Process for preventing adhesion or caking of coal

Disclosed is a method of preventing adhesion or caking of raw materials such as oil or coal as it is subjected to hydrogenation gasification while being heated to above 700 DEG K. as it passes downwardly through a reaction vessel. The particles of raw materials as they pass through the vessel in a temperature zone of about 600 to 700 DEG K. directly contact a medium intermittently at a temperature above 1000 DEG K. to rapidly heat the surfaces of the particles to above 700 DEG K. by direct contact with the hot medium alone, in the absence of combustion reaction, to cause the particles to become non-caking in its further downward passage through the reaction vessel.