MULTIFLOW TUBULAR AIR HEATER

A multiflow two-pass tubular air heater has tube bundles (27,28) extending vertically along a gas flow path in two tiers in each of a plurality of gas ducts (29,30) and comprises air conduits supplying air into the space between the tubes in each of the tube bundles of a first tier in the same general direction with respect to the gas flow. Air conduits exhaust air from the space between the tubes in each of the tube bundles of a second tier in the same direction. Connecting air conduits (26) have separating partitions extending over their height to connect in the said general direction each of the tube bundles in the first tier with the tube bundle in the second tier of an adjacent gas duct. The first (29) and last (30) gas ducts in the direction of air flow have tube bundles of a width equal to a half of the width of the remaining gas ducts and the tube bundles in their first and second tiers are joined in each of the said gas ducts into a single air conduit (31,34). The supplying air conduit (31) of the first gas duct (29) and the exhausting air conduit (34) of the last gas duct (30) and also the adjoining connecting air conduit are connected to both tiers of the tube bundles in the said gas ducts and the connecting air conduits of the last gas duct (30) connecting it to the bundles in the first tier of the last but one duct.