Abstract
This study utilizes life cycle analysis to compare three steel manufacturing off-gas utilization systems: a status quo system, which produces electricity via a low-pressure steam turbine; a combined cycle power plant system, which produces electricity using gas and steam turbines; and a methanol production system, which converts coke oven gas and blast furnace gas into methanol. This research seeks to compare the environmental impacts of each system based on equivalent raw material inputs. Since the systems have different products, system expansion is used to ensure that they have the same outputs/functional units and are therefore comparable. The system boundary consists of a combination of cradle-to-gate and gate-to-gate boundaries. The environmental effects of each system are compared at five locations—Ontario, the USA, Finland, Mexico, and China—using TRACI, CML-IA baseline, ReCiPe2016, and IMPACT2002+ in SimaPro v9. The results show that due to different electricity carbon intensities, different natural gas supply chains, and different methanol supply chains, the Ontario, Finland, and China case studies had the lowest environmental impact when the steel refinery is retrofitted to include a methanol production system, while the USA and Mexico case studies had the lowest impact when retrofitting a combined cycle power plant system. The status quo system had the greatest environmental impact for all of the studied locations, except for the USA. This environmental assessment, combined with previous economic analysis, demonstrates that the methanol production system is the optimal choice in Ontario and China. In the USA, plants might be better off adopting combined cycle power plant systems when carbon taxes reach $50/tonne. For Mexico, the combined cycle power plant system is the most environmentally friendly choice, while the methanol production system is the most profitable. Finally, the results indicate that status quo systems are not recommended in Mexico or China in any foreseeable circumstance.
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