Enhancing the performance of iron ore by introducing K and Na ions from biomass ashes in a CLC process

Highlights: • Two decoration methods of iron ore with biomass ashes were innovatively proposed. • BA-decorated iron ore performed well during the coal CLC process. • The dry calcination method has a more remarkable effect in promoting the reactivity of iron ore. • The sintering of oxygen carrier was observed under high temperature. -- Abstract: Oxygen carrier holds a significant role in chemical looping combustion (CLC) process. High redox rate is a prerequisite for oxygen carrier when solid fuel is applied in CLC. The present work proposed iron ore modified by rape stalk ash (RSA) and wheat stalk ash (WSA). Dry calcination and wet impregnation methods were used. Effects of biomass ashes species, temperature, biomass ashes/undecorated iron ore (BA/UIO) mass ratio and cycle number on the performance of oxygen carrier were investigated in a laboratory fluidized bed reactor. The cumulative conversions of CO for BA-decorated oxygen carriers is significantly higher than that for UIO, especially for the oxygen carrier with BA/UIO mass ratio of 20/100 using dry calcination method. In the coal CLC batch tests, the water-gas shift reaction was accelerated, the time for carbon conversion stabilization was shorten and the conversion of CO to CO₂ was improved with BA-decorated iron ore as oxygen carriers. Nevertheless, the promotive effect was weaken when temperature rose to 950 °C because of the sintering of oxygen carrier due to the generation of low-melting-point potassic compounds. The circulation experiments showed that the reactivity of two BA-decorated oxygen carriers was more stable during the 10 redox cycles compared with UIO.