Catalytic Gasification with Carbon Dioxide Characteristics of Alkali and Alkaline Earth Metals Catalysts in the Fixed-bed Reactor

摘要

Low temperature gasification is a talent technology to reduce the energy consumption and improve the heat value of gasification products. Catalytic gasification has advantage in accelerating reaction rate, and the catalytic gasification technology has gained great attention, alkali and alkaline earth metals have proved as effective catalysts for the catalytic gasification reaction. Effects of temperature, catalyst types and catalyst loadings on carbon dioxide gasification reaction were investigated on a fixed-bed reactor in this paper. Catalyst dispersion effect, BET specific surface area and crystallite constituents of Jinyou coal char with different loadings of K and Ca were also analyzed by energy-dispersive X-ray analyzer (EDX), N_2 adsorption at 77K and X-ray diffraction (XRD). Results showed that Potassium carbonate (K_2CO_3), as a catalyst, could improve gasification rate significantly, when gasification temperature was above 850°C Cation species of the catalyst could influence its catalytic activity, and the main effects of the catalysts were the alkali and alkaline earth metal elements, the catalytic effect order was K_2CO_3>KOH>Na_2CO_3>NaOH>Ca(NO_3)_2. The reactivity of coal char increased continuously with the catalyst loadings, and showed a loading saturation level (LSL) which was 10% for K. K and Ca added to Jinyou coal could decrease its BET specific surface area, compared to the raw char. Moreover, K and Ca added to Jinyou coal could change its crystallite constituent during the process of coking and gasification, which indicated that some K and Ca reacted with minerals in the Jinyou coal char during the process of coking and gasification, resulting deactivation of some K and Ca. SiO_2 was the main mineral constituent in the raw char and its gasification residue. During the coking process, the soluble K and Ca would reacted with the minerals in Jinyou coal to produce insoluble salt of KAlSiO_4, MgSiO_3 and Ca(OH)_2 and Ca_2Al_2SiO_7, respectively. During the gasification of CO_2 process, some soluble K in the char became into insoluble salt of K_2MgSi_3O_8, and CaO diffraction peak appeared in its gasification residue, which indicated that some soluble K and Ca deactivated during the CO_2 gasification process.