Steam gasification behavior during coal combustion and CaO regeneration in O2/CO2/steam atmosphere

Abstract

In this study, limestone was calcined in O2/CO2/steam atmosphere with heat supplied from coal combustion. Steam was supplied to the calciner to improve CaO reactivity. However, steam gasification behavior during coal combustion in O2/CO2/steam atmosphere is unclear. This experimental study was conducted to clarify the role of steam in coal combustion using an isotope tracer technique. H218O was used to continuously trace the reaction proceeding. In a fuel-rich environment, both CO2 and steam gasification occurred, generating H2, C16O, C18O, C16O2 and C16O18O. In an oxygen-rich environment, steam gasification still occurred and generated C16O18O. The combustion reaction equation should be described as C+H218O+16O2=C16O18O+H216O at high temperature and with high CO2 and steam concentrations. The generation of C16O18O highly depends on O2 concentration in a fuel-rich environment but the O2 supply has little influence on C16O18O formation in an oxygen-rich environment. Moreover, the increase of steam supply accelerated C16O18O formation. Steam gasification is generally involved in coal combustion reaction. C18O and H2 are first locally generated within coal particles through steam gasification and they are reconverted to C16O18O and H216O through combustion during the boundary layer reactions.