US2926009A - Device in a shaft furnace - Google Patents

Description

INVENTOR WM 5 y 1 j g Filed March 29, 1956 J E- WIKLUND DEVICE IN A SHAFT FURNACE Feb. 23, 1960 ATTORNEYS 2,926,009 DEVICE IN A SHAFT FURNACE: Johan Elof Wiklund; Halsingborg, Sweden Application March 29, 1956, Serial No. 574,899

Claims priority, application Sweden April 13, 1955 3 Claims. (Cl. 263-29) This invention relates to a shaft furnace and particular- 1y to means for the introduction of gas, preferably a hot gas, into the shaft and withdrawal of the same therefrom.

The problem of blowing in or withdrawing hot gas through the wall of a shaft furnace arises e.g. in connection with pelletizing recuperative furnaces, i.e. wherein the material is chilled by means of air, which then is introduced into a combustion chamber to act as combustion air for injected oil, and the hot combustion gases thus produced are introduced into the shaft through inlet orifices in the wall of the shaft.

In order to prevent clogging of said inlets attempts have been made to give the inlets several difierent shapes. It has been tried, for instance, to considerably increase the cross sectional area of the shaft in the zone where the hot gas is introduced, the idea thereof being that the material moving downwardly might form a free cave surface at the level of the widening of the shaft, and that said inlets when placed adjacent said free cave surface might be maintained free from material. It has been found, however, that the material tends to jam where the shaft widens. One circumstance that contributes to this is that no upper pressure will be exerted on the material that forms the free cave surface, for which reason said material tends to adhere to the wall of the furnace. Once such adherence has occurred the amount of adhered material continuously increases so that the flow in the furnace ceases.

It also has been suggested to form the hot gas inlets as perforated blocks, constituting a part of the furnace wall. It has been found, however, that the material enters into the perforations far too easily and chokes up said perforations.

According to the present invention these drawbacks are avoided, so that the gas may be fed into the shaft furnace without danger of clogging and jamming in the furnace. The furnace according to the invention comprises ducts, extending through the wall of the furnace, and is characterised in that the cross sectional area of the ducts increases from the internal surface of the furnace wall to the external surface of said wall, and that the lowermost surface of the ducts is inclined so as to form an acute angle with the internal furnace Wall surface.

Inasmuch as the ducts are formed with an outwardly directed draft, i.e. their cross sectional area increases outwardly from the internal wall surface, pieces of material that inadvertently enter the ducts may easily pass and do not jam up in the ducts.

Inasmuch as the lowermost surfaces of the ducts are inclined downwardly these surfaces do not provide any hold for the material wherefore pieces thereof that have entered into a duct slide outwardly along said inclined surfaces.

Theoretically the ducts may be formed with any cross sectional area desired, provided that the above mentioned requirements are complied with. However, it

- United tates Patent M 2,926,009 Patented Feb. 23, 1960 ICC has been found particularly advantageous to form the ducts as vertically extending slots. Therefore, the invention will hereinafter be described more in detail with reference made to a sintering furnace with gas inlets and outlets having the formof such vertically extending slots.

In the drawing Fig. 1 shows a shaft furnace with its combustion chamber in a vertical section and Fig. 2 is a section along line IIII of Fig. 1.

The assembly comprises a shaft furnace 1, having a combustion chamber 2. The wall 3 between the furnace and the combustion chamber is built up as two upright vaults, having the shape of arcs with centres at the points 7 and 8 respectively in the opposite combustion chamber Wall 9. In the vaults there are arranged one above the other two rows of wedge-shaped bricks, positioned so as to form between themselves vertically extending slots or ducts 5 and 6 respectively. The bricks are shaped so that the lowermost surfaces of the slots are inclined at an acute angle with respect to the internal furnace surface. Each of the slots 5, 6 between the bricks 4 has a horizontal cross section that widens from the shaft towards the combustion chamber.

Inasmuch as the Wall 3 has an arcuate shape and the bricks extend radially therein the slots 5 will be readily accessible for cleaning from the center of the arc, i.e. the points 7 and 8 respectively. At these points there are arranged openings 11 and 13 respectively, having the dual purpose of serving as cleaning and inspection openmgs.

Openings 15 for oil burner nozzles are arranged in the combustion chamber walls. In the bottoms of the combustion chambers there are arranged outlet openings 17 for material that enters through the slots 5 and falls down into the combustion chambers. openings 17 the material then by means of devices that are not shown is passed away to join the material which is fed from the bottom of the furnace. The amount of material entering into the combustion chambers is very low. This is due partly to the inherent tendency of the material to form bridges and partly to that the material is partially melt and thus less mobile.

The operation of the sintering furnace is as follows: The material to be sintered, e.g. ore slick balls is loaded in at the top portion of the furnace. Air is blown in at the bottom portion of the furnace and flows upwardly to meet the hot sintered material, which then will be chilled. The air, having thus been pro-heated, flows on the one hand straight upwardly through the shaft and on the other hand into the combustion chamber 2 through the slots 5. Oil is injected into the combustion chamber and will burn with the pre-heated air acting as combustion air. The hot combustion gases leave the combustion chamber through the upper slots 6. The proportion of the air blown in at the bottom of the furnace which passes through the combustion chamber will be determined by the relation between the flow resistances of the combustion chamber and the material column of corresponding height respectively.

In order to permit distribution of the hot combustion gas over the entire cross sectional area of the shaft the height of the vertical slots should at least correspond to half the width of the shaft.

I claim:

1. In a shaft furnace having a vertical shaft adapted to receive a downwardly directed load of material to be treated and an upwardly directed passage of air, a combustion chamber secured externally to one wall of said shaft and extending laterally outwardly therefrom, and having a wall opposite the said one wall of the shaft, said wall of said combustion chamber opposite said shaft From the outlet 3 wall having vertically spaced openings therein, a portion of said shaft wall having an arcuate configuration in horizontal cross section, the center of the are being located on a vertical line extending centrally through said combustion chamber opposite wall openings, said shaft wall arcuate portion having a plurality of lower ducts therein opposite one of said combustion chamber opposite wall openings for admitting the upwardly directed air from the vertical shaft into the combustion chamber and also a plurality of upper ducts therein oppositeione of said combustion chamber opposite wall openings for introducing the heated gases of the combustion chamber substantially vertically into the vertical shaft, the vertical cross sectional area of each of said ducts increasing outwardly from the internal shaft surface of the furnace wall toward the combustion chamber and the lower surface of each of said ducts being downwardly inclined and forming an acute angle with the internal furnace wall surface, whereby said ducts may be readily cleaned from the openings in the opposite wall of the combustion 4 chamber located at the center of the arc of the furnace shaft arcuate portions.

2. A shaft furnace as defined in claim 1 wherein the bottom of said combustion chamber has an outlet opening therein for discharging solid material entering into' said combustion chamber through said ducts.

3. A shaft furnace as defined in claim 1 wherein each of the ducts has a height at least as great as half the distance between the wall intermediate the combustion chamber and the vertical shaft and the opposite wall of said vertical shaft.

References Cited in the file of this patent UNITED STATES PATENTS

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