A conveyor belt system includes a frame with a conveyor belt driven by at least two rollers so that an upper belt functions as transport surface and a lower belt functions as return, wherein the frame has an upper segment extending substantially above the upper belt and a lower segment extending substantially under the upper belt, wherein the upper segment has at least two upper standing walls with a mutual spacing which, at least at the position of the upper belt, is smaller than the width of the conveyor belt, and wherein the lower segment has at least two lower standing walls with a mutual spacing which is greater than the width of the conveyor belt, wherein the upper belt is supported on either side by a plate extending respectively from below the upper belt to an outer side of the lower standing wall.