DE4332799C2 - Sludge dewatering method and apparatus - Google Patents

Description

The invention relates to a method according to the preamble of Pa claim 1 and to a device according to the preamble of the patent Proverb 24. A method and a device of this type are known from WO 93/00562 known.

In known systems for dewatering sludge, especially from sewage plants, is the liquid sludge using a solid bowl centrifuge, one Chamber filter press or a screen belt press mechanically part of the ge withdrawn bound water. The liquid sludge with a water content of for example 95% by weight is in a clumping, moist thick material with a Dry matter content of about 15 wt .-% to about 35 wt .-% transferred. The dick Substance represents a residual mass to be disposed of, depending on the drainage achieved degree of approx. 1/4 to 1/7 of the original sludge mass.

A further reduction in water content with the help of mechanical drainage is generally not possible with sludge. Will a lower water level of the thick matter is required, the mechanical drainage device one or more thermal drying stages downstream. With the above Drying levels are short-term dryers, for example paddle dryers according to EP-A-0 538 653, or long-term dryer, for example fluidized bed dryer or disc dryer.

From WO 93/00562 it is already known to use a solid bowl screw centrifuge to surround the housing of an atomizing dryer and thereby the radial Ab Throw openings of the solid bowl centrifuge as a dispersing device for the cer to use dust dryer. That at high speed as a particle veil centrifuged thick matter particles are traversed with drying gas on their trajectory rinses and pre-dried. For higher dry matter contents is however after as before drying the pre-dried particles in the discharge of the  Atomizing dryer required.

In contrast, the object of the invention is one in sludges higher dry matter content with comparatively less equipment and to achieve energy expenditure.

This task is procedurally through the characteristics of Claim 1 and apparatus by the features of Claim 24 solved.

Advantageous refinements and developments of the method according to the invention rens result from subclaims 2 to 23.

Advantageous refinements and developments of the device according to the invention tion result from subclaims 25 to 47.

The invention is based on the consideration of being energetically special as a hub inexpensive paddle dryer the rotating jacket of a dewatering centrifuge to be used to step from the liquid sludge in one structural unit a free-flowing solid granulate with a high dry matter content without the It is necessary to carry out further drying.

The invention is explained in more detail below with the aid of exemplary embodiments explained. It shows:

Figure 1 shows a longitudinal section through an embodiment of a dewatering, drying and granulating device according to the invention, consisting of a paddle dryer with an integrated solid bowl screw centrifuge.

FIG. 2 shows a schematic overview of a sludge drying installation, partially operated in a closed circuit, with an inventive device according to FIG. 1;

. Fig. 3 is a schematic overview of a similar system as in Figure 2, in which in addition a purification of the exhaust gas in the dust-Zentratzone the solid-bowl screw centrifuge is effected;

Fig. 4 is a schematic view of turbine blades of the blade dryer of the device of Fig. 1;

Fig. 5 is a perspective view of axial fan blades of the paddle dryer of the apparatus of FIG. 1;

Fig. 6 shows a schematic longitudinal section through reaming blades of the paddle dryer of the apparatus of Fig. 1, and

Fig. 7 is a schematic longitudinal section through a further embodiment of a dewatering, drying and granulating device according to the invention.

The dewatering, drying and granulating device for sludge, in particular sewage sludge, industrial sludge and biological sludge shown in FIG. 1 has a solid bowl screw centrifuge 10 of known design in the example shown. Instead of a solid-bowl screw centrifuge, other centrifuges suitable for sludge dewatering, for example sieve-bowl screw centrifuges, can also be used.

The solid-bowl screw centrifuge 10 , hereinafter referred to briefly as the "dewatering centrifuge", has a rotating drum shell 12 , which is rotatably mounted on roller bearings 14 at its axial ends. The drum jacket 12 tapers approximately from its axial center and is provided at its conically tapered end with discharge openings 13 which are uniformly distributed over its circumference and form the discharge zone of the sludge centrifuge 10 . Within the drum shell 12 , a drainage screw 11 with a screw core 11 a and helical screw webs 11 b is arranged along the axis thereof, which is rotatably mounted on roller or slide bearings 15 at its axial ends. The screw 11 is driven at a slightly higher speed than the drum shell 12 by a drive 16 , so that the material introduced into the screw flights corresponding to the differential speed between the screw 11 and drum shell 12 is moved axially in the direction of discharge openings 13 .

Via a sludge pipe 17 11 a supplied liquid slurry 1 entering the interior of the screw core via a c by radial partition walls 11, 11 d of the worm core 11 a limited entry zone 11 e in the screw flights Zvi rule screw core 11 a, screw flights 11 b and the drum casing 12 and there with in the centrifugal force field of the centrifuge 10 . As a result of the centrifugal force effect, sludge water flows radially inward from the capillaries of the sewage sludge, which accumulates as a centrate 4 near the screw core 11 a and flows spirally between the screw webs 11 b to the right axial end of the screw 11 . There the centrate 4 is stowed on a weir 12 a of the drum jacket 12 . The flowing over the weir 12 a centrat is thrown into a hood-shaped central chute 3 , which surrounds the right axial end of the drum casing 12 as a closed, fixed housing at its passage through the central chute 3 sealingly. From the central chute 3 , the central 4 is returned directly to the sewage treatment plant.

The sewage sludge 2 dewatered by the centrifugal force field forms on the inner wall of the drum shell 12 , is moved to the left against the discharge openings 13 by the screw conveyor 11 and is thickened as a result of progressive compression, the longer it is in the centrifugal force field of the centrifuge 10 , The resulting thick matter is further pressed by reducing the screw flight height between the conically tapering, left end portion of the drum shell 12 and the screw core 11 a, so that as a result the dry matter content of initially about 5% by weight in the liquid sludge 1 up to a maximum of about 35% by weight in the thick material when it is ejected in the radial direction through the ejection openings 13 .

According to the invention, the rotating drum jacket 12 of the centrifuge 10 forms the hub of a blade (“turbo”) dryer 20 , the housing jacket 22 of which surrounds the centrifuge 10 , forming an annular channel 30 . The blades 21 of the blade dryer 20 are attached to the outside of the rotating drum shell 12 and rotate within the ring channel 30 . Alternatively, as indicated by the embodiment according to FIG. 7, the drum jacket 12 following the discharge openings 13 has an axial extension 12 a, which forms the hub of the paddle dryer 20 a. The free axial end of the extension 12 a is mounted on a roller bearing, not specified, the drive 16 being located at the free axial end of the extension 12 a. In this example case, the housing jacket 22 a of the paddle dryer 20 surrounds the axial extension 12 a and the end section of the centrifuge 10 with the discharge openings 13 . The diameter of the housing shell 22 a can be chosen to be smaller than the diameter of the housing shell 22 in the exemplary embodiment according to FIG. 1, in order to reduce the peripheral speed of the blades 21 a attached to the axial extension 12 a. As a result of this reduction in the initial speed, the wear of the blades 21 is reduced. Furthermore, the length of the dryer 20 a can be selected regardless of the dimensions of the mechanical drainage space of the centrifuge 10 . Finally, the embodiment of FIG. 7 ensures easy retrofitting existing centrifuge conditions with the dryer 20 a.

The in both embodiments of FIGS. 1 and 7 as a radial particle veil from the discharge openings 13 ejected thick matter is in the immediate vicinity of the discharge openings 13 with hot drying gas 40 flows transversely to its discharge direction, so that the trajectory of the ejected thick matter particles into the annular channel 30 ( Fig. 1) or 30a ( Fig. 7) is deflected. The drying gas 40 can be supplied axially or tangentially. To support the drying effect of the drying gas 40 , as shown in FIG. 1, the housing jacket 22 of the dryer 20 is heated, for example with the aid of a heating jacket 50 heated electrically or with superheated steam or hot oil, which is insulated from the outside by an insulating jacket 51 , The superheated steam or the hot oil is fed in countercurrent with respect to the direction of transport of the thick matter particles at the right axial end of the heating jacket 50 via a feed line 52 and discharged at the left axial end of the heating jacket 50 via a return 53 . In order to cool the dried thick matter particles before they leave the dryer 20 or 20 a, the section of the heating jacket 50 arranged in the area of the particle discharge can be charged with a cooling medium in a manner not shown. In the embodiment of FIG. 7 is additionally provided by the form of a hollow shaft axial extension 12 a heating medium 6, for example. B. superheated steam or hot oil, to additionally heat the blades 21 .

For the shown axial supply of the hot drying gas 40 , a ring-shaped air guide hood 41 is provided which encloses the left axial end of the drum shell 12 and at the same time forms the left axial end of the housing shell 22 of the dryer 20 Ge. The annular air outlet opening of the housing 41 surrounds the discharge openings 13 , forming a narrow annular gap, in order to make the axial inflow of the thrown off thick material particles particularly effective. The hot drying gas 40 , e.g. B. hot flue gas is introduced into the annular hood 41 at an upper peripheral point. The exhaust air 43 mixed with dried thick matter particles is discharged at the right axial end of the annular channel 30 via egg NEN nozzle 42 of the housing shell 22 .

A case of the system of FIG. 2 is fed to the exhaust air 43 a dust collector 110, and (to a lesser extent) a mixer 140 which mixes the air with hot fresh air 131st In addition or as an alternative to the cooling within the dryer 20 , cooling of the thick matter particles discharged with the exhaust air 43 from the dryer 20 can be provided on the way to the dust separator 110 or within the dust separator 110 . The hot fresh air 131 is obtained in a heat exchanger 130 from cold air 132 , hot flue gas 133 being used as the heat exchange medium, which in this way is not used directly as drying gas 40 . The waste heat from the waste air 43 can also be used in a manner not shown for heating the fresh air. The mixture of hot fresh air 131 and exhaust air 43 is compressed by means of a compressor 150 and fed to the annular hood 41 . The cleaned in the dust separator 110 exhaust air 111 in the case of FIG. 2 again leads to a very fine dust filter 120 , in order then to be fed back to the heat exchanger 130 in a closed circuit as cold air 132 via a compressor 151 . The separated from the exhaust air 43 in the dust separator 110 and 111 from the exhaust air in the dust filter 120, respectively dust particles are discharged through a rotary valve 112 and 121 at the bottom of the separator 110 and filter 120th The fine dust from the filter 120 is, as shown in FIG. 2, through one or more openings 60 in the housing jacket 22 in the vicinity of the hood 41, the thick material particles to be mixed when the dry matter content is to be increased even further. In the case of very fine-grained thick matter particles, a granulating liquid can also be mixed into the annular channel 30 via one or more feeds 61 in order to promote the formation of granules.

To further increase the dry matter content, the sludge 1 can additionally be shown in FIG. 3 before it enters the centrifuge 10 in a mixer 90, which sera absorbing drying substances 6 or drainage-promoting substances, eg. B. CaO (branded lime), fly ash or dust from the separator 110 or filter 120 to be mixed. Furthermore, the sludge can 1 according to FIG. 3 prior to its entry into the centrifuge 10 in a heat exchanger 80 by means of a hot flue gas 133 or the like. Are heated, whereby the removal of water within the centri fuge 10 is improved. For heating the liquid sludge 1 , the waste heat of the exhaust air 43 can alternatively be used. The centrate 4 can be used in accordance with FIG. 3 in a centrate washer 70 for washing out vapors 5 who are sucked off from the annular channel 30 in the region of its right axial end.

While be discharged in the embodiments according to FIGS. 1 and 2, the dried sludge particles with the exhaust 43 of the dryer 20, in the embodiments according to FIGS. 3 and 7 in the region of the discharge end of the housing shell 22 and 22a on the underside of a chute 23 attached with a cellular wheel sluice 24 , through which coarse fractions of the dried and granulated thick matter particles are discharged. To clean the dryer 20 are in the embodiment of FIG. 1 in the region of both axial ends of the Ge housing shell 22 on the underside cleaning flaps 25 , 26 attached.

The blades 21 are generally used both for cleaning the wall of the housing wall 22 and for transporting the thick matter particles in the ring channel 30 , the residence time of the thick matter particles in the ring channel 30 and thus the heat transfer from the drying gas 40 and the heating device 50 to the particles Can control the blades 21 .

The blades 21 of the paddle dryer 20 are designed differently depending on their axial distance from the entry of the particle veil into the ring channel 30 (discharge openings 13 ). In the exemplary embodiment according to FIG. 1, the blades closest to the discharge openings 13 are designed as clearing bars 21 a, the scraping edges of which rotate at a short distance from the inner surface of the housing shell 22 in order to mechanically detach agglomerations of moist thick matter from the surface and into to transport the ring channel 30 back.

At the clearing bars 21 a adjoins at the transition from the conical to the cylindrical portion of the drum shell 12 (that is, where the annular channel 30 has narrowed to the maximum) a ring of axially directed blades 21 b ( FIG. 5), which together form one Form axial fan. With the help of this axial fan, the axial flow of the drying gas 40 and the thick matter particles within the ring channel 30 and thus the residence time of the particles can be controlled. For this purpose, the positions of the blades 21 b of the axial fan in relation to one another are to be selected in the desired manner.

Immediately axially behind (seen in the direction of discharge of the particles) the fins 21 b, a ring of lying in a common radial plane of the annular channel 30 clearing blades 21 c is provided, which have a similar effect to the clearing bars, but shorter scraping edges than the clearing bars 21 a point. Another ring of scraper blades 21 c is also located in the area of the right axial end of the ring channel 30 . The clearing blades 21 c shown in FIG. 6 are rotatably supported about an axis 210 perpendicular to the inner surface of the housing shell 22 by an angle alpha. By a suitable choice of the rotary position of the clearing blades 21 c, their propelling effect in the axial direction on the particles and thus the length of time the particles remain in the annular channel 30 can be increased or decreased. For example, the blades 21 c are aligned so that they direct the particles against the flow direction of the drying gas 40 , as a result of which the particles remain in the annular channel 30 longer than the drying gas 40 .

In the axial region between the two rings of clearing blades 21 c, one or more ring blades of turbines 21 d shown in FIG. 4 are provided, which are placed on a common support ring 21 e. The turbine blades 21 d, as shown in FIG. 4, are curved in the radial plane and have a mixing effect on the fluidized layer 7 of thick matter particles, which is formed in the vicinity of the housing shell 22 . As a result of this mixing, the heat transfer between drying gas 40 and particles and between heating jacket 50 and particles is improved.

Claims (47)

1. Process for dewatering and drying sludge, in particular sludge from sewage treatment plants, industrial sludge or biological sludge, in which the sludge is dewatered by a rotating drum jacket dewatering centrifuge to a thick matter and then the thick matter in a drying room , which at least partially forms a structural unit with the centrifuge, the residual water portion is at least partially withdrawn, the thick matter at the discharge of the centrifuge being thrown into the drying room at high speed in dispersed form as a particle veil, characterized in that the transport of the thick matter Particles and the heat transfer to the thick matter particles within the drying room are controlled by rotating blades on the outer circumference of the drum shell of the centrifuge or on an axial extension of the drum shell. 2. The method according to claim 1, characterized in that the thick matter Particles are affected in size by the rotating blades. 3. The method according to claim 1 or 2, characterized in that in the Drying room a drying gas is introduced. 4. The method according to claim 3, characterized in that as dry Hot air or combustion exhaust gases is used.   5. The method according to claim 1 or 2, characterized in that as Drying gas superheated steam is used. 6. The method according to any one of claims 1 to 5, characterized in that the drum jacket of the centrifuge and / or the walls of the drying room be heated at least in those places where the thick particles collide. 7. The method according to any one of claims 1 to 6, characterized in that the drum jacket of the centrifuge and / or the walls of the drying room in the Area of discharge of the dried thick matter particles from the drying be cooled. 8. The method according to any one of claims 1 to 7, characterized in that the size of the spun off thick matter particles and the influence of them Residual water content is controlled via the speed of the dewatering centrifuge. 9. The method according to any one of claims 1 to 8, characterized in that a solid-bowl screw centrifuge is provided as the dewatering centrifuge. 10. The method according to any one of claims 1 to 8, characterized in that as a dewatering centrifuge, a full-shell sieve centrifuge with approximately uniform according to, continuous thick matter discharge is provided. 11. The method according to any one of claims 1 to 10, characterized in that the drying gas the spun off thick matter particles across their main flight direction flow flows. 12. The method according to any one of claims 1 to 11, characterized in that the drying gas is circulated and after purging the centrifuged thick particles cleaned, dehumidified and / or ver with fresh gas sets and is heated. 13. The method according to any one of claims 1 to 12, characterized in that the drying gas between the thrown-off thick particles between is temporarily heated.   14. The method according to any one of claims 1 to 13, characterized in that the pre-dried thick matter particles through the drying gas in a pneumati transported conveyor system and to a separator and / or to or several downstream long-term dryers can be transported. 15. The method according to any one of claims 1 to 14, characterized in that the dispersed thick matter particles when they are flushed with drying gas a dy Namely size sorting process and that larger thick matter Particles are exposed to the drying gas for longer than smaller thick matter particles. 16. The method according to any one of claims 1 to 14, characterized in that the thrown off thick matter particles in the area of the discharge zone of the drainage centrifuge dry material and / or granulating liquid are added. 17. The method according to any one of claims 3 to 16, characterized in that the liquid sludge is preheated before it enters the centrifuge. 18. The method according to any one of claims 1 to 17, characterized in that the used drying gas discharged from the drying room as exhaust air is used to preheat the liquid sludge. 19. The method according to any one of claims 1 to 18, characterized in that the sludge before it enters the centrifuge water-absorbing drying sub punches are added. 20. The method according to any one of claims 1 to 18, characterized in that favoring the sludge prior to its entry into the centrifuge drainage, liquid or solid substances are mixed. 21. The method according to any one of claims 1 to 18, characterized in that CaO, fly ash, or ground dry matter made from sewage sludge mixed. 22. The method according to any one of claims 1 to 21, characterized in that the thick matter under the pressure of the centrifugal field inside the drum jacket of the centrifuge is heated supercritically, such that in the pressure release  of the thick matter evaporates after it has been discharged by capillary water. 23. The method according to any one of claims 1 to 22, characterized in that the sludge is granulated after or during dewatering and drying. 24. Device for dewatering and drying sludge, in particular sludge from sewage treatment plants, industrial sludge or biological sludge, with a dewatering centrifuge ( 10 ), the drum shell ( 12 ) of which rotates at a differential speed with respect to an axial screw conveyor ( 11 ) and which one has at its axial end radially directed discharge openings ( 13 ) for the pre-dewatered sludge (thick material), and with a dryer, which at least partially forms a structural unit with the dewatering centrifuge, characterized in that a paddle dryer ( 20 ) is provided as the dryer whose axial, ro tierender hub two or more blades ( 21 ) are attached, and that the Ent dewatering centrifuge ( 10 ) is at least partially arranged inside the paddle dryer ( 20 ) as its hub, the blades ( 21 ) of the paddle dryer ( 20 ) on the rotating drum jacket ( 12 ) of the drainage center joint ( 10 ) or on an axial extension ( 12 a) of the drum shell ( 12 ) are attached. 25. The device according to claim 24, characterized in that a drying space (annular channel 30 ) between the rotating drum jacket ( 12 ) of the dewatering centrifuge ( 10 ) and a housing jacket ( 22 ) of the paddle dryer ( 20 ) one or more inlet openings ( 41 ) for has a hot drying gas ( 40 ). 26. The apparatus according to claim 25, characterized in that the inlet opening (s) ( 41 ) are aligned in the axial or tangential direction with respect to the annular channel ( 30 ). 27. The apparatus of claim 25 or 26, characterized in that the one opening (s) ( 40 ) in the vicinity of the discharge openings ( 13 ) of the drainage centrifuge ( 10 ) are arranged. 28. Device according to one of claims 25 to 27, characterized in that for extracted, used drying gas ( 40 ) from the annular channel ( 30 ) Einrichtun gene ( 70 , 110 , 120 , 130 ) for reprocessing, such as washing out vapors, Ent dust and / or reheating are provided. 29. The device according to claim 28, characterized in that a washing device ( 70 ) through which the centrate of the dewatering centrifuge ( 10 ) flows is provided for washing out vapors from the exhausted, used drying gas ( 40 ) from the annular channel ( 30 ). 30. The apparatus of claim 28 or 29, characterized in that a device ( 140 ) for mixing used or partially processed drying gas with fresh drying gas and a device ( 150 ) for introducing mixed drying gas into the annular channel ( 30 ) are provided , 31. Device according to one of claims 24 to 30, characterized in that a heating device ( 50 ) is provided for the housing jacket ( 22 ) of the paddle dryer ( 20 ). 32. Device according to one of claims 24 to 29, characterized in that for the housing jacket ( 22 ) of the paddle dryer ( 20 ) a cooling device in the region of the discharge of the thick matter particles from the paddle dryer ( 20 ) is easily seen. 33. Device according to one of claims 24 to 32, characterized in that a further cooling device is provided for the thick material particles discharged from the paddle dryer ( 20 ). 34. Device according to one of claims 25 to 33, characterized in that the annular channel ( 30 ) in the region of the entry of the thick matter particles has one or more inlet opening (s) ( 60 ) for the admixture of dry material. 35. Apparatus according to claim 34, characterized in that the ring channel ( 30 ) in the region of the entry of the thick matter particles has one or more inlet openings ( 61 ) for the admixture of granulating liquid. 36. Device according to one of claims 24 to 35, characterized by means ( 80 ) for preheating the sludge prior to its entry into the dewatering centrifuge ( 10 ). 37. Device according to one of claims 24 to 36, characterized by means ( 90 ) for admixing water-absorbing drying substances or drainage-promoting, liquid or solid substances, such as CaO, fly ash or ground dry matter made from sewage sludge, to the sludge before it is introduced into the dewatering centrifuge ( 10 ). 38. Device according to one of claims 24 to 37, characterized in that blades ( 21 a) in the region of the discharge openings ( 13 ) in the form of Räumleis th ( 21 a) are formed, which have scraping edges that are at a short distance from the inner surface of the casing shell ( 22 ) of the paddle dryer ( 20 ) rotate. 39. Device according to one of claims 24 to 38, characterized in that a ring of substantially axially aligned blades ( 21 b) forms an axial fan. 40. Apparatus according to claim 39, characterized in that the blades ( 21 b) of the axial fan are attached at the transition from a conical portion to a cylindrical portion of the drum shell ( 12 ). 41. Device according to one of claims 24 to 40, characterized in that clearing blades ( 21 c) are rotatably mounted about an axis ( 210 ) which is oriented perpendicular to the inner surface of the housing shell ( 22 ) 42. Apparatus according to claim 41, characterized in that scraper blades ( 21 c) are arranged in the region of the discharge of the particles from the annular channel ( 30 ). 43. Apparatus according to claim 41 or 42, characterized in that clearing blades ( 21 c) - seen in the discharge direction of the particles - are arranged axially behind the blades ( 21 b) of the axial fan. 44. Device according to one of claims 24 to 43, characterized in that a ring of blades arranged in a common radial plane ( 21 d) are designed as turbine blades. 45. Apparatus according to claim 44, characterized in that the blades designed as a tower blades ( 21 d) are attached to a common support ring ( 21 e). 46. Apparatus according to claim 44 or 45, characterized in that the door bin blades ( 21 d) seen in the discharge direction of the particles - are arranged axially behind the blades ( 21 b) of the axial fan. 47. Device according to one of claims 24 to 46, characterized in that facilities for granulating are provided.