Abstract: Apparatus for cooling granular material such as petroleum coke comprises an elongated drum characterized by a generally cylindrical shell wall having spaced apart circular segment pockets extending radially inwardly from the shell wall toward the central axis of the drum to provide extended heat transfer surfaces and flow spaces for cooling water. The cooling pockets are welded to the shell wall along the edges of opposed sidewalls of the pocket or conduit members themselves. The somewhat flexible drum shell resulting from the aforedescribed construction is strengthened and held substantially rigid for rotation about its central axis by a plurality of circumferentially spaced tension rods which extend from one end of the drum to the other and are engagable with a support plate.