Environmental benefits of urea production from basic oxygen furnace gas

Abstract

Basic oxygen furnace gas (BOFG) is a multi-component residual flow from integrated steel mills composed of CO, CO2, O2, N2 and H2. In this study, we use the life cycle assessment method to quantify the environmental impacts of six applications of BOFG: heat for internal use in the steel mill, heat combined with CO2 storage, electricity production, urea production, urea production combined with CO2 storage and flaring. Urea can be produced from solely BOFG components, making use of the sorption enhanced water–gas shift technology. This application of BOFG is described here for the first time. The environmental impacts of these six applications were compared in light of the impacts of their conventional production (‘counterfactual’). Using BOFG for the production of electricity and urea would result in net greenhouse gas emissions of 0.87 tCO2-eq/tBOFG and 0.69 tCO2-eq/tBOFG, respectively. When excess CO2 is transported and stored, net emission savings could be achieved when producing urea (−0.11 tCO2-eq/tBOFG) and heat (−0.12 tCO2-eq/tBOFG) from BOFG, again as compared to their counterfactual of conventional production. Overall environmental impacts were slightly lower for electricity (5.2E−4 DALY/tBOFG, 1.9E−6 species.yr/tBOFG) compared to urea (6.2E−4 DALY/tBOFG, 1.9E−6 species.yr/tBOFG). Sensitivity analysis showed, however, that when replacing cleaner electricity (e.g. under future power decarbonisation), these relative environmental benefits of electricity production from BOFG are diminished. We conclude that urea production, rather than the current practice of electricity production, is the best investigated option to reduce environmental impacts of BOFG, which can lead to net environmental benefits when combined with CO2 storage.