Effect of alkali and alkaline earth metals on agglomeration in biomass chemical looping gasification

By reasonably controlling the lattice oxygen of oxygen carrier (OC), the biomass chemical looping gasification (CLG) technology can convert biomass into syngas dominated by H₂ and CO, which is a prevalent topic in the world. However, in practical applications, the mechanism underlying OC agglomeration induced by alkali and alkaline earth metals (AAEMs), along with effective countermeasures, remain ambiguous. In this paper, AAEM elements were added to the biomass after pickling to explore the effects of K, Na, Ca, and Mg on agglomeration. The results indicated that with the increase of K and Na additions from 0.5 % to 18 %, the deformation temperature (DT) of spent OC decreased, leading to a marked intensification of agglomeration, with degree of agglomeration increases from 2.88 % and 1.74 % to 17.44 % and 13.91 %, respectively. In contrast, with the increase of Ca and Mg additions from 0.5 % to 18 %, the DT of spent OC increased, and the degree of agglomeration remained lower than that of K and Na, with values ranging only from 1.03 % and 0.95 % to 11.17 % and 2.66 %, respectively. Besides, with augmented alkali metal chloride addition, the amount of low melting point aluminosilicates formed from SiO₂ and Al₂O₃ increased, further exacerbating the OC agglomeration.