PROCEDE DE PREPARATION D'UNE LIQUEUR DE CUISSON PERMETTANT D'OBTENIR UN PRODUIT SEMI-FINI FIBREUX

PROCESS FOR PREPARING A PULP-COOKING SOLUTION

Abrégé français

La présente invention se rapporte au domaine de la fabrication de pâte à papier, et concerne plus particulièrement un procédé de préparation d'une liqueur de cuisson permettant d'obtenir un produit semi-fini fibreux. Ce procédé consiste à saturer, à l'aide d'une quantité d'anhydride sulfureux variant de 2,5 à 5,5 % en poids de la liqueur de cuisson et à une température de 35 à 45· C, les produits suivants: (a) soit une solution de carbonate de sodium dans des eaux usées qui proviennent de la purification biologique d'effluents industriels issus de la production de pâte à papier, et qui possèdent une concentration en boues excédentaires actives allant de 18 à 40 g/l, ladite solution possédant une concentration en carbonate de sodium de 1,55 à 2,5 % en poids en unités Na¿2?O; (b) soit un hydrolysat alcalin obtenu par le traitement des eaux usées qui proviennent de la purification biologique d'effluents industriels issus de la production de pâte à papier, et qui possèdent une concentration en boues excédentaires actives allant de 18 à 40 g/l. Dans ce dernier cas, le traitement des eaux usées se fait à l'aide d'un mélange de base comprenant de 50 à 90 % en poids de carbonate de sodium et de 10 à 50 % en poids d'oxyde de calcium, ceci dans une quantité de 1,55 à 2,5 % en poids en unités Na¿2?O et à une température allant de 25 à 40· C, puis à éliminer le précipité solide qui s'est formé. Ce procédé permet d'accroître sensiblement la production du produit semi-fini fibreux, d'accroître son indice physico-mécanique, ainsi que d'utiliser les déchets issus de la purification biologique des eaux usées provenant de la production de pâte à papier, et d'étendre la gamme de matières premières utilisées dans la production de liqueurs de cuisson.

Abrégé anglais

The invention relates to the paper pulp industry, specifically to a process
for preparing a pulp cooking solution used for obtaining a fibrous semi-
finished product. This involves saturating a solution of sodium carbonate in
waste water obtained from the biological purification of paper industry
effluent with a concentration of surplus active sludge of 18-40 g/l, having a
sodium carbonate concentration of 1.55-2.5 wt.% in units of Na2O, or an
alkaline hydrolysate obtained by treating waste water obtained from the
biological purification of paper industry effluent with a concentration of
surplus active sludge of 18-40 g/l with a mixed base containing 50-90 wt.%
sodium carbonate and 10-50 % calcium oxide, in a quantity of 1.55-2.50 wt.%
per unit Na2O at a temperature of 25-40 ~C with subsequent removal of the
solid precipitate, at a temperature of 35-45 ~C until it accounts for 2.5-5.5
wt.% of the cooking mixture. The proposed process significantly increases the
yield of fibrous semi-finished product and improves its physical and
mechanical indicators. It also permits the use of waste obtained from the
biological purification of paper industry effluent and widens the range of raw
materials which can be used to produce pulp cooking solutions.

Revendications

CLAIMS 1
FORMULA OF THE INVENTION
The cooking liquor preparation method for producing a fibrous
semi-fabricate is carried out by the water medium saturation with sulfurous
anhydride differs from the others owing to the fact that the water medium
being in fact either a biologically treated pulp and paper mill waste water
that contains the following: activated sludge biomass in the range of
18-40g/l and soda ash running between 1,55-2,50% by weight based on
Na2O or alkali hydralyzate produced in treatment of the same waste water
by a mixture of base salts containing sodium carbonate (50-90% by
weight based on Na2O) at the temperature 25-40°C followed up with a
solid sediment removal is used to be saturated with sulfurous anhydride at
the temperature 35-45°C until the concentration thereof is 2,5-5,5% by
weight.

Description

. ~, ' CA 02238100 1998-0~-20
'
METHOD FOR PREPARING A PULP COOKING LIQUOR
The proposed invention deals with pulp and paper production, in
particular, with the process for preparing pulp cooking liquors to
manufacture a fibrous semifabricate.
A method for preparing a pulp cooking liquor by adding a sulfate
into a water medium is known (1).
Saturation of a water medium with sulfurous anhydride until the
required pH-value is reached represents another well known method to
prepare acid cooking liquor (2,3).
The disadvantages of the methods enumerated are as follows: a
considerable amount of fresh water needed to prepare the cooking liquor,
a rather costly treatment needed for the resultant emuents and a low yield
of the final pulp occurs.
The closest to the proposed invention is a well known method for
preparing a cooking liquor to manufacture a fibrous semifabricate. The
method in question requires waste water that has been treated biologically
be used as a water medium. This waste water that normally contains an
excessed activated sludge in the range of 0,5 - 17,0 g/l is to be withdrawn
from a secondary thickener to dissolve sulfates. Should sulfite or bisulfite
cooking methods are used the abovementioned water medium is to be
saturated with sulfurous anhydride until the required pH value is reached
(4).
This method may offer cost advantages resulting from replacement
fresh water with waste one after biological treatment thereof. However,
this method leads to a comparatively low pulp yield and doesn't secure
that the required level of its quality parameters needed now will be
reached.
Besides, waste water at low activated sludge concentration is used as a
water medium here.
The proposed invention is aimed at creating a method for preparing
a pulp cooking liquor to manufacture a fibrous semifabricate in a way that
makes it possible to increase the yield of the final product, improve its
quality as well as to extend a stock of row materials needed for preparing
sulfite cooking liquors.
The abovementioned objectives of the invention are reached in such
an event when either soda ash (1,5 - 2,50 % by weight based on Na2 O)
in form of a solution in biologically treated emuents of pulp and paper
manufacture which in turn run between 18 and 40 g/l suspended solids or
alkaline hydrolizate generated at the treatment of the same emuents by a
mixture of basic salts (both Na2CO3 - 50 - 90 % by weight and CaO - 1,5 -
2,5 % by weight based on Na2 O) at the temperature of 25 - 40OC

, CA 02238100 1998-0~-20
accompanied by removal of resulting precipitate are used as water
medium while saturating thereof with sulfurous anhydride at 35-40~C until
its content in the cooking liquor is 2,2-5,5 % by weight based on the total
mass of the solution.
The proposed method differs from the well known one by the
following features: soda ash (1,5 - 2,50 % by weight based on Na2 O) in
form of a solution in biologically treated effluents of pulp and paper
manufacture running between 18 and 40 9/l suspended solids or alkaline
hydrolizate generated at the treatment of the same effluents by a mixture
of basic salts
( Na2CO3 - 50 - 90 % by weight and CaO - 1,5 - 2,5 % by weight based
on
Na2 O) at 25 - 40~C accompanied by removal of resulting precipitate are
used as a water medium.
The usage of either soda ash dissolved in pulp and paper effluents
or hydrolizate originated from the same effluents makes it possible to
enhance efficiency of pulping since the products of alkaline or acid
hydrolysis that found their way into the cooking liquor act as inhibitors
thus eliminating the processes of thermo-oxidizing destruction of
carbohydrates.
When sulfurous anhydride is used to saturate soda ash solution in
biologically treated waste water containing an excessed activated sludge
there is an acid hydrolysis of the bio-organic part thereof occurs there
since that part accounts for 83% by weight based on dry residue.
Should the mixture of basic salts is used to treat the
abovementioned waste water a reaction of caustization will proceed prior
to complete saturation thereof
Na2CO3+CaO+H20=2NaOH+CaCO3
accompanied by alkali hydrolysis of bio-organic part of the activated
sludge.
The major components of both acid and alkali hydrolizate of activated
sludge biomass are aminoacids and their sodium salts (approximately 68 -
80% by weight based on total organic substances passed into solution),
carboxylic acids or their salts (10 - 15% by weight), neutral ether-soluble
substances (5 - 12% by weight) and phenols (2- 12% by weght).
It's necessary to stress that activated sludge biomass from a pulp
and paper waste water treatment plant contains a significant amount of
fiber fines, slime-lignin and saw dast the total amount of which accounts
for up to 17% by weight based on dry residue.

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When mixed carefully calcium carbonate produced according the
above referred to reaction of caustization distributes proportionally among
solid non-hydrolyxed particles of activated sludge biomass. As a result,
non-hydrolyzed sediments of activated sludge biomass which normally
retain water firmly and therefore can hardly be separated are bound to
obtain a favorable structure that makes it possible to dispose them easily
by filtration or sedimentation.
The proposed method means the use of industrial waste water after
biological treatment with concentration of activated sludge biomass in the
range of 18 - 40g/l. Such concentration obtained by preliminary
consolidation of a*ivated sludge biomass in special settlers, is optimal
since it mantains higher than usual content of acid and alkali hydrolysis
products in a cooking liquor that are formed during its preparation and
thus, as it has been mentioned, making cooking more effective. Besides,
the usage of industrial waste water with high concentration of activated
sludge (18-40g/l) allows to utilize activated sludge biomass.
Water medium saturation with sulfurous anhydride at 35-40~C up to
concentration of 2,5-5,5% by weight first of all makes it possible to reach
complete acid hydrolysis of activated sludge biomass followed by
generation of substances that increase the quality of the cooking liquor,
and secondly it means the optimal conditions of cooking namely the
increase of fibrous semi-fabricate yield and the improvement of its
mechanical properties.
As it has already been mentioned, the usage of alkali hydrolyzate as
a water medium allows to get rid effectively (by means of co-precipitation
with calcium carbonate) from a non-hydrolized part of activated sludge
biomass, which makes up to 17% by weight based on absolutely dry
substance thus improving the quality characteristics required for a fibrous
semi-fabricate.
The proposed conditions for alkali hydrolizate production (treatment
by mixed base salts containing 50-90% of sodium carbonate by weight
and 10-15% of calcium oxide by weght in amount of 1,55-2,50% by
weight based on Na20 at the temperature 25-40~C followed up with
removal of sediment) makes it possible to reach a complete alkali
hydrolysis of bio-organic part of activated sludge and to remove an
insoluble slime. All this in turn, increases the efficiency of cooking process
and makes the quality of the fibrous semi-fabricate better.
The method is carried out in the following way:
Sodium carbonate (in amount that makes its concentration in
solution equal to 1,55-2,50% by weight based on Na20) is added to
biologically treated waste water of a pulp and paper mill after settling

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. . 4
thereof in a radial or vertical thickener until the activated sludge
concentration in it has reached the level of 18-40g/l. The resultant soda
ash solution is sent to an absorber for saturation with sulfurous anhidride
at the temperature 35-45~C until its concentration is of 2,5-5,5% by
weight and organic part of the sludge is dissolved. Or a pulp and paper
mill waste water that has been treated biologically and then stored in a
thickener until the excessed activated sludge concentration in it has
reached the level of 18-40g/l is delivered to a mixer to be treated with a
mixed base salts in amount of 1,55-2,50% by weight based on Na20 at
the temperature of 25-40OC provided that it is accompanied by thorough
mixing until the activated sludge biomass is dissolved completely.
Then the resulting mixture containing alkali hydrolizate, undissolved
slime and calcium carbonate is to be dewatered by filtration or
precipitation.
The resultant clarified alkali hydrolyzate is sent to an absorber for
saturation with sulfurous anhydride at the temperature of 35-45~C until
the concentration thereof is 2,5-5,5% by weight is reached.
The metod is illustrated by the following examples:
Example 1.
360 9. of air dry chips were loaded into 15-litre autoclave made of
stainless steel with 9 litres of cooking liquor added in it. The cooking liquor
has been prepared by saturation of a waste water from a pulp and paper
mill and the latter has in it the following: activated sludge biomass in the
amount of 30g/l and soda ash in the amount of 2% by weight based on
Na20. The saturation is to be proceeded at the temperature of 40~C until
sulfurous anhydride concentration is 4,5% by weight.
The cooking process was carried out during 2 hours 15 minutes
while the temperature being raised from 25OC to 100~C; then during 45
minutes the temperature was kept at 120~C and during another 1 hour
and a half it had been raising from 120~C to 160~C. Then the process
proceeded at that temperature (160~C) for another 1 hour. When the
cooking is over a 75g/l sample of the resultant semifabricate was used to
dertermine both its whiteness and mechanical characteristics. The results
obtained are given in the Table.
Example 2

CA 02238100 1998-0~-20
The cooking liquor was prepared in the following way:
The waste water from a pulp and paper mill with activated sludge making
up 309/1 in it was treated by a mixed base containing the equal parts of
sodium carbonate and calcium oxide in amount of 2,5% by weight based
on Na20 at the temperatute 35~C. After the sediment had been removed
the alkali hydrolyzate was saturated with sulfurous anhydride at the
temperature 40~C until the concentration thereof was reached 5,5% by
weight. The resultant cooking liquor with products yielded by the alkali
hydrolysis of activated sludge had 1,9 pH value. The cooking process was
carried out under the same conditions as it was in the Exarnple I. The
results are given in the Table.
The data obtained shows that the combination of the conditions
needed for the preparing of the cooking liquor leads both to the
considerable increase in the yield and improving in mechanical
characteristics of the final product in contrast to that of the well known
method.
Moreover, the usage of fresh water for a cooking liquor preparation
is eliminated and a stock of raw materials ~or its production is expanded.
At the same time it gives a way of utilizing of all waste water produced by
a pulp and paper mill and posing a real threat to the environment.
TABLE
Example Pulp output, Characteristics of fibrous semi-finished product.
number %
Delignific~tion Tearing Tearing Pressing Whitf nf!c.~7
degree, length, m r~ t~nr~7 g r~si~t~n~7 %
Kappa kg/sm2
73 79 11 280 64 3,5 58,8
2 78 86 11 920 67 3,8 59,7
3* 52 57 10 360 61 2,9 55,8
* Example 3 illustrates a well-known cooking preparation method, according to
author's certif1cate of the USSR N~ 746002.
The cooking process is held in conditions of Example 1.