Graphite bricks in AGRs have a complex pore structure that can determine how gases such as methane and CO interact with the graphite in controlling oxidation reactions. These gases are transported by advection and diffusion in the bulk CO2 gas.
Plymouth University have used their PoreXpert software to analyse porosimetry data for small (cm scale) graphite samples. This creates possible structures of pores and throats which connect them. QPAC was used to import these structures, typically on a 15x15x15 grid, and undertake flow and transport simulations. This allowed new insights to be developed regarding the controlling mechanisms, with the potential for improvements to models of graphite evolution at the brick scale.
The movie shows an example tracer transport calculation. Initially the system has a unit concentration of a tracer gas in the bulk CO2 which flow through the system. The concentration reduces by advection and diffusion. Some pores quickly lose material while others retain it for a long time. This arises because the gas flow is predominantly in a small fraction of the pores that are well connected; the other pores only connect to these through diffusive pathways. The pores and throat are hidden in the movie once their concentration falls below 10% of the initial value – enabling the progress of the transport processes to be seen more clearly.