Carbon Capture, Utilization, and Storage (CCUS): Absorption Kinetics, Transport Thermodynamics, and Geological Storage Mechanics

Carbon Capture, Utilization, and Storage (CCUS) infrastructure provides a critical engineered pathway for deep industrial decarbonization, capturing $\text{CO}_2$ emissions from large point sources such as thermal power plants, steel mills, and cement kilns. The CCUS chain encompasses chemical separation, high-pressure pipeline transport thermodynamics, and long-term geological sequestration in deep saline aquifers or depleted hydrocarbon reservoirs.

Post-combustion chemical absorption relies on reversible reactive amine solvents (such as Monoethanolamine [MEA]). The mass transfer flux ($N_{\text{CO}_2}$) of $\text{CO}_2$ into the liquid absorbent interface in a packed column is modeled using two-film theory enhanced by the chemical reaction enhancement factor ($E$):

$$N_{\text{CO}_2} = E \cdot k_L \cdot \left( C_{\text{CO}_2, i} - C_{\text{CO}_2, b} \right)$$

Where $k_L$ is the physical liquid-phase mass transfer coefficient, $C_{\text{CO}_2, i}$ is interfacial $\text{CO}_2$ concentration, and $C_{\text{CO}_2, b}$ is bulk liquid concentration. The enhancement factor $E$ for pseudo-first-order fast chemical reactions is governed by the Hatta Number ($\text{Ha}$):

$$E \approx \text{Ha} = \frac{\sqrt{D_{\text{CO}_2} \cdot k_2 \cdot C_{\text{amine}}}}{k_L}$$

Where $D_{\text{CO}_2}$ is the diffusion coefficient of $\text{CO}_2$ in solution and $k_2$ is the second-order reaction rate constant.

For efficient pipeline transport, $\text{CO}_2$ is compressed into a dense supercritical phase ($P > 7.38\text{ MPa}$, $T > 31.1^\circ\text{C}$). Continuous pressure drop ($\Delta P$) along a transmission pipeline of length $L$ and diameter $D$ is evaluated using the Darcy-Weisbach equation adjusted for density changes ($\rho$):

$$\Delta P = f \cdot \left( \frac{L}{D} \right) \cdot \left( \frac{\rho \cdot v^2}{2} \right)$$

Geological storage trapping integrity within porous formations relies on structural, capillary, and residual trapping mechanics. The maximum capillary entry pressure ($P_c$) of the impermeable caprock seal that prevents upward $\text{CO}_2$ plume leakage is expressed as:

$$P_c = \frac{2 \cdot \gamma \cdot \cos\theta}{r_{\text{pore}}} \ge (\rho_{\text{brine}} - \rho_{\text{CO}_2}) \cdot g \cdot h_{\text{plume}}$$

Where $\gamma$ is interfacial tension between brine and supercritical $\text{CO}_2$, $\theta$ is contact angle, $r_{\text{pore}}$ is maximum caprock pore throat radius, and $h_{\text{plume}}$ is vertical $\text{CO}_2$ plume height.

Historically, industrial carbon emissions across major manufacturing hubs in India were vented directly into the atmosphere due to high capital costs of gas separation and the absence of dedicated point-to-sink transmission infrastructure.

Under modern climate goals targeting Net-Zero transitions, Indian engineering entities and energy corporations are actively developing regional CCUS Hubs and Infrastructure Clusters. Current engineering initiatives focus on integrating solid-sorbent Direct Air Capture (DAC) systems and energy-efficient membrane separation units with heavy industrial plants. Captured $\text{CO}_2$ is increasingly utilized in Mineral Carbonation processes—converting industrial slag and fly ash into carbon-negative building materials—and injected into depleted onshore oilfields for Enhanced Oil Recovery (EOR). Furthermore, civil engineers are conducting hydrogeological risk assessments to construct multi-modal pipeline networks and secure long-term offshore deep saline aquifer storage options along India's continental shelf.

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