The invention provides a dryer for drying particulate material, comprising at least one substantially vertical elongate container having: an upper inlet for receiving a charge of moisture containing particulate material; a lower outlet for discharging dried particulate material, whereby the particulate material travels under the influence of gravity from the inlet to the outlet; at least one substantially vertical gas permeable wall through which a drying gas can pass to contact the particulate material; the dryer also comprising at least one plenum on an exterior surface of the at least one gas permeable wall, covering ingress and egress openings within the at least one gas permeable wall.