Investigation and regulation of flow properties of rice straw ash for the slagging gasifier

Abstract

Gasification is one of many prospective ways to utilize straw biomass efficiently and economically. However, despite the low fusion temperatures of rice straw ash, the high silica content and the consequent high viscosity hinder the application of this biomass to the slagging gasifiers. To regulate the rice straw ash slag fluidity, two kinds of basic oxides (Fe₂O₃ and CaO) were selected as additives and mixed with the ash in several ratios respectively. Based on the results of ash fusion temperatures (AFTs) test, X-ray diffraction (XRD) analysis and thermodynamic calculation, it was found that the basic additives combined with SiO₂ and reduced the flow temperature at low additions. When the addition continued to increase, Fe₂O₃ combined with SiO₂ to form fusible minerals such as olivine, while CaO reacted with SiO₂ to generate refractory wollastonite. The influence mechanisms of basic additives on slag viscosity were further explored through viscosity tests and Fourier transform infrared spectroscopy (FTIR) analysis. Both additives could reduce the slag viscosity by increasing the content of the network modifiers. Compared with Fe³⁺ and Fe²⁺, Ca²⁺ had a smaller ionic potential and a superior ability to depolymerize the silicate network, so CaO had a better effect on viscosity reduction.