A Vortex Contactor for Carbon Dioxide Separations

Introduction Many analysts 1,2,3 identify carbon dioxide (CO 2) capture and separation as a major roadblock in efforts to cost effectively mitigate greenhouse gas emissions via sequestration. An assessment 4 conducted by the International Energy Agency (IEA) Greenhouse Gas Research and Development Programme cited separation costs from $35 to $264 per tonne of CO 2 avoided for a conventional coal fired power plant utilizing existing capture technologies. Because these costs equate to a greater than 40% increase in current power generation rates, it appears obvious that a significant improvement in CO 2 separation technology is required if a negative impact on the world economy is to be avoided. The improvement of current separation technologies is one possible solution to this dilemma. According to the IEA study, chemical or physical absorption technologies possess the highest near term potential for the low-cost and effective separation of dilute CO 2 from mixed gases. In practice, this technology utilizes a basic two step process design; first, multi-tray gas-liquid scrubbers affect CO 2 removal via absorption to a liquid phase or solvent; and second, liquid absorbent is regenerated by heating, pressure reduction or both. Capture efficiency is predicated largely on liquid circulation rate and gas residence time. 5 Under the best of conditions, conventional towers operate at 80% of the equilibrium absorbent loading capacity. This means that at least 20% of the absorbent is needlessly regenerated at a significant cost. (Nearly 90% of the process energy requirement is associated with solvent regeneration.) Additionally, conventional towers cannot be operated below 60% of their design capacity. This limits their utility for power generation applications in which peak and minimum demands may exceed this operating range. In the context of dilute CO 2 removal from large volume gas flows (> 100 million standard cubic feet per day (MMscfd)), it is also apparent that very large conventional scrubbers and regenerators will be required. Consequently, anticipated capital and operating expenses will be high and new technologies that decrease the size of these units, increase their operational flexibility, and improve their capture efficiency will be preferred. Given the proposed scale for CO 2 capture to mitigate global warming, a high efficiency, compact, and operationally flexible absorber is required. Namely, improved contactor designs to process high volume flue gas would eliminate the need for physically large scrubbers that require high liquid absorbent throughputs, incur high operating costs to regenerate absorbent, and have …