Keywords: absorption, CO2, FGD, mass transfer coefficients, Mg(OH)2, reaction rate
CO2 absorption study in a bubble column reactor with Mg(OH)2
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 KAG with NaOH solution was found to be 8.88x10-6 cm/s.