Small once-through boiler

Abstract

A small once-through boiler can avoid burning caused due to excessive heating of water pipes and burning around a fire hole of a burner in particular and heighten the heat load of a combustion chamber to further reduce the size of the system as compared with a prior art boiler. In the small once-through boiler, at least one regenerative burner system 20 is provided in a combustion chamber 1, the regenerative burner system 20 carrying out supply of combustion air A and exhaust of combustion gas E through a regenerator 22 and relatively changing flows of the combustion gas E and the combustion air A with respect to the regenerator 22 so as to supply the combustion air A via the regenerator 22 heated by heat of the combustion gas. Water pipe group 4 is provided apart from the combustion chamber wall surface 3 to form a passage 12 between the rear surface of the water pipe group 4 and the combustion chamber wall surface 3. Communicating openings 10 and 11 through which the combustion gas C passes are formed between adjacent water pipes at upper and lower ends of the water pipe group 4 so that a part of the combustion gas C can pass through the passage 12 provided at the rear of the water pipe group 4, whereby a part of the combustion gas C flows from the lower communicating openings 11 into the passage 12 to move upward and again flows from the upper communicating openings 10 into the combustion chamber 1.