In this study, we propose a "washing-calcination-conversion of washed fly ash into cement material with bottom ash" (WCCB) system to reduce the amount of fly ash that must be specially treated so it can be used as raw cement material. Calcium hydroxide (Ca(OH)(2)) is widely used in air-pollution control devices of incinerators while Sodium bicarbonate (NaHCO(3)) is not. We conducted single-, double-, and triple-washing experiments to compare the washing characteristics of two types of fly ash. Unlike NaHCO(3) fly ash, Ca(OH)(2) fly ash has almost twice as much washed residue and almost 2.5 times more chlorine after the same washing procedure. After washing once, the washing frequency is also important for NaHCO(3) fly ash, while the mixing time and liquid/solid ratio are more critical for Ca(OH)(2) fly ash. The use of NaHCO(3) is more suitable for the WCCB system. (C) 2008 Elsevier Ltd. All rights reserved.