Coal gasification offers one of the most versatile and clean ways to convert coal into electricity, hydrogen, and other energy forms. The freeboard being defined as the space between surface of the bed and the gas exit at the top of the container and its height is freeboard height. The freeboard above a fluidized bed is the dilute phase region. The freeboard container is normally cylindrical and usually of the same diameter as the bed but sometimes larger. When the bubble burst at the fluidized bed surface, particles are entrained in the freeboard region. The entrained particles with a terminal velocity greater than actual gas velocity (ut>u) will reach a certain height within the freeboard before they fall back into the bed. However those particles with a terminal velocity smaller than actual gas velocity (ut