SCREW PRESS

Abstract: A screw press, which compresses and dewaters more or less moist cellulose-containing and/or fibrous materials in pieces, e.g. waste paper, wood, grass, straw and other harvest products, cellulose, peat, bark and the like, includes a feed device (2) having an input portion (3) for material, which is to be compressed, and at least one first pressure cone (13) for a forceful compressing of the material, a discharge opening (26) for the compressed and dewatered product, a rotary screw (11), which extends from the input portion at least into said first pressure cone (13) as well as driving means (8, 9) to make the screw rotate. The core (27) of the screw and/or its thread (28) is eccentric in relation to the rotation axis (30) of the screw and in relation to the mean screw line of the core respectively, in at least some of the thread turns in one zone (V) of said first pressure cone, and the jacket of this pressure cone (13) is impermeable in said zone (V).

Description: Screw Press The Technical Field The present invention relates to a screw press, which compresses and dewaters more or less moist cellulose-con¬ taining and/or fibrous materials in pieces, e.g. waste pa¬ per, wood, grass, straw and other harvest products, peat, bark, cellulose and the like, in order to produce bri¬ quettes, which screw press comprises a feed unit having an input portion for the material, which is to be comp¬ ressed, at least a first press cone for a forceful comp¬ ressing of the material, an output opening for the co p- ressed and dewatered product, a rotary screw, which ex¬ tends from said feeding unit at least into said first press cone, as well as driving means to turn the screw. The Background of the Present Invention Presses for briquette production from fibrous materials of the kind mentioned above commonly use cylinders and pis¬ tons as compressive devices. By means of available const¬ ructions, based on this principle, it is feasible to pro- duce briquettes from materials having moisture precentages of less than 20%. Screw presses are also known in a plura¬ lity of designs for dewatering fiber materials and other compressible materials in the form of pieces. Embodiments of such screw presses are shown in US-A-2 615 385 and in US-A-4 121 967. By means of these and other known screw presses materials having a very high moisture content can be dewatered but not to such an extent as is requried when producing fuel briquettes. A fundamental problem, which cannot be solved according to known technique, is how to be able to drain off the water from the pressure zone at the very high pressures, which are needed in order to at- tain a high water removal without simultaneously forcing out the compressed material together with the water. It is customary to provide the pressure cone with dewatering openings, e.g. in those constructions, which are shown in the above-mentioned patent specifications, but they ren¬ der impossible the high pressures required to remove the water up to very high dry contents in the compressed ma¬ terial. In case the pressure in the pressure cone is ele¬ vated to very high levels, the compressed material will simply be "sprayed" out through the openings. In case on the other side these drainage openings are eliminated in order to create conditions for very high pressures in the pressure cone, the water will be locked up in the same. - This set of problems seems to be the primary reason why screw presses so far could not be used to dewater moist, fibrous materials to very high dry contents while produ¬ cing continuous compressed bodies. A Description of the Present Invention The object of the present invention is to design a screw press of that kind, which is stated in the preamble and by means of which " it is possible to dewater and to produce briquettes from the above-mentioned materials having ois- ture contents of as high as 60%, when hard, quite continu¬ ous briquettes having very high dry contents are produced. These and other objects can be attained, if the core of the screw and/or its thread is eccentric in relation to -the rotation axis of the screw and in relation to the mean screw line of the thread respectively , in at least one or two of the thread turns in the area, in which said first pressure cone is situated. Also, the wall of the pressure cone is impermeable, at least in one zone of the same, where it is substantially axially extended, so that local, very high pressures can be built up. We have found that if a screw press is designed in this way, it can very effici- ently be dewatered, also in case the moisture content of the starting material is very high. The present invention is not based on any particular theory, which claims that it can explain scientifically why this effect is achieved. However, experiments, which have been carried out, indicate that the screw during its rotary movement kneads the mate¬ rial by subjecting it repeatedly to large local pressure increases and pressure drops, which seem to lead to voids being formed in the compressed material in the thread turn, in which voids water in the liquid and/or the gaseous phase can be accumulated under pressure in order to be evacuated backwards in the thread turn, during the rotary movement of the screw and while it is influenced by the pressure of the compressed material. When testing various designs of the screw it could not be fully determined whether eccentrici¬ ties of the screw shaft or of the thread were the main cause of the desired result. Probably a cooperation between the eccentricities in the screw core and in the thread is achieved and thus, the core as well as the thread ought to be made eccentric in this area. The eccentricity of the thread is preferably attained by making it waved. In order to be able to remove the moisture, which is pressed backwards in the press,a jacket section preferably is ar- ranged between the feed portion and the fully jacketed pres¬ sure cone or pressure cone zone, which jacket section is provided with drainage openings. This water must not be locked up inside the central portion of the compressed bo¬ dy without a chance to be pressed out towards the drainage openings in the jacket and hence, the screw press is, acc¬ ording to a preferred embodiment, designed in such a man¬ ner that the compressed body in or adjacent to the area of the drainage openings is cracked, so that the water from the central portion of the compressed body can be evacuated through the cracks outwards towards the jacket and then through the drainage openings in it. Additional characterizing features and attributes as well as advantages of the present invention are stated in the enclosed patent claims and in the following description of a preferred embodiment. A Brief Description of the Drawings In the following description of a preferred embodiment re¬ ference will be made to the accompanying drawings, in which: Figure 1 is a longitudinal section of the screw press; Figure 2 is a lateral view of the screw; and Figure 3 shows the screw in a view III-III in Figure 2; Figure 4 is a longitudinal section of a dewatering cylin¬ der and an attached first pressure cone. A Description of a Preferred Embodiment The screw press shown in Figure 1 is mounted on a base 1. The screw is mounted on .base 1 by means of its feed por¬ tion 2, which is provided with an input portion 3. A feed hopper 4 is arranged above the input portion. In hopper 4 a down-feeder 5 is disposed, which oscillates in i vertical direction and is driven via a crank 6 and transmission means 7 by driving shaft 8 of an electric motor 9. Driving shaft 8 is extended through a shaft housing 10 and is designed to drive a screw 11. Screw 11 extends through input portion 3, also through a dewatering cylinder 12 and finally into a first pressure cone 13. A second pressure cone, which constitutes a di¬ rect extension of first pressure cone 13, has a reference numeral 14 and a terminating nozzle having a third conical constriction 16 has reference numeral 15. Dewatering cylinder 12 and the preliminary portion of the connecting first pressure cone 13, Figure 4, are on their interior sides in a way known per se provided with longi¬ tudinal bars 17, which prevent the compressed material from rotating in the thread turn together with screw 11. In its rear portion - the reference numeral of this zone is 18 - the jacket of dewatering cylinder 12 is provided with a plurality of drainage holes 19, which are distribu¬ ted around the jacket. They have a diameter of 3 mm. Drai- nage zone 18 is surrounded by a casing 20, which collects water, which flows or is forced out through holes 20. A drainage duct from casing 20 har reference numeral 21. First pressure cone 13 is in its central portion surrounded by a cooling jacket 22, through which cooling water flows. The thread or wings 28 of screw 11 are not extended into second pressure cone 14, which by means of threads 23 is tightened to first pressure cone 13, but in return an ex¬ tension of core 27 of the screw is extended with an ex- tension piece 45 into said second pressure cone 14. This second pressure cone 14 is surrounded by a cooling jacket 24, through which cooling water flows in order to carry off heat, which is generated also in this second pressure cone. The terminating nozzle 16, the terminating inner di- ameter 25 of which is chosen in accordance with the desi¬ red diameter of the briquettes, is also mounted on the pre¬ ceding pressure cone by means of screwing. Core 27 of screw 11 has a decreasing diameter along its length and partly also a varying shape. Thread 28 has a varying pitch along the length of the screw. Along its main portion thread 28 has a cylindric exterior contour, which in the area of first pressure cone 13 is transformed into a conical shape. Screw 11 can as far as the varying pitch of thread 28 is concerned be divided into a plura¬ lity of zones I-VI. Zone I - a large pitch - one thread turn 28A Zone II - a moderate pitch - three thread turns 28B Zone III - a very large pitch - one thread turn 28C Zone IV - a moderate pitch - three thread turns 28D Zone V - a small waved pitch - three thread turns 28E The large pitch in first thread turn 28A, zone I, makes it easier for screw 28 to receive coarse materials, e.g. large paper lumps, boards and the like. In the next zone II in input portion 3 the thread pitch is somewhat smaller and during these three thread turns 28B a certain compressing of the material takes place. In the preliminary thread turn 28C, zone III, in dewatering cylinder 12, the very large thread pitch leads to a tearing apart of the comp- ressed material anew, which results in a multitude of cracks in the material with a predominantly radial direc¬ tion. Subsequently, the material is compacted again in the following three thread turns 28D in zone IV in dewatering cylinder 12. In terminating zone V in pressure cone 13 screw 11 has a conical shape. The terminating thread turn in zone IV extends into pressure cone 13 with a moderate pitch. The following three thread turns 28E have a very small waved pitch. This feature as well as the conically decreasing shape of the thread turn lead to a very force- ful additional compressing of the compressed material, while a very high pressure and heat is generated. The waved or winding shape of the thread results in a compressing of the compressed material by jerks, which has proved to be particularily effective, when trying to achieve a maximal compressing, and at the same time seems to facilitate the water removal. The latter effect seems to occur in the clearance or unloading phases, which follow every crest of a wave on the thread. Core 27 of the screw is shaped in the thread path between the thread turns in such a way, that the thread path bot- torn in axial sections is bowl-shaped, which is known per se. The mean diameter of screw core 27 is in the first three zones I-III and also in about half the fourth zone IV unalterably the same. However, the shape of screw core 27 in the remaining part is quite complicated. Thus, the diameter of thread path X is smaller than in the preceding thread turn. Susbsequently the diameter decreases further but to different degrees on different sides of the rota¬ tion axis, as is shown in Figures 2 and 3. While the diame- ter of the core decreases symmetrically, conically in an axial section, Figure 2, it decreases unsymmetrically in a section, which is transverse to the preceding one, Figure 3. Thus, the smallest radius R, in thread path bottom 40 is considerably smaller than the smallest radius R 2 in thread path bottom 41 on the opposite side of the screw. The same relation exists in the next thread turn, in which radius R., is less than R.. An additional particular feature is that radius R, is smaller than the largest radius R 5 in thread path bottom 42. Thus, thread 28 as well as core 27 are designed in such a manner, that the compressed material is subjected to forceful local pressure increases, followed by pressure drops in pressure cone 13, which is imperme¬ able. This certainly implies that the compressed material is throughly kneaded in pressure cone 13, so that voids are formed, in which water and vapor can be accumulated under a high pressure and at a high temperature. These voids are forced backwards. Why this happens is difficult to explain and it can only be observed as a fact. Thus, -water and vapor, which are accumulated in these voids, is gradually transported backwards, which takes place by jerks. Also, since only a limited amount of vapor is comp¬ ressed under a high pressure in each void, the risks, which otherwise are connected with a high vapor pressure, are eliminated. The terminating pin 45 is eccentrically disposed but is parallell with the screw axis, which means that its point 46 while it is rotating describes a small circle, which prevents the packing of the canal, which screw core 27 has formed in the middle of the compressed body. Thus, the fi¬ nished briquette material, which is pressed out through the terminating nozzle 15, is tube-shaped, so that steam also can leave pressure cone 13 in this central channel, in which a passage is kept open all the time by means of eccentric rotary pin 45. The waved or winding shape of the thread in terminating zone 5 is shown in Figure 2. Thus, threads in this zone are, in the two preliminary thread turns, provided with two forwardly directed portions 46,47 as crests of a wave. Thus, there is an angle between the tangents 50 of these crests and an imaginary tangent against the normal shape of the thread. This angle has a reference designation A in Figure 2. In order to facilitate the clearance in the terminating nozzle, the same can be made rotary. Driving means used to turn the nozzle has symbolically been indicated with nume¬ ral 51.

Claims: Claims : 1. A screw press, which compresses and dewaters more or less moist cellulose-containg and/or other fibrous mate- rials in pieces * e.g. waste paper, wood, grass, straw and other harvest products, cellulose, peat, bark and the like, which press includes a feed device (2) having an input portion (3) for the material, which is to be comp¬ ressed, and at least one first pressure cone (13) for a forceful compressing of the material, a discharge opening (26) for the compressed and dewatered product, a rotary screw (11) , which extends from the input portion at least into said first pressure cone (13) , as well as driving means (8,9), which make the screw rotate, c h a r a c - t e r i z e d in that the core (27) and/or the thread (28) o the screw is eccentrically disposed in relation to the ro¬ tation axis (30) of the screw and in relation to the mean screw line of the core respectively, in at least some of the thread turns in a zone (V) of said first pressure cone, and that the jacket of said pressure cone (13) is imperme¬ able in said zone (5) . 2. A screw press according to claim 1, c h a r a c ¬ t e r i z e d in that a jacket portion (12) having drai- nage holes (19) is disposed behind said first pressure cone. 3. A screw press according to claim 1, c h a r a c ¬ t e r i z e d in that the thread in the area of the first pressure cone is waved. 4. A screw press according to any of claims 1-3, c h a r a c t e r i z e d in that the screw core is pro¬ vided with an extension in the form av an eccentric pin (45). 5. A screw press according to claim 3, c h a r a c ¬ t e r i z e d in that the thread has a substantially larger pitch in a zone of the area for or adjacent to said drainage holes in order to tear apart the compressed material, so tha_t water can flow from the central por¬ tions of the compressed material towards the jacket and the drainage holes.

Inventors: KVARNSTROEM HANS-ERIK, KVARNSTROEM, HANS-ERIK
Applicants: GNII KVARTSEVOGO STEKLA, KVARNSTROEM, HANS-ERIK
Application year: 1987
Main classification: C10F5
IPC codes: B30B9