The relationship between the tendency of lignites to agglomerate and their fusion characteristics in a fluidized bed combustor

Abstract

Agglomeration temperatures of six lignite ashes were measured in a laboratory scale fluidized bed of quartz sand. The results were compared with the characteristic temperatures of the lignite ashes. The agglomeration temperatures of the burning lignites were determined by measuring the active bed temperature and pressure drop across the bed. The results show that, in such a fluidized bed, agglomeration can begin at temperatures well below the ash fusion temperature. For the six lignites tested, agglomeration started at 860–1060 °C, which is about 125–200 °C lower than their initial ash deformation temperatures and 300–400 °C lower than their ash fusion temperatures. Considering the fact that burning particles in a fluidized bed are 150–200 °C hotter than the bed, the results suggest that lignite ashes can agglomerate at temperature levels about the initial deformation temperature. Although the agglomeration tendency appears to decrease with increasing ash initial deformation or fusion temperatures, no meaningful correlation was found, at least for the lignite ashes tested, between the agglomeration and characteristic ash temperatures. In the fluidized bed combustor burning lignites, agglomeration temperature of ashes decreases with Na 2O content and increases with Al 2O 3 content. Fluidized bed combustor, on the other hand, becomes more vulnerable to agglomeration as the total basic oxide content of bed inventory increases.