(368d) Steady State and Dynamic Modeling of a Flexible Carbon Capture-Equipped Power Plant Integrated with Lime-Based Direct Air Capture.

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. Here, we evaluate the steady state and dynamic operation of a novel low-carbon power plant concept that combines flue gas CO₂ capture with a lime-based DAC process in a way that minimizes impact on power generation equipment flexibility. The process involves three main elements: 1) the power plant flue gas, such as from a combined cycle gas turbine plant, is fed to a calciner, where limestone is thermally decomposed to lime and CO₂. 2) the CO₂ rich gas (>30 vol%) from the calciner goes to an electrically-driven separation system based on well-established membranes and cryogenic distillation units, to recover high purity liquid carbon dioxide (>98 vol%), which can be sent for sequestration. 3) the lime produced from the calciner would be used to capture additional CO₂ from air via passive contacting DAC process that is operated in a batch manner. The coupling between the operation of the CO₂ capture process (calciner + separation system) and the power plant is minimized because the calciner operations are also dependent on additional CO₂ supplied from the feed limestone.

This study will investigate two main strategies for flexible plant operation. Detailed process simulations will be carried out using Aspen Plus for both steady state and dynamic operations. The steady state model will be performed for different power plant loading levels (i.e., different flue gas flow rates) ranging from 100% power plant loading to power plant shut down conditions (i.e., from maximum flue gas flow rate to no flue gas). These different steady state simulations will be used to quantify the performance of the two CO₂ capture process operating strategies in terms of their impact on process power balance at each flue gas flow rate (which is directly related to operating cost), as well as equipment sizing (which is related to plant capital cost). The dynamic modeling will be used to understand the transient behavior of the various unit operations (e.g., calciner, membrane, liquefaction) in moving from one steady state to another, which will inform the practicality of the above-mentioned flexibility strategies as well as power plant dispatch under time-varying electricity prices. The flexible operation will be achieved by two process operation decisions: A) adjusting limestone inlet flow rate while keeping the captured carbon dioxide flow rate near constant, and B) adjusting the captured carbon dioxide flow rate while keeping the inlet limestone flow rate constant. Findings of this study including process performance (overall efficiency), process economics (cost of different process options), and operational flexibility will be presented.