METHOD FOR REDUCING AND/OR AVOIDING THE BUILD UP OF WOOD COMPONENTS

PROCEDE POUR REDUIRE ET/OU EVITER LES DEPOTS DE COMPOSANTS DU BOIS

English Abstract

The invention relates to a method for avoiding and/or reducing the deposition
of volatile and non-volatile wood components in gas-bearing systems, whereby
at least one of the volatile wood components, at least partly, condenses in
the gas-bearing system and the gas contains at least one compound with a
similar condensation profile to the volatile wood component and which at least
reduces the deposition of volatile wood components or the reaction products
thereof. The invention further relates to a method for reducing and/or
avoiding the deposition of wood components on machines and/or equipment
components for the production of wood fibre material, from wood chippings, in
which the shredding of the wood is achieved in the presence of a compound
which forms a film on the surfaces of the above machines and/or equipment
components and at least reduces the deposition of volatile wood components
and/or the reaction products thereof.

French Abstract

La présente invention concerne un procédé pour éviter et/ou réduire les dépôts de composants volatils et non volatils du bois dans des systèmes conducteurs de gaz. Selon ledit procédé au moins quelques-uns des composants volatils se condensent au moins partiellement dans les systèmes conducteurs de gaz et le gaz contient au moins un composé qui présente un comportement de condensation semblable à celui des composants du bois volatils et qui réduit les dépôts des composants du bois volatils et/ou de leurs produits réactionnels. La présente invention concerne en outre un procédé pour réduire et/ou éviter les dépôts de composants du bois sur des machines et/ou des parties d'installations utilisées pour la production de matériaux en fibre de bois à partir de copeaux de bois, procédé selon lequel la trituration se fait en présence d'un composé qui forme un film sur les surfaces des machines et/ou des parties d'installations et qui, au moins, réduit les dépôts de composants volatils du bois et/ou de leurs produits réactionnels.

Claims

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Claims:
1. A process for avoiding and/or reducing deposits of volatile and non-
volatile
wood constituents in gas-bearing systems, wherein volatile wood
constituents underga at least partial condensation in the gas-bearing
systems, characterized in that the gas contains at least one compound
which
- has condensation characteristics similar to those of said volatile wood
constituents, and
- at least reduces deposits of volatile wood constituents and/or reaction
products thereof.
2. The process according to claim 1, characterized in that said compound is a
dicarboxylic ester.
3. The process according to claim 2, characterized in that said dicarboxylic
ester is a di-n-alkyl adipate and/or a diisoalkyl adipate.
4. The process according to claim 2, characterized in that said dicarboxylic
ester is dibutyl adipate.
5. The process according to any of claims 1 to 4, characterized in that the
gas-bearing system is part of:
- a wood processing plant, particularly a plant for producing wood fiber
material and/or wood fiber boards,
- a plant for producing cellulose,
- a cellulose-processing plant,
- a paper or cardboard production plant, and/or
- a plant for producing components or articles made of molded fiber.

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6. The process according to any of claims 1 to 5, characterized in that the
gas
includes steam.
7. A process for reducing and/or avoiding deposits of wood constituents on
machines arxtlor plant components used in the production of wood fiber
materials from wood chips, characterized in that wood is defiberized in the
presence of at least one compound which:
- forms a film on the surfaces of the machines and/or plant
components, and
- at least reduces deposits of volatile wood constituents and/or reaction
products thereof.
8. The process according to claim 7, characterized in that said compound is a
dicarboxylic ester.
9. The process according to claim 8, characterized in that said dicarboxylic
ester is a di-n-alkyl adipate and/or a diisoalkyl adipate.
10. The process according to claim 8, characterized in that said dicarboxylic
ester is dibutyl adipate.
11. The process according to any of claims 7 to 10, characterized in that the
machines and/or plant components used in the production of wood fiber
- materials from wood chips include at least one refiner.
12. The process according to claim 11, characterized in that the dicarboxylic
ester is metered into the first refiner together with the clear filtrate.
13. The process according to claim 11 or 12, characterized in that the
concentration of dicarboxylic ester is 100-5000 ppm, preferably 200-2000
ppm, and more preferably 300-1000 ppm.

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14. The process according to any of claims 7 to 13, characterized in that the
machines and/or plant components are components of a plant used in the
production of thermomechanical pulp.

Description

CA 02394173 2002-06-07
Method for Reducing andlor Avoiding the Build-up of Wood Components
The present invention relates to a process for avoiding and/or reduang
deposits
of volatile and non-volatile wood constituents in gas-bearing systems, wherein
the volatile wood constituents undergo at least partial condensation in the
gas-
bearing systems.
The present invention also relates to a process for reducing and/or avoiding
deposits of wood constituents on machines and/or plant components used in the
production of wood fiber from wood chips.
In the treatment of wood, in the production and processing of cellulose,
andlor in
the production of paper, cardboard or molded fibers, volatile wood
constituents
frequently are released which then undergo condensation in gas-bearing
systems, forming solid deposits therein. For example, such deposits increase
the
pressure drop in pipings, reduce the separation performance of cyclones option-
ally present, and block control means, so that the gas pipes must be opened
and
cleaned using e.g. high-pressure apparatus. Such cleaning is highly cost-
intensive, interfering with the respective production process.
The present invention therefore is based on the object of providing a process
that would at least reduce deposits of volatile andlor non-volatile wood
constituents in gas-bearing systems.
According to the invention, said object is accomplished by means of a process
for avoiding andlor reducing deposits of volatile and non-volatile wood
constituents in gas-bearing systems, wherein at least some of the volatile
wood
constituents undergo at least partial condensation in the gas-bearing systems,
and the gas contains at least one compound which

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_2_
- has condensation characteristics similar to those of said volatile wood
constituents, and
- at least reduces deposits of volatile wood constituents and/or reaction
products thereof.
In the meaning of the invention, volatile wood constituents are all those wood
constituents exhibiting a vapor pressure at temperatures above 20°C.
Reaction
products in the meaning of the invention are any products forming volatile
wood
constituents upon condensation, e.g. as a result of polymerization.
Condensed volatile wood constituents and the reaction products thereof
frequently form a tacky film on the surfaces of gas-bearing systems and
therefore, the deposits generally include non-volatile wood constituents as
well,
e.g. fine wood particles precipitating from the gas stream and adhering to the
tacky films.
According to the invention, said compound exhibits condensation
characteristics
similar to those of the wood constituents, i.e., the compound and wood
constituents undergo condensation preferably at the same location in the gas-
bearing system, preferably forming a film there.
The compound preferably is a dicarboxylic ester. More preferably, said
dicarboxylic ester is a dicarboxylic acid dialkyl andlor diisoalkyl ester of
CZ-C,Z
dicarboxylic acids with C,-C,3 n- andlor isoalkanols, such as di-n-butyl
oxalate,
di-n-butyl malonate, di-n-butyl succinate, di-n-butyl glutarate, di-n-butyl
adipate,
di-n-butyl suberate, di-n-butyl sebacate, dimethyl adipate, di-n-propyl
adipate,
diisopropyl adipate, diisobutyl adipate, di-tert-butyl adipate, diisoamyl
adipate, di-
n-hexyl adipate, di(2-ethylbutyl) adipate, di(2-ethylhexyl) adipate,
diisodecyl
adipate, as well as dirnethyl phthalate, diethyl phthalate, di-n-butyl
phthalate,
diisobutyl phthalate, di(2-ethylhexyl) phthalate, and diisodecyl phthalate, as
well
as the corresponding terephthalic esters and diesters of a C9 dicarboxylic
acid
(trimethyladipic acid) and of dodecanedicarboxylic acid.

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However, it is particularly preferred that the compound be a di-n-alkyl
adipate
andlor a diisoalkyl adipate. Most preferably, the compound is di-n-butyl
adipate.
The process according to the invention is suitable in avoiding and reducing
deposits of volatile or non-volatile wood constituents in gas-bearing systems
of
any type. However, the gas-bearing systems preferably are part of:
- a wood processing plant, particularly a plant for producing wood fiber
material andlor wood fiber boards,
- a plant for producing cellulose,
- a cellulose-processing plant,
- a paper or cardboard production plant, and/or
- a plant for producing components or articles made of molded fiber.
More preferably, the gas-bearing system is part of a plant for producing
thermomechanical pulp (TMP), or a chip refiner plant such as described in WO
96/41914 which hereby is incorporated by reference and is thus deemed part of
the disclosure.
The gas flowing through the gas-bearing pipings can be any gas, but preferably
includes water vapor.
Preferably, the compound is metered into the gas in gaseous state. However,
those skilled in the art will recognize that the compound may also be metered
into the gas in liquid state, being transformed to the gaseous state therein.
Metering preferably is effected continuously.
The amount of compound metered depends on the concentration of the volatile
wood constituents in the gas and on the gas volume flow. The concentration
preferably is 100-5000 ppm, more preferably 200-2000 ppm, with 300-1000 ppm
being particularly preferred.

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Preferably, the amount of compound metered into the gas is such that no
deposits of volatile or non-volatile compounds andlor reaction products
thereof
will form on the surfaces of the gas-bearing systems, or compounds already
having formed will be removed andlor dissolved. Consequently, metering of the
compound preferably is subject to automatic cantrol. Preferably, the pressure
drop in the piping of the gas-bearing system andlor the separation efficiency
of
cyclones present in the gas-bearing system are taken as control parameters. It
is
also preferred to use the gas volume flow and the concentration of volatile
wood
constituents in the gas, or the surface deposit as control parameters.
As a rule, the above-mentioned production processes are performed in the
presence of water, the water being at least partially evaporated and
therefore, in
another preferred embodiment of the process according to the invention, the
compound is metered directly into the water. In this event, the compound must
also be steam-volatile.
The present invention is advantageous in that the gas-bearing systems require
less frequent cleaning, and the plants therefore have longer operating life.
For
example, cyclones are no longer clogged by deposits, so that their separation
capability is maintained. Deposits already existing are reduced.
It is another object of the present invention to provide a process for
reducing
andlor avoiding deposits of wood constituents on machines andlor plant
components used in the production of wood fiber from wood chips (chips).
According to the invention, said object is accomplished by means of a process
for reducing andlor avoiding deposits of wood constituents on machines andlor
plant components used in the production of wood fiber materials from wood
chips, wherein the wood is defiberized in the presence of at least one
compound
which:
- forms a film on the surfaces of the machines andlor plant components, and
- at least reduces deposits of volatile wood constituents andlor reaction
products thereof.

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Deposits in the meaning of the invention are any deposits of wood constituents
in gas-bearing and/or water-bearing systems andlor on other components of
plants or machinery used in the production of wood fiber materials.
The compound preferably is a dicarboxylic ester. More preferably, said
dicarboxylic ester is a dicarboxylic acid dialkyl andlor diisoalkyl ester of
C2-C,z
dicarboxylic aads with C,-C,3 n- andlor isoalkanols, such as di-n-butyl
oxalate,
di-n-butyl malonate, di-n-butyl sucxinate, di-n-butyl gfutarate, di-n-butyl
adipate,
di-n-butyl suberate, di-n-butyl sebacate, dimethyl adipate, di-n-propyl
adipate,
diisopropyl adipate, diisobutyl adipate, di-tert-butyl adipate, diisoamyl
adipate, di-
n-hexyl adipate, di(2-ethylbutyl) adipate, di(2-ethylhexyl) adipate,
diisodecyl
adipate, as well as dimethyl phthalate, diethyl phthalate, di-n-butyl
phthalate,
diisobutyl phthalate, di(2-ethylhexyl) phthalate, and diisodecyl phthalate, as
well
as the corresponding terephthalic esters and diesters of a C~ dicarboxylic aad
(trimethyladipic acid) and of dodecanedicarboxylic acid.
However, it is particularly preferred that the compound be a di-n-alkyl
adipate
andlor a diisoalkyl adipate. Most preferably, the compound is di-n-butyl
adipate.
The esters may be employed alone or in combination with water-soluble or
water-insoluble solvents as an anhydrous or aqueous solution or as an aqueous
dispersion, preferably emulsion. Suitable solvents are n- and isoalkanols,
liquid
hydrocarbons, acetone, and other well-known solvents. In particular, natural
oils
or modified natural oils such as rape oil methyl ester are used.
Non-ionogenic, ionic and amphoteric, particularly non-ionic surfactants are
used
as emulsifiers in the production of the dispersions.
For example, suitable non-ionic emulsifiers are oxyalkyl ethers, preferably
oxyethylates and/or terminally blocked oxyethylates of fatty aicohols and
fatty
acids or oils. Alkyl- andlor arylsulfonates, a-olefinsulfonates,
a-sulfofatty acid esters, sulfosuccinic acid esters, as well as alkyl sulfates
and

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ether sulfates, as well as carboxymethylated oxyethylates and soaps are
suitable
as anionic emulsifiers. The preparation of the preferably stable emulsions is
well-
known. For example, the hydrophobic phase is added to the aqueous phase
containing the emulsifier and dispersed with stirring or pump-circulating.
Preferably, the plant for producing the wood fiber materials has at feast one
refiner such as known from WO 96141914 or from WO 96/35016. These patent
applications are hereby incorporated by reference and are thus deemed as part
of the disclosure.
The dicarboxylic ester is preferably metered into the refiner together with
the
clear filtrate. Said metering preferably is effected in a continuous fashion.
In a preferred embodiment, the dicarboxylic ester concentration in the first
refiner
is 100-5000 ppm, more preferably 200-2000 ppm, with 300-1000 ppm being
particularly preferred.
The process according to the invention is suitable for any type of machine and
plant used in wood defiberizing. However, the machines and/or plants are
preferably part of the TMP process or of a process such as described in WO
96141914.
Using the present invention, a substantial prolongation of the operating life
of
machines and plants used in the production of wood fiber materials is
achieved,
The plants are easier to control, and it is possible to prolong the service
life of
the refiner milling equipment. It is possible to integrate the process
according to
the invention in already existing plants. Deposits already present will be
reduced
by the process of the invention.
With reference to Figure 1, the invention will be illustrated below. The
explanations are given merely by way of example and do not limit the general
idea of the invention.

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Figure 1 shows a process flow chart for the production of thermomechanical
pulp
(TMP). Purified chips are fed into the 1 ~ refiner stage and reduced
mechanically
therein in the presence of clear filtrate and 330 ppm of TALLOFIN~ TMP.
TALLOFIN~ TMP is a product of Stockhausen GmbH & Co. KG, which contains
40 wt.% of di-n-butyl adipate and 60 wt.-% of a non-ionogenic emulsifier. The
TALLOFIN~ TMP is metered info the clear filtrate before the latter flows into
the
refiner. The exceedingly high energy input (up to 22 MW) gives rise to
temperatures of more than 200°C and pressures of 2-3 bars in the
refiner, so
that a considerable portion of the water undergoes evaporation in the refiner.
The steam is removed from the refiner through steam pipings and fed into a
heat
recovery. In addition to volatile and non-volatile wood constituents, the
steam
also contains a certain percentage of di-n-butyl adipate, so that the steam
pipings, the cyGones and control elements in the steam pipings show no or
merely minor deposits. Also, no or massively reduced deposits of wood
constituents are formed in the refiner itself, so that the refiner requires
less
frequent cleaning and the service life of the milling equipment is increased.
Following defiberization in the first refiner, the wood fibers are reduced
mechanically in the 2"° refiner stage once more, before they are
subjected to
further treatment well-known to those skilled in the art. In the 2"°
refiner stage as
well, huge amounts of steam are formed which is fed into a heat recovery.
Again,
in addition to volatile and non-volatile wood constituents, the steam also
contains
a certain percentage of di-n-butyl adipate, so that the steam pipings, the
cyclones and control elements in the steam pipings show no or merely minor
deposits. Again, no or massively reduced deposits of wood constituents are
formed in this refiner itself, so that it requires less frequent cleaning and
the
service life of the milling equipment is increased.