1. Field of Invention
The present invention relates to a reformer for reforming reformate fuel into a desired fuel such as hydrogen-rich gas, and more particularly to an apparatus for controlling the temperature of such reformate fuel. This invention also relates to a method of controlling a reformer using the apparatus.
2. Description of Related Art
A reformer for generating gas mainly composed of hydrogen gas by using methyl alcohol (methanol) and water as reformate fuel materials is known. In this reformer, a copper alloy or the like is used as catalyst, and the active temperature of the catalyst is, for example, 280xc2x0 C., and when the temperature is lower than the activation temperature, the methanol is not reformed sufficiently, and the amount of residual methanol in the reformate gas increases. Moreover, because the reforming reaction of methanol is an endothermic reaction, heat is supplied from an external source in order to promote the reforming reaction as well as to maintain the catalyst temperature.
The heating method includes, aside from heating by a burner, a method of generating heat by an oxidation reaction and transferring the heat to the reforming portion. The latter method is a so-called partial oxidation reaction method, in which, for example, air is mixed in methanol vapor, and it is oxidized in the presence of catalyst to generate hydrogen, and the heat generated at this time is utilized. Therefore, by utilizing this partial oxidation reaction, the heat accompanying reforming reaction is replenished by the partial oxidation reaction, and the heat absorption and heat generation are balanced, so that heating from an external source is not necessary. In this method, however, only the thermal balance is achieved in the reforming portion so as not to cause temperature changes due to reforming or oxidation, and it is not intended to be applied to setting of the reforming portion to a desired temperature.
That is, to set the temperature of the reforming portion to an appropriate temperature for the reforming reaction or catalyst activity, heating from an external source is required. Accordingly, in this kind of reformer, by the heat generated in the combustion portion, steam of a specified temperature is obtained from a mixture of methanol and water, and the steam is supplied into the reforming portion.
When this reformer is used, for example, to generate fuel gas in a fuel cell, it is necessary to control the reaction in the reformer depending on variation of load of the fuel cell. That is, along with an increase of load, the production of reformate gas must be increased. When the load drops, the production of reformate gas must be decreased. To increase or decrease the generation of reformate gas, it is required to increase or decrease the material to be supplied to the reforming portion, that is, the mixed steam of methanol and water, but for this purpose it is necessary to increase or decrease the heating calorific value for generating the mixed steam of methanol and water at a desired temperature.
The amount of heat required to generate a mixed steam of methanol and water can be controlled by increasing or decreasing the amount of fuel for heating such as methanol. However, the burner or heat generating device using an oxidation catalyst conventionally used as a heating device for heating the mixture of methanol and water is low in the response of heat generation, and it is hence difficult to control heating promptly coping with load fluctuations in such known reformers. That is, in the event of a sudden load increase, the heat generation is insufficient for the amount of methanol and water to be heated, and the steam temperature or catalyst temperature drops. Consequently, the reforming reaction becomes dull, or the residual methanol amount in the reformate gas increases, and the performance of the fuel cell declines. To the contrary, if the load drops suddenly, due to delay in drop of heating amount, the steam temperature or catalyst temperature may elevate excessively, and the activity of the catalyst is lowered.
To eliminate such disadvantage, the invention disclosed in Japanese Patent Publication No. HEI 7-105240 is intended to control the temperature depending on load fluctuations by controlling the steam ratio. That is, by decreasing the amount of water mixed as reformate fuel, the amount of heat required for heating and evaporation drops, and the temperature of the mixed steam of methanol and water as reformate fuel rises. However, when the amount of water is increased, the amount of heat required for raising the temperature and evaporating increases, so that the temperature of the mixed steam of methanol and water as reformate fuel declines.
The method of temperature control disclosed in this publication comprises changing the amount of water, changing the amount of heat consumed or absorbed by the water, and thereby controlling the temperature. Therefore, as compared with the method of controlling the heat generation amount by changing the amount of fuel for combustion, the response of temperature control is improved. This published method, however, consumes part of the heat generated for heating and evaporation on the condition that the heat generation by combustion of the fuel is constant. For example, in the case of lowering the reformate gas amount due to small fluctuations in the fuel cell, the amount of heat generation by combustion is maintained higher than the amount of heat determined theoretically. As a result, the combustion is controlled to generate more heat than the heat actually required for reforming the reformate fuel, and the fuel is consumed more than necessary, and thus the fuel economy drops. Also in this published invention, spent fuel containing residual hydrogen is used as a part of the fuel for heating the reformate fuel, and the reformate fuel is heated by burning the residual hydrogen by a burner. Yet, if the reformate fuel is heated by burning the residual hydrogen by a burner, the amount of heat is not controlled. Thus, because the temperature is controlled by the steam ratio, the consumption of the heating fuel containing residual hydrogen that is required is more than the amount needed for heating of reformate fuel. In this respect, also, the residual hydrogen is consumed excessively, and thus this known method has been susceptible to improvement in a more effective use of fuel.
The invention has been made in the light of the above-described background. It is an object of the present invention to provide a control apparatus that can control combustion fuel for heating reformate fuel, control the reformate fuel temperature to a desired temperature suitable for the reforming reaction, and utilize the reformate fuel effectively.
To achieve this object, the invention uses unreacted flammable gas in the emission resulting from energy conversion of reformate gas for heating of reformate fuel, and controls the amount of unreacted flammable gas for combustion for heating at an appropriate amount depending on the required amount of reformate fuel, as well as on other factors.
In a first aspect of the invention, a control apparatus is provided for controlling a reformer. The reformer can comprise a reformate gas generator that gasifies a reformate fuel by a reforming reaction, the combustion portion that heats the reformate fuel by burning the emission including unreacted flammable gas generated at the time of conversion of the reformats gas obtained from the reformate gas generator into another energy form by an energy converter. The control apparatus comprises a reformed amount assessing device that assesses the amount of reformate fuel to be gasified, and an emission amount assessing device that assesses the amount of emission to be supplied into a combustion portion on the basis of the assessed reformate fuel amount.
Therefore, according to the invention, when the amount of the reformate fuel varies depending on fluctuations of load in the energy converter or the like, the amount of emission including the unreacted flammable gas to be supplied into the reformer accordingly is assessed. By supplying the assessed amount of emission into the reformer, the unreacted flammable gas contained in the emission burns, and the reformate fuel is heated. In this case, because the amount of the reformate fuel and the amount of flammable gas to burn correspond to each other, the reformate fuel is heated to a desired temperature. As a result, the flammable gas is not consumed more than necessary, and the reformate fuel temperature can be controlled to a desired temperature. Moreover, the reforming reaction proceeds desirably, and the reformate gas of high quality is obtained.
Moreover, in other embodiments, the control apparatus can also comprise a heat detector that detects a shortage in the amount of heat for burning the emission including the unreacted flammable gas in the combustion portion necessary for heating the reformate fuel, and a fuel supplying device that supplies the heating fuel into the combustion portion if a shortage of heat is detected.
According to such embodiments, if the necessary amount of heat to be generated in the combustion portion exceeds the amount of heat obtained by combustion of unreacted flammable gas, the heating fuel is supplied into the combustion portion. Therefore, the heating fuel is used only when the amount of heat generated is insufficient by the use of unreacted flammable gas only, and the unreacted flammable gas is used to the maximum extent for heating of the reformate fuel, so that the consumption of heating fuel is decreased, and the energy efficiency is enhanced on the whole.
Additionally, in embodiments, the control apparatus can also comprise a combustion portion temperature detector that detects the temperature of the combustion portion, and a heating fuel adjuster that adjusts (decreases) the amount of heating fuel consumed in the combustion portion on the basis of the detected temperature of the combustion portion.
According to such embodiments, if the temperature of the reformate fuel is higher than necessary, supply of heating fuel into the combustion portion is stopped. As a result, it is possible to prevent a drop of energy efficiency due to excessive combustion of the heating fuel, or a drop of reforming reaction efficiency due to an excessive elevation of temperature of the reformate fuel.
Preferably, the control apparatus further comprises a reformate fuel temperature detector that detects the temperature of the reformate fuel heated in the combustion portion, and a heating fuel arrester that stops supply of heating fuel to the combustion portion when the detected temperature of the reformate fuel exceeds a predetermined temperature.
In such embodiments, when the temperature of the combustion portion becomes higher than the predetermined temperature, the amount of material consumed in the combustion portion decreases, and the heating amount in the combustion portion decreases. Accordingly, abnormal temperature rise of the combustion portion and related damage can be prevented.
In addition to the constitution of the first aspect, the control apparatus can also comprise a flammable gas amount estimator that estimates the amount of unreacted flammable gas in the emission, on the basis of the reformate fuel amount reformed to supply into the energy converter and the load of the energy converter.
In such embodiments, the amount of the unreacted flammable gas used in heating of reformate fuel is more accurate, control of the heating temperature of the reformate fuel is precise, and the unreacted flammable gas can be utilized effectively.
Preferably, the control apparatus further comprises a reformate fuel temperature detector that detects the temperature of the reformate fuel supplied for the reforming reaction, and a temperature adjuster that adjusts the emission amount to be supplied into the reformer on the basis of the detected temperature of the reformate fuel.
According to such embodiments, when the temperature of the reformate fuel is low, or high, the emission amount, that is, the unreacted flammable gas amount, consumed can be increased or decreased. As a result, the temperature of the reformate fuel is adjusted, and a suitable temperature is obtained.
In addition to the constitution of the first aspect, it may also comprise a delay adjustor that adjusts the emission amount to be supplied to the reformer, on the basis of the time delay until the reformate fuel supplied in the reformer is gasified.
According to such embodiments, prior to sufficient supply of reformate fuel, if the unreacted flammable gas is burned relatively much, or to the contrary if the reformate fuel decreases, it is possible to avoid a decrease of the combustion amount of unreacted flammable gas in advance, so that the heating temperature of the reformate fuel is optimized.
In addition to the constitution of the first aspect, the control apparatus can also comprise a combustion aid gas amount determiner that determines the amount of a combustion aid gas for burning the flammable gas in the emission supplied into the reformer, on the basis of the amount of the unreacted flammable gas supplied into the reformer.
According to such embodiments, the combustion aid gas is supplied into the reformer depending on the amount of the flammable gas supplied for heating the reformate fuel. As a result, the rate of two gas amounts is appropriate, and a desired heating calorific value is obtained, so that the heating temperature of the reformate fuel is optimized.
The control apparatus can further comprise a heating temperature detector that detects the temperature for heating the reformate fuel to be supplied for the reforming reaction, and a temperature adjuster that adjusts the amount of combustion aid gas to be supplied into the reformer on the basis of the detected heating temperature.
According to such embodiments, when the heating temperature is low, for example, the combustion aid gas amount is decreased and the heat taken away by the combustion aid gas is decreased, so that the temperature of the reformate fuel is raised. When the heating temperature is high, for example, the combustion aid gas amount is increased and the heat taken away by the combustion aid gas is increased, so that the temperature of the reformate fuel is lowered. As a result, the heating temperature of the reformate fuel is optimized.
The control apparatus can further comprise a delay adjustor that adjusts the combustion aid gas amount to be supplied into the reformer on the basis of the delay until the reformats fuel supplied into the reformer is gasified.
According to such embodiments, the heat value given to the reformate fuel by combustion of unreacted flammable gas is changed by the amount of combustion aid gas, and this change occurs depending on the delay of supply of reformate fuel, or on the delay of decrease of supply amount. As a result, the reformate fuel can be heated to an appropriate temperature.
Preferably, the control apparatus can also comprise an A/F detector that detects the ratio of the flammable gas amount to be consumed for heating the reformate fuel and the amount of combustion aid gas for burning the flammable gas, and an A/F adjuster that adjusts the emission amount to be supplied into the reformer.
According to such embodiments, therefore, a surplus or shortage of combustion aid gas amount is adjusted, and the unreacted flammable gas is burned as desired, so that the heating temperature of the reformate fuel is optimized.
Preferably, the control apparatus can comprise a first temperature detector that detects the temperature at the supply side of combustion aid gas of the combustion portion, a second temperature detector that detects the temperature at the exhaust side of the combustion portion, and a combustion aid gas amount controller that increases the supply amount of the combustion aid gas when the temperature at the supply side of combustion aid gas detected by the first temperature detector is higher than the temperature at the exhaust side detected by the second temperature detector, and that decreases the supply amount of the combustion aid gas when the temperature at the supply side of combustion aid gas detected by the first temperature detector is lower than the temperature at the exhaust side detected by the second temperature detector.
According to such embodiments, when the temperature at the inflow side of the combustion portion is high, the supply amount of combustion aid gas increases, and the amount of heat taken away by the combustion aid gas increases and the combustion temperature is lowered. To the contrary, when the temperature at the exhaust side is high, the supply amount of combustion aid gas is decreased, and the amount of heat taken away from the inflow side of the combustion aid gas is decreased, such that the heat value sent to the exhaust side declines, the temperature at the inflow side of the combustion aid gas elevates, and the temperature at the exhaust side drops. Ultimately, the temperature in the inflow side and exhaust side of the combustion aid gas is balanced, and local overheating is prevented.
A second aspect of the invention provides a control apparatus for a reformer. The reformer can comprise a reformate gas generator that gasifies a reformate fuel by a reforming reaction, and a combustion portion that heats the reformate fuel and supplies into the reformate gas generator by burning the emission including the unreacted flammable gas generated at the time of conversion of the reformate gas by the reformate gas generator into energy of other form by an energy converter. The control apparatus comprises a reformed amount assessing device for assessing the amount of reformate fuel to be gasified; a flammable gas amount assessing device that assesses a necessary amount of flammable gas supplied into the combustion portion on the basis of the assessed amount of reformate fuel; and an emission amount assessing device that assesses the emission amount to be supplied into the combustion portion on the basis of the assessed necessary amount of flammable gas.
According to the second aspect, the amount of the reformate fuel to be gasified is assessed depending on the load at the energy converter or the like, and the amount of flammable gas necessary for heating the reformate fuel is assessed on the basis of the assessed reformate fuel amount. The emission amount including the necessary amount of flammable gas is assessed. Therefore, the unreacted flammable gas for heating the reformate fuel can be used, and the reformate fuel is heated appropriately by the unreacted flammable gas, so that a favorable reforming reaction takes place, thereby obtaining a reformate gas of high quality. At the same time, the fuel can be utilized effectively.
In addition to above-described embodiment of the second aspect, the control apparatus can further comprise a combustion aid gas amount assessing device that assesses the amount of combustion aid gas to be supplied together with the unreacted flammable gas into the reformer, on the basis of the amount of flammable gas assessed by the flammable gas assessing device.
According to such embodiments, the unreacted flammable gas supplied together with emission can be effectively burned so that the heating temperature of the reformate fuel can have a desired temperature, the temperature of the reformate fuel and the accompanying reforming reaction are favorable, and a reformate gas of high quality is obtained.
A third aspect of the invention relates to a control apparatus for a reformer. The reformer can comprise a reformate gas generator that gasifies a reformate fuel by a reforming reaction, and a combustion portion that bums a combustion material, heats the reformate fuel and supplies it into the reformate gas generator. The control apparatus comprises a target combustion temperature setting device that sets the target combustion temperature in the combustion portion on the basis of the target temperature of the reformate fuel, and a combustion material amount setting device that sets the amount of combustion material to be consumed in the combustion portion on the basis of the target combustion temperature determined in the target combustion temperature setting device.
According to the third aspect, because the amount of combustion material supplied into the combustion portion is set on the basis of the target combustion temperature, an abnormally high temperature in the combustion portion is prevented, and damage of the combustion portion is avoided. Moreover, because the target combustion temperature is determined on the basis of the target temperature of the reformate fuel, the reforming combustion temperature is optimized, and the reforming reaction takes place efficiently.