Furnaces – Including fluid fuel burner – Powdered solid fuel
Reexamination Certificate
2002-03-19
2004-04-06
Rinehart, Kenneth (Department: 3749)
Furnaces
Including fluid fuel burner
Powdered solid fuel
C110S264000, C110S265000, C110S347000
Reexamination Certificate
active
06715432
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a solid fuel burner and a method of combustion using the same for combusting a solid fuel carried by air flow; and in particular, to: a solid fuel burner and a method of combustion using the same which are applicable in a wide range of furnace loads and hence suitable for combusting a moisture-rich and volatile-matter-rich fuel such as pulverized coal, wood, and peat, and further permitting combustion by reducing the concentration of nitrogen oxides (NOx) in the exhaust gas; a combustion apparatus, such as a furnace, a heating furnace, and a hot blast stove, using said burner, and a method of operation thereof; a coal-fired boiler and a system using the same; and a coal-fired power generation system.
BACKGROUND ART
Pollution control regulations have been tightened in recent years for the purpose of environmental protection. In particular, for the above-mentioned kind of pulverized-coal boilers for combusting coal, reduction in the generation of NOx in the exhaust gas (NOx reduction, hereafter) is seriously required. Two-stage combustion methods are known as combustion techniques (NOx reduction techniques) for reducing the concentration of NOx generated in exhaust gas. The two-stage combustion methods are classified into the following two approaches. One approach is to reduce the NOx generation of a furnace as a whole, while the other approach is to reduce the NOx generation of a single burner. In the approach to reduce the NOx concentration of a furnace as a whole, the air ratio (ratio of the amount of supplied air to the amount of necessary air for completely combusting an amount of fuel; the air ratio of unity corresponds to one stoichiometric equivalent) in the burner zone of the furnace is maintained below unity. In this fuel-rich condition, generated NOx is chemically reduced, and hence NOx reduction is achieved. The unburnt carbon resulting from this approach is completely combusted with air added through an air inlet provided downstream of the burner zone.
In the approach to reduce the NOx generation of a single solid fuel burner (simply a burner, in some cases hereafter) such as a pulverized-coal burner, secondary and tertiary air flows are swirled, thereby delaying the mixing thereof with the flow of pulverized-coal burning with primary air alone. By virtue of this, a large chemical reduction region is formed (such a burner is called a NOx-reduced burner, hereafter). This approach is implemented in a NOx reduction pulverized-coal burner (Japanese Unexamined Patent Publications Nos. Sho-60-176315 and Sho-62-172105).
These techniques have achieved a reduction of NOx concentration in the exhaust gas down to 130 ppm (fuel ratio=fixed carbon/volatile matter=2, nitrogen content in the coal=1.5%, and unburnt carbon content in the ash=5% or less). Nevertheless, the regulated value of NOx concentration in the exhaust gas has been tightened year by year, and the required value of NOx concentration in the exhaust gas for the near future is 100 ppm or less.
NOx-reduced burners capable of reducing NOx generation down to 100 ppm or less have been developed. Such burners include: a burner having an internal flame stabilizing ring for reinforcing the NOx-reduced combustion in the burner section; and a burner having a flame stabilizing ring for bridging between an internal flame stabilizing ring as described above and an external flame stabilizing ring provided in the outer periphery of the combustion nozzle through which the mixture of pulverized coal and carrier gas flows.
By the way, in geological areas where an increase in energy demand is expected, a majority in the near future will use low-quality coal which is rich in moisture and ash matter and has a low calorific value. Among various low-quality coals, high-moisture content coal, such as brown coal and subbituminous coal, is found in abundance. Nevertheless, such coal has a problem of poor fuel performance, such as a lower flame temperature and poor combustibility, in comparison with bituminous coal. Brown coal is found mainly in Eastern Europe, and is a rather young coal containing 20% or more ash matter and 30% or more moisture.
Further, low-coalification coal (such as brown coal and lignite), wood, and peat are rich in volatile matter which is released in gaseous form while being heated, and are also rich in moisture. Such kinds of fuel have a lower calorific value than that of high-coalification coal such as bituminous coal and anthracite, and in addition, are generally poor in pulverizability. Further, the ash of such kinds of fuel has a lower melting point. The richness in volatile matter easily causes spontaneous ignition during storage and pulverization processes in air. This causes difficulty in handling processes in comparison with the case of bituminous coal and the like. In order to avoid this difficulty, when brown coal and lignite are pulverized and combusted, a mixture of exhaust gas and air is used as the fuel carrier gas. Since the mixture gas has a lower oxygen concentration, the spontaneous ignition of fuel is prevented. Further, the residual heat in the exhaust gas helps evaporation of moisture in the fuel carried by the mixture gas.
Nevertheless, since the fuel is carried by the low-oxygen-concentration gas, the combustion reaction does not proceed until the fuel ejected from the burner is mixed with air. That is, the combustion reaction is limited by the rapidity of mixing of the fuel with air. This causes a slower combustion rate than that of bituminous coal which can be carried by air. Accordingly, the time necessary to burn out is longer than that of bituminous coal. This causes an increase in unburnt carbon in the furnace exit.
A method for accelerating the ignition of the fuel carried by the carrier gas of low oxygen concentration is to provide an air ejection nozzle in the tip of the fuel nozzle so as to increase the oxygen concentration of the fuel carrier gas. For example, Japanese Unexamined Patent Publication No. Hei-10-73208 discloses a burner having an air nozzle outside a fuel nozzle. Further, commonly used is a burner having an air nozzle at the center of a fuel nozzle so as to accelerate the mixing of the fuel with air at the exit of the fuel nozzle.
Further, Japanese Unexamined Patent Publication No. Hei-4-214102 discloses a burner comprising: a fuel nozzle for ejecting a mixture of pulverized coal and carrier gas; and a secondary air nozzle and a tertiary nozzle provided outside the fuel nozzle; where in a flame stabilizing ring for maintaining the flame obtained by the pulverized coal ejected from the fuel nozzle is provided at the tip of a septum between the fuel nozzle and the secondary air nozzle.
As described above, brown coal is an inexpensive fuel. Nevertheless, its characteristics of a high ash content, a high moisture content, and a low calorific value cause problems in combustibility and ash cohesion. As for combustibility, the key technology to efficient combustion depends on how to accelerate the ignition and form a stable flame. The ash cohesion to the burner structure and the furnace wall surface is caused by the low melting point of the ash. This is because the brown coal is rich in calcium, sodium, and the like. Further, the ash cohesion is accelerated by the fact that the brown coal needs to be supplied in a larger amount in order to compensate the lower calorific value in comparison with the bituminous coal, thereby generating a larger amount of ash. Such slagging and fouling is a disadvantage of the brown coal. Accordingly, in order to use low-quality coal, such as brown coal and lignite, for burner combustion, both efficient combustion and ash cohesion reduction need to be achieved.
Methods for combusting brown coal generally used abroad are a tangential firing method and a corner firing method. In the former method, a burner compartment composed of fuel passages and combustion air passages is provided in each sidewall of a furnace. In the latter method, a burner compartment composed of fuel
Kikuchi Hitoshi
Kiyama Kenji
Kobayashi Hironobu
Kuramashi Kouji
Morita Shigeki
Babcock-Hitachi Kabushiki Kaisha
Intellectual Property Law Group LLP
Jackson Juneko
Lee Otto O.
Rinehart Kenneth
LandOfFree
Solid fuel burner and method of combustion using solid fuel... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solid fuel burner and method of combustion using solid fuel..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solid fuel burner and method of combustion using solid fuel... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3188264