(246d) Multi-Scale Design of Interplant Water-Allocation and Heat-Exchange Network with Fixed Flow-Rate and Fixed Contaminant-Load Processes

Water and energy are two of the most essential resources in process industries. Large amount of water is needed not only as an effective mass-separating agent, but also as heat carriers in the utility systems. In aforementioned usages, both wastewater-treatment units and large amount of energy in the form of cooling and heating utilities are needed to satisfy both the concentration and temperature requirements. At present, escalating costs of freshwater, effluent treatment and energy have motivated integrated water-allocation and heat-exchange network (WAHEN) designs, which facilitate optimal distribution of water and energy resources simultaneously to satisfy process demands as well as environmental regulations at minimum total cost.

In the past few years, the tasks of designing single WAHEN have been examined in several works [1-3]. However, since industrial practices have necessitated the management of both quality and temperature of water across plants, there is therefore a need to consider both WANs and HENs for conceptual designs on an interplant scale simultaneously. In this work, the multi-scale state-space superstructure, a framework that considers all intra- and inter-plant configurations, are presented for interplant WAHEN design for both fixed flow rate (FF) and fixed contaminant-load (FC) processes. In particular, the proposed superstructure is capable of capturing all the water reuse, recycle and heat recovery opportunities at both intra- and inter-plant levels [4]. Additionally, in this work, both direct integration by process streams and indirect integration with interplant transfer network (ITN), which consists of junctions, treatment units and heat exchangers, are introduced for interplant WAHEN designs. To the best knowledge of the authors, this is the first time that the aforementioned problems have been addressed in its entirety. Finally, considering the costs of (1) utilities, (2) heat exchangers and water treatment units and (3) ITN, an mixed-integer nonlinear programming (MINLP) model has been developed for the interplant WAHEN model. It can be shown that better network design with 10-50% improvement in total annualized cost (TAC) can be obtained in all example studies.

References

(1)   Savulescu, L. E.; Kim, J. K.; Smith, R. Studies on simultaneous energy and water minimization-Part II: systems with maximum re-use of water. Chem. Eng. Sci. 2005, 60, 3291.

(2)   Dong, H. G.; Lin, C. Y.; Chang, C. T. Simultaneous Optimization Approach for Integrated Water-Allocation and Heat-Exchange Networks. Chem. Eng. Sci. 2008, 63, 3664.

(3)   Bogataj, M.; Bagajewicz, M. Synthesis of non-isothermal heat integrated water networks in chemical processes. Comput. Chem. Eng. 2008, 32, 3130.

(4)   Zhou, R. J.; Li, L. J.; Dong, H. G.; Grossmann, I. E. Synthesis of Interplant Water-Allocation and Heat-Exchange Networks. Part 1: Fixed Flow Rate Processes. Ind. Eng. Chem. Res. In Press