Reducing Tar Emissions during Coal Gasification by Optimizing the Cracking/Reforming over Char in a Fluidized Bed

In this study, we aimed to reduce tar emissions during coal gasification using a fluidized bed by promoting contact between tar and char and determining the operating conditions required to reduce tar emissions. When steam gasification was conducted under the top-feed method, in which coal was fed over the fluidized bed, tar emission could not be suppressed until char accumulated in the bed. Once tar can readily come in contact with the char in the bed, tar emission can be suppressed. On the other hand, under the bottom-feed method, in which coal is fed into the fluidized bed, even if char is not accumulated in the bed, the process of heavy tar reforming in the gas phase in the bed occurs to suppress its emission. Furthermore, once the char was concentrated in the bed, the interaction between the tar and char was strengthened to further suppress tar emission. If the char concentration in the bed is quite high, heavy tar emissions can be almost fully suppressed, and light tar, excluding benzene, can be almost fully suppressed up to approximately 0.03 wt % by optimizing the operating conditions.