Fragmentation of dolomite bed material at pressurized conditions in the presence of H2O and CO2: Implications for pressurized fluidized bed gasification

Abstract

Dolomite shows superior tar cracking and anti-agglomeration abilities in gasification processes, while its fragmentation at elevated temperatures is still a major obstacle inhibiting its applications in fluidized bed (FB) applications. To improve the understanding of its performance in pressurized FB gasification, we investigated fragmentation behaviors of crystalline Glanshammar and amorphous Sala dolomite at both isothermal and non-isothermal modes under pressurized H2O and CO2 conditions. A series of tests under various conditions, i.e. pressure, temperature, heating rate, gas atmosphere, and dolomite types, was conducted. The primary fragmentation of Glanshammar is significantly reduced at 10 bar. Dolomite exposed to a PH2O of 10 bar has the lowest fragmentation among all cases. Both dolomites were also loaded into a pressurized fluidized bed gasifier as bed material. Glanshammar exhibits approximately 14% loss of its initial mass of bed, a much higher loss compared to the Sala dolomite with only 5.5%. Fragmentation mechanisms at pressurized conditions in the presence of H2O and CO2 and measures to mitigate dolomite fragmentation in pressurized FB gasifiers are proposed. During gasification, both high operating pressure and high PH2O are beneficial for fragmentation mitigation. To mitigate an initial fragmentation of dolomite during the reactor heating-up stage, a pressurization to the operating pressure before reaching the initial fragmentation temperature of dolomite (400 °C) is recommended. Crystalline dolomite, is the preferred choice, if a pretreatment at a high-pressure using H2O is applied.