Fluidized Bed Agglomeration Temperatures as a Function of Impurities Content in Low-Temperature Black Liquor Gasification, 2005 Engineering, Pulping & Environmental Conference

This investigation demonstrates the effect of potassium chloride (KCl) and reactor bed temperature on the propensity for agglomeration in a fluidized-bed reactor. The bed material consisted of either sodium carbonate (Na2CO3) or sodium sulfate (Na2SO4). Data show that for pure Na2CO3 and Na2SO4, the fluidized bed begins to agglomerate at 520 ºC and 490 ºC, respectively. An addition of 0.5 weight percent KCl caused a decrease in agglomeration temperatures to 480 ºC for Na2CO3 and 460 ºC for Na2SO4. Increasing KCl concentration continues to approximately 2.0%, decreases agglomeration temperatures to about 460 ºC for Na2CO3 and 440 ºC for Na2SO4. An x-ray diffraction analysis of the agglomerated particles shows the KCl surrounding the Na2CO3 bed material indicating two possible types of mass diffusion as the mechanism for sintering. The first mechanism is mass diffusion due to differences in lattice energy between surface and bulk material. The second mechanism is mass diffusion due to a concentration gradient between bed material and added impurities. SEM analyses qualitatively show the onset of sintering for pure Na2CO3 at 520 ºC. Sintering and agglomeration occur more rapidly in stagnant regions of the reactor and along the top sides of heater surfaces where particle residence times are longer. Agglomeration tests with a carbon-coated commercial bed material showed no signs of sintering and agglomeration.