Life cycle assessment applied to process design: Environmental and economic analysis and optimization of a nitric acid plant

Life Cycle Assessment (LCA) is an environmental auditing tool that quantifies the environmental burdens of an activity inclusive of all its related systems. In the past, LCA has been applied primarily to products, but recent literature suggests it also has potential as an analysis and design tool for processes and services. This potential arises from the unique ability of LCA to link the environmental burdens of a process with its mass and energy flows. The aim of this work is to apply LCA as a tool for process design rather than one for product assessment. A nitric acid plant formed the basis for a case study wherein LCA was used to quantify and compare environmental performance of a number of design alternatives aimed at waste reduction. Economic models for the alternatives were formulated and linked to the environmental models to perform a multiobjective optimization with the express aim to maximize economic returns and minimize environmental impact. The comparative study showed that one design alternative teas clearly superior from an environmental point of view. The optimization demonstrated that operational changes could result in significant environmental improvement at minimal economic cost. Future work in this area should focus on the allocation of environmental burdens from multiple-output processes as well as extending the analysis to include environmental and economic impacts of all related downstream processes.