Furnaces – Utilizing powdered fuel – Having secondary air mixing means
Patent
1996-05-02
1998-09-01
Bennett, Henry A.
Furnaces
Utilizing powdered fuel
Having secondary air mixing means
110347, 431 8, F23D 100
Patent
active
057995940
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for burning pulverized fuel in a tangentially fired boiler and for creating reducing conditions in order to reduce nitrogen oxide emissions.
The invention also concerns an apparatus for implementing the method.
DESCRIPTION OF RELATED ART:
Today reducing harmful emissions in a power plant's exhaust gases has become one of the main objectives to developing modern combustion technologies and apparatures. Emissions of, for example, sulphur oxides and solids can be controlled to a great extent with modem technologies, but emissions of nitrogen oxides are still a problem that has not been entirely solved. It is well known that NO.sub.x formed in the combustion process is one of the main causes of air pollution; thus, certain basic improvements in burners or improvements in the whole combustion system have been made. A particular problem raised in the combustion of pulverized fuel is that organically bound nitrogen (nitrogen content is, for example, 1-2 wt % in coal and peat) is released to gas phase during the combustion process, generating large amounts a lot of NOx emissions.
During pyrolysis, the first stage of coal combustion, most of the fuel-N release to gas phase and gaseous compounds such as HCN and NH.sub.3 occurs. After pyrolysis, smaller volumes of fuel-N are retained in the after pyrolysis progression to remaining solid particles, called "char-N". If, during this process, sufficiently oxygen is present, most of NH.sub.3 and HCN is oxidized to NO.sub.x. If the oxygen concentration is sufficiently low, these compounds tend to reduce to molecular N.sub.2. It is also known that HCN and NH.sub.3 can reduce the already formed NO.sub.x, to molecular N.sub.2 under the conditions of low oxygen content and high temperature.
Another fact is that some chemical radicals, especially CH.sub.i radicals, which are intermediate combustion products, can reduce NO.sub.x. As a consequence, NH.sub.3 and HCN are again formed, which can further reduce NO.sub.x. With higher the temperatures and lower oxygen content, these reducing reactions are more liable to proceed. Accordingly, in order to suppress the generation of NO.sub.x during combustion of coal or other pulverized fuels, the technical problem is how to create such an atmosphere that has a suitably low oxygen concentration and high temperature.
In general, a combustion process referred to as two-stage combustion applies to this low-oxygen region for reducing the emissions of NO.sub.x. In this process, an air-deficient zone is formed in the burner zone of a combustion furnace, and an amount of air corresponding to the above deficient amount of air is supplied through the so-called after-air port provided downstream of burners to effect complete combustion, whereby combustion over the whole of the combustion furnace is improved, thereby reducing the amount of NO.sub.x discharged. However, in case of a two-stage combustion like this, half-burned coal particles (char) are formed in the air-deficient zone of the burner, and a large free space is required in the furnace for complete combustion of the char with after-air. Thus, although the above combustion process (two-stage combustion) is rather efficient in lowering NO.sub.x emissions of the combustion, it has still certain limitations, such as creating unburned carbon and unstable flame conditions.
Thus, a new type low-NO.sub.x burner has been constructed so that the air-deficient zone is formed very close to the tip end of the burner, and the two-stage combustion is carried out by means of a single-burner. This single burner staging technique combined with staging in the whole furnace (OFA, Over Fire Air technique) is very efficient in lowering NO.sub.x emissions. The U.S. Pat. No. 4,545,307 describes this kind of a low-NO.sub.x burner. The burner described in the U.S. Pat. No. 4,545,307 is designed to be mounted perpendicularly in the wall of the furnace. These burners are equipped with a flame holder at the open end of the fuel feeding pipe, which promotes
REFERENCES:
patent: 4422391 (1983-12-01), Izuha et al.
patent: 4545307 (1985-10-01), Morita et al.
patent: 4570551 (1986-02-01), Derbidge et al.
patent: 4838185 (1989-06-01), Flament
patent: 4907962 (1990-03-01), Azuhata et al.
patent: 4915619 (1990-04-01), LaRue
patent: 5020454 (1991-06-01), Hellewell et al.
patent: 5263426 (1993-11-01), Morita et al.
patent: 5431114 (1995-07-01), Morita et al.
Dernjatin Pauli
Lepikko Juha
Savolainen Kati
Bennett Henry A.
IVO International Oy
Wilson Gregory A.
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