The Development of a Chemical Kinetic Mechanism for Combustion in Supercritical Carbon Dioxide

TL;DR

This paper develops and validates a new chemical kinetic mechanism for high-pressure combustion of methane in supercritical CO2, improving modeling accuracy for oxyfuel power cycles with inherent carbon capture.

Contribution

A novel sCO2 chemical kinetic mechanism was created, specifically optimized for high-pressure conditions, outperforming existing mechanisms in modeling ignition delay times.

Findings

The UoS sCO2 mechanism best fits ignition delay data at high pressures.

CH3O2 chemistry is crucial for modeling methane combustion above 200 atm.

The new mechanism shows lower average error than existing models.

Abstract

Direct fired supercritical CO2 (sCO2) power cycles allow for the combustion of gaseous fuels under oxyfuel conditions with inherent carbon capture. As the CO2 is captured intrinsically, the efficiency penalty of capture on the overall plant is small, meaning that power plants achieve a similar efficiency to traditional fossil fuel power plants without carbon capture and storage. However, at high pressures and in large dilutions of CO2, combustion mechanisms are poorly understood. Therefore, in this paper sensitivity and quantitative analysis of four established chemical kinetic mechanisms have been employed to determine the most important reactions and the best performing mechanisms over a range of different conditions. CH3O2 chemistry was identified as a pivotal mechanism component for modelling methane combustion above 200 atm. The University of Sheffield (UoS) sCO2 mechanism created in the present work better models the ignition delay time (IDT) of high-pressure combustion in a large dilution of CO2. Quantitative analysis showed that the UoS sCO2 mechanism was the best fit to the greatest number of IDT datasets and had the lowest average absolute error value, thus indicating a superior performance compared to the four existing chemical kinetic mechanisms, well-validated for lower pressure conditions.