Furnaces – Refuse incinerator – Refuse suspended in or supported by a fluid medium
Patent
1985-04-29
1986-12-16
Yuen, Henry C.
Furnaces
Refuse incinerator
Refuse suspended in or supported by a fluid medium
34 57A, 122 4D, 432 15, F23G 500
Patent
active
046288317
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a hearth and a process for the treatment of a fuel consisting of solid particles, which is maintained in a fluidised bed, during treatment, within a treatment chamber limited in its lower part by a grid. This grid has an assembly of gas passage channels via which there arrives a gas for fluidising, treating and, if appropriate, conveying the particles of fuel to be treated.
By treatment is meant, here, any operation which can be carried out on the fuel in the form of grains, which is maintained in a fluidised state. Gasification, combustion, etc., may be mentioned as examples of treatment.
The invention relates more particularly to a treatment hearth which comprises an upper fuel-supply means as well as a means which is likewise located above the level of the grid and which serves for discharging the treated fuel or for discharging waste or possible by-products. Thus, in a hearth with which the invention is concerned, there are, above the grid, means for the intake and discharge of the fuel, and the grid serves exclusively for the passage of channels for admission of the fluidisation and treatment gas.
The process of the invention relates to the method of supplying fluidisation and treatment gas to the hearth via the grid.
In the state of the art, French Pat. Nos. FR 1,422,198 and FR 2,171,945 are known, and these describe fluidisation gratings which incorporate orifices consisting of cavities widened towards the top and located next to one another. Such grids make it possible to adjust and ensure a regular flow of gases over the entire extent of the fluidised zone.
Japanese Pat. No. JP-55-99334 is also known, and this relates to a fluidised-bed apparatus in which a fluidisation grid has cavities widened towards the top; there terminates at this grid a first pipe line for the admission of fluidisation gas and a second assembly of spaced pipe lines which serve for supplying the grid with material to be fluidised. In this Patent, there is therefore only a single fluidisation-gas circuit.
The published European Patent Application Nos. EP-50 518 and EP-50 519 are also known, and in these there is a perforated grid in the form of a truncated cone which ends towards the bottom in a vertical discharge pipe; vertical tubes, some of which serve as ignition burners, pass through this grid. Air is conveyed through the grid either via the perforations in this or via some of the vertical tubes, but this air comes from a single air-supply circuit.
Since one of the important uses, but not the only one, of the hearth according to the invention is combustion of fuel in the form of grains, it will also be rembered that there has already been a proposal to use fluidised beds as combustion hearths. Their main advantage is that it is possible to burn various particulate fuels with a very high content of incombustible residues. On the other hand, their operating flexibility is limited.
In fact, in a fluidised-bed hearth, it is noted, when there is a constant excess of air, that the quantity of heat generated is practically proportional to the velocity of the gases passing through the fluidised bed. In a chamber equipped with a fluidisation grid working at a nominal velocity of the gases of 2.5 meters per second, it may be expected that the treatment capacity, that is to say the productivity, will be reduced in a ratio of 1 to 2 (at most 1 to 3). In contrast to this, as regards the same chamber, it is difficult to see how it is possible to double or triple the nominal productivity, by increasing the flow of fluidisation air, without creating a high velocity of the air passing through the grid and thereby causing an excessive loss of charge (the loss of charge being proportional to the square of the velocity of the gases). This would result in problems affecting: and a risk of deformation of this grid,
The fluidisation and/or forcing processes developed at the present time make it possible to operate within two quite separate sectors when a material consisting of particles is to be treated: second
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Delessard Serge L.
Kita Jean C.
Puff Roger M.
Virgilio Ange
Charbonnages de France
Yuen Henry C.
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