A rewriting grammar for heat exchanger network structure evolution with stream splitting

The design of cost optimal heat exchanger networks is a difficult optimisation problem due both to the nonlinear models required and also the combinatorial size of the search space. When stream splitting is considered, the combinatorial aspects make the problem even harder. This paper describes the implementation of a two level evolutionary algorithm based on a string rewriting grammar for the evolution of the heat exchanger network structure. A biological analogue of genotypes and phenotypes is used to describe structures and specific solutions respectively. The top level algorithm evolves structures while the lower level optimises specific structures. The result is a hybrid optimisation procedure which can identify the best structures including stream splitting. Case studies from the literature are presented to demonstrate the capabilities of the novel procedure

Optimisation of complex distillation colomn systems using rigorous models

Since distillation is still the most widely used separation technique used in the petrochemical industry, optimisation of these unit operations are important to minimise costs and maximise production. This thesis focuses on the development of a tool using rigorous non-equilibrium distillation models to optimise complex columns. Non-equilibrium distillation models are usually avoided in optimisation studies due to the time required to solve them, but this has been overcome by using a technique called orthogonal collocation in which the profiles in the columns are represented by polynomials of a lower order than would be required normally. This significantly reduces the process times and makes the use of non-equilibrium models a possibility in optimisation studies. The orthogonal collocation technique was applied to a packed distillation column model and shown to be effective in modelling the system. A system consisting of a distillation column with integrated external side reactors was chosen as a case study to investigate the use of the methods. These systems have been shown to be effective in certain circumstances in literature, when comparing them to other forms of process intensification, such as reactive distillation. The toluene disproportionation reaction was considered as a potential use for the technology and the optimisation tool was used to find optimum system configurations for achieving maximum toluene conversions and minimum costs. Nonlinear programming techniques were used initially to optimise these systems, but due to the discontinuities associated with multiple side streams, they were replaced by a genetic algorithm. Various system configurations were identified as achieving maximum conversions and minimum costs. These results were used in a comparison with results obtained from a literature study and the results showed significant promise. Unfortunately, the two studies did not have enough in common to truly produce a comprehensive result. This iv lead to further comparisons with another system using the same information. The results obtained in the toluene disproportionation case study showed that there was some possible benefits for using the side reactor systems, but the conventional system was still 30 and 60% cheaper in terms of capital and utility costs respectively. Another case study was investigated that looked at the synthesis of methyl acetate from acetic acid and methanol. The packed collocation model was used as a comparison with another investigation performed in literature (using equilibrium distillation models). Both showed comparable results, but still had significant differences. Costs were also compared between the side reactor system and a more conventional system for methyl acetate synthesis. The side reactor systems were found to be more cost effective than the conventional system. Additionally, an increase in the number of external reactors resulted in lower utility costs (mainly as a result of lower flow rates in the side streams). Overall, the reaction and process conditions are important considerations when deciding whether or not to use a side reactor system. For the gas phase toluene disproportionation reaction, the side reactor systems were not cost effective, when compared to the conventional system. However, the liquid phase methyl acetate reaction proved to be more conducive to side reactor systems in terms of cost. This thesis has shown the applicability of using rigorous disequilibrium distillation models in optimisation studies. The side reactor systems have been found to be complex systems that require a holistic approach to find optimum configurations instead of optimising individual process units

Systematic Methods for Reaction Solvent Design and Integrated Solvent and Process Design

Otto-von-Guericke-Universität Magdeburg, Fakultät für Verfahrens- und Systemtechnik, Dissertation, 2016by: M. Sc. Teng ZhouLiteraturverzeichnis: Seite 100-10

Hybrid simulation-equation based synthesis of chemical processes

A challenging problem in the synthesis and design of chemical processes consists of dealing with hybrid models involving process simulators and explicit constraints. Some unit operations in modular process simulators are slightly noisy or require large CPU times to converge. In this work, this problem is addressed by combining process simulators and surrogate models. We have replaced some unit operations, which cannot be used directly with a gradient-based optimization, by surrogate models based on Kriging interpolation. To increase the robustness of the resulting optimization model, we perform a degree of freedom analysis and aggregate (or disaggregate) parts of the model to reduce the number of independent variables of the Kriging surrogate models (KSMs). Thus, the final model is composed of KSMs, unit operations (maintained in the process simulator) and also explicit equations. The optimization of the well-known vinyl chloride monomer (VCM) production process is performed to test the proposed approach. The effect of the heat integration is also studied. In addition, the economic feasibility of the optimized process is calculated assuming uncertainty in raw material and product prices.The authors gratefully acknowledge the financial support by the Ministry of Economy and Competitiveness from Spain, under the project CTQ2016-77968-C3-02-P (AEI/FEDER, UE), and Call 2013 National Sub-Program for Training, Grants for pre-doctoral contracts for doctoral training (BES-2013-064791)

Optimization of reactive distillation column

The reactive distillation combines both chemical reaction and multi component separation into a single unit. It is a unit operation in which chemical reaction and distillative separation are carried out simultaneously within a fractional distillation apparatus. Reactive distillation (RD), the combination of chemical reaction and distillation in a single unit operation, has proven to be advantageous over conventional process systems consisting of separate reactor and distillation units. A simulation model based on an extension of conventional distillation is proposed for the simulation step of the optimization problem. A reactive distillation column has been synthesized for the production of ethylene glycol for the given number of trays, feed distribution, liquid hold up in each plate, boil up fraction assuming ideal vapor liquid equilibrium relation. The objective function is the minimization of the total annualized cost and to evaluate the objective function, the operating conditions determined by the column simulation for each decision vector have to be calculated. The optimization of the objective function has been done by using genetic algorithm, and the results obtained are similar to those previously reported

Integration of modular process simulators under the Generalized Disjunctive Programming framework for the structural flowsheet optimization

The optimization of chemical processes where the flowsheet topology is not kept fixed is a challenging discrete-continuous optimization problem. Usually, this task has been performed through equation based models. This approach presents several problems, as tedious and complicated component properties estimation or the handling of huge problems (with thousands of equations and variables). We propose a GDP approach as an alternative to the MINLP models coupled with a flowsheet program. The novelty of this approach relies on using a commercial modular process simulator where the superstructure is drawn directly on the graphical use interface of the simulator. This methodology takes advantage of modular process simulators (specially tailored numerical methods, reliability, and robustness) and the flexibility of the GDP formulation for the modeling and solution. The optimization tool proposed is successfully applied to the synthesis of a methanol plant where different alternatives are available for the streams, equipment and process conditions.Spanish Ministry of Science and Innovation (CTQ2012-37039-C02-02)

Economic and environmental strategies for process design

This paper first addresses the definition of various objectives involved in eco-efficient processes, taking simultaneously into account ecological and economic considerations. The environmental aspect at the preliminary design phase of chemical processes is quantified by using a set of metrics or indicators following the guidelines of sustainability concepts proposed by . The resulting multiobjective problem is solved by a genetic algorithm following an improved variant of the so-called NSGA II algorithm. A key point for evaluating environmental burdens is the use of the package ARIANE™, a decision support tool dedicated to the management of plants utilities (steam, electricity, hot water, etc.) and pollutants (CO2, SO2, NO, etc.), implemented here both to compute the primary energy requirements of the process and to quantify its pollutant emissions. The well-known benchmark process for hydrodealkylation (HDA) of toluene to produce benzene, revisited here in a multiobjective optimization way, is used to illustrate the approach for finding eco-friendly and cost-effective designs. Preliminary biobjective studies are carried out for eliminating redundant environmental objectives. The trade-off between economic and environmental objectives is illustrated through Pareto curves. In order to aid decision making among the various alternatives that can be generated after this step, a synthetic evaluation method, based on the so-called Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) (), has been first used. Another simple procedure named FUCA has also been implemented and shown its efficiency vs. TOPSIS. Two scenarios are studied; in the former, the goal is to find the best trade-off between economic and ecological aspects while the latter case aims at defining the best compromise between economic and more strict environmental impact

Achievements and perspectives of process integration in cis countries

Due to the rapid growth in the world population, there has been an increase in energy consumption globally. The problem of efficient energy use becomes more relevant and stimulates research and development of new energy and resource-saving technologies. This task is becoming more complicated when the other factors are accounted for, resulting in multiple-factor trade-offs, such as the water-energy-food nexus. This paper highlights the main points for the development of Process Integration in the Commonwealth of Independent States (CIS) countries. It shows the main achievements in the field to date and demonstrates the scientific schools that are working on these problems. A comprehensive review of modern approaches and methods, which are now being developed or have been recently developed, was done. It shows a research gap in Process Integration in CIS and other leading countries. It demonstrates the significant research potential as well as practical applications. The main challenges in process systems engineering and for the sustainable development of industrial energy systems are also discussed. Industry digital transformation, energy transition, circular economy, and stronger energy and water integration are pointed out as priorities in analysis, design, and retrofit of society in the future. A state-of-the-art review in the area of integration of continuous and batch processes, mass integration technologies, and process intensification is presented to show the variety of existing approaches. The necessity of Process Integration development in the CIS is shown to be a necessary condition for building a more sustainable society and a resource-efficient economy