Calcium ion exchange was performed in Indonesian low-rank coal using saturated aqueous solutions of Ca(OH)(2) at 30.0 +/- 0.1 degrees C without pH adjustment. The Ca2+ concentration and pH were monitored during ion exchange. A coal product was obtained with 3.2 mass% Ca2+. Gasification of the ion-exchanged samples was conducted in a circulating dual bubbling fluidized bed (CDBFB) reactor at 700 degrees C, 800 degrees C, and 900 degrees C. Coal carbon conversion into carbonaceous gases (CO, CO2, CH4, and C-2 hydrocarbons) using the Ca2+-exchanged coal achieved 78% at 900 degrees C in the CDBFB. The Ca catalyst led to the greatest rate enhancement at 800 degrees C, resulting in a twofold increase in the gas product yield compared to that without Ca. A comparison of carbon conversion between the CDBFB and fixed-bed reactors revealed that the conversion value using the CDBFB at 700 degrees C was very small. Regarding an examination of this influence in detail, it seems that the existing H-2 adhered primarily to the active sites of the char, and the use of Ca2+-exchanged coal led to a reverse shift reaction.