EP0197171A1 - Low-temperature dryer for pressed fibrous material - Google Patents

Abstract

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.

Description

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

Such a dryer is known for example from GB-PS 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 frame-fixed floors, to which are assigned transfer chutes extending from floor to floor and guide or scraper plates arranged above the floors, by means of which the goods are distributed and cleared alternately towards the center or towards the outside (see GB-PS 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-PS 28 077).

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, 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 top layer on each sieve tray is flowed through from top to bottom over the entire ring width of the tray by the warm air, which is distributed or collected in closed annular chambers both above and below the tray.

The hot air flow can be controlled very precisely in this way and evenly distributed over the entire sieve 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 heat exchangers and air delivery devices underneath the blowers the bottom floor can be arranged directly on the foundation of the dryer, specifically so that a ring-shaped heat exchanger arranged in the cross-sectional area of the sieve plates on the tower floor can be flowed through over a large area via an outer fresh air chamber, while the heated air from the interior of the ring-shaped heat exchanger without flow resistances can be introduced into the central distribution shaft. This results in a significant weight reduction in the design of the low-temperature dryer. A plurality of fans are preferably arranged distributed in the circumferential direction. Each of these circumferential fans has a separate intake duct for fresh air, the inlet openings of these intake ducts being in the region of the top of the tower-like low-temperature dryer, while the exhaust air can escape into the open from the outer exhaust air collector near the bottom of the low-temperature dryer. This prevents any contamination of the fresh air drawn in. The suction shafts for the blowers 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 formation of the air duct arrangement can also be used with other tier-shaped low-temperature dryers according to the teaching of claim 17.

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 in the area of the radially outer Exhaust air collector frame-fixed goods transfer chutes arranged and equipped with convertible guide devices so that the goods can be passed directly to the next but one floor if necessary by skipping one floor. This makes it easier to adapt the throughput to the requirements, and repairs can be carried out on individual floors if necessary; 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 material onto the sieve bottom. The take-up and clearing auger is advantageously assigned a drivable reel, which forcibly conveys the good layer to the clearing auger.

Since fine particles are produced by the work of the reels and screws 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 drying air does not flow through the sieve tray in the clearing and feeding area, calmer zones can be created here for collecting the fine parts, through which the fine parts, e.g. are fed to the next lower sieve tray via a pressure lock. The cleaning devices necessary and customary for cleaning the sieves, 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, several heat exchangers 11 are arranged on the foundation to form an annular structural unit. The heat exchangers are traversed by a heat transfer fluid, which obtains its heat from the waste heat generated in other processes in the factory. The ring-shaped arrangement gives a large inflow and heat exchange surface, as is desired especially in low-temperature processes. By arranging the heat exchanger directly on the foundation 2, the actual dryer construction is relieved of force. Outside the heat exchanger ring 11, several blowers 13 are arranged in the circumferential direction, the outlets of which open into the outer annular space 12 and which are connected to the air inlet opening 31 on the ceiling 3 of the dryer by ducts 30 extending over the entire height of the dryer. The heat exchanger ring 11 surrounds the lower end 10 of a central hot air distributor shaft 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 axis 47 of the dryer.

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

Each level is determined by an annular sieve plate 20. In the example shown, it is assumed that each sieve tray 20 is driven to rotate around the central axis 47 of the dryer, the direction of rotation changing from floor to floor, so that the forces arising from the drive largely cancel each other out, which further contributes to relieving the load on the dryer construction. There is a ring above each sieve plate Pressure chamber 18a is arranged, which is delimited radially on the inside by the air inlet opening provided with the blind or an equivalent closure 17, on the top by a frustoconical cover 18 and on the outside by a cylindrical wall 19, the flow cross section of the pressure chamber 18a in the radial direction from the inside outside decreases. Furthermore, an annular exhaust air collecting chamber 24 is provided between the sieve bottom 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 surrounded at a radial distance by an outer protective jacket 26, which is arranged concentrically to the tower axis 47, extends down to below the bottom floor 6 and is closed at 27 at the top level 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. The sections 30 form the fresh air intake ducts for the blowers 13 already mentioned. Between these are sectors 25 which are directly connected to the ring-shaped exhaust air collecting chambers 24 and thus take care of the removal of the exhaust air, as indicated by the arrow 29 is. The sectors 25 are open at the bottom at 28, 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 sheath together with those used to subdivide sectors 25 and 30 radial partitions further contribute significantly to the stability of the dryer construction. In the ring zone 25, inspection and maintenance platforms 25a can also be assigned to each floor.

From Fig.l 1 it can be seen that the fresh air is drawn in through the opening 31 at 32 and reaches the fans 13 via the vertical shafts 30. From the outlet of the blower, the fresh air 14 is distributed in the annular chamber 12 over the inlet surface of the heat exchanger 11. Warm air rises from the bottom 10 of the central shaft 5 according to the arrows 15 and is distributed according to the arrows 16 via the inlet openings into the pressure chamber 18a . From there, the drying air is distributed according to the arrows 23 over the surface of the material layer, penetrates it and the sieve and enters the annular collecting chambers 24, from which the exhaust air exits into the atmosphere at 28 according to the arrows 29. At the transition between the intake shafts 30 and the exhaust air collecting shafts 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 discharged from the bottom of the bottom floor 6, as indicated at 79.

As is particularly clear from FIG. 2 and FIG. 4, the distributor and clearing devices 3.3 in the preferred exemplary embodiment shown consist of a twin screw 67, 68 which is assigned to each floor. This twin screw is arranged fixed to the frame in the circumferential direction and can optionally be opposite in height the corresponding floor. In Fig. 4 it is assumed that the upper floor shown in the figure is floor 8. It is assumed that the sieve bottom of the tier 8 is driven in the direction of arrow 60 and the sieve 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 are clamped in a sector shape are via spoke-like members 48 and pivot bearing on the central dryer 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 floor 20. The radially inner run 43 engages on a partial circumference of the rotatable sieve bottom, its radially outer ring 21 having corresponding teeth or teeth which -. engage in the chain loop 39.

The screw 67 of the twin screw of the floor 8 serves as a feed and distribution screw. Here the goods are normally fed through the shaft or chute 62. A corresponding distribution slot ensures a uniform exit of the material onto the ring-shaped sieve tray 20. The clearing screw 68 lying directly in front of it in the direction of rotation, on the other hand, picks up the material that is guided through a circulation via the floor 8 and leads it to the inlet end of the shaft leading to the next floor 7 . In order to ensure a secure absorption of the crop layer, at least the pick-up and clearing worm 68 is assigned a driven pick-up reel 70 which throws the crop into the screw flights. A corresponding reel 69 can also be arranged in the circumferential direction in front of the distributor screw 67 in order to support the even distribution of the material.

If the floor 8 is to be passed over from above-mentioned green spaces, a deflection element 65 is pivoted via the actuating device 64 from a position in which the shaft 62 is released into the position shown in FIG. 4 in order to move the goods from the floor 9 in to promote the shaft 63 and from there directly into the area of the auger 68 or into the inlet 80 of the shaft 34 below it.

In the clearing or feed zone the sieve tray in question must not be flowed through in order to prevent air breakthrough in the areas of the sieve 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 at the clearing and loading position and to feed them to the underlying floor. In order to show these devices, in the middle of FIG. 4 the shaft effective between the floors 8 and 7 is shown partially broken away. One can see funnel-shaped chambers 73 below the two reels, which are closed at the bottom by a cell lock 74, which releases the collected fine material onto the sieve tray underneath. Between the collecting chambers 73 there is a central collecting chamber 71 which is open at 72, so that the goods can also fall onto the floor below. At least the collecting chamber 71 (counter-pressure camera) can (not shown) be subjected to a pressure which corresponds to the distributor pressure in the central shaft 5.

The devices (not shown) necessary for cleaning the screen, such as brushes, blowing nozzles or the like, are also arranged in the central collecting chamber 71. so that the cleaned particles are also transported through the chamber 71 to the underlying floor 7.

The inlet 80 of the shaft 34 lies in the middle shaft, not shown in FIG. 4, differently than under the floor 7 under the outlet of the screw 68, since the floors 8 and 7 are driven in opposite directions, which also applies to the floors of the floors 8 , 9 or 7., 6 applies.

The endless screen covering of the floors can be made of 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 area of the counter-pressure chambers 71, 73.

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 11 is reliably avoided.

If necessary, mufflers can be installed in the vertical upwardly open air intake ducts 30. These are also kept free from the influence of dust in the intake air due to the arrangement.

Claims (17)

1. Low-temperature dryer for pressed fibrous material, in particular leached sugar beet pulp, in which the material fed in via a feed device (81) above can be passed from top to bottom in succession over several plate-shaped levels (6-9), each level in a housing-like pressure chamber (18, 19) is arranged, a flat, air-permeable floor (20), a distributor (67, 69) which spreads the material in a uniform thickness and a clearing device which clears the material approximately in a radial direction from the floor and conveys it via an outlet (34) to the floor below (68,70) and a drying air conveying device consisting of fan and low-temperature heating units (11, 13) is provided, by means of which the drying air can be supplied to the pressure chambers (18) and after passing through the floors (20) and the material layers located thereon can be removed, characterized in that a central dry air distribution extends over all floors (6-9) shaft (5) is provided, which is sealed at the top and whose lower end is connected to the fan and heating units (11, 13) arranged under the bottom floor (6), that each pressure chamber (18a) acts as the shaft (5) concentrically surrounding closed annular chamber (18a) and connected to the drying air distribution shaft (5) via closable air inlets (17), and that each permeable bottom (20) with the closed annular chamber (18a) of the underlying floor is an annular outflow chamber (24) limited for the exhaust air, which is open radially on the outside to an exhaust air collector (25) concentric with the shaft. 2. Low-temperature dryer according to claim 1, characterized in that the height - measured parallel to the shaft axis (47) - of each closed annular chamber (18a) decreases in the radially outward direction. 3. Low-temperature dryer according to claim 1, characterized in that the closable air inlets (17) of the annular chambers are associated with blinds. 4. Low-temperature dryer according to one of claims 1 to 3, characterized in that the annular exhaust air collector (25) is closed at the top and is formed with an exhaust air outlet (28) below the bottom floor (6). 5. Low-temperature dryer according to one of claims 1 to 4, characterized in that the or each blower unit (13) has an air intake shaft (30) with an air inlet opening (31) arranged above the top floor (9). 6. Low-temperature dryer according to claim 4 and 5, characterized in that the air intake shaft (30) is arranged in the annular exhaust air collection chamber (25). 7. Low-temperature dryer according to one of claims 1 to 6, characterized in that the or each blower unit (13) is assigned a closable suction opening for exhaust air (5 ⁰ ) for operating the system in recirculation mode from the floors (6, 9). 8. Low-temperature dryer according to one of claims 1 to 6, characterized in that in the case of ring floors (20) which can be driven in rotation about the shaft axis (47), frame-fixed material transfer chutes (34) or equivalent elements between successive floors (6, 9) are arranged in such a manner and with switchable deflection devices (64.65) are equipped so that the goods can optionally be supplied by bypassing the next floor to one of the next floors. 9. Low-temperature dryer according to claim 8, characterized in that the transfer chutes (34) and the receiving and discharge ends of the distributors (67, 69) and the clearing device (68, 70) are arranged radially outside the annular base regions (20). 10. Low-temperature dryer according to one of claims 1 to 9, characterized in that in the area of each floor (20) in which the frame-fixed distributor and clearing devices (34) are arranged, collecting chambers (73) are provided for fine parts, which are designed as closed collecting chambers arranged under this floor area, which are covered by the floor area and have a transfer device (74) for returning the fine material into the main stream of material. 11. Low-temperature dryer according to claim 10, characterized in that the collecting chambers (back pressure chambers) (71) can be acted upon with a pressure corresponding approximately to the distribution pressure in the central shaft (5). 12. Low-temperature dryer according to claim 10 or 11, characterized in that devices for cleaning the sieve trays are arranged in the region of the collecting chambers (71, 73). 13. Low-temperature dryer according to one of claims 1 to 12, characterized in that the distributor and clearing device is provided only a height of the double rotating screw (34) which is adjustable relative to the floor of the storey. 14. Low-temperature dryer according to claim 13, characterized in that at least the screw from the sieve bottom (20) receiving screw (68) is assigned a take-up reel (70). 15. Low-temperature dryer according to one of claims 8 to 14, characterized in that the rotating, circulating sieve trays (20) can be driven in opposite directions from floor to floor (6-9) (39). 16. Low-temperature dryer according to one of claims 1 to 15, characterized in that the bottom end (10) of the central shaft (5) is delimited by an annular heat exchanger device (11) which is fed from the outside by one or more fans (13) Fresh air distribution chamber (12) is surrounded. 17. Low-temperature dryer for squeezed fibrous material, in particular leached sugar beet pulp, in which the material fed in via a feed device (81) above from top to bottom in succession can be guided over several plate-shaped floors (6-9), each floor is arranged in a housing-like pressure chamber (18, 19), a flat, air-permeable floor (20), a distributor (67, 69) spreading the goods and one the goods has clearing device (68, 70) clearing the floor and a drying air conveying device consisting of fan and low-temperature heating units (11, 13) is provided, by means of which the drying air can be supplied to the pressure chambers (18a), characterized in that all floors ( 6-9) are connected in parallel to one another to a common warm air distributor (5) and a common exhaust air collector (25) and the outlet (28) of the exhaust air collector (25) near the lower end and the fresh air inlet (31, 32) of the drying air conveying device are located near the top of the dryer.

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