Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21S9748
P- 944
METHOD FOR INCREASING PULP CONSISTENCY
FIELD OF THE INVENTION
The present invention deals with a chemical addition to a pulp
washing system which causes less liquid to remain with the pulp when it
5 is formed into a mat, effectively increasing the pulp consistency. This
increase in mat consistency during pulp washing allows for a washing
operation to run cleaner and at a higher production rate.
BACKGROUND OF THE INVENTION
It is customary to wash pulp following chemical and/or mechanical
pulping of wood chips in order to remove excess contaminants within the
liquid fraction. These contaminants occur both naturally from the wood
(lignin and pitch) or are by-products from the pulping operation. The
15 wash liquor is later evaporated so that the organics can be burned for
energy or sold (crude tall oil, lignin), and the pulping chemicals can be
reclaimed.
21S9748
Pulp is commonly washed by subjecting it to a series of dilution/
thickening phases, in which the stock consistency (% fiber) is diluted to
approximately 0.5 - 5% and is thickened to approximately 10 - 30%.
Generally, showers are also used to displace part of the dirty liquid frac-
5 tion held by the pulp during the thickening phases. As a way of saving onfresh water (as well as later evaporation costs), the water runs counter-
current to the flow of pulp. In this way, filtrate from the cleaner phase is
used to shower and/or redilute a dirtier phase in the process. The most
commonly used pulp washer is a vacuum drum system with 3 to 4 stages
10 in series. There are a wide variety of systems in use, however, some of
which do not use both dilution/thickening and displacement between
phases, but rather only one or the other.
It is desirable to achieve maximum consistency (minimizing the
15 liquid, where the contaminants exist, remaining in the pulp mat) during
the various stages of washing as this can either result in increased pro-
duction and/or less contaminants remaining from stage to stage and in
the final washed stock. The advantage of increased production is obvi-
ous, especially in systems which are limited by their washing capacity.
20 Reducing the carryover of contaminants out of the process is also ad-
vantageous as it can reduce subsequent bleaching costs, reduce toxic
chemicals in bleach plant effluents, and increase the amount of reclaimed
cooking chemicals.
Reducing the amount of conta",inants that leave with the brown
stock is particularly important in bleachable grades; the bleaching proc-
ess follows brown stock washing. The effluent from bleaching is com-
monly discharged from the mill, and this effluent contains chlorinated
organics, which may be toxic. Substances currently of concern include
dioxins, furans, absorbable organic halogens, and color. Increased
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organics removal in brown stock washing has been shown to decrease
the environmental impact of bleaching. Furthermore, reducing the level
of contaminants sent to the bleach plant or within the bleach plant (by
improved washing) may reduce the bleach chemical demand.
The liquor, commonly referred to as black liquor in the often used
Kraft pulping process, tends to be very foamy due to its makeup (contain-
ing lignin and soaps or pitch) and the general nature of the process itself.
Because of this, defoamers are a necessary additive in the washing proc-
10 ess in order to efficiently thicken the stock (increase its consistency) inthe various stages of washing, as a foamy stock tends to hold liquid
rather than separate from it.
Certain surfactants have been discovered, that when added in ad-
15 dition to a defoamer, can increase the consistency of stock leaving the
washing process beyond that of the defoamer alone. These surfactants
are the subject of the present invention.
SUMMARY OF THE INVENTION
The present invention refers to a method of enhancing the process
of pulp washing, to remove from the pulp contaminants contained in the
liquid fraction, by decreasing the tendency of the liquid to remain with the
pulp (increase the pulp's consistency). This is particularly important in
25 grades that will be bleached. By adding a surfactant or surfactant mixture
to the pulp thickening operation, e.g., to the washing process (at about
0.5 - 2,000 parts per million parts of pulp) in addition to the defoamer
which is already present, the liquid holding capacity of the pulp can be
reduced. This increase in mat consistency during pulp washing can allow
30 a washing operation to run cleaner and/or faster. Surfactants of tne
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following general formula are the subject of the present invention:
R-X(CH2CH20)nyz
O O
ll ll
5 wherein R is alkyl or alkylaryl, X is C - O, C-N or O, and n is from about
1 - 30; Y is hydrogen, sulfate, sulfonate, phosphate or carboxylate; and Z
is a water soluble cation, wherein Z is not present when Y is hydrogen.
The water soluble cation may be Na+, K+, NH4+, Ca2+, Mg2+ or H+.
Thus, the surfactants of the present invention may be either nonionic or
1 0 anionic.
Note that the pulp thickening operation may occur under vacuum
pressure or gravity, while the pulp may be produced from wood chips
using mechanical or chemical means. The pulp may be deinked secon-
15 dary fiber.
R is preferably from about C4 - C22 alkyl or C2 - C12 alkylaryl. The
ethylene oxide unit may optionally be ethylene oxide with propylene oxide
in blocks within the chain or capping the chain, or a short C1 - C4 alkyl
20 group.
The surfactants may be added to the washing process through the
stock washing showers and/or directly to the stock/liquor mixture either
within the washer or anywhere prior to the stock reaching the washer.
25 Many of these surfactants tend to be inherently foamy materials as is the
stock itself, therefore a defoaming agent may need to be present in the
system in order to obtain benefits from these materials.
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It is aiso expected that the present invention would find utility in
any other operation in the pulp/paper industry where pulp is thickened.
In these instances, a defoamer would only be necessary where the stock/
liquid was inherently foamy.
The treatments of the present invention may be added anywhere
prior to the pulp thickening process, e.g., to the chips, in the digester or
screens. The treatments may also be added after initial washing stages
in order to benefit subsequent thickening operations (decker, bleach
10 plant washers, market pulp machines, deink plants).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be further understood by reference to the follow-
15 ing examples.
Example 1
Brown stock collected from a Southern Kraft softwood mill was
20 diluted to 0.7% consistency stock with black liquor. The black liquor hadbeen previously diluted to contain roughly 4% dissolved solids. Liquor
used to shower the brown stock was diluted to contain roughly 1% dis-
solved solids. These solids levels correspond to a typical second stage
of brown stock washing in a three stage vacuum drum setup. The diluted
25 stock and shower liquor were heated to 1 60F. Using a laboratory de-
vice, the diluted stock (300 ml) was vacuum filtered on a polyester mesh
at 1.3 inches Hg for 10 seconds. The shower liquid (25 ml) was then ap-
plied and the system subjected to vacuum for an additional 10 seconds.
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The consistency of the mat was then measured. When treatments
were added they were added to the stock and shower liquid prior to incu-
bation. The defoamer (a) used in this study, containing a combination of
oil and ethylene bis stearamide, or EBS (typical components in brown
5 stock washing defoamers), was added at 100 ppm (total weight basis).
The surfactant used in this example was Rhodapex N-70 (available from
Rhone Poulenc) which is an alcohol ethosulfate, added at 100 ppm ac-
tives. The results are contained in Table l.
TABLE I
Brown Stock Mat Consiste"cy in
Simulated Second Stage of Washing
Treatment Mat ConsistencY
Untreated 1 6.3%
Defoamer A 15.3%
Rhodapex N-70 15.3%
DefoamerAand 16.5%
Rhodapex N-70
This laboratory device, unlike a typical brown stock washer, is de-
signed to minimize the generation of foam. This explains why the un-
25 treated sample actually has a higher consistency than that treated withthe defoamer. The defoamer apparently inhibits liquid removal versus
that of a non-foamy system. Unfortunately, brown stock washers cannot
be operated without defoamers as the turbulent process tends to gener-
ate foam.
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The addition of the surfactant in combination with the defoamer, in
the above example, surprisingly counteracted the negative effect of the
defoamer alone treated system.
5 Example 2
In the following example, a similar type of study as described in
Example 1 was conducted over a series of days. The results for the in-
dividual days are listed as variations in stock and liquor age, tempera-
10 ture, and starting consistency can affect the results. The simulationswere all conducted as described in Example 1. In each case, Defoamer
A was added to the stock (at 100 ppm). The treatment was added to the
stock and displacement shower liquid (at 100 ppm actives). The resultant
mat consistencies are listed along with the percent increase or decrease
15 in mat consistency that was observed with the treatment addition, in
Table ll (anionic materials) and Table lll (nonionic materials).
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-
TABLE ll
Brown Stock Mat CG.ISjSte~l-,Y in
Simulated Second Stage of Washing
5(Effect of Anionic Materials)
%Mat %Mat
Consistency Consistency
Test DefoamerDefoamer+% Increase (I)
Dav Material Alone Material or Decrease (D)
a Rhodapex N70 13.9 14.6 5 I
b Rhodapex N70 15.3 16.5 8 I
e Rhodapex N70 13.6 15.3 12 I
g Rhodapex N70 14.2 16.0 13 I
e Alipal EP115 13.6 15.0 10I
e Alipal C0436 13.6 15.2 12 I
f Gafac RE410 13.6 14.7 8 I
f Gafac RB400 13.6 14.9 10 I
f PolyTergent CS1 13.6 15.3 12 I
g PolyTergent CS1 14.2 15.2 7 I
e lgeponT33 13.6 15.4 13I
f lgeponT33 13.6 16.4 21 I
g lgepon T33 14.2 16.3 15 I
a Tamol SN 13.9 14.2 2 I
- ` 21S97~8
Material Description:
RhodapexN70 = alcohol ethosulfate (2 EO)
Alipal EP115 = nonyl phenol ethosulfate (20 EO)
Alipal C0436 = nonyl phenol ethosulfate (4 EO)
Gafac RE410 = alcohol based phosphate ester
Gafac RB400 = nonyl phenol based phosphate ester
PolyTergent CS1 = carboxylated alkoxylated alcohol
Igepon T33 = fatty sulfonate amide
Tamol SN = naphthalene sulfonate
(Materials available under the above tradenames from Rhone Poulenc,
Rohm & Haas, and Olin Chemicals)
As is demonstrated in Table ll, all of the anionic materials, with the
exception of naphthalene sulfonate, significantly increased the consis-
tency of the brown stock mat.
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TABLE lll
Brown Stock Mat Consistency in
Simulated Second Stage of Washing
(Effect of Nonionic Materials)
% Mat % Mat
Consistency Consistency
Test Defoamer Defoamer+ % Increase (I)
DaY Material Alone Materialor Decrease (D)
d SurfonicL24-7 13.8 ~ 14.9 8I
e Surfonic L24-7 13.6 15.7 15 I
g Surfonic L24-7 14.2 15.5 9 I
e Surfonic L24-12 13.6 15.2 12 I
f Surfonic LF17 13.6 14.6 7 I
e Antarox LAEP16 13.6 15.0 10 I
f Antarox LAEP59 13.6 15.6 15 I
f Antarox LAEP73 13.6 15.2 12 I
g Antarox LAEP73 14.2 15.0 6 I
e Surfonic JL80X 13.6 15.5 14 I
f Surfonic JL80X 13.6 15.4 13 I
d Tergitol Minfoam 1X13.8 14.4 4 I
e Tergitol Minfoam 1X13.6 15.4 12 I
g Tergitol Minfoam 1X14.2 15.4 8 I
e Tergitol Minfoam 2X13.6 15.3 12 I
f Tergitol XD 13.6 14.6 7 I
e Surfonic N95 13.6 15.3 12 I
d Pluronic F108 13.8 13.5 2 D
g Pluronic F108 14.2 14.6 3 I
a PVP K90 13.9 13.7 1 D
b PVP K90 15.3 14.8 3 D
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.
11
Material Description:
Sur~onic L24-7 = Alcohol Ethoxylate (7 EO)
Surfonic L24-12 = Alcohol Ethoxylate (12 EO)
5 Surfonic LF17 = Alcohol Ethoxylate capped in Propylene oxide
Antarox LAEP16 = Alcohol Ethoxylate capped in Propylene oxide
Antarox LAEP59 = Alcohol Ethoxylate with some Propylene oxide
Antarox LAEP73 = Alcohol Ethoxylate with some Propylene oxide
Surfonic JL80X = Alcohol Ethoxy-Propoxy-Ethoxylate Blocks
10 Terg. Minfoam 1X = Alcohol Ethylene Oxide/Propylene Oxide Random
Terg. Minfoam 2X = Alcohol Ethylene Oxide/Propylene Oxide Random
Tergitol XD = Alcohol Ethylene Oxide/Propylene Oxide Random
SurfonicN95 = Nonyl Phenol Ethoxylate
Pluronic F108 = Ethoxy-Propoxy-Ethoxy Block Surfactant
15 PVP K90 = Polyvinyl pyrrolidone
(Materials available under the above tradenames from Texaco, Rhone
Poulenc, Union Carbide, and BASF.)
20 As can be observed from Table lll, all of the nonionic materials tested
tended to increase the consistency of the brown stock mat, with the ex-
ception of polyvinyl pyrrolidone and the block surfactant of ethylene oxide
and propylene oxide.
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Example 3
In this example, as with the previous examples, a second stage of
brown stock washing was simulated. A formulation containing a combi-
5 nation of alcohol ethoxylate and alcohol ethosulfate was utilized (called
Formula 1) along with three types of defoamer. Defoamer A was based
on oil and EBS (used in previous examples), Defoamer B was based on
silicone and surfactant, and Defoamer C was based on ethoxylated/pro-
poxylated glycerin. The results are listed in Table IV.
TABLE IV
Brown Stock Mat Consiste..cy i
Simulated Second Stage of Washing
Effect of Surfactant Formula with Different Defoamers
Consistency (%) with
Defoamer (100 ppm) Formula I Dosa~e
0 ppm 100 ppm 200 ppm
A 15.7 16.3 16.2
B 16.0 16.5 16.8
C 15.7 16.7 16.8
As the above data indicates, the present invention is effective in
increasing mat consistency in the presence of different types of de-
25 foamer.
21~974~
Example 4
A mill trial was conducted using Formula 1, discussed in Example3, added to the system at 0.75 Ibs/ton (Ibs Formula I per ton of dry pulp
5 produced). The mill was in a northern location using softwood pulped
with the Kraft process. A typical three stage counter current, vacuum
drum washer was used to wash the stock prior to bleaching. The brown
stock defoamer used in the process was based on hydrocarbon oil and
silica. A washing aid (made up of an anionic dispersant, nonylphenol
10 ethoxylate, and an ethoxy/propoxy/ethoxy block surfactant) was also fed
to the system (1.4 Ibs per ton) where the second stage mat was diluted
just before the pulp entered the third stage of washing during the pretrial
period. This wash aid was replaced by Formula I for the trial period.
Table V contains the results for third stage mat consistency, the
carryover (Ibs per ton) of contaminant solids in the liquor leaving with the
third stage mat, and the vacuum that the third stage drum was pulling.
TABLE V
Results from Northern Mill Trial
Mat
Trial ConsistencY Carrvover Vacuum
(%) (#/T) (in Hg)
Pretrial 11.4 43.7 ------
25period 10.8 53.7 17.8
10.7 109.4 16.8
11.9 24.3 17.4
10.4 30.0 16.0
10.8 46.5 ------
10.3 53.4 14.0
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_
TABLE V (cont'd)
Results from Northem Mill Trial
Mat
Trial ConsistencY CarrYover Vacuum
(%) (#/T) (in Hg)
Trial 11.6 16.1 16.8
period 11.7 19.1 13.8
12.0 21.0 15.5
11.7 17.9 15.0
11.2 43.5 16.0
11.8 22.1 14.2
Pretrial avg.10.9 51.6 16.4
std devØ6 27.8 1.5
Trial avg. 11.7 23.3 15.2
std devØ3 10.1 1.1
The results show that with the use of Formula I there was a signifi-
cant increase in mat consistency, decrease in contaminant solids carry-
over with the mat, and a decrease in the vacuum being pulled on the mat.
The decrease in contaminant solids carryover, caused by the increase in
20 mat consistency through the washing process, is significant as it offers
two potential advantages. One advantage is that the pulp with greater
cleanliness will require less bleaching chemicals over a long period of
time and will provide increased recovery of pulping by-products. A mill
will also be able to either increase its production or decrease the wash
25 water necessary to produce pulp of the same degree of cleanliness as
before.
21~, 4~
The increase in consistency of the mat also caused a decrease in
the vacuum of the drum washer. With a greater amount of liquid removed
from the mat, air could be pulled through the mat, decreasing the meas-
ured vacuum.
Example 5
A second trial was conducted using Formula 1, described in Exam-
ple 3. This trial was conducted at a southern location utilizing softwood
pulped using the Kraft process. This pulp mill used a belt washer tsome-
10 times referred to as a "chemi-washer"). In this type of system, pulp is not
rediluted in between stages of washing, but is rather carried along on an
open mesh belt under vacuum, where a series of showers spray the mat
of pulp to clean it. As with the vacuum drum washer described in Exam-
ple 4, the liquor used to shower the pulp is moved in a counter current
15 flow pattern to the pulp, so that the cleaner liquid is showering the clean-
er pulp and the dirtier liquor is showering the dirtier pulp (shower liquor
being cleaner than the pulp it is showering).
This mill was using two different defoamers, one based on oil/EBS,
20 the other on silicone oil. Formula I was fed to the third shower out of six.
The pulp exiting the washer was diluted prior to sampling it; therefore
consistency measurements of the mat were not possible. However, the
vacuum could be measured at seven locations along the washer.
Therefore, vacuum was used to evaluate mat consistency.
As there are many parameters that can be altered on a machine
such as this to change the vacuum, the vacuum was monitored for a short
time before and after changes were made to the Formula I addition rate.
Within each of these time periods, major parameters such as production
30 rate remained relatively constant.
21S9748
16
TABLE Vl
Results from Southem Mill Trial
(Pre-trial to First Dosage Rate of Formula 1)
Vacuum at Positions Across Washer
Dav Time 1 2 3 4 5 6 7
Pretrial 1 10:33 12 21 26 21 22 20 10
10:40 12 20 25 19 21 20 10
10:54 12 20 28 23 23 18 13
11:15 13. 22- 31 20 21 18 6
Trial 1 11:28 8 17 20 13 16 16 4
(0.5 Ibs/T) 11:42 9 18 25 12 15 12 5
Formula 1 11:53 5 15 17 12 17 15 6
12:06 7 18 17 12 15 11 6
Pretrial average 12 21 28 21 22 19 10
Trial average 7 17 20 12 16 14 5
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TABLE Vll
Results from Southem Mill Trial
(First Dosage Compared to Second Dosage Rate of Formula 1)
Vacuum at Positions Across Washer
Dav Time _ 2 3 4 5 6 7_ _ _ _ _
Trial A ll5:28 16 23 26 24 24 27 15
(0.5 Ibs/T) 6:28 14 19 - 19 18 19 25 12
7:29 13 19 20 21 20 27 13
7:40 14 23 20 20 21 27 13
8:30 16 24 26 18 20 26 9
9:40 11 20 19 14 18 21 6
Trial B ll10:05 14 24 19 12 15 19 6
(0.71bs/T) 10:13 14 22 17 9 13 18 3
10:29 13 23 19 9 16 15 8
10:47 11 22 20 10 16 14 8
11:00 10 21 19 12 16 16 9
11:14 10 21 18 11 16 14 8
Trial A average 14 21 22 19 20 26 11
Trial B average 12 22 19 11 15 16 7
The reduction in vacuum observed on this belt washer indicated
25 that a greater amount of air was being pulled through the mat due to an
increase in the fiber consistency of the mat (reduction in the liquor held
there).
-- 21Sg748
18
ExamPle 6
Unbleached Kraft pulp was diluted to 0.7% consistency using de-
ionized water and heated to 1 60F. The stock was thickened using the
5 laboratory device described in Example 1 with the exception that no dis-
placement liquid was applied. The results are contained in Table Vlll.
TABLE Vlll
Defoamer A (ppm) Consistency (%) with Formula I Dosa~e
0 ppm 100 Ppm
0 11.8 15.7
100 11.4 14.4
The above example demonstrates that the present invention is ef-
fective in increasing the consistency of a stock which is relatively clean of
contaminants. It also shows that the addition of a defoamer is not neces-
sary when the stock is not inherently foamy.
Example 7
In this example, hardwood, produced from the sulfite pulping proc-
ess, was sampled from the vat of an extraction stage bleach plant washer
25 (the vat contains both the stock and extraction stage liquor just prior to
being thickened on the drum). The extraction stage consisted of caustic
extraction with some peroxide and oxygen. This stock was thickened in
the laboratory and showered with deionized water in the same manner as
in Example 1. The stock was treated with Formula I from Example 3; no
30 defoamer was added to the test. The dissolved solids contained in the
'21597~8
resulting mat were also measured so that the Ibs. solids per ton of oven
dry fiber which would be carried on to the next process could be calcu-
lated (termed carryover). The results are contained in Table IX.
TABLE IX
Results Simulating Bleach Plant Washer
Formula I MatConsis- Carryover
Dosa~e (ppm)tency (%) (Ibs/ton)
0 10.2 31.6
100 12.5 25.2
200 13.5 21.8
These results demonstrate that Formula I was able to increase the
mat consistency in bleach plant washers. Because of the increase in mat
consistency, there was also less carryover of contaminants caused by
Formula 1.
Example 8
In this example, pulp and liquor were sampled from two washers
(two different mills) using pulp produced from the sulfite process. The
25 studies were performed in the same manner as previous examples and
Defoamer A (from Example 3) was also added. The results are found in
Table X.
. 21~g74~
TABLE X
Results Using Sulfiite Pulp
Stock from Mill 1 Stock from Mill 2
Formula I Mat Consis- Mat Consis-
Dosaqe (ppm) tencv (%) tencv (%)
0 10.9 10.2
100 11.2 11.1
200 1 1.4 14.4
This example shows that the present invention not only works in
pulp produced from the Kraft pulping process, but also pulp produced in
15 the sulfite process.
Note also that the treatments of the present invention may be used
in combination with various detackification products ( i.e., various water
soluble surface active polymers such as those noted in U.S. Patent
20 4,744,865) which are commonly used in the pulp mill in order to, e.g.,
control pitch outbreaks.
While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and modi-
25 fications of this invention will be obvious to those skilled in the art. Theappended claims and this invention generally should be construed to
cover all such obvious forms and modifications which are within the true
spirit and scope of the present invention.
