Fate of chromium with the presence of HCl and steam during oxy-coal combustion: Quantum chemistry and experimental study

Quantum chemistry combined with kinetic simulation and drop tube furnace (DTF) experiments were conducted to reveal the transformation behavior of chromium at the presence of steam and HCl under oxy-coal combustion. A completed kinetic system Cr-O-H-Cl containing 107 elementary reactions was firstly proposed. The unknown microcosmic reaction paths and corresponding Arrhenius parameters were calculated via quantum chemistry. Kinetic simulations on the basis of Cr-O-H-Cl system clarified that HCl promoted the oxidation of chromium to hexavalent CrO2Cl2. Coexistence of HCl and steam divided the transition of chromium into two stages. At the early stage, reaction rate between chromium and steam was faster than chromium with HCl, chromium mainly transformed to CrO(OH)2. Hereafter, HCl was dominant in the transformation of chromium, then chromium mainly presented as CrO2Cl2. Moreover, DTF experimental results indicated that introduction of HCl into combustion atmosphere induced more chromium release. Presence of steam reinforced the effect of HCl on chromium attributing to the significant transition of CrOx(OH)y to CrO2Cl2. Although CaO and Fe2O3 both exhibited good reactivity with chromium, presence of HCl largely suppressed chromium capture by CaO and Fe2O3. Moreover, the inhibition effect of HCl on Fe2O3 was stronger than CaO for Cr capture.