Liquid heaters and vaporizers – Miscellaneous
Reexamination Certificate
1999-08-05
2001-05-15
Lu, Jiping (Department: 3749)
Liquid heaters and vaporizers
Miscellaneous
C122S00700A, C110S238000, C110S245000, C110S251000, C110S348000
Reexamination Certificate
active
06230664
ABSTRACT:
BACKGROUND OF THE INVENTION
In fluidized bed boilers, various ways of supplying air are used, the aim being that the fuel would burn as efficiently as possible and yet the combustion process could be controlled in a desired manner in both the horizontal and the vertical directions of the boiler. Typically, air is supplied from one or more levels in the vertical direction of the fluidized bed boiler so as to cause sub-stoichiometric combustion in the gas flow direction as far as possible, i.e. in the vertical direction of the fluidized bed boiler. The final air causing stoichiometric combustion is not fed until the final, typically tertiary step. To fluidize the material in the fluidized bed, primary air is supplied from below the fluidized bed through a grate so as to achieve the desired fluidizing level and the desired circulation of the fluidized bed material in the fluidized bed.
To make the combustion efficient, the fuel and the combustion air must be made to mix as well as possible. It has-been noted, however, that the fluidizing air coming from below the grate allows the fine fuel particles to move with the gas flow to the upper parts of the furnace, which defers the combustion step so much that the combustion is no longer efficient and the emissions are not reduced efficiently. The most advantageous solution with regard to the emissions would be if the combustion were sub-stoichiometric as far as possible, so that essentially no No
x
compounds would be formed. The fact that the fuel particles move up with the gas flow and burn there may make the temperature close to the superheaters rise too high, which speeds the corrosion of the superheaters and thereby shortens their effective life. Problems are posed by the channelling of the flows in the upper part of the furnace and by different vertical backflows, whereby the volume of the furnace is not actually used efficiently with respect to the reactions, and so the walls. cannot be used efficiently for heat transfer.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and an arrangement by which air can be supplied to the fluidized bed boiler efficiently, and advantageously and reliably with respect to the combustion and the other operation of the boiler, simultaneously avoiding the problems of the earlier solutions. The method of the invention is characterized in that at at least one air supply level the air is supplied to the fluidized bed boiler such that four vortexes spinning around vertical axes are formed above the fluidized bed, the vortexes spinning, in pairs, in opposite directions so that the adjacent vortexes always spin in opposite directions; and that to form the vortexes, air is supplied from at least two opposite walls of the fluidized bed boiler so that the air flows flow in the spinning directions of at least two vortexes spinning in opposite directions, at least primarily parallel to the tangents of the vortexes.
The arrangement of the invention is characterized by comprising nozzles at at least one air supply level, the nozzles being directed to blow air so that four vortexes are formed in the fluidized bed boiler, the rotation axes of the vortexes being vertical and the adjacent vortexes always spinning in opposite directions.
The essential idea of the invention is that air is supplied to the fluidized bed boiler at at least one air supply level above the fluidized bed so that four vortexes are formed therein at substantially the same level, two of these vortexes spinning in one direction and two in the other direction. This can be achieved in many different ways, but the essential point is that the air jets are injected primarily in the spinning direction of a vortex, parallel to the tangent of the vortex, thereby forming vortexes and strengthening the already existing vortexes. The simplest way of achieving this is to supply air to the fluidized bed boiler from two opposite walls by air jets arranged in the middle of the walls and, in addition to these jets, to supply air from the corners of the two other opposite walls of the boiler directly toward each other. In this way four vortexes are formed in which the air flow directions at the points where the spinning vortexes touch one another are the same. The vortexes are then easy to control, and they can be either strengthened or allowed to weaken in the vertical direction of the fluidized bed boiler in a desired manner.
The advantage of the invention is that due to the vortexes the fuel particles, gases and the combustion air mix efficiently. By the effect of the vortexes, the fluidized bed material above the fluidized bed is simultaneously separated partly in this step from the mixture of fuel and gas that flows upward by centrifugal forces, and so less fluidized bed material moves on as far as the flue gas duct. Further, the dead areas at the corners of the fluidized bed boiler are small, and so the cross-sectional area of the whole furnace can be used efficiently in the combustion process, and simultaneously the heat transfer capacity of the walls can be used efficiently. This makes it possible to effect the combustion and the mixing of the combustion air and the fuel in the fluidized bed boiler in a desired manner both in respect of the cross-section and in the vertical direction, and so the combustion in the lower part of the fluidized bed boiler is rendered efficient.
Another essential advantage of the invention is that to form vortexes, the air jets are not required to have deep penetration. The reason is that the four vortexes as such cause mixing, and that the essential point for the formation of the vortexes is that the momentum of the air jets transfers to the spinning motion to be achieved. To achieve this, shallow penetration is sufficient. The advantage of the invention is that it can be implemented with nozzles of very different shapes arranged in various ways, The invention also readily allows any solutions that are advantageous to both the different air distribution systems required by the combustion conditions, and the structure of the boiler. In addition, the option of arranging the air nozzles in different ways makes the invention easy to implement as regards the structure: for example, the already existing air apertures in the old boilers can be utilized so that entirely new air apertures are either not needed at all or at most only a small number of such apertures are needed.
REFERENCES:
patent: 4442796 (1984-04-01), Strohmeyer, Jr.
patent: 4469050 (1984-09-01), Korenberg
patent: 5205227 (1993-04-01), Khinkis et al.
patent: 5341753 (1994-08-01), Russell
patent: 5450802 (1995-09-01), Horvath et al.
patent: 5450803 (1995-09-01), Svensk et al.
patent: 5771817 (1998-06-01), Olausson et al.
patent: 6006683 (1999-12-01), Janka et al.
Janka Kauko
Ruohola Tuomo
Ylitalo Matti
Kvaerner Pulping Oy
Lu Jiping
Rockey Milnamow & Katz Ltd.
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