In recent years, batch processes have been getting more attention due to their suitability for the production of small volume, high value added products. The flexibility of batch plants allows the production of different products within the same facility which mandates equipment sharing. Batch manufacturing is typically used in the pharmaceutical, polymer, food and specialty chemical industries as demands for such products are highly seasonal and are influenced by changing markets. Despite the advantage of batch plants being flexible, they also pose a challenging task to design, synthesize and operate, compared to their continuous counterparts. The profitability of these batch plants is highly dependent on the way the synthesis, design and operation is optimized. Since different types of resources (raw materials, equipment, utilities and manpower) need to be shared by a number of process operations to produce a variety of products, modeling and optimizing the design and operation of batch plants are important for economic benefits. The growing awareness of civil society for the environment and the resulting regulations introduced by national states have resulted in chemical industries considering process integration to reduce their energy and process water requirements. Energy optimization and the optimization of water use have mainly been treated as separate problems in literature. The batch production schedules resulting from each of these formulations do not guarantee that the plant is operated optimally. Consequently, it is required to develop a formulation that caters for opportunities that exist for both wastewater minimization and energy integration. This may result in production schedules that improve the operation of the batch plant when compared to optimizing water and energy separately. Presented in this thesis is a mathematical technique that addresses optimization of both water and energy, while simultaneously optimizing the batch process schedule. The scheduling framework used in this study is based on the formulation by Seid and Majozi (2012). This formulation has been shown to result in a significant reduction of computational time, an improvement of the objective function and leads to fewer time iii points required to solve the scheduling problem. The objective is to improve the profitability of the plant by minimizing wastewater generation and utility usage. From a case study it was found that through only applying water integration the total cost is reduced by 11.6%, by applying only energy integration the total cost is reduced by 29.1% and by applying both energy and water integration the total cost is reduced by 34.6%. This indicates that optimizing water and energy integration in the same scheduling framework will reduce the operating cost and environmental impact significantly. This thesis also presents a mathematical model for design and synthesis of batch plants. The conceptual design problem must determine the number and capacity of the major processing equipment items, pipe connections and storage tanks so as to meet production objectives at the lowest possible capital and operating cost. A recent robust scheduling model based on continuous-time representation is used as a platform for the synthesis and design problem. An improved objective value (revenue) of 228.6% is obtained by this work compared to the recent published models for the design and synthesis problem. Compared with other formulations, the formulation presented in this thesis gives a smaller size mathematical model that required less binary variables, continuous variables and constraints. The presented model also considers costs that arise from the pipe network and consequently, determines the optimal pipe network which should exist between different pieces of equipment. Finally, the medium-term scheduling problem for a multiproduct batch plant is addressed. The intractability of the short-term scheduling models when directly applied to the medium-term scheduling problems is solved by applying a decomposition method. The decomposition method has two level mathematical models. The first level determines the type of products and their amount to be produced in each scheduling subproblem to satisfy the market requirement. The second level determines the detailed sequencing of tasks for the tractable size of the subproblems. The recently published robust short-term scheduling model based on continuous time is extended for solving the scheduling supbroblems of the second level decomposition model. The model is applied in solving the medium-term scheduling problem of a pharmaceutical facility specializing in animal vaccines using the actual plant data. The model effectively solved a makespan minimization problem for the medium-term scheduling horizon of almost 13 weeks. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Chemical Engineering / unrestricted

Aquest treball de tesi s'adreça a la indústria de procés químic d'operació discontínua tot i que també pot resultar profitós per altres situacions de fabricació per lots. Aquests tipus d'indústries són molt variats i s'inclouen en sectors com el de la química fina, el farmacèutic, l'agroalimentari i, en definitiva, l'elaboració d'especialitats. La seva importància econòmica rau tant en el seu significatiu volum de producció com en l'alt valor afegit que sovint tenen els productes.L'objecte de l'estudi és la gestió dels recursos de fabricació i l'optimització de l'operació de la planta per tal d'ajustar la producció resultant als requeriments de la demanda. La natura discontínua i dinàmica dels processos que hi tenen lloc reclama la presa de decisions en termes d'assignació de tasques a equips (reactors, filtres i altres aparells), de seqüenciació de productes i temporització de les operacions. Es tracta, doncs, d'un problema de programació d'activitats.El primer pas vers la solució d'aquest problema és la modelització del sistema estudiat. Aquest treball proposa un model d'operació detallat que inclou, a més de la compartició per part dels diferents productes de recursos generals (temps, equips, serveis...), aspectes més específics de la indústria química. Són les necessitats de transferència i emmagatzamatge de productes, tant intermedis com acabats, de natura molt probablement fluïda. I són també, les tasques de preparació i neteja que, depenent de la seqüència de productes, cal aplicar als equips emprats.La modelització de l'emmagatzemament també considera la possible inestabilitat de certs intermedis i la conseqüent limitació de l'espera abans de ser processats. De fet, la modelització incorpora un nou esquema conceptual que permet la segmentació de les receptes dels diferents productes en sèries de tasques lligades als intermedis estables. Llavors, la descripció d'un programa d'operacions complex mitjançant una sèrie d'ordres de fabricació d'aquests intermedis proporciona una notable simplificació del problema que redueix el número de restriccions a considerar i facilita el procediment d'optimització.L'optimització mitjançant mètodes rigorosos ja establerts només resulta indicada per problemes molt simples en comparació amb el que es planteja en aquest treball. És per això que s'ha desenvolupat una metodologia heurística general que permet abordar aquest problema patró sota les diferents circumstàncies de cada cas particular. En una primera part es procedeix a la generació d'alternatives de producció considerant els casos possibles i eliminant els ineficients sota una sèrie de criteris preestablerts. Aquestes alternatives s'expressen com seqüències de fabricació d'intermedis estables i posteriorment poden ser millorades sota diferents objectius bé manualment o bé emprant mètodes sistemàtics.La validació de la metodologia proposada és possible gràcies a la comparació amb casos de la literatura. En proposar exemples de major complexitat, la utilització de mètodes estocàstics es demostra molt eficient per resoldre problemes per als quals és difícil trobar regles de solució. Llavors, la validació d'aquest casos és possible estadísticament.En conclusió, d'aquest treball en resulta una metodologia general i flexible que s'adapta a la majoria de característiques d'un tipus de problemes que, de moment i en última instància, han de ser resolts de manera particular. La seva complexitat continua reclamant la nostra intuïció. / This thesis concerns batch chemical process industries, although it may be of interest in other batch processing areas. This kind of industry is diverse and includes a variety of sectors such as fine chemicals, pharmaceuticals, food and agriculture industry and speciality manufacturing. The economical significance of this industrial activity resides on both, its large production volume and its high added value. The thesis is aimed at studying the management of limited resources and the optimization of plant operation in order to have the production meet the demand requirements. The inherent discontinuous and dynamic nature of this kind of processes needs decision-making in terms of unit-to-task assignment (reactors, filters and other apparatuses), in terms of product sequencing and in terms of operation timing. The first step towards the solution of this problem is system modelling. This work proposes a detailed operation model that includes the general sharing of resources (time, equipment, utilities, etc.), as well as more specific aspects related to the chemical industry. These aspects are the special needs for material transfer and storage, both final and intermediate, which are likely to be of fluid nature. Additionally, these aspects also include the special set-up and cleaning tasks that the equipment units require depending on the sequence of tasks performed.Storage modelling also considers the different stability of the intermediate substances and the resulting limitation of the waiting time before processing. Thus, the modelling incorporates a novel conceptual framework allowing the segmentation of the recipes into different series of tasks defined by the stable intermediate products. Hence, the description of a complex operation schedule by a sequence of production orders related to these intermediate products allows a significant problem simplification, which results in the reduction of the number of constraints to be considered and enhances the performance of the search. Optimization via established rigorous methods is only suitable for problems simpler than those addressed in this thesis. This is the reason for the development of a general heuristic methodology. The first part generates production alternative paths through an enumerative procedure that eliminates inefficient options according to given pre-established criteria. These alternative paths are characterized as production sequences of storable intermediate products that are next improved regarding different objective functions either manually or automatically.The validation of the proposed methodology is achieved through a comparative study using cases reported in the literature. For those more complex cases, the use of stochastic methods has demonstrated to be very effective when scheduling rules are not available. For these cases, the assessment and validation is achieved through statistical analysis.In conclusion, this thesis results in a general and flexible methodology that accommodates the most of the features of a kind of scheduling and planning problems that finally require particular solution strategies. The more complex the problem, the more the human intuition is to some extend still required.

Pour atteindre une haute efficacité énergétique dans l'industrie, des méthodes d'intégration énergétique ont été développées. La plupart de ces travaux traitent des procédés continus. Or 50 % des procédés industriels sont des procédés discontinus ou variables dans le temps. D'où la problématique : comment effectuer l'intégration énergétique des procédés discontinus ou variables dans le temps en incluant le stockage thermique et les systèmes de conversion d'énergie tout en minimisant l'exergie consommée ? Et comment dimensionner les utilités dans ce type de procédés pour répondre aux contraintes imposées par le réseau et aux obligations d'effacement ? La première partie présente le modèle de conception de l'architecture d'intégration énergétique des procédés discontinus en incluant les stockages thermiques et des systèmes de conversions d'énergie (pompes à chaleur, ORC, machines trithermes) dans la phase de conception. Ce modèle permet le dimensionnement et la détermination de la température des stockages thermiques ainsi que des systèmes de conversion d'énergie en minimisant l'exergie consommée dans le procédé. La deuxième partie présente le modèle de dimensionnement des utilités, en prenant en compte leur fonctionnement réel à charge partielle ou soumises à des contraintes imposées par le réseau. C'est une optimisation économique permettant de déterminer le nombre, le type et la capacité des utilités permettant de satisfaire les besoins du procédé en l'intégrant énergétiquement. / Many heat integration methods were developed to achieve high-energy efficiency in industry. Most of them are dedicated to continuous processes. However, statistics show that 50 % of processes are variable or batch. Hence: how to energetically integrate variable or batch processes including heat storages and energy conversion systems while minimizing the consumed exergy in the process? How to design utilities while considering the constraints on the energy network like the fluctuation of energy prices (imposed to reduce the energy consumption on peak hours) and the energy availability (resulting from the use of renewable energies)?The first part of the thesis presents the model to design the optimal architecture of heat integration in discontinuous processes including heat storages and energy conversion systems (heat pumps, tri-thermal machines, ORC etc.). This model allows the design of heat storages. The capacity and temperatures of energy conversion systems are also determined using this model. The objective is to reduce the consumed exergy in the process.The second part present the model for utilities design taking into account the real behavior of those under part load conditions or under constraints imposed by the network. It is an economic optimization.