A moving bed reactor for the treatment of fluid in a countercurrent process includes a reactor vessel having, in an upper region thereof, an inlet for receiving particulate material and an outlet for discharging treated fluid, the reactor vessel also having, in a lower region thereof, a downward tapering first funnel leading to an outlet, the first funnel guiding the particulate material to the outlet for discharge from the reactor vessel, the first funnel being formed by wall sections which mutually overlap in louvre fashion to create slot-shaped passages for the fluid to be treated to enter the vessel. A second funnel is provided, surrounding the first funnel and communicating with the slot-shaped passages, the second funnel having an inlet for receiving the fluid to be treated, there being provided an annular canal between the second funnel and the first funnel at the lower regions thereof, which annular canal communicates with the particulate discharge outlet so that any particulate material which enters the second funnel by the slot-shaped passages is guided to the particulate discharge outlet through the annular canal.