Australian coal was gasified in an internally circulating fluidized bed (0.3 m-I.D. × 2.7 m-high) with a draft tube (0.1 m-I.D. × 0.9 m-high). The effects of reaction temperature (780 - 900℃), oxygen/coal ratio (0.30 - 0.53), coal feed rate (5.3 - 12.1 kg/hr), air flow rate (7 - 15 $U_{mf}$), and steam/coal ratio (3.5 - 5.0) on product gas compositions, carbon conversion, cold gas efficiency, gas yield, and calorific value of the product gas have been determined in an internally circulating fluidized bed. In the fluidized bed, Coal combustion (draft tube) and gasification (annulus) zones can be divided by inserting a centrally located draft tube. By using a separator over the draft tube, high calorific value gas can be obtained in the gasification section (annulus).
The contents of hydrogen, carbon monoxide, gas yield, carbon conversion, and cold gas efficiency increases with reaction temperature. Calorific value of the product gas, gas yield and cold gas efficiency decrease, but carbon conversion increases with increasing oxygen/coal ratio. With increasing coal feed rate, calorific value of the product gas increase whereas, gas yield, cold gas efficiency and carbon conversion decrease. On the other hand, steam/coal ratio does not produce any significant effect on the gasifier performance. With increasing gas velocity, calorific value of the product gas and gas yield increase, but carbon conversion and cold gas efficiency decrease.
In the gasification zone (annulus), the product gas compositions (dry base) are found to be 31.8~46.2%-$H_2$, 18.8~25.6%-CO, 13.2~20.4%-$CO_2$, 5.3~10.4 %-$CH_4$ with calorific value of 8.6~13.2 MJ/㎥ which is higher those from conventional fluidized bed or spout bed gasifier and other types of internally circulating fluidized bed gasifiers.
The obtained gas compositions, gas yield, calorific value, carbon conversion, and cold gas efficiency have been correlated with the pertinent dimensionless operating variables as:
${Y=K(m_s/m_c)^a (m_O_2/m_c)^b (T')^c (y_O_2)^d}$
with the known operating variables of $(m_s/m_c)$, $(m_O_2/m_c),$ (T'), and $(y_O_2)$, gas composition, calorific value of the product gas, gas yield, carbon conversion, and cold gas efficiency can be successfully determined in the present coal gasifier.
