Water-tube boiler

Abstract

Boiler efficiency is further improved and the whole boiler body is slimmed down by totally improving heat transfer surfaces confronting gas flow passages, i.e., by forming the heat transfer surface structure into three stages, and moreover by making effective use of the whole heat transfer surfaces of water tubes equipped with fully circumferentially finned water tubes. The water-tube boiler includes: an annular first water tube array made up of a plurality of water tubes and having a first opening; an annular second water tube array made up of a plurality of water tubes and having a second opening, the second water tube array being arranged outside the first water tube array; a combustion chamber provided inside the first water tube array; and a gas flow passage leading from the first opening to the second opening and defined between the two water tube arrays, wherein heat transfer surfaces confronting the gas flow passage are structured into a high-temperature heat transfer surface structure, a middle-temperature heat transfer surface structure, and a low-temperature heat transfer surface structure, as viewed from an upstream side along gas flow.