METHOD AND APPARATUS FOR DEWATERING AND SQUEEZING MATERIAL

Abstract: A feed and dewatering device for dewatering and squeezing material in form of sludge, sediment, suspensions, peat, etc., comprises two co-operating sections (1; 2), each comprising a feed screw (19, 20; 21, 22) and a seave mantle (4; 15) surrounding the feed screw. The first section (1) in the feed direction is formed for dewatering mainly by self-drainage. The section has a rotating seave mantle (4) and is provided with means (33) for cleaning the seave mantle holes (5). The second section (2) is formed for increased compression of the material, wherein the thread height for the feed screw (21, 22) is less at the outlet (24) of the section (2) than at the inlet to this section.

Description: METHOD AND APPARATUS FOR DEWATERING AND SQUEEZING MATERIA The present invention relates to a method and an apparat for dewatering and squeezing material in form of sludge, sediment, suspensions such as paper pulp, peat, etc. Roller presses, disc presses, wire belt presses and screw presses are used today for dewatering and pressing mate¬ rials. The three first-mentioned types are in relation to their capacity large and expensive machines, have high operation costs and are unrealistic e.g. for purifying plants and small industries. In this connection it has therefore been necessary to use some form of screw presse however existing constructions have several disadvantages and limitations. Enclosed drawing illustrates in Figs. 1 and 2 two differe basic principles for such screw presses. Fig. 1 illustrates a conventional press having a sieve ma in combination with diverging screw body and an adjustabl throttle device at the outlet of the press. When dewatering a material of the kind mentioned above th press usually is fed with a pumpable inlet concentration, meaning a range of 2% to maximum 6% dry substance. It is desirable that the concentration after the press shall be highest possible, preferably within the range 35% - 45%. Such a dewatering requires a compression of the material in the order of magnitude 1:10. However, a press according to Fig. 1 has a maxiumum com¬ pression ratio - counted as transport volume per thread inlet/transport volume per thread outlet - in the order of magnitude 1:2 and by experience maximum 1:2,3. This means that the press must be dimensioned for the incoming volume and for that reason the end portion, where the squeezing work takes place, must be made with large di¬ mensions. For obtaining a dewatering e.g. from 4% up to 40% concentration with a screw press having a compression ratio e.g. 1:2,3 a strong throttling must take place at the outlet of the press. This results in a compression backwards in the press resulting in friction and un- necessary energy consumption. Moreover, such a throttling in the end portion causes that the material receives ten¬ dencies to rotate with the screw, whereby the entire press can be blocked owing to overloading. Another disadvantage with this known screw press is, that upon incoming low material concentration - particularly when a large play exists between thread top and sieve mantl owing to worn screw threads - a cloth formation consisting of fibres on the inlet side of the sieve mantle is obtained in the inlet portion. In this type of press there are no possibilities for readjustment of the play between thread top and sieve mantle. The fact that the final squeezing in this known screw press takes place at an unecessary large diameter, which is de¬ termined by the inlet volume for the material, is accompa¬ nied by the disadvantage of a large moment on the screw for feeding/compression work resulting in a high energy consumption. Owing to the fact that the press must be dimensioned after the incoming volume, the disadvantage accordingly exists that the press must have large diameter and also large length. Since in a screw press considerable radial loads exist, the construction of a press shown in Fig. 1 is ex¬ pensive and the operation costs are high. The known screw press illustrated in Fig. 2 has in the out¬ let portion a somewhat converging sieve mantle in combi- nation with a converging screw and at the outlet an axially operating throttle device in the form of a reciprocating piston. In this construction it is possible to achieve suff cient compression ratio. The main problem of this screwpres is that the distance screen body and sieve mantle is larg at the outlet and squeezed water cannot penetrate through the thick fibre cake but is encased at the screw body. Th results in that the discharged material becomes varying i concentration. Moreover, problems arise due to the fact that the water collected at the centre shaft is compresse and "pushes" the material out with sharp water jets throu the outlet. Owing to the geometry of the device it is her difficult to arrange dwatering both radially outwards through the sieve mantle and radially inwards through a perforated centre shaft. The object of the present invention is to provide a screw press in which the disadvantages of conventional construc ions are eliminated while existing advantages are maintain ed. The invention relates to a method for dewateringand squeez materials in form of sludge, sediment, suspensions such as pulp, peat, etc., wherein the material from an inlet to an outlet is dewatered and squeezed during feeding between threads of a rotating feed screw and this surrounding siev mantle, and the method according to the invention is cha¬ racterized in that the material firstly is fed through a first section between feed screw and rotating sieve mantle with dewatering through the sieve mantle during mainly sel -drainage and during at least intermittent cleaning of the seave mantle holes and thereafter is fed through a second section between feed screw and sieve mantle in this sectio with dewatering through the sieve mantle during increased compression of the material and with higher compression pressure at the end of the feeding through the section tha at its beginning. The invention provides an advantageous combination of said sections. A complete filling of the material in the sectio is obtained thereby obtaining an axial movement of the mat rial through both sections and eliminating sliding of the material in the feed direction and tendencies for blocking caused by rotation of the material with the feed screw. An even continuous in-feed of the material from the first sec¬ tion to the second section is obtained. The rotation of the sieve mantle and the cleaning of the sieve mantle holes con tribute to the achievement of said advantages, and the seco section with its increased compression and its increased co pression pressure afford the condition precedent for a high total compression ratio, viz. a compression ratio counted as thread volume inlet/thread volume outlet in the magnitud of 1:5 to 1:15, preferably 1:7 to 1:10. Moreover, the invention gives a condition precedent for for ing the second section with comparatively essentially less dimensions. Since just this section is subjected to large loads, this factor is important from a constructional point of view. A less diameter gives furthermore the advantage by the fact that thereby a less movement is required resulting in a lower energy consumption for the squeezing work. In the first section, in which the dewatering mainly takes place by self-discharge and only light squeezing, the stre on feed screw and sieve mantle are moderate, which affords condition precedent for the further advantage that this sec -tion can be made in relatively small dimension to the benef of low cost. The moderate stresses also contributes to the fact that the sieve mantle in the first section can be sep rate and rotating. Such a rotation affords advantages in t respects. Cleaning of the sieve mantle holes can be perfor ed with simple means, e.g. as in a preferred embodiment by using a spray pipe arranged outside the sieve mantle and operating with water under pressure and with intermittent function. Moreover, the sieve mantle can be driven with a relative rotation in relation to the rotation of the feed screw and furthermore the compression of the material in t second section can be varied upon variation of the rotation speed of the sieve mantle. Such a possibility for variation is advantageous since thereby the capacity of the press an the dry content of the discharge material can be varied a furthermore the dry content of the discharge material can kept constant when the conditions of e.g. concentration a dewatering ability of the in-coming material are varied. I shall furthermore be noted that a variable operation commo is an expensive device and the price increases essentially faster than the effect of the drive device. However, the s parate drive of the sieve mantle of the section only requi a small part of the effect for driving the feed screw and therefore the regulation is a good economic solution. In c the regulation device for driving the sieve mantle is gove on the basis of a constant movement - as well constant fil of the second section - such a regulation method also cont butes to the conditions precedent for said axial movement the material and to the achievement of a continuous pressi feeding from behind in the second section. The invention also relates to an apparatus which is built- for carrying out the above mentioned method. The apparatus "according to the invention includes an inlet for the mate¬ rial to be dewatered and pressed, an outlet for the dewate material, feeding and dewatering device for the material c sisting of feed screw and surrounding sieve mantle between the inlet and the outlet, and means for rotating the feed screw, and the apparatus is characterized in that said feeding and dewatering device comprises at least two sections arranged after each other in the feed directi of the material, each provided with feed screw and sieve mantle, the first section in the feed direction being form for mainly only dewatering by self-discharge and being con nected to means for rotating the sieve mantle in this sec¬ tion and to means for cleaning the sieve mantle holes, and the second section in the feed direction being formed for increased compression of the material,the thread height of the feed screw in this section being less at said outlet than at the inlet to the section. By the configuration of the first section can beside the above mentioned advantages be obtained the advantage that also after a certain wear of the threads near contact bet¬ ween the thread tops and the inside of the sieve mantle can be maintained by adjusting the axial position of the sieve mantle. In a preferred embodiment of the invention the feed screws in the two sections consist of a common feed screw through the sections. In an alternative embodiment the sections mak an angle with each other and separate feed screws are arranged in the sections. The first mentioned embodiment has the advantages of being cheaper in manufacture, allows less complicated operation for particularly the screw and seave mantle of the first section and requires lower energy upon equal performance. The last mentioned embodiment has the advantage of less space in length, shorter distance bet ween the bearings for the second section, which can be of advantage in case very high squeezing pressure must be app¬ lied to the material (e.g. for squeezing peat) , and choice of rotation speed and rotation direction for the screw and seave mantle of the first section independent of the screw in the second section (its rotation speed and thread pitch, respectively) . For the drainage of the very large water amounts in the first section the dewatering effect can for this section be very heavily increased by rotating the seave mantle with high rotation speed (e.g. 200 rpm) and the screw with somewhat lower rotation speed (e.g. 150 rpm) hear utilizing the centrifugal force for increasing the drainage. * The invention is in the following described in embodiments more in detail and with reference to the enclosed drawings, wherein Figs. 1 and 2 illustrate, as mentioned above, two different embodiments of conventional screw presses. Fig. 3 is a section through one embodiment of the invention and Fig. 4 is a section through another embodiment of the in¬ vention. The apparatus shown in Fig. 3 includes a first section or 5 inlet section 1 for dewatering the material mainly by self -drainage and a second section or outlet section for furt dewatering the material by squeezing. In the trough-formed casing 3 the two sections 1 and 2 are divided by means of an partition wall 37. A common central screw 18 is arrange ° through the two sections 1 and 2. The first section 1 has in the shown embodiment a conical and in the feed direction converging cylindrical sieve or screen mantle 4, which is perforated with conical holes 5. 5 The seave mantle 4, which in this embodiment is arranged t rotate separately from the screw 18, is fastened to gable element 6 and is supported by two bearings 7 mounted on axle spindle 8. The gable element 6 is furthermore joumalled i a bearing housing 9 resting on two longitudinal supporting beams 10. The sieve mantle 4 is driven e.g. by a pivot gear mounted on axle journal 11. A removable partition wall 12 is pro¬ vided for adjusting the play between thread tops and seave mantle. Conventional sealings are arranged for sealing against the material. The second section 2 includes a seave mantle 15 perforated with conical holes 16. The seave mantle 15 is fixed 'to the partition wall 37 and wall 17. The central screw 18 common for the sections 1 and 2 has in the section , 1 a converging screw body 19 and thread 20. In section 2 the screw body 21 of the central screw diverges and is provided with thre 22. The central screw 18 has an axle 8 which in section 1 joumalled in bearing 7 and in section 2 in Rearing 23. At the outlet 24 for the material a stationary perforated sleeve 25 is arranged and also a throttling device in the form of a reciprocating cone 26 for throttling the material flow. The throttling device is attached to gable element 27 and for collecting of discharge water through the sleeve 25 a collecting casing 38 is arranged. The material to be dewatered and pressed is supplied throug inlet 29 and the pressed material is discharged through out let 30. Outlet for the drainage water through the seave mantles 4 and 15 takes place through pipe 31 and outlet for the drainage water through the sleeve or cylinder 25 takes place through discharge pipe 28. Cleaning means in form of a spray tube 33 is arranged out¬ side the seave mantle 4 for cleaning the seave mantle holes 5. The spray tube is fed with water under pressure through tube 34. The central screw 18 is preferably driven by a conventional pivot gear mounted on axle pivot 35. In the section 1 is obtained a dewatering mainly only by self-drainage but also to a less part by easy squeezing, while in section 2 the real squeezing takes place. Moreover in section 2 the thread height for the thread 22 is less at the outlet 24 of the section than at its inlet at the par- tition wall 37, thereby obtaining an increased squeezing effect as the dry content of the material increases. As shown, the thread height of the thread 22 continuously de- creases in direction towards the section outlet 24. The apparatus operates in the following way. The material to be dewatered and squeezed is fed from a pump or a level box through the pipe 29 and further throug holes 36. During the feeding by means of thread 20 the a- terial, as mentioned above, is dewatered mainly by self- -drainage. The compression in the section 1 is in the order of magnitude of 1:2 to 1:3.5, preferably 1:3. The water pass through the seave holes 5, is collected in trough 3 and is descharged through the pipe 31. When the material has passed the seave mantle 4 the threa 20 feeds the material further into the section 2. Owing t the fact that the screw body 21 in this embodiment diverg in section 2, i.e. the thread height for the thread 22 de creases in direction towards the section outlet 24 since the seave mantle 15 is cylindrical, the material is in th section subjected to a radial compression which can be in the order of magnitude of 1:2.0 to 1:3.5 and preferably c be 1:3.0. In the end of the section 2, i.e. at the outlet 24, the m terial is compressed in axial direction with the aid of a counter force from the reciprocating cone or piston 26. D ring the final squeezing the water is discharged in two d rections, viz. outwardly through the seave mantle 15 and also inwardly through holes in the stationary cylinder 25. The water passing through the seave mantle 15 is collecte in trough 3 and is discharged through tube 31 , while the water passing through the cylinder 25 is guided into a channel around the shaft 8 and further out through the di charge pipe 28. Drive means arranged on the pivot 35 is preferably a con- ventional pivot gear having constant speed rotation and drive means mounted on the pivot 11 is preferably also a conventional pivot gear but preferably provided with moto for adjustable speed rotation. By having a relation between speed rotation for screw thread 20 and seave mantle 4, respectively, it is possible to vary the dewatering in section 1 and also to establish a complete filling of the sections 1 and 2. Such a filling uniform in time is possible to control e.g. by sensing the movement for the drive means of the seave mantle 4. The drive means for the pivot 11 can preferably be in the magn tude of 20% of the effect compared with the drive means fo the pivot 35. This is of advantage since the price for a variable drive increases essentially with the effect. When operating an apparatus according to the invention, e.g the apparatus shown in Fig. 3, the high total compression ratio (e.g. in the order of magnitude of 1:10) is utilized and a mainly radial compression on the material is obtained along the whole length between screw and seave mantle, wher by only a small degree needs to be utilized for the axial compression in the end portion of the second section, in th embodiment caused by the piston 26. Thus, the energy-requir sliding of the material in the direction of the spiral ob- tained in conventional screw presses is eliminated as well as blocking caused by the fact that the material in conven¬ tional screw presses attends to rotate with the screw. The dewatering in section 1 is made more effective in the embodiment according to the invention due to the rotation of the seave mantle in the section. This rotation contri- butes to the dewatering per se and also makes it possible to continuously keep the holes in the seave mantle clean by intermittent spraying with water under pressure from the spray tube 33. This cleaning operation makes it also possib to use considerably less holes in the seave mantle, thereby limiting losses of dry substance in the discharge backwater. By adjustment of a relative speed rotation between screw and seave mantle in section 1 and also axial pressure in the end of section 2, very good conditions for flexibility is obtained and thereby an adapted range of application for the appa ratus. Such a flexibility is not possible to predict by using only section 1 or only section 2 but it is first rea- lized when using these section in co-operation in accordance with the invention. The embodiment shown in Fig. 4 coincides in all essential parts with the embodiment shown in Fig. 3 ? disregarding that the first section and the second section make an angle with each other, as shown a right angle, that the driving of the first section is separate from the driving of the second section, and that the sections have separate outlets for dewatered water. It shall be noted that the inlets and o lets shown with dash-dotted lines are arranged perpendic to what is shown. The apparatus shown in Fig. 4 is more expensive in manu¬ facture, requires more complicated drive for screw and se mantle of the first section and requires higher energy at equal performance compared with the apparatus of Fig. 3. ever, it requires less space in length, shorter distance ween bearings for the squeezing screw in the second secti which may be of advantage in case of very high squeezing pressure applied on the material (e.g. for squeezing peat and rotation speed and rotation direction for the screw a sieve mantle of the first section can be chosen independe of rotation speed and thread pitch, respectively, of the screw in the second section. For the drainage of very lar water amounts in the first section (low incoming concent¬ ration) the dewatering effect can considerably be increase by rotating the seave mantle with a high rotation speed (e.g. 200 rpm) and the screw with somewhat lower rotation speed (e.g. 150 rpm), thereby utilizing the centrifugal f for making the drainage more effective.

Claims: CLAIMS : - 1. A method for dewatering and squeezing material in form of sludge, sediment, suspensions such as pulp, peat, etc., in which method the material from an inlet to an out¬ let is dewatered and squeezed during feeding between threads of rotating feed screw and the screw surrounding seave mantle, c h a r a c t e r i z e d in that the ma¬ terial first is fed through a first section between feed screw and rotating seave mantle during dewatering through the seave mantle with substantially self-drainage and with at least intermittent cleaning of the seave mantle holes, and thereafter is fed through a second section between feed screw and seave mantle in this section with dewatering thro the seave mantle during increased compression of the materi and with higher compression pressure at the end of the feed ing through this section than at its beginning. 2. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the material is fed through the first sec tion along a converging path from said inlet to the other section and is fed through the other section along a path continuously decreasing in cross-section towards said out¬ let. 3. A method according to claim 1 or 2, c h a r a c - t e r i z e d in that the seave mantle in the first sec¬ tion is driven with a relative rotation in relation to the rotation of the feed screw. 4. A method according to claim 3, c h a r a c t e r - i z e d in that the seave mantle and the feed screw are " driven with oppositie rotation directions. 5. A method according to any of the preceding claims, c h a r a c t e r i z e d in that the cleaning of the seave mantle takes place with water under pressure directed towards the outside of the seave mantle. 6. An apparatus for dewatering and squeezing material form of sludge, sediment, suspensions such as pulp, peat, etc. , including an inlet for the material to be dewatered and squeezed, an outlet for the dewatered material, feeding and dewatering device for the material comprising feed screw and the screw surrounding seave mantle between said inlet and said outlet, and means for rotating drive of the feed screw, c h a r a c t e r i z e d in that said feeding and dewatering device comprises at least two sections (1; 2) arranged after each other in the feed di¬ rection of the material, each provided with feed screw (1 20; 21, 22) and seave mantle (4; 15), the section (1) bei arranged first in the feed direction being formed ' for mai only dewatering by self-drainage, means being connected to said first section (1) for rotat of the seave mantle (4) in thissection and means (33) bei connected to said first section (1) for cleaning the hole (5) of said seave mantle, the second section (2) arranged in the feed direction bei formed for increased compression of the material, the thr height for the feed screw (21, 22) in this section being at said outlet (24, 30) than at the inlet to the section. 7. An apparatus according to claim 6, c h a r a c t i z e d in that the feed screw (19, 20) in the first se (1) is formed with a core (19) converging from said inlet 36) in the direction towards the second section (2) , and the feed screw (21, 22) in the second section (2) is forme with a core (21) diverging in the direction towards said o let (24, 30). 8. An apparatus according to claim 6 or 7, c h a r a t e r i z e d in that the feed screws (19, 20; 21, 22) i the two sections (1; 2) consist of a common feed screw thr the sections. 9. An apparatus according to claim 6 or 7, c h a r a t e r i z e d in that the sections make an angle to each other and that separate feed screws are arranged in the sec tions. 10. An apparatus according to any of the claims 7-9, c h a r a c t e r i z e d in that the seave mantle (4) in the first section (1) has converging form with a converging angle substantially corresponding to the converging angle of the screw core (19). 11. An apparatus according to any of the claims 6-10, c h a r a c t e r i z e d in that the seave mantle (15) in the second section is stationary arranged. 12. An apparatus according to any of the claims 6-11, c h a r a c t e r i z e d in that said cleaning means (33) consists of a spray device for spraying water under pressur against the external side of the seave mantle (4) .

Inventors: BERGGREN LENNART, BERGGREN, LENNART
Applicants: HEDEMORA AB
Application year: 1988
Main classification: B30B9
IPC codes: B30B9