Lattice Boltzmann simulation of the gas-solid adsorption process in reconstructed random porous media

The gas-solid adsorption process in reconstructed random porous media is numerically studied with the lattice Boltzmann (LB) method at the pore scale with consideration of interparticle, interfacial, and intraparticle mass transfer performances. Adsorbent structures are reconstructed in two dimensions by employing the quartet structure generation set approach. To implement boundary conditions accurately, all the porous interfacial nodes are recognized and classified into 14 types using a proposed universal program called the boundary recognition and classification program. The multiple-relaxation-time LB model and single-relaxation-time LB model are adopted to simulate flow and mass transport, respectively. The interparticle, interfacial, and intraparticle mass transfer capacities are evaluated with the permeability factor and interparticle transfer coefficient, Langmuir adsorption kinetics, and the solid diffusion model, respectively. Adsorption processes are performed in two groups of adsorbent media with different porosities and particle sizes. External and internal mass transfer resistances govern the adsorption system. A large porosity leads to an early time for adsorption equilibrium because of the controlling factor of external resistance. External and internal resistances are dominant at small and large particle sizes, respectively. Particle size, under which the total resistance is minimum, ranges from 3 to 7 μm with the preset parameters. Pore-scale simulation clearly explains the effect of both external and internal mass transfer resistances. The present paper provides both theoretical and practical guidance for the design and optimization of adsorption systems.

Figure 1

Schematic of the adsorption process in a channel filled with circular adsorbent particles.

Figure 2

Disordered random porous media reconstructed with the QSGS and BRCP (a) the phase image and (b) the boundary recognition. The domains are 1008 × 520 lattice units in size.

Figure 3

Illustration of the 14 types of boundary nodes, namely, four flat wall nodes (B1)–(B4), four convex corner nodes (B5)–(B8), four concave corner nodes (B9)–(B12), and two convex-to-convex nodes (B13)–(B14).

Figure 4

Diagram of three porous media with different resolutions by scaling structure $D1$ two and four times.

Figure 5

The permeability-viscosity relation for structures $P1$ and $D1$.

Figure 6

Results of the transient velocity vector profile and adsorbate concentration contour in bulk fluid (left) as well as the resulting adsorbed amount in porous structures (a) $P1$, (b) $P2$, (c) $P3$, and (d) $P4$, at 510 μs (right). The velocity vectors of the four cases have the same reference length and density.

Figure 7

The time history of the averages of the dimensionless adsorbed amount ${\overline{N}}_{\mathrm{tot}\left(t\right)}$ for structures $P1, P2, P3$, and $P4$.

Figure 8

Results of (a) lattice permeability, (b) dimensionless interparticle transfer coefficient, and (c) interfacial average of the dimensionless adsorbed amount ${\overline{N}}_{\mathrm{surf}\left(t\right)}$ for structures $P1, P2, P3$, and $P4$.

Figure 9

Results of the transient velocity vector profile and adsorbate concentration contour in bulk fluid (left) as well as the resulting adsorbed amount in porous structures (a) $D1$, (b) $D2$, (c) $D3$, (d) $D4$, (e) $D5$, (f) $D6$, (g) $D7$, and (h) $D8$ at 510 μs (right). The velocity vectors of the eight cases have the same reference length and density.

Figure 10

Results of the (a) time history of the average of the dimensionless adsorbed amount ${\overline{N}}_{\mathrm{tot}\left(t\right)}$ and (b) the required time to reach 80% of the saturated adsorbed amount for structures $D1, D2, D3, D4, D5, D6, D7$, and $D8$.

Figure 11

Results of the (a) lattice permeability, (b) dimensionless interparticle transfer coefficient, and (c) interfacial average of the dimensionless adsorbed amount ${\overline{N}}_{\mathrm{surf}\left(t\right)}$ for structures $D1, D2, D3, D4, D5, D6, D7$, and $D8$.