Liquid heaters and vaporizers – Industrial – Waste heat
Reexamination Certificate
2003-07-15
2004-09-21
Wilson, Gregory A. (Department: 3749)
Liquid heaters and vaporizers
Industrial
Waste heat
C122S367300
Reexamination Certificate
active
06792895
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a combustion method for NO
x
reduction, as well as an apparatus therefor, to be applied to water-tube boilers, reheaters of absorption refrigerators, or the like.
Generally, as the principle of suppression of NO
x
generation, there have been known (1) suppressing the temperature of flame (combustion gas), (2) reduction of residence time of high-temperature combustion gas, and (3) lowering the oxygen partial pressure. Then, various NO
x
reduction techniques to which these principles are applied are available. Examples that have been proposed and developed into practical use include the two-stage combustion method, the thick and thin fuel combustion method, the exhaust gas recirculate combustion method, the water addition combustion method, the steam jet combustion method, the flame cooling combustion method with water-tube groups, and the like.
With the progress of times, NO
x
generation sources even of relatively small capacity such as water-tube boilers have been coming under increasingly stricter regulation of exhaust gas, and so further reduction of NO
x
is demanded therefor. The present applicant proposed NO
x
reduction techniques for these demands by the Specification of U.S. Pat. No. 6,029,614 and the like.
However, the extent of NO
x
reduction by these prior arts is up to about 25 ppm actually, and there has not yet been developed so far any NO
x
reduction technique of under 10 ppm in practical use. It is noted that NO
x
reduction with the value of NO
x
generation being not more than 10 ppm will hereinafter be referred to as super NO
x
reduction.
The reason of that lies in that NO
x
reduction and CO reduction are contradictory technical issues. That is, if the combustion gas temperature is abruptly lowered to facilitate NO
x
reduction so that the temperature is suppressed to as low as 900° C. or less, a large amount of CO is generated and moreover the generated CO is discharged as it is unoxidized, with a result of increased CO emission. Conversely, if the combustion gas temperature is suppressed to a rather higher one in order to reduce the CO emission, the suppression of NO
x
generation becomes insufficient.
The NO
x
reduction technique proposed in the aforementioned prior art is also intended to suppress the combustion gas temperature so that the quantity of CO generated along with the NO
x
reduction is minimized, and that generated CO is oxidized. As a result of this, it has been the case that the prior art technique is limited in the selection of means for NO
x
reduction and poor in the suppression of combustion gas temperature, hence incapable of fulfilling the super NO
x
reduction.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a combustion method for NO
x
reduction, as well as an apparatus therefor, capable of facilitating NO
x
reduction without requiring considerations of CO generation and easily achieving NO
x
reduction with the value of exhaust NO
x
under 10 ppm, and still capable of achieving CO reduction at the same time.
The present invention having been accomplished to solve the above object, in a first aspect of the invention, there is provided a NO
x
reduction combustion method for fulfilling NO
x
reduction by suppressing temperature of combustion gas derived from a burner, comprising: a NO
x
reduction step for suppressing combustion gas temperature in such a manner that suppression of NO
x
generation is preferred to reduction of exhaust CO value, thereby keeping NO
x
value not more than a specified value; and a CO reduction step for thereafter reducing exhaust CO value resulting from the NO
x
reduction step to not more than a specified value.
In a second aspect of the invention, there is provided a NO
x
reduction combustion method for fulfilling NO
x
reduction by suppressing temperature of combustion gas derived from a burner, comprising: a NO
x
reduction step for suppressing combustion gas temperature in such a manner that suppression of NO
x
generation is preferred to reduction of exhaust CO value, thereby keeping NO
x
value not more than 10 ppm (at 0% O
2
in the exhaust gas, dry basis); and a CO reduction step for thereafter reducing exhaust CO value resulting from the NO
x
reduction step to not more than a specified value.
In a third aspect of the invention, there is provided a NO
x
reduction combustion method for fulfilling NO
x
reduction by suppressing temperature of combustion gas derived from a burner, comprising: a NO
x
reduction step for suppressing combustion gas temperature in such a manner that suppression of NO
x
generation is preferred to reduction of exhaust CO value, thereby keeping NO
x
value not more than a specified value; and a CO reduction step for thereafter reducing exhaust CO value resulting from the NO
x
reduction step to not more than a specified value, the CO reduction step being performed in a zone where the combustion gas temperature is not more than 900° C.
In one embodiment, there is provided a NO
x
reduction combustion method as described in any one of the first to third aspects, wherein the NO
x
reduction step is performed with an excess air ratio which is determined from a NO
x
reduction target value and an excess air ratio versus NO
x
characteristic of the NO
x
reduction step.
In one embodiment, there is provided a NO
x
reduction combustion method as described in any one of the first to third aspects, wherein the CO reduction step is performed with a CO oxidation catalyst member.
In a fourth aspect of the invention, there is provided a NO
x
reduction combustion apparatus for fulfilling NO
x
reduction by suppressing temperature of combustion gas derived from a burner, comprising: NO
x
reduction means for suppressing combustion gas temperature in such a manner that suppression of NO
x
generation is preferred to reduction of exhaust CO value, thereby keeping NO
x
value not more than a specified value; and CO reduction means for reducing exhaust CO value resulting from the NO
x
reduction means to not more than a specified value.
In a fifth aspect of the invention, there is provided a NO
x
reduction combustion apparatus for fulfilling NO
x
reduction by suppressing temperature of combustion gas derived from a burner, comprising: NO
x
reduction means for suppressing combustion gas temperature in such a manner that suppression of NO
x
generation is preferred to reduction of exhaust CO value, thereby keeping NO
x
value not more than 10 ppm (at 0% O
2
in the exhaust gas, dry basis); and CO reduction means for reducing exhaust CO value resulting from the NO
x
reduction means to not more than a specified value.
In a sixth aspect of the invention, there is provided a NO
x
reduction combustion apparatus for fulfilling NO
x
reduction by suppressing temperature of combustion gas derived from a burner, comprising: NO
x
reduction means for suppressing combustion gas temperature in such a manner that suppression of NO
x
generation is preferred to reduction of exhaust CO value, thereby keeping NO
x
value not more than a specified value; and CO reduction means for reducing exhaust CO value resulting from the NO
x
reduction means to not more than a specified value in a zone where the combustion gas temperature is not more than 900° C.
In one embodiment, there is provided a NO
x
reduction combustion apparatus as described in any one of the fourth to sixth aspects, wherein the NO
x
reduction is performed with an excess air ratio which is determined from a NO
x
reduction target value and an excess air ratio versus NO
x
characteristic (NO
x
emission characteristic) of the NO
x
reduction means.
In one embodiment, there is provided a NO
x
reduction combustion apparatus as described in any one of the fourth to sixth aspects, wherein the CO reduction means is a CO oxidation catalyst member.
In one embodiment, there is provided a NO
x
reduction combustion apparatus as described in any one of the fourth to sixth aspects, wherein the NO
x
reduction means is implemented by heat transfer tu
Kayahara Toshihiro
Takubo Noboru
Miura Co., Ltd.
Wilson Gregory A.
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