Abstract
Clinker formation was a serious problem that prevented continuous operation of more than a week in cocurrent up-flowing moving bed gasifiers operated for pellets from Japanese cedar. In this work we investigated the clinker formation characteristics in gasifiers of this particular type by analyzing the pellets fed to and the clinker samples collected from gasifiers of the Oobae-Kuroshio Power Plant. We found that the major compounds of the clinkers were lime, CaCO3, K2CO3, KAlO2, and Larnite, and identified that they were formed with the CaCO3-K2CO3 melt as an adhesive. The pellet ash had a deformation temperature (DT) of over 1300 °C in an oxidizing atmosphere, but around 770 °C in a reducing atmosphere (CO 60%-CO2 40%). In the gasification atmosphere with high CO2 partial pressure, a melt consisting of CaCO3-K2CO3 is supposed to form from 735 °C due to eutectic of the CaCO3-K2CO3 system, which should be the main cause of clinker formation. Furthermore, we observed a trace of foaming with gas bubbles in low viscosity melts on the ash samples. On the other hand, we found that the DT of ash from pellets commercially available in Germany measured in both oxidizing and reducing atmospheres was above 1200 °C showing no foaming phenomenon in reducing atmospheres of 750- 800 °C, indicating completely different ash formation characteristics from Japanese cedar pellets case, which cannot be detected by conventional method assigned by ISO.
