Cooling acetylated wood elements

Abstract

To provide better cooling methods for acetylated wood elements, and processes incorporating such methods.SOLUTION: A process for the production of acetylated wood elements, a cooling system, and a wood acetylation plant are described. The process for the production of acetylated wood elements comprises acetylating wood elements and cooling the acetylated wood elements, where the cooling comprises supplying liquid water to the acetylated wood elements to provide wetted wood elements and exposing the wetted wood elements to a gas flow.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a process for the manufacture of acetylated wood elements comprising a cooling step in which the wood elements are cooled from a temperature preferably in the range of 120°C to 180°C, preferably to a temperature below 60°C. [Background technology]

[0002] Acetylation of wood has long been recognised as a method to improve the durability of non-durable soft wood species. Acetylation can be used to improve wood properties such as hardness and dimensional stability. Background references on such processes include WO2013 / 117641 and WO2013 / 139937. Wood acetylation generally involves contacting the wood elements with an acetylation fluid containing acetic anhydride and / or acetic acid while heating. The acetylation fluid is generally recirculated.

[0003] Acetylation of wood typically results in hot acetylated wood elements having a temperature of at least 120°C, or at least 150°C, often between 160°C and 180°C. The acetylated wood elements are therefore too hot for storage and further processing. Storage of acetylated wood elements having such temperatures entails the risk of smoldering (flameless combustion), even while the wood elements cool slowly against the surroundings. Cooling of the acetylated wood elements is therefore necessary, especially if the acetylated wood elements are not immediately subjected to further processing.

[0004] However, current cooling methods are insufficient for (acetylated) wood elements. Wood elements are difficult to cool due to their low heat transfer coefficient. This low heat transfer coefficient causes problems, especially in the case of gas cooling and cooling by indirect heat exchange. Cooling by flowing cooling gas over the acetylated wood elements is not efficient enough and would require very high gas flows and long residence times of the wood elements. Indirect cooling does not result in uniform and rapid cooling, since the heat transfer from the cooled equipment to the wood elements is very poor. The further method of immersing the acetylated wood elements in a cooling bath is not attractive, since it results in wet acetylated wood elements. The cooled wood elements may even drip. Furthermore, there is a risk of residual acetylation fluid leaching from the acetylated wood elements into the cooling liquid.

[0005] Therefore, there is a need for better cooling methods, particularly for acetylated wood elements, and processes incorporating such methods, which are preferably rapid and efficient and do not suffer from the above-mentioned disadvantages of the prior art methods.

[0006] Japanese Patent Application Laid-Open No. 6-198610 describes a process in which wood fibers obtained by chopping wood are acetylated in a liquid phase, and then the acetylated wood fibers are accumulated and integrated into a molded product. Summary of the Invention

[0007] In order to better address one or more of the aforementioned needs, the present invention in one aspect provides a process for producing an acetylated wood element, comprising the steps of acetylating a wood element and cooling the acetylated wood element, the cooling step comprising the steps of supplying liquid water to the acetylated wood element to obtain a moistened wood element and exposing the moistened wood element to a gas flow.

[0008] In a further aspect, the present invention relates to a cooling system comprising a water spray chamber, an evaporative section downstream of said water spray chamber, and a gas recirculation loop, said water spray chamber comprising: , an inlet for wood elements, a liquid distributor for spraying water, and an outlet for wood elements, and the evaporation section includes an inlet and an outlet for wood elements, a conveyor for continuously feeding wood elements from the inlet to the outlet, an inlet conduit having at least one opening for introducing gas into the evaporation section, and an outlet conduit having at least one opening for extracting gas from within the evaporation section, each of the conduits being connected to the gas recirculation loop, and each of the openings of each of the conduits being different from the inlet and outlet for the wood elements.

[0009] The present invention also relates to a wood acetylation plant. [Brief description of the drawings]

[0010] [Figure 1] 1 shows a process mechanism for a non-limiting exemplary embodiment of a cooling process for wood elements according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention generally relates to the production of acetylated wood elements and the cooling of acetylated wood elements. In one aspect, the invention is based on the enlightened insight that the combination of wetting hot acetylated wood elements with a liquid and evaporating the liquid from the wetted wood elements results in efficient cooling of the acetylated wood elements. The process thus comprises the steps of supplying a liquid, preferably water, to the acetylated wood elements to obtain wetted wood elements and exposing the wetted wood elements to a gas flow. The exposure to the gas flow causes evaporation of the aqueous liquid in contact with the wood elements, resulting in a decrease in the temperature of the wood elements. In the present invention, wetting and exposure are used to result in evaporative cooling of the hot acetylated wood elements. This can be contrasted with air conditioning methods, for example, where evaporative cooling is used to cool the air.

[0012] The process includes a step of acetylating the wood elements, which generally involves contacting the wood elements with an acetylation fluid comprising acetic anhydride and / or acetic acid, during which the temperature of the wood elements is increased to a temperature in the range of 120°C to 180°C, more preferably to a final temperature in the range of 150°C to 180°C.

[0013] The acetylation step is preferably a continuous process step. The process may be a batch or continuous process or may include a combination of batch and continuous process steps. Preferably, the cooling step is a continuous process step. More preferably, the exposure step is a continuous process step.

[0014] Preferably, the acetylation comprises removing excess acetylation liquid from the acetylated wood elements, for example under reduced pressure. Preferably, the process comprises a finishing step between the acetylation and cooling steps. The finishing step generally aims at reducing the content of unreacted acetic anhydride and formed acetic acid of the wood elements. The finishing step preferably comprises exposing the acetylated wood elements to reduced pressure and / or to elevated temperatures, such as about 130°C or higher. Often, the wood elements resulting from the finishing step have a temperature above 120°C, such as above 150°C.

[0015] Preferably, the acetylated and optionally finished wood element has a temperature of 120°C or more, such as 150°C or more, and preferably has an acetyl content, preferably at its geometric centre, of more than 15% by weight, or more than 17% by weight, or more than 20% by weight, or more than 21% by weight. Preferably, the acetylated wood element also has a residual acid content, e.g. obtained by the finishing process, of less than 1% by weight, or less than 0.9% by weight, or less than 0.5% by weight on a dry basis. Preferably, the cooled wood element has such an acetyl content and / or residual acid content.

[0016] The acetyl content of wood can be determined as follows: Each sample is ground into wood particles. Residual traces of acetic acid and / or acetic anhydride are removed from the samples by washing with water followed by drying at 103±2°C for 14 to 24 hours. The dried samples are weighed and then saponified with sodium hydroxide solution at elevated temperature, typically 90°C, to release the acetyl groups from the wood in the form of acetate ions. The saponification reaction is allowed to proceed for 4 hours with stirring every 15 minutes. Acetate ions are quantified by high pressure liquid chromatography (HPLC) calibrated with standard acetic acid solutions, using sodium butyrate as an internal standard.

[0017] Residual acetic acid (RA) content is a measure of the residual unbound acetic acid in wood (including acetic acid formed by hydrolysis of residual unbound acetic anhydride). Acetic acid can also come from the wood itself, so RA measures both the original acetic acid and the acetic acid remaining from the acetylation reaction. To determine the residual acid content (RA), a well-defined amount of sample material, between 3g and 5g, is shaken in demineralized water for 1 hour. After this extraction step, the sample is separated from the aqueous fraction by filtration. This aqueous fraction can then be titrated with a known solution of sodium hydroxide (NaOH) using phenolphthalein as an indicator to calculate the residual acid concentration of the sample.

[0018] The process includes a step of cooling the acetylated wood elements. Preferably, the wood elements are cooled to a temperature below 100°C, or below 80°C, more preferably below 60°C, or below 40°C, such as ambient temperatures, generally above 5°C. Preferably, the temperature of the wood elements is reduced by at least 30°C, or at least 50°C, more preferably at least 80°C, during said cooling, more particularly during exposure to the gas flow. Preferably, the wood elements at the outlet of the evaporation section have a temperature below 100°C, or below 80°C, more preferably below 60°C, or below 40°C, for example at ambient temperature. If an atmosphere different from the ambient, for example an inert atmosphere, is maintained in the evaporation section, the outlet of the evaporation section is optionally characterized by a transfer of the wood elements to the ambient atmosphere and / or to an atmosphere different from the gas flow. Preferably, this cooling is achieved in less than 30 minutes or less than 15 minutes.

[0019] The cooled wood elements have, for example, a moisture content of less than 35% by weight, in particular at the outlet of the evaporation section, for example in the range of 1% to 8% by weight, or 5% to 10% by weight.

[0020] The present invention relates generally to the production of acetylated wood elements. In particular, wood chips, strands, and particles are acetylated to obtain a specific surface area (m 2 The surface area per kg of wood is lower, so e.g. It is more difficult to cool than fibers.

[0021] The wood elements may, for example, comprise or consist of one or more selected from the group consisting of wood chips, wood strands, and wood particles. The process and system of the present invention may, for example, be used for the acetylation of durable and non-durable hardwoods and durable and non-durable softwoods. The wood elements preferably belong to non-durable wood species, such as non-durable hardwoods or softwoods, typically conifers such as spruce, pine, or fir. Preferred types of wood are spruce, Siberian spruce, pinus maritime, Scots pine, radiata pine, eucalyptus, red alder, European alder, beech, and birch.

[0022] Typical dimensions of some types of wood elements are given in Table 1 below. Preferred are wood chips, strands and particles as defined in Table 1, and optionally slivers. Preferably, to achieve a more uniform cooling, the wood elements consist of one of the types of wood elements as defined in Table 1. In some embodiments, the wood particles are 1.0 mm or less in diameter. Preferably, the wood elements have a width and / or thickness of at least 0.15 mm.

[0023] [Table 1]

[0024] Cooling comprises supplying the wood elements with liquid water to obtain moistened wood elements, optionally as a liquid stream comprising other components or as a liquid stream consisting essentially of water, for example more than 99% by weight.

[0025] Preferably, liquid water is provided to the surface of the wood elements, preferably the wood elements are contacted with liquid water. Preferably, the process comprises the steps of introducing the wood elements into a moist chamber and introducing liquid water into the moist chamber. In some embodiments, the moistening does not involve condensation in the moist chamber. In some optional embodiments, the process does not include the step of introducing steam into the moist chamber in contact with the wood elements, for example. Preferably, the amount of liquid water provided to the wood elements ranges from 10 g to 500 g water, more preferably 50 g to 400 g water, or 100 g to 500 g water, even more preferably 100 g to 250 g water, such as 100 g to 150 g water per kg of dry wood elements. Preferably, the wood elements are contacted with 10 g to 500 g water, more preferably 50 g to 400 g water, even more preferably 100 g to 250 g water per kg of dry wood elements, such as 100 g to 150 g water per kg of dry wood elements. This results in better cooling. Preferably, the stream containing wood elements contains such an amount of water per kg of dry wood at the outlet of the humidity chamber and still contains such an amount at the inlet of the evaporation section. Preferably, the gas stream is contacted with a stream containing wood elements having such an amount of water.

[0026] The temperature of the liquid water introduced into the wetting chamber ranges for example from 5°C to 95°C, such as between 10°C and 50°C. Wetting is preferably carried out at ambient pressure, such as between 1 bara and 5 bara. Preferably, the wetting acetylated wood elements have a temperature of 100°C or more, or 120°C or more, such as 150°C or more.

[0027] Preferably, the moistened acetylated wood elements are maintained under low oxygen conditions, such as under inert gas and / or vacuum, from the acetylation step to the entrance of the moist chamber. In the present specification, low oxygen conditions include, for example, an oxygen partial pressure of less than 5 kPa, or less than 2 kPa. This advantageously makes it possible to prevent carbonization of the wood elements. Thus, the moistened acetylated wood elements are at high temperatures, for example 120°C or higher, such as 150°C or higher, from the acetylation step to the entrance of the moist chamber and also at the entrance of the moist chamber.

[0028] The hot acetylated wood elements are then transferred to the wet chuck, for example by gravity flow or using a conveyor. The liquid may be fed through a chamber.

[0029] Preferably, some or all of the water is supplied to the wood elements by spraying, thereby obtaining preferably uniformly moistened wood elements. The spraying also results in limited sensible heat exchange during moistening of the wood elements. Preferably, the wood elements are moistened in a chamber comprising at least one liquid distributor for spraying water. Preferably, the water is sprayed through a nozzle. Optionally, the water is sprayed as droplets having a volume mean diameter of at least 100 μm, or at least 250 μm, such as in the range of 250 μm to 550 μm. In a preferred process, spraying is used to distribute and supply liquid water on the surface of the hot acetylated wood elements and in the gaps between the hot acetylated wood elements, rather than promoting evaporation of the droplets. The spraying may include pouring the water, for example, using a moving head. Optionally, less than 10% by weight of the introduced liquid water evaporates in the moistening chamber, optionally without contacting the acetylated wood elements.

[0030] The cooling further comprises an evaporation step which involves exposing the moistened wood elements to a gaseous medium, in particular a gas stream, usually in an evaporation section. Preferably, the acetylated moistened wood elements at the start of the exposure to such a gas stream and / or at the inlet of such an evaporation section have a temperature of 120° C. or more, such as 150° C. or more. As a result of this exposure, water evaporates from the wood elements and the necessary heat of vaporization is extracted from them, thereby reducing their temperature. Preferably, during the exposure to the gas stream the temperature is reduced by at least

[0031] Preferably, the moistened wood elements are exposed to a gaseous stream such that water vapor is continuously removed from the wood elements. Preferably, the wood elements are exposed to a gaseous stream having a relative humidity of less than 50%, or less than 20%, or less than 10% at the temperature of the moistened wood elements. More particularly, this refers to the moisture content of the gas stream at the inlet of the evaporation section, calculated as a relative humidity based on the temperature of the wood elements at the inlet for the wood elements of the evaporation section. This gas stream at the inlet generally has a temperature at least 10°C, or at least 20°C, or at least 50°C, or at least 100°C lower than the wood elements introduced into the evaporation section.

[0032] The evaporation section is preferably operated at a pressure in the range of 0.5 bara to 5.0 bara, such as between 1 bara and 2 bara, preferably ambient pressure.

[0033] Preferably, the moistened wood elements are conveyed through the evaporation section, preferably continuously. The moistened wood elements may also be exposed to an air flow during immobility. The residence time of the wood elements in the evaporation section is, for example, less than 30 minutes, or less than 15 minutes, or less than 10 minutes, such as in the range of 5 to 10 minutes.

[0034] Preferably, the gas stream has a lower oxygen concentration than the ambient atmosphere so as not to oxidize the hot wet acetylated wood elements. The hot wet acetylated wood elements are, for example, at 120°C or higher, or at 150°C or higher. Thus, in general, the gas stream (regardless of the oxygen content) is contacted with the hot wet acetylated wood elements, for example at 120°C or higher, or at 150°C or higher. Preferably, the gas stream contains less than 10% by volume of oxygen, or less than 5% by volume, or less than 2% by volume, or less than 1% by volume of oxygen at the inlet into the evaporation section. More preferably, the gas stream contains at least 90% by volume, or at least 99% by volume, of inert gases such as nitrogen, carbon dioxide and / or flue gas. Nitrogen is preferred. It is also possible to use oxygen-depleted and / or nitrogen-enriched air compared to the ambient. In view of these preferred compositions of the gas stream, the gas is preferably recirculated.

[0035] Preferably, the evaporation step comprises evaporating the wood elements in an evaporation section through which the wood elements are continuously conveyed. The method includes supplying a gas flow, preferably an inert gas, onto the elements. The conveying direction defines the length of the evaporation section. Thus, a gas flow having a flow direction is introduced into the evaporation section, in particular into the space through which the wooden elements are conveyed. The gas flow is further discharged from the evaporation section. The gas flow generally has a direction essentially parallel, counter-current or perpendicular (cross-current) to the conveying direction of the wooden elements. A cross-current is preferred. The gas flow direction is defined by one or more inlets and one or more outlets for the gas in the evaporation section, which may be separate from the inlets and outlets for the wooden elements.

[0036] In some embodiments, the wood elements are transported horizontally in the evaporation section. The gas flow flows horizontally, for example, from left to right, or from top to bottom, or from bottom to top (and inside) of the evaporation section. Preferably, said evaporation section comprises a conveyor system including an inlet and an outlet for the wood elements, a conveyor, and a shell, the shell providing a space through which the wood elements are transported by a conveyor (such as a belt, chain or screw). The shell is configured to maintain an atmosphere in the space different from the surroundings. Preferably, the evaporation section comprises a number of inlets for the gas flow into the space and a number of outlets for exhausting or extracting gases including water vapor from the space. Preferably, each opening of the multiple inlets and outlets for these gas flows is different in size from the inlets and outlets for the wood elements. Preferably, they are located between the inlets and outlets for the wood elements. Optionally, these openings are provided through the shell. Optionally, these openings are provided in a number of gas conduits provided in the evaporation section, generally extending into said space and connected to openings in said shell or extending to or through inlets or outlets for the wood elements. Preferably, each opening for gas is smaller in size than the inlets and outlets for the wood elements, preferably smaller than the size of the wood elements. Preferably, the inlet gas conduit comprises a manifold for distributing the gas flow over at least a part of the length of the evaporation section. Preferably, each opening and the inlets and outlets for the wood elements are arranged for cross-flow.

[0037] Screw conveyors are preferred because, in addition to feeding, they can provide a homogenization of the wood elements. The screw action can increase the uniformity of the temperature of the wood elements. This can advantageously reduce the residence time. Furthermore, the screw action can allow mixing of the wood elements with the water, for example by shuffling and / or tumbling. The screw action can also allow a redistribution of the water on the wood elements, which can lead in particular from a slow drying of the wood elements to a fast drying of the wood elements. The screw action can also optimize the exposure of the wood elements surface to the dry atmosphere. Horizontal screw conveyors are preferred. A filling level, for example of at least 70%, or at least 80% volumetric filling, can be used to provide a homogenous flow and to prevent shortcuts of the gas flow through low-filled parts. Belt conveyors, tubular belt conveyors, bucket conveyors and chain conveyors can also be used.

[0038] The process preferably includes the step of withdrawing gas from the evaporation section, preferably comprising an inert gas saturated or nearly saturated with water vapor. The gas is preferably recirculated using a recirculation loop connected to the evaporation section. In the recirculation loop, the gas is preferably cooled, water vapor is condensed from the gas, the condensate is preferably removed from the recirculated gas, and the gas is recirculated back to the evaporation section, for example using a fan. Purge gas may be withdrawn and / or gas may be added to control the pressure and oxygen level. Condensation of water vapor in the recirculation loop and removal of condensate at least partially controls the relative humidity and temperature of the recirculated gas stream and maintains the drying capacity of the gas stream. The amount of condensate is also an indication of the effective withdrawal of latent heat of vaporization from the wood elements. Thus, preferably, at least 3% by weight, or at least 5% by weight, of water, based on the weight of the wood elements, is condensed in the recirculation loop, for example per minute, which is formed and preferably Or based on kg of condensate extracted per kg of wood on a dry basis, e.g. per kg of wood elements passing through the outlet of the evaporation section.

[0039] Optionally, the gas stream is passed through the evaporation section multiple times, for example through separate zones arranged in series within the evaporation section, before being subjected to condensation. Optionally, the cross flow within a zone is combined with countercurrent flow through multiple zones.

[0040] Cooling in the recirculation loop preferably involves indirect heat exchange against a cooling fluid. Optionally, the heat of condensation released during condensation is recovered, for example by heat exchange against a fluid stream to be heated. The condensate is also separated from the gas and optionally recycled to a wetting step or disposed of, for example after further processing. The recirculation loop preferably includes a fan for reintroducing the dried gas as a gas stream into the evaporation section. Preferably, the temperature drop of the gas in the recirculation loop is at least 5°C, or at least 10°C. Preferably, the water vapour content of the reintroduced gas stream is less than 50% of the water vapour content when the gas stream was withdrawn from the evaporation section.

[0041] Optionally, the process further comprises storing and / or treating the cooled wood elements. The described cooling may also be used to cool non-acetylated wood elements.

[0042] A further aspect of the invention relates to a cooling system (1). A non-limiting embodiment is shown in Fig. 1. The cooling system (1) comprises a water spray chamber (2), an evaporation section (6) downstream of said water spray chamber (2) with respect to the wood elements, and a gas recirculation loop (11). The water spray chamber (2) comprises an inlet (3) and an outlet (5) for the wood elements (3) and preferably a liquid distributor (4) for spraying water. The downstream evaporation section (6) comprises an inlet (7) and an outlet (13) for the wood elements, a shell (9) and preferably a conveyor (8) for continuously feeding the wood elements through said shell (9) from said inlet (7) to said outlet (13). The outlet (5) is connected to said inlet (7). Preferably, the evaporation section (6) comprises a number of openings (10) for introducing gas into the evaporation section (6) and for withdrawing gas from the evaporation section (6). These openings are connected, for example in fluid communication, to the gas recirculation loop (11). Each opening (10) is different from and separate from the inlets (7) and outlets (13) for the wood elements. Preferably, the evaporation section comprises an inlet conduit (10a) and an outlet conduit (10b) for the gases containing each such opening (10). Each conduit is connected to the gas recirculation loop (11). Each conduit (10a, 10b) is preferably provided in the shell, for example at least partially through the shell or at the inner wall of the shell. The inlet conduit (10a) allows the gases to be distributed over and within at least a part of the space defined by the shell (9). The outlet conduit (10b) allows the gases to be collected, for example over the length of the shell, and to be extracted from the shell (9) into the recirculation loop (11). Both conduits preferably have a wall separate from the shell, said openings (10) being provided in said wall.

[0043] Preferably, the evaporation section (6) is configured in a screw conveyor, the conveyor (8) being at least one screw. Preferably, each opening (10) is arranged in said screw conveyor for cross-flow gas flow relative to the conveying direction of said screw.

[0044] Preferably, the recirculation loop (11) comprises a cooler (12) and a condenser vessel (14), which may be combined with each other, and has an outlet (15) for the condensate. The loop further comprises a recirculation fan (16) for reintroducing the gas flow into the evaporation section. The recirculation loop may further comprise an inlet (17) for gas and optionally a gas purge outlet (not shown). The gas recirculation loop is connected in fluid communication with the evaporation section, in particular with the space inside the shell through which the wood elements are transported.

[0045] Preferably, the gas inlet conduit (10a) is arranged radially opposite the gas outlet conduit (10b). In this description, the radial direction is perpendicular to the length of the evaporation section. Optionally, a gas conduit extends parallel to the conveying direction over at least a portion, preferably more than half, of the length of the evaporation section, said gas conduit comprising a plurality of openings preferably distributed over at least a portion of its length, more preferably over at least half of the length of the evaporation section.

[0046] For example, a manifold can be used as the gas inlet conduit, which advantageously provides good gas distribution across the conveying direction. Optionally, a wedge wire screen can be used as the gas outlet conduit.

[0047] The shell (9) and / or the outlet (13) are preferably configured to maintain an atmosphere different from the ambient atmosphere in the evaporation section, in particular a lower oxygen partial pressure. Further preferred configurations of the cooling system (1) are as described in connection with the process. During operation, the wood elements are acetylated in section (18) and moistened by spraying it with water in the chamber (2). The moistened wood elements are exposed to the gas flow present during conveyance through the evaporation section (6) so that the water evaporates. The water vapor condenses in the condensation vessel (14). Cooled wood elements, such as wood chips, are obtained at the outlet (13).

[0048] The evaporation section optionally comprises one or more evaporation units or one or more zones arranged in a unit or shell that optionally also comprises other zones such as wet zones. The evaporation section optionally comprises one or more evaporation zones, e.g. differing in temperature, pressure and / or composition of the gas stream. The cooling system can be used in a method for producing acetylated wood elements as described. The cooling system can be used in a method for cooling acetylated or non-acetylated wood elements.

[0049] In a still further aspect, the present invention also relates to a wood acetylation plant comprising a wood acetylation section (18) downstream of said cooling system (1), the outlet of which is connected to the inlet for said wood elements (3) of said water spray chamber for feeding said wood elements. Preferably, the wood acetylation plant is configured to feed the wood elements from said acetylation section to said cooling system without exposing the wood elements to ambient air and / or a controlled atmosphere.

[0050] The wood acetylation section comprises a reaction unit such as a chamber, or a vessel, or a conveying unit. Preferably, the wood acetylation section further comprises a heater for heating the acetylation fluid. The wood acetylation section preferably further comprises a part downstream of the reaction chamber configured for removing the acetylation fluid. Preferably, the reaction chamber is designed for continuous feeding of the wood elements from its inlet to its outlet. Optionally, the reaction unit comprises a vertically arranged plug flow reactor. Optionally, the reaction unit comprises a screw conveyor, preferably substantially horizontally arranged (including obliquely), for contacting the wood elements with the acetylation fluid. The plant may comprise an impregnation unit upstream of the acetylation section, configured for vacuum impregnation of the wood elements with the acetylation fluid.

[0051] Although features are described herein as part of the same or separate embodiments for clarity and concise description, the scope of the present invention may include embodiments having all or some combination of the described features. It will be apparent to one skilled in the art that the present invention is not limited to any embodiment described herein, and modifications are possible. The preferred and illustrated features of each process and apparatus and system may be combined with each other. The process of the present invention optionally includes a wood acetylation process or method. The term "comprising" is used to consider the presence of additional elements and / or steps other than those described, and includes preferred embodiments in which the referenced item consists substantially or essentially of the described elements and / or steps. Additionally, the words "a" and "an" shall not be construed as being limited to "only one" and are used to mean "at least one" and do not exclude a plurality. Features not specifically or explicitly described or claimed may additionally be included in the structure of the present invention without departing from the scope of the present invention. The use of expressions such as "preferably" is not intended to limit the present invention.

Claims

1. A process for producing an acetylated wood element, comprising the steps of: acetylating a wood element; and cooling the acetylated wood element, the cooling step including the steps of supplying liquid water to the acetylated wood element to obtain a moistened wood element; and exposing the moistened wood element to a gas flow.

2. 2. The process of claim 1, wherein the gas stream is contacted with a stream of wood elements containing from 10 g to 500 g of water per kg of dry wood elements.

3. 3. The process according to claim 1 or 2, wherein the wood elements have at least two dimensions of at least 0.15 mm.

4. 4. The process according to claim 1, wherein the wood elements comprise one or more selected from the group consisting of wood chips, wood strands, and wood particles.

5. 10. The process according to any of the preceding claims, wherein the gas stream is contacted with moistened wood elements having a temperature of at least 120°C.

6. 10. The process according to any of the preceding claims, wherein the temperature of the wood elements is reduced by at least 30°C during exposure of the moistened wood elements to the gas flow.

7. contacting the gas stream with a stream of wood elements containing from 100 g to 250 g of water per kg of dry wood elements; The wood elements include one or more selected from the group consisting of wood chips, wood strands, and wood particles; contacting said gas stream with moistened wood elements having a temperature of at least 120°C; 2. The process according to claim 1, wherein the temperature of the wood elements is reduced by at least 30°C during exposure of the moistened wood elements to the gas flow.

8. 10. The process of any preceding claim, wherein the gas stream contains less than 5% by volume of oxygen.

9. 10. The process of any preceding claim, comprising conveying the moistened wood elements through an evaporation section during exposure to said gas flow.

10. 2. The process according to any of the preceding claims, wherein the cooling step comprises spraying water onto the acetylated wood elements to obtain uniformly moistened wood elements, followed by supplying, in the evaporation section, a gas flow containing less than 5% by volume of oxygen onto the moistened wood elements.

11. The process according to claim 10, wherein the gas flow is supplied in cross-flow to the wood elements.

12. 12. The process according to claim 11, wherein the evaporation section comprises a screw section, the screw action of which provides feeding and homogenization of the wood elements.

13. 10 g to 500 g of liquid water per kg of dry wood elements for wood elements having a temperature of 150° C. or higher, an acetyl content of more than 20% and a residual acid content of less than 0.5% by weight; 10. A process according to any of the preceding claims, preferably spraying between 100g and 500g of liquid water per kg of dry wood elements to obtain uniformly moistened wood elements.

14. 10. The process according to any of the preceding claims, wherein the process further comprises the step of storing and / or processing the cooled wood elements.

15. 15. The process of any of claims 8 and 10 to 14, further comprising the step of recirculating gas of the gas stream through a recirculation loop connected to the evaporation section, wherein water vapor is condensed within the recirculation loop and the condensate is withdrawn from the recirculation loop.

16. 16. The process according to claim 15, wherein in the recirculation loop at least 3% by weight of water is condensed, based on the dry weight of the wood elements.

17. A cooling system comprising a water spray chamber, an evaporation section downstream of the water spray chamber and a gas recirculation loop, the water spray chamber comprising an inlet for wood elements, a liquid distributor for spraying water and an outlet for wood elements, the evaporation section comprising an inlet and an outlet for wood elements, a conveyor for continuously feeding wood elements from the inlet to the outlet, an inlet conduit having at least one opening for introducing gas into the evaporation section and an outlet conduit having at least one opening for extracting gas from within the evaporation section, each of said conduits being connected to the gas recirculation loop, each of said openings of each of said conduits being different from the inlet and outlet for the wood elements.

18. 20. The cooling system of claim 17, wherein the recirculation loop includes a possibly combined cooler and condenser vessel, an outlet for condensate, and a recirculation fan.

19. 19. A wood acetylation plant comprising a wood acetylation section and downstream thereof a cooling system as claimed in claim 17 or 18, wherein an outlet of the wood acetylation section is connected to an inlet for the wood elements of the water spray chamber.

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