For example, as a fuel gas, a gas chiefly containing hydrogen (hereinafter also referred to as a hydrogen-containing gas) is supplied to a fuel cell. For use as the hydrogen-containing gas, in general, a reformed gas produced by obtaining a reformed raw fuel from a hydrocarbon fuel, such as methanol or a fossil fuel, e.g., LNG, and processing the reformed raw material gas by steam reforming, partial oxidation reforming, or autothermal reforming, or the like, is used.
For example, in the reforming apparatus disclosed in Japanese Laid-Open Patent Publication No. 2003-192304, as shown in FIG. 14, pure water supplied to an evaporator 1 is evaporated inside the evaporator 1 by a combustion exhaust gas. Then, the resulting water vapor is supplied to a reformer 3 through a heat exchanger 2. The evaporator 1 includes an evaporation heat exchanger 4 having a heat exchange unit for evaporating water to produce water vapor, as a result of the combustion exhaust gas, which acts as a heat exchange gas. The evaporation heat exchanger 4 includes a plurality of pipes 5 disposed in parallel, together with an inlet manifold 6 and an outlet manifold 7 serving as openings at an upstream end and a downstream end of the pipes 5. Further, a fabric material 8, for preventing protrusion of the pipes 5, is disposed inside the inlet manifold 6.
In the reforming apparatus, the evaporator 1, the heat exchanger 2, and the reformer 3 are arranged in a flow direction of the water vapor, in the direction indicated by the arrow X. In practice, although not shown, the evaporator 1, the heat exchanger 2 and the reformer 3 are connected by pipes. Since plural pipes are used, the overall size of the reforming apparatus tends to be large. Further, heat tends to radiate easily from the pipes, and as a result of the heat energy loss due to heat radiation, heat efficiency is lowered.
Further, in the evaporator 1, water flows along the pipes 5 in the direction indicated by the arrow X, whereas the combustion exhaust gas is supplied in the direction indicated by the arrow Y, perpendicular to the direction of the arrow X. At this time, in order to reliably produce water vapor by evaporating pure water passing through the pipes 5, it is necessary to supply a predetermined amount of heat energy from the combustion exhaust gas to the pure water. Therefore, in order to ensure that heat exchange is performed between the pure water and the combustion exhaust gas for a sufficient period of time, the pipes 5 are required to be considerably long in the direction of the arrow X. Thus, the size of the evaporator 1 tends to be significantly large in the direction indicated by the arrow X, such that a reduction in the overall size of the reforming apparatus cannot be achieved.