle ratio and channel thickness ratio are suitably selected under the operating conditions of interest.     

MASS-TRANSFER FLOW IN A PARALLEL-PLATE CHANNEL WITH PERMEABLE BARRIERS INSERTED FOR COUNTERCURRENT MULTI-PASS OPERATIONS

The mass-transfer flow of a multi-pass counterflow laminar mass exchanger by inserting three permeable barriers with external refluxes was investigated theoretically, and the mathematical formulation was developed as well. With the use of an orthogonal expansion technique and the eigenfunction expanding in power series, the analytical solutions were obtained for finding the outlet concentration and mass transfer efficiency. The influences of the design parameters, the channel thickness ratio (β) and barrier characteristics (γ), and the operating parameters, the mass-transfer Graetz number (Gz_m) and recycle ratio (R), are examined. Theoretical predictions of the new multi-pass operations are compared with those in the single- (without the permeable barrier inserted) and double-pass operations under the same working dimensions and represented graphically. The results show that the influences of the recycle ratio and channel thickness ratio in the present device with external refluxes are dominant in low and high mass-transfer Graetz number regions, respectively. Therefore, an optimal economic feasibility of multi-pass mass exchangers was found when the recycle ratio and channel thickness ratio are suitably selected under the operating conditions of interest.     

AN EFFICIENT META-HEURISTIC ALGORITHM FOR ROUTING PRODUCT COLLECTING VEHICLES OF DEHYDRATION PLANTS. II. ALGORITHM PERFORMANCE AND CASE STUDIES

Routing of vehicle fleet for collecting newly cropped raw materials for multi-product dehydration plants is a component of plant production schedule of utmost significance. A meta-heuristic algorithm for efficiently solving the collecting vehicle routing problem was developed and analyzed in detail in Tarantilis and Kiranoudis (2000). Meta-heuristic algorithms are broadly characterized by a stochastic nature in producing tender solution configurations in linear search terms, which sweep the huge solution space in a guided and rational way. Algorithm performance is examined through an analysis of the impact of model parameters on solution procedure during the execution of typical routing problems. The most important model parameter examined was found to be the value of the initial threshold as well as the way that the value of this actual parameter is appropriately adjusted during the optimization process. The main characteristic of the algorithm is the way that threshold is not only lowered but also raised, or backtracked, depending on the success of the inner loop iterations to provide for an acceptable new solution that would replace an older one. An important feature of the algorithm is the fact that appearance of better configurations within a process run is distributed according to the Poisson probability distribution. The suggested algorithm is tested against typical literature benchmarks as well against real-world problem encountered in the production planning procedures of dehydration plants in Greece.     

AN EFFICIENT META-HEURISTIC ALGORITHM FOR ROUTING PRODUCT COLLECTING VEHICLES OF DEHYDRATION PLANTS. II. ALGORITHM PERFORMANCE AND CASE STUDIES

Routing of vehicle fleet for collecting newly cropped raw materials for multi-product dehydration plants is a component of plant production schedule of utmost significance. A meta-heuristic algorithm for efficiently solving the collecting vehicle routing problem was developed and analyzed in detail in Tarantilis and Kiranoudis (2000). Meta-heuristic algorithms are broadly characterized by a stochastic nature in producing tender solution configurations in linear search terms, which sweep the huge solution space in a guided and rational way. Algorithm performance is examined through an analysis of the impact of model parameters on solution procedure during the execution of typical routing problems. The most important model parameter examined was found to be the value of the initial threshold as well as the way that the value of this actual parameter is appropriately adjusted during the optimization process. The main characteristic of the algorithm is the way that threshold is not only lowered but also raised, or backtracked, depending on the success of the inner loop iterations to provide for an acceptable new solution that would replace an older one. An important feature of the algorithm is the fact that appearance of better configurations within a process run is distributed according to the Poisson probability distribution. The suggested algorithm is tested against typical literature benchmarks as well against real-world problem encountered in the production planning procedures of dehydration plants in Greece.     

A PARAMETER PLANE METHOD FOR THE PID CONTROL OF A MULTIRATE, SAMPLED-DATA CHEMICAL REACTOR SYSTEM WITH A TRANSPORTATION LAG

The control of a multirate sampled-data, stirred-tank chemical reactor system using a parameter plane method is considered. Due to wide acceptance of proportional-plus-integral-plus-derivative (PID) control in the chemical process industries, a PID controller with a “slow-fast”multirate scheme is used for the chemical reactor system. Based on two related stability equations and using the PID gains as the adjustable parameters, the set of all possible PID gains to maintain the chemical reactor system's stability, and at the same time, to make the system having a specified gain margin, phase margin, damping ratio, and damping factor is determined. The effects of changing the integer N (which is the ratio of the sampling rates between a slow- and a fasl-samplcr)and (he basic sampling period Ton the set of PID gains satisfying the specifications are examined. The results for single-rate and multirate cases are also studied.     

一种研究风轮叶片固有频率的方法

提高风轮叶片挥舞频率以避免风机运行时发生共振问题,是叶片铺层设计的一个重要环节。本文在风轮叶片铺层设计实践的基础上提出了一种研究复合材料风轮叶片频率的方法,给出了该方法的理论基础,并通过一个风轮叶片铺层实例说明了该方法的具体实施过程,验证了其可行性和可靠性。该方法能够定量地表征叶片每个截面的铺层方案对叶片频率的影响,可指导叶片铺层设计者如何更快找到调整叶片铺层的最优方案,从而更有效地提高叶片挥舞频率。     

氨合成催化剂颗粒曲折率的一种测定方法

利用微观、宏观化学反应动力学实验数据,引入修正的THIELE模数,推导出计算非定形颗粒曲折率的方法。计算得6.7mm～9.4mm级剐的国产A11O氨合成催化剂颗粒曲折率为3.02。     

烷烃结构异构数新的计算方法

设W_n、Q_n和X_n分别表示n-碳烷(C_nH_(2n n2)n-碳炔(C_nH_(2n-2))和n-碳烯(C_nH_(2n))的同分异构体数,作者发现了下列公式: W_n=Q_(n 2) (1-(-1)~n)/2Q_(n 3)/2-X_(n 1)并算出W_(40)=62,481,801,147,341。(Henze和Blair算出W_(40)=62,491,178,805,831)和W_(50)=1,117,743,651,746,953,270     

磁性活性炭的一种制备方法

将磁化剂吸附于活性炭上 ,于室温下干燥即可得到磁性活性炭。这种活性炭用于黄金生产 ,可使提金得率提高 4 %。     

延长导热油寿命5～8年的新方法

首次揭示了导热油在高温运行中变化趋势呈曲线状，提出了导热油在线清洗概念，通过在线清洗清除导热油中垃圾，减缓导热油的变化速率，使导热油在高温运行时的变化速率呈线性状，可使导热油的使用寿命延长5—8年。     

一种测定尼龙-11特性粘度的方法

在采用稀释作图外推法测定尼龙 - 11特性粘度的大量实验基础上 ,研究确定了用乌氏粘度计单点法测定尼龙 - 11特性粘度经验公式中的经验常数 ,通过与稀释法的比较 ,检验其准确度和精确度。结果表明 ,误差小于± 0 5%的单点法可用于测定尼龙 -11的特性粘度     

DEVELOPMENT OF A FUZZY EXPERT SYSTEM FOR THE SELECTION OF BATCH DRYERS FOR FOODSTUFFS

ABSTRACT

The selection of dryers is an art in which knowledge, experience and science all play important roles. Historically, dryer selection has been made by experts on the basis of their extensive knowledge. However, in recent years, computer-based techniques have been developed, which have the potential of at least partially deskilling this process. Of the various possibilities, fuzzy expert systems, in which the selection qualifiers are represented as linguistic rather than numerical variables, are the most promising. This paper describes the development of a fuzzy system for the selection of batch dryers for food products. It featured a novel modular approach in which independent selection goals for dryer type, atmospheric, vacuum or freeze operation, and single or multiple units were adopted. This made the system particularly flexible and amenable to adaptation. The program starts from a ‘ drying process checklist“ in which the principal process variables are specified, and provides a ranked list of feasible alternative dryers. The algorithm was extensively tested and provided quite plausible results. Four representative case studies are presented and discussed.     

DEVELOPMENT OF A FUZZY EXPERT SYSTEM FOR THE SELECTION OF BATCH DRYERS FOR FOODSTUFFS

The selection of dryers is an art in which knowledge, experience and science all play important roles. Historically, dryer selection has been made by experts on the basis of their extensive knowledge. However, in recent years, computer-based techniques have been developed, which have the potential of at least partially deskilling this process. Of the various possibilities, fuzzy expert systems, in which the selection qualifiers are represented as linguistic rather than numerical variables, are the most promising. This paper describes the development of a fuzzy system for the selection of batch dryers for food products. It featured a novel modular approach in which independent selection goals for dryer type, atmospheric, vacuum or freeze operation, and single or multiple units were adopted. This made the system particularly flexible and amenable to adaptation. The program starts from a ' drying process checklist“ in which the principal process variables are specified, and provides a ranked list of feasible alternative dryers. The algorithm was extensively tested and provided quite plausible results. Four representative case studies are presented and discussed.     

焦炭颗粒耐压强度表征方法探讨

在分析焦炭颗粒强度系数存在问题的基础上，提出了一种新的表征焦炭颗粒耐压强度的方法。经试验验证，用耐压强度系数评价焦炭颗粒抵抗压碎的能力，不仅可以得到比较精确的结果，而且还可以解决多粒度组成焦炭颗粒混合料耐压性能的评价问题。     

测定陶瓷材料断裂韧性的压痕弯曲梁法的改进

考虑残余应力对压痕弯曲梁应力场强度的贡献后,对相应的K_(IC)表达式进行了修正。研究表明:在合适的压痕压制荷载范围内,弯曲梁强度σ_r与压痕裂纹深度的倒数平方根(1/a)~(1/2)之间存在线性关系;压痕处的残余应力效应可以用σ_(?)-(1/a)~(1/2)直线关系式中的强度修正项加以描述。高温下强度修正项的值随温度的升高而减小,说明残余应力在高温作用下得到了部分消除;退火处理也导致了强度修正项的减小。采用强度修正项后的K_(IC)计算公式,压痕弯曲梁法可望应用于各种温度下的K_(IC)测试;由σ_(?)(1/a)~(1/2)直线斜率求得的K_(IC)值不受残余应力影响。