Design of a water allocation and energy network for multi-contaminant problems using multi-objective optimization

• Published in: Process safety and environmental protection 2016-09, Vol.103, p.348-364
• Main Authors: De-León Almaraz, S., Boix, M., Montastruc, L., Azzaro-Pantel, C., Liao, Z., Domenech, S.
• Format: Article
• Language: English
• Subjects: Case studies; Change of phase; Chemical and Process Engineering; Chemical engineering; Chemical Sciences; Contaminants; Contamination; Design; Design optimization; Energy; Engineering Sciences; Feasibility studies; Heat exchange; Heat transfer; HEN; Mathematical programming; Multiple objective analysis; Phase transitions; Pinch; Regenerated water; Regeneration; Streams; WAHEN; WAN; Wastewater; Water allocation; Water pollution; Water purification; Wide area networks
• ISSN: 0957-5820; 1744-3598; 0957-5820
• DOI: 10.1016/j.psep.2016.03.015

•Design of Water Allocation and Heat Exchange Networks in the process industries.•Two-step optimization for large multi-contaminants problems.•Multi-objective optimization is used to solve WAN problem.•Pinch analysis and mathematical programming are used to solve the HEN problem.•A change of phase is treated in the studied case study for the HEN design. In this paper, a solution strategy based on an optimization formulation is proposed for the design of Water Allocation and Heat Exchange Networks (WAHEN) in the process industries. Such typical large problems involve many processes, regeneration units and multi-contaminants. For this purpose, a two-stage methodology is proposed. The first step is the Water Allocation Network (WAN) design by multi-objective optimization, based on the minimization of the number of network connections and of the global equivalent cost (which includes three criteria, i.e., freshwater, regenerated water and wastewater). The ɛ-constraint method is used to deal with the multi-criteria problem. In a second step, the Heat Exchange Network (HEN) is solved by two approaches, Pinch analysis and mathematical programming (MP). In both cases the HEN structure is found when the minimal energy requirement and the total annual cost are minimized for Pinch and MP, respectively. These results are compared and the best HEN network is then coupled to the WAN to verify the feasibility of the network. A case study including a change of phase among the streams is solved. The results show that this two-step methodology can be useful for the treatment of large problems.