The invention also relates to a method of cleaning a sieve system in a screw press comprising threads and at least one rotatable hollow stem as well as a sieve cylinder surrounding the stem in portions of or essentially in its entire periphery, thereby providing a drainage gap between the outer surface of the stem and the inner surface of the sieve cylinder, said stem being disposed in a housing, said stem comprising a drainage pipe in its interior, said drainage pipe communicating with the drainage gap at an inlet opening via a first piping system, said drainage pipe communicating with a liquid connection disposed outside the screw press, said sieve cylinder al- lowing passage of liquid from a drained substance disposed outside the stem, said liquid being conveyed into the drainage gap from which the liquid/drainage liquid is conveyed away in a first direction to a liquid con- nection, and a gap liquid preferably water for cleaning the sieve system is conveyed from a liquid connection through the drainage gap.

US-A-4 565 124 discloses a press having an incorporated drainage system for the cleaning of a surrounding sieve housing. However, feeding of liquid for the cleaning of the drainage gap takes place at the end where the sub- stance has the highest viscosity, and the feeding additionally takes place by

means of a single valve, which provides a local supply of liquid to the drain- age gap. Thus, in this structure, insufficient cleaning of the drainage gap takes place, as the drainage gap is not cleaned by supplied flushing liquid in its entire circumference, just as the highly viscous material results in a poorer utilization of the flushing liquid.

Also known are screw presses in which a given substance is pressed to drain the liquid out of it, said liquid being conveyed through a sieve system which partly surrounds the stems of the screw presses, is partly provided in the wall of the housing to drain the substance such that a suitable consis- tency is imparted to it.

During drainage of the liquid within the actual stem, the system will be clogged such that the drainage effect is reduced during the operation of the screw press. To remove such clogging, it is therefore necessary to clean the screw press, following which liquid from a liquid basin or a direct liquid connection disposed outside the screw press is fed through a channel in- side the interior of the stem and through a piping system extending radially from it to the gap which is present between the outer surface of the stem and the inner faces of the surrounding sieve, by which flushing the sticking substance will be removed. The cleaning liquid used, which is preferably water, will be returned via the same piping system to a liquid basin where it is optionally cleaned.

Accordingly, the object of the present invention is to remedy the above- mentioned problem and thus ensure that the sieve of the screw press and its drainage duct system surrounding the stem may be cleaned continu- ously, so that the cloggings are removed by flushing which is carried out while the screw press is still in operation, i. e. while the screw press works and carries out drainage of the substance.

This object is achieved with a screw press of the type stated initially, wherein, spaced from the first piping system, there is also at least a second communication via a second piping system which connects the drainage gap with at least a second pipe, said second pipe comprising an inlet opening for connection/communication with a liquid connection.

The same is achieved with a method as stated initially, wherein also gap liquid and drainage liquid are returned to a liquid connection for collection of the liquid, said circulation being established via a system comprising a sec- ond pipe which connects the liquid connection with at least a second piping system, said second piping system communicating with the drainage pipe.

Thus, it is characteristic of this process that the direction of operation of the gap liquid is opposite to the direction of operation of the known systems and processes.

Thus, the apparatus and the method operate in that, during drainage of a given substance which may e. g. be sugar beet pulp, slaughterhouse offal, fish offal, sludge, etc., cleaning of the substance takes place in that the stem of the screw press rotates about its axis and carries out pressing of the substance with its threads. Preferably, the screw press will consist of at least two stems having threads, which threads mate with each other and press the substance.

This pressing thus causes drainage, partly through the sieve system of the surrounding housing, partly inwards toward the stem which is surrounded by a sieve. A drainage gap exists between the sieve and the outer surface of the stem where the water is collected, said liquid being discharged through a star-shaped and radially extending first piping system, said drained liquid being conveyed inwards into the interior of the stem to a drainage pipe, which is disposed there and which'optionally extends axis-

parallel and co-axially with the axis of rotation of the stem, from where the liquid is conveyed to a liquid connection, e. g. a liquid basin. However, the drainage pipe may extend in any other way in the interior of the stem, e. g. offset from the axis and forming an angle with it.

Liquid will be pumped in simultaneously and intermittently or continuously, there being provided in the area from a second liquid connection or from the liquid basin and to a second piping system, which is configured like the first piping system, a second pipe optionally arranged around the drainage pipe and c-axially with this, said liquid being conveyed from the connection to the second piping system from where liquid is pumped up to the drainage gap. Preferably, the second piping system is closest to the liquid connec- tion, while the first piping system is at the greatest possible distance from the liquid connection and at the end of the stem where the substance is thickest, i. e. also furthest away from the inlet opening in the housing. The advantage of this will thus be that the liquid to flush the drainage pipe will have a maximum travel from the outlet opening of the second piping system in the drainage gap to the outlet opening of the first piping system in the drainage pipe. The flushing liquid thus removes the substance which has got stuck in the sieve system and will be pressed into the radial outlet openings of the first piping system and from there further on to the drainage pipe itself, from which it is e. g. returned to a liquid basin in which cleaning may take place.

Thus, with such a structure it is possible to carry out the cleaning at regular intervals, while the screw press, by its rotation, continues to press the sub- stance, and therefore it is not necessary to stop the entire system, and therefore, because of the circuit which is established, there will be no clog- ging of the sieve system.

By providing a screw press according to the invention and as stated in

claim 2, the most expedient shape of the second pipe is achieved, thereby optimizing the possibility of carrying out drainage during the operation of the press.

By providing a screw press according to the invention and as stated in claim 3, a simple configuration of the piping systems is achieved.

By providing a screw press according to the invention and as stated in claim 4, optimum pressing of the substance is achieved because of a mini- mum shape of the screw press.

By providing a screw press according to the invention and as stated in claim 5, it is ensured that both the liquid from the substance and the liquid which has been used for flushing the sieve system, may be re-used.

By providing a screw press according to the invention and as stated in claim 6, the greatest possible drainage area is achieved.

As mentioned, the invention also relates to a method as stated in claim 7, having the previously mentioned advantages.

By providing a method according to the invention and as stated in clalim 8, recirculation of the liquid is achieved.

By providing a method according to the invention and as stated in claim 9, optimization of the system is achieved.

The invention also relates to a use of the apparatus according to claims 1- 6, as stated in claim 10.

The invention will now be explained more fully with reference to the draw-

ing, in which fig. 1 shows a hollow stem for a screw press comprising the surrounding sieve cylinder and the piping systems and seen in cross-section, fig. 2 shows a water basin in general view, fig. 3 shows a detail view of the inlet area for gap liquid, fig. 4 shows a cross-sectional view of the piping systems of fig. 1.

Fig. 1 shows a stem 2 for use in a screw press 1 according to the invention.

The stem 2 is shown in section and, in the example shown, it is a hollow conical cylinder with turns/threads 3 mounted thereon. The stem is more- over surrounded by a sieve cylinder 4, said sieve cylinder 4 being posi- tioned c-axially with the stem 2, and the longitudinal axis of both the stem and the sieve cylinder coincides with the axis of rotation L of the stem. The threads 3 are preferably mounted on the sieve cylinder 4. The threads may be mounted directly on the stem at one or both end areas. The sieve cylin- der consists of a conical-cylindrical pipe having openings through which the liquid may pass. When the stem 2 is used for a screw press 1 for the pressing of substance, e. g. sugar beet pulp, sludge, fish offal, etc., pressing of the substance takes place between the threads 3 of the stem, and the drained water will be separated from the substance via the housing in which the threads are positioned (not shown in the drawing) and which comprises a sieve, or will pass through the openings of the sieve cylinder 4 into the drainage gap 6 which is provided between the outer surface 5 of the stem and the inner surface of the sieve cylinder 4 itself. The substance is con- veyed into the housing via an inlet opening. The drainage liquid will be col- lected in the gap and will be conveyed from there out to a liquid basin 12

arranged outside the actual screw press 1 and the stem 2. This will be ex- plained more fully below.

The stem 2 comprises a hollow cylindrical drainage pipe 8 in its interior op- tionally c-axial with it, said cylindrical drainage pipe 8 having an inlet opening 9 communicating with a first piping system 10, said piping system 10 being shown in detail in fig. 4. The drainage pipe may have any position in the stem, e. g. parallel with or forming an angle at the longitudinal axis L of the stem. However, in the axis pin, the drainage pipe will normally extend in parallel with the longitudinal axis. In general, several drainage pipes may be provided. The individual hollow pipes 15 of the piping system 10, which extend radially from the inlet opening 9 of the drainage pipe 10, terminate in the drainage gap 6, and the drained liquid will therefore run into these hol- low pipes 15, further through the inlet opening 9 of the drainage pipe, and from there pass through the drainage pipe to its outlet opening 11, as shown in fig. 3. From there, the drainage liquid will e. g. run down into a collection chamber, as shown in fig. 2 and designated 16, where the liquid is optionally cleaned and may be used as a flushing liquid, said liquid being conveyed back to the stem 2 via a line for cleaning of the sieve cylinder 4, as will be explained in the following.

In addition to the first piping system 10, mentioned above, said first piping system being disposed at the greatest possible distance from the outlet opening of the drainage pipe 8, the stem 2 also comprises a second piping system 13 which is constructed essentially like the first piping system 10, said second piping system 13 being spaced from the first piping system 10 and close to the outlet opening 11 of the drainage pipe 8. This piping sys- tem 13 provides communication between the drainage gap 6 and an outlet opening 19, which belongs to a so-called second pipe 14. This second pipe 14 communicates with a liquid basin 12 or a liquid connection and is pref- erably arranged co-axially relative to the drainage pipe 6 and terminates in

the outlet opening 19, as mentioned. However, like the drainage pipe, the second pipe may have any extent in the stem, and will extend axis-parallel to the longitudinal axis L also in the axis pin area. In general, several drain- age pipes may be provided. Liquid from the liquid basin 12 or the liquid connection will be sprayed into the inlet opening 18 of the second pipe, as shown in fig. 3, preferably at a stub which is arranged outside the actual stem, and which thus communicates with the gap which is provided be- tween the inner face of the second pipe 14 and the outer face of the drain- age pipe 8.

Because of the dimensions of the screw press-the length may e. g. be 10- 12 m-it is perhaps necessary to have spacer stays arranged to extend radially between the inner walls of the stem and from its centre line L.

The liquid is now pressed in at a high pressure, the liquid pressure being up to about 10 bars, and from there via the second piping system 13 up to the actual drainage gap 6, where liquid is pressed through and thereby flushes the sieve cylinder system, thus removing the substance which has got stuck, and drained liquid is therefore again allowed to pass into and through the drainage gap 6 from the surrounding space. The drainage liquid mixed with the gap liquid now runs down to the first piping system 10, from which it is removed from the drainage gap and further into the drainage pipe 8, from which it is removed from the system via the outlet opening 11 of the drainage pipe down to a liquid basin 16 where the liquid is optionally cleaned. The liquid may subsequently be recirculated via valve devices to the inlet openings 18 of the second pipe, optionally supplemented with a fresh water supply from a valve 17.

The first piping systems and the second piping systems 10 and 13 them- selves are shown in detail in fig. 4 and thus consist of hollow pipes 15 forming a spoke-shaped system, where they optionally extend from a

housing 9,19, which, in this case, constitutes the inlet opening 9 of the drainage pipe 8 and the outlet opening 19 of the second pipe 14, respec- tively, and from which there is thus a connection to these. Communication is provided from these housings via the hollow pipes 15 out to the drainage gap 6 itself. This structure ensures an even flushing when this system is used in connection with the second piping system and smooth drainage is achieved in connection with the use of the system for the first piping system where the drained liquid is returned via the drainage pipe.

The flushing liquid is thus sent into the drainage gap where the drained substance has a low viscosity, and leaves the drainage gap where the sub- stance has a high viscosity. This means that the second piping system is positioned at the same end of the press as the one where the substance to be drained is admitted. If desired, the process may be reversed, and the first piping system will take over the function of the second piping system, and vice versa, and the liquid connections outside the press will likewise be interchanged.

The press may be used for various forms of substance, including sugar beet pulp, fish offal, sludge, bone waste, etc. In other words, all forms of substance where pressing and disintegration of the substance are to be effected, partly to have it in smaller parts, partly to press excess liquid out, which may be water or oil, etc.

The liquid, however, which is always used for flushing the sieve system, will be relatively clean water or cleaned drainage liquid to which clean water has been added.