Theoretical and experimental investigations into chemical kinetics models for supercritical CO2 oxidation

Lead Research Organisation: University of Sheffield
Department Name: Mechanical Engineering

Abstract

High-pressure combustion is a possible route to clean power generation. Combustion under high pressure (>7.3773 MPa), oxygen-rich conditions would produce a mixture of supercritical carbon dioxide (sCO2) and water vapour. Separation of sCO2 would be facile via condensation of water vapour, giving high purity sCO2 which could easily be transported for storage or repurposing. A further advantage of high-pressure combustion is the requirement for a smaller reaction chamber to give the same energy output as a reactor undergoing combustion at a lower pressure. This would lead to a smaller combustion plant and reduce capital costs.

This project aims to theoretically and experimentally study the chemical kinetic mechanism for the production of sCO2 at pressures exceeding 80 bar. A better understanding of the chemical kinetic model of sCO2 production would lead to more detailed and accurate model calculations to be used in the construction of high-pressure power plants by aiding in design optimization. Furthermore, an accurate chemical mechanism is required to ensure control over combustion at pressures exceeding 80 bar. The project will initially involve looking at past research to determine which mechanisms have been previously studied, the accuracy of any rate coefficients determined and if they can be used as a starting point for modelling the high-pressure combustion reaction.

Current combustion schemes have been developed for systems at atmospheric pressure, using experimental data collected at pressures much lower than the critical point for sCO2. The experimental rate coefficients determined from these experiments cannot be accurately extrapolated and used to model combustion at pressures exceeding 80 bar, leading to inaccuracies when applying current models to high-temperature combustion. The inaccuracy arises as these models may have missed reactions which become important at high pressures or just give an incorrect rate coefficient when extrapolated so far from the experimental data.

For this project, the combustion kinetics will be modelled using ANSYS Chemkin. Sensitivity analysis will be applied on ANSYS Chemkin to identify reactions which are important in the combustion mechanism at high pressures. The reactions identified will be studied experimentally using a shock tube. Part of this project also involves assisting in the construction of the shock tube which is set to begin construction in autumn 2020. The shock tube will be used to experimentally determine the rate coefficients of the reactions believed to be important at high pressures. The rate coefficients will then be input into the ANSYS Chemkin model to produce an accurate chemical kinetic model for sCO2 production upon completion of the project.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S022996/1 01/10/2019 31/03/2028
2293668 Studentship EP/S022996/1 01/10/2019 30/09/2023 James Harman-Thomas