Yafei Guo,Chang Tan,Peng Wang,Jian Sun,Junjie Yan,Weiling Li,Chuanwen Zhao,Ping Lu
Coal and biomass fly ash was impregnated with tetraethylenepentamine (TEPA) to prepare solid CO 2 sorbent. Experimental CO 2 adsorption capacities of the sorbent in fixed-bed column were fitted to several kinetic equations. The modified Avrami fractional kinetic model could accurately predict the CO 2 adsorption kinetic behaviors of the sorbent under different conditions. CO 2 adsorption rate increases with the increase in temperature, initial CO 2 concentration and gas flow rate, as a result of the decreased CO 2 diffusion resistance. A mathematical model was proposed and demonstrated to well predict the CO 2 adsorption breakthrough curves in the fixed-bed column. Effects of temperature, initial CO 2 concentration and gas flow rate on the mass transfer kinetic behaviors of the desired sorbent were investigated. The positive effect of these factors on promoting the overall mass transfer coefficient and the internal mass transfer coefficient is not significant. The external mass transfer coefficient will be remarkably reinforced with the increase in these operating parameters, due to the change in viscosity and density of the gas phase and the reduced external mass transfer resistance. Internal mass transfer process is determined as the rate-limiting step for CO 2 adsorption. The results will lay the groundwork for future scale-up application of the sorbent in post-combustion CO 2 capture.
An experimental study of single carbon dioxide (CO 2 ) bubbles ascending in aqueous solutions of carboxymethyl cellulose (CMC) is performed as a means to obtain further understanding of the rising behavior and mass transfer of soluble bubbles in shear-thinning non-Newtonian fluids. High-speed photography and digital image processing technique are employed to quantify the characteristic parameters of the bubble rising process. The rising behavior of single CO 2 bubbles in a Newtonian fluid (tap water) is measured as a reference. It has been found that the rheology of the liquid phase significantly influenced the rising behavior of the bubbles. In CMC aqueous solutions, CO 2 bubbles mostly followed a straight rising path characterized by increasing aspect ratio and decreasing vertical velocity. Increase in initial bubble size led to bubble deformation in less concentrated CMC aqueous solutions which resulted in an irregular rising path. The evolution of bubble equivalent diameter can be mainly divided into two stages: a fast reduction stage followed by a slow one. Meanwhile, the variation of liquid-side mass transfer coefficient k L of CO 2 bubbles in tap water and CMC aqueous solution with different weight percentages is discussed. The mobility of gas-liquid interface is considered to have significant impact on gas-liquid mass transfer. A dimensionless correlation considering the rheology of the liquid phase is proposed to describe the evolution of the motion and deformation of single soluble CO 2 bubbles in infinite stagnant shear-thinning non-Newtonian liquids.
Guanyi Lin,Shan Jiang,Chunying Zhu,Taotao Fu,Youguang Ma
The mass-transfer process of CO2 absorption into aqueous solution of N-methyldiethanolamine (MDEA) + diethanolamine (DEA) in a T-shaped microchannel was studied using a high-speed camera. The effects of two-phase flow rates and diethanolamine concentration on CO2 absorption efficiency, liquid mass-transfer coefficient kL, specific surface area a, and volumetric mass-transfer coefficient kLa were investigated under slug flow. Results showed that the CO2 absorption efficiency increased with the increase of DEA concentration and liquid flow rate, and decreased with increasing gas flow rate. The kL increased with the increase of liquid flow rate and DEA concentration, while it was insensitive to gas flow rate. For a given liquid flow rate, both kLa and a increased rapidly with gas flow rate and then the trend was slowing down. The increase of liquid flow rate and DEA concentration led to the decrease of the a, whereas the kLa was improved. The enhancement of the liquid flow rate on kL and kLa was more obvious under low DEA concentration. An empirical correlation for predicting the volumetric mass-transfer coefficients kLa was proposed by taking the Hatta number Ha into account for characterizing the effect of chemical reaction.
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