(545y) Modeling a Water Wash Sieve Tray for Aerosols Scavenging Using Computational Fluid Dynamics

　The chemical absorption method of post-combustion CO2 capture is widely used in the capture of carbon dioxide processes, which is flue gas post-process. Flue gas composition is complex and has fine size condensation nucleus. After the chemical absorption process, part of the solvent will be adsorbed on the nucleus surface to form aerosols and emission into the atmosphere with the flue gas. Because the size of the aerosol is extremely fine, it does not only cause environmental pollution but if inadvertently inhaled, it will harm the human body. Therefore, as CO2 capture technology matures, aerosol becomes a challenge for the next generation.

　The sieve plate is widely used in gas-liquid contact, because of its simple structure, low price, and low power loss. We expect to solve the problem of aerosol emission with the most basic sieve washing towers, so we build a water wash sieve tray to simulate the removal behavior of aerosols. Therefore, the purpose of this study is to use CFD (Computational Fluid Dynamics) model to establish a sieve-plate tray to observe the aerosol movement behavior and removal efficiency in the tower.

　In this study, a two-dimensional sieve plate model was constructed and Euler-Lagrangian framework was used to model the hydrodynamics between water, air, and water-aerosol. The geometry includes inlet and outlet and downcomers. The momentum balanced equation uses the standard k-ε turbulence model. The drag coefficient between the liquid phase and the gas phase uses the relation equation by Krishna et al. [2], which is widely used to simulate the froth regime in sieve plates. The liquid holdup uses the empirical equations proposed by Bennett et al. [3], and the drag coefficient between the liquid phase and the water-aerosol phase uses Brucato. The boundary conditions of the aerosol phase are set to reflect when hitting the wall surface and can be escaped from the gas and the liquid outlet. The model also considers the gravity, pressure gradient force, and Brownian motion of the aerosols, and uses particle tracking to observe the flow direction. It can be used to compare the impact on the scavenging efficiency of aerosol size, aerosol concentration, and gas-liquid ratio.

　The results show that the scavenging efficiency of aerosols on the sieve tray is not significant. Only a small part of the aerosol will be carried to the liquid outlet through the drag force of water, but the most of them will be driven to the gas outlet by high-speed airflow. The aerosol particles can easily break through the discontinuous liquid film and spill into the atmosphere.

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