Title: CO₂ absorption study in a bubble column reactor with Mg(OH)₂

Authors: Kyung Sook Jung, Tim C. Keener, Vicki C. Green, Soon-Jai Khang

Addresses: Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH, USA. ' Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH, USA. ' Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH, USA. ' Department of Chemical Engineering, University of Cincinnati, Cincinnati, OH, USA

Abstract: CO₂ from the combustion of fossil fuels is the largest source of greenhouse gas emissions in the USA. Recently, there has been a growing interest in economical processes for the separation and sequestration of CO₂ emissions from flue gas. The goal of this study was to study the absorption characteristics of CO₂ from a simulated flue gas using reclaimed Mg(OH)₂ slurries. Mg(OH)₂ has been selected as the scrubbing agent because of a number of beneficial technical and economic factors. Magnesium hydroxide slurries provide for high CO₂ uptake capabilities, and as a by-product of magnesium-enhanced FGD systems, the material will be readily available, and its production will not result in the release of additional CO₂ emissions to the atmosphere. The experimental results included a detailed analysis of the absorption chemistry in a bubble column reactor. A number of experiments were conducted to determine the activation energy and order of reaction for this gas-liquid reaction. It was found that the reaction rate between magnesium hydroxide and CO₂ follows a first-order reaction, and the activation energy was calculated to be 7700 cal/mol. In addition, a study was undertaken to determine the mass transfer characteristics of the bubble column reactor. A model describing CO₂ absorption into clear solutions from a bubble was developed assuming a known bubble size, solution equilibrium chemistry and overall mass transfer coefficients from the gas phase to the liquid. The overall mass transfer coefficients were found to vary from 6.05x10^-6~6.63x10^-7 cm/s for the temperature range of 22°C~60°C. Absorption experiments were also conducted with sodium hydroxide solutions and the value of K_AG with NaOH solution was found to be 8.88x10^-6 cm/s.

Keywords: absorption; CO₂; FGD; mass transfer coefficients; Mg(OH)₂; reaction rate.

DOI: 10.1504/IJETM.2004.004625

International Journal of Environmental Technology and Management, 2004 Vol.4 No.1/2, pp.116 - 136

Published online: 26 May 2004 *

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