Insights into corn straw gasification with K2CO3 and CaO additives: From the aspect of micro, macro to mechanism

Abstract

This study provided a total study on the corn straw gasification with K2CO3 and CaO additives from the aspect of micro, macro and mechanism. During the devolatilization process, K2CO3 was beneficial to enhance the depolymerization and fragmentation of CS thus yielding more char, while CaO showed the inhibition. The CO and COOH cracking and reforming was promoted under the K2CO3 to generate more CO2, while CaO can adsorb CO2 to form CaCO3 and then remained in the char. Moreover, K2CO3 was beneficial for the decomposition lignin and hemicellulose to generate more CO and the thermal devolatilization of methoxyl groups to yield more CH4. In addition, K2CO3 and CaO all can improve the C-C/C-O-O formation. When the K2CO3/CaO mixture was utilized, the co-existence of K2CO3 and CaO exhibited a synergy on catalyzing the cracking and reforming of CO, C-C and C-O-C, resulting in a higher CO yield during devolatilization process. Moreover, K2CO3 and CaO exhibited a synergy on CO2 and char formation, thus improving the reaction between these two substance to form more CO duing the solid-gas reaction process. The CaO in char could also adsorb the CO2 to form CaCO3 following the CaO carbonation. Since this reaction was exothermic, the gasification process was enhanced and water gas shift reaction was driven to generate more CO2 and H2 formation. The K2CO3 in char played a positive effect on the reaction between char and H2 to yield more CH4. The synergy between K2CO3 and CaO reached an optimum under the mixing ratio of 4:2. The generated bimetallic carbonate K2Ca(CO3)2 during devolatilization process was postulated to be the reason for the synergy. Under this condition, the highest LHV of gas products of 6.68 MJ/Nm3, lowest tar content of 3.69 g/Nm3 and highest cold gas efficiency (CGE) of 86.49% were achieved