CO2 Separation Using Regenerable Magnesium Solutions Dissolution, Kinectics and VLSE Studies
Fossil fuel power plants are responsible for a considerable amount of total anthropogenic CO2 emissions throughout the world. CO2 capture and sequestration from point source emitters like fossil fuel power plants is essential to mitigate the harmful effects of greenhouse gases. A novel post-combustion CO2 capture technique has been proposed, where CO2 from flue gases can be absorbed by magnesium hydroxide (Mg(OH)2) slurry at 52 °C in a column followed by a regeneration step in a stripper. CO2 absorption in a Mg(OH)2 slurry solution involves physical absorption of CO2 gas into the aqueous phase and subsequent chemical reactions in the aqueous and solid phases. Three critical phenomena influencing the CO2 absorption process, namely: the dissolution of Mg(OH)2 for continuous CO2 absorption, formation of an unwanted by-product magnesium carbonate (MgCO3), and vapor-liquid-solid equilibrium (VLSE) of the system were studied. The dissolution of Mg(OH)2 and the release of magnesium ions into the solution to maintain a level of alkalinity is a crucial step in the CO2 absorption process. The dissolution process was modeled using the shrinking core model and surface chemical reaction was found to be the rate controlling mechanism. The formation of MgCO3 will reduce a regenerative capacity of Mg(OH)2 solvent. The impact of pH control and temperature on the kinetics of magnesium carbonate formation was also studied. The vapor-liquid equilibrium data for a solvent-CO2 system is essential for the design and operating conditions of an absorber and a desorber. It can be used to determine an amount of Mg(OH)2 feed for CO2 absorption and also to determine the operating conditions for CO2 separation and Mg(OH)2 regeneration from a CO2 desorber. These three individual studies will provide a fundamental understanding of CO2 absorption in a Mg(OH)2 slurry solution and basic engineering data for the design and operation of a Mg(OH)2-based CO2 absorption system.
Chemical Engineering, Dissolution, Magnesium hydroxide, CO2 capture, Shrinking-core-model, Coal-fired power plants, VLSE
Networked Digital Library of Theses and Dissertations