May 1-5, 2011
Chemical looping gasification (CLG) of biomass in a circulating fluidized bed is an excellent option for production of separate streams of hydrogen rich and carbon dioxide rich gases. This process uses H2O (steam) instead of air or oxygen for gasification, and thereby produces high value nitrogen free product gas. An important feature of this process is in-process removal of carbon dioxide from the reaction site by CaO. This allows the reaction to move towards higher yield of hydrogen. Circulating fluidized bed (CFB) provides an ideal reactor configuration for such a looping reaction. A CFB based CLG unit operates somewhat similar to the FCC reactor except that the bubbling bed in the loopseal serves as the gasifier where calcined limestone absorbs carbon dioxide forming calcium carbonate. The riser works as the regenerator of CaCO3, the CO2 sorbent. Thus, the sorbent particles move back and forth between the riser calciner and loopseal carbonizer. To study this process closely and to determine how well the sorbent retains its reactivity through such a cyclical process, an experiment was carried out in a Quartz wool matrix reactor (QWM), which closely simulates the highly expanded ambience of a fast-fluidized bed. An empirical relation was developed for the conversion of calcium carbonate (CaCO3) as a function of temperature and residence time. A simple reaction kinetic model for calcination in presence of N2, CO2 and H2O has been developed and compared. Loss in effectiveness of the sorbent has been studied and another empirical relation was developed for the estimation of extent of carbonation with the number of cycle.
Prabir Basu, Bishnu Achayra, and Animesh Dutta, "Study of Calcination-Carbonation of Calcium Carbonate in Different Fluidizing Mediums for Chemical Looping Gasification in Circulating Fluidized Beds" in "10th International Conference on Circulating Fluidized Beds and Fluidization Technology - CFB-10", T. Knowlton, PSRI Eds, ECI Symposium Series, (2013). http://dc.engconfintl.org/cfb10/36