The HEN synthesis problem is one amongst many engineering problems which can be characterized as highly combinatorial, nonlinear and nonconvex, all contributing to computational difficulties shown either in a form of long computational times and/or in identifying poor locally optimal solutions. In this work, a new strategy for global optimization of heat exchanger networks (HENs) is presented. We first introduce a concept of stage-wise super structure augmented by an aggregated substructure. On this basis, the HEN synthesis problem is formulated as a mixed integer nonlinear program (MINLP). The strategy for providing globally optimal solutions relies on solving a single convex MINLP which incorporates piecewise linear and nonlinear convex under-estimators of the nonconvex linear fractional terms present in the nonconvex MINLP. It is shown that the optimal solution of the convex MINLP can provide a lower bound, tight enough that the gap between the upper and lower bound falls below 1 %. In addition, an algorithm for identifying good locally optimal solutions is presented. The approach was tested on two examples, showing that we are currently able to solve small HEN synthesis problems to global optimality with reasonable computational effort, while good locally optimal solutions can be identified for larger problems.
COBISS.SI-ID: 15815190
This paper addresses the optimization-based design of water networks having complexity of industrial relevance. To overcome the challenges associated with the large scale processes, we focused on the integration of wastewater engineering concepts and models, together with optimization methods and solution algorithms. We proposed a computer-aided framework for the design of water treatment and reuse networks. In the framework, optimization methods, problem analysis tools and waste-water engineering knowledge were integrated in a computer-aided environment, in order to facilitate the formulation and solution of the design problems.
COBISS.SI-ID: 17185046
This paper presents the design of a large water system within the production and packaging areas of a brewery. In order to accomplish the task, mathematical models were developed based on a Mixed Integer Nonlinear Programming (MINLP) formulation from the open literature. These models enable the investigation of several integration options: a) direct water re-use between batch and semi-continuous consumers operating within the same time interval and b) regeneration re-use options, by designing and scheduling an on-site waste-water treatment system. A multilevel strategy was applied for this large-scale industrial problem, which firstly decomposes the design problem into several smaller integration problems concerning water consumers within each section of the brewery. At the following level, water re-use and regeneration re-use opportunities between the brew-house and the packaging areas were explored for each working day. Finally, the design of an integrated water system was performed over the entire working week by fixing identified intra-daily matches between sections. An optimum water integration scheme is proposed based on the results obtained.
COBISS.SI-ID: 15125014
Breweries are responding to some sustainability challenges but many of them find sustainability assessment and reporting to be very complex, difficult, and time-consuming tasks. Despite several existing frameworks for the sustainability assessment of companies, none of them specifically addresses breweries. They do not provide them with a transparent, comprehensive, and integrated approach to sustainability assessment, adjusted to the particular circumstances of traditional beer production. In view of these requirements by the brewing industry, this article aims to support breweries in sustainability assessment activities by proposing a methodology for integrated performance assessment. This methodology proposes environmental, societal, economic, and integrated indicators reflecting the characteristics of the brewing industry, compatible with those general indicators proposed by the Global Reporting Initiative (GRI). Although it is important to assess sustainability using several indicators, it may sometimes be difficult to make decisions based on a wide number of performance measurements. Thus, the proposed methodology gradually aggregates sustainable development indicators into sustainability sub-indices and, finally, to a composite sustainability index that tracks integrated information on the economic, environmental, and societal performances of a brewery over time. They can be used both internally, for the identification of 'hot spots' and externally, for sustainability reporting and stakeholder engagement. Since breweries strive to outperform their competitors, the proposed methodology enables the benchmarking of a brewery against best performance practices, as a catalyst for improvement and innovation, by providing benchmark values for each indicator. The case study presented in this article illustrates how the proposed methodology could be easily applied in practice, and stimulates breweries to test their effectiveness themselves.
COBISS.SI-ID: 15021334
This paper presents an approach to designing a large-scale water system which integrates water-using operations and wastewater treatment units in different production sections within the same network. This approach uses a mixed-integer nonlinear programming (MINLP) model for water re-use and regeneration re-use in batch and semi-continuous processes. The application of this mathematical formulation to large-scale industrial problems with changing daily production schedule leads to huge and complex mathematical models. Two alternative multilevel strategies are proposed to solve such problems by means of temporal decomposition. The approach is illustrated with a brewery case study that integrates water consumers in two production sections. The results obtained show that, despite the high piping cost, integration of both sections yields better result than the separate water network design in each section.
COBISS.SI-ID: 14929174