Coal gasification with CO2 (the Boudouard reaction: C + CO2 = 2CO, Delta(r)H degrees = 169.2 kJ/mol at 1150 K), which can be applied to a solar thermochemical process to convert concentrated solar heal into chemical energy, was conducted in the molten salt medium (eutectic mixture of Na2CO3 and K2CO3, weight ratio = 1/1) to provide thermal storage. When CO2 gas was bubbled through the molten sail higher reaction rates were observed compared to the case without CO2 gas bubbling (CO2 gas was streamed over the surface of the molten salt). Thus the coke formed by coal pyrolysis was well suspended in the molten salt by CO2 gas bubbling. When the CO2 flow rate was increased from 15 to 60 mu mol/s, the CO evolution rate was increased (15 to 26 mu mol/s). However, CO2 conversion efficiency was decreased (50 to 22%). Based on the maximum CO evolution rate (26 mu mol/s), solar thermal energy from a solar farm (300 x 300 m(2)) could be converted to chemical energy at a rate of 50,000 kJ/s by the coal (23 ton as C) gasification process studied here. This assumes 50% solar heat to chemical energy conversion efficiency which can be generally obtained by the actual solar experiments. (C) 2000 Elsevier Science Ltd. All rights reserved.