Transition Behavior of Main Elements in Fly Ash During High Alkali Coal Combustion

To study the fouling and slagging properties of fly ash from combustion of Xinjiang high alkali coal, XRF and SEM-EDX analysis were carried out to ash samples taken from various heating surfaces in a 300 MW subcritical boiler burning high alkali coal. Results show that in the gas temperature range of 800-1 100 ℃, mass fractions of CaO, MgO and SO3 in ash samples are relatively high; whereas for in temperature range of 600-800 ℃, mass fractions of Na2O, Fe2O3 and SO3 are relatively high, in which case serious fouling on high-temperature convection heating surfaces is caused by Na2SO4, CaSO4 and NaFeSO4 during combustion of high alkali coal. For locations where the gas temperature is in the range of 669-915 ℃, both the initial melting temperature of ash samples and corresponding liquid slag ratio are higher than those in other places. Na2SO4 particles with sizes of 2-4 μm rich in Na and S are found to stick on surface of ash sample C, which at high temperatures have high sticky properties and low melting temperatures, and therefore may lead to serious fouling problems.