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

In this study, limestone was calcined in O-2/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 O-2/CO2/steam atmosphere is unclear. This experimental study was conducted to clarify the role of steam in coal combustion using an isotope tracer technique. H-2 O-18 was used to continuously trace the reaction proceeding. In a fuel-rich environment, both CO2 and steam gasification occurred, generating H-2, (CO)-O-16, (CO)-O-18, (CO2)-O-16 and (COO)-O-16-O-18. In an oxygen-rich environment, steam gasification still occurred and generated (COO)-O-16-O-18. The combustion reaction equation should be described as C + H-2 O-18 + O-16(2) = (COO)-O-16-O-18 + H-2 O-16 at high temperature and with high CO2 and steam concentrations. The generation of (COO)-O-16-O-18 highly depends on O-2 concentration in a fuel-rich environment but the O-2 supply has little influence on (COO)-O-16-O-18 formation in an oxygen-rich environment. Moreover, the increase of steam supply accelerated (COO)-O-16-O-18 formation. Steam gasification is generally involved in coal combustion reaction. (CO)-O-18 and H-2 are first locally generated within coal particles through steam gasification and they are reconverted to (COO)-O-16-O-18 and H-2 O-16 through combustion during the boundary layer reactions. (C) 2016 Elsevier Ltd. All rights reserved.