OPTIMAL DESIGN AND OPERATION OF BATCH PROCESSES

The economical design of continuous chemical processes to produce commodity products has reached an advanced state of development. Modern computer tools are used routinely to simulate and optimize these processes. This is not the case, however, for the manufacture of speciality products which must be made in batch operations. The continuing shift towards the production of higher value-added specialty products by the CPI has stimulated efforts aimed at developing good computer assisted design strategies for batch processes.

This paper discusses the formulation of the problem for the optimal design and operation of batch processes. The batch problem differs from the continuous one in a number of important ways. First, batch plants do not operate at steady state. There are important trade-offs between the processing time and the severity (intensity) of processing in single units. Cycle time and performance trade-offs also exist among the various units in the process. Second, batch plants produce multiple products in many cases. There is often a competition for shared resources (labor, utilities, and equipment) among the various products. This paper presents a hierarchical solution approach for the design and optimization of a batch process. The approach is demonstrated by solving an example problem which illustrates the fundamental economic trade-offs.     

Fettsäurehydrierung: Kontinuierlich oder diskontinuierlich?

Hydrogenation of Fatty Acids: Continuous or Discontinuous? Costs of investment, operation and auxiliaries are compared for a continuous and a discontinuous process of hydrogenation. Savings in the operation of a continuous hydrogenation plant with a capacity of 80 t/24 h over a discontinuous plant are presented, and advantages and disadvantages of the individual processes with respect to the other are discussed. At sufficiently high daily capacity and adequately large batches of fatty acids, continuous process of hydrogenation can offer great advantages.     

基于浓度间隔分析的用水系统集成(Ⅱ)不连续过程

The first part of the series of this article proposed a systematic method for the synthesis of continuous water-using system involving both non-mass-transfer-based and mass-transfer-based operations.This article,by ex- tending the method,proposes a time-dependent concentration interval analysis(CIA)method to solve the problems associated with the synthesis of discontinuous or batch water-using systems involving both non-mass-transfer-based and mass-transfer-based operation.This method can effectively identify the possibility of water reuse and the amount of water reused under time constraints for minimizing the consumption of freshwater in single or repeated batch/discontinuous water-using systems.Moreover,on the basis of the heuristic method adapted from concentra- tion interval analysis method for the continuous process network design,the network design for the discontinuous or batch process can be obtained through the designs for every time interval.Case study illustrates that the method presented in this article can simultaneously minimize the freshwater consumption in single or repeated batch/discontinuous water system and can determine a preferable storage tank capacity for some problems.     

Synthesis of Water Utilization System Using Concentration Interval Analysis Method （Ⅱ） Discontinuous Process

The first part of the series of this article proposed a systematic method for the synthesis of continuous water-using system involving both non-mass-transfer-based and mass-transfer-based operations.This article,by extending the method,proposes a time-dependent concentration interval analysis（CIA）method to solve the problems associated with the synthesis of discontinuous or batch water-using systems involving both non-mass-transfer-based and mass-transfer-based operation.This method can effectively identify the possibility of water reuse and the amount of water reused under time constraints for minimizing the consumption of freshwater in single or repeated batch/discontinuous water-using systems.Moreover,on the basis of the heuristic method adapted from concentration interval analysis method for the continuous process network design,the network design for the discontinuous or batch process can be obtained through the designs for every time interval.Case study illustrates that the method presented in this article can simultaneously minimize the freshwater consumption in single or repeated batch/discontinuous water system and can determine a preferable storage tank capacity for some problems.     

Scale-up of binder agglomeration processes

This review article describes scale-up of batch and continuous granulation processes where liquid binder is added to fine powder in order to form a granular product. The technical goal of scale-up is to maintain similarity of critical product attributes as the production scale and/or throughput of a manufacturing process is increased. This paper provides a framework for scaling-up that considers critical process transformations in relation to the desired product attributes. A similar approach can be taken in developing process control strategies. In any agglomeration process, transformations can be used to describe how raw materials (typically fine powders and liquid binders) are converted into a granular product. Often the critical product attributes are characterized on the scale of individual granules (e.g., size, shape, porosity, mechanical strength, etc.). On the other hand, industrial scale-up requires predictive relations for the sizing, design and operation of process equipment. Considering scale-up on the basis of transformations is one way to link the macro-scale equipment decisions with micro-scale product attributes. This approach can be applied to the scale-up of batch and/or continuous granulation processes as well as transitioning from small batch prototypes to continuous production circuits.     

Design of batch operations: Systematic methodology for generation and analysis of sustainable alternatives

The objective of this paper is to present a new methodology that is able to generate, screen and identify sustainable alternatives to continuous chemical processes as well as processes operating in the batch mode. The methodology generates the sustainable (design) alternatives by locating the operational, environmental, economical and safety related problems inherent in the process (batch or continuous). Alternatives that are more sustainable, compared to a reference, are generated and evaluated by addressing one or more of the identified problems. A decomposition technique as well as a set of batch indicators for batch operations has been developed and added to the methodology so that a wide range of processes that operate in continuous mode, in semi-continuous and/or in batch modes can be improved. The principal calculation steps of the methodology for applications to continuous and batch processes are described, highlighting the main differences between them. Through two case studies, the application of the methodology, to obtain sustainable design alternatives for batch plants, is highlighted.     

A method of alarm system analysis for process plants

The design and improvement of alarm systems in process plants has been given considerable attention recently. A methodology is presented in this paper which can be used as an aid in the design of new alarm systems or in the improvement of existing alarm systems. The methodology is incorporated in computer software into which expert knowledge of a given process plant can be entered and used to select alarm systems.

Scope—Alarm systems play a very important role in process plants. They aid the operator in his primary tasks of detecting and interrupting progression of a failure, and diagnosing and providing corrective actions for fault conditions. There are, however, operator difficulties in handling alarms. A particular alarm system design can significantly affect the operator's success likelihood in receiving and processing alarms.

Several factors are important in the design or improvement of a given system. Human likelihood of success using a given alarm system under a given fault condition is one obvious factor. Economical aspects of selecting alarm systems, given probable types and frequencies of fault conditions, should also be considered in the design or improvement of alarm systems. A systematic approach is necessary to consider the effects of all these factors in evaluating a set of proposed alarm systems and in selecting the most appropriate alarm system. The purpose of this paper is to provide a method for determining the worth of a given alarm system by considering all factors which influence that worth.

In complex process plants, applications of the methodology presented in this paper can be very difficult without the aid of a computer. Therefore, a computer program is also described to carry out the methodology. Information regarding the process plant is entered into the program using the goal-tree concept. The goal tree contains the expert knowledge of the process which in turn is used in the design or modification of alarm systems.

Conclusions and Significance—A methodology has been presented to perform systematic evaluation of alarm systems. The methodology is based on the goal-tree concept through which process plants can be modeled.

Goal trees excellent tools for cause-consequence determination. The methodology makes use of decision trees which are constructed in parallel to goal trees to show all operator action(s) required to achieve each goal, and to show the consequences of operator's failure to achieve each goal. The decision trees can also model the progression of an initiating fault condition. The operator's likelihood of success of achieving each goal for a given alarm system design or alarm system modification can be estimated and used in the decision tree to estimate anticipated consequences of a given alarm design or modification. Anticipated consequence is defined as the probability of not achieving a goal times the consequence of not achieving that goal. Finally, alarm system designs or modifications with a low anticipated consequence and low implementation cost can be identified for further evaluation as potential alarm systems for the process.

The methodology has been modeled in a system of computer codes called UMPIRE-I. Process knowledge is entered into the computer through a goal tree coupled with human success likelihoods. The rest of the analysis is performed by UMPIRE-I. The code is user-friendly and can be used with minimal training. An example is provided in the paper to further clarify the methodology.

This method has been applied to several limited-scale engineering processes with rather significant success.     

Optimal control and operation of drum granulation processes

Process optimisation and optimal control of batch and continuous drum granulation processes are studied in this paper. The main focus of the current research has been: (i) construction of optimisation and control relevant, population balance models through the incorporation of moisture content, drum rotation rate and bed depth into the coalescence kernels; (ii) investigation of optimal operational conditions using constrained optimisation techniques; (iii) development of optimal control algorithms based on discretized population balance equations; and (iv) comprehensive simulation studies on optimal control of both batch and continuous granulation processes. The objective of steady state optimisation is to minimise the recycle rate with minimum cost for continuous processes. It has been identified that the drum rotation-rate, bed depth (material charge), and moisture content of solids are practical decision (design) parameters for system optimisation. The objective for the optimal control of batch granulation processes is to maximize the mass of product-sized particles with minimum time and binder consumption. The objective for the optimal control of the continuous process is to drive the process from one steady state to another in a minimum time with minimum binder consumption, which is also known as the state-driving problem. It has been known for some time that the binder spray-rate is the most effective control (manipulative) variable. Although other possible manipulative variables, such as feed flow-rate and additional powder flow-rate have been investigated in the complete research project, only the single input problem with the binder spray rate as the manipulative variable is addressed in the paper to demonstrate the methodology. It can be shown from simulation results that the proposed models are suitable for control and optimisation studies, and the optimisation algorithms connected with either steady state or dynamic models are successful for the determination of optimal operational conditions and dynamic trajectories with good convergence properties.     

Periodic section modeling of convective continuous powder mixing processes

This study aims to develop a general model of the convective continuous mixing process. The main idea is that continuous mixing can be considered as a combination of powder flow and mixing processes. Although powder flow is characterized by the residence time distribution (RTD), powder mixing can be described by a batch mixing process simulated in one periodic section of the continuous mixer. By characterizing the two processes separately, we can calculate the number of sections required to achieve certain homogeneity. In this study, continuous mixing is simulated using the discrete element method, and segregating and non‐segregating mixing cases are tested to investigate the applicability of the model. Results show satisfactory predictions by the model, which is able to characterize the continuous mixing performance of both mixing cases. On the basis of this study, we were also able to suggest a novel method in design and control of continuous powder mixing systems. © 2011 American Institute of Chemical Engineers AIChE J , 2012     

氢氧化锂连续冷冻结晶脱硝生产工艺与设备介绍

氢氧化锂冷冻结晶脱硝最早采用的是间歇生产工艺和设备。采用间歇生产工艺和设备,氢氧化锂冷冻母液中硫酸根等杂质含量较高,且芒硝晶体附液量大,锂损失多。介绍了氢氧化锂连续冷冻结晶脱硝生产工艺与设备。通过采用连续生产工艺和设备,使氢氧化锂冷冻母液中硫酸根的质量浓度由45~50 g/L降低到35~40 g/L,芒硝晶体附液质量分数由10%左右降低到5%左右,降低了后续氢氧化锂生产的能耗,提高了锂的回收率。     

一类连续/间歇过程的迭代学习模型预测控制

An iterative learning model predictive control (ILMPC) technique is applied to a class of continuous/batch processes. Such processes are characterized by the operations of batch processes generating periodic strong disturbances to the continuous processes and traditional regulatory controllers are unable to eliminate these periodic disturbances. ILMPC integrates the feature of iterative learning control (ILC) handling repetitive signal and the flexibility of model predictive control (MPC). By on-line monitoring the operation status of batch processes, an event-driven iterative learning algorithm for batch repetitive disturbances is initiated and the soft constraints are adjusted timely as the feasible region is away from the desired operating zone. The results of an industrial appli-cation show that the proposed ILMPC method is effective for a class of continuous/batch processes.     

聚氯乙烯生产过程全流程调度

研究了电石法制聚氯乙烯(PVC)全流程生产调度问题, 包括从电石生产、盐水电解到氯乙烯(VCM)聚合产品出厂各环节, 其中电石生产和VCM聚合是间歇过程, 其他生产环节是连续过程, 是一个混杂系统调度问题。本文针对过程特性对该问题进行了合理假设, 以包括电耗、库存、产品型号切换、交货延迟等的成本最小为目标, 建立了基于离散时间表示的混合整数线性规划(MILP)调度优化模型, 并针对一个案例进行了调度优化求解和分析, 验证了模型的可行性。     

Optimization and nonlinear Model Predictive Control of batch polymerization systems

This paper addresses the optimization of batch polymerization systems, using a feasible path approach, with roots on Model Predictive Control (MPC) theory. The approach allows the reuse of many concepts previously developed for nonlinear MPC of continuous plants. It also provides an efficient and well-integrated methodology for the optimal supervision of discontinuous chemical processes. The application of this technique to the optimization of the batch suspension polymerization of vinyl chloride and the solution polymerization of methyl methacrylate is considered. Significant advantages associated to the use of this methodology are demonstrated with both examples, in terms of productivity gains and the capability of manufacturing products with pre-specified properties.     

Design of continuous ion exchange process for the wastewater treatment

A generic design procedure for the continuous ion exchange process is proposed. The procedure is based on the optimized arrangement of parallel batch columns. The continuity of the process is achieved by proper shifting of the inlet conditions. The method for the optimization of the process variables is presented.The concept is demonstrated on the example of ammonia removal from wastewaters. Two flowsheet schemes are considered utilizing fresh or recycled regenerating agent.The superiority of the optimized process over the periodic operation is demonstrated.     

Synthesis of mass exchange network for batch processes—Part I: Utility targeting

Synthesis of optimal mass exchange network (MEN) for continuous processes based on Pinch Analysis has been rather well established. In contrast, very little work has been done on mass exchange network synthesis (MENS) for batch process systems. The batch process systems referred to in this work can be defined as processes which operate discontinuously and deliver the products in discrete amounts, with frequent starts and stops. There is a clear need to develop a MENS procedure for batch process systems which are industrially very common as well as important. Techniques developed in this paper for the batch MENS involved the first key steps in the synthesis task, i.e. setting the utility targets ahead of batch MEN design. The utility-targeting approach employs the vertical and horizontal cascading approaches in a newly developed tool, i.e. time-dependent composition interval table that has been adapted from heat exchange network synthesis for batch processes. Prior to MEN design, the targeting procedure establishes the minimum utility (solvent) and mass storage targets for a maximum mass recovery network. These targets are essential for network design and batch process rescheduling.     

光化学微反应技术的基础及研究进展

光化学转化是有效利用光能实现化学反应的重要途径,微反应技术为提高其过程效率提供了一个强有力的平台。本文首先指出微反应器相比于传统釜式光反应器,在光强分布、过程放大、光能利用效率等诸多方面存在明显的优势,能够实现光化学反应过程的高效强化。简要地介绍了光化学转化及光化学微反应技术的基本特征,然后系统地综述了光化学微反应器的设计构建及其在有机合成、聚合等方面的应用,并详细介绍了自动化控制的光化学微反应系统及应用。重点介绍了微反应技术在紫外光、可见光辐照下的光化学合成进展及其过程放大。最后,对光化学微反应技术的研究进展进行总结,并对其发展趋势进行了展望。     

Iterative learning reliable control of batch processes with sensor faults

An iterative learning reliable control (ILRC) scheme is developed in this paper for batch processes with unknown disturbances and sensor faults. The batch process is transformed into and treated as a two-dimensional Fornasini-Marchesini (2D-FM) model. Under the proposed control law, the closed-loop system with unknown disturbances and sensor faults not only converges along both the time and the cycle directions, but also satisfies certain H_∞ performance. For performance comparison, a traditional reliable control (TRC) law based on dynamic output feedback is also developed by considering the batch process in each cycle as a continuous process. Conditions for the existence of ILRC scheme are given as biaffine and linear matrix inequalities. Algorithms are given to solve these matrix inequalities and to optimize performance indices. Applications to injection packing pressure control show that the proposed scheme can achieve the design objectives well, with performance improvement along both time and cycle directions, and also has good robustness to uncertain initialization and measurement disturbances.     

Hydrogenation of palm and lauric oils

The technology and equipment for hydrogenating fats and oils is described. Advantages and disadvantages of various batch and continuous processes are discussed. Continuous hydrogenation is suggested for plants that process essentially only one type of oil. When several different feedstocks are to be processed in the same equipment, batch autoclaves may be advantageous. Hydrogenated palm kernel and coconut oils or fractions have many uses in food products, especially in products where specific melting points and good oxidative stabilities are important. Trends in hydrogenation indicate that more and more energy-saving and automation devices will be used to reduce energy and labor costs and to make more uniform products, especially in batch processes.     

Treatability studies on domestic wastewater using UV/H2O2 process

Advanced oxidation processes (AOPs) are emerging and promising technology both as an alternative treatment to conventional wastewater treatment methods and enhancement of current biological treatment methods especially dealing with highly toxic and low biodegradable wastes. In this paper, the results of domestic wastewater treatment using H₂O₂/UV process in both batch and continuous mode are presented. Over 95% reduction in COD was achieved in less than 60 min of reaction time. Optimum conditions for pH and H₂O₂ dosage for this process was found to be 3 and 50 mg L⁻¹, respectively. A pretreatment in the form of removal of turbidity is recommended for the success of the process in the long run. Electric energy required is estimated to be 10 kWh kg⁻¹ COD on the average.