A granular moving-bed apparatus is introduced to have an inlet louvered wall, an outlet louvered wall opposing to the inlet louvered wall, a granular path formed in between, a plurality of serial roof-shaped flow-corrective elements located along the granular path, and a predetermined type of granular materials flowing inside the granular path. The inlet louvered wall and the outlet louvered wall are particularly constructed to form serial hopper-shaped structures that define the granular path. The roof-shaped flow-corrective element is systematically displaced with respect to the hopper-shaped structure by specific criteria so that problems of corrosions, plaques and stagnant zones formed to the louvered walls of the apparatus can be avoided.