(304f) Systematic Analysis and Optimization of Water-Energy Nexus

Securing scarce energy and water resources from the environment, while at the same time satisfying on-growing water and energy demands for end-use consumption is crucial [1]. The intermediate processing facilities, energy sources (acting also as water sinks) and water sources (acting as energy sinks), receive energy and water natural resources respectively, process, exchange and deliver them as usable electricity, fuels and water for consumption. It is important to quantify the performance and the efficiency of this water-energy nexus, and understand how it is affected by the selection of the energy and water sources’ technologies, operating capacities and their connectivity.

To this end, we present a scalable, graph-theoretic representation of a nexus for the design and optimization of complex water-energy systems [2]. We define a nexus as a directed bipartite graph with water and energy flows and show that for specified external grid demands, the optimal nexus configuration with minimum water and energy generation is the one without any redundant subgraphs. We then introduce the water-energy (WEN) diagram that can systematically identify and eliminate those redundant subsystems. This leads to (i) minimum generation/extraction of water and energy resources from the environment, or (ii) maximum yield of water and energy to meet external demands. Our approach is simple to implement and results in optimal nexus configurations that also consider operational constraints, connectivity restrictions and water quality specifications. In the second part, we develop mathematical programming-based algebraic method that provides the same results but for more complicated and large-scale nexus design. This also takes into account the intensity factors of the sources, restrictions on source-sink matching, and quality specifications. The model is further extended to include capital and operating costs of the processing facilities, as well as geographic distances. The approach is demonstrated using case studies on water-energy nexus systems focusing on power generation, seawater desalination, groundwater and surface water at regional and national scales.

References:

[1] D. J. Garcia and F. You, "The water-energy-food nexus and process systems engineering: a new focus," Computers & Chemical Engineering, vol. 91, pp. 49-67, 2016.

[2] S. Tsolas, M. N. Karim, M. M. F. Hasan, " Optimization of Water-Energy Nexus: A Network Representation-based Graphical Approach," Applied Energy, Submitted.