Integrated Analysis of the Water-Energy-Environmental Pollutant Nexus in the Petrochemical Industry.

China has set high water-conservation, energy-saving, and pollutant-reduction goals for the petrochemical industry. This represents a challenge to petrochemical enterprises because of the complex coupling between water, energy, and environmental pollutant (WEE) subsystems, elements (different types of WEE), and production units. However, there has been little research on the element-level coupling relationship. The connection and difference between the coupling relationships of the system, element, and unit levels are not well understood. Therefore, an integrated analysis method was developed to quantify the petrochemical WEE nexus (WEEN) at these three levels, including a generic WEEN model, material and energy flow analysis, and a WEEN analysis matrix. Three indicators were proposed to analyze three-level coupling quantitatively and to formulate improvement strategies for water-conservation, energy-saving, and pollutant-reduction. A case study demonstrated significant three-level coupling. The coupled percentage of WEE subsystems were 95.87%, 61.97%, and 54.99%, respectively. The dominant energy subsystem was the root of high consumption and pollution. Based on synergies and trade-offs, we proposed element optimization priorities: High priority (deoxidized water and fuel), medium priority (steam, circulating water, and wastewater), and low priority (fresh water, demineralized water, waste gas, and electricity). The identified unit improvement potential revealed overestimation (hydrotreating and delayed coking units) and underestimation (crude distillation units) of conventional methods that overlook three-level coupling.