Combustion – Process of combustion or burner operation – In a porous body or bed – e.g. – surface combustion – etc.
Reexamination Certificate
1998-12-18
2001-10-16
Lazarus, Ira S. (Department: 3743)
Combustion
Process of combustion or burner operation
In a porous body or bed, e.g., surface combustion, etc.
C431S268000, C431S170000, C060S723000
Reexamination Certificate
active
06302683
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for igniting And controlling a catalytic combustion chamber, wherein the combustion chamber comprises a first catalytic reactor and at least a second catalytic reactor arranged in series with the first catalytic reactor. More particularly, the present invention relates to such a combustion chamber wherein the first catalytic reactor is heated to a temperature which exceeds or is equal to the ignition temperature of the catalytic reactor, whereafter a mixture of fuel and air is introduced to the catalytic reactor, whereby catalytic combustion is started in the first catalytic reactor.
Still more particularly, the present invention relates to a method for igniting a catalytic reactor and a catalytic combustion chamber comprising at least two serially arranged catalytic reactors.
BACKGROUND OF THE INVENTION
In order to achieve efficient combustion in a combustion chamber even at low temperatures, and to avoid the emission of high amounts of nitric oxides, it has been suggested that the combustion be performed in the presence of a catalyst. By using a catalyst it is thus possible to achieve almost complete combustion of fuel/air-mixtures in which the percentage of fuel is very low. In this way, operation of the catalytic combustion chamber can be very safe, since the gas mixture which is used is not inflammable at atmospheric pressure in the absence of a catalyst. Accordingly, there is no risk of explosion if the air/fuel mixture should leak out of the catalytic combustion chamber. In addition, a catalytic combustion chamber is reliable, and does not generate irritating noise when in operation.
In Japanese Patent Application No. 2-197245 a catalytic combustion chamber is described comprising two catalytic reactors, wherein a main catalytic reactor is heated by the exhaust gases from a preheating catalytic reactor. The preheating catalytic reactor is heated to its ignition temperature by means of an electrically heated heater. A portion of the heat generated by combustion in the preheating catalytic reactor is utilized for heating a carburetor in order to vaporize the fuel. An ignition process of this type is comparatively slow, and requires a large initial consumption of electricity. It also results in high emissions of carbohydrates and carbon monoxide.
A further catalytic combustion chamber comprising two serially coupled catalytic reactors is described in Japanese Patent Application No. 60-27994. This publication also utilizes a two-step process for initiating catalytic combustion. Instead of heating the first catalytic reactor when igniting the catalytic combustion chamber, the gas which is conducted through the catalytic reactor is heated, thereby accomplishing ignition. An ignition process of this type demands a high initial energy supply and, consequently, involves a large energy consumption during the ignition process.
These previously known two-step ignition processes do not significantly diminish either the emissions of incompletely combusted fuel or the consumption of electricity during the ignition process. For this reason, there remains considerable demand for a simple, quick and electricity saving ignition process for a catalytic combustion chamber having low emission of carbohydrates and carbon monoxide.
SUMMARY OF THE INVENTION
In accordance with the present invention, these and other objects have now been realized by the discovery of a method of operating a catalytic combustion chamber including a first catalytic reactor, a second catalytic reactor including an end surface facing the first catalytic reactor, the second catalytic reactor disposed in series with the first catalytic reactor, and an intermediate chamber between the first and second catalytic reactors, the method comprising heating the first catalytic reactor to a temperature at least equal to the ignition temperature of the first catalytic reactor, introducing an air and fuel mixture to the first catalytic reactor, whereby catalytic combustion is initiated in the first catalytic reactor, and increasing the mass flow through the first catalytic reactor whereby combustion of the air and fuel mixture takes place in the gas phase in the intermediate chamber and the end surface is heated to a temperature at least equal to the ignition temperature of the second catalytic reactor and ignition takes place in the second catalytic reactor. In accordance with a preferred embodiment, the method includes adjusting the mass flow through the second catalytic reactor after the ignition in the second catalytic reactor whereby substantially all of the combustion takes place in the second catalytic reactor. In a preferred embodiment, the method also includes adjusting the mass flow through the second catalytic reactor after substantially all of the end surface of the second catalytic reactor is heated to a temperature at least equal to the ignition temperature of the second catalytic reactor.
In accordance with another embodiment of the method of the present invention, the method includes preheating the first catalytic reactor to the ignition temperature of the first catalytic reactor prior to introducing of the air and fuel mixture to the first catalytic reactor, the air and fuel mixture having a &lgr; value of greater than about 1, whereby the combustion is initiated in the first catalytic reactor and the temperature of the first catalytic reactor is raised above the ignition temperature of the first catalytic reactor, increasing the mass flow of the air through the first catalytic reactor at a temperature corresponding to from between about 60% and 100% conversion in the first catalytic reactor and the &lgr; value is increased, and further increasing the mass flow of the air through the first catalytic reactor at a substantially constant &lgr; value whereby at least part of the combustion takes place in the gas phase in the intermediate chamber.
In accordance with another embodiment of the method of the present invention, the method includes electrically preheating the first catalytic reactor.
In accordance with another embodiment of the method of the present invention, substantially all of the combustion upstream of the second catalytic reactor takes place in the gas phase in the intermediate chamber during the ignition in the second catalytic reactor.
In accordance with the present invention, a catalytic combustion chamber has been invented comprising a first catalytic reactor having a first volume and a second catalytic reactor having a second volume disposed in series with the first catalytic reactor, the ratio of the first volume to the second volume being from about 4.5×10
−3
to 0.18. Preferably, the ratio of the first volume to the second volume is from about 0.16 to 0.05.
In accordance with one embodiment of the catalytic combustion chamber of the present invention, the chamber comprises a first catalytic reactor and a second catalytic reactor disposed in series with the first catalytic reactor, at least one of the first and second catalytic reactors comprising a net.
In accordance with one embodiment of the catalytic combustion chamber of the present invention, the chamber includes a static mixer mounted upstream of the first catalytic reactor.
In accordance with another embodiment of the catalytic combustion chamber of the present invention, the chamber includes a first flow equalizing net mounted upstream of the first catalytic reactor. In accordance with another embodiment, the chamber includes a second flow equalizing net mounted between the first catalytic reactor and the second catalytic reactor.
In accordance with another embodiment of the catalytic combustion chamber of the present invention, the chamber includes an air blower for supplying air to the catalytic combustion chamber, and a conduit for returning at least part of the exhaust gases from the catalytic combustion chamber to the air blower from a location downstream of the second catalytic reactor.
In accordance with another embodiment of the catalytic combustion c
Jobson Edward
Lundgren Staffan
Vestin Anders
AB Volvo
Cocks Josiah C.
Lazarus Ira S.
Lerner David Littenberg Krumholz & Mentlik LLP
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