Effect of temperature and pressure on the transformation characteristics of inorganic elements in cotton straw ash

The transformation characteristics of inorganic elements in biomass ash are crucial for the efficient and continuous operation of gasifiers. Cotton straw ashes produced initially at 500 degrees C were heated under different temperatures and pressures, and then the resulting ash samples were analyzed by XRF, XRD, and SEM-EDS. The results indicated that increasing reacting temperature aggravated ash melting and the ash loss rose linearly, reaching up to 18.1 % at 1000 degrees C and 0.1 MPa. Reversely, high pressure effectively declined ash loss and melting degree. Under 2 MPa and 4 MPa, the weight loss at 1000 degrees C was only 8.0 % and 4.3 %, respectively. High pressure decreased ash loss by inhibiting the decomposition and vaporization of low-temperature minerals (K2SO4 , Na8Al6Si6O24SO4 , CaCl2 , and CaSi2) and promoting the reactions among minerals in ash. At 1000 degrees C, KCl was present in ash, and its content rose with increasing pressure at the same temperature. The SEM-EDS images revealed that the structure of ash varied from melted to adhesion with increasing pressure at 1000 degrees C. KCl particles were present in large ash particles at 1000 degrees C and 2 MPa. As the temperature increased from 700 degrees C to 1000 degrees C, K2O content decreased more than 5.0 %, while that of CaO increased 6.0 % at 0.1 MPa. At 4 MPa, the K2O and CaO increased and reduced 0.6 %, respectively. Compared to atmospheric pressure, pressurization significantly reduced the release of inorganic elements from ash.