Abstract: 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.

Abstract: In an air heater, an initial group of passes on the airside is arranged in the form of a package wherein the passes consisting of banks of tubes are connected in parallel with the uptake gases.The passes of the package are located predominantly at the same horizontal level, are made of tubes of the same length and run in a zone of the same gas temperatures which is dangerous insofar as corrosion can be provoked therein.The width of the packaged passes progressively increases directly with the increase in the rates of air flow through the passes, and a feeding air duct admitting the last inflow of cold air is connected downstream of the last and widest pass to the connecting air duct serving the rest of the passes of the air heater.In an apparatus like this one, assembled from standard components, minimum overall dimensions and low weight are combined with high thermal efficiency.

Abstract: In an air heater, mixers of hot and cold air are built into circulating air ducts between the passes of that portion of the air heater which is exposed to the danger of corrosion. Said mixers are provided in the form of tubes perforated lengthwise and located frontally in the respective pass. Headers serving the mixers are connected to cold air feeding ducts.Perforations the tubes of each mixer are provided with serve to direct jets of cold air at right angles to the flow of hot air.The tubes of the mixer are blanked off at the opposite ends of the adjacent tubes while the open ends of these tubes are connected to different cold air headers. Used as the tubes of a mixer can be a bunch of frontal tubes in the respective passes of the air heater.The air heater disclosed offers protection against corrosion by heating a mixture of cold and hot air to a minimum temperature, and said protection is achieved in a compact light-weight apparatus requiring minimum labor for its fabrication.