JPH0242762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an evaporator that is a component of a methanol reformer.

In general, a methanol reformer consists of an evaporator heated by a burner, a superheater, and a reforming catalyst bed. First, the methanol aqueous solution is gradually evaporated while flowing through the evaporator, and this is turned into superheated steam at about 300℃ in the superheater. This is then supplied to the reforming catalyst bed and converted into hydrogen-rich gas. This hydrogen-rich gas is supplied to the fuel electrode as a fuel gas of the fuel cell, and a cell reaction is performed between it and air, which is supplied as an oxidant to the air electrode, to generate electric power.

As shown in FIG. 3, a conventional evaporator consists of a main coiled tube (A), an inlet tube (B), and an outlet tube (C) before and after the coiled tube (A), all of which have the same diameter.
However, since the burner heat is sent downward rather than upward, the amount of evaporation in the upper coil section is large, and the volume of gas and liquid increases significantly as it moves downward. Therefore, with coils having the same diameter, the flow velocity becomes high, and there is a risk that the steam will condense due to insufficient heat received at the lower part of the coil.

This occurs especially when the amount of supplied liquid is increased by using a coil with a small number of turns due to the demand for miniaturization. There was a problem that the necessary evaporation temperature could not be obtained.

The present invention solves the above problems and provides an evaporator that can completely vaporize an aqueous methanol solution even if the amount of the aqueous methanol solution supplied is increased.

In this invention, the diameter of the coiled tube of the evaporator is gradually increased from the upper part near the burner to the lower part.
The diameters of the inlet tube leading to the coiled tube for the aqueous methanol solution and the outlet tube for the evaporated gas to the superheater are made to match the diameters of the upper and lower portions of the coiled tube, respectively.

According to this invention, even if the volume of gas and liquid increases due to evaporation in the upper part of the coiled tube, this is absorbed in the lower part, which is gradually expanding in diameter, so that the flow velocity does not increase significantly. The amount of heat received does not decrease even at the bottom of the tank, so the gas phase does not condense as in the conventional case.
Despite its small size, even if the amount of methanol aqueous solution supplied increases, it is possible to smoothly evaporate the methanol aqueous solution.

Embodiments of the invention are described below with reference to the figures.

The methanol reformer has a burner 2 in the upper part of a heat-insulating outer can 1, and inside the outer can 1, there is an annular chamber 3 filled with a reforming catalyst inside and outside double walls, and an annular chamber concentrically with this annular chamber. A superheater 4 and an evaporator 5 are arranged.

As shown in FIG. 2, the evaporator 5 has a coiled tube 6 whose diameter gradually increases from the top near the burner 2 to the bottom, and this coiled tube 6 is divided into three sections, each of which The diameter of the upper coil 6 ₁ is the same as that of the liquid introduction tube 7 (this is taken as 1), and the diameter of the middle coil 6 ₂ is 1.5.
The ratio of the tube cross-sectional area is 1 for _the upper coil, 2.25 for the middle coil, and 4 for the lower coil. The steam outlet pipe 8 leading to the superheater 4 has the same diameter as the lower coil ₆₃ . The coils 6 ₁ , 6 ₂ , 6 ₃ having different diameters are connected using appropriate connectors.

Methanol aqueous solution (methanol:water = 1 mol%:
1.3 mol %) passes through the introduction tube 7 and gradually evaporates while flowing down into the coiled tube 6 from above. In this case, the amount of evaporation is large in the upper coil 6 ₁ near the burner 2, and the gas-liquid volume increases significantly, but this is absorbed by the intermediate coil 6 ₂ , which has a sequentially larger diameter, and then the lower coil 6 ₃ , so that the flow rate does not increase significantly. The amount of heat received by the lower coil ₆₃ , which is separated from the burner, does not decrease, and therefore the gas phase does not return to the liquid phase.

This steam is sent to the superheater 4 through the outlet pipe 8,
At this point, it becomes superheated to about 300°C and enters the annular chamber 3 through the conduit 9. In this chamber 3, it is converted into hydrogen-rich gas (H ₂ :CO ₂ =80:20) by the action of a reforming catalyst, and is supplied from the delivery pipe 10 as fuel gas for the fuel cell. The blower 11 provides fuel air to the burner 2 and sends the heat downward.

An example of the design of a methanol reformer is that the external dimensions are 400 mm in height, 200 mm in diameter, and the height of the evaporator coil portion 6 is 100 to 150 mm. A reformer with this capacity can be used as a fuel gas source to supply a small fuel cell with an output of about 3 to 5 kW.

As described above, according to the present invention, the coil portion of the evaporator gradually expands in diameter from the upper part near the burner toward the lower part, so that the increase in volume of the gas-liquid phase due to evaporation of the methanol aqueous solution can be absorbed. Since the flow rate is controlled and the amount of heat received by the lower coil does not decrease, the gas phase does not condense, and even if the amount of methanol aqueous solution supplied increases, it can be smoothly evaporated.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a methanol reformer equipped with an evaporator of the present invention, FIG. 2 is a front view of the evaporator of the present invention, and FIG. 3 is a conventional evaporator. 2: Burner, 3: Annular chamber, 4: Superheater, 5:
Evaporator, 6 ₁ , 6 ₂ , 6 ₃ : coils with different diameters,
7: Inlet pipe, 8: Outlet pipe.

Claims (1)

[Claims] 1. The diameter of the coiled tube is gradually increased from the upper part near the burner to the lower part, and the diameter of each of the inlet pipe leading to the coiled pipe for methanol aqueous solution and the outlet pipe leading to the superheater for evaporated gas is increased respectively. An evaporator for a methanol reformer, characterized in that the diameters of the upper and lower portions of the coiled tube match each other.