Combustion – Timer – programmer – retarder or condition responsive control – By condition of burner feed or feed means
Reexamination Certificate
2003-07-21
2004-09-21
Basichas, Alfred (Department: 3749)
Combustion
Timer, programmer, retarder or condition responsive control
By condition of burner feed or feed means
C431S012000
Reexamination Certificate
active
06793485
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a combustion apparatus for NO
x
reduction 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 Japanese Patent Laid-Open Publication HEI 11-132404 (Specification of U.S. Pat. No. 6,029,614).
This prior art technique is intended to achieve NO
x
reduction by a combination of cooling of burning-reaction ongoing gas with water tubes and cooling of burning-reaction ongoing gas with exhaust gas recirculation. However, the technique was capable of NO
x
reduction up to only about 25 ppm, other than one that allows NO
x
reduction to below 10 ppm to be achieved. 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.
Also, from recent years' regulations of NO
x
value, there has been an increasing demand for achieving regulation values not only at some operating points but also over a wider range of operating points, i.e., those throughout a day or a year. The above-mentioned prior art technique was not one that could meet this demand.
Further, the present applicant, through continued studies on the super NO
x
reduction technique of steam boilers in response to the society's demand, has reached a practicalization of a super NO
x
reduction technique with steam boilers. During the process of studies on this super NO
x
reduction technique, the applicant found out that in order to realize a stable super NO
x
reduction, controlling the excess air ratio to a constant one is of importance and the greatest factor of variations in excess air ratio is outside-air temperature.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a combustion apparatus for NO
x
reduction capable of achieving stable NO
x
reduction with simple means.
The present invention having been accomplished to solve the above object, the invention provides a combustion apparatus for NO
x
reduction by suppressing temperature of combustion gas derived from a burner, comprising: NO
x
reduction means having an excess air ratio versus NO
x
characteristic (NO
x
emission characteristic) that generated NO
x
value decreases with increasing excess air ratio of the burner, and an excess air ratio versus CO characteristic that exhaust CO value increases with increasing excess air ratio; and excess-air-ratio control means for controlling the excess air ratio of the burner to a specified excess air ratio, wherein the excess-air-ratio control means includes outside-air temperature detection means and controls the excess air ratio to the specified excess air ratio based on a detection signal derived from the outside-air temperature detection means.
In one embodiment, there is provided a combustion apparatus for NO
x
reduction as described above, wherein the excess-air-ratio control means includes combustion-use-air flow rate adjusting means provided on an air supply passage and serving for feeding combustion-use air to the burner, and the combustion-use-air flow rate adjusting means controls an opening of the combustion-use-air flow rate adjusting means based on a detection signal derived from the outside-air temperature detection means, thereby fulfilling the control to the specified excess air ratio.
In one embodiment, there is provided a combustion apparatus for NO
x
reduction as described above, wherein the combustion-use-air flow rate adjusting means includes: a damper; positioning means for determining rotational position of the damper; and fine adjustment means for acting on the positioning means to finely adjust the rotational position of the damper in response to a detected temperature of the outside-air temperature detection means.
In one embodiment, there is provided a combustion apparatus for NO
x
reduction as described above, wherein the excess-air-ratio control means controls rotational speed of a blower, which feeds combustion-use air to the burner, based on a detection signal derived from the outside-air temperature detection means, thereby fulfilling the control to the specified excess air ratio.
Further, aspects of the present invention will be described according to the embodiments. Before the description of the embodiments, terms used herein and the drawings are explained. The combustion gas includes burning-reaction ongoing (under-combustion-process) combustion gas, and combustion gas that has completed burning reaction. Then, the burning-reaction ongoing gas refers to combustion gas that is under burning reaction, and the burning-completed gas refers to combustion gas that has completely burning-reacted. The burning-reaction ongoing gas is indeed a concept of substance, but can also be referred to as flame as a concept of state because it generally includes a visible flame so as to be in a flame state. Therefore, herein, the burning-reaction ongoing gas is referred to also as flame or burning flame from time to time. Further, the exhaust gas (flue gas) refers to burning-completed gas that has decreased in temperature under an effect of endothermic action by heat transfer tubes or the like.
Also, the combustion gas temperature, unless otherwise specified, means the temperature of burning-reaction ongoing gas, equivalent to combustion temperature or combustion flame temperature. Further, the suppression of combustion gas temperature refers to suppressing the maximum value of combustion gas (combustion flame) temperature to a low one. In addition, normally, burning reaction is continuing although in a trace amount even in the burning-completed gas, and so the combustion completion does not mean a 100% completion of burning reaction.
Further, the excess air ratio, which is expressed as (actual amount of combustion air)/(theoretical amount of combustion air), corresponds in a specified relationship to exhaust-gas O
2
(%) (oxygen concentration in exhaust gas), therefore being expressed in exhaust-gas O
2
(%). Also, the value of NO
x
shows a value at 0% O
2
in the exhaust gas, dry basis, while the value of CO shows not an equivalent value but a reading value.
Next, as a detailed description of the foregoing characteristics of the present invention, embodiments of the present invention are described. The present invention is applied to thermal equipment (or combustion equipment) such as small-size once-through boilers or other water-tube boilers, water heaters, reheaters of absorption refrigerators or the like. The thermal equipment has a burner and a group of heat absorbers to be heated by combustion gas derived from the burner.
An embodiment of the apparatus according to the present invention is a NO
x
reduction combustion apparatus for fulfilling NO
x
reduction by controlling temperature of combustion gas derived from a burner, comprising: NO
x
reduction means having an excess air ratio versus NO
x
characteristic that generated NO
x
value decreases with increasing excess air ratio of the burner, and an excess air ratio versus CO characteristic that exhaust CO value increases with incr
Furukawa Hideo
Kayahara Toshihiro
Kondo Kanta
Takeda Tomohisa
Basichas Alfred
Miura Co., Ltd.
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