Clean Combustion Flue Gas Polishing Through Catalytic Combustion in an Integrated Heat Exchanger Reactor System

Abstract

Combustion flue gas from various sources contains contaminants requiring removal prior to pipeline transport for carbon, capture, utilization and storage. Depending on the combustion method, the main contaminants are often residual fuel such as CH₄, partial combustion product CO, and oxidizer such as O₂. Process intensified heat exchange reactors known as integrated heat exchange reactors (IHXR) can be designed to facilitate contaminant removal while recovering the heat of combustion generated during the removal process. This work describes the formulation and use of a 1-dimensional reduced order reactor model in facilitating the IHXR design for oxy-fuel combustion flue gas where the contaminant of concern is O₂.

The heat exchanger sections of the IHXR can be described by a 2-dimensional reduced order heat exchanger model (2-D ROM), accounting for the cross-flow pattern of the proposed design. A micro-channel cross-flow heat exchanger plate was manufactured as part of a bench-scale experimental set-up, the gas and solid phase temperatures of the experimental set-up were collected and used as the basis for a Nusselt number correlation. The 2-D ROM fitted with the Nusselt number correlation was then used to aid in generating a 3-D OpenFOAM model, in which the heat fluxes between the curved flow channels were calculated to confirm the that the conduction shape factor was near (0.8 to 0.9) unity.

The bench-scale heat transfer experiments were also used to validate the transient modelling capabilities of the 2-D ROM, which was then used along with a reduced order reactor model to create process models of several proposed IHXR designs. The process models were then used to investigate the ability of the IHXR to reject inlet temperature disturbances through Bode diagrams. The results show that the IHXR designs are generally stable, with their stability increasing as the number of flow channels increases.

Another source of combustion flue gases, pressurized chemical looping combustion (PCLC), was used for IHXR design via process simulation. The contaminants of concern are CH₄ and CO, where the IHXR design features the equilibrium reactor from Aspen HYSYS to determine the effluent species concentration, and plug flow reactor for reactor sizing. A sensitivity analysis was performed on the potential scenario where fuel conversion within the PCLC unit was reduced to 97% from 98.5% to simulate variable combustion efficiency.