Verfahren und Vorrichtung zur Reinigung eines Abgasstromes

The invention relates to a method for cleaning a resulting in the processing of wood materials, such as organic carbon compounds with pollutants laden exhaust gas stream, wherein the exhaust stream is brought into contact with a liquid absorbent in an absorption zone, wherein the pollutants are absorbed in the liquid absorbent.

Furthermore, , the invention relates to a device for cleaning a resulting in the processing of wood materials, such as organic carbon compounds with pollutants laden exhaust gas flow, for absorption of pollutants contained in the exhaust gas stream with a absorbing means in a liquid absorbent.

For the purposes of this disclosure as a timber processing methods particularly the drying of wood can, the preparation of pellets, the drying of partially glued wood fibers, the pressing of fibers with additives for preparing wood fiber insulating materials or fibre boards, the drying of shavings or the pressing of chips with additives for the production of particle boards, the drying of strands, the pressing of so-called strands with additives for preparing rough chip boards , also called OSB-plates (english: [...] beach board), as well as in the preparation of plywood boards be provided.

For such process, in particular in the simultaneous effect of elevated temperatures, with organic Polluted exhaust air flows, which have to be cleaned prior to the discharge to the ambient air.

To this end it is in the known State of the Art, to provide for a absorption zone, in which the pollutants are discharged from the gaseous phase in an aqueous phase. This operation is referred to as absorption. When used, for example, a spray scrubber State of the Art There will, wherein a scrubbing liquid introduced is loaded with the pollutants. To material exchange to be able to continue, the washing liquid must either continuously or at intervals are regenerated. In the absence of measures for regeneration of the washing liquid would it depending on the process conditions, as circulating water temperature[...] , concentrations of the organic compounds in the exhaust air, after a certain operating time of, for example, 5-30 hours for the individual connections to a saturation, i.e. a maximum concentration, the washing liquid come. Afterwards the Member pollutant could not further from the exhaust stream are deposited, so that the reduction of these pollutants to stall. So State of the Art necessary when it is, the washing liquid continuously or at intervals by biological or chemical condition and partly by fresh water or waste water treatment to replace unloaded process water. [...]unfavorable-proves a high energy requirement, as well as a high water consumption, however is thus taking hand in hand.

The task of the present invention consists, a method and a device for cleaning the exhaust gas streams arising in the wood industry to create, with which or with which the disadvantages of the prior art are remedied or alleviated. The invention is therefore in particular the objective, the exhaust gas streams effectively and with the smallest possible amount of energy in the wood industry to free of pollutants.

To solve this task, the invention relates to a method with the features of claim 1 and a device having the features of claim 17, above. Preferred embodiments of the invention are recited in the dependent claims.

according to invention is at least a partial flow of the liquid absorbent and heated liquid for transporting the pollutants by thermal regeneration of the pollutants is freed.

Advantageously, therefore at the time of removal of the pollutants from the exhaust gas streams State of the Art usual chemical The separation process for wood manufacturing be dispensed with. This the energy requirement for the cleaning of exhaust gases can be substantially reduced. Also no chemicals are required.

One specially the consumption of liquid absorbent be considerably reduced. For the purposes of this disclosure means the thermal regeneration compared for absorbing higher temperatures in each executed separation process, with which the proportion of pollutants in the exhaust gas streams is reduced.

In accordance with a particularly preferred embodiment the partial flow is guided by a said liquid absorbent for the thermal regeneration with a reduced pressure distillation zone which is acted upon. In this design is therefore a partial flow of the liquid absorbent is branched off after the absorption, and thereafter the heated distillation zone, in which a vacuum is produced. This pollutants are converted into the gaseous phase from the liquid absorbent, wherein a concentrate is withdrawn from the distillation zone of pollutants. This concentrate can be comparatively easily processed advantageously, wherein, for example, a thermal post-combustion can be carried out. This construction is distinguished by a particularly low energy consumption during the thermal regeneration of the liquid absorbent from.

In accordance with a further preferred embodiment of the partial stream is brought in a desorption zone with a stripping gas for the thermal regeneration said liquid absorbent in contact, wherein in the liquid absorbent are delivered to the stripping gas pollutants absorbed by desorption. Advantageously it can either via the multi-step process occurring during wood processing pollutants from waste gas streams are enriched in the stripping gas, which is comparatively simple and inexpensive to clean. As stripping gas is preferably used fresh air, preheated fresh air, but also steam. For Reducing the vapor pressure can be applied in said desorption zone, a reduced pressure.

For achieving a large area it is favorable exchange zone, when the partial flow of the liquid absorbent is introduced into the via a spray scrubber [...] distillation zone.

In the absorption zone for the exhaust gases from the wood processing not only carbon compounds are received, but also wood fibres, paraffins and resins deposited. This deposited substances mean that subsequent components, such as heat exchanger or internals in the wood fibers are partially or completely within a short time by [...] distillation zone also have to be cleaned and expensive by the maintenance operator clogged. In the period of the cleaning is not available unfavorable-proves the installation.

Therefore it is advantageous, when the partial flow of the liquid absorbent prior to thermal regeneration, preferably by sedimentation and/or flotation and/or screening is freed from solids and resin. Moreover, such a device for purifying solids or resin can also be provided in a circuit line of said adsorption means, with which the liquid absorbent is introduced into the absorption zone. Advantageously, therefore an extensive [...][...] distillation zone are provided for inlet cleaning , to ensure a trouble-free operation permanently. The resins can be separated by a combination of sedimentation and flotation. additive dosageforce of gravity separation may also be provided to support the a. The wood fibers can also be separated by a combined sedimentation and flotation or by sieving.

Depending on the application is preferably provided that the exhaust stream in the absorption zone by a wet electrostatic precipitator and/or a is a spray scrubber press exhaust air scrubber and/or guided. The absorption zone can therefore as Wet electrofilter, but be constructed as a spray scrubber press exhaust air scrubber or as. Moreover, said adsorption means may comprise a wet- electrostatic filter or a spray scrubber press exhaust air scrubber and subsequently an.

To is dissolved in the liquid absorbent is increased to improve the discharge of the pollutants to the stripping gas efficiently, it conveniently located, when the temperature of the liquid absorbent prior to thermal regeneration by heat exchange with a heat exchange medium.

In return the absorption in the absorption zone can be increased of pollutants, when the temperature of the liquid absorbent is lowered after the thermal regeneration by heat exchange with a heat exchange medium.

Therefore the liquid absorbent is cooled before it is returned to the absorption zone.

Energy efficiency of the process can be improved in a very favorable manner, when the liquid absorbent after the thermal regeneration for preheating the liquid absorbent prior to thermal regeneration is used. Therefore the heat energy can be used after flowing through the said liquid absorbent [...] distillation zone, the liquid absorbent prior to entering the preheat [...] distillation zone. Advantageously, therefore for the desorption or. Distillation energy required are recovered in part. The heat exchange between the flows of the liquid absorbent prior to thermal regeneration comprises heat displacement system forms or of, with which the energy balance of the process can be significantly improved. The heat exchange between the flows of the different temperature levels may be achieved in a compatible heat exchanger liquid absorbent, which is customary per se and therefore need not have specific State of the Art Explanatory Notes in the.

To heat displacement system between the flows is heated to compensate for the energy losses of the is said liquid absorbent, it advantageously, when the liquid absorbent by the preheating with a second heat exchange medium further.

Zur absorption of pollutants within the liquid absorbent Low Energy Costs it is advantageous, if the liquid absorption medium in the absorption zone is in a circuit branched off guided, wherein a portion of the liquid absorbent from the circuit of the absorption zone, and thereafter cleaned by thermal regeneration is recycled into the circuit of the absorption zone. Depending on the execution the whole flow or only a portion thereof through the said liquid absorbent can promoted and into the circuit of the absorption zone are recycled [...] distillation zone.

Particularly is preferably an execution, wherein the volume flow of the stripping gas is between 5% and 35% of the volumetric flow of the exhaust stream in the desorption zone. The essential advantage of this embodiment lies therein that the small-volume flow of the stripping gas freed by the pollutants are much more easily, than the bulk exhaust stream of the forest-based method can.

Zur according to a preferred embodiment is provided with the stripping gas enrichment of the pollutants that the liquid absorbent in the desorption zone is guided by a countercurrent- [...].

Preferably is passed by a droplet separator after the desorption, the stripping gas. The water vapour saturation of the stripping gas can be adjusted, for example, to 95%.

To is mixed in a subsequent discharge line for the stripping gas is to prevent a condensation, it conveniently located, when a guided by the desorption zone with a branched off before the desorption zone after the drop separation stripping gases part flow of the and by heat exchange with a third heat exchange medium heated partial flow of the stripping gas. Split into at least two partial flows is therefore the stripping gas, wherein the one partial flow through the desorption zone and the other partial flow guided past on the desorption zone is guided via a bypass line.

To in the stripping gas at a high concentration to remove this pollutants, it is favourable, when the is subjected to a thermal post-combustion with pollutants enriched stripping gas. Due to the concentration of the pollutants no additional energy is needed for the afterburning in the advantageously stripping air or it can even energy for the treatment of other exhaust gas streams are recovered.

When in the processing of wood materials resulting cleaning apparatus according to the invention, by hazardous substances such as organic carbon compounds is a device for thermal regeneration of at least one the pollutants laden exhaust gas streams of heated air substream of the liquid absorbent provided. The advantages and technical effects were already above in connection with the method explained in this embodiment.

In accordance with a preferred, since particularly energy-efficient execution, the means points for the thermal regeneration of the partial flow of the liquid absorbent with a negative pressure generating unit connected to a distillation device. As negative pressure generating unit is preferably provided a vacuum pump, which is connected to the distillation zone.

In accordance with an alternative embodiment is provided that the device for thermal regeneration to desorb at a desorption device in the liquid absorbent has absorbed pollutants in contact with a stripping gas.

To has to clean the exhaust gas streams arising during wood processing is, it conveniently located, when said adsorption means a wet electrostatic precipitator and/or a spray scrubber press exhaust air scrubber and/or a.

In order to achieve an effective thermal regeneration of the liquid absorbent is provided is, advantageous, if in the direction of flow of the liquid absorbent in front of the means for the thermal regeneration at least one heat exchanger, preferably two heat exchangers, to increase the temperature of the liquid absorbent by heat exchange with a heat exchange medium. As seen in the direction of flow of the liquid absorbent is Preferably, [...] formed the first heat exchanger, wherein the second heat exchanger the liquid absorbent in the direction of flow of the liquid absorbent for the thermal regeneration as seen on the required temperature level brings.

On it is in the absorption zone in order to achieve a high absorbent power appropriate, in the direction of flow of the liquid absorbent when a heat exchanger for lowering the temperature after the establishment of thermal regeneration by heat exchange with a heat exchange medium is provided said liquid absorbent.

The energy balance of the device can be improved, when the heat exchanger to a heat exchange between a flow of the liquid absorbent according to the device for thermal regeneration and a flow of the liquid absorbent is arranged in front of the means for thermal regeneration. So [...] of the be.

Distillation device and the flow of the liquid absorbent from the [...] to be supplied. Distillation device discharged flow of the liquid absorbent into separate guided thermal conduction channels of the heat exchanger, a heat exchange between the flows of the liquid absorbent of different temperature levels to bring about. Advantageously, so the heat energy for the thermal regeneration partially are recovered.

In [...] a preferred embodiment of the distillation device is a. Regulating device for controlling the volumetric flow of the stripping gas in the 5% to 35% of the volumetric flow of the exhaust stream provided on desorption device. Therefore a comparatively low volume flow will be promoted by the desorption device of the stripping gas, so that the pollutants are present in high concentration after the desorption. This can advantageously the after-treatment of the stripping gas, in particular by thermal afterburning, significantly more energy-efficient design.

Furthermore, it is favourable, when a stripping air feedstripping gases by a first supply line section for conveying a first substream of the desorption zone with a third heat exchanger and a second supply line section has connected, which is connected with a drain of the desorption device, bypassing the desorption zone.

The invention is shown in the drawings is intended to be limited in detail on the basis of embodiments, to which they, however, not, be further explained. Specifically shows:

Fig. 1 a functional principle according to the invention in the processing of wood materials resulting a device for cleaning a, by hazardous substances such as organic carbon compounds laden exhaust gas stream, which comprises an absorbing means and a desorption device;

Fig. 2 a functional principle of the desorption device of the apparatus according to 1 Fig.;

A further device according to the invention 3 a functional principle Fig., wherein the adsorption means comprises a wet-Electric filter;

A further device according to the invention a functional principle 4 Fig., wherein the adsorption means comprises a press exhaust air scrubber ; and

A further device according to the invention a functional principle 5 Fig., wherein is provided a distillation device for distillation of the liquid absorbent;

Fig. 1 shows a device 1 for cleaning a resulting in the processing of wood materials, such as organic carbon compounds with pollutants laden exhaust gas stream 2.

2 contained in the exhaust air Many of the organic pollutants, such as formaldehyde, methanol, acetaldehyde, acrolein, formic acid or acetic acid and other are water soluble and can effectively and permanently on the device shown in 2 1 1 Fig. are removed from the exhaust stream.

The apparatus 1 has an absorbing means 3 on, in which pollutants contained in the exhaust gas stream to a liquid absorbent 2, in particular water, are left absorbed, so that purified exhaust gases 3 4 said adsorption means. The Absorption device 3 is 5 connected with a circuit, with which the liquid absorbent is promoted by the absorption zone 2 countercurrent to the exhaust gas stream. In the first process step is therefore created a sufficiently large mass transfer zone, so as to allow the transfer of the pollutants from the gaseous phase into the aqueous phase. This operation is designated by absorption. The Absorption device 3 3 1 a spray scrubber has of Fig.' on, wherein by many fine drops a corresponding surface for material exchange is made available. Additionally, bring about the desired mass transfer scrubber grounds 3 is wetted in the adsorption means. In order to prevent blockage by fibers and or resins, said adsorption means is free of [...] or sprinkled packages 3. In the absorption zone is loaded the scrubbing liquid introduced, i.e. the liquid absorbent, 2 with the pollutants of the exhaust gas stream. To must be regenerated to maintain material exchange, the liquid absorbent either continuously or at intervals.

As 1 further evident from Fig., said adsorption means is 6 connected with a branch 3, with which a partial flow of the liquid absorbent from the circuit 3 is branched off 5 of said adsorption means. The branch 6 7 for the thermal regeneration of the means connected said liquid absorbent substream-entraining the pollutants. This a saturation can be prevented in continuous operation with the pollutants said liquid absorbent.

Pursuant Fig. 7 7 1 the device has a desorption device for the thermal regeneration ' for desorption of in the liquid absorbent in contact with a stripping gas absorbed pollutants on. The desorption device 8 connected to a supply line 7 for supplying a stripping gas is therefor, which is guided in the desorption zone countercurrent to the liquid absorbent, to receive a portion of the pollutants dissolved in the liquid absorbent by desorption. The stripping gas leaves 7 via a discharge line 9 the desorption device, so as to be subjected to a thermal post-combustion, for example. Between 5% and 35% in the desorption zone volume flow of the stripping gas is The the volumetric flow of the exhaust gas stream 2, so that the stripping gas in the discharge line 2 has a substantially higher concentration of harmful substances than the exhaust-gas flow 9, whereby the after-treatment can be carried out much more easily and with a lesser amount of energy of the pollutants. Therefore the device shown has a desorption stage 1 following the absorption stage 7 to 3. The desorption forms the Reverse process as for the absorption, wherein a selective transition of dissolved liquid pollutants in the gas phase. This operation is often also referred to as stripping. The loaded washing liquid can by desorption, i.e. a thermal washing water preparation , are regenerated and is thereafter again available for the absorption and hence to the exhaust side of the reduction of pollutants.

As Fig. 1 can be seen, the device 1 has two heat exchangers 10, 11 in the branch 6 between the absorbing means and the desorption device 3 to 7, with which the temperature of the liquid absorbent is increased to an appropriate level for the desorption functional level. So guided at least a portion of the pollutant-laden liquid absorbent over a desorption column and regenerated. First of the temperature level is raised by the said liquid absorbent, in particular with steam or thermal oil operated heat exchanger 11, at about 60 to 100 °C. Following the heating takes place in a stripping column of the desorption device the task 7, which is a spray, can act trickling filter scrubber[...] (cf. Fig. 2).

Here [...] is in countercurrent with the liquid absorbent. Fresh air, the so-called stripping gas, brought into contact. In all this the absorbate is converted into the gaseous phase from the liquid. By steady supply of stripping gas in the gas phase in the desorption zone is the partial pressure of the held [...] low. Also the phase equilibrium is determined to a large extent by the temperature of the washing liquid to be cleaned. She consequently an efficient substance is by raising the temperature level of the supplied desorber column reaches-transition in the desorbent. In order to achieve the necessary cleaning performance and therefore the ratio between the volumetric flow rates of desorbens be adjusted, as well as the stripping gas as essential influence quantities temperature spreading between desorbens and shot stripping gas. The Interchange Direction is therefore reversed for absorption process , [...] by high temperatures and low partial pressure the solubility of the increase in the stripping gas.

As 1 further evident from Fig., the liquid absorbent is discharged via a discharge 12 after flowing through the desorption zone. Then the temperature is lowered said liquid absorbent, for the absorption in the absorbing means 3 to increase. In the depicted variant takes place in the first heat exchanger after the desorption in the discharge 12 10 a heat exchange between the higher temperature and the discharged flow of the liquid absorbent from the absorption zone 6 branched off flow of the liquid absorbent for the desorption in the diversion of lower temperature. This the flow after the desorption for preheating the flow of the liquid absorbent can of the liquid absorbent prior to the desorption be used, which then is further heated in the second heat exchanger 11. Following the first heat exchanger 10 the purified and cooled flow is recycled into the said liquid absorbent absorbing means 3.

As evident from 2 Fig., the desorption device 7 comprises performing in the embodiment shown a countercurrent- [...] 13 on, with which the liquid absorbent in contact with the stripping gas is sprayed into the desorption zone, so that the pollutants in the stripping gas to be enriched. In direction of flow of the stripping gas is a drop separator 13 14 provided after the countercurrent- [...] seen, with which the stripping gas is dehumidified 9 prior to being exhausted. The fortified stripping gas leaves the drop separator 7. the desorption device 14 via condensate formation in the subsequent pipeline to reduce To, the 95% is adjusted to approximately water vapour saturation.

As 2 further evident from Fig., the 8 features, on one hand, a first supply line section stripping air feed 8', with which a first part flow of the 13 will be promoted by the desorption zone with the countercurrent- [...]stripping gases , and on the other hand, a second supply line section 8" on, which bypassing the desorption zone 9 of the desorption device is connected with the discharge duct 7. In the second supply line section 8" of the 8 is a third heat exchanger 14 provided stripping air feed , with which the second part flow of the upstream of the combination with the first part flow of the stripping gasesstripping gases 9 is heated in the discharge line. The inlet sections 8 ', 8" have valve elements 15' on, with which the division of the partial flows of the stripping gas can be adjusted on the two inlet sections. In this design will therefore immediately after the drop separation a preheated air stream the enriched desorber air working leads, so as to avoid condensation in the subsequent transport line.

As 2 schematically evident from Fig., [...] is a.

Regulating device 15 provided, with which, on the one hand, the device 7 in the desorption zone [...][...] of the stripping gas 35% the volumetric flow of the exhaust stream to 5% to the desorption can be adjusted. Moreover, the faces [...].

Regulating device 15 in the feed conduit 8', 8 "valve elements 15" on, with which the division of the partial flows 8 ", 8" on the two inlet sections the stripping gas can be adjusted. With the described methods may be achieved from levels of separation [...] typi 50-90%.

In order to improve the deposition the apparatus 1 by a particulate substances can Wet electrofilter, venturi stage or by a wet cyclone separator a (not shown) be extended. Besides the reduction of organic pollutants from absorption stage and desorption stage 3 7 the combination of central solids separated from the wash water can be removed by means of integrated water purification systems[...] would be from the. The cleansing of the wash water to be regenerated by suitable methods of solids, such as sedimentation, flotation, filtration, screening, hydrocycloning, centrifugation, a trouble-free and safe operation makes it easy for the absorption and desorption stages.

In carrying out 3 has a 3 3 the adsorption means in Fig. Fig. according to wet electrostatic filter 16 on represented schematically. Surrounded by a dryer 17 by injection of water in a raw gas line is shown next raw gas (not) until the saturation level (so-called quench) cooled. At the same time the inside is kept free of deposits the raw gas line 17. The cooled exhaust gas enters into the wet electrostatic filter 16 a and is distributed uniformly over the entire cross-section by a [...]gas distribution ground. [...] gaseous organic compounds are largely deposited. The dryer exhaust gaswet electrostatic filter elements 16 flows vertically from below through pre-cleaned now ', which have vertically disposed and centrally arranged emission electrodes honeycomb bundle than collecting electrodes. The emission electrodes produce a corona discharge by a high DC voltage, at which the gas is ionized. The still in the gas dust particles and aerosols ("Blue haze") are located and migrate in the electric field to the grounded negative charged, positive inner wall of the honeycomb. This will deposited under the visibility limit also the aerosols. By a nozzle system arranged over the honeycomb 16" of the deposited dust is periodically precipitation surfaces with process water to the rinsed off. For the untreated-gas line 17, the water circuit of the scrubber and for rinsing the honeycombs are available two pumps. The whole is shown in the (not) collected in a water collection pool water injected Wet electrofilter, in which solids contained in the water a decrease in said enable sedimentation installations , and via an internal water treatment (not shown) circulated with Screen device and Decanter. The water storage tank collecting sludge in the bottom of the (not) is discharged and via an eccentric screw pump with an endless screw shown for Decanter pumped and dewatered. The filtrate outlet of the decanter is returned into the water collection pool. After the filtration in the wet electrostatic filter 2 is guided via a line 16 the exhaust stream 17 'into the spray scrubber 3'. The thermal regeneration of the liquid absorbent, i.e. the circulation water, has already been on the basis of the 1 Fig., explained 2.

As 3 further evident from Fig., features, on one hand, and, on the other hand, the circuit line 18 5 6 the diversion means for freeing the respective flow of the liquid absorbent of solids and resin on. The [...]filter modules[...] /or 18 can have device/or. So the solids are deposited and resins, on the one hand, and, on the other hand, from the partial flow of the liquid absorbent from the flow of the liquid absorbent prior to thermal regeneration before introduction into the spray scrubber 3'.

In carrying out said adsorption means 19 for a 3 has a 4 Fig. press exhaust air scrubber according in which 20 wood pressingcontinuous press on 2 with a resulting exhaust gas stream. The exhaust gas stream 21 and 22 with extractor hood 2 is detected in an exhaust passage by introducing recirculated water with nozzles 23 until the saturation level (so-called quench) cooled. The inside of the exhaust pipe 22 is largely kept free of interfering Simultaneously deposits. The cooled exhaust gas is sucked out of the 21 by a preseparator [...] extractor hood 24, in which a separation of coarse material and exhaust gas takes place with [...]. The purified exhaust gas is derived via a line 25. The liquid absorbent, here water is guided via a circuit line 26 and 27 to the nozzles in a 23 recycled water treatment. The 6 for thermal regeneration device 26 is connected to the tap water treatment 7, which on the basis of the already 1 Fig., 2 has been described. Moreover, the water treatment device 18 for the separation of solids on drawn in 26 has a schematically.

Fig. 5 shows another embodiment of the apparatus 1 for cleaning the exhaust gas streams resulting from wood manufacturing 2, wherein the means 7 for the thermal regeneration of the partial flow of the liquid absorbent a distillation device 7" has, with a negative pressure generating unit 28, for example a vacuum pump 28' is connected. It represents a reduced pressure in the distillation zone establishment, whereby the pollutants absorption with tel desorbed and as the gaseous from the liquid concentrate via a discharge line 9' are discharged.