RESUMEN
Both the global steel and chemical industries contribute largely to industrial greenhouse gas (GHG) emissions. For both industries, GHG emissions are strongly related to the consumption of fossil resources. While the chemical industry often releases GHGs as direct process emissions, steel mills globally produce 1.78 Gt of off-gases each year, which are currently combusted for subsequent heat and electricity generation. However, these steel mill off-gases consist of high value compounds, which also can be utilized as feedstock for chemical production and thereby reduce fossil resource consumption and thus GHG emissions. In the present work, we determine climate-optimal utilization pathways for steel mill off-gases. We combine a nonlinear, disjunctive model of the steel mill off-gas separation system with a large-scale linear model of the chemical industry to perform environmental optimization. The results show that the climate-optimal utilization of steel mill off-gases depends on electricity's carbon footprint: For the current electricity grid mix, methane, hydrogen, and synthesis gas are recovered as feedstocks for conventional chemical production and enable a methanol-based chemical industry. For low electricity footprints in the future, the separation of steel mill off-gases supports CO2-based production processes in the chemical industry, supplying up to 30% of the required CO2. By coupling the global steel and chemical industry, industrial GHG emissions can be reduced by up to 79 Mt CO2-equivalents per year. These reductions provide up to 4.5% additional GHG savings compared to a stand-alone optimization of the two industries, showing a limited potential for this industrial symbiosis.
RESUMEN
Mitigating life-cycle greenhouse gas emissions of plastics is perceived as energy intensive and costly. We developed a bottom-up model that represents the life cycle of 90% of global plastics to examine pathways to net-zero emission plastics. Our results show that net-zero emission plastics can be achieved by combining biomass and carbon dioxide (CO2) utilization with an effective recycling rate of 70% while saving 34 to 53% of energy. Operational costs for net-zero emission plastics are in the same range as those for linear fossil-based production with carbon capture and storage and could even be substantially reduced. Realizing the full cost-saving potential of 288 billion US dollars requires low-cost supply of biomass and CO2, high-cost supply of oil, and incentivizing large-scale recycling and lowering investment barriers for all technologies that use renewable carbon feedstock.