Optimization of a combined power plant CO2 capture and direct air capture concept for flexible power plant operation

Abstract

The cost-effective integration of variable renewable energy (VRE) generation is critical for power sector decarbonization but is contingent on designing power systems to be more flexible. Deployment of carbon capture and storage (CCS) equipped fossil fuel power plants on the supply-side and direct air capture (DAC) technologies on the demand side can address the dual challenge of lower carbon emissions while providing grid flexibility. Historically, these two technologies have been contemplated for independent deployment where challenges related to high capital cost and flexible operation remain barriers. In this work, we consider the design and operations optimization of a flexible natural gas power plant concept with the potential for negative emissions that integrates three technologies: calcium looping, membrane and cryogenic CO2 separation, and DAC. Global optimization using surrogate modeling approaches is performed to determine the optimal design and scheduling of the process with respect to different time varying electricity profiles, carbon price scenarios and fuel price scenarios expected in a high VRE penetration electricity grid. In general, we find that positive net present values are achievable for the negative emissions power plant concept while retaining flexibility of the power plant and high capacity utilization of all CO2 capture related units, if the carbon price is at or above $150/tonne. At these carbon price scenarios, which are in the range of available policy credits for DAC in some regions (e.g. U.S.) as of 2021, we also substantiate the synergistic integration of the proposed concept, where: a) the proposed process results in 52% higher NPV vs. a standalone calcium looping + DAC system and b) 7% higher NPV, 3% higher negative emissions and 2% higher net power production vs. a decoupled process where the natural gas power plant flue gas is not used within the calcium looping + DAC system.