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

Abstract

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. Here, we evaluate a flexible natural gas power plant concept with the potential for negative emissions that integrates calcium looping, membrane and cryogenic CO2 separation, and DAC. Process optimization is performed to determine the design and scheduling of the process for different scenarios of carbon prices, fuel prices and electricity prices. 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. In this case, 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. Finally, we quantify the value of the proposed technology for power system decarbonization by analyzing its impact on the cost-optimal investment and operation of a stylized power system under different carbon prices. Results indicate that the inclusion of the proposed system at a carbon price of $150/tonne reduces system costs by 54% and CO2 emissions from 0.065 to −0.679 tonne CO2/MW h.