Investigating the energy-water-carbon nexus of mega-scale chemicals production from Appalachian shale gas

This paper is concerned with techno-environmental modeling of large-scale chemicals production from Appalachian shale gas and investigates its environmental impacts. We first develop shale gas supply and plant design models to estimate pipeline distances, numbers of wells, well-sites, gathering systems needed in the near/mid-term, as well as the plant-level energy and materials balances. Next, we conduct a life cycle analysis (LCA) to evaluate the energy-water-carbon nexus in terms of energy consumption (η_le), freshwater footprint (η_lw), and greenhouse gas emissions (η_ghg). The results show, based on a mass-based allocation approach, the η_le, η_lw, and η_ghg are 13.8–17.2 GJ/t olefins, 3.31–4.28 kg/kg olefins, and 0.83–1.17 kg CO₂-eq/kg olefins, respectively. However, if we use an economic value based allocation method, these values are updated to 37.4–28.7 GJ/t olefins, 7.28–9.42 kg/kg olefins, and 1.80–2.49 kg CO₂-eq/kg olefins, respectively. The values of η_ghg indicate that shale gas can be categorized as a lowcarbon feedstock based on a mass-based allocation approach, or high-carbon feedstock based on an economic value-based allocation approach.