DE10011177A1 - Drying of wood particles as chips or fibers and the like has an initial drying stage partially heated by cleaned exhaust gas from the main drier where hot gases are the drying medium from a combustion chamber - Google Patents

Abstract

A method for the direct drying of particles, such as wood chips, wood fibers or the like, is described, in which hot gases are generated in a combustion chamber and are supplied as a hot gas stream to a dryer. The particles are also placed in the dryer and dried in the dryer by direct contact with the hot gases. The dried particles are removed from the dryer in an exhaust gas stream and then separated from the exhaust gas stream. The remaining exhaust gas flow contaminated with fine dust and odorous substances is at least partially reintroduced into the combustion chamber. A partial stream of the exhaust gas stream is divided before the remaining exhaust gas stream is introduced into the combustion chamber, this partial stream being fed back past the combustion chamber to the dryer. Furthermore, an apparatus for performing the method is described.

Description

The present invention relates to a method for direct drying of particles such as wood chips, wood fibers or the like, in which in ei ner combustion chamber hot gases are generated, which as a hot gas flow Dryer are fed, the particles also entered the dryer be brought and in the dryer through direct contact with the Hot gases are dried, the dried particles in an ab gas flow discharged from the dryer and then from the Ab gas flow are separated, and the remaining with fine dust and Ge exhaust gas flow contaminated at least partially back into the Combustion chamber is initiated. Furthermore, the invention is based on a Direction for direct drying of particles such as wood chips, wood fibers or the like directed with a combustion chamber for generating Heating gases, one with the combustion chamber via a hot gas pipe connected, on the input side with a feed unit for the particles ver see dryer, a separation unit downstream of the dryer to separate the dried particles from one with fine dust and Exhaust gas flow contaminated with odorous substances, as well as an exhaust gas flow from the Separation unit leading to the combustion chamber leading gas duct, esp especially for performing the method mentioned at the beginning. The part Chen can also by other, smells or organic carbon compounds (gaseous and aerosol compounds) emitting Bulk goods, for example in the form of beet pulp, fish meal, Cereals, fertilizers, rubber granules and sewage sludge.

DE-OS 24 61 415 is a drying system with a direct known dryer heated by flue gases, the flue gases in  a combustion chamber upstream in the dryer. For the Exhaust gases leaving the dryer have been cyclone dedusted hen, through a division of the exhaust gas leaving the dryer current takes place in two partial flows. One part of the stream becomes the Brennam always recycled and there for combustion of the residues on fine dusts and odors are injected into the hottest zone, so that a intensive mixing with the flue gases takes place, which then like which are fed to the dryer. The other partial flow is due to the Evaporation performance of the dryer and the technology in the cycle mass balance to be complied with and is via an exhaust gas released into the atmosphere.

The problem here is that the exhaust gas part released into the atmosphere electricity contains pollutants, either polluting the environment arises, or which must be reduced by filtering.

The present invention is based on the object of the method how to develop the device of the type mentioned so that it work particularly low emissions and at the same time work economically.

Based on the procedure mentioned at the outset, the procedure Ren relevant part of this task solved according to the invention in that a partial flow of the exhaust gas flow before the introduction of the remaining exhaust gas Stream is divided into the combustion chamber and that this partial flow the combustion chamber is returned to the dryer.

The part of the task relating to the device is based on a Device of the type mentioned solved in that from the gas line  a branch line branches off, via which a partial flow of the Ab gas flow past the combustion chamber back to the dryer becomes.

This configuration makes an emission-free direct long-term Drying is achieved because it contains pollutants such as fine dust and odor polluted exhaust gas flow in a ge compared to the atmosphere closed cycle is performed. A part of the pollutants is through the high temperatures in the combustion chamber of übli burned completely over 800 ° C, while in the abge pollutants contained in the second partial stream remain in the cycle and ultimately this way after one or more further rounds be burned in the combustion chamber. Due to the limited ver evaporation performance of the dryer and the technology in the cycle Keeping the mass balance of excess pollutants not released into the atmosphere, but kept in circulation for so long until they are completely burned in the combustion chamber.

According to an advantageous embodiment of the invention, the part stream with the hot gas stream emerging from the combustion chamber its entry into the dryer mixed. This variant is done thus an immediate return of the partial flow to the dryer, so that the inventive method is carried out very economically can be.

Accordingly, in a device according to the invention Section of the hot gas pipeline from the burner on the combustion chamber side chamber to a first entrance of a mixing chamber, with a  Output of the mixing chamber through a section of the dryer Hot gas pipeline is connected to the dryer and from the gas line branches a branch line, which at a second input of the Mixing chamber is connected.

According to an advantageous embodiment of the invention takes place in the Dryer the main drying of the particles, from which the Combustion chamber exiting still unmixed hot gas flow a hot divided gas partial flow and ver for direct predrying of the particles is applied. The pre-drying takes place especially with a gerin lower temperature than the main drying.

According to a further embodiment of the invention, it is also possible that the main drying of the particles takes place in the dryer and that the Partial flow as a hot gas partial flow for direct predrying of the particles is used before it is ultimately at least partially towards the dryer is returned.

Typical temperature values for the main drying are the combustion chamber temperatures of over approx. 750 ° C, in particular of more than approx. 800 ° C, so that the fine supplied to the combustion chamber with the partial exhaust gas flow dust and the smells are completely burned.

By using a partial hot gas flow for a direct, short-term pre-drying of the particles, especially at a lower temperature temperature than with direct long-term main drying, is a very good one Energy balance of the entire system achieved. In particular, the fore the particles dry them and the hot gas partial flow in a pre-dryer  fed the pre-dried particles in a pre-drying exhaust gas electricity is removed from the pre-dryer and then from the pre-dryer drying exhaust gas flow separated in the predrying exhaust gas flow remaining residues separated from this and the cleaned pre drying exhaust gas flow mixed with the hot gas partial flow. The one from that Predrying exhaust stream separated residues, in particular Cellulose, lignin, as well as various resins and acids include only in small quantities, the odor emission of for example organic carbon compounds is minimized or completely eliminated.

A subsequent disposal of the ge separated from the predrying exhaust gas flow There are no small residues because these residues are only in a second mixing chamber with that from the combustion chamber of the main dryer branched hot gas partial flow are mixed. Since the right relatively low temperatures of the pre-dryer, for example approx. 250 up to 400 ° C, in particular about 300 to 350 ° C, in the exhaust gases contained pollutants remain essentially inactive by this low temperatures and the short pre-drying even one Emission avoidance achieved so that environmental pollution with Pollutants are eliminated.

Further advantageous embodiments of the invention are in the Un claims specified.

The invention is described below using exemplary embodiments Reference to the drawings explained in more detail; show in these  

Fig. 1 is a schematic representation of a first embodiment of a drying device designed according to the invention and

Fig. 2 is a schematic representation of a second embodiment of a drying device designed according to the invention.

The drying system shown in FIG. 1 is divided into a pre-dryer unit 1 shown in the upper area of FIG. 1 and a main dryer unit 2 shown in the lower area of FIG. 1.

The main dryer unit 2 comprises a combustion chamber 3, which has a a combustion chamber side portion 4 'and a dryer side cut 4 from "full hot gas pipe 4 to the input-side loading reaching a dryer formed as a drum dryer 5 is connected.

The combustion chamber-side section 4 ′ of the hot gas pipeline 4 is connected to a first inlet 6 of a mixing chamber 7 , while the dryer-side section 4 ″ of the hot gas pipeline 4 connects an outlet 8 of the mixing chamber 7 to the dryer 5 .

The dryer 5 is further provided on the input side with a feed unit 9 for supplying pre-dried particles and connected on the output side via an exhaust gas line 10 to a particle separator unit 11 designed as a cyclone.

The particle separation unit 11 has at its lower end a discharge line 12 for the separated dried particles and a discharge line 13 forming an emergency failure. The GE of the particles separated exhaust gas stream leading output 14 of the Teilchenabscheideein unit 11 is connected via a Umgasleitung 15 with the combustion chamber 3, with a conveying blower 16 is arranged in the Umgasleitung 15th

In the flow direction in front of the combustion chamber 3 branches off from the Umgaslei device 15 a branch line 17 which is connected to a second input 18 of the mixing chamber 7 .

Similarly, the hot gas pipe 4 to an input 20 he most branches from the combustion chamber side portion 4 ', a further branch line 19, a further mixing chamber 21 of the Vortrocknereinheit 1 performs. The further mixing chamber 21 has a second inlet 22 , to which a fresh air line 23 is connected.

On the output side, the further mixing chamber 21 is connected via a further hot gas pipeline 24 to the input region of a pre-dryer 25 , which is also designed as a dryer drum, which in a similar way to the main dryer 5 on the input side is additionally provided with a unit 26 for the particles to be dried.

The output of the pre-dryer 25 is in turn connected via an exhaust gas line 27 to a further particle separation unit 28 , which is designed as a cyclone analogous to the particle separation unit 11 .

The discharge line 29 leading the separated particles of the further particle separation unit 28 is connected via a transport line 30 to the feed unit 9 of the main dryer 5 .

The separated exhaust gas flow leading output 31 of the other part separating unit 28 is connected via a gas line 32 and via a delivery fan 33 provided in the gas line with a Schadstoffab separating unit 34 , which is designed in the present embodiment as a vortex tube. Of the separated from the pollutants from gases laxative output 35 of the Schadstoffabscheideeinheit 34 is connected to an exhaust pipe 36, during which the deposited pollutants laxative output 37 of the Schadstoffabscheideeinheit 34 is connected via a return line 38 to a third input 39 of the further mixing chamber 21st

The function of the drying system shown in Fig. 1 is described in more detail below.

The particles to be dried are fed via the feed unit 26 to the before dryer 25 together with a hot gas stream flowing through the further hot gas pipeline 24 . This hot gas stream has a temperature of, for example, 300 to 350 ° C.

In the pre-dryer 25 is a direct, short-term predrying by the contact of the particles with the hot gas stream, the existing pollutants being released by the heating. The particles are supplied together with the released pollutants and the cooled gas via the exhaust line 27 of the particle separator unit 28 , from which the separated particles are transported via the feed line 29 and the transport line 30 to the feed unit 9 of the main dryer unit 2 .

The particles predried in this way are fed to the main dryer 5 together with a hot gas stream supplied via the hot gas pipeline 4 . Through the contact of the pre-dried particles with the hot gas stream within the main dryer 5, there is direct long-term drying, through which the particles obtain the desired degree of drying. At the same time, pollutants and odorous substances still contained in the particles are released, which, together with the dried parts and the dried gas stream, are supplied to the particle separation unit 11 via the exhaust line 10 . The particles separated in this are fed via the discharge line 12 to the desired produc tion, while the exhaust gas stream contaminated with pollutants, fine dust and odors is conveyed by the delivery fan 16 via the gas line 15 to the combustion chamber 3 . The circulating air gases are injected into the hottest zone of the combustion chamber 3 , so that due to the high temperatures existing in this zone, for example over 800 ° C., the residues in the circulating air gases are completely combusted.

The hot gases generated in the combustion chamber 3 will then be on the combustion chamber side portion 4 'of the hot gas pipe 4 which a gear 6 of the mixing chamber 7, respectively. At the same time, a partial flow of the circulating air gases is fed via the branch line 17 to the second input 18 of the mixing chamber 7 , so that in the mixing chamber 7 there is an intimate mixing of the very hot hot gases from the combustion chamber 3 with the branched drying waste gas containing slight residues. The mixed gas is fed to the main dryer 5 at a temperature of, for example, 500 ° C. via the dryer-side section 4 ′ of the hot gas pipeline 4 . In this way, the main dryer unit 2 forms a closed circuit so that the pollutants strongly activated by the relatively high temperatures within the main dryer 5 are not released to the outside.

From the guided by the extremely high temperatures of the combustion chamber 3 in the combustion chamber-side section 4 'of the hot gas pipe 4 hot gas stream, a partial stream is passed via the further branch line 19 to the first inlet 20 of the further mixing chamber 21 of the pre-dryer unit 1 . A hot gas mixture is formed by this very hot partial hot gas stream, for example having a temperature of more than 800 ° C., together with a fresh air stream supplied via the fresh air line 23 and the residual gas stream led via the return line 38 , which is fed to the pre-dryer 25 via the further hot gas pipeline 24 .

The drying device shown in FIG. 2 differs from the drying device according to FIG. 1 in that the part stream divided by the gas line 15 is not mixed with the hot gas stream emerging from the combustion chamber 3 , but directly as a hot gas part stream, for the direct drying of the particles is used.

For this purpose, a branch line 17 'is connected to the input 40 of a predrying combustion chamber 41 , a hot gas partial stream being generated from the partial stream by the high temperatures present in the predrying combustion chamber 41 , which partial flow is generated via an outlet 42 of the predrying combustion chamber 41 and a branch pipe 19 'connected to it is led to the first inlet 20 of the further mixing chamber 21 of the pre-dryer unit 1 . The further branch line 19 shown in FIG. 1 is thus replaced by the continuing branch line 19 '. The other function of the embodiment according to FIG. 2 corresponds completely to that according to FIG. 1.

Due to the very hot, for example, more than 800 ° C, emerging from the predrying combustion chamber 41 hot gas partial flow, a hot gas mixture is formed in the further mixing chamber 21 together with the residual gas flow 38 via the return line 38 and a fresh air flow supplied via an optional fresh air line 23 , which is fed to the pre-dryer 25 via the further hot gas pipeline 24 .

The invention ensures that the main dryer unit working with relatively high temperatures and relatively long dwell times is practically emission-free, the technologically compliant mass balance to be complied with by branching within the gas line 15 . At the same time, the pre-dryer unit connected to the main dryer unit according to the invention and which operates with relatively short dwell times achieves a high level of economy of a system designed according to the invention.

Reference list

1

Pre-dryer unit

2

Main dryer unit

3rd

Combustion chamber

4

Hot gas pipeline

4

'' Section of the hot gas pipeline on the combustion chamber side

4

"Section of the hot gas pipeline on the dryer side

5

Main dryer

6

first entrance of the mixing chamber

7

Mixing chamber

8th

Output of the mixing chamber

9

Task unit

10th

Exhaust pipe

11

Particle separation unit

12th

Discharge line

13

Discharge line

14

output

15

Gas duct

16

Conveyor blower

17th

Branch line

17th

'Branch line

18th

second entrance of the mixing chamber

19th

further branch line

19th

'' further branch line

20th

first entrance of the further mixing chamber

21

another mixing chamber

22

second entrance of the further mixing chamber

23

Fresh air line

24th

further hot gas pipeline

25th

Pre-dryer

26

Task unit

27

Exhaust pipe

28

Particle separation unit

29

Discharge line

30th

Transport line

31

output

32

Gas duct

33

Conveyor blower

34

Pollutant separation unit

35

output

36

Exhaust pipe

37

output

38

Return line

39

third entrance of the further mixing chamber

40

entrance

41

Predrying combustion chamber

42

output

Claims (27)

1. A method for the direct drying of particles, such as wood chips, wood fibers or the like, in which hot gases are generated in a combustion chamber, which are supplied as a hot gas stream to a dryer, the particles are also introduced into the dryer and in the dryer by the direct Contact with the hot gases are dried, the dried particles are removed from the dryer in an exhaust gas stream and then separated from the exhaust gas stream, and the remaining exhaust gas stream contaminated with fine dust and odorous substances is at least partially introduced into the combustion chamber, characterized in that a partial stream the exhaust gas flow is divided into the combustion chamber before the introduction of the remaining exhaust gas flow and that this partial flow past the combustion chamber leads back to the dryer. 2. The method according to claim 1, characterized, that the partial flow with that emerging from the combustion chamber Hot gas stream is mixed before entering the dryer. 3. The method according to claim 1 or 2, characterized, that except for the partial stream of the mixed with the hot gas stream Exhaust gas flow is the total remaining exhaust gas flow into the combustion chamber is initiated.   4. The method according to claim 1, 2 or 3, characterized, that the main drying of the particles takes place in the dryer and that of the emerging from the combustion chamber is still not mixed hot gas stream divided a hot gas stream and for one direct predrying of the particles is used. 5. The method according to claim 1, characterized, that the main drying of the particles takes place in the dryer and that the partial flow as a hot gas partial flow for a direct pre Drying of the particles is used before ultimately at least is partially returned to the dryer. 6. The method according to claim 5, characterized, that to generate the hot gas partial flow of the exhaust gas flow branched partial flow fed to a predrying combustion chamber becomes. 7. The method according to any one of claims 4 to 6, characterized, that predrying at a lower or a higher Temperature than the main drying or at one of the main drying appropriate temperature takes place.   8. The method according to any one of claims 4 to 7, characterized, that the predrying of the particles takes less than their main drying. 9. The method according to any one of claims 4 to 8, characterized, that for pre-drying the particles this and the hot gas partial flow a pre-dryer, the pre-dried particles abge in a pre-drying exhaust gas stream from the pre-dryer leads and then ge from the predrying exhaust gas stream are separated, the remaining in the predrying exhaust gas stream Residues are separated from this and the cleaned before drying exhaust gas flow is mixed with the hot gas partial flow. 10. The method according to any one of claims 4 to 9, characterized, that the cleaned predrying exhaust gas flow via an exhaust pipe is dissipated. 11. The method according to any one of claims 4 to 10, characterized, that the residues contained in the predrying exhaust gas stream in a particle separator, in particular designed as a vortex tube be separated.   12. The method according to any one of claims 4 to 11, characterized, that the pre-dried particles are fed to the main dryer become. 13. The method according to any one of claims 4 to 12, characterized, that by mixing the hot gas partial flow with the purified Predrying exhaust gas flow and possibly also with fresh air the temperature of the mixed gas stream fed to the pre-dryer at about 250 to 500 ° C, especially at about 300 to 350 ° C is posed. 14. The method according to any one of the preceding claims, characterized, that the hot gas in the combustion chamber to more than about 750 ° C, ins particular more than about 800 ° C is heated, so that the burning chamber with the partial exhaust gas supplied fine dust and the Ge fragrance substances are completely burned. 15. The method according to any one of the preceding claims, characterized, that the particles in a cyclone from the exhaust gas stream and / or the pre-drying exhaust gas flow.   16. Device for direct drying of particles, such as wood chips, wood fibers or the like, with a combustion chamber ( 3 ) for generating hot gases, one connected to the combustion chamber ( 3 ) via a hot gas pipe ( 4 ), on the input side with a feed unit ( 9 ) for the particle provided dryer ( 5 ), the dryer ( 5 ) downstream separation unit ( 11 ) for separating the dried particles from a particulate matter and Ge polluted exhaust gas flow, and one the exhaust gas flow from the separation unit ( 11 ) to the combustion chamber ( 3 ) leading gas line ( 15 ), in particular for performing the method according to one of the preceding claims, characterized in that a branch line ( 17 , 17 ') branches off from the gas line ( 15 ), via which a partial flow of the exhaust gas stream at the combustor mer ( 3 ) over to the dryer ( 5 ) is returned. 17. The apparatus according to claim 16, characterized in that a combustion chamber-side section ( 4 ') of the hot gas pipe ( 4 ) from the combustion chamber ( 3 ) to a first inlet ( 6 ) of a mixing chamber ( 7 ) that an outlet ( 8 ) the mixing chamber ( 7 ) is connected to the dryer ( 5 ) via a section ( 4 ") of the hot gas pipe ( 4 ) on the dryer side, and that the branch pipe ( 17 ) is connected to a second inlet ( 18 ) of the mixing chamber ( 7 ). 18. The apparatus according to claim 16 or 17, characterized in that on the combustion chamber side section ( 4 ') of the hot gas pipe line ( 4 ) a further branch line ( 19 ) is provided, which is connected as a hot gas supply to a predrying unit ( 1 ). 19. The apparatus according to claim 16, characterized in that the branch line ( 17 ') is connected to the input ( 40 ) of a pre-drying combustion chamber ( 41 ) and that the output ( 42 ) of the predrying combustion chamber ( 41 ) via a further Branch line ( 19 ') is connected to a predrying unit ( 1 ). 20. Device according to one of claims 18 or 19, characterized in that the further or the further branch line ( 19 , 19 ') is connected to a further mixing chamber ( 21 ), the output side via a further hot gas pipe ( 24 ) with an input of a Pre-dryer ( 25 ) of the pre-drying unit ( 1 ) is connected, and that a further input ( 39 ) of the further mixing chamber ( 21 ) with an exhaust gas of the pre-dryer ( 25 ) leading further Umgaslei device ( 32 , 38 ) is connected. 21. The apparatus according to claim 20, characterized in that the pre-dryer ( 25 ) is provided on the input side with a device ( 26 unit ) for the particles. 22. Device according to one of claims 20 or 21, characterized in that in the further gas line ( 32 ) a further Abscheideein unit ( 28 ) is provided for separating the pre-dried particles from the exhaust gases contaminated with residues. 23. The apparatus according to claim 22, characterized in that the further separation unit ( 28 ) with the feed unit ( 9 ) of the dryer ( 5 ) via a transport line ( 30 ) for transporting the pre-dried particles is connected. 24. The method according to claim 22 or 23, characterized in that the further separating unit ( 28 ) is followed by a third separating unit ( 34 ) for separating the residues from the Abga sen of the pre-dryer ( 25 ) and that the third separating unit ( 34 ) is connected to the further inlet ( 39 ) of the further mixing chamber ( 21 ). 25. Device according to one of claims 16 to 24, characterized in that at least some of the separating units ( 11 , 28 , 34 ) are each designed as a cyclone or as a vortex tube. 26. The apparatus according to claim 24, characterized in that at least the third separation unit ( 34 ) is formed as a vortex tube. 27. The device according to one of claims 14 to 26, characterized in that the gas line ( 15 ) or the gas lines ( 32 , 38 ) are provided with egg nem or more delivery fans ( 16 , 33 ).