Scaling Mechanism of Fly Ash on Rear Heating Surfaces Under H2SO4/NH4HSO4

Abstract

The high-intensity scale on the heating surface of a boiler holds up its security and economic efficiency. To clarify the scaling mechanism， scaling experiments where H2SO4/NH4HSO4 reacted with fly ash were carried out. Scanning electron microscope morphology analysis and X-ray diffraction composition analysis were used to analyze the ash-scale morphology and composition supplemented with thermodynamics equilibrium calculation for determining cementing minerals which lead to scaling. The results showed that the flocculent and needle-like crystals formed on the surface of ash particles mixed with H2SO4/NH4HSO4； ash particles adhered and cemented into large agglomerates to form ash-scale， and agglomeration was more remarkable mixed with NH4HSO4. The experiment and thermodynamic equilibrium calculation showed that the fly ash reacted with H2SO4 to generate gypsum-like gelatinous sulfate substances； NH4HSO4 reacted with fly ash to generate gypsum-like gelatinous substances and a large amount of （NH4）2SO4 that tend to scaling. Under H2SO4/NH4HSO4， the gelatinous sulfates generated from actions of deposited ash consolidated the incompact ash particles， leading to the accumulation of ash scale on heating surface.

Keywords

• fly ash
• scaling
• cementing material
• h2so4
• nh4hso4