Economically optimal CO₂ utilization via flexible chemical production facilities

Utilizing carbon dioxide (CO _2 ) to produce methanol, by combining it with hydrogen sourced from renewable-powered electrolysis, or urea, by combining it with ammonia made from this electrolytic hydrogen, provides an opportunity to monetize CO _2 captured from industrial sources. Methanol is predominantly used as a platform chemical for polymer production with emerging uses as marine fuel or as aviation fuel feedstock, while urea is the most widely used nitrogen fertilizer in the world. In this work, we optimize the levelized cost of producing methanol and urea using only variable renewable energy and CO _2 . Our analysis incorporates recent research and development advances in improving the flexibility of methanol and ammonia synthesis processes, making them more amenable to use with variable renewables. We develop an optimal combined design and scheduling model for CO _2 utilization facilities to maximize the benefit of these flexible technologies toward minimum levelized cost. We perform a case study in Minnesota in which we consider the utilization of CO _2 from bioethanol production, iron and steel production, and waste-to-energy facilities. We find that optimal deployment of flexible methanol or ammonia synthesis reduces levelized costs by at least 25% compared to the traditional approach of operating close to steady state. This cost reduction is achieved by shifting the burden of modulating renewable energy variability from hydrogen to the liquid effluents of these synthesis processes. Depending on location and production scale, we determine that methanol production costs are between $494 mt ^−1 and $830 mt ^−1 while urea production costs are between $386 mt ^−1 and $641 mt ^−1 . Urea via CO _2 utilization is more competitive with the conventional market for urea in Minnesota, while methanol production requires less renewable generation and electrolysis capacity to utilize a given amount of CO _2 . The future market for methanol may also be an order of magnitude larger than that for urea.