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In terms of carbon storage and enhanced oil recovery, CFD simulations can be applied at various scales in a way similar to the methodology discussed earlier in this chapter for amine scrubbers. The most interesting scale appears to be (according to the number of articles published) the small scale though, where it is possible to utilize the VOF method to analyze the flow across a small portion of a solid porous medium representing the geometry of the pores. In this direction, He et al. [56] studied the two‐phase flow between supercritical CO₂ and water in the walls of a saline aquifer. The porous rock was assumed to be formed by detached spheres in a body‐centered cubic (BCC) arrangement. Their simulation setup allowed visualization of the displacement process (the porous medium was initially filled with water). The effect of wettability (i.e. contact angle), surface tension, and viscosity ratio was also assessed, obtaining the permeability saturation curves. The latter certainly constitutes essential information in terms of carbon sequestration, but the approximation of considering the porous medium as a network of perfect spheres with an ideal BCC arrangement might lead to undesired errors. Similar examples are the simulations reported by Dezfully et al. [57] and Gharibshahi et al. [58] (Figure 2.4), which also considered spheres but in a random arrangement.

Table 2.3 Summary of published CFD studies concerning oxy‐fuel technologies.

Authors	Aspect studied	Short comment on findings
Gharebaghi et al. [51]	Single‐phase combustion simulation for a test facility	Comparison between turbulence modeling strategies, i.e. large eddy simulation (LES) and Reynolds averaged Navier–Stokes (RANS), and experimental data
Mayr et al. [52]	3‐D steady‐state simulation of a natural gas furnace including radiation models and the eddy dissipation concept (EDC) model. Effect of O2/N2 ratios on furnace efficiency	To increase the O2‐to‐N2 ratio resulted in better furnace efficiency. Good matching between simulated and experimental results
Bhuiyan and Naser [50]	Co‐firing biomass + coal using the Eulerian–Lagrangian approach	The authors included factors describing the irregular shape of the biomass particles. The effect of changing the fuel ratio combustion atmosphere in the performance parameters of the furnace
Carrasco‐Maldonado et al. [53]	Single‐phase approach to simulate the effect of integrating oxy‐fuel technologies in a cement production plant	Validation against experimental data accomplished. The k–ω turbulence model gave way to the best results
Wu et al. [49]	Study of oxy‐fuel combustion in a circulating fluidized bed (CFB). The model uses the Eulerian approach and thus this is a multiphase case that deviates from common oxy‐fuel CFD studies in the literature	Detailed profiles of temperature and hydrodynamic variables are obtained, which match the experimental results. Gas hold‐up is also studied, resulting in identification of gas accumulation spots

Figure 2.4 (a) Details of the volume fraction map describing the liquid flow within the porous medium.

Source: Dezfully et al. [57]. © Trans Tech Publication.

(b) Details of the pore geometry considered.

Source: Gharibshahi et al. [58]. © Elsevier.

The main hurdle to get accurate simulations of CO₂ trapping in porous rocks appears to be the correct representation of the intricate geometry of the pore. To overcome this, a recent trend in the simulation of the flow through porous media microchannel networks consists in applying imaging techniques, which are subsequently exported into computer‐aided design (CAD) files and spatially discretized. This approach has been applied in other fields where CFD simulations are of great help to gain insight into the flow within such geometries. For instance, Sznitman et al. point out the possibility of using micro‐computed tomography (μCT) or scanning transmission X‐ray microscopy (STXM) to reproduce the alveoli network within the lungs. Other examples are the use that Owens et al. [23] did of X‐ray computed tomography (CT) to obtain a geometric representation of a structured packing, or the work of Isoz and Haidl [21] also applied to structured packing columns. The use of such imaging techniques to be coupled with VOF‐CFD simulations remains rather unexplored and will surely constitute an important research avenue in the future.