(17c) Techno-Economic Analysis of a Combined Power Plant CO2 Capture and Direct Air Capture Concept for Flexible Power Plant Operation

Carbon capture and storage (CCS) equipped power plants can reduce the cost of decarbonizing power systems. However, deeply decarbonized power systems also will see significant penetration of variable renewable energy resources that will necessitate flexible operation of other balancing resources in the system such as energy storage and low-carbon dispatchable power plants, including those relying on CCS. Here, we investigate a new concept for power plant flue gas capture integrated with a novel lime-based direct air capture technology in a way that allows for flexible operation of the power plant while having the potential for negative emissions under all operational scenarios. A process simulation and an accompanying techno-economic model is developed to evaluate the capital and operating expenditures and to investigate the economic viability of such concept under different electricity price scenarios.

The proposed concept is composed of three main technologies: calcium looping, membrane + cryogenic separation, and lime-based direct air capture. The system is designed to treat flue gas from a conventional natural gas combined cycle (NGCC) power plant. The flue gas from the NGCC power plant is fed to the calcium looping system which is composed of two reactors: a calciner and a carbonator. Calcium carbonate (CaCO₃) is fed to the calciner where it breaks down into lime (CaO) and carbon dioxide (CO₂) at a high temperature. Part of the lime goes to a novel direct air capture (DAC) process that operates in a batch mode to capture additional CO₂ from the air in the form of solid CaCO₃ that can be sequestrated or recycled to the calciner. The rest of the lime goes to the carbonator where it captures CO₂ from the power plant flue gas in the form of solid CaCO₃ that is recycled to the calciner. The CO₂-rich gas from the calciner goes to a separation system based on commercially available membrane and cryogenic purification technologies to recover high purity CO₂. It is important to note that the DAC process will continue working even when the power plant is not operating. Steady state simulation model for the process is developed in Aspen Plus to investigate the implications of the system under various operational scenarios. Sensitivity analysis is carried out on key process variables to understand the trade-offs associated with the proposed system through detailed process modeling. Results on the process simulation are presented at three different power plant loading levels: 100% (full loading), 40% (part loading), and 0% (shut down). The results show that the system can achieve negative emissions at all power plant loading levels. The results show that the system is net power exporter at full and part loading operational scenarios while being net importer when the power plant is turned off. The developed economic model is used to estimate the levelized cost of electricity (LCOE) under different future scenarios of electricity price, carbon price and natural gas prices.