Process air unit for heating process air

A process air unit for heating a process air, comprising:

• a process air duct through which a process air can flow and which comprises, in the region of a first duct end, an inlet opening for taking in a process air to be heated and, in the region of a second duct end opposite the first duct end, an outlet opening for discharging a heated process air;
• a combustion chamber for burning a combustion air, which is arranged at least partially within the process air duct so that the combustion chamber is overflowed by the process air and thereby transfers heat to the process air;
• and
• a tube bundle arrangement being connected to the combustion chamber and including at least one tube bundle having a plurality of tubes through which the flue gas from the combustion chamber can flow,
• wherein the plurality of tubes of the at least one tube bundle is oriented transversely to the process air flow direction and is arranged at least partially within the process air duct so that they are overflowed by the process air and thereby transfer heat from the flue gas to the process air, and
• wherein the tube bundle arrangement is arranged, with respect to the process air flow direction, upstream of the combustion chamber in the process air duct.