Furnace

A furnace for the thermal treatment of fibers, comprising:

• a) a furnace housing;
• b) a process space which is located in an interior space of the furnace housing and is delimited by a process space housing having a process space atmosphere and into which a material to be treated can be introduced, the process space housing comprising an inlet opening formed therein, wherein the material passes through the inlet opening into the process space to be treated;
• c) a heating system having a heating element located inside the process space housing and by means of which a process space atmosphere present in the process space can be heated;
• d) an insulation space existing between an interior side of the furnace housing and an exterior side of the process space housing, the insulation space housing an insulation layer which thermally insulates the process space, the insulation space comprising at least one intermediate wall dividing the insulation space into at least two insulation sections,
• e) a plurality of closable openings formed in an exterior surface of the furnace housing, each closable opening having a respective insulation section accessible therethrough to allow for the insulation layer in the respective insulation section to be supplemented
• wherein
• f) the insulation layer is an insulating bed composed of a solid particulate material that is configured adjacent to the process space housing such that at least a portion of an exterior of the process space housing adjoins the insulation layer and at least a portion of an interior side of the process space housing bounds the process space and process space atmosphere.