Formation of Donded Fireside Deposits in Pulverizedcoal-fired Boilers of Thermal Power Station

Yamasaki Tatsuo, Matsumoto Yukio, Yamada Yukio

doi:10.3775/jie.43.10_706

The bonded deposits of fly ash and slag on the fireside of furnacetube in boilers installed in thermal power stations have frequently caused severe deteriorationin thermal efficiency. But the problems about fouling of heat transfer surface, particulary in connection with occurrence, chemical composition, mineral constituent, 'structure and origin of these deposits, have not been studied in detail. Reviewing theresults obtainec by our study of the deposits for the purpose of clarification of theirorigin, they are classified into the following three main groups .<BR>(1) Fly ash is characterized by its aggregate strueture composed mainly of minuteglobular particles of quartz, cristobalite, glass etc. It is almost the same in chemical compositions compared with the original coal ash (SiO2 57%, Al2O3 25%, Fe2O3 6%), except that it is sightly higher in Fe2O3 .<BR>(2) Siliceous slag is composed of the same particles as of fly ash, though the formerare combined mutually by the minerals recrystalized in the part of furnace higher in temperature (1, 000-1, 400°C), such as cristobalite, mullite etc.<BR>(3) Rigid ferruginous slag consists mainly of ferric iron (hematite) adhered togetherin reticulum and occurs in the part of furnace lower in temperature (±950°C>).Compared with the other deposits, it shows a marked difference by an excessive concentration of iron (Fe2O3, 50-65%).

Formation of Donded Fireside Deposits in Pulverizedcoal-fired Boilers of Thermal Power Station

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