Circulating-Fluidized-Bed-Based Calcium-Looping Gasifier: Experimental Studies on the Calcination-Carbonation Cycle

The interest in hydrogen energy is rising. Biomass could be its potential resource. Steam gasification of biomass in the presence of the sorbent calcium oxide (CaO) can produce a gas rich in hydrogen along with in situ capture of the carbon dioxide (CO2) produced. Calcium-looping gasification (CLG) produces a gas rich in hydrogen and at the same time captures CO2 during the process while also regenerating sorbent producing pure CO2. However, deposition of char and tar, sintering because of high-temperature operation, and cyclic heating and cooling in the looping system can drastically reduce the ability of sorbent to capture CO2 and at the same time for its regeneration. Therefore, this paper presents the study conducted to examine the performance of the sorbent as it goes through a number of alternating calcination-carbonation cycles. This research is carried out using two rigs. With the first one, kinetic rates are developed for calcination in the presence of three media: nitrogen (N-2), CO2, and steam (H2O). With the second one, the effects of the particle size, medium, and temperature on the calcination and carbonation reactions are studied. An empirical relationship, in order to predict the loss during carbonation as the sorbent goes through successive calcination-carbonation cycles, is developed and presented here. With the calcium-looping system at the laboratory scale, (a) assessment of the fluid dynamics of the process, distribution of the pressure, and particles lost by attrition and (b) a study of the calcination-carbonation cycle are made and presented in this paper.