Continuous experiment regarding hydrogen production by Coal/CaO reaction with steam (II) solid formation

Abstract

Integration of coal gasification and CO 2 separation reactions in one reactor may produce a high concentration of hydrogen. To design a reactor for this new reaction system, it is necessary to know all reaction behaviors in the integrated reaction system. In our previous study, we performed a continuous reaction experiment of coal/CaO under high steam pressure and confirmed that H 2 concentration higher than 80 vol% with little CH 4 was produced; and that almost all CO 2 was fixed by adding CaO. In this study, the behaviors of solid products during the continuous experiment were investigated. It was found that, CaO first reacted with high-pressure steam to form Ca(OH) 2 (hydration), then the Ca(OH) 2 absorbed the CO 2 generated by coal gasification to form CaCO 3. The hydration of CaO restored sorbent reactivity. Eutectic melting of Ca(OH) 2/CaCO 3 was found to occur in the experiment at 973 K, and this eutectic melting led to the growth of large particles of solid materials. However, at the relatively low temperature of 923 K, eutectic melting could be avoided. Carbon conversion of the coal in the continuous reaction of the coal/CaO mixture with steam was high as 60–80%, even at the lower temperature of 923 K.