Device for producing expanded granulated material

A device for producing an expanded granulated material from mineral material in the form of grains of sand with an expanding agent, the device comprising

• a furnace with a substantially vertically positioned furnace shaft having an upper end and a lower end,
• wherein a conveying section extends between the two ends and passes through a plurality of heating zones arranged separately from one another in a conveying direction,
• wherein the heating zones each comprise at least one heating element which can be controlled independently of one another in order to heat the material at least to a critical temperature and to expand the sand grains,
• wherein furthermore at least one feeding means is provided, which is adapted to feed at least the unexpanded material at one of the two ends of the furnace shaft into the furnace shaft in the direction of the other of the two ends of the furnace shaft in order to expand the material, as viewed in the conveying direction, in the last half of the conveying section,
• wherein at least one directing element is provided, which is arranged at least in sections in the furnace shaft, wherein the directing element forms a gap with an inner wall of the furnace shaft at least in the region of the one of the two ends of the furnace shaft,
• wherein the at least one feeding means is adapted for feeding the unexpanded material into the gap,
• wherein releasable fastening means are provided for the at least one directing element in order to be able to remove the at least one directing element from the furnace shaft and reinsert it as required.