CARBON DIOXIDE CAPTURE FROM FLUE GAS USING DRY REGENERABLE SORBENTS

Abstract

The objective of this project is to develop a simple, inexpensive process to separate CO{sub 2} as an essentially pure stream from a fossil fuel combustion system using a regenerable, sodium-based sorbent. The sorbent being used in this project is sodium carbonate which is converted to sodium bicarbonate, ''baking soda,'' through reaction with carbon dioxide and water vapor. Sodium bicarbonate is regenerated to sodium carbonate when heated, producing a nearly pure CO{sub 2} stream after condensation of water vapor. Testing conducted previously confirmed that the reaction rate and achievable CO{sub 2} capacity of sodium carbonate decreased with increasing temperature, and that the global rate of reaction of sodium carbonate to sodium bicarbonate increased with an increase in both CO{sub 2} and H{sub 2}O concentrations. Energy balance calculations indicated that the rate of heat removal from the particle surface may determine the reaction rate for a particular particle system. This quarter, thermogravimetric analyses (TGA) were conducted which indicated that calcination of sodium bicarbonate at temperatures as high as 200 C did not cause a significant decrease in activity in subsequent carbonation testing. When sodium bicarbonate was subjected to a five cycle calcination/carbonation test, activity declined slightly over the first two cycles but was constant thereafter. TGA tests were also conducted with two other potential sorbents. Potassium carbonate was found to be less active than sodium carbonate, at conditions of interest in preliminary TGA tests. Sodium carbonate monohydrate showed negligible activity. Testing was also conducted in a 2-inch internal diameter quartz fluidized-bed reactor system. A five cycle test demonstrated that initial removals of 10 to 15 percent of the carbon dioxide in a simulated flue gas could be achieved. The carbonation reaction proceeded at temperatures as low as 41 C. Future work by TGA and in fixed-bed, fluidized-bed, and transport reactor systems is planned to demonstrate the feasibility of this process in large scale operations to separate carbon dioxide from flue gas.