Chemical apparatus and process disinfecting – deodorizing – preser – Control element responsive to a sensed operating condition – Control element responds proportionally to a variable signal...
Reexamination Certificate
1998-05-26
2004-05-04
Johnson, Jerry D. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Control element responsive to a sensed operating condition
Control element responds proportionally to a variable signal...
C422S105000, C422S108000, C422S111000, C422S186220, C422S186220, C422S198000, C429S006000, C429S006000
Reexamination Certificate
active
06730271
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel reforming apparatus which converts a hydrocarbon crude fuel to a hydrogen-rich gaseous fuel through a reforming reaction and feeds a supply of the gaseous fuel to fuel cells. The present invention also pertains to a method of the same and a fuel-cells system with the fuel reforming apparatus incorporated therein.
2. Description of the Prior Art
Fuel cells convert the chemical energy of a fuel not via mechanical energy or thermal energy but directly into electrical energy and thereby realize a high energy efficiency. A well-known structure of the fuel cells includes a pair of electrodes arranged across an electrolyte layer. A supply of hydrogen-containing gaseous fuel is fed to one electrode or a cathode, whereas a supply of oxygen-containing oxidizing gas is fed to the other electrode or an anode. The fuel cells generate an electromotive force through electrochemical reactions proceeding on the electrodes. Equations (1) through (3) given below represent electrochemical reactions proceeding in the fuel cells. Equation (1) shows the reaction proceeding at the cathode, whereas Equation (2) shows the reaction proceeding at the anode. The reaction shown by Equation (3) accordingly proceeds as a whole in the fuel cells.
H
2
→2H
+
+2
e
−
(1)
(½)O
2
+2H
+
+2
e
−
→H
2
O (2)
H
2
+(½)O
2
→H
2
O (3)
The fuel cells are classified, for example, by the type of the electrolyte and the driving temperature. An oxidizing gas and a gaseous fuel containing carbon dioxide may be used in polymer electrolyte fuel cells, phosphate fuel cells, and molten carbonate fuel cells, because of their properties of the electrolytes. In these fuel cells, the air is generally used as the oxidizing gas, and the hydrogen-containing gas produced by steam reforming a hydrocarbon crude fuel, such as methanol or natural gas, as the gaseous fuel.
A reformer functioning as the fuel reforming apparatus is incorporated in a fuel-cells system including such fuel cells. The reformer converts the crude fuel into a gaseous fuel through the reforming reactions. By way of example, the following reforming reactions proceed in the reformer to steam reform methanol used as the crude fuel:
CH
3
OH→CO+2H
2
−90.0(kJ/mol) (4)
CO+H
2
O→CO
2
+H
2
+40.5(kJ/mol) (5)
CH
3
OH+H
2
O→CO
2
+3H
2
−49.5(kJ/mol) (6)
In the process of steam reforming methanol, the decomposition reaction of methanol expressed by Equation (4) proceeds simultaneously with the conversion reaction of carbon monoxide expressed by Equation (5). The reaction of Equation (6) thus occurs as a whole. Since the reaction for reforming the crude fuel is endothermic, an external heating unit, such as a burner or a heater, is attached to the reformer to supply the heat required for the endothermic reforming reaction.
When the heat required for the reforming reaction is supplied externally to the reformer, a large portion of the supply of heat is not used for the reforming reaction but is wasted. This lowers the energy efficiency of the whole system with the reformer. When the hot combustion gas from the burner supplies the heat required for the reforming reaction, for example, the hot combustion exhaust containing a considerable quantity of energy that has not been used for the reforming reaction is wastefully discharged from the reformer. In another example, when the heater is used as the heating unit, a considerable quantity of energy produced by the heater is used not to promote the reforming reactions but to heat a reaction vessel of the reformer.
In the method of supplying heat from the burner or the heater, when the quantity of the reforming reactions (that is, the quantity processed through the reforming reactions) is significantly varied with a significant change in amount of the crude fuel fed to the reformer, it is difficult to keep the internal temperature of the reformer within a desirable temperature range suitable for the reforming reactions and ensure the sufficient activity of the reforming reactions. When the amount of the crude fuel, such as methanol, fed to the reformer is increased to increase the quantity processed through the reforming reactions, the internal temperature of the reformer is lowered with the progress of the endothermic reforming reaction. The temperature decrease results in deactivating the reforming reaction. It may be considered that an increase in quantity of heat supplied from the burner or the heater prevents the temperature decrease in the reformer. This method, however, can not sufficiently follow the temperature variation due to an abrupt increase in quantity processed through the reforming reactions, since there is a limit in rate of heat transfer in the reformer.
When the amount of the crude fuel fed to the reformer is decreased to decrease the quantity processed through the reforming reactions, on the other hand, a decrease in heat consumed by the reforming reactions raises the internal temperature of the reformer. In case that the temperature increase causes the internal temperature of the reformer to exceed the desired temperature range, undesired reactions other than the reforming reactions expressed by Equations (4) through (6) given above proceed in the reformer and cause the gaseous fuel to be contaminated with undesirable products. The excessive increase in temperature of the reformer deteriorates the reforming catalyst included in the reformer and shortens the life of the reformer. It may be considered that a decrease in quantity of heat supplied from the burner or the heater prevents the temperature increase in the reformer. This method, however, can not sufficiently follow the temperature variation due to an abrupt decrease in quantity processed through the reforming reactions, since the reformer itself has a predetermined heat capacity.
Another known method of supplying the heat required for the reforming reaction feeds a supply of oxygen-containing oxidizing gas as well as a supply of the crude fuel to the reformer and causes the exothermic oxidation reaction to proceed with the endothermic reforming reaction in the reformer, in order to supply the heat required for the reforming reaction by the heat produced by the oxidation reaction (for example, JAPANESE PATENT LAYING-OPEN GAZETTE No. 4-160003). A reformer
134
shown in
FIG. 5
is an example of such known reformers. The reformer
134
has a reforming reaction unit
180
including a catalyst layer
181
. The catalyst layer
181
receives a supply of crude fuel gas containing, for example, methanol and a supply of the air ingested from outside via an air supply unit
190
. A temperature sensor
186
is disposed in the catalyst layer
181
. The driving state of a flow control valve
192
located in the air supply unit
190
is controlled, based on the temperature in the catalyst layer
181
measured by the temperature sensor
186
. The control of the driving state regulates the amount of the air fed to the catalyst layer
181
.
The amount of the air supplied to the catalyst layer
181
is regulated according to the observed temperature of the catalyst layer
181
. Regulation of the supply of the air fed to the catalyst layer
181
in order to keep the internal temperature of the catalyst layer
181
within a desired temperature range accordingly makes the heat consumed by the reforming reaction well balance the heat produced by the oxidation reaction and ensures the sufficiently high activity of the reforming reactions proceeding in the reformer
134
. In the reformer
134
of this structure, the heat required for the reforming reactions is supplied inside the reformer. This structure effectively reduces the quantity of heat that is not used for the reforming reactions but is wasted, and thereby ensures the high energy efficiency.
In the proposed structure where the oxidatio
Doroshenk Alexa A.
Johnson Jerry D.
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