PROBLEM TO BE SOLVED: To provide a compound steam boiler employing a chain stoker fire grate for solid fuel capable of minimizing imperfect combustion and maximizing heat transfer effects.SOLUTION: At an upper part of a combustion chamber 17 in which a solid fuel is combusted, an upper steam drum 1 is disposed which incorporates a number of smoke pipes 6 each for transferring a combustion gas. At both right and left ends of a lower part of the combustion chamber 17, lower water drums 2 are disposed and a fixed interval therebetween is kept via a fin member for keeping air-tightness within the combustion chamber and increasing a heat transfer area. The compound steam boiler also comprises a number of vertical curved pipes 3 keeping a vertical state in a direction from the lower water drums 2 to the upper steam drum 1, and a chain stoker fire grate 12 which is disposed in lower parts of the lower water drums 2 and forms a bottom of the combustion chamber 17. A number of vertical curved pipes 3 are formed from a plurality of vertical curved pipe groups that are connected to the upper steam drum 1 in such a manner that paths become different, and a passage 15 for a combustion gas flow is provided between the different paths.SELECTED DRAWING: Figure 2
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