A fluidized bed separator (1) includes a feed section (4) between an upper separation chamber (19) and a main separation chamber (6). The feed section (4) has one or more feed pipes (11) extending horizontally and transversely with respect to a body wall (10) of the fluidized bed separator (1). The one or more feed pipes (11) are positioned completely and entirely underneath the inclined plates (17). An external oversize protection apparatus (3) which is separate from and external to the body wall (10) may be operatively coupled to the one or more feed pipes (11). One or more lamella cartridges (49) may be provided within channels (18) of the upper separation chamber (19), and one or more breakaway plates (54, 55) may be inserted within channels (18) to prevent sanding and facilitate insertion and extraction of the lamella cartridges (49).