Reactor

A reactor comprising:

• a reaction tube aligned in an up-down direction and comprising, in a bottom section thereof, a catalyst supporter receiving packed catalyst grains and allowing a processed gas to flow therethrough;
• and
• a burning unit configured to heat an outer face of the reaction tube,
• wherein the reaction tube has a cylindrical catalyst support face that is in contact with the catalyst grains in the reaction tube and that have, in the up-down direction, a plurality of engaging recesses each capable of receiving a portion of the catalyst grain in contact with the catalyst support face in such a manner that the portion of the catalyst grain is fitted into the engaging recess,
• wherein the reaction tube comprises an outer tube having a closed bottom section and a supported upper end section, and an inner tube having an open bottom section and located inside the outer tube such that an upper end section of the inner tube is supported,
• wherein the catalyst grains are packed between the outer tube and the inner tube,
• wherein the catalyst supporter is located in a bottom section of the inner tube,
• wherein the burning unit is configured to heat an outer face of the outer tube,
• wherein the inner tube has an outer face serving as the catalyst support face and having the engaging recesses, and
• wherein the outer tube has an inner face serving as the catalyst support face and having a flat shape.