EP0197171B1 - Low-temperature dryer for pressed fibrous material - Google Patents

Description

The invention relates to a low-temperature dryer for pressed fibrous material, in particular leached sugar beet pulp, with the features of the preamble of claim 1.

Such a dryer is known for example from GB-A-491 858. The tower-like dryer has several fixed levels, over the bottoms of which the feed material above is distributed or cleared alternately in the radial direction in the radial direction by means of driven screws rotating around the tower axis, and the discharge of material under the last floor he follows. A suction fan is assigned to one of the middle floors, while a fresh air suction device with filter and heating device is assigned to the top and bottom floors.

It is also known to provide floors which run around the tower axis instead of fixed floors, to which transfer chutes extending from floor to floor and guide or scraper plates arranged above the floors are assigned, by means of which the goods are distributed and cleared alternately towards the center or towards the outside (see GB-A-281 664). The material travels through the floors of the drying tower from top to bottom, while the warm air is fed in from the bottom floor and, after passing through all the floors, is extracted at the top. It is also known to distribute the warm air to the individual floors via vertical hollow columns, which are distributed over the circumference of the drying tower, the air flowing inward via the floors in the radial direction being discharged upward via a central collecting space (cf. DE-C-28 077).

Dryers are also known (DE-C-362 358), in which between two coaxial, rotatable drums of different diameters in several. Floors arranged floors are provided. In order to convey the dry material from floor to floor, the floors consist of sector-shaped plates that can be tilted one after the other about their radial longitudinal axis. The inner drum is closed at the top and connected to a warm air supply at the bottom, and is equipped with widely distributed air outlet openings between the floors. A flow through the floors and the material layers on them does not occur when these dryers are in operation. The floors are also not arranged in housing-like pressure chambers.

Furthermore, low-temperature dryers with several levels arranged one above the other are known, each of which is equipped with conveyor belts that are permeable to the drying air. By adjusting the speed of the very long and several meter wide belts, the layer thickness of the material on the belts can be adjusted.

The structure of the known dryer is relatively complicated and prone to failure and often gives rise to difficulties in operation.

It is an object of the invention to develop a low-temperature dryer with the features of the preamble of claim 1 in such a way that, with a simple, clear structure and reduced weight, a significantly better utilization of the heat for drying purposes is ensured in operation which does not pollute the environment.

This object is solved by the features of claim 1.

With this design, the heat losses are low, since the freshly supplied warm air is guided in the center of the tower-like low-temperature dryer, the dryer is surrounded on the outside by a jacket protecting the tower against external influences, in particular wind, which at the same time has an annular collecting shaft for the tower Exhaust air forms, which also protects the drying zones against heat loss. The individual floors are each directly and to the same extent acted upon by the hot air, so that there is a high drying efficiency. If necessary, individual floors can be switched off by the drying air flow. This can be useful when there is less space required, i.e. less crop. But it also helps to maintain operations if repair work is required on one floor or the other. For this purpose, the arrangement according to the features of claim 8 is provided in a further development of the low-temperature dryer. The layer of material on each ring base is flowed through from top to bottom over the entire ring width of the base by the warm air, which is distributed or collected in closed ring chambers both above and below the base. The hot air flow can be controlled very precisely in this way and evenly distributed over the entire ring floor of a floor.

Since waste heat is used to heat the drying air in such low-temperature dryers, the new low-temperature dryer also has a particular advantage in that the associated heating units as heat exchangers and the fans that serve to promote air can be arranged directly on the foundation of the dryer below the bottom floor. over a large area so that a ring-shaped heat exchanger arranged in the cross-sectional area of the ring bottoms on the tower floor can be flowed through over a large area via an external fresh air chamber, while the heated air can be introduced from the interior of the ring-shaped heat exchanger into the central distributor shaft without flow resistance. This results in a significant weight reduction in the design of the low-temperature dryer. Several fans are preferably arranged distributed in the circumferential direction. Each of these fans has a separate the intake duct for fresh air, the inlet openings of these intake ducts being in the area of the top of the tower-like low-temperature dryer, while the exhaust air from the external exhaust air collector can escape into the open near the bottom of the low-temperature dryer. This prevents any contamination of the fresh air drawn in. The intake shafts for the fans can form sector-shaped sections within the ring-shaped exhaust air collector. If a part of the exhaust air is to be returned to the air circuit, closable suction openings can be provided between the successive exhaust air discharge sectors and fresh air supply sectors.

The ring bottoms can advantageously be driven about the axis of the low-temperature dryer, in opposite directions from floor to floor, so that the forces originating from the drive cancel each other out. Between the floors are preferably arranged in the area of the radially outer exhaust air collector fixed shaft-like goods transfer chutes and equipped with convertible guide devices so that the goods can be passed on to one floor after another by skipping one floor if necessary. This makes it easier to adapt the throughput to the requirements and, if necessary, repairs can be carried out on individual floors without the operation of the low-temperature dryer having to be stopped.

For feeding and distributing and for clearing the individual floors, twin screws which are fixed to the frame are expediently provided, the feed and distribution screw being assigned a corresponding exit and distribution slot for the exit of the goods onto the ring base. The take-up and clearing auger is advantageously assigned a drivable reel, which forcibly conveys the good layer to the clearing auger.

Since fine work particles arise from the work of the reels and snails in the feed and clearing area, which can easily be carried away by the air flow and can be discharged to the outside with pollution of the environment, measures according to claims 10 and 11 are expediently taken. Since in the clearing and application area of the ring base is not flowed through by the drying air, calm zones can be created here for collecting the fine parts, through which the fine parts, e.g. B. via a pressure lock, the next lower sieve tray. The cleaning devices necessary and customary for cleaning the sieves forming the ring bottoms, such as brushes, cleaning nozzles or the like, can also be arranged in this calmed area.

The invention is explained in more detail below with the aid of schematic drawings using an exemplary embodiment.

• Fig. 1 einen senkrechten Schnitt durch einen Niedertemperaturtrockner gemäß der Erfindung,
• Fig. 2 einen horizontalen Schnitt in der Schnittebene A-A,
• Fig. 3 einen horizontalen Schnitt entlang der Schnittlinie B-B der Fig. 1 und
• Fig. 4 eine Ansicht gemäß dem Pfeil C in Fig. 1 mit Blickrichtung radial von außen nach innen auf den Bereich der Aufgabe und Räumung des Gutes.

Show it :

• 1 is a vertical section through a low temperature dryer according to the invention,
• 2 shows a horizontal section in the section plane AA,
• Fig. 3 is a horizontal section along the section line BB of Fig. 1 and
• Fig. 4 is a view according to arrow C in Fig. 1 looking radially from the outside inward to the area of the task and clearance of the goods.

The tower-like low-temperature dryer according to FIG. 1 is preferably intended for drying leached sugar beet chips. The low-temperature dryer has a closed outer jacket 1, which is seated on a foundation 2 and is closed on the ceiling 3 at the top. At one point of the ceiling area, a ceiling opening 31 is provided, which in the example shown serves at the same time for feeding in according to arrow 81 and for supplying fresh air according to arrow 32. Separate ceiling openings can also be arranged for both processes. The goods are loaded using conventional loading devices, which do not need to be explained in more detail here.

As clearly shown in FIGS. 1 and 3, an annular heat exchanger device 11 formed from a plurality of heat exchangers is arranged on the foundation 2. The heat exchanger device 11 is traversed by a heat transfer fluid, which receives its heat from the waste heat generated in other processes of the factory.

The ring-shaped arrangement provides a large inflow and heat exchange surface, as is desired especially in low-temperature processes. By arranging the heat exchanger device 11 directly on the foundation 2, the actual dryer construction is relieved of force. Outside the heat exchanger device 11, in the example shown, a plurality of fans 13 are arranged distributed in the circumferential direction, the outlets of which open into the annular fresh air distribution chamber 12 and which are connected to the air inlet openings 31 on the ceiling 3 of the dryer by air intake shafts 30 extending over the entire height of the dryer. The heat exchanger device 11 encloses the bottom end 10 of a central drying air distributor shaft 5 which extends over the entire height of the dryer and which, with negligible flow resistance, distributes the warm air over the entire height of the dryer. The shaft 5 is arranged concentrically to the central shaft axis 47 of the dryer.

Several drying levels, in the present case four drying levels 6-9, are distributed over the height of the drying air distributor shaft 5. Each drying level 6-9 is connected to the shaft 5 via an annular inlet opening 17 which can be closed by an operable shutter.

Each level 6-9 is determined by a sieve-shaped ring base 20. In the example shown it is assumed that each ring base 20 is driven to rotate around the central shaft axis 47 of the dryer, the direction of rotation changing from floor to floor, so that the forces generated by the drive largely cancel each other out, which further contributes to relieving the load on the dryer construction. Above each annular base there is an annular pressure chamber 18a which is delimited radially on the inside by the air inlet opening 17 provided with the blind or an equivalent closure by a frustoconical ceiling 18 and on the outside by a cylindrical wall 19, the flow cross section of the pressure chamber 18a in radial direction decreases from the inside to the outside. Furthermore, an annular outflow chamber 24 for the exhaust air is provided between the ring base 20 of one level and the frustoconical ceiling 18 of the pressure chamber 18a of the level below, the flow cross section of which increases in the radial direction to the outside.

The jacket 1 of the dryer is at a radial distance from an outer protective jacket. 26 surrounded, which is arranged concentrically to the shaft axis 47, extends down to below the bottom floor 6 and is closed at 27 at the top of the upper floor 9. This outer protective jacket 26 provides thermal protection for the low-temperature dryer, since it eliminates the influence of the ambient atmosphere, in particular wind, on the dryer. The protective jacket also has other tasks to perform. It forms with the jacket 1 of the dryer an annular zone which is divided into individual sector-shaped sections in the circumferential direction. Some sections form the fresh air intake shafts 30 already mentioned for the fans 13. Between these are sectors which are directly connected to the annular outflow chambers 24 and, as exhaust air collectors 25, ensure that the exhaust air is removed. The exit of the exhaust air from the exhaust air collector 25 is indicated by the arrow 29. The exhaust air collectors 25 are open at 28 at the bottom, so that the exhaust air exits near the foundation 2 below, while the fresh air is drawn in according to the arrow 32 on the ceiling of the tower. The protective jacket 26 together with the radial dividing walls serving to subdivide the exhaust air collectors 25 and intake shafts 30 further contributes significantly to the stability of the dryer construction. Inspection and maintenance platforms 25a can also be arranged in the exhaust air collectors 25 on each floor.

From Fig. 1 it can be seen that the fresh air is sucked in through the opening 31 in the direction of arrow 32 and reaches the fans 13 via the vertical suction shafts 30. From the outlet of the fans, the fresh air is distributed according to arrow 14 in the fresh air distribution chamber 12 over the entry surface of the annular heat exchanger device 11. The warm air rises from the bottom end 10 of the central drying air distributor shaft 5 in accordance with the arrows 15 and is distributed in accordance with the arrows 16 the inlet openings into the pressure chambers 18a. From there, the drying air is distributed according to the arrows 23 over the surface of the material layer, penetrates it and the respective ring base 20 and reaches the annular outflow chambers 24, from which the exhaust air exits into the atmosphere through the opening 28 according to the arrow 29. At the transition between the intake ducts 30 and the exhaust air collectors 25, closable openings can be provided, so that, according to the arrows 50 in FIG. 3, parts of the exhaust air can be returned to the drying circuit during recirculation mode.

The material fed through the opening 31 according to the arrow 81 passes through the dryer from floor to floor and is removed from the ring floor 20 of the lowest floor 6, as indicated at 79.

As is particularly clear from FIGS. 2 and 4, the distributor and the clearing device in the exemplary embodiment shown consist of a twin screw 67, 68, which is assigned to each tier 6-9.

This twin screw 67, 68 is arranged fixed to the frame in the circumferential direction and, if necessary, can be adjusted in height relative to the associated floor. In Fig. 4 it is assumed that the upper floor shown in the figure is floor 8. It is assumed that the ring bottom of the tier 8 is driven in the direction of arrow 60 and the ring bottom of the underlying tier 7 in the opposite direction according to arrow 61. The two support rings 21, 22, on which the sieve plates forming the ring bottom are clamped in a sector shape via spokes-like members 48 and pivot bearings on the central shaft axis 47 rotatably guided. An endlessly rotating chain loop 39, which is guided over deflection wheels 40, 41, 42, one of which is driven, is used to drive each ring base 20. The radially inner strand 43 engages on a partial circumference of the rotatable ring base, the radially outer ring 21 of which has corresponding teeth or teeth which engage in the chain loop 39.

The screw 67 of the twin screw 67, 68 of the floor 8 serves as a feed screw and distributor. The goods are normally fed through the chute-like chute 34 along the chute section 62. A corresponding distribution slot ensures a uniform exit of the goods onto the sieve-shaped ring base 20. The clearing screw 68 located directly in front of it in the direction of rotation, on the other hand, picks up the goods that are passed through one circulation via the floor 8 and guides them to the incoming end of the goods transfer chute 34 leading to the next floor 7 to. In order to ensure a secure absorption of the crop layer, at least the auger 68 is assigned a driven take-up reel 70 which throws the crop into the screw flights. A corresponding reel 69 can also in front of the as Feed screw and screw 67 designed as a distributor can be arranged to support the uniform distribution of the material on the ring base 20.

If the floor 8 is to be passed over for reasons mentioned above, a deflection element 65 in the goods transfer chute 34 is pivoted via an actuating device 64 from a position in which the shaft section 62 is released into the position shown in FIG the floor 9 into the shaft section 63 and from there directly into the area of the auger 68 or into the inlet 80 of the goods transfer chute 34 lying below it.

The ring base in question must not be flowed through in the clearing or feed zone in order to prevent air breakthroughs in the areas of the ring base not covered by the good layer. This is used in the exemplary embodiment shown in order to collect the passage of fine particles of the goods occurring in the clearing and feeding zone and to feed them to the floor below. In order to show these devices, in the middle of FIG. 4 the effective transfer chute between the floors 8 and 7 is shown partially broken away. One can see under each of the two reels 69, 70 funnel-shaped collecting chambers 73, which are closed at the bottom via transfer devices 74 designed as cell locks, which discharge the collected fine material onto the ring base underneath. A further central collecting chamber 71 is arranged between the collecting chambers 73 and is open at the bottom at 72, so that the material can also fall onto the ring base 20 underneath. At least the collecting chamber 71 can be acted upon as a back pressure chamber with a pressure which corresponds to the distributor pressure in the central drying air distributor shaft 5.

In the central collecting chamber 71, devices such as brushes, blowing nozzles or the like, which are not shown in the figures, are also arranged in the figures, so that the cleaned particles are also transported through the central collecting chamber 71 to the ring base underneath.

The inlet 80 of the chute-like crop transfer chute 34 is located in the central crop transfer chute, not shown in FIG. 4, differently than under the ring floor of floor 7 under the outlet of clearing screw 68, since the ring floors of floors 7 and 8 are driven in opposite directions, which in each case also for the floors of floors 8.9 and 7.6 apply.

The sector-shaped clamped screens forming the ring base 20 can be produced as a perforated stainless steel sheet which is completely smooth on the top and bottom.

Because of the arrangement described, it is clear that all fine particles formed are reliably collected and thus safely removed from the air flow, since there is no flow in the region of the collecting chambers 71, 73 when they are designed as counter-pressure chambers.

The dust particles discharged with the exhaust air are released near the foundation 2 with the exhaust air. The cold fresh air, on the other hand, is drawn in in the dust-free area above the tower dryer. As a result, the otherwise usual contamination of the heat exchanger device 11 is reliably avoided.

If necessary, mufflers can be installed in the vertical upwardly open air intake shafts 30. Because of the arrangement, these are also kept free from the disturbing influence of dust in the intake air.

Claims (17)

1. A low temperature drier for a pressed fibrous material, in particular leached sugar beet pulp, in which the material supplied at the top by a supply device can be conveyed downwards over a plurality of successive plate-shaped tiers (6-9), each tier is arranged in a housing-like pressure chamber, comprises a flat, air-permeable annular floor (20), a distributor (67, 69) which spreads out the material in an even thickness and a clearing device (68, 70), which clears the material from the annular floor approximately in a radial direction and supplies the material via a through opening, to the underlying tier, and a dry air conveyor is provided formed by fans (13) and heating installations (11), by means of which dry air conveyor dry air can be supplied to the pressure chambers and can be drawn off after passing through the annular floors (20) and the layers of material disposed thereon, characterised in that a central dry air distribution shaft (5) is provided, which extends over all tiers (6-9), is sealed at the top and whose lower end is connected to the fans (13) and heating installations (heat exchanger 11) arranged beneath the lowermost tier (6), in that each pressure chamber is designed as a closed annular chamber (18a) concentrically enclosing the dry air distribution shaft (5) and is connected with the dry air distribution shaft (5) via closable air inlets (17) and in that each permeable annular floor (20) with the closed annular chamber (18a) of the underlying tier defines an annular outflow chamber (24) for the exhaust air, which chamber opens radially outwards into an exhaust air collector (25) concentric to the shaft.

2. A low temperature drier according to claim 1, characterised in that the height - measured parallel to the shaft axis (47) - of each closed annular chamber (18a) descreases in a radially outward direction.

3. A low temperature drier according to claim 1, characterised in that louvre seals are associated with the closable air inlets (17) of the annular chambers (18a).

4. A low temperature drier according to one of claims 1 to 3, characterised in that the exhaust air collector (25) is closed at the top and is designed with an exhaust air outlet (28) beneath the lowermost tier (6).

5. A low temperature drier according to one of claims 1 to 4, characterised in that each fan (13) comprises and air intake shaft (30) with an air inlet opening (31) arranged above the uppermost tier (9).

6. A low temperature drier according to claims 4 and 5, characterised in that the air intake shaft (30) is arranged in the exhaust air collector (25).

7. A low temperature drier according to one of claims 1 to 6, characterised in that a closable intake opening for exhaust air from the tiers (6-9) is associated with each fan (13) for operating the drier in recirculation mode.

8. A low temperature drier according to one of claims 1 to 6, characterised in that with annular floors (20) which can be driven so as to rotate about the shaft axis (47), fixed shaft-like material transfer chutes (34) or similar elements are arranged between successive tiers (6-9) and are provided with switchable deflector devices (64, 65), so that the material can optionally by-pass the next tier and be supplied to one of the subsequent tiers.

9. A low temperature drier according to claim 8, characterised in that the transfer chutes (34) and the intake and delivery ends of the distributor (67, 69) and the clearing device (68, 70) are arranged radially beyond the annular floors (20).

10. A low temperature drier according to claim 8 or 9, characterised in that in the region of each annular floor (20), in which the fixed shaft-like material transfer chutes (34) are arranged, collecting chambers (71) and additional collecting chambers (73) for material particles are provided, which are designed as closed receiving chambers arranged beneath said floor region, are covered by the floor region and comprise a transfer device (74) for returning the fine material to the main flow of the material.

11. A low temperature drier according to claim 10, characterised in that the collecting chambers (71, 73) can be acted upon by a pressure approximately corresponding to the distribution pressure in the central dry air distribution shaft (5).

12. A low temperature drier according to claim 10 or 11, characterised in that devices for cleaning the sieve floors are arranged in the region of the collecting chambers (71, 73).

13. A low temperature drier according to one of claims 1 to 12, characterised in that a double screw conveyor (67, 68), which is adjustable only in its height relative to the tier floors, is provided as a distribution and clearing device.

14. A low temperature drier according to claim 13, characterised in that a receiving reel (70) is associated with at least the screw conveyor (68) lifting the material from the annular floor (20).

15. A low temperature drier according to one of claims 1 to 15, characterised in that the rotating circulating annular floors (20) can be driven in opposite directions from tier to tier (6-9).

16. A low temperature drier according to one of claims 1 to 15, characterised in that the end (10) of the central dry air distribution shaft (5) facing the floor is defined by an annular heat exchanger device (11), which is surrounded on the outside by a fresh air distribution chamber (12) supplied by the fans (13).

17. A low temperature drier according to one of claims 1 to 16, characterised in that the outlet (28) of the exhaust air collector (25) is arranged in the vicinity of the lower end of the drier and upwardly projecting air intake shafts (30) which open in the vicinity of the upper end of the drier are provided for the supply of fresh air to the dry air conveyor.

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