(168b) Modeling of Simultaneous Absorption of CO2 and NH3 in a Type I Turbulent Contact Absorber

A turbulent contact absorber (TCA), also named turbulent bed contactor or mobile bed contactor, is a countercurrent gas–liquid–solid fluidized bed in which liquid flows down through a turbulent bed of inert and spherical particles supported by continuous gas phase. TCA with low pressure drop and high contact efficiency has the advantages of enhanced heat and mass transfer rate, non-choking and self-cleaning owing to the tumbling motion of the packing. This makes the TCA more suitable over packed or tray columns for many physical, chemical and biochemical processes especially for CO₂ capture form coal-fired flue gas. However, the difference of the countercurrent gas–liquid contact structure operating at different flow regimes of a TCA significantly affects the interfacial area and mass transfer coefficients calculation. An accurate prediction of the mass transfer coefficients is very important for the design and optimization of TCA.

• This article presents the modeling and experimental investigation of the simultaneous absorption of CO₂ and NH₃ into water in a TCA.
• A theoretical model is developed to describe the gas-liquid countercurrent flow characteristic and interfacial area for the prediction of the mass transfer coefficients K_Ga in a type I TCA with fully fluidization operation.
• The dispersed liquid flows in the TCA are assumed to be comprised of film flows adhere to the packing hollow balls and droplets flows in the void of the fluidization bed.The overall gas-side mass transfer area consists of the mass transfer coefficient of the packing and mass transfer coefficient of the droplets.
• The thickness of the film to determine the liquid holdup adhere to the packing balls is modeled as applying the shear stress boundary condition at the liquid-gas interface and the non-slip boundary condition at the sphere surface.
• The saunter mean diameter of droplets is obtained as based on the balance relationship between total surface free energy of liquid droplets and turbulent kinetic energy of gas flow based on the locally isotropic turbulence of Kolmogorov.
• The concentration profile equations and mass transfer coefficients of CO₂ absorption in the droplet and in the film of the TCA are analyzed respectivelly.
• Model reliability is verified by comparing the model results with the experimental investigation of simultaneous absorption of NH₃ and CO₂ into water in a fully fluidized TCA under the superficial liquid velocity of 0.001~0.005m/s and superficial gas velocity of 1.24~2.07m/s with different packing diameters of 0.01~0.025m and static packing heights of 0.1~0.25m. The theoretical overall volumetric mass transfer coefficients are calculated to be 5×10^-5~8×10^-5mols^-1m^-3Pa^-1 including the gas-liquid mass transfer across the droplets and liquid film adhere to the packing balls.The model prediction compared reasonably to the experimental results with the maximum deviation of approximately 27%.