Method for continuously drying bulk goods, in particular wood fibers and/or wood chips

Abstract

A method for drying bulk goods, in particular wood fibers and/or wood chips, wherein the bulk goods is continuously dried in a dryer (1), in particular a drum dryer. The vapor-gas mixture flows through the drum dryer (1) in a dryer circuit and is indirectly heated via at least one heat exchanger (4) by a burner waste gas that is heated in at least one burner (5). The drying vapors are supplied to the at least one heat exchanger (4). Upstream, downstream and/or within the at least one heat exchanger (4), at least a partial flow of the drying vapors are branched off to be conducted into the burner (5). The remaining partial flow is conducted to the dryer (1) again. The partial flow of drying vapors to the burner (5) is driven by at least one regulable partial vapor fan (10).

Claims

1. Method for continuously drying bulk goods in a dryer, which is supplied with bulk goods and through which a vapor gas mixture passes in a drying circuit, the method comprising: indirectly heating the vapor gas mixture via at least one heat exchanger by a burner exhaust gas, wherein the drying vapors are guided and heated up in the at least one heat exchanger; branching off upstream, downstream and/or within the at least one heat exchanger at least a partial flow of the drying vapors to be conducted into the burner wherein the partial flow to the burner is driven by at least one regulable partial vapor fan, which is regulated via the pollution level of the burner exhaust gases and which regulable partial vapor fan increases the flow volume and flow rate of the partial flow of the drying vapors to the burner, if the moisture content in the drying vapors rises; and supplying cooling air in the burner via an inner nozzle ring and an outer nozzle ring provided in the ceiling of the combustion chamber; wherein the inner nozzle ring and the outer nozzle ring are controlled separately from each other.

2. A method according to claim 1, wherein the pollution level of the burner exhaust gases are nitrogen oxides and/or carbon monoxides.

3. A method according to claim 1, wherein the burner exhaust gas is cleaned by at least one filter.

4. A method according to claim 3, wherein the filter is operated in suction mode.

5. A method according to claim 3, wherein the filter is an electrostatic precipitator.

6. A method according to claim 1, wherein, at least partially, solids are used as fuel for the burner.

7. A method according to claim 1, wherein the drying vapors are cleaned after passing through the dryer.

8. A method according to claim 7, wherein as cleaning apparatus at least one cyclone is used.

9. A method according to claim 1, wherein the drying vapors after the dryer are driven by at least one drying vapor fan.

10. A method according to claim 1, wherein the water content in the dryer is regulated, whereby the bulk goods are metered depending on the moisture of different bulk good fractions when supplying the dryer.

11. A method according to claim 1, wherein the burner is supplied with at least one further exhaust gas as combustion air and/or cooling air.

12. A method according to claim 11, wherein the additional exhaust gas is preheated before it is supplied as combustion air.

13. A method according to claim 1, wherein the inner and the outer nozzle ring have an entering angle between approximately 0 and approximately 60 degrees.

14. A method according to claim 13, wherein the angle is adjustable depending on the fuel used.

15. The method of claim 1, wherein: the supplied cooling air in the burner is branched off from the drying vapors and driven via the regulable partial vapor fan; and an air flow of the supplied cooling air is supplemented by an additional air supply.

16. A method for the manufacturing of wooden material boards, wherein wood logs are stripped of bark and are processed in a crushing apparatus to wood chips and/or fibers, wherein the wood chips and/or fibers are dried in a drying apparatus, wherein the dried wood chips and/or fibers are processed to boards in a pressing arrangement, if necessary by adding binders and/or further additives, and are preferably cut into size, wherein for drying of the wood chips and/or fibers a method according to claim 1 is carried out.

17. Arrangement for drying of bulk goods, comprising: a dryer, at least one burner comprising a combustion chamber ceiling with an inner nozzle ring and an outer nozzle ring that are separately controllable, at least one heat exchanger provided to indirectly heat a vapor gas mixture for drying the bulk goods in the dryer, at least one branch line, upstream, downstream and/or within the at least one heat exchanger to the burner to branch off a partial flow of the drying vapors, and at least one line for the remaining partial flow to the dryer, wherein the branch line to the burner at least one regulable partial vapor fan is provided, wherein the partial flow to the burner is driven by the at least one regulable partial vapor fan, which is regulated via the pollution level of the burner exhaust gases and which regulable partial vapor fan is configured to increase the flow volume and flow rate of the partial flow of the drying vapors to the burner, if the moisture content in the drying vapors rises.

18. An apparatus according to claim 17, wherein the pollution level is nitrogen oxide and/or carbon monoxide.

19. An apparatus according to claim 17, wherein for the cleaning of burner exhaust gases at least one filter is provided.

20. An apparatus according to claim 19, wherein a burner exhaust gas fan is positioned downstream of the filter.

21. An apparatus according to claim 19, wherein the filter is an electrostatic precipitator.

22. An apparatus according to claim 17, wherein for cleaning of the drying vapors a cleaning arrangement is provided.

23. An apparatus according to claim 22, wherein the cleaning arrangement is at least one cyclone.

24. An apparatus according to claim 17, wherein downstream of the dryer at least one drying vapor fan is provided.

25. An apparatus according to claim 17, wherein to regulate the water content in the dryer, a metering device is provided.

26. An apparatus according to claim 17, wherein at least one supply line for additional exhaust gases as combustion air into the burner is provided.

27. An apparatus according to claim 26, wherein heat exchanger, are provided for a preheating of the additional exhaust gases before the same are supplied to the burner.

28. An apparatus according to claim 17, wherein the inner and outer nozzle ring comprises an entering angle of approximately 0 degrees to approximately 60 degrees.

29. The arrangement of claim 17, wherein: cooling air is supplied in the burner via the inner nozzle ring and the outer nozzle ring; the supplied cooling air in the burner is branched off from the drying vapors and driven via the regulable partial vapor fan; and an air flow of the supplied cooling air is supplemented by an additional air supply.

30. An arrangement for the manufacturing of wooden material boards with at least one crushing device, at least one drying device and at least one pressing device, wherein a drying arrangement according to the apparatus of claim 17 is provided.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 shows a schematic illustration of a process picture for an apparatus, which is suitable for a preferred embodiment of the inventive method;

(3) FIG. 2 shows a schematic illustration of a process picture for an apparatus to realize a preferred embodiment of the inventive method with extension in the air circuitry; and

(4) FIG. 3 shows a schematic illustration of a process picture for an apparatus to put one preferred embodiment of the inventive method with an integrated boiler arrangement into practice.

DETAILED DESCRIPTION

(5) The process picture shown in FIG. 1 of an apparatus to put the inventive method into practice comprises a drum dryer 1, a removal housing 2, a cleaning apparatus 3, heat-exchanger 4, a combustion chamber 5, filter 6 as well as a chimney 7. A drying vapor fan 8 is arranged between the drum dryer 1 and the cleaning apparatus 3, a burner exhaust fan 9 is arranged between filter 6 and chimney 7 and between heat-exchanger 4 and combustion chamber 5 a regulable partial vapor fan 10 is arranged.

(6) Dryer 1 may be provided with a slow-down zone 11 and a metering device 12.

(7) The drum dryer 1 is supplied with bulk goods, as for example with wooden chips and/or wooden fibers. The drying gases, which are supplied to the drum dryer 1 are heated-up via the heat exchanger 4 and have temperatures in the range of approximately 250 C. up to approximately 600 C. The heating of the drying gases in the heat-exchangers 4 is achieved in cross counter flow by means of exhaust gases from the combustion chamber 5. The exhaust gases have temperatures in the range of approximately 750 C. up to approximately 900 C. Inside of the combustion chamber 5 temperatures of approximately 750 C. up to 1050 C. are achieved, wherein as fuel for example natural gas, oil and/or wood dust or other waste materials from the production of wooden material boards may be used. The different fuels may be used alone or in any combination with each other.

(8) After the drying goods have passed the drum dryer one slow-down zone 11 may be provided for the drying goods and/or a removal housing 2 to remove the dried bulk goods. The drying gases respectively the drying vapors are driven via the drying vapor fan 8 to one or more cleaning apparatuses 3, preferably cyclone separators. Alternatively or additionally a drying vapor fan may be arranged between the cleaning device 3 and the heat exchanger 4. In the cleaning device 3, fine dust and other particles are separated. The separated material may than advantageously be passed to the production. After the drying vapors have passed the cleaning device 3, they are guided to one or more heat-exchangers 4. Two parallel operating heat-exchangers are preferred. Inside of the heat-exchanger 4 the drying vapors are heated from approximately 110 C. to 130 C. up to 250 C. to approximately 600 C. This is done in a cross counter flow operation by means of the exhaust gases of the burner from the combustion chamber 5. Inside of the heat-exchanger 4 a part of the vapor is separated and led to the combustion chamber 5 as combustion air and/or cooling air. This part of the vapor is driven by the regulable partial vapor fan 10. The exhaust gas of the burner, which serves to heat-up the drying gases in heat-exchanger 4, is guidedafter passing through the heat-exchanger 4to a filter 6. This is in particular an electrostatic precipitator, preferably a dry type electrostatic precipitator. The filter 6 is preferably operated in a suction operation, whereby after the filter 6 a fan 9 for the exhaust gas of the burner is provided. The thus cleaned exhaust gas of the burner is released via chimney 7 into the environment.

(9) According to the invention, the drying of the wood chips is done in a dedicated vapor circuit. Thereby a high vapor content can advantageously be achieved and thus a gentle drying can be realized, which has a positive effect to the quality of the drying goods. Further, thereby the pollution and thus the wear of the drying circuit can be kept to a minimum. Also the fire protection can be improved due to the indirect heating of the dryer and the dedicated drying circuit.

(10) The regulation (i.e. control) of the regulable partial vapor fan 10 is done in a preferred embodiment via the pollution level of the exhaust gases of the burner, as for example by means of the concentration of nitrogen oxides and/or the concentration values of carbon monoxide. Further, the regulable partial vapor fan may be controlled via a maximum inert gas content in the drying circuit or via the oxygen contend in the exhaust gas of the burner.

(11) In a preferred embodiment, the supply of the drum dryer 1 with bulk goods is done while controlling the water content in the dryer by means of the metering device 12, whereby the bulk goods are metered depending on the moisture of different bulk good fractions upon supply to the drum dryer 1.

(12) Preferably different exhaust gases from the manufacturing of the wooden material boards are used as combustion air for the burner, as for example exhaust gases from the press arrangements, exhaust gases from the sawing arrangements and/or exhaust gases from the boiler. The different exhaust gases are preferably pre-heated before they are supplied as combustion air, in particular by means of heat-exchangers.

(13) FIG. 2 shows a process picture of an inventive apparatus for the continuously drying of bulk goods, wherein different possibilities of air flow are shown. The different elements of the apparatus have the same reference number as in FIG. 1. The drying vapor fan 8 is arranged between the cleaning apparatus 3 and the heat-exchangers 4. This arrangement can be provided alternatively or in addition to the arrangement of the drying vapor fan 8 between a dryer 1 and cleaning apparatus 3. The cooling air is led to the burner 5 via two rings arranged in the ceiling of the combustion chamber. This cooling air is branched off from the drying vapors inside of heating exchanger 4 and driven via the regulable partial vapor fan 10. This air flow may be supplemented or replaced by an additional air supply 13. Further, this air flow may be supplemented by separating a part of the heated drying gases after the heat-exchanger 4. These switchable air flows are shown by dashed lines in FIG. 2. The exhaust gases of the burner which leave the burner 5 can be provided before they are passed to the heat-exchangers 4 with additional exhaust gases of the burner, which already passed through the heat-exchanger 4, and in particular with exhaust gases of the burner, which already have passed through the filter 6. These exhaust gases of the burner may alternatively or in addition be provided as cooling air for the muffle and/or combustion air for the combustion chamber 5. Fans 14 and 15 are preferably provided to drive these exhaust gases of the burner.

(14) The combustion air for burner 5 can preferably be taken from different sources. For example, one can use exhaust gases from the press air 16 and/or exhaust gas from the sawing arrangements 17. This exhaust gas is driven via a further fan 18 and provided to the combustion chamber 5 as combustion air. Preferably, this combustion air is pre-heated before it is passed to the combustion chamber 5, in particular via a heat-exchanger 19, which is heated from boiler exhaust gas 20. Preferably, this boiler exhaust gas is passed after being led through heat-exchanger 19 to filter 6 and released via chimney 7 to the environment.

(15) FIG. 3 shows a further embodiment of an apparatus for the inventive method with an integrated boiler arrangement and with different air flows. The different elements of this apparatus are provided with the same reference numbers as in FIG. 1. The apparatus comprises a dryer 1, a removal housing 2, a cleaning apparatus 3 in form of two cyclone separators and a heat-exchanger 4 in the actual drying circuit. The heat-exchanger 4 is supplied with exhaust gases of the burner from burner 5. Inside of the heat-exchanger 4 a partial flow of the drying vapors is branched off. This partial flow is driven via the regulable partial vapor fan 10 and led to the burner 5 as cooling air. The cooling air supply is done via inner and outer nozzle rings 13 being arranged in the ceiling of the combustion chamber of burner 5.

(16) Muffle 21 of burner 5 is cooled by supply of cooling air. This cooling air is driven via fan 15. The supply of this cooling air respectively the cooling of muffle 21 can be achieved by different lines. For example, the cooling of the muffle may be done with fresh air 25. Alternatively or in addition to this a supply of a part of vapors 22, a supply with exhaust gas of the burner after heat-exchanger 23, or a supply with an exhaust gas after the electrical precipitator 24, can be arranged. The supply of these different air flows can be done by correspondingly provided valves. The combustion air for burner 5 is driven by fan 18. As combustion air one may use exhaust air from press 16 respectively from the saw 17 and/or other kind of exhaust gases 27 can be used. These exhaust gases are heated via a heat-exchanger 19 in particular with an air-to-air heat-exchanger.

(17) The supply as combustion air is controlled via a heating pot 26. The heat-exchanger 19 is fed with exhaust gases from the boiler, which result from the boiler arrangement 28. In order to control the temperature of the exhaust gases from the boiler being directed to heat-exchanger 19, an additional heat-exchanger 29 may be provided, in particular a thermo oil heat-exchanger. The pre-heated combustion air may be guided by a corresponding switching arrangement inside of the heating pot 26 to the burner 5, to the boiler arrangement 28 and/or the chimney 7.