EP2202474A1 - Drying system for products of wood disintegration - Google Patents

Abstract

The system (10) has a combined radiation- and convection part (24) is arranged between a combustion boiler (12) and a dryer. The radiation- and convection part is formed such that flow velocity of exhaust gas (20) lies above 22 m/second in a radial inner rising channel (26) and below 19 m/second in a downstream channel (32) to make the radiation- and convection part to work as an ash separator. The radiation-and convection part is provided with an automatic ash drain. The downstream channel radially surrounds the rising channel. An independent claim is also included for a method for drying wood disintegration products.

Description

The invention relates to a wood crushing product drying plant, in particular for wood chips, wood chips or wood fibers, with a combustion boiler comprising a furnace for burning Holz- andloder wood materials and an additional firing, a flue gas line for conducting the resulting during combustion flue gases and a dryer for the wood crushing products , which is fed by the flue gas line. According to a second aspect, the invention relates to a method for drying wood chipping products, in particular wood chips, wood shavings and / or wood fibers.

Wood shredder drying equipment is used to dry wood shredded products prior to further processing. For this purpose, material is burned in the combustion vessel, which is obtained in the production of wood-based panels as waste, such as bark, wood fibers or residual waste. Optionally, the flue gas temperature is further increased via the additional firing, which is, for example, a gas firing.

Since the resulting flue gases for the dryer are usually too hot, it is known to cool the flue gases through heat exchangers in which thermal oil flows. This also has the advantage that the heated thermal oil can be used as an energy source in production processes, for example when pressing wood-based panels.

A disadvantage of known Holzzerkleinerungsprodukt-Trocknungsaniagen is that ash constituents of the flue gas can be deposited in the heat exchangers. This results in a high maintenance, the downtime of the plant after pulls that reduce the effectiveness of the plant. In the worst case, the deposits are so strong that an accident can occur as a result of which thermal oil can escape and ignite. This can even lead to the destruction of the solid fuel firing.

The invention has for its object to provide a wood crushing product drying plant, with a continuous operation in combustion, among other things of wood fibers with high moisture content with reduced maintenance is certainly possible.

The invention solves the problem by a generic wood crushing product drying plant, in which a combined radiating and convection part, through which thermal oil flows, for heating the thermal oil is arranged between the combustion boiler and the dryer.

According to a second aspect, the invention solves the problem by a method for drying wood chipping products, comprising the steps of (a) burning wood and / or wood materials, optionally with additional firing, in a combustion vessel to produce flue gas, (b) passing the Flue gas in a combined radiation and convection section first upwards and then downwards, whereby the flue gas cools and a thermal oil is heated, and then from top to bottom through a convection part, so that the flue gas is further cooled and heated thermal oil, and ( c) then passing the flue gas into a dryer for the wood chipping products.

An advantage of the invention is that existing equipment can be easily retrofitted. Existing wood shredder drying systems often have a combustion boiler that is poorly modifiable. By the downstream, combined radiation and convection part of the old combustion boiler can continue to be used and it also achieves a high level of operational safety.

It is also advantageous that the combined radiation and convection part makes it possible to lower the flow velocity of the flue gas so far that a large proportion of the ash constituents fails. The combined radiation and convection part thus acts at least partially as an ash separator, so that in a possibly downstream pure convection part as good as no longer can lead to the formation of deposits, thereby the reliability of the system is significantly increased.

In the context of the present description, a combustion vessel is understood to mean, in particular, any technical device which is set up for burning wood and / or wood-based materials, as well as wood chips, wood chips, barks and / or residual waste. The apparatus for burning wood and / or wood materials may be for example a traveling grate, which is also referred to as a feed grate. Alternatively, the combustion boiler is a fluidized bed boiler in which the wood waste is burned in a fluidized bed. The additional firing may be, for example, a gas firing. Alternatively, it is also possible, for example, to burn mineral oil or other energy sources.

A combined radiation and convection part is understood in particular to mean a component of the drying plant in which the heat transfer between the smoke and the radiation and convection part is neither dominantly due to heat radiation nor dominant to heat conduction. Pure radiation parts and pure convection parts are optimized for their respective task. For example, in radiation parts trying to avoid turbulence of the flue gas in order not to slow down the flue gas unnecessarily. The radiation part is essentially advantageous only in the case of very hot flue gases, since the power transmitted by heat radiation increases in the fourth power with the absolute temperature. In the case of pure convection parts, on the other hand, the most turbulent flow possible is sought, since then the heat transfer coefficient is particularly high. But that leads to losses in the flow velocity. The combined radiation and convection part is thus neither a pure radiation part nor a pure convection part.

According to a preferred embodiment, the at least one combined radiation and convection part is designed such that the flue gas initially flows vertically upwards and subsequently vertically downwards. The advantage of this is that the hot flue gas in the section in which it flows vertically upward, can have a high flow velocity, since the heat is released to a large extent via heat radiation to heat exchanger tubes. In the section where the flue gas flows vertically downwards, the flow velocity may be reduced and optionally more turbulent, which may cause ash particles to precipitate. In this section, the flue gas is already moving downwards, so that the deposition of the ash particles is promoted.

The fact that the flue gas initially flows upward and then vertically downward, is thus achieved that ash particles are deposited to a large extent in the combined radiation and Konvektionsteil, which minimizes its pollution and any subsequent pure convection and reduces the probability of failure of the system ,

Particularly preferably, the combined radiation and convection part has a radially inner riser channel and a drop duct radially surrounding the riser duct. This ensures that the flow rate drops sharply when the flue gases pass from the riser channel into the drop channel. If baffles are arranged in the fall channel to swirl the flue gas stream for a better convective heat transfer, the energy losses are therefore lower. Namely, a reduction in the flow velocity means the less energy loss, the lower the overall flow velocity is, because the flow energy depends quadratically on the flow velocity.

It is also advantageous that, as described above, the gravity and the flow velocity in the drainage channel cause the ash particles to fail.

The combined radiation and convection part is particularly compact if the riser channel and the drop channel have a common wall. Particularly preferably, the common wall is at least partially formed by heat exchanger tubes. This is achieved, for example, in that the combined radiation and convection part has a pipe-web-pipe structure at this point. But it is also possible that the heat exchanger tubes are mounted on the common wall.

According to a preferred embodiment, the combined radiation and convection part is designed so that a flow velocity of the flue gas is at least in a possibly existing drop channel below 19 m / sec, for example at about 18 m / sec. It has been shown that such a particularly efficient ash separation with simultaneous high heat transfer between the flue gas and the thermal oil is possible.

Preferably, the flow rate of the flue gas before entry into the combined radiation and convection part is greater than 22 m / sec and is for example 24 m / sec. If the combined radiation and convection part has a riser channel, the flow velocity there may also be above 22 m / sec. The advantage of this is that heat losses between the combustion boiler and the combined radiation and convection are avoided and an ash separation is suppressed before the fall channel by the high flow rate.

It can be provided that a pure radiation part and / or a pure convection part are arranged behind the combined radiation and convection part between the combustion boiler and the combined radiation and convection part. In this way, on the one hand particularly hot thermal oil can be generated, on the other hand, the heat content of the flue gas is utilized particularly efficiently.

It is particularly advantageous when the combined radiation and convection acts as an ash separator and has an automatic ash removal. This is to be understood that in particular more than 85% of the ash leaving the combustion boiler is deposited in the combined radiation and convection part.

The wood shred product drying plant preferably comprises at least two combined radiation and convection parts, which are connected in such a way that their flue gases are brought together before they enter the at least one convection part. In this way, the system can be operated continuously, even if one of the combined radiation and convection parts is serviced.

It is possible, but not necessary, for the combustion boiler, ie the immediate vicinity of the firing point, to be burned in the wood particles to comprise heat exchanger pipes through which thermal oil flows. In particular, it is advantageous in the invention that the combustion boiler does not have to have such heat exchanger tubes. It is thus possible to clean the combustion boiler particularly easy, since it does not have to be taken into account on sensitive heat exchanger tubes.

Known wood crushing product drying plants generally have a mixing chamber in which a portion of the flue gas is removed immediately behind the combustion boiler. This hot gas is passed through multicyclones and sent directly to the dryer to raise the temperature. Disadvantages are the high costs for the mixing chamber, which according to a preferred embodiment of the invention are avoided in that the wood shredder drying plant comprises a controllable branching device which is arranged to remove flue gas from the combined radiation and convection section. This branching device is easy to implement and therefore inexpensive.

Preferably, the branching device is designed to direct the flue gas in a path to the dryer, in which no cooling heat exchanger is arranged. Thus, particularly hot flue gas can be introduced into the dryer. Preferably, in the path in front of the dryer, a flue gas cleaning device is arranged, for example a multi-cyclone,

Preferably, the branching device is arranged so that it takes the flue gas in the flow direction behind the riser channel and in particular before the drop channel. Alternatively it can be provided that the branching device is arranged to remove the flue gas behind the combined radiation and convection part.

In a method according to the invention, it is preferably provided that air is added to the flue gas behind the combined radiation and convection part and that the resulting dry gas mixture is subsequently passed into the dryer. But it is not necessary that the air is mixed directly behind the combined radiation and convection part. If a pure convection section is still connected downstream, air is preferably mixed in behind it. This makes it possible to control the total amount of dry gas required, simply and independently of the combustion vessel.

According to a preferred embodiment, the flue gas temperature of the flue gas when entering the combined radiation and convection part is above 850 ° C. At the outlet from the combined radiation and convection part, the exhaust gas temperature is below about 600 ° C in particular. In this way it is achieved that a particularly large amount of energy is taken from the flue gas. In addition, the flue gases remain for a certain time in the combined radiation and convection part, whereby the ash deposition is promoted.

Figur 1

eine Schemazeichnung einer erfindungsgemäßen Holzzerkleinerungsprodukt-Trocknungsanlage von der Seite,

Figur 2

die Holzzerkleinerungsprodukt-Trocknungsanlage gemäß Figur 1 in einem Schnitt von oben,

Figur 3

eine detaillierte Zeichnung der Trocknungsanlage gemäß den Figuren 1 und 2 von der Seite und

Figur 4

die Trocknungsanlage gemäß Figur 3 in einer Ansicht von oben.

In the following the invention will be explained in more detail with reference to the accompanying drawings. It shows

FIG. 1

a schematic drawing of a Holzzerkleinerungsprodukt-drying plant according to the invention from the side,

FIG. 2

the wood shredder drying plant according to FIG. 1 in a section from above,

FIG. 3

a detailed drawing of the drying plant according to the FIGS. 1 and 2 from the side and

FIG. 4

the drying plant according to FIG. 3 in a view from above.

FIG. 1 shows a wood crushing product drying plant 10 according to the invention, which is referred to below as a drying plant. The drying plant 10 comprises a combustion boiler 12 with a device for burning wood waste in the form of a traveling grate 14, a supplementary firing 16, which is operated with gas, and a supply line 18 to a only in FIG. 4 marked dryer for wood shredded products. The drying plant 10 is for example part of a production plant for wood-based panels.

The combustion boiler 12 is designed for a thermal output of 42 megawatts and a combustion temperature of more than 850 ° C, in the present case 950 ° C. Emerging flue gas 20 is, as indicated by the arrow P1, passed through a flue gas duct 22 in a combined radiation and convection 24.

The flue gas 20 enters the bottom of the radiation and convection part 24 and flows in a radially inner riser channel 26 upwards. The riser 26 is bounded by heat exchanger tubes 28 radially outward. In a header 30 changes the flue gas 20 its flow direction and flows in a fall channel 32 vertically downward, as indicated by the arrows P2. The drop channel 32 surrounds the riser channel 26 radially.

The riser 26 has a riser channel cross-sectional area A ₂₆ which is smaller than a drop channel cross-sectional area A ₃₂ . This reduces a flow velocity V ₂₆ in the riser channel 26, which is about 24 m / sec, to a flow velocity v ₃₂ of about 18 m / sec. Due to the different flow velocities v ₂₆ and v ₃₂ prevails in the riser 26, the heat transfer by heat radiation, in the case channel 32, however, outweighs the heat transfer by convection.

The flue gas 20, which comes from the combustion boiler 12, leads a variety of ash particles 34.1, 34.2, ... with. Between the combustion chamber 12 and the drop channel 32, the flow velocity v of the flue gas is always greater than 22 m / sec, which ensures that the ash particles 34 hardly deposit on inner sides of the flue gas duct 22. In the case channel 32 of the combined radiation and convection part 24, however, the flow velocity v ₃₂ is so low that the ash particles settle to the bottom, as indicated by the ash particles 34.4 and 34.5, whereupon they are drawn off via an automatic ash removal not shown.

The now ash-poor flue gas 20 passes through a second supply line 36 in downstream pure convection parts 38.1, 38.2, in which further heat exchanger tubes 40 are provided and the flue gas 20 to cool further. The flue gas 20 leaves the convection part through a discharge line 42, as the arrows P3 show.

FIG. 2 shows a section through the drying plant 10 according to FIG. 1 in the plane BB. Vice versa FIG. 1 a section along the line AA according to FIG. 2 , It can be seen that the flue gas 20, as indicated by the arrows P1, in Brennkessel 12 flows upwards.

In FIG. 2 can also be seen that the flue gas 20 initially enters a pure radiation part 44 and flows there from top to bottom. The radiation part 44 is likewise lined with heat exchanger tubes, in which, as with all other heat exchangers, a thermal oil flows and absorbs heat of the flue gas.

The flue gas flows out of the radiation part 44 into a first radiation and convection part 24 FIG. 1 is shown, and a second radiation and convection 24.2. Subsequently, the flue gas flows through four pure convection parts 38.1, 38.2, 38.3 and 38.4. In this case, it can be provided that the two pure convection parts 38.1, 38.2 are exposed to flue gas from the radiation and convection part 24.1, whereas the convection parts 38.3 and 38.4 are exposed to flue gas from the radiation and convection part 24.2. Hereinafter, the reference numeral 38 designates the convection parts as such.

FIG. 3 shows the drying plant 10 with the combustion boiler 12, the supply line 18 and the radiation and convection part 24.1, which has an ash discharge 46. There is provided a branching device 47, which is arranged so that the flue gas 20 can get into a branch line 50. The closer function will be described below.

FIG. 4 shows a view from above of a detail of the drying plant 10 according to FIG. 3 with the radiation part 44, the combined radiation and convection parts 24.1. and 24. 2 and the convection parts 38, can also be seen the riser 26.1 of the radiation and Konvektionsteils 24.1 and the riser 26.2 of the radiation and Konvektionsteils 24.2. These components form a flue gas cooling 48 of the drying plant.

Flue gas 20 flowing out of the discharge line 42 flows into a schematically depicted dryer 49 in which wood comminution products, for example wood chips, be dried. The circulating in the heat exchanger tubes thermal oil is passed to not marked presses to drive them and cooled back to flow back into the heat exchanger.

The branching device 47 comprises a first flap 52.1 and a second flap 52.2. The first flap 52.1 is connected to the radiation and convection part 24.1 such that the flue gas 20 is partially withdrawn from the riser channel 26.1 before it enters the fall channel 32.1. The second flap 52.2 is correspondingly connected to the radiation and convection part 24.2. The flaps 52 are designed so that the amount of extracted flue gas is adjustable.

The flue gas 20 is passed by means of the branch line 50 directly to a not shown mixing device, where it is mixed with flue gas, which has previously flowed through at least one of the convection parts 38. Based on the mixing ratio, a temperature of the mixed gas is controlled, which then enters the dryer 49.

LIST OF REFERENCE NUMBERS

10

drying plant

12

burning boiler

14

traveling grate

16

supplementary firing

18

supply

20

flue gas

22

Flue gas line

24

Radiation and convection part

26

rising channel

28

heat exchanger tube

30

head area

32

channel case

34

ash particles

36

second supply line

38

convection

40

heat exchanger tube

42

derivation

44

radiation part

46

ash removal

47

branching device

48

Flue gas cooling

49

dryer

50

branch line

52

flap

A ₂₆

Rising channel cross-sectional area

A ₃₂

Case channel cross-sectional area

v ₂₆

Flow velocity in the riser

v ₃₂

Flow velocity in the fall channel

Claims (15)

Wood shredder product drying plant, in particular for wood chips, wood chips or wood fibers, with (a) a combustion vessel (12), the (I) a device (14) for burning wood waste and (ii) an additional firing (16), (b) a flue gas duct (22) for directing the flue gases (20) produced during combustion and (c) a dryer (49) for the wood chippings fed by the flue gas duct (22),
characterized in that (D) between the combustion boiler (12) and the dryer (49) is arranged a thermal fluid flowed through combined radiant and convection part (24) for heating the thermal oil. Wood shredded product drying plant according to claim 1, characterized in that the at least one combined radiation and convection part (24) is formed so that the flue gas (20) initially flows vertically upwards and subsequently vertically downwards. Wood shredded product drying plant according to claim 2, characterized in that the combined radiation and convection part (24) - A radially inner riser channel (26) and - Has a the riser channel (26) radially surrounding drop channel (32). Wood shredder-drying plant according to claim 3, characterized in that the riser channel (26) and the drop channel (32) have a common wall. Wood shredded product drying plant according to claim 4, characterized in that the common wall is at least partially formed by heat exchanger tubes (28, 40). Wood shredder-drying plant according to one of the preceding claims, characterized in that the combined radiation and convection part (24) is formed so that a flow velocity (v) of the flue gas (20) is less than 19 m / s. Wood shred product drying plant according to one of the preceding claims, characterized in that the flow velocity (v) of the flue gas (20) before entry into the combined radiation and convection part (24) is above 22 mls. Wood shredded product drying plant, according to one of the preceding claims, characterized in that - Between the combustion chamber (12) and the combined radiation and convection (24) a radiation part (44) and - Behind the combined radiation and convection (24) a convection part (38) is arranged. Holzzerkieinerungsprodukt-drying plant, according to any one of the preceding claims, characterized in that the combined radiation and convection (24) acts as an ash separator and has an automatic ash removal. Wood shredded product drying plant according to one of claims 8 or 9, characterized by at least two combined radiation and convection parts (24), which are connected so that their flue gases (20) are merged before entering the at least one convection part (38). A wood shredder drying system according to any one of claims 3 to 10, characterized by a controllable branching device (47) arranged to extract a portion of the flue gas (20) from the combined radiant and convection section (24). A wood shredder-drying plant according to claim 11, characterized in that the branching device (47) is adapted to guide the flue gas (20) in a path to the drier (49), wherein in the path no heat exchanger is arranged. Wood shredder-drying plant according to claim 11 or 12, characterized in that the branching device is arranged to remove the flue gas in the flow direction behind the riser channel (26) and in particular in front of the drop channel (32). A wood shred product drying plant according to any one of claims 11 to 13, characterized by a controller adapted to control a temperature in the drier (49) at least also by means of a flow of flue gas (20) through the branching device (47). Process for drying wood shredded products, in particular wood chips, wood shavings and / or wood fibers, comprising the steps of: (a) burning wood waste, possibly with additional firing (16), in a fuel tank (12) to produce flue gas (20), (b) passing the flue gas (i) in a combined radiation and convection section (24) first upwards and then downwards, whereby the flue gas (20) cools down and a thermal oil is heated, and (ii) subsequently through a convection part so that the flue gas (20) continues to cool and the thermal oil is heated, and (c) then passing the flue gas (20) into a dryer (49) for the wood shredded products.

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