Washing Characteristics of Calcinated Washed-Fly-Ash from Municipal Solid Waste Incinerators

摘要

WCCB—Washing, Calcinating and Changing the treated fly ash into the raw material in cement industry— has been proposed to recycle fly ashes from municipal solid waste incinerator. We have studied the washing process and calcination process. Here we will discuss the post-washing step after the fly ash was washed and then calcinated. As we have studied the hierarchy of parameters and chlorides distribution in the washing step, and as most of the chlorides have been reduced in washing and calcination step, it is not so important to discuss the operation condition for post-washing here. So the purpose of this study is that one is to make sure that calcination is necessary to reduce chlorine besides the function of evaporation, and the other is to discuss the characteristics of chlorides in the residues. The operation condition of post-washing is once-washing (Liquid (ml)/ Solid (gram)=3, mixing time=10min, disturbing speed=150 rpm). We also studied three kinds of fly ashes: raw fly ash from the boiler or economizer of incineration system (RFA), fly ash collected in bag filter with the injection of Ca(OH)2 for acid removal (CaFA) and fly ash collected in bag filter with the injection of NaHCO3 for acid removal (NaFA). The residue we used is from the washing process and calcinated by several conditions we selected from the calcination process by checking the calcination results. It was found that the sequence of WCCB system is reasonable and can effectively reduce chlorine content in fly ash, and calcination can decompose some insoluble chlorides to soluble chlorides. As to CaFA-II# during calcination, some chlorides reacted with some other compounds in the residues and then be fixed. As to RFA-II# and NaFAIl#, higher temperature got better results, however, when the heating temperature is higher than 400 °C, the increasing portion of soluble chlorides did not go as fast as the rising of heating temperature.