Water Targeting Models for Simultaneous Flowsheet Optimization
2013
Yang, Linlin | Grossmann, Ignacio E.
This paper presents an approach to perform simultaneous optimization of heat and water integration for a process flowsheet. As opposed to the sequential integration approach where heat and water integration are performed for flowsheets with fixed operating conditions, the simultaneous optimization method allows for variable stream qualities (e.g., flowrates, pressures, and temperatures) to account for potential trade-offs among raw material, investment cost, and utility and water consumption. Since detailed heat-exchange network and water network designs are generally formulated as nonconvex mixed-integer nonlinear programming and nonconvex nonlinear programming models, respectively, reducing constraint complexities for these two networks is of utmost priority. To this end, simultaneous handling of process flowsheet with heat integration has already been demonstrated by Duran and Grossmann [AIChE J.1986, 32, 123–138]. In order to reduce the computational requirement for water integration, we have developed a novel LP targeting model for minimizing freshwater consumption of multicontaminant systems. This water targeting model, which is either exact or else predicts tight upper bounds, is incorporated along with the available heat targeting model into flowsheet optimization process to achieve the best operating conditions through the proposed simultaneous framework in this work. Several examples are presented to illustrate the effectiveness of the simultaneous approach in improving both the quality and computational effort of the solution.
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