The present invention relates to a screw conveyor for raising powdered or granular material, comprising a first cylindrical casing with a closed lower end, an upper end with an outlet opening, a conveyor screw rotatably mounted in the casing, and a second casing arranged to one side of the plane of the conveyor casing at the lower part of the conveyor casing, in which second casing a screw is rotatably mounted and is coupled to a drive means, said second casing having an inlet opening and an overflow opening and forming with its screw a feeder device for forced feeding of material into the conveyor casing via openings in the lateral surfaces of the casings.

Swedish Patent Application 8405096-9 reveals a screw conveyor with a feeder device of the above- mentioned type, in which a short vertical screw conveyor of greater diameter assists a vertical screw conveyor of lesser diameter in order to thereby increase the degree of filling of the latter. If both screws rotate with the same peripheral velocity, the capacity of the vertical conveyor can be increased to at most what the feeder screw can provide. Its degree of filling is as low as the mean screw conveyor itself, but due to the fact that it has a greater area, it can feed in more material and thus achieve an increase in the degree of filling of the conveyor. In this solution there is, however, the risk that material with a great angle of repose will not be captured at all because the screw may merely drill a hole in the material.

The purpose of the present invention is to achieve a screw conveyor of the type described by way of introduction, which makes it possible using the same diameter for the feeder and the conveyor to

achieve a significant increase in the degree of filling of the latter and to make possible the conveyance of material with a high angle of repose, such as pulverized coal. This is achieved in accordance with the invention by virtue of the fact that the axis of the feeder device forms an angle with the axis of the conveyor casing, the inlet opening of the feeder device lying at the same or a lower level than the overflow opening and being located in a hopper.

The invention is based on the insight that it is possible in a horizontal screw conveyor to achieve a degree of filling of up to 100%. By using a hori¬ zontal screw conveyor as a feeder, it is therefore possible to achieve a significant increase in the capacity of a vertical conveyor. With a completely horizontal feeder, the level of the overflow opening will at most be the same level as the inlet, which means that this arrangement is limited to fluidizable materials in order for the overflow to work, which has proved to be one of the basic preconditions for being able to achieve in practice exceptional increases in the degree of filling.

In accordance with a further development of the invention, the feeder axis is placed at an angle to the axis of the vertical screw which lies midway between vertical and horizontal, viz approximately 45° relative to the vertical screw, and this can provide a threefold increase in the degree of filling, and this means for most heavy non-fluidizable materials a degree of filling of about 30 as opposed to the normal 10 . Inclining the feeder involves a compromise between material fed to the vertical screw and overflow material, which eliminates the risk of the feeder screw jamming and keeps its power requirement at an optimal level. A greater degree of filling than that stated above, which is achieved with the same diameter of

feeder and conveyor screw, can be achieved if the feeder has a larger diameter than the conveyor screw in the known manner. It is not difficult to then achieve a fivefold increase in filling degree. ⁵ The invention will be described in more detail with reference to an example shown in the accompanying drawing, where the figure shows a partially section- side view of a vertical screw conveyor with an inclined feeder. ° In the figure, 1 designates a vertical screw conveyor with a cylindrical casing 2 and an inner screw 3. To one side of the screw conveyor 1 there is a short screw conveyor 4 with a cylindrical casing 5 and an inner screw 6 driven by a motor 13. Between the casing 5 and the casing 2 there is a passage 7 so that material can be fed from the conveyor 4 serving as a feeder to the vertical conveyor 1.

In the embodiment shown, the axis a of the feeder 4 forms an angle C - 45 with the axis b of the conveyor 1. The conveyor casing 2 is closed at its lower end by an end wall 8 and it has at its upper end (not shown) an outlet for the conveyed material. The feeder casing 5 extends into a hopper 9 and its inlet opening 10 is located therein. The hopper has an upwardly directed opening 11 for supplying material. The casing 5 has an overflow opening 12 through which material which is not able to be fed into the vertical screw casing can flow back to the hopper.

Material supplied to the hopper 9 is fed into the opening 10 of the inclined feeder casing 5 and is transported by the screw 6 to the passage 7 between the casing 5 and the casing 2 and into the latter. By controlling the rotational speed of the feeder screw, the desired flow from the vertical conveyor can be set. Uneven flow, due to suddenly sliding material for example, which rapidly increases the flow of material into the feeder, can be evened out by overflow back to

the hopper, so that an essentially constant flow can be maintained without the risk of the screw becoming jammed.

Tests have shown that the inclined feeder makes it possible to convey material with high angles of repose, e.g. coal. A vertical screw in a common hopper only drills a hole in materials such as powderized coal without any conveyance taking place. For non- fluidizable materials, the angle of incline ot between the axes a and b can vary between ca 30° and ca

70 depending on the type of material, while the angle for fluidizable material can be 90 , i.e. the feeder axis can be completely horizontal.