NZ749855B2 - Cooling acetylated wood elements - Google Patents
Cooling acetylated wood elements Download PDFInfo
- Publication number
- NZ749855B2 NZ749855B2 NZ749855A NZ74985517A NZ749855B2 NZ 749855 B2 NZ749855 B2 NZ 749855B2 NZ 749855 A NZ749855 A NZ 749855A NZ 74985517 A NZ74985517 A NZ 74985517A NZ 749855 B2 NZ749855 B2 NZ 749855B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- wood elements
- wood
- elements
- process according
- gas flow
- Prior art date
Links
- 239000002023 wood Substances 0.000 title claims abstract description 278
- 238000001816 cooling Methods 0.000 title claims abstract description 64
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 79
- 238000000034 method Methods 0.000 claims abstract description 45
- 238000006640 acetylation reaction Methods 0.000 claims abstract description 39
- 239000007788 liquid Substances 0.000 claims abstract description 28
- 238000004519 manufacturing process Methods 0.000 claims abstract description 10
- 230000000397 acetylating Effects 0.000 claims abstract description 9
- 239000007789 gas Substances 0.000 claims description 102
- 238000001704 evaporation Methods 0.000 claims description 71
- 239000007921 spray Substances 0.000 claims description 15
- 239000001301 oxygen Substances 0.000 claims description 12
- 229910052760 oxygen Inorganic materials 0.000 claims description 12
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 12
- 238000005507 spraying Methods 0.000 claims description 11
- 238000009833 condensation Methods 0.000 claims description 9
- 230000005494 condensation Effects 0.000 claims description 9
- 239000002245 particle Substances 0.000 claims description 8
- 239000002253 acid Substances 0.000 claims description 5
- 238000000265 homogenisation Methods 0.000 claims description 2
- 230000003134 recirculating Effects 0.000 claims description 2
- 125000000218 acetic acid group Chemical group C(C)(=O)* 0.000 claims 1
- 238000004642 transportation engineering Methods 0.000 claims 1
- QTBSBXVTEAMEQO-UHFFFAOYSA-N acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 27
- 238000009736 wetting Methods 0.000 description 18
- 239000012530 fluid Substances 0.000 description 12
- WFDIJRYMOXRFFG-UHFFFAOYSA-N acetic anhydride Chemical compound CC(=O)OC(C)=O WFDIJRYMOXRFFG-UHFFFAOYSA-N 0.000 description 10
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 229910052799 carbon Inorganic materials 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 5
- 238000010924 continuous production Methods 0.000 description 5
- 238000001035 drying Methods 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 241000196324 Embryophyta Species 0.000 description 4
- 125000002777 acetyl group Chemical group [H]C([H])([H])C(*)=O 0.000 description 4
- 239000011261 inert gas Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-M acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 3
- 239000003570 air Substances 0.000 description 3
- 239000000835 fiber Substances 0.000 description 3
- 238000004128 high performance liquid chromatography Methods 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000000523 sample Substances 0.000 description 3
- 239000011122 softwood Substances 0.000 description 3
- 241000218657 Picea Species 0.000 description 2
- 239000012223 aqueous fraction Substances 0.000 description 2
- 238000010923 batch production Methods 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 239000011121 hardwood Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000005470 impregnation Methods 0.000 description 2
- 238000010926 purge Methods 0.000 description 2
- 238000007127 saponification reaction Methods 0.000 description 2
- 241000894007 species Species 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 238000009834 vaporization Methods 0.000 description 2
- 241000219498 Alnus glutinosa Species 0.000 description 1
- 241001564395 Alnus rubra Species 0.000 description 1
- 241000219495 Betulaceae Species 0.000 description 1
- 240000001200 Eucalyptus globulus Species 0.000 description 1
- 235000004694 Eucalyptus leucoxylon Nutrition 0.000 description 1
- 235000010705 Eucalyptus maculata Nutrition 0.000 description 1
- 235000009683 Eucalyptus polybractea Nutrition 0.000 description 1
- 235000009687 Eucalyptus sargentii Nutrition 0.000 description 1
- 240000000731 Fagus sylvatica Species 0.000 description 1
- 241000218595 Picea sitchensis Species 0.000 description 1
- 235000008331 Pinus X rigitaeda Nutrition 0.000 description 1
- 241000018646 Pinus brutia Species 0.000 description 1
- 235000011613 Pinus brutia Nutrition 0.000 description 1
- 241001236212 Pinus pinaster Species 0.000 description 1
- 235000005105 Pinus pinaster Nutrition 0.000 description 1
- 241000218621 Pinus radiata Species 0.000 description 1
- 235000008577 Pinus radiata Nutrition 0.000 description 1
- 241000218626 Pinus sylvestris Species 0.000 description 1
- 235000008582 Pinus sylvestris Nutrition 0.000 description 1
- MFBOGIVSZKQAPD-UHFFFAOYSA-M Sodium butyrate Chemical compound [Na+].CCCC([O-])=O MFBOGIVSZKQAPD-UHFFFAOYSA-M 0.000 description 1
- 229920002522 Wood fibre Polymers 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 239000012080 ambient air Substances 0.000 description 1
- 235000018185 birch Nutrition 0.000 description 1
- 235000018212 birch Nutrition 0.000 description 1
- CURLTUGMZLYLDI-UHFFFAOYSA-N carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000004320 controlled atmosphere Methods 0.000 description 1
- 239000000112 cooling gas Substances 0.000 description 1
- 239000000110 cooling liquid Substances 0.000 description 1
- 230000003247 decreasing Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 235000001612 eucalyptus Nutrition 0.000 description 1
- 235000001617 eucalyptus Nutrition 0.000 description 1
- 235000001621 eucalyptus Nutrition 0.000 description 1
- 235000006356 eucalyptus Nutrition 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 230000014509 gene expression Effects 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000006011 modification reaction Methods 0.000 description 1
- 235000005227 red mallee Nutrition 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Abstract
The invention pertains to a process for the production of acetylated wood elements, a cooling system and a wood acetylation plant are described. There is a need for better cooling methods for in particular acetylated wood elements and processes incorporating such methods. The inventive process for the production of acetylated wood elements, comprises acetylating wood elements and cooling the acetylated wood elements by supplying liquid water to the acetylated wood elements to provide wetted wood elements and exposing the wetted wood elements to a gas flow thereby providing for evaporative cooling of hot acetylated wood elements. he production of acetylated wood elements, comprises acetylating wood elements and cooling the acetylated wood elements by supplying liquid water to the acetylated wood elements to provide wetted wood elements and exposing the wetted wood elements to a gas flow thereby providing for evaporative cooling of hot acetylated wood elements.
Description
Title: COOLING ACETYLATED WOOD ELEMENTS
Field of the Invention
The invention pertains to a process for the production of acetylated
wood elements comprising a cooling step. In the cooling step, wood elements
are cooled from a temperature preferably in the range of 120 to 180 °C to
preferably less than 60 °C.
Background of the Invention
Acetylation of wood has long been recognized as a method to
improve the durability of otherwise non-durable softwood species.
Acetylation can be used to improve wood properties, such as hardness and
dimensional stability. Background references for such processes include
and . Acetylating wood generally involves
contacting wood elements with acetylation fluid comprising acetic anhydride
and/or acetic acid while heating. The acetylation fluid is generally
recirculated.
Acetylation of wood provides hot acetylated wood elements with a
temperature of, typically, at least 120 °C or at least 150 °C, often between
160 and 180 °C. The acetylated wood elements are hence too hot for storage
and further handling. Storage of acetylated wood elements with such
temperatures involves a risk of smoldering (flameless combustion), even
while the wood elements are slowly cooling against ambient. Cooling of the
acetylated wood elements is therefore necessary, in particular if the
acetylated wood elements are not immediately further processed.
However, current cooling methods are unsatisfactory for
(acetylated) wood elements. The low heat transfer coefficient of wood
elements makes cooling challenging. In particular for gas cooling and
cooling with indirect heat exchange, the low heat transfer coefficient causes
problems. 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 provide for
homogenous and fast cooling in view of the very poor heat transfer from
cooled equipment to wood elements. A further method of submerging
acetylated wood elements in a cooling bath is not attractive because this
would result in wet acetylated wood elements. The cooled wood elements
may even be dripping. Moreover, there is a risk of leaching of residual
acetylation fluid from the acetylated wood elements into the cooling liquid.
Accordingly, there is a need for better cooling methods for in
particular acetylated wood elements and processes incorporating such
methods. Desirably, these methods are fast and efficient and do not involve
the above-mentioned disadvantages of prior art methods. It is an object of
the present invention to go at least some way to meeting this need; and/or to
at least provide the public with a useful choice.
JP H06-198610 describes a process wherein wooden fiber obtained
by shredding wood is acetylated in a liquid phase, then this acetylated
wooden fiber is accumulated and formed in one piece.
Summary of the Invention
In order to better address one or more of the foregoing desires, the
invention provides, in an aspect, a process for the production of acetylated
wood elements, comprising acetylating wood elements and cooling the
acetylated wood elements, wherein 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, thereby providing for
evaporative cooling of hot acetylated wood elements, wherein the
temperature of the wood elements decreases by at least 30 °C during said
exposing of the wetted wood elements to a gas flow.
Described is a process for the production of acetylated wood
elements, comprising acetylating wood elements and cooling the acetylated
wood elements, wherein 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, thereby providing for evaporative
cooling of hot acetylated wood elements.
Described is a process for the production of acetylated wood
elements, comprising acetylating wood elements and cooling the acetylated
wood elements wherein 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.
Described is a cooling system comprising a water spray chamber,
an evaporation section downstream of said water spray chamber, and a gas
recirculation loop, wherein said water spray chamber comprises an inlet for
wood elements, a liquid distributor for spraying water, and an outlet for
wood elements, and wherein the evaporation section comprises an inlet and
an outlet for wood elements, a conveyor for continuously transporting wood
elements from said inlet to said outlet, and an inlet conduit having at least
one opening for introducing gas into said evaporation section and an outlet
conduit having at least one opening for withdrawing gas from said
evaporation section, wherein said conduits are coupled to said gas
recirculation loop and wherein said openings of said conduits are different
from said inlet and outlet for wood elements.
The invention also relates to a wood acetylation plant comprising a
wood acetylation section and downstream thereof a cooling system, wherein
said cooling system comprises a water spray chamber, an evaporation
section downstream of said water spray chamber, and a gas recirculation
loop, wherein said water spray chamber comprises an inlet for wood
elements, a liquid distributor for spraying water, and an outlet for wood
elements, and wherein the evaporation section comprises an inlet and an
outlet for wood elements, a conveyor for continuously transporting wood
elements from said inlet to said outlet, and an inlet conduit having at least
one opening for introducing gas into said evaporation section and an outlet
conduit having at least one opening for withdrawing gas from said
evaporation section, wherein said conduits are coupled to said gas
recirculation loop and wherein said openings of said conduits are different
from said inlet and outlet for wood elements, wherein the outlet of said wood
acetylation section is coupled to the inlet for wood elements of said water
spray chamber.
In the description in this specification reference may be made to
subject matter which is not within the scope of the appended claims. That
subject matter should be readily identifiable by a person skilled in the art
and may assist in putting into practice the invention as defined in the
appended claims.
Brief description of the drawings
Fig. 1 shows a process scheme for a non-limiting illustrative
embodiment of a process for the cooling of wood elements according to the
invention.
Detailed description
The invention generally relates to the production of acetylated
wood elements and to the cooling of acetylated wood elements. The
invention is in an aspect based on the judicious insight that a combination
of wetting of hot acetylated wood elements with a liquid and evaporating the
liquid from the wetted wood elements provides efficient cooling of acetylated
wood elements. Accordingly, the process comprises supplying a liquid,
preferably water, to the acetylated wood elements to provide 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 which is in
contact with the wood elements, resulting in a temperature decrease of the
wood elements. In the present invention, the wetting and exposing are used
to provide for evaporative cooling of hot acetylated wood elements. This may
be contrasted to for example air conditioning methods using evaporative
cooling to cool air.
The process comprises acetylating wood elements. The step of
acetylating wood elements generally involves contacting wood elements with
acetylation fluid comprising acetic anhydride and/or acetic acid. During the
contacting, the temperature of the wood elements increases to a
temperature in the range of 120 to 180 °C, more preferably to a final
temperature in the range of 150 to 180 °C.
The acetylation step is preferably a continuous process step. The
process can be a batch or continuous process or comprise 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.
Preferably, the acetylation comprises removal of excess acetylation
liquid from the acetylated wood elements, for example under reduced
pressure. Preferably, the process comprises a finishing step between the
acetylation and the cooling step. The finishing step generally has the
purpose of reducing the content of non-reacted acetic anhydride and formed
acetic acid of the wood elements. A finishing step preferably comprises
exposing acetylated wood elements to reduced pressure and/or high
temperatures, such as about 130 °C or higher. Frequently, the wood
elements as obtained from a finishing step have a temperature of more than
120 °C, such as more than 150 °C.
Preferably, the acetylated and optionally finished wood elements
have a temperature of 120 °C or more, such as 150 °C or more, and
preferably an acetyl content of more than 15 wt.% or more than 17 wt.% or
more than 20% or more than 21 wt.%; preferably at its geometrical centre.
Preferably the acetylated wood elements also have a residual acid content of
less than 1 wt.%, or less than 0.9 wt.% or less than 0.5 wt.%, on dry basis,
for example obtained by a finishing step. Preferably, the cooled wood
elements have such acetyl content and/or residual acid content.
The acetyl content of the wood can be determined as follows.
Samples are ground to wood particles. From these samples residual trace
amounts of acetic acid and/or acetic anhydride are removed by washing with
water and subsequent drying at 103±2 °C for between 14 to 24 hrs. After
weighing these dried samples, the acetyl groups are released from the wood
in the form of acetate ions by saponification with sodium hydroxide solution
at elevated temperature, typically 90° C. This saponification reaction runs
for 4 hrs, with stirring every 15 minutes. The acetate ions are quantified by
means of high-pressure liquid chromatography (HPLC), after calibrating
this HPLC with standard acetate solutions and using sodium butyrate as
internal reference.
The residual acetic acid (RA) content is a measure of the residual,
non-bound acetic acid contained in the wood (including acetic acid formed by
hydrolysis of residual, non-bound acetic anhydride). Acetic acid may also
originate from the wood itself, therefore the RA measures both the original
acetic acid and the acetic acid left from the acetylation reaction. For
determining the residual acid content (RA) a well-defined amount of 3-5 g of
sample material is shaken in demineralised water for 1 hr. After this
extraction step the sample is separated from the water fraction by filtration.
Subsequently this water fraction is titrated with a known sodium hydroxide
(NaOH) solution, using phenolphthaleine as an indicator, from which the
residual acid concentration of the sample can be calculated.
The process comprises 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 to ambient
temperature, generally above 5 °C. Preferably, the temperature of the wood
elements decreases by at least 30 °C or at least 50 °C, more preferably by at
least 80 °C during said cooling, more in particular during the exposure to
the gas flow.. Preferably, the wood elements at the outlet of an evaporation
section have a temperature below 100 °C or below 80 °C, more preferably
below 60 °C or below 40 °C, for example ambient temperature. In case an
atmosphere different from ambient is maintained in an evaporation section,
e.g. an inert atmosphere, then an outlet of an evaporation section is
optionally characterized by transfer of wood elements to 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.
The cooled wood elements can for instance have a water content of
less than 35 wt.%, for example in the range of 1 to 8 wt.% or 5 to 10 wt.%, in
particular at the outlet of an evaporation section.
The invention generally relates to producing acetylated wood
elements. In particular wood chips, strands and particles are challenging to
cool compared to e.g. wood fibres in view of the lower specific surface area
(m² surface area / kg wood).
The wood elements 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 invention are for example used for
the acetylation of durable and non-durable hardwoods, as well as durable
and nondurable softwoods. The wood elements preferably belong to non-
durable wood species such as non-durable hardwoods, or soft woods, for
example, coniferous trees, typically spruce, pine or fir. Preferred types of
wood are spruce, sitka spruce, maritime pine, scots pine, radiata pine,
eucalyptus, red alder, European alder, beech and birch.
Typical dimensions of some types of wood elements are given in the
following table 1. Preferred are wood chips, strands, and particles as defined
in table 1 and optionally slivers. Preferably, the wood elements consist of
one of the types of wood elements as defined in table 1, to achieve more
homogenous cooling. In some embodiments, wood particles have a width
and/or thickness of 1.0 to 5.0 mm. Preferably, the wood elements have at
least two dimensions (in orthogonal directions) of at least 0.15 mm.
Table 1: Typical dimensions of types of wood elements
length
width (mm) thickness (mm)
Type of wood element (mm)
from to from to from to
Chips 5 75 5 50 1.5 25
Strands 20 1205 40 0.25 1.5
Splinters (slivers) 5 75 0.15 0,5 0.15 0.5
Particles 1.5 20 0.15 5 0.15 5
Fibre bundles 1.5 25 0.15 0.5 0.15 0.5
Fibres 1 5 0.05 0.1 0.05 0.1
The cooling comprises supplying liquid water to the wood elements
to provide wetted wood elements. The water is optionally supplied as liquid
stream comprising other components, or as liquid stream essentially
consisting of water, such as for more than 99 wt.%.
Preferably, liquid water is provided on the surface of the wood
elements and preferably the wood elements are brought in contact with
liquid water. Preferably, the process comprises introducing wood elements
into a wetting chamber and introducing liquid water into the wetting
chamber. In some embodiments, the wetting does not involve condensation
in the wetting chamber. In some optional embodiments, the process for
example does not comprise introducing steam into the wetting chamber in
contact with wood elements. Preferably, the amount of liquid water supplied
to the wood elements is in the range of 10 to 500 g water, more preferably 50
to 400 g water, or 100 – 500 g water, even more preferably 100 to 250 g
water, such as 100 to 150 g water per 1 kg dry wood elements. Preferably,
the wood elements are contacted with 10 to 500 g water per 1 kg dry wood
elements, more preferably 50 to 400 g water, even more preferably 100 to
250 g water, such as 100 to 150 g water per 1 kg dry wood elements. This
provides for better cooling. Preferably, a stream comprising wood elements
at an outlet of the wetting chamber comprises such amounts of water per kg
dry wood, and still comprises such amounts at the inlet of the evaporation
section. Preferably, the gas flow is contacted with a stream comprising wood
elements having such amounts of water.
The temperature of the liquid water as introduced into the wetting
chamber is for example in the range of 5 to 95 °C, such as between 10 and
50 °C. The wetting is preferably performed at ambient pressure such as
between 1 and 5 bara. Preferably, the wetted acetylated wood elements have
a temperature of 100 °C or more, or 120 °C or more, such as 150 °C or more.
Preferably, wetted acetylated wood elements are maintained under
low oxygen conditions, such as under inert gas and/or vacuum, from the
acetylation step to inlet of the wetting chamber. Herein, low oxygen
conditions include an oxygen partial pressure of for example less than 5 kPa
or less than 2 kPa. This advantageously allows for preventing charring of
the wood elements. Accordingly, the wetted acetylated wood elements are
hot, e.g. 120 °C or more, such as 150 °C or more, from the acetylation step to
inlet of the wetting chamber and also at the inlet of the wetting chamber.
The hot acetylated wood elements may be transported through the
wetting chamber for instance by gravity flow or using a conveyor.
Preferably, a part or all of the water is supplied to the wood
elements by spraying, preferably to provide homogenously wetted wood
elements. Spraying also provides for limited sensible heat exchange during
wetting of wood elements. Preferably, the wood elements are wetted in a
chamber comprising at least one liquid distributor for spraying water.
Preferably, the water is sprayed through nozzles. Optionally, 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 to 550 μm. In the preferred
process, spraying is used for distributing and providing liquid water over
the surfaces of the hot acetylated wood elements and in the voids between
hot acetylated wood elements, rather than to promote evaporation of
droplets. Spraying may include showering water, for example with a moving
head. Optionally, less than 10 wt.% of the introduced liquid water
evaporates in the wetting chamber, optionally without contact with
acetylated wood elements.
The cooling further comprises an evaporation step comprising
exposing the wetted wood elements to a gaseous medium, in particular to a
gas flow, usually in an evaporation section. Preferably, the acetylated
wetted wood elements at the beginning of such exposure to the gas flow
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 required heat of vaporisation is
withdrawn from the wood elements, thereby decreasing the temperature of
the wood elements. Preferably, during the exposure to the gas flow, the
temperature decreases by at least
Preferably, the wetted wood elements are exposed to a gas flow
such that water vapour is continuously removed from the wood elements.
Preferably, the wood elements are exposed to a gaseous flow having a
relative humidity of less than 50% or less than 20% or less than 10% at the
temperature of the wetted wood elements. More in particular, this refers to
water content of the gas flow at an inlet of the evaporation section,
calculated as relative humidity based on the temperature of the wood
elements at the inlet for wood elements of the evaporation section. The gas
flow 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.
The evaporation section is preferably operated at a pressure in the
range of 0.5 to 5.0 bara, such as between 1 and 2 bara, preferably at
ambient pressure.
Preferably, the wetted wood elements are conveyed through an
evaporation section, preferably in a continuous manner. The wetted wood
elements may also be exposed to an air flow while not moving. 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.
Preferably, the gas flow has a lower oxygen concentration than
ambient atmosphere, so as to not oxidise the hot wetted acetylated wood
elements. The hot wetted acetylated wood elements are e.g. 120 °C or more,
or 150 °C or more.. Hence, generally, the gas flow (irrespective of oxygen
content) is contacted with hot wetted acetylated wood elements of e.g. 120
°C or more, or 150 °C or more. . Preferably, the gas flow comprises, at the
inlet into the evaporation section, less than 10 % oxygen by volume, or less
than 5 % or less than 2% or less than 1% oxygen by volume. More
preferably, the gas flow comprises at least 90 % or at least 99 % by volume
of inert gas such as nitrogen, carbon dioxide and/or flue gas. Nitrogen is
preferred. Also possible is using oxygen depleted and/or nitrogen enriched
air, compared to ambient. In view of these preferred compositions of the gas
flow, the gas is preferably recirculated.
Preferably, the evaporation step comprises providing a gas flow
over the wood elements, preferably of inert gas, in an evaporation section
wherein the wood elements are conveyed in a continuous manner. The
conveying direction defines the length of the evaporation section. Hence, a
gas flow having a flow direction is introduced in the evaporation section, in
particular into the space through which the wood elements are conveyed.
The gas flow is further vented from the evaporation section. The gas flow
generally has a direction essentially co-current, counter-current or
perpendicular (cross-current flow) to the conveying direction of the wood
elements. Cross-current flow is preferred. The gas flow direction is defined
by the one or more inlets and one or more outlets for gas of the evaporation
section, which may be separate from the inlet and outlet for wood elements.
In some embodiments, the wood elements are horizontally
conveyed in the evaporation section. The gas flow is for example horizontally
from side to side, or from top to bottom, or from bottom to top of (and inside)
the evaporation section. Preferably, said evaporation section comprises a
conveyor system comprising the inlet and outlet for wood elements, a
conveyor and a shell, wherein the shell provides a space through which
wood elements are conveyed by the conveyor (such as a belt, chain or screw).
The shell is configured for maintaining an atmosphere in the space different
from ambient. Preferably, the evaporation section comprises inlets for the
gas flow into the space and outlets for venting or withdrawing gas
comprising water vapour from the space. Preferably, the openings of these
inlets and outlets for gas flow are different in size to the inlet and outlet for
wood elements. Preferably, they are positioned between the inlet and outlet
for wood elements. Optionally, these openings are provided through the
shell. Optionally, these openings are provided in gas conduits provided in
the evaporation section and generally extending in said space and connected
to an opening in said shell, or extending to or through an inlet or outlet for
wood elements. Preferably, the openings for gas have a smaller size than the
inlet and outlet for wood elements, and preferably have a size smaller than
the size of the wood elements. Preferably, the inlet gas conduit comprises a
manifold for distributing the gas flow over at least part of the length of the
evaporation section. Preferably the openings and the inlet and outlet for
wood elements are arranged for cross-flow.
A screw conveyor is preferred, as this may provide for
homogenisation of the wood elements, in addition to transport. The screw
action may provide for increased homogeneity of the temperature of the
wood elements. This may advantageously allow for a reduced residence
time. Moreover, the screwing movement may allow for mixing of wood
elements and water, such as by shuffling and/or tumbling. The screw
movement may also allow for redistribution of water over the wood
elements, in particular from slowly drying wood elements to quickly drying
wood elements. The screwing movement may also provide for optimising
exposure of the wood element surfaces to the drying atmosphere. A
horizontal screw conveyor is preferred. A filling level of for example at least
70% or at least 80% volumetric fill can be used to give homogeneous flow
and prevent shortcutting of gas flow through low fill sections. Belt
conveyors, tubular belt conveyors, bucket conveyors, and chain conveyors
can also be used.
The process preferably comprises withdrawing gas comprising inert
gas, preferably saturated or nearly saturated with water vapour, from an
evaporation section. The gas is preferably recirculated using a recirculation
loop coupled to the evaporation section. In the recirculation loop, the gas is
preferably cooled, water vapour is condensed from the gas, the condensate is
preferably removed from the recirculating gas, and the gas is recirculated
back to the section using e.g. a fan. A purge of gas may be withdrawn and/or
gas may be added in order to control pressure and oxygen level. By
condensation of water vapour in the recirculation loop and removal of
condensate, the relative humidity and temperature of the recirculated gas
stream are at least partly controlled and the drying capacity of the gas flow
is maintained. The amount of condensate also indicates the effective
withdrawal of the latent heat of vaporisation from the wood elements.
Accordingly, preferably, at least 3 wt.% or at least 5 wt.% water is
condensed in the recirculation loop based on weight of the wood elements,
e.g. per minute, based on kg condensate formed and preferably withdrawn
per kg wood on dry basis, e.g. per kg wood elements passing through the
outlet of the evaporation section.
Optionally, the gas flow is passed through the evaporation section
multiple times before being subjected to condensation, for example through
separate zones arranged in series in the evaporation section. Optionally,
cross-current flow within a zone is combined with overall counter-current
flow through multiple zones.
The cooling in the recirculation loop preferably comprises indirect
heat exchange against a cooling fluid. Optionally, the heat of condensation
released during the condensation is recovered e.g. by heat exchange against
a fluid stream to be heated. Furthermore, the condensate is separated from
the gas and is optionally recycled to the wetting step, or for example further
processed and disposed of. The recirculation loop preferably comprises a fan
for reintroducing the dried gas as gas flow into the evaporation section.
Preferably, the temperature decrease 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 flow is less than 50% of the water vapour content as the
gas flow withdrawn from the evaporation section.
Optionally, the process further comprises storing and/or handling
the cooled wood elements. The described cooling may also be used for cooling
wood elements that are not acetylated.
Also described is a cooling system (1). A non-limiting embodiment
is shown in Figure 1. The cooling system (1) comprises a water spray
chamber (2), an evaporation section (6) downstream, with respect to wood
elements, of said water spray chamber (2), and a gas recirculation loop (11).
The water spray chamber (2) comprises an inlet (3) and an outlet (5) for
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 wood elements, a shell (9), and preferably a conveyor (8) for
continuously transporting wood elements through said shell (9) from said
inlet (7) to said outlet (13). Said outlet (5) is connected to said inlet (7).
Preferably, the evaporation section (6) is provided with openings (10) for
introducing gas into evaporation section (6) and withdrawing gas from
evaporation section (6). These openings are coupled to said gas recirculation
loop (11), e.g. in fluid communication. The openings (10) are different and
spaced apart from the inlet (7) and outlet (13) for wood elements. Preferably,
the evaporation section comprises an inlet conduit (10a) and an outlet
conduit (10b) for gas comprising such openings (10). The conduits are
coupled to the gas recirculation loop (11). The conduits (10a, 10b) are
provided preferably in said shell, e.g. at least partly through said shell or at
the inside wall of said shell. The inlet conduit (10a) allows for distributing
gas over and into at least part of the space defined by the shell (9). The
outlet conduit (10b) allows for collecting gas, e.g. over the length of the shell,
and withdrawing gas from the shell (9) into the recirculation loop (11). Both
conduits preferably have a wall distinct from the shell, wherein said
openings (10) are provided in said wall.
Preferably, the evaporation section (6) is constructed in a screw
conveyor, wherein the conveyor (8) is at least one screw. Preferably openings
(10) are arranged in said screw conveyor for flow of gas in cross-flow with
the conveying direction of said screw.
Preferably, said recirculation loop (11) comprises a cooler (12) and
a condensation vessel (14), which may also be combined with each other,
and has an outlet for condensate (15). Preferably the recirculation loop
further comprises a recirculation fan (16) for reintroducing the gas flow into
the evaporation section. The recirculation loop may further comprise an
inlet for gas (17) and optionally a gas purge outlet (not shown). The gas
recirculation loop is coupled in fluid communication with said evaporation
section, in particular with the space inside said shell through which wood
elements are conveyed.
Preferably, the gas inlet conduit (10a) is arranged radially opposed
to the gas outlet conduit (10b). Herein, 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 part, preferably more than
half, of the length of the evaporation section, wherein the gas conduit is
provided with openings, preferably distributed over at least part of its
length and more preferably over at least half of the length of the
evaporation section.
For example a manifold can be used as a gas inlet conduit. This
advantageously provides for introducing the gas with a good distribution
over the conveying direction. Optionally, a wedge-wire screen is used as a
gas outlet conduit.
The shell (9) and/or outlet (13) are preferably configured for
maintaining an atmosphere different from ambient atmosphere in the
evaporation section, in particular for maintaining a lower oxygen partial
pressure. Further preferences for the cooling system (1) are as described in
connection with the process. In operation, wood elements are acetylated in
section (18) and wetted by spraying water on it in chamber (2). The wetted
wood elements are exposed to a gas flow being while conveyed through the
evaporation section (6) such that water evaporates. Water vapour condenses
in condensation vessel (14). Cooled wood elements such as wood chips are
obtained at the outlet (13).
An evaporation section optionally comprises one or more
evaporation units, or optionally comprises one or more zones provided in a
unit or shell which also comprises other zones, such as a wetting zone. The
evaporation section optionally comprises one or more evaporation zones
which for example have different temperature, pressure, and/or composition
of gas flow. 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 of cooling wood elements that are acetylated or are not acetylated.
In yet a further aspect, the invention also relates to a wood
acetylation plant comprising a wood acetylation section (18) and
downstream thereof said cooling system (1), wherein the outlet of said wood
acetylation section is coupled for transport of wood elements to said inlet (3)
for wood elements of said water spray chamber. Preferably, the wood
acetylation plant is configured for transport of wood elements from said
acetylation section to said cooling system without exposure of the wood
elements to ambient air and/or under controlled atmosphere.
The wood acetylation section comprises a reaction unit, such as a
chamber or vessel or conveying unit. Preferably, said wood acetylation
section further comprises a heater for heating acetylation fluid. The wood
acetylation section preferably further comprises a part downstream of said
reaction chamber configured for removing acetylation fluid. Preferably, said
reaction chamber is designed so as to provide for continuous transport of
wood elements from the inlet to an outlet thereof. Optionally, said reaction
unit comprises a vertically arranged plug flow reactor. Optionally, said
reaction unit comprises a screw conveyor, preferably substantially
horizontally arranged (including oblique), for contacting wood elements with
acetylation fluid. The plant may comprise an impregnation unit upstream of
the acetylation section configured for vacuum impregnation of wood
elements with acetylation fluid.
For the purpose of clarity and a concise description features are
described herein as part of the same or separate embodiments, however, it
will be appreciated that the scope of the invention may include
embodiments having combinations of all or some of the features described.
It will be clear to the skilled person that the invention is not limited to any
embodiment herein described and that modifications are possible. The
preferred and exemplified features of the processes and the apparatus and
system can be combined with each other. The process of the invention
optionally comprises a wood acetylation process or method. The term
“comprising” is used to allow for the presence of further elements and/or
steps than those recited; and encompasses preferred embodiments wherein
the referenced item substantially or essentially consists, or consist, of the
recited elements and/or steps. Furthermore, the words ‘a’ and ‘an’ shall not
be construed as limited to ‘only one’, but instead are used to mean ‘at least
one’, and do not exclude a plurality. Features that are not specifically or
explicitly described or claimed may be additionally included in the structure
of the invention without departing from its scope. The use of expressions
like "preferably” is not intended to limit the invention.
In this specification where reference has been made to patent
specifications, other external documents, or other sources of information,
this is generally for the purpose of providing a context for discussing the
features of the invention. Unless specifically stated otherwise, reference to
such external documents is not to be construed as an admission that such
documents, or such sources of information, in any jurisdiction, are prior art,
or form part of the common general knowledge in the art.
Claims (21)
1. A process for the production of acetylated wood elements, comprising acetylating wood elements and cooling the acetylated wood elements, wherein the cooling comprises: supplying liquid water to the acetylated wood elements to provide wetted wood elements and exposing the 5 wetted wood elements to a gas flow, thereby providing for evaporative cooling of hot acetylated wood elements, wherein the temperature of the wood elements decreases by at least 30 °C during said exposing of the wetted wood elements to a gas flow. 10
2. A process according to claim 1, wherein the gas flow is contacted with a stream of wood elements containing 10 to 500 g water per 1 kg dry wood elements.
3. A process according to claim 1 or 2, wherein the wood elements 15 have at least two dimensions of at least 0.15 mm.
4. A process according to any one of claims 1-3, wherein the wood elements comprise one or more selected from the group consisting of wood chips, wood strands, and wood particles.
5. A process according to any one of the preceding claims, wherein the gas flow is contacted with wetted wood elements having a temperature of at least 120 °C. 25
6. A process according to claim 1, wherein: - the gas flow is contacted with a stream of wood elements containing 100 to 250 g water per 1 kg dry wood elements; - the wood elements comprise one or more selected from the group consisting of wood chips, wood strands, and wood particles; and - the gas flow is contacted with wetted wood elements having a temperature of at least 120 °C.
7. A process according to any one of the preceding claims, wherein said gas flow comprises less than 5% oxygen by volume.
8. A process according to any one of the preceding claims comprising 10 conveying wetted wood elements through an evaporation section during said exposing to a gas flow.
9. A process according to any one of the preceding claims, wherein said cooling comprises spraying water over the acetylated wood elements to 15 provide homogenously wetted wood elements and subsequently providing a gas flow comprising less than 5% oxygen by volume over the wetted wood elements in said evaporation section.
10. A process according to claim 9, wherein said gas flow is provided in 20 cross-flow with the wood elements.
11. A process according to claim 10, wherein said evaporation section comprises a screw section wherein the screw movement provides for transport and homogenization of the wood elements.
12. A process according to any one of the preceding claims, wherein wood elements having a temperature of 150 °C or more and an acetyl content of more than 20% and a residual acid content of less than 0.5 wt.% are sprayed with liquid water in an amount of 10 – 500 g water per 1 kg dry 30 wood elements, to give homogeneously wetted wood elements.
13. A process according to claim 12, wherein the wood elements are sprayed with liquid water in an amount of 100 - 500 g water per 1 kg dry wood elements.
14. A process according to any one of the preceding claims, wherein said process further comprises storing and/or handling of the cooled wood elements. 10
15. A process according to any one of claims 7 and 9-14, comprising recirculating gas of said gas flow through a recirculation loop coupled to said evaporation section, wherein in said recirculation loop water vapour is condensed and wherein condensate is withdrawn from the recirculation loop.
16. A process according to claim 15, wherein at least 3 wt.% water is condensed in the recirculation loop based on dry weight of the wood elements. 20
17. A wood acetylation plant comprising a wood acetylation section and downstream thereof a cooling system, wherein said cooling system comprises a water spray chamber, an evaporation section downstream of said water spray chamber, and a gas recirculation loop, wherein said water spray chamber comprises an inlet for wood elements, a liquid distributor for 25 spraying water, and an outlet for wood elements, and wherein the evaporation section comprises an inlet and an outlet for wood elements, a conveyor for continuously transporting wood elements from said inlet to said outlet, and an inlet conduit having at least one opening for introducing gas into said evaporation section and an outlet conduit having at least one 30 opening for withdrawing gas from said evaporation section, wherein said conduits are coupled to said gas recirculation loop and wherein said openings of said conduits are different from said inlet and outlet for wood elements, wherein the outlet of said wood acetylation section is coupled to the inlet for wood elements of said water spray chamber.
18. The wood acetylation plant according to claim 17, wherein said recirculation loop comprises a cooler and a condensation vessel, an outlet for condensate, and a recirculation fan. 10
19. The wood acetylation plant according to claim 18, wherein the cooler and condensation vessel are combined.
20. The process according to any one of claims 1-16, substantially as herein described with reference to any example thereof and with or without 15 reference to the accompanying drawing.
21. The wood acetylation plant according to any one of claims 17-19, substantially as herein described with reference to any example thereof and with or without reference to the accompanying drawing.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP16175947 | 2016-06-23 | ||
EP16175947.7 | 2016-06-23 | ||
PCT/EP2017/065520 WO2017220772A1 (en) | 2016-06-23 | 2017-06-23 | Cooling acetylated wood elements |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ749855A NZ749855A (en) | 2020-11-27 |
NZ749855B2 true NZ749855B2 (en) | 2021-03-02 |
Family
ID=
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US20230278253A1 (en) | Cooling acetylated wood elements | |
FI106722B (en) | Acetylation of lignocellulosic materials | |
US20210299907A1 (en) | Reactor system and process for wood modification | |
BR112014023437B1 (en) | process for continuous acetylation of wood elements and plant for acetylation thereof | |
US10668645B2 (en) | Process for the acetylation of wood | |
US20170173819A1 (en) | Method for the modification of wood | |
Ozgenc et al. | ATR-FTIR spectroscopic analysis of thermally modified wood degraded by rot fungi | |
NZ749855B2 (en) | Cooling acetylated wood elements | |
US11338468B2 (en) | Method for continuous acetylation of wood elements | |
CA2982030C (en) | Method for the acetylation of wood | |
JP6946192B2 (en) | Continuous acetylation method for wood-based materials | |
Vladimirovich et al. | ANALYSIS OF SKIMMED MILK POWDER TECHNOLOGY | |
DE102008045201A1 (en) | Device for utilization of energy of condensable gases from gas flow, has evaporation space equipped with distribution device for fluid, where energy of condensable gases is used directly for processing of fluids by evaporation |