A two-level model to assess the economic feasibility of renewable urea production from agricultural waste

This work proposes a two-level model, combining process and supply chain models, and an optimization framework for an integrated biorefinery system to convert agricultural residues into renewable urea via gasification routes. The process model of the gasification, ammonia and urea synthesis was developed in Aspen Plus� to identify key performance indicators such as energy consumption and relative yields for urea for different biomasses and operating conditions; then, these key process data were used in a mixed-integer linear programming (MILP) model, designed to identify the optimal combination of energy source, technological route of urea production and plant location that maximizes the net present value of the system. The model was applied to the whole Brazilian territory, divided into 5569 cities and 558 micro-regions. Each region�s agricultural production was evaluated to estimate biomass supply and urea demand. The Assis microregion, in close proximity with sugarcane and soybean crops, was found to be an optimal location for the plant, with an NPV of 110 MMUSD. Urea demand was found to be the main limiting factor, with more than 30 microregions needed to consume the plant�s production. The results indicate the feasibility of producing renewable urea from agricultural waste and the importance of considering a two-level approach to assess the economic performance of the entire system.