Furnaces – Process – Burning pulverized fuel
Patent
1989-10-18
1991-04-30
Favors, Edward G.
Furnaces
Process
Burning pulverized fuel
110102, 110110, 110229, 110346, 110257, F23D 100
Patent
active
050108310
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to a burner comprising two coaxially mounted tubes, provided with means to introduce air as well as particulate matter in the space between both tubes and means to discharge burnt matter from that space, wherein the inner tube being at least partially gas porous, said inner tube being provided with means to introduce a combustion agent.
Such a burner is known for instance from GB-A-1590341. In the prior art attempts have been made to improve combustion of materials layerwise. At layerwise burning of particular material the draw back exists that the material is not burnt completely. Furthermore the temperature can rise very high such that dangerous fumes can develop which have to be extracted before discharging of the flow. To obviate these problems fluid bed combustion has been proposed, wherein the particulate material is burnt from all sides in a continuous homogenous way. Because of this the material will burn more completely whereas the temperature of combustion will be lower not giving rise to much harmful bits. In GB-A-1590341 it is described that such a fluid bed is maintained by introducing of air. This air keeps the particulate material floating within the combustion space. The space for burning the particles according to this specification has a special disk-like shape. This is necessary to maintain the particles in a fluid state. However, this gives a restriction with regard to the possibilities of constructions of the burner and its capacity. Furthermore it is not possible to fluidize all kinds of materials. Some materials can have such a weight/volume ratio that it is impossible to fluidize them. Furthermore it is often desirable to burn mixtures of materials, in which the individual components have different specific weight. In using air as fluidizing means a non-uniform distribution is obtained in this case. Although combustion with a fluidized bed is normally much cleaner than other methods for burning it is not possible to prevent that some harmful substances, such as aromatic components are produced.
The invention aims to obviate these drawbacks. This aim is realized in that in the space between both tubes screw conveyor means are provided. According to the invention transport of the material to be burnt is forced through mechanical means, whilst because of the large surface to volume ratio conditions are obtained approaching a fluidized bed. In this way it is possible to burn mixtures of materials having components with different specific weight. It is also possible to burn materials which are difficult to fluidize.
After the material to be burnt is introduced it is preheated by the heat from the inner tube. During heating decomposition occurs. The gaseous part leaves the burner and can directly be burnt or further processed. This gaseous part contains possible harmful components. The solid matters remaining are transported by the screw conveyor means and gasified by air introduced in the burner. The gas resulting from this process (such as CO) is introduced in the inner tube and burnt partially to heat this tube to the fore-mentioned decomposition temperature.
According to a preferred embodiment the screw conveyor means are connected to the inner tube, being rotatably suspended. In this manner a very simple embodiment of the burner according to the invention can be realised. To transfer gaseous products being formed in the space between the inner and outer tube and which are not completely burnt, filter openings can be comprised in the inner tube. For optimizing the combustion a vacuum air injection member can be provided. The burner can be provided with air with a blower introducing air with over-pressure in the space between the two tubes.
According to a further preferred embodiment the means for introducing of air can comprise an air box surrounding at least a part of the outer tube. This outer tube being air permeable and the lower part of the air box is connected to further conveyor means. Particulate material being able to move in the air box ca
REFERENCES:
patent: 4361100 (1982-11-01), Hinger
patent: 4470358 (1984-09-01), Prochnow
patent: 4593629 (1986-06-01), Pedersen et al.
patent: 4782765 (1988-11-01), Miller et al.
patent: 4856438 (1989-08-01), Peugh
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