Multipass corrosion-proof air preheater

The herein disclosed multipass corrosion-proof preheater comprises a plurality of passes. The passes are formed by bundles of heat-transfer tubes for the passage of heating gases and interconnected in series, with respect to air supply, by means of connecting air lines. Air is supplied to the tubefield of the heat-transfer tubes via air supply line accommodating a device designed for high-temperature preheat of part of the air supplied to the tubefield of the heat-transfer tubes of the first pass. The air preheater further comprises a bypass air line serving to communicate the air line with the connecting air line via mixer mounted in the latter. In addition, the air preheater is provided with a device for low-temperature preheat of air, mounted in the air line upstream of the device when viewed in the direction of air flow. The bypass air line is connected to the air line between the devices for low- and high temperature air preheat.