Abstract: 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.degree. 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.degree. K. directly contact a medium intermittently at a temperature above 1000.degree. K. to rapidly heat the surfaces of the particles to above 700.degree. 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.