A process is presented whereby hot Carbon Monoxide (CO) gas is generated under pressure in an external Combustor by the partial oxidation of a carbon-based solid fuel. This pressurized, hot CO gas or CO gas mixture is then transferred to a desulfurizing vessel containing a second carbon-based solid fuel. The hot CO laden gas and solid material contact in a counter-flow arrangement where the CO reacts with and removes sulfur impurities from the second carbon fuel. The temperature of the pressurized CO laden gas from the Combustor is controlled by varying the oxidizer feed gas composition. The Combustor also contains a means for desulfurizing its feed fuel by flowing a portion of the hot CO gas generated up through the inlet solid fuel feed line.