Investigation into Ca/Na compounds catalyzed coal pyrolysis and char gasification with steam

Highlights: • Combined effect of Ca and Na during catalytic gasification was revealed. • Na and Ca favor the formation of micropores and mesopores respectively during gasification. • Interactions between Ca/Na compounds with char make the carbon matrix more vulnerable to steam. • Redox experiments show that Ca/Na-char produce more active intermediates during gasification. -- Abstract: The main aim is to investigate the effects of Ca/Na compounds on coal pyrolysis, gasification reactivity as well as char characteristics during gasification. The pyrolysis and gasification tests of different metal loaded coals were performed on thermogravimetric analyzer and fixed bed reactor. The raw and gasified chars were prepared and characterized by nitrogen adsorption, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results indicate that Ca coexist with Na has a better catalytic activity compared to Ca and Na alone. The addition of metals can promote the pyrolysis gas release in advance and increase the release amount of H₂ and CO₂. The present of Ca/Na compounds have no significant effect on pore structure evolution during pyrolysis, but it inhibits the aromatic structure condensation of the coal char. The addition of Na and Ca is beneficial to the formation of micropores and mesopores respectively during gasification, the simultaneous existence of Ca and Na results in a more abundant pore structure. Both Ca and Na can inhibit the condensation of aromatic structures during coal char gasification, Ca together with Na will make the char has a higher degree of disorder. The interaction between Ca and Na with coal char makes the carbon matrix easier to be attacked by H₂O to form more active intermediates. Redox experiments further verified that more active intermediates were generated during the gasification of Ca/Na loaded char.