PURPOSE: To provide an ultracritical variable pressure once-through type axial boiler constructed such that a temperature unbalanced state is not produced among groups of pipes at outlet part of evaporating pipes at a circumferential wall of a furnace as a degree of over-heating at the evaporating pipes at the circumferential wall of the furnace is increased. ;CONSTITUTION: This boiler comprises an intermediate pipe complex 21 of a circumferential wall of a furnace in which circumferential wall evaporating pipes 2 of a furnace 14 are divided into an upper furnace circumferential wall evaporating pipe 15 and a lower furnace circumferential wall evaporating pip 16, respectively. The evaporating pipe coming out of the intermediate pipe complex 21 of the circumferential wall of the furnace as the upper furnace circumferential wall evaporating pipe 15 is provided with an orifice 20. Although a friction loss is increased at the upper furnace circumferential wall evaporating pipe 15, an entire pressure loss is increased to reduce a flow rate and further to cause a temperature difference to be increased, the orifice 20 is installed there to control the flow rate in correspondence with a thermal absorption distribution at the upper furnace circumferential wall evaporating pipe 15, and then an enthalpy level of the fluid at the outlet of the furnace is made uniform.;COPYRIGHT: (C)1996,JPO
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