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: Air enters each pass of a two-pass air heater in the same direction with respect to gas flows. Bypass air conduits connect each tube bundle of a first tier to the tube bundle of a second tier of adjacent gas ducts and are located between inlet and outlet air conduits and have common walls therewith.The bypass air conduits connect the tube bundles of all the gas ducts in a single closed (ring) circuit. It is possible to set the gas ducts either along the radius on a single circumference or in a joined-up arrangement with the gas ducts divided into two halves by a vertical partition.In an alternative embodiment, the bypass air conduits connect the tube bundles of all the gas ducts in an open circuit, the tube bundles of both tiers of the extreme gas ducts are half as wide and are arranged to form a single pass with respect to the air flow.The thermal efficiency of the air heater is the same as that of a Z-criss-cross type air heater.

Abstract: A device for heating air by flue gases in steam boilers and furnaces, comprises a supply flue, sections mating therewith, and a device for protection of heat-exchange tubes against abrasive wear arranged in the flue. Each section comprises heat-exchange tubes attached to tube plates. The device for protection of the heat-exchange tubes against abrasive wear incorporates at least one screen formed by corrugated sheets facing each other and mating along the lines of contact of sheet convex portions, whereby cells are made up.

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.