Cleaning waste air of volatile organic compound (VOC)

Abstract

The invention relates to a washing liquid for cleaning waste air, which arises during the drying of wood raw materials, of volatile organic compounds, the washing liquid having water and at least one emulsifier. The invention also relates to a method for cleaning the waste air, which arises during the drying of wood raw materials, wherein the waste air is mixed with a washing liquid according to the invention. The washing liquid at least partially separates a volatile organic compound of the waste air.

Description

[0001] Cleaning of exhaust air from volatile organic compounds (VOCs)

[0002] In the manufacture of wood-based materials, such as particleboard, OSB, HDF, or MDF, a key production step is drying wood raw materials to the level required for production. For all wood-based materials, this level is below 10% moisture by weight. Wood drying, which is usually carried out using preheated air in drum or tube dryers, not only emits significant amounts of water but also wood constituents. These include terpenes (mainly monoterpenes), carboxylic acids, and other hydrocarbon compounds. In addition, the drying process also leads to degradation processes in the wood. This also results in the emission of aldehydes, formaldehydes, and similar substances. Depending on the type of wood used, these emissions can reach a significant concentration of » 500 mg / Nm 3in the exhaust air. In particular, some of the released terpenes and aldehydes cause nuisance to residents due to their low odor thresholds and unpleasant smell. Furthermore, the legislature has set limit values ​​for the gaseous organic components collectively known as VOCs (volatile organic compounds). Depending on the wood material and the dryer, these limit values ​​under standardized conditions are a maximum concentration of 400 mg / Nm3. 3 in the exhaust air.

[0003] This situation makes it necessary to achieve a reduction of VOCs in the stack exhaust air through technical measures. However, it should be noted that VOCs, particularly the longer-chain aldehydes and terpenes, are chemically less reactive. This makes reduction by scavengers or chemical conversion almost impossible. A further problem is that terpenes and longer-chain aldehydes are poorly soluble in water. This means that washing out the compounds in a conventional scrubber is also ineffective. Known processes involve cleaning the exhaust air through condensation processes. DE 38 22 943 A1, for example, relates to a process and device for cleaning dryer air. The exhaust air stream is saturated by cooling, mixed with condensation nuclei, and the resulting droplets are separated.

[0004] EP 1 278 588 B1 relates to a process and a system for separating wood constituents from gases produced during wood combustion, which are discharged as exhaust air. In the process, the exhaust air is purified in two steps. First, the exhaust air is washed by contact with a liquid, whereby resins, organic acids, and dust particles from the exhaust air are enriched in the liquid. In the second step, the thus purified exhaust air is cooled while simultaneously condensing the constituents still present in the exhaust air, such as terpenes, methanol, ethanol, and carboxylic acids. The washing step alone is not sufficient because, as already described, terpenes and longer-chain aldehydes in particular are poorly soluble in water. In order to remove these from the exhaust air, the condensation step is therefore necessary.

[0005] US 3,596,496 relates to a process for cleaning air of organic contaminants. In the process, the contaminated air is humidified in a first chamber and then mixed with an aerosol in a second chamber. The mixture of aerosol and air is passed through a third chamber, which has offset baffles, thus extending the contact time between the aerosol and the air. The purified air and the aerosol are then separated, and the purified air is dehumidified. The aerosol is produced from a solution of water and lecithin and is used in the process to create the largest possible surface area for binding dirt particles. However, to ensure a sufficiently long contact time, an extra chamber with baffles through which the gas mixture is passed must be provided, as described.The disadvantage of this process is that it cannot be implemented in existing production lines without additional equipment. For example, a device for humidifying the contaminated air and the chamber with baffles must be provided. Since this requires expansions or modifications to existing systems, this process is economically inefficient.

[0006] DE 42 12 164 A1 describes a complex process for extracting airborne contaminants generated during the pressing of particleboard and for cleaning the extracted air stream of these contaminants. Airborne contaminants such as fats, paraffins, resins, phenols, and formaldehydes are separated using a wet scrubbing process. In the wet scrubbing process, the contaminated air is mixed with an unspecified scrubbing liquid. The process is characterized by a highly complex structure of distribution lines, pre-nozzles, and a separation zone, which also makes integration into existing systems of a production line difficult.

[0007] Other technical solutions, such as post-combustion of exhaust air using natural gas, using parts of the exhaust air as air for a boiler room, etc., do lead to a reduction in VOCs, but are expensive or limit the variability of the underlying process. Post-combustion of exhaust air with natural gas is also viewed rather critically from an ecological perspective, even if the heated air is further used in a technical process.

[0008] Based on the state of the art, the object of the invention is to enable efficient purification of exhaust air, in particular the exhaust air generated during the drying of wood raw materials. The exhaust air should be purified, in particular, of volatile organic compounds. The disadvantages of the prior art should be eliminated, and the purification should be able to be integrated into existing technical systems and processes in a cost-effective manner without the need for additional technical equipment. Furthermore, the underlying technical processes should not become more technically complex.

[0009] This object is achieved by the present invention by a washing liquid according to claim 1, a method according to claim 8 and a use of the washing liquid according to the invention in the method according to the invention.

[0010] Description

[0011] The present invention provides a washing liquid for at least partially separating at least one volatile organic compound from exhaust air. In a particularly preferred embodiment, the invention provides a washing liquid for at least partially separating at least one volatile organic compound from exhaust air, wherein the exhaust air arises during the drying of wood raw materials. In particular, during the drying of wood raw materials in the production of OSB, particleboard, HDF, or MDF boards.

[0012] In one embodiment, the washing liquid is suitable for at least partially separating several volatile organic compounds from exhaust air. In one embodiment, the washing liquid is suitable for separating volatile organic compounds from the exhaust air in such a way that the exhaust air, after addition of the washing agent, contains volatile organic compounds below a predetermined limit, preferably below a legally prescribed limit. In one embodiment, the exhaust air from the drying of wood raw materials in the production of OSB, after addition of the washing agent, contains volatile organic compounds below a limit of 400 mg / Nm 3 In one embodiment, the exhaust air from the drying of wood raw materials in the production of particle boards after addition of the washing agent contains volatile organic compounds below a limit value of 200 mg / Nm 3In one embodiment, the exhaust air from the drying of wood raw materials in the production of HDF or MDF boards contains volatile organic compounds below a limit value of 120 mg / Nm 3 All of the limit values ​​mentioned apply to all dryer types used in the drying of wood raw materials in the production of particleboard, OSB, HDF, or MDF boards. The unit is mg / Nm 3 the standard volume (standard cubic meter, Nm 3) is used and the amount of VOCs is given in milligrams. Since this unit is pressure and temperature dependent, it refers to the volume under standard conditions: temperature 0°C and pressure 1013 mbar. The limit values ​​listed implement the requirements of the European Union in accordance with Directive 2010 / 75 / EU [Best Available Techniques (BAT) Reference Document for the Production of Wood-based Panels, 2016, EUR 277732 EN; ISBN 978-92-79-54949-6]. The limit value refers to the total amount of VOCs in the exhaust air, with the VOCs in the exhaust air being measured in accordance with EN 12619.

[0013] According to the invention, separation means that at least a portion of the concentration of at least one volatile organic compound from the exhaust air is bound in a portion of the scrubbing liquid and forms an emulsion with it. The concentration of the at least one volatile organic compound in the exhaust air is thereby reduced. In a preferred embodiment, several different VOCs from the exhaust air are bound in a portion of the scrubbing liquid and form an emulsion with it.

[0014] Volatile organic compounds (VOCs) are defined as volatile organic compounds. These include hydrocarbons, alcohols, aldehydes, and organic acids. According to the definition of the Economic Commission for Europe (UNECE), VOCs are organic compounds emitted in industrial processes that have an ozone creation potential (POCP). In one embodiment of the present invention, the volatile organic compounds separated from the exhaust air are selected from the group consisting of terpenes, carboxylic acids, aldehydes, ketones, aromatic hydrocarbons, and other hydrocarbons.

[0015] According to the invention, the washing liquid comprises water and at least one emulsifier. In one embodiment, the washing liquid consists of water and one emulsifier. In one embodiment, the washing liquid consists of water and several emulsifiers.

[0016] In one embodiment of the present invention, the washing liquid contains between 0.05 wt.% and 2 wt.%, preferably between 0.1 wt.% and 0.5 wt.%, of the at least one emulsifier. According to the invention, the at least one emulsifier is therefore water-soluble.

[0017] Particularly preferably, the at least one emulsifier is suitable for separating at least one volatile organic compound from the exhaust air, forming an emulsion of water, emulsifier, and the at least one separated volatile organic compound. Preferably, the emulsifier is suitable for separating more than one volatile organic compound from the exhaust air. Particularly preferably, the emulsifier is suitable for separating all volatile organic compounds from the exhaust air whose concentration in the exhaust air must be reduced before the exhaust air may be released into the environment. Advantageously, exhaust gases can thus be purified of volatile organic compounds in order to meet environmental standards, in particular Directive 2010 / 75 / EU of the European Union.In one embodiment, the scrubbing liquid according to the invention is suitable for absorbing VOCs from exhaust air if the scrubbing liquid, upon contact with exhaust air, is capable of reducing the concentration of VOCs in the exhaust air such that the environmental standards of Directive 2010 / 75 / EU of the European Union are met.

[0018] In one embodiment, the at least one emulsifier is selected from the group consisting of fatty alcohols, quaternary ammonium salts, fatty acid amides, lecithins, and the like. In a particularly preferred embodiment, the at least one emulsifier is a lecithin.

[0019] In one embodiment, the washing liquid consists of water and a lecithin as an emulsifier. In one embodiment, the washing liquid consists of water and a fatty alcohol as an emulsifier. In one embodiment, the washing liquid consists of water and a quaternary ammonium salt as an emulsifier. In one embodiment, the washing liquid consists of water and a fatty acid amide as an emulsifier. Lecithins are phosphatidylcholines and, as such, are a component of the cell membrane of animal and plant organisms, for example. They are constituents of fats and fatty oils and are particularly abundant in egg yolks and plant sperm cells.

[0020] In one embodiment of the invention, the washing liquid contains exactly one emulsifier. In another embodiment, the washing liquid contains a mixture of emulsifiers. In one embodiment of the present invention, the washing liquid preferably contains a mixture of 2, 3, or 4 emulsifiers.

[0021] In one embodiment, the washing liquid comprises water, a lecithin, and optionally one or more further emulsifiers. In one embodiment, the washing liquid consists of water, a lecithin, and optionally one or more further emulsifiers. In one embodiment, the washing liquid consists of water, a lecithin, and a fatty alcohol. In one embodiment, the washing liquid consists of water, a lecithin, and a quaternary ammonium salt. In one embodiment, the washing liquid consists of water, a lecithin, and a fatty acid amide.

[0022] In one embodiment, the washing liquid comprises water, lecithin and one or more further emulsifiers or consists of water, a lecithin and one or more further emulsifiers.

[0023] In one embodiment, the washing liquid comprises between 0.05 wt.% and 2.0 wt.%, preferably between 0.1 wt.% and 0.5 wt.% of the at least one emulsifier or a mixture of emulsifiers.

[0024] In one embodiment of the present invention, the at least one emulsifier or the mixture of emulsifiers is suitable for separating at least one substance from the group of hydrocarbon compounds from the exhaust air. An emulsion of water, emulsifier, and the at least one substance from the group of hydrocarbon compounds is formed.

[0025] Advantageously, the at least one emulsifier or the mixture of emulsifiers is not an environmentally hazardous substance, or the emulsifier or the mixture of emulsifiers is used in a concentration that does not pose an environmental hazard. Furthermore, the invention provides a method for purifying the exhaust air generated during the drying of wood raw materials. According to the invention, the exhaust air is mixed with a washing liquid according to the invention in a wet washing process, wherein the washing liquid at least partially separates at least one volatile organic compound from the exhaust air.

[0026] All features described for the washing liquid apply equally to the process according to the invention and vice versa.

[0027] In one embodiment of the present invention, the scrubbing liquid is sprayed into the exhaust air using at least one or more nozzle rings, one or more nozzle bars, one or more individual nozzles, or other suitable devices known to those skilled in the art, or a combination of the aforementioned devices. The scrubbing liquid according to the invention is sprayed in liquid form. In particular, the scrubbing liquid is not sprayed in the form of an aerosol. The exhaust air is preferably guided through a chimney.

[0028] In a further embodiment of the present invention, exhaust air is guided through a stack, and scrubbing liquid is sprayed into at least two locations along the stack, each using at least one or more nozzle rings, one or more nozzle bars, one or more individual nozzles, or other suitable devices known to those skilled in the art, or a combination of the aforementioned devices. Scrubbing liquids with the same composition or different compositions can be used. The scrubbing liquids can differ in the concentration of the emulsifier in the scrubbing liquids, or scrubbing liquids with different emulsifiers can be used.

[0029] In one embodiment of the present invention, the scrubbing liquid is used at room temperature; heating the scrubbing liquid is not necessary. Furthermore, in one embodiment, no special pressure is maintained in the stack. The exhaust gas is preferably removed from the stack by fans, as is common in such systems.

[0030] It is particularly advantageous that nozzle rings for spraying water into chimneys with exhaust air scrubbers, such as those used in the processing of wood-based materials, for example in the production of OSB, MDF boards or HDF boards, are generally available. Advantageously, these can be used in their existing form. Additional technical components are therefore not necessary. This is possible because, according to the invention, the scrubbing liquid is sprayed in liquid form and not introduced as an aerosol, as described in the prior art. The integration of additional system components into a production line is no longer necessary thanks to the method according to the invention. The method according to the invention can therefore be integrated into existing process sequences, thereby keeping the costs for carrying out the method low.

[0031] In a particularly preferred embodiment of the invention, the exhaust air is therefore generated during the drying step in the production of OSB, chipboard, MDF boards or HDF boards.

[0032] OSB is also known in German as coarse chipboard. The term OSB stands for "oriented strand board" and describes a board made of aligned chips. OSB are multi-layer boards made from long, slender chips ("strands").

[0033] MDF and HDF boards are medium-density fiberboard (MDF) and high-density fiberboard (HDF), respectively. These consist of finely shredded, primarily bark-free wood. Pressing produces a wood-based material that is equally homogeneous in both the longitudinal and transverse directions.

[0034] Particleboard is primarily made from wood scraps and thinnings. Different wood particles are used, which can vary in both wood species and particle size.

[0035] During the production of particleboard, OSB, HDF, or MDF boards, the wood particles, chips, or wood fibers are dried. In a preferred embodiment, the resulting exhaust air is at least partially purified of at least one volatile organic compound by the inventive process before being discharged, for example, into the environment.

[0036] In one embodiment of the present invention, the emulsion formed from water, emulsifier and the separated volatile organic compounds is collected together with any residual washing liquid that may be present. Any residual washing liquid and the emulsion form the wastewater. The emulsion can then be washed out in a wastewater treatment device and subsequently separated off and disposed of. In an alternative embodiment, usable substances can be separated from the emulsion and used for further purposes. In one embodiment, terpene can be obtained for further technical applications. In one embodiment of the process according to the invention, at least one substance is recovered from the emulsion of washing liquid and at least one volatile organic compound. In a further embodiment, several substances are recovered from the emulsion.In one embodiment, the emulsion collects on the surface of the wastewater and can be separated, for example, by flotation. In another embodiment of the invention, the emulsion in the wastewater is separated by decanting.

[0037] In one embodiment of the present process, the exhaust air after addition of the detergent contains volatile organic compounds below legally prescribed limits, in particular below the limits set out in Directive 2010 / 75 / EU of the European Union. In a preferred embodiment of the process according to the invention, the exhaust air from the drying of wood raw materials in the production of OSB contains volatile organic compounds below a limit of 400 mg / Nm 3In a further embodiment of the process according to the invention, the exhaust air from the drying of wood raw materials in the production of particle boards, after addition of the washing agent, contains volatile organic compounds below a limit value of 200 mg / Nm 3 In one embodiment of the process according to the invention, the exhaust air from the drying of wood raw materials in the production of HDF or MDF boards, after addition of the detergent, contains volatile organic compounds below a limit value of 120 mg / Nm 3 The process according to the invention can therefore advantageously reduce VOCs in the exhaust air that arise during the drying of wood raw materials in the production of OSB, particleboard, MDF, or HDF boards.

[0038] The invention further relates to the use of the washing liquid according to the invention in a method according to the invention. In particular, the invention relates to the use of the washing liquid according to the invention in a wet washing process. All features described with regard to the washing liquid according to the invention and the method according to the invention apply equally to the use according to the invention. The invention is explained in more detail below with reference to two figures and an exemplary embodiment.

[0039] Figure 1 schematically shows the process of producing an MDF / HDF board using the method according to the invention;

[0040] Figure 2 schematically shows the process of producing an OSB using the method according to the invention.

[0041] Figure 1 schematically shows the process of producing an MDF / HDF board 80 using the method according to the invention.

[0042] Fresh wood 10, wood chips 11, and / or recycled wood 12 are used as raw materials for wood fiber production. The fresh wood 10 is generally debarked and shredded into wood chips, for example, in a disc chipper. The wood chips are then transferred to a pre-cooker 20 for hydrochemical treatment, then to a cooker 21, and finally to a fiberizer ("refiner") 22. In a further process step 23, the fibers are coated with a glue and transferred to a dryer 40.

[0043] The fiber is dried in a dryer 40, where excess water is removed. The dryer 40 is supplied with warm air by a burner 32. The burner 32 is operated via a fuel supply 30 and an air supply 31. The exhaust air generated during drying is discharged via a chimney 100.

[0044] After drying, the fibers are usually cleaned in a fiber sifter 50. For this purpose, the fibers can be introduced into an air stream, for example, and freed of foreign matter (e.g., glue lumps, metal, rubber) either by vortex formation, sharp deflection, impact sifting, rising air sifting, or a combination of several effects. The fibers are then forwarded to the scattering station 60. In the scattering station 60, the fibers are formed into a blank, which is then pressed in a hot press 70 to form the finished MDF / HDF board 80.

[0045] The exhaust air discharged into chimney 100 is sprayed with the scrubbing liquid according to the invention through a nozzle ring. The scrubbing liquid is formed by mixing water 120 and at least one emulsifier 110. The scrubbing liquid separates volatile organic compounds from the exhaust air and, together with a portion of the scrubbing liquid, forms an emulsion. The emulsion and the remaining scrubbing liquid are collected in a wastewater tank 102. The exhaust air can then be passed through a wet electrostatic precipitator 101. In the wet electrostatic precipitator 101, further particles can be removed from the exhaust air. Optionally, the exhaust air can be brought into contact again with a scrubbing liquid according to the invention through another nozzle ring in order to separate any volatile organic compounds still present from the exhaust air. The scrubbing liquid is in turn formed by mixing water 121 and at least one emulsifier 111.The resulting emulsion and the remaining washing liquid are also collected in the wastewater tank 102. The purified exhaust air 130 is released into the environment through the chimney 100.

[0046] Figure 2 schematically shows the process of manufacturing an OSB 81 using the method according to the invention.

[0047] Fresh wood 10 is used as the raw material, and alternatively, recycled wood is used for the middle layer. The raw material is debarked if necessary 15 and then processed lengthwise into chips ("strands") 16 by rotating knives. The natural moisture content of the chips is reduced in a dryer 40. The dryer 40 is supplied with warm air by a burner 40. The burner 40 is operated via a fuel supply 30 and an air supply 31. The exhaust air generated during drying is discharged via a chimney 100.

[0048] The chips are then separated at a screening station 50 into chips for the top layer and chips for the middle layer. Both the chips for the top layer and the middle layer are coated with glue in further process steps 51, 52 and then arranged in layers at a spreading station 60. For example, this can be done using a throwing process such that the chips are arranged lengthwise and crosswise in three layers in the form of a top layer, middle layer, top layer. The layers are then pressed together in a hot press 70 to form the finished OSB 81.

[0049] The exhaust air discharged into chimney 100 is sprayed with the scrubbing liquid according to the invention through a nozzle ring. The scrubbing liquid is formed by mixing water 120 and at least one emulsifier 110. The scrubbing liquid separates volatile organic compounds from the exhaust air and, together with the scrubbing liquid, forms an emulsion. The emulsion and the remaining scrubbing liquid are collected in a wastewater tank 102. The exhaust air can then be passed through a wet electrostatic precipitator 101. In the wet electrostatic precipitator 101, further particles can be removed from the exhaust air. Optionally, the exhaust air can be brought into contact again with a scrubbing liquid according to the invention through another nozzle ring in order to separate any volatile organic compounds still present from the exhaust air. The scrubbing liquid is in turn formed by mixing water 121 and at least one emulsifier 111.The resulting emulsion and the remaining washing liquid are also collected in the wastewater tank 102. The purified exhaust air 130 is released into the environment through the chimney 100.

[0050] Example 1

[0051] A defined amount of a terpene aerosol (a-pinene) was injected from below into a tubular chimney (height approximately 1 m, diameter: 0.5 m). Nozzles on the sides of the lower section of the reactor introduced a continuous air stream into the chimney (air velocity: 10 m / min). A mixture of water and a soy-based lecithin as an emulsifier was sprayed into the chimney from above via a nozzle ring. The water contained 0.3 wt.% of the lecithin. The weight ratio of water to terpene aerosol was approximately 100:1. The mixture of water and emulsion that collected at the bottom of the reactor was collected, and the emulsion was then separated by decantation. The ratio of injected terpene aerosol to collected emulsion was then determined. 71% of the aerosol was recovered in the emulsion.

[0052] Reference symbols

[0053] 10 fresh wood

[0054] 11 wood chips

[0055] 12 recycled wood

[0056] 15 debarking

[0057] 16 rotating knives

[0058] 20 pre-cookers

[0059] 21 cookers

[0060] 22 shredders

[0061] 23, 50, 51 Process step gluing

[0062] 30 Fuel supply

[0063] 31 Air supply

[0064] 32 burners

[0065] 40 dryers

[0066] 50 fiber sifters

[0067] 60 spreading station

[0068] 70 hot press

[0069] 80 MDF / HDF board

[0070] 81 OSB

[0071] 100 fireplace

[0072] 101 Wet electrostatic precipitator

[0073] 102 wastewater tanks

[0074] 110, 111 Emulsifier

[0075] 120, 121 Water

[0076] 130 purified exhaust air

Claims

Claims 1. Washing liquid for at least partially separating at least one volatile organic compound from exhaust air, characterized in that the washing liquid comprises water and at least one emulsifier (110, 111).

2. Washing liquid according to claim 1, characterized in that the washing liquid comprises water, lecithin and one or more further emulsifiers.

3. Washing liquid according to claim 1, characterized in that the washing liquid comprises a mixture of emulsifiers (110, 111).

4. Washing liquid according to one of the preceding claims, characterized in that the washing liquid contains between 0.05 wt.% and 2.0 wt.% of the at least one emulsifier (110, 111) or a mixture of emulsifiers (110, 111).

5. Washing liquid according to one of the preceding claims, characterized in that the at least one emulsifier (110, 111) or a mixture of emulsifiers (110, 111) is suitable for separating at least one substance from the group of hydrocarbon compounds from the exhaust air.

6. Washing liquid according to one of the preceding claims, characterized in that the at least one emulsifier (110, 111) is selected from the group comprising fatty alcohols, quaternary ammonium salts, fatty acid amides, lecithin and the like.

7. Washing liquid according to one of the preceding claims, characterized in that the volatile organic compounds which are separated from the exhaust air are selected from the group comprising terpenes, carboxylic acids, aldehydes, ketones, aromatic hydrocarbons and other hydrocarbons.

8. A method for cleaning exhaust air, in particular exhaust air which arises during the drying of wood raw materials, characterized in that the exhaust air is mixed with a washing liquid according to one of claims 1 to 7 in a wet washing process, wherein the washing liquid at least partially separates at least one volatile organic compound from the exhaust air.

9. The method according to claim 8, characterized in that the emulsion formed from washing liquid and the at least one separated volatile organic compound is collected.

10. Method according to one of claims 8 or 9, characterized in that the washing liquid is sprayed into the exhaust air with at least one or more nozzle rings, one or more nozzle bars, one or more individual nozzles or a combination thereof.

11. Method according to one of claims 8 to 10, characterized in that the exhaust air is guided in a chimney (100) and washing liquid is sprayed at at least two points of the chimney using one or more nozzle rings, one or more nozzle bars, one or more individual nozzles or a combination of these.

12. The method according to any one of claims 8 to 11, characterized in that the exhaust air after addition of the detergent contains volatile organic compounds below predetermined limit values.

13. Process according to one of claims 8 to 12, characterized in that at least one substance is recovered from the emulsion of washing liquid and volatile organic compounds.

14. Method according to one of claims 8 to 13, characterized in that the exhaust air is generated during the drying step in the production of chipboard, OSB (81), MDF boards or HDF boards (80).

15. Method according to claim 14, characterized in that the exhaust air from the drying of wood raw materials in the production of OSB (81) after the placement with the detergent volatile organic compounds below a limit of 400 mg / Nm 3 or that the exhaust air from the drying of wood raw materials in the production of particle boards after addition of the washing agent contains volatile organic compounds below a limit value of 200 mg / Nm 3 or that the exhaust air from the drying of wood raw materials in the production of HDF or MDF boards (80) after addition of the washing agent contains volatile organic compounds below a limit value of 120 mg / Nm 3 has.

16. Use of the washing liquid according to one of claims 1 to 7 in a process according to one of claims 8 to 15.

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