Interaction of the behavior of lead and zinc with alkalis in fluidized bed combustion or gasification of waste derived fuels

R Backman, Mikko Hupa, M Hiltunen, K Peltola

    Research output: Chapter in Book/Conference proceedingConference contributionScientificpeer-review

    23 Citations (Scopus)


    Combustion of waste derived fuels in fluidized bed boilers may result in fly ashes containing increased amounts of lead and zinc, besides the common alkali and alkaline earth metal compounds. Although the absolute concentrations of lead and zinc may be relatively low, around 1%, in the bulk ash, they may induce unwanted effects in combustors, partly due to their significant enrichment in the fly ash. First, lead and zinc in fly ashes may lead to unwanted heavy metal emissions. Further, they can also alter the behavior of the fly ash and cause it to become sticky and possibly corrosive. This paper discusses the mechanism of volatilization of lead and zinc and stickiness properties of their fly ash compounds under different conditions, based on data from a FBC gasifier using waste fuels with significant amounts of lead and zinc. Advanced thermochemical calculations using the data bases developed at Abo Akademi show that both lead and zinc can form volatile compounds and thus be strongly enriched in the fly ash. They can be volatilized as elemental gases, Pb(g) and Zn(g), or they can form gaseous chlorides, PbCl2(g) and ZnCl2(g). But they can also form non-volatile oxides. Thus their behavior is very dependent on the combustion conditions, particularly on the availability of chlorine. This way there is also a direct coupling of the volatilization behavior of lead and zinc with the chemistry of the alkali metals and calcium, all of which govern the availability of chlorine. Simplified thermochemical diagrams are shown to explain the complex interaction of the lead and zinc chemistry with the rest of the flue gas and fly ash chemistry. The thermochernical data can be used to explain the practical results from full scale boilers.
    Original languageUndefined/Unknown
    Title of host publicationProceedings of the 18th International Conference on Fluidized Bed Combustion
    EditorsL Jia
    PublisherAmerican Society of Mechanical Engineers, ASME
    ISBN (Print)0-7918-4698-9
    Publication statusPublished - 2005
    MoE publication typeA4 Article in a conference publication
    Eventconference; 2005-05-22; 2005-05-25 - Toronto, Canada
    Duration: 22 May 200525 May 2005


    Conferenceconference; 2005-05-22; 2005-05-25

    Cite this