Synthesis of large-scale total water network with multiple water resources under seasonal flow rate constraints

Abstract

In recent decades, numerous studies have been conducted on freshwater conservation by improving industrial water networks. However, most previous industrial water networks utilize freshwater supplies without defining the freshwater origin; besides, they also ignore the practical issue of seasonal utility flow rate fluctuations. In practice, industrial freshwater supply can be obtained from many raw water resources, including municipal water, groundwater, surface water, municipally treated wastewater, and seawater. Each type of raw water resource with different properties can use a specific pre-treatment technology with fixed removal and production ratios to produce freshwater. These pre-treatment technologies directly impact the total annual cost (TAC) of the industrial water network. This paper proposes a superstructure-based mathematical model for the optimum synthesis of an integrated total water network, including multiple water resources, along with water pre-treatment technologies. A superstructure-based mathematical model is framed, considering relative equations of water reuse/recycling connections, including the pre-treatment system, utility system, water-using system, and wastewater treatment system. A large-scale coastal oil refinery is selected to implement the proposed approach. Different scenarios of individual and multiple water resources under seasonal utility flow rate constraints are developed to check the applicability of the proposed model. A significant reduction in freshwater demand in all seasons is achieved. The TAC for the individual water resource is reduced by 4.5% and 2.8% using the groundwater and surface water compared to the preliminary design. For multi-resourced water networks, the TAC increased due to the higher investment cost of the treatment system for municipal treatment water and seawater.