Investigating and optimizing the water footprint in a typical coal energy and chemical base of China.

The water scarcity in China's coal bases is intensifying due to rapid development of modern coal chemical industry and inefficient water utilization. Previous studies on industrial water optimization were predominantly focused on direct water, overlooking the associated indirect water consumptions throughout supply chains. In this study, a water footprint (WF)-based allocation optimization framework is developed to obtain optimal solutions for water resources utilization constrained by quantity of water supply and coal chemical production related limiting factors. The framework comprises a novel WF accounting model especially used for the coal-to-chemical industry and a water allocation optimization model that integrates direct and indirect water consumptions. A typical major large-scale coal base in China was chosen as the study area. Results showed that the cradle-to-gate WF of the various coal-based products ranged from 2.01 m/t to 70.85 m/t, in which the internal operational and supply-chain blue WFs were the dominant contributors. Statistical analysis suggested that the volumetric WF of the coal-based products was strongly correlated with both market price and production stage while the variation of WF increased as products were further processed. Optimization result indicated that the maximized economic income of the products under current scenario was 66.23 billion CNY/year in the study area, whereas the overlapping of limited water resources and the insufficiency of downstream production capacity restricted the economic performance by over 20%. In addition, sensitivity analysis was conducted and the results showed that, in order to improve the overall economic income, deployment of more advanced technologies for saving water should be prioritized over that for saving feedstock, while conservation of power was the least preferable.