In connection with the manufacture of papermaking pulp, in different steps of the process material is transported in the form of chips or pulp. In certain parts of the process the material must be fed uniformly from containers for storage and/or treatment of the material to a subsequent treatment step, for example feeding of chips from a storage container to a digester. The problem in this case is to bring about a uniform flow through the container. The material can adhere to the walls of the container and thereby cause arching and/or the material can move at different speeds in different parts of the cross-section of the container. The feed of the material through the container can thereby be stopped or the stay-time of the material in the container can vary. This is particularly unfavourable when the material is subjected to some kind of treatment in the container, for example preheating with steam or treatment with chemicals.

Many different solutions of the above problem have been suggested. The walls of the container, for example, can be given different configuration and angles, and different types of discharge means can be placed in the container. All these solutions, however, have disadvantages, which imply that the problem at least partially remains.

The present invention offers a solution of the problem, in that the container at the bottom is provided with a discharge device comprising two counter-rotating parallel screws located above a narrow down pipe. The characterizing features of the invention are apparent from the attached claims.

According to the invention, a substantially cylindric container converges at its lower portion from two opposed sides down to an oblong space in the bottom of the container.

In said space, which suitably has a substantially rectangular or at the ends rounded cross-section, two co-operating counter-rotating screws are placed. The screws shall be placed adjacent each other without partition wall, and the shafts of the screws shall be horizontal and in parallel and be located in the same horizontal plane.

The central line of the shaft of each screw suitably shall be placed at the same level as the upper edge of the space, or the shafts should be placed so that at least the upper edge of the thread flanks of the screws is located above the upper edge of the space. The bottom of the space suitably is adapted to the diameter of the screw threads so that a longitudinal edge is formed between the screws. A narrow down pipe is connected to the bottom of the space for receiving the material discharged from the container. Said down pipe suitably has a diameter corresponding to the width of the space.

According to a preferred embodiment, the down pipe is placed centrally beneath the container, and the screws are arranged to feed the material from two directions inward to the down pipe. Alternatively, the down pipe can be placed at one end of the oblong space, and the screws are formed for feeding only to this direction.

It is suitably according to the invention to form the screws with a space between the threads increasing in the direction to the down pipe. This can be achieved in that the thread pitch increases in the direction to the down pipe or in that the diameter of the shafts of the screws decreases in the direction to the down pipe or by a combination of these alternatives. Hereby a more uniform feed of the material can be maintained across the cross-section of the container.

According to another preferred embodiment with centrally located down pipe, each screw is formed with a distributor in the form of a radial disc located centrally above the down pipe. The disc should have a diameter corresponding to the diameter of the screw threads, and it should have a thickness decreasing to the circumference. By this design the feed down through the down pipe is still more improved.

According to another embodiment, the down pipe is located directly above a pump, by which the material fed down through the down pipe is pumped to a subsequent treatment step. As the discharge screws bring about a uniform discharge from the container, the flow through the pump also becomes uniform and stable, which results in high operation safety and uniform treatment of the material.

According to another embodiment, a means for the addition of a treatment medium is connected to the discharger. This supply means suitably is formed with a plurality of nozzles for the supply of the medium along the length of each screw, preferably through the walls of the space beneath the container at the same level as the shafts of the screws.

This position is especially favourable for the supply of the medium, because the material is in motion and, thus, the admixing will be good.

The invention is described in greater detail in the following with reference to the accompanying Figures illustrating an embodiment of the invention.

Figs. 1 and 2 are two different lateral views of a device according to the invention; Fig. 3 is a view from above of the device shown in Figs. 1 and 2.

The illustrated embodiment comprises a container 10, which has a cylindric upper portion 11 and a lower portion 12, which converges from opposed sides to a space 13 at the bottom of the container. Said space has a substantially rectangular cross-section and is adapted to two feed screws 14, 15, which have horizontal and parallel shafts located in a common horizontal plane. The screws are provided with threads for feeding the material and are arranged so that the outer circumferences of the screw threads are located at a small distance from each other without a partition wall between the screws.

The thread flanks of the screws 14,15 extend upwards above the upper edge of the space 13. The bottom of the space 13 follows the diameter of the screw threads whereby a longitudinal edge 22 is formed between the screws 14,15. Said edge 22 is located highest at the same level as the centre line of the screws.

Centrally beneath the space 13 a down pipe 16 is connected for receiving material from the container. The down pipe 16 has a diameter corresponding to the width of the space 13. The screws 14,15 are formed with threads for feeding the material inward to the down pipe 16. The rotation direction of the screws is opposed, so that the upwardly turned portion of the screws moves from the outer wall of the space 13 inward to the centre of the space. This implies that the thread pitch at the end of a screw 14,15 is opposed. Centrally on each screw 14,15 a distributor 17 is located. This distributor 17 is formed with a radial disc, the thickness of which decreases successively from the centre outward to its circumference. The distributor 17 has the same diameter as the screw thread, and its object is to interrupt the axial feed of the screws and direct the material down into the down pipe 13.

The screws 14,15 are driven each by its motor 18,19 at uniform speed, and the two screws suitably have the same speed. In order to additionally ensure that the material is fed from the entire cross-section of the container, the screws can be formed with a space between the threads increasing inward to the down pipe, for example increasing thread pitch or decreasing screw shaft diameter.

Beneath the down pipe 13 a pump 20 is located. The pump inlet, thus, is directly connected to the down pipe, which implies that the pump 20 can deliver a uniform outgoing material flow to a subsequent treatment step.

According to the embodiment shown, a plurality of nozzles 21 are connected to the space 13 for the supply of treatment medium in the form of gas or liquid, such as steam and chemicals. These nozzles 21 are located at both long sides of the space 13 at the same height as the shafts of the screws so that an optimum admixing to the material is obtained.

By forming the container with a discharger with two feed screws according to the invention it has proved possible to improve the discharge and effectively to prevent that the material adheres or is fed non-uniformly in the container. It is at the same time possible to obtain an even and operationally safe pumping of the. material directly from the discharge out of the container to subsequent treatment steps.

The invention, of course, is not restricted to the embodiments shown, but can be varied within the scope of the claims with reference to the description and Figures.