Profitability as a criterion of batch process control design

Batch processes have in some cases many advantages in comparison with continuous processes even though continuous processes are becoming common.

The main disadvantages of batch processes are the discontinuous usage of raw materials and energy as well as the discontinuous production thus causing difficulties in power plant and other continuous processes connected with the batch process in question. If there are several parallel process units, difficulties can arise with parallel process unit sequencing and product quality equalization. However, with the aid of computer control these and other disadvantages are eliminated or minimized so that total automation of batch processes is possible.

In this paper the basic principles of batch process control design are considered, with particular emphasis on the economic justification criterion. As an example, a computer control design of sulphate batch digesters is considered. This approach is based on more than 20 implementations of batch process automation.     

Scheduling of a mixed batch/continuous sugar milling plant using Petri nets

Scheduling of processes in mixed batch/continuous plants, due to their hybrid nature, can become very complex. This paper presents the Timed Hybrid Petri net (THPN) as a suitable tool for modelling and scheduling of hybrid systems. One of the major benefits over traditional methods is a significant reduction in complexity during problem formulation. A sugar milling plant containing both batch and continuous processing units is used to illustrate the application of the proposed scheduling algorithm.     

An efficient MILP continuous-time formulation for short-term scheduling of multiproduct continuous facilities

This paper presents a new MILP mathematical formulation for the scheduling of resource-constrained multiproduct plants involving continuous processes. In such facilities, a sequence of continuous processing steps is usually carried out to produce a significant number of final products and required intermediates. In order to reduce equipment idle time due to unbalanced stage capacities, storage tanks are available for temporary inventory of intermediates. The problem goal is to maximize the plant economic output while satisfying specified minimum product requirements. The proposed approach relies on a continuous time domain representation that accounts for sequence-dependent changeover times and storage limitations without considering additional tasks. The MILP formulation was applied to a real-world manufacturing facility producing seven intermediates and fifteen final products. Compared with previous scheduling methodologies, the proposed approach yields a much simpler problem representation with a significant saving in 0–1 variables and sequencing constraints. Moreover, it provides a more realistic and profitable production schedule at lower computational cost.     

Design,synthesis and scheduling of multipurpose batch plants via an effective continuous-time formulation

Design, synthesis and scheduling issues are considered simultaneously for multipurpose batch plants. An earlier proposed continuous-time formulation for scheduling is extended to incorporate design and synthesis. Processing recipes are represented by the State-Task Network (STN). The superstructure of all possible plant designs is constructed according to the potential availability of all processing/storage units. The proposed model takes into account the trade-offs between capital costs, revenues and operational flexibility. Computational studies are presented to illustrate the effectiveness of the proposed formulation. Both linear and nonlinear models are included, resulting in MILP and mixed-integer nonlinear programming (MINLP) problems, respectively. The MILP problems are solved using a branch and bound method. Globally optimal solutions are obtained for the nonconvex MINLP problems based on a key property that arises due to the special structure of the resulting models. Comparisons with earlier approaches are also presented.     

Optimal design of multiproduct batch plants considering duplication of units in series

A generalized disjunctive programming (GDP) model for the optimal design of multiproduct batch plants is presented. This general model manages the duplication of units in series to perform a given operation in the process, which is an alternative that has not been considered in previous general approaches. Unlike duplication in parallel, duplication in series is only applicable to some operations which present trade-offs between duplication and other cost-impacting elements in the batch process. In order to use a fixed time and size factor model some assumptions had to be made in the operations that allow the duplication in series. To show the effectiveness of this approach, a plant that produces multiple recombinant proteins is presented and solved.     

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.     

Usage of inherent storage for minimisation of wastewater in multipurpose batch plants

Wastewater minimisation in batch plants is gaining importance due to intensifying environmental legislation and the gradual reduction in the number of freshwater sources. Intrinsic in the minimisation of wastewater in batch plants is the reuse of wastewater through intermediate storage vessels. However, the intermediate storage vessels take up unnecessary space which is undesirable in processes which are generally undertaken in limited spaces. Furthermore, in any batch process there are processing units that are not used extensively in the time horizon. In other words, these units remain idle for the major part of the time horizon, amounting to wasted return on capital investment. The idle processing units can be used as storage vessels, since any processing unit is, in essence, a storage vessel. In doing this one can reduce the size of the central storage and increase the utilisation of capital intensive processing units. The methodology presented in this paper deals with the minimisation of single contaminant wastewater by exploiting the inherent storage possibilities in idle processing units. The methodology is applied to two cases. In the first case the objective is to minimise the amount of effluent and the size of the central storage vessel through the usage of inherent storage, as commonly encountered in grassroot design. In the second case the objective is to determine the minimum wastewater target through the usage of both inherent storage and fixed central storage, as encountered in retrofit design.     

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.     

OPTIMAL DESIGN OF MULTISITE BATCH-STORAGE NETWORK UNDER SCENARIO-BASED DEMAND UNCERTAINTY

An effective methodology is reported for the optimal design of multisite batch production/transportation and storage networks under uncertain demand forecasting. We assume that any given storage unit can store one material type that can be purchased from suppliers, internally produced, internally consumed, transported to or from other plant sites, and/or sold to customers. We further assume that a storage unit is connected to all processing and transportation stages that consume/produce or move the material to which that storage unit is dedicated. Each processing stage transforms a set of feedstock materials or intermediates into a set of products with constant conversion factors. A batch transportation process can transfer one material or multiple materials at once between plant sites. The objective for optimization is to minimize the probability averaged total cost, which consists of the raw material procurement cost, the cost of setting up processes, inventory holding costs of the storage units, and the capital costs of processes and storage units. A novel production and inventory analysis formulation, the PSW (periodic square wave) model, provides useful expressions for the upper/lower bounds and average level of the storage inventory. The expressions for the Kuhn-Tucker conditions of the optimization problem can be reduced to two sub-problems. The first yields analytical solutions for determining lot sizes, and the second is a separable concave minimization network flow sub-problem whose solution yields the average material flow rates through the networks for the given demand forecast scenario. The result of this study will contribute to the optimal design and operation of large-scale supply chain systems.     

Detailed design of multipurpose batch plants

A formulation is presented for the optimal selection of both the equipment units and the network of connections for multipurpose batch plants so as to satisfy given production requirements for a variety of products. The model includes very general constraints and objective functions and permits to optimize simultaneously the structural aspects of the plant and the associated production schedule, accounting for both capital costs of equipment units and pipework, operating costs and revenues. A special novelty of the formulation is that it provides the possibility of generating directly the optimal connectivity between the process units, optimal sizing and costs of the transfer lines, and the optimal storage policies (and associated vessel sizes, if any) for stable intermediates without the need for a priori assumptions (e.g. unlimited storage, etc.).The resulting MILP problem is solved using a branch and bound method. Several examples are detailed, demonstrating the generality of the approach and the importance of including structural and operational aspects at the design stage.The flexibility of the formulation permits utilizing various design strategies, from a simultaneous optimization of all problem decisions (equipment, connections and schedule) to a sequential optimization of main equipment, followed by the design of connections etc. These strategies are also illustrated by an example.     

Neuere technische Entwicklungen der industriellen Herstellung von Speisefetten I

Recent Technical Developments in the Industrial Manufacture of Edible Fats The development in the oilseed processing during the past decade was aimed toward increasing the capacity of the production units, especially of extraction plants, and, in connection herewith, towards reduction of costs. In the field of fat-refining considerable progress from chemical and technological view-point was achieved during the same decade. The advances in processing technique comprise primarily of efforts to change over to continuous or semi-continuous processes apart from the technical requirements that are to be fulfilled due to chemical developments and modifications. In the present contribution, processes are reported which were either found to be totally successful in the actual practice or whose projecting and trial have already been successfully completed. In the general technology, the decisive step towards automation could be scaled by a systematic approach, which led to a well-defined characterization of the fat-refining process. The important features of the above are: multi-channelled and multi-step processes or sequence of processes of various types with frequent change of material over a main path, numerous multi-channelled process-loops and a few subsequent single or multi-channelled processes for the treatment of by-products and waste products.     

并联连续再生/再循环的多杂质间歇用水系统优化方法

为了有效地减少多杂质间歇用水系统的新鲜水消耗量和再生处理量,针对多杂质间歇过程用水网络提出连续操作并联再生处理单元水网络结构模型及其优化设计方法。通过在用水网络中设置中间储罐和再生单元以实现对不同水质废水并联分质处理,建立了减少用水系统的新鲜水用量和再生水量以及废水排放量的数学规划模型,采用GAMS软件对一个实例进行求解。计算和分析表明：提出的水网络结构与优化设计方法可有效地解决按水质对废水进行并联处理的间歇用水系统,使系统的新鲜水用量和再生水流率同时达到最小。     

On the solution of scheduling problems for multi-purpose batch chemical plants

A solution strategy for solving the scheduling problem in the case of multi-purpose batch chemical plants is described. The plant may contain several identical examples of any of the types of process unit. The problem is characterized by requirements such as —branching in batch and device —maintenance of a fixed time regime in the production of one batch —changeover times when products are changed, etc. The centre of the heuristic strategy of solution is an exact algorithm which examines whether or not a batch with a given starting time can be scheduled. The appropriate subprogram can be easily incorporated into programs realizing known heuristic scheduling principles, which were developed for solving simpler problems. Examples with 68 process units, 600 shits and 350 batches have been computed on a EC 1040 computer in 10–15 minutes.     

A modeling strategy for integrated batch process development based on mixed-logic dynamic optimization

This paper introduces an optimization-based approach for the simultaneous solution of batch process synthesis and plant allocation, with decisions like the selection of chemicals, process stages, task-unit assignments, operating modes, and optimal control profiles, among others. The modeling strategy is based on the representation of structural alternatives in a state-equipment network (SEN) and its formulation as a mixed-logic dynamic optimization (MLDO) problem. Particularly, the disjunctive multistage modeling strategy by Oldenburg and Marquardt (2008) is extended to combine and organize single-stage and multistage models for representing the sequence of continuous and batch units in each structural alternative and for synchronizing dynamic profiles in input and output operations with material transference. Two numerical examples illustrate the application of the proposed methodology, showing the enhancement of the adaptability potential of batch plants and the improvement of global process performance thanks to the quantification of interactions between process synthesis and plant allocation decisions.     

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 and Planning Optimization of Multiplant Complexes in the Food Industry

Multiplant complexes are very common in food industry because residues from one plant become raw materials for others, or several plants can use the same raw material or power resource that comes from a plant inside the complex. The integration problem between several plants that produce different products and share diverse resources among them poses significant challenges. In this work, a detailed non linear programming (NLP) model for the design of a multiplant complex is developed considering the integration between plants simultaneously with the optimal operation and production planning of each plant of the multiplant complex. The simultaneous optimization establishes different trade-offs between design, operation, and production planning decisions which are analysed in this paper. In the food industry raw materials availability, product prices, demands and other seasonal matters can vary throughout the production time horizon. For this reason, a multiperiod model is presented in which design and planning decisions have to be adjusted to the posed seasonal scenario. Several cases are presented which correspond to different scenarios. For each case, a detailed analysis of each plant solution and their integration is made.     

Design of multipurpose production facilities: A RTN decomposition-based algorithm

A general mathematical formulation for the design of multipurpose facilities has recently been presented by Barbosa-Póvoa and Pantelides (1997). The model proposed permits a detailed consideration of the design problem taking account of trade-offs between capital costs, revenues and operational flexibility. The optimal solution involves the selection of the required processing and storage equipment items and the required levels of provision of other production resources such as utilities, manpower, cleaning and transportation equipment.In order to guarantee solution optimality, the above design formulation has to consider a large number of equipment items, out of which it will select the ones that will actually be incorporated in the plant. This may result in large mixed-integer linear programming (MILP) problems that are expensive to solve.This paper presents a decomposition approach for the solution of large batch process design problems. The approach involves the iterative solution of a master problem (representing a relaxation of the original design problem) and a design sub-problem (in which several of the design decisions are already fixed).An example illustrating the effectiveness of the proposed decomposition approach is presented.     

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.     

应用Aspen Batch对年产25吨鲁拉西酮原料药工艺设计优化

采取专利CN 102863437 A的工艺,设计间歇工艺过程,将Aspen Batch Process Developer软件应用于盐酸鲁拉西酮原料药车间设计的全流程模拟和优化。间歇操作具有显著的优势：生产灵活,同一设备可生产不同产品,可根据市场需要调节生产能力及变更产品。适合于小批量,高收益的精细化学品。过去的四十年里,使用计算机对化工连续化生产进行模拟和设计已经十分普及。制药工业与传统化工最大的区别是生产过程多采用间歇法操作。目前世界上应用于化工间歇生产的计算机软件有BATCHES、gPROMS和Aspen Batch Process Developer。本文所用版本为Aspen Tech V8.6,以年产25t盐酸鲁拉西酮原料药车间为例,对车间进行全流程模拟及优化。整个设计贯彻质量源于设计理念,运用元葱模型,将盐酸鲁拉西酮的生产工艺分为磺化、氨解、氢化、缩合、成盐、精烘包等6个模块。     

化学产品过程开发实验平台--公斤实验室的建设和应用

以化工产品设计和过程开发为导向,建立了一个化工产品过程开发实验平台--化工产品公斤实验室Kilo-lab.该公斤规模试验装置可进行反应、结晶、分离、提纯等系列产品的开发过程,研究了流程装置集成和柔性生产系统的规律和特征,为小批量、多品种、高附加值化学产品快速响应市场的变化和需求,以及过程开发的工业化放大提供理论和实验依据.