of most any suitable type well known in the art such as a cyclone separator to control the passivation reaction temperature within the reaction vessel 16 in one embodiment the process gas 44 containing some uncollected coal char 26 particles exits the dust collector 50 and is cooled indirectly in a heat exchanger 52 the heat exchanger 52 may be either an air cooled or liquid cooled heat exchanger positioned externally of the reaction vessel 16 the temperature of the process gas 44 downstream of the reaction vessel 16 is monitored and the quantity of cooling air supplied to the heat exchanger 52 is controlled thereby controlling the temperature of the process gas leaving the heat exchanger in an alternative embodiment as shown in fig2 for illustrative purposes the passivation reaction temperature may be controlled by transfer of heat within the reaction vessel 16 to cooling tubes 40 positioned within the coal char 26 the cooling fluid passes through the cooling tubes and is recirculated in a closed loop through an external shell and tube heat exchanger as well known in the art for transfer of heat to a secondary cooling fluid as previously described the temperature of the process gas.