EP0222925B1 - Steam dryer for compressed fibrous material - Google Patents

Abstract

A steam dryer for pressed fibrous material, such as sugar beet cossettes, has a pressurized, horizontally arranged pipe or drum (1) closed at both ends and provided with a diametrically opposed supply manifold and exhaust manifold piping (5, 6) for the steam. At least one heat exchanger (7) is arranged in a lengthwise half of the pressurized pipe and extends across the entire steam flow-through cross-section. Endless loop screen or mesh belts (8, 8', 8'') are arranged one above the other in the other lengthwise half of the pressurized pipe. These belts are driveable in opposite directions for conveying the material to be dried, and to transfer the material from an upper belt to a lower belt. The mesh belts (8) define separation planes between pressure and exhaust chambers (24, 25) which are alternatingly arranged above and below each respective mesh belt. The pressure chambers (24) comprise inflow cross-sections open to the lengthwise half with the heat exchanger (7), and the exhaust chambers (25) comprise outflow cross-section open to at least one exhaust space (26). The steam flows in an essentially closed loop cycle, except for a small portion which is extracted and replaced by fresh steam, whereby the steam passes through the heat exchanger (7) and the separate mesh belts as it flows through this cycle.

Description

The invention relates to a steam dryer for squeezed fibrous material, in particular leached, possibly pre-dried sugar beet pulp, in which the steam, which is predominantly guided by a circuit arrangement, is brought into direct contact with the material and the material is moved along a conveying path.

In the course of saving energy and reducing the environmental impact, efforts are being made to use the steam dryers to make the large proportion of primary energy previously used for drying pressed fibrous material, in particular sugar beet pulp, cheaper and more environmentally friendly. The steam required for the operation of the steam dryers can essentially be provided by the steam generation systems which are already present in the factories. The steam, which is predominantly passed through the steam dryer through a circuit arrangement, can be fed to other devices for utilization of the residual heat, as long as it is withdrawn from the circuit and replaced by steam expelled from the material, for example fed to the evaporation crystallization via heat exchangers, in order in this way to conduct a further one Achieve improvement in energy yield.

The previously known steam dryers for pressed fibrous material, such as sugar beet pulp, generally consist of a drum provided with internals and drivable about its longitudinal axis, through which the steam flows during the rotational movement, with a direct intimate contact between the steam and the fibrous material in that the material is taken along by the drum during part of the rotational movement during the drum rotation and then falls freely down through the drum interior onto the drum jacket and is thereby loosened up continuously and brought into contact with the steam.

The drying effect of this rotatable steam-flow-through drum is relatively low, since the fibrous good particles are only washed around by the steam during the free fall of the good particles, while the steam only sweeps over the other good on the drum wall without penetrating deeper into the good.

Steam dryers have also become known (EP 0 058 651 A1), in which, in order to produce a cattle feed from sugar beet chips, these are loosened after preheating, pressing and subsequent expansion and transferred into a tube through which steam flows and are thereby carried away by the steam flow. The pipe through which steam flows forms part of the circuit arrangement of the dryer, which essentially consists of a meandering arrangement of steam pipes through which the entrained chips are also conveyed as a result of the steam flow in order to be separated from the steam by a separator at the outlet of the meandering arrangement, while the steam continues to be circulated except for a small amount, which is drawn off and replaced by live steam.

In this known arrangement, relatively high flow velocities of the steam are required in order to ensure the transport of the chips through the meandering pipes and to avoid deposits on the pipe walls. The operating conditions of such a steam dryer can only be changed within very narrow limits, since the flow rate of the steam is determined by the need to convey the chips through the meandering tubes and the duration of the treatment of the chips during the drying process can practically not be influenced. It is therefore necessary to introduce cutlets with a constant moisture content into the dryer and the amount of cutlets fed per unit of time can hardly vary. Even at high steam speeds, deposits of the chips on the pipe migrations can scarcely be avoided, the elimination of the faults which occur as a result being very costly. In addition, the known dryer requires a relatively large amount of construction work with a corresponding space requirement.

The invention has for its object to provide a steam dryer of the type described in the introduction so that with a simple and space-saving construction generates a steam flow that is uniformly water-absorbent over its cross-section, thus achieving a uniform treatment of all good particles and, moreover, the duration of the action of the steam on the Good particles can be changed within wide limits.

To solve the above problem, the steam dryer mentioned at the outset is characterized in that a pressure pipe, which is closed at both ends and is arranged horizontally, is divided along a vertical plane into two longitudinal halves, one of which has inflow devices arranged on its long side and at least one over the entire flow cross section for receives the steam-extending heat exchanger and the other outflow devices diametrically opposite the inflow devices for the steam and a plurality of endless sieve belts arranged one above the other in the manner of a belt dryer, which can be driven in opposite directions, for conveying and transferring the material from belt to belt and above the top sieve belt an entry device and below the bottom one Sieve belt has a discharge device for the material, the flow planes for the steam between alternately arranged one above the other, delimited by partition walls K and outflow chambers are formed by the conveyor runs of the sieve belts and the pressure chambers have inflow cross sections open to the longitudinal half with the heat exchanger and the outflow chambers open to at least one outflow cross sections.

In the aforementioned formation of the steam skirt In addition, the material layer on the sieve belts is flowed through in the direction transverse to the layer plane, the flow velocity of the steam within the layer in the individual cavities being greater than the flow velocity of the steam. Since unsaturated steam is used for such steam dryers, the strong warming of the good particles results in an increased moisture transfer from the good particles into the unsaturated steam and thus a correspondingly favorable drying effect. By adjusting the drive speed of the belts, it is in your hand to adjust the layer thickness of the goods on the belts differently and according to the respective drying conditions and / or by changing the movement speeds of the driven belts together, the total dwell time of the goods in the steam stream within wide limits adjust. Since all of the belts are acted upon in parallel by the steam or the steam passed over the entire flow cross section of the one heat exchanger, the steam supplied to the layers of material on the sieve belts has the same water absorption capacity when the individual layers of material flow against them. This results in a very effective and uniform drying of the good particles.

Although it is known from DE-A 3 414 853 drying systems in which a building is also divided into two halves by a longitudinal wall, heat exchangers being arranged in a closed half designed as a pressure chamber and several being arranged one above the other in the other longitudinal half in the manner of a belt dryer Air-permeable belts are arranged, similar to the case with the device designed according to the invention, but it is a system that works with heated air and in which the air is not predominantly passed through a circuit arrangement, but after flowing through the respective good layer is led outdoors. In this known embodiment, flow openings for the air are provided in the longitudinal wall of the building, into which heat exchangers assigned to them are installed. Separate chambers, one above the other, adjoin the through-flow openings, along the open underside of which one of the strips is guided.

The intended heating of the drying air without a circuit arrangement leads to an extremely high energy consumption. In addition, due to the arrangement of the individual heat exchangers in the individual throughflow openings, despite the great effort involved, different heating of the drying air to be transferred into the chambers cannot be avoided, and thus a uniform treatment of the good particles in this drying system cannot be guaranteed.

The evacuation of the moisture-laden air leads to environmental pollution in the known system through the formation of vapors and through the fine particles carried outside by the drying air.

The aforementioned disadvantages are avoided by the inventive design of the steam dryer.

It is particularly expedient if, in the steam dryer according to the present invention, as seen over the length of the pressure pipe, a plurality of outflow spaces which are arranged separately next to one another and are each connected to the suction side of a blower are provided, and if the blowers are connected on the pressure side to the longitudinal half of the pressure pipe containing the heat exchanger, which encloses a continuous pressure chamber adapted to the heat exchanger and in open communication with all fans. As a result, the flow of the sieve belts is evened out over their entire length by the steam.

It is advantageous if the individual outflow spaces each extend over the cross section of the overflow chambers. Despite this described division into the outflow spaces arranged next to one another, uneven flows through the individual screen surfaces or the material layers located on the screen surfaces can take place. In order to achieve an equalization here, in an advantageous embodiment, the outflow spaces up to the transition into the suction line of the respective blower can be divided into parallel channels assigned to the individual outflow chambers, and separately controllable throttle valves can be provided in the channels. By means of flow measurements in the individual channels, the throttle flaps can then be individually adjusted so that a uniform or, if appropriate, also a stronger flow in one or the other material layer takes place by means of the steam.

Since in the course of the drying of the material, inevitably smaller solid particles or light fibrous constituents are taken along by the steam flowing through the layers of material and the steam in the circuit is to be distributed as evenly as possible in the pressure chamber, it is possible in the pressure chamber between the inflow devices for the steam and the Heat exchanger a diffuser and cleaning screen consisting of cloth or fabric can be provided. This sieve should be arranged and designed such that it is slightly inflated and agitated by the steam flow so that it cleans itself and the smaller particles and fibers retained by the sieve from the steam flow can slide down along the sieve. A discharge screw is then expediently provided there below the diffuser and cleaning sieve.

The arrangement of the sieve belts is expediently made such that the empty strand of each sieve belt is arranged above the conveying strand of the next lower sieve belt, and that both strands extend over the entire flow cross-section for the steam from the pressure chamber into the outflow chamber. This ensures that the empty strand with its downward-facing contact surface for the goods already delivered to the transfer point is flowed through by the steam in the direction from top to bottom and the small particles that may still adhere to the support surface for the goods are carried with the steam flow onto the Good layer of the conveyor run of the next lower sieve belt. This arrangement thus results in an additional cleaning effect, although such sieve belts, as is customary in belt dryers, are additionally equipped with other mechanical cleaning devices, such as brushes or the like.

Since the material fed to the lowest belt is already largely pre-dried and the removal of the residual water with increasing enrichment of this residual water by salts or other water-binding substances is difficult to achieve the desired degree of drying, it is advisable to add an additional flow cross-section below the lowest belt heat exchanger filling this band.

The arrangement of this heat exchanger is particularly important, for example, when using the dryer for sugar beet pulp because the chips are still wetted with syrup when they are placed on the bottom belt, from which the residual water can only be removed with the help of a higher steam temperature can.

In order to achieve the greatest possible water removal from the fibrous material, it is expedient if the material is already introduced into the dryer at a relatively high temperature. For this purpose, the feed device for the goods can be equipped with a preheating device, which can expediently be designed as a ring screw through which steam flows.

The drawing shows an embodiment of the invention in a schematic representation.

• Fig. 1 eine Seitenansicht des Trockners nach der Erfindung, jedoch ohne die Tragkonstruktion für das Druckrohr,
• . Fig. 2 eine Draufsicht auf die Anordnung nach Fig. 1,
• Fig. 3 einen Schnitt durch die Anordnung nach Fig. 1 entlang der Schnittlinie A - A,
• Fig. 4 ein Schnittbild durch die Anordnung nach Fig. 1 entlang der Schnittlinie B - B.

Show it:

• 1 is a side view of the dryer according to the invention, but without the support structure for the pressure pipe,
• . 2 is a plan view of the arrangement of FIG. 1,
• 3 shows a section through the arrangement according to FIG. 1 along the section line A - A,
• 4 is a sectional view through the arrangement of FIG. 1 along the section line B - B.

The steam dryer shown in the figures is of a type which is used in particular for the treatment of pre-dried sugar beet pulp.

In the figures, a pressure pipe, which is closed at both ends and is generally designated 1, can be seen, which, in view of the generally very long length, is composed of several sections, each of which is connected to one another via flanges and interposed seals. The pressure tube 1 is closed at the ends by dome-like end parts 2, in which, like in the individual cylindrical sections of the pressure tube, manholes which are closed by covers are provided, through which access to the interior of the pressure tube 1 is made possible for revision and repair work.

The pressure pipe 1 rests on a support frame 4 shown in FIGS. 3 and 4 and is equipped with diametrically opposite inflow and outflow devices (FIG. 4), designated 5 and 6 respectively, which extend over the essential length of the pressure pipe 1 .

A heat exchanger 7 is arranged in the inside of the pressure tube 1 in one longitudinal half, as can be clearly seen from FIGS. 3 and 4. This heat exchanger 7 can be formed in several parts by a row arrangement of individual exchangers and is connected to a steam feed device not shown in the drawing.

In the other half of the pressure tube 1, a plurality of endless sieve belts, which are arranged in the manner of a belt drier and are arranged in opposite directions and are denoted overall by 8, are provided. In the example shown, three sieve belts 8 are arranged one above the other.

The uppermost sieve belt 8 is driven in accordance with the arrow 9 shown in FIG. 1, so that the material placed on the upper conveyor run 8a of the upper sieve belt is transferred to the next lower sieve belt 8 at the end of this sieve belt by the longitudinally offset arrangement of the sieve belts provided one above the other and from there to the bottom sieve belt 8.

The sieve belts 8 are held in a supporting frame 9, to which partition walls 10 arranged one above the other and extending in the longitudinal direction of the pressure tube are fastened.

A feed device, generally designated 11 (FIGS. 1 and 3) is used to feed the material to the uppermost belt 8 or its conveyor run 8a, while a discharge device, designated overall by 12, is connected below the bottom sieve belt 8 (FIG. 3). In the example shown, the entry device 11 consists of a cellular wheel 13, which is arranged above a driven screw conveyor 14, which in turn opens into a shaft 15, which is located above two distributor screws 16 arranged in the pressure pipe. The housing of the screw 14 is connected to a steam feed line 17 in the region above the shaft 15 (FIG. 1). In this example, the worm 14 is designed as an annular worm, into which the steam supplied penetrates and through which the preheat is well preheated during the transfer into the pressure tube 1.

According to FIG. 3, the discharge device 12 consists of a discharge screw 18 and an adjoining lock 19, from which the goods are transferred in the direction of arrow 20 to a further conveyor not shown in the drawing.

To apply the material layers located on the conveyor runs 8a, that is to say the upper runs of the belts 8, steam is predominantly passed through the pressure pipe 1 in a circuit, which passes through the inflow devices 5 into the pressure pipe 1 and is again removed from the pipe through the outflow devices 6 becomes. To convey the steam, seen over the length of the pressure pipe, several blowers 21 are provided, which are connected to the outflows via suction lines 22; directions 6 and with their pressure lines 23 are connected to the inflow devices 5.

The arrangement of the partitions 10 in the Support frame 9 for the sieve belts 8 is forced to flow through the upper runs 8a dl: 'Sieve belts 8 in the direction of the arrows shown in Fig. 4 in the right half, ie the material located on the conveyor run 8a is practically in the direction perpendicular to the layer plane of the flows through the conveyed steam 21. Thus, pressure chambers 24 are formed above each of the conveyor runs 8a between these and the partition walls 10 located above them, and discharge chambers 25 below the conveyor runs 8a, which open into discharge chambers 26, which in turn are connected to the suction line 22 of the blowers 21.

The conveyor runs 8a of the sieve belts 8 thus form the throughflow plane between the pressure chambers 24 and the outflow chambers 25.

Seen over the length of the pressure pipe 1, a plurality of outflow spaces 26 are arranged separately next to one another and each connected on the suction side to a blower 21 (FIG. 2), in which the outflow chambers 25 each open out without the interposition of any built-in parts.

The outflow spaces 26 can be divided into parallel channels, assigned to the individual outflow chambers 25, up to the transition into the suction line 22, in which separately controllable throttle valves are provided, as is indicated in FIG. 4. As a result, different flow resistances occurring in the individual material layers on the conveying runs 8a can be compensated for, so that a uniform flow through all the conveying runs 8a or all the good layers located on these conveying runs is achieved.

On the inflow side of the steam through the inflow devices 5, the steam passes into a continuous pressure chamber 28 which is adapted to the heat exchanger 7 and which is limited only according to FIG. 2 by lateral walls 29 adjoining the heat exchanger 7, so that the conveyed steam is forced through to flow through the heat exchanger 7 and cannot flow around it laterally.

In the heat exchanger 7, the steam brought under increased pressure by the fan is heated, whereby the moisture absorption capacity of the steam is correspondingly increased.

Part of the steam is continuously removed from the circuit, specifically via a bypass line 30, which is connected to the blower 21 on the pressure side and is connected to a separator 31, from which the steam removed from the circuit and freed from entrained fine particles for further use, for example at sugar factories for evaporation crystallization.

Depending on the amount of steam discharged, a corresponding amount of live steam is fed to the heating circuit, which is taken from the steam generating plant at sugar factories. The steam supply and discharge is not shown in detail in the drawing shown, but these are known measures which are not the subject of the invention.

1, funnel-shaped collecting spaces 32 are provided below the separators 31, which at the same time form calming spaces for the separated material and are connected to a discharge device for the separated material.

From Fig. 4 it can be seen that in the pressure chamber 28 between the inflow devices 5 for the steam and the heat exchanger 7 there is a diffuser and cleaning screen 33 shown in dashed lines made of cloth or fabric. This sieve is used to separate any solid particles that may be entrained in the steam carried in the circuit and, at the same time, to achieve a V, -.- uniformity of the flow. Below this sieve 33, which is expediently only loosely tensioned in the pressure chamber 28 of the pressure tube 1, a discharge screw 34 can be seen, via which the particles separated on the sieve 33 and falling down are discharged.

It has already been explained that the conveyor runs 8a of the sieve belts 8 form the respective flow plane between the pressure chambers 24 and the outflow chambers 25. The empty runs 8b belonging to the individual conveyor runs 8a are guided in the described arrangement in such a way that they are arranged directly above the conveyor run 8a of the next lower screen belt, so that the empty run 8b must first be flowed through by the steam before the steam reaches the one below it reached with the good layer conveyor strand 8a of the next lower belt. Since the empty strand 8b of the belt faces downward, small particles still adhering to it are carried along by the steam flowing through and transferred to the good layer of the conveyor strand 8a located underneath. The empty run 8b is thus cleaned, each empty run simultaneously forming a diffuser screen and contributing to the uniformity of the flow through the conveying run 8a of the next lower belt located under the empty run 8b.

From Fig. 4 it can also be seen that an additional heat exchanger 35 filling the inflow cross section to this belt is arranged above the lowermost wire belt 8. This heat exchanger further heats the steam supplied to the material on the lower sieve belt 8, whereby the degree of final drying of the material is considerably increased.

Claims (10)

1. Steam drier for pressed fibrouS material, in particular washed out, optionally pre-dried, sugar beet slices, wherein steam, which is mainly supplied through a circulation arrangement, is brought directly into contact with the material whilst the material is moved along a conveyor path, characterised in that a pressure pipe (1) which is closed at both ends and which is arranged in a lying-down position is divided along a vertical plane into two longitudinal halves, whereof the one has, arranged on its longitudinal side, inflow installations (5) and accommodates at least one heat exchanger (7) which extends over the entire cross section of throughflow for the steam, and the other has outflow installations (6) for the steam which lie diametrically opposite to the inflow installations, and several endless screening belts (8) which are arranged superimposedly in the manner of a belt-type drier and which can be driven in contrary directions, for conveying and transferring the material from belt to belt, and has, above the uppermost screening belt, an input installation (11) and also, below the lowermost screening belt, has an output installation (12) for the material, and wherein the throughflow planes for the steam, between alternately overlappingly arranged pressure- and outflow- chambers (24; 25) which are bounded by partition walls (10), are formed by the conveying side of the screening belts, and the pressure chambers (24) have cross sections of inflow which are open towards the direction of the longitudinal half with the heat exchanger (7), and the outflow chambers (25) have cross sections of outflow which are open towards the direction of at least one outflow space (26).

2. Drier according to claim 1, characterised in that viewed over the length of the pressure pipe (1 there are provided several separate but adjacently arranged outflow spaces (26) which are in each case connected with the suction side of a fan (21), and in that the fans are connected on the pressure side with the longitudinal half of the pressure pipe which contains the heat exchanger (7), which half encloses a through-extending pressure space (28) which is adapted to fit the heat exchanger and which stands in open connection with all the fans.

3. Drier according to claim 1 or 2, characterised in that the individual outflow spaces (26) extend in each case over the cross section of the superimposedly arranged outflow chambers (25).

4. Drier according to claim 3, characterised in that the outflow spaces (26) are divided, up to as far as the place of transition into the suction pipe (22) of the fan (21) concerned in each case, into parallel ducts which are associated with the individual outflow chambers, and in that in the ducts, separately controllable throttle valves are provided.

5. Drier according to any one of the claims 1 to 4, characterised in that in the pressure space (28) between the inflow installations (5) for the steam, and the heat exchanger (7), there is provided a diffusing-and purifying- screen (33) which is made of cloth or fabric.

6. Drier according to claim 5, characterised in that below the diffusing- and purifying- screen (33) there is provided an output worm (34) for the particles. separated out of the steam.

7. Drier according to any one of the claims 1 to 6, characterised in that the return side (8b) of each screening belt (8) is arranged above the conveying side (8a) of the screening belt which is next to it below, and in that in each case both belt sides extend over the entire cross section of throughflow for the steam from the pressure- into the outflow- chamber (24 and/or 25).

8. Drier according to any one of the claims 1 to 7, characterised in that above the lowermost screening belt (8) there is provided an additional heat exchanger (35) which fills-up the cross section of oncoming flow to this belt.

9. Drier according to any one of the claims 1 to 8, characterised in that the input installation (11) for the material is equipped with a pre-heating installation.

10. Drier according to claim 9, characterised in that the pre-heating installation is constructed in the form of an annular worm (14) through which steam flows.

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