In this paper a study on using spent grains as a fuel in an incineration process is presented. The results indicate that incineration is economically viable. By incinerating the grains, the brewery could replace approximately 65 % of the total heat demand. By installing a heat and power system, the brewery could replace 23 % of electricity. In addition to providing greater independence from natural gas, the spent grains have a potential to contribute significantly to reducing CO2 emissions.
COBISS.SI-ID: 16293654
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 using two examples, showing that currently we are able to solve small HEN synthesis problems reaching global optimality with reasonable computational effort, while good locally optimal solutions can be identified for larger problems.
COBISS.SI-ID: 15815190
This paper presents an approach to designing a large-scale water system which integrates water-using operations and waste water 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 (Tokos and Novak-Pintarič1). 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