United States Patent [19]
Gill et ale
[11]
[45]
4,138,312
Feb. 6, 1979
[56]
1,906,886
2,120,287
2,842,489
3,347,739
3,367,735
3,909,344 9 Claims, 1 Drawing Figure
3,954,552 5/1976 Lukes et aI 162/DIG. 8
FOREIGN PATENT DOCUMENTS
928008 6/1973 Canada 162/DIG. 8
2159935 6/1973 France 162/DIG. 8
Primary Examiner-S. Leon Bashore
Assistant Examiner-Peter F. Kratz
Attorney, Agent, or Firm-Merriam, Marshall & Bicknell
ABSTRACf
The incinerator product obtained from the incineration
of black liquor and other spent liquors from a soda
pulping process is treated to remove contaminants including
chlorides, sulphates and potassium compounds
and to recover a high proportion of the sodium carbonate.
The incinerator product is treated with water to
form a slurry in which substantially pure sodium carbonate
monohydrate is crystallized and a major proportion
of the contaminants are dissolved, the sodium carbonate
monohydrate is then separated and dissolved
sodium carbonate is recovered as a bicarbonate or sesquicarbonate
precipitate by carbonation of the solution.
The preferred process involves an initial flue gas carbonation
of the separated mother liquor after removal
of sodium carbonate monohydrate to produce a sodium
sesquicarbonate precipitate and a subsequent carbonation
of the mother liquor, after separation of the sodium
sesquicarbonate therefrom, with pure carbon dioxide
to precipitate sodium bicarbonate.
[57]
[21] Appl. No.: 797,563
[22] Filed: May 16, 1977
[30] Foreign Application Priority Data
May 19, 1976 [ZA] South Africa 76/2995
[51] Int. C1.2 D21C 11/04
[52] U.S. C1 162/30 R; 162/33
[58] Field of Search 162/30 R, DIG. 8, 33;
423/182, 183, 184, 186, 189, 190,207,208,421,
422,425,427, DIG. 3
References Cited
U.S. PATENT DOCUMENTS
5/1933 Richter 162/30 R
6/1938 MacMullin 423/427
7/1958 Svanoe 423/425
10/1967 Tomlinson 162/30 R
2/1968 Hanway et aI 423/189
9/1975 Lukes 162/30 R
[54] PROCESS OF RECOVERING SODIUM
CARBONATE FROM SPENT PULPING
LIQUORS
[75] Inventors: Ronald A. Gill, Johannesburg;
Waldemar S. Wojtowicz,
Krugersdorp, both of South Africa;
Cornelius E. Berthold, Littleton,
Colo.; Cecil M. Wheeler, Oak Brook,
Ill.
[73] Assignee: Sappi Limited, Johannesburg, South
Africa
9
./8
U.S. Patent
Vl!OO'D C.HIPS
Feb. 6, 1979
9
./8
4,138,312
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an
alternative and more efficient process for the removal
of chlorides, sulphates and potassium compounds from
a sodium carbonate incinerator product.
According to the invention in a process for the manufacture
of cellulose pulp by means of a soda process in
which spent liquors are concentrated by evaporation
and the concentrated liquors are incinerated in a fluidised
bed. incinerator to produce a granular sodium
carbonate incinerator product contaminated by chlorides,
sulphates and potassium compounds, the incinerator
product being dissolved in water and causticised in
known manner to form white liquor comprising essentially
sodium hydroxide, which white liquor is re-used
in the said soda process to provide a closed system, the
improvemen.t comprising treating the incinerator product
with water to form a slurry, agitating theslurry so
as to dissolve incinerator product with its contaminants
and at the same time crystallise substantially pure sodium
carbonate monohydrate leaving a major proportion
of the contaminants in solution, separating the substantially
pure sodium carbonate from the liquor containing
the contaminants, converting sodium carbonate
in solution to sodium bicarbonate by carbonation with
2
phate and potassium compounds when the patent is
applied to a sulphur free soda process.
A further patent concerned with the recovery of
pulping chemicals from spent digester liquors, namely,
5 U.S. Pat. No. 1,906,886 (Richter), describes a process
for the crystallisation of sodium carbonate from smelt
liquors in order to recover a portion of the sodium
carbonate from a furnace smelt product. This patent,
however, is not concerned with the removal of contam-
10 inants but rather with the removal of some sodium carbonate
for use as a raw material in another process and
only the balance of the chemicals is capable of re·use in
the original pulp making operation from which the
spent cooking liquor arose. Thus the Richter process
15 will usually involve separation ofthe recovered components
for use in different though simultaneous pulping
operations and Richter is not, therefore, concerned with
a single closed circuit in which the recovered chemicals
are re-used in the same pulping process. Contaminants
are not removed in ac.cordance with the Richter process
and, although substantially pure sodium carbonate is
recovered by the crystallisation or carbonation, too
small a proportion of the sodium carbonate is recovered
in order effectively to operate a closed circuit recovery
system.
Our co-pending application No. 727,579 describes a
process for removing chlorides, sulphates and potassium
compounds, from an incinerator product. This
process consists of leaching the incinerator product
with water to dissolve contaminants together with a
portion of the sodium carbonate leaving the bulk of the
sodium carbonate in solid form and substantially more
pure and recovering sodium carbonate from the solution
by subjecting the solution to carbonation thus precipitating
sodium bicarbonate and sodium sesquicarbonate.
In the preferred method of our co-pending application
a sodium carbonate decahydrate crystallisation step
is carried out on the solution after the leaching step and
prior to the carbonation step. The method described
results in the removal of contaminants to a high degree
making it possible to utilise a fluidised bed incinerator in
a closed chemicals recovery system.
4,138,312
1
DESCRIPTION OF THE PRIOR ART 50
Prior work has been carried out in order to remove
chloride contaminants from furnace smelts. For example
U.S. Pat. No. 3,909,344 describes a process ofleaching
and/or crystallisation of the furnace smelt for the
recovery of sodium carbonate and the removal of so- 55
dium chloride by precipitation of sodium chloride from
the mother liquor from the crystallisation stage. However
this process makes no provision for removal of
other contaminants such as sulphates and potassium
compounds, a build up of which is unacceptable in a 60
fluidised bed reactor operating on a soda recovery process.
Canadian Pat. No. 928,008 likewise describes a process
for the removal ofchlorides from furnace smelts by
leaching and crystallisation procedures but this process 65
also centres around the crystallisation of sodium chloride
in order to remove this contaminant from the circuit.
No provision is made however for removing sul-
In sodium based pulp mills the black liquor contain- 20
ing spent chemicals from the digestion of cellulosic
vegetable fibres and in some cases the spent liquor from
an oxygen bleachingldelignification stage is passed to a
chemical recovery system where the black liquor is first
reduced in volume by evaporation. Thereafter the con- 25
centrated material is incinerated, for· example, ina furnace
or by means of a fluidised bed reactor. Finally the
incinerator product, which in soda processes contains a
high percentage of sodium carbonate, is dissolved in
water and causticised to convert the sodium carbonate 30
to sodium hydroxide and the "white liquor" so obtained
is returned for re-use in the digestion process.
Although soda processes exclude the use of sulphur
containing chemicals for the digestion of wood and
while oxygen bleaching of the pulp excludes the use of 35
chlorine, both of these contaminants may be introduced
into the process as constituents of the raw materials and
process water used. Potassium compounds are also contained
in wood and of course where sea water floated
logs are concerned substantial quantities of chlorides 40
are introduced into the process. In a closed pulping and
recovery circuit, a build-up of contaminants such as
chlorides, sulphates and potassium compounds may
therefore occur.
When a fluidised bed reactor is used to· incinerate 45
concentrated liquor containing these contaminants, loss
of fluidisation of the reactor bed will occur if the concentration
of the contaminants exceeds a critical level.
PROCESS OF RECOVERING SODIUM
CARBONATE FROM SPENT PULPING LIQUORS
FIELD OF THE INVENTION
This invention relates to a process for the recovery of
chemicals employed in soda and/or oxygen pulping of
cellulosic vegetable matter and/or oxygen bleaching/
delignification of the resulting pulp, such processes
which use sodium hydroxide or sodium carbonate as the
pulping or bleaching chemical hereinafter being called
"soda processes". More particularly the invention is
concerned with the removal of contaminants from fluidised
bed incinerator recovered products derived from
chemical recovery systems employed in soda processes.
Such contaminants include chlorides,sulphates and
potassium compounds.
BACKGROUND OF THE INVENTION
4,138,312
3
carbon dioxide, separating the precipitate so formed
from the mother liquor, converting the precipitate thus
recovered to substantially pure sodium carbonate, utilising
the various fractions of sodium carbonate recovered
for the formation of the said white liquor, and discharg- 5
ing the contaminant bearing mother liquor from the
system.
Such separation may be accomplished by fIltration or
by means of a centrifuge or by permitting the solids to
settle and decanting off the supernatant liquor or by any 10
other suitable means. Formation of the slurry may be
effected -in a crystallisation vessel equipped with a stirrer
or any other suitable means for agitating the slurry.
The spent liquors derived from a soda process include
those emanating from a soda cooking stage as well as an 15
oxygen bleaching or delignification stage carried out in
the presence of sodium hydroxide or sodium carbonate
and these liquors may be treated separately or in combination.
The temperature of the slurry should be kept above 20
35· C., and preferably at 85· C. The incinerator product
should be added in pelletised or ground form and preferably
such product is at a temperature exceeding 260·
C. when introduced into the crystallisation. vessel.
After separation of the solids from the slurry a por- 25
tion of the separated liquor should be recycled back to
the crystalliser for the formation of slurry with incoming
incinerator product, the solution of further contaminants
and the precipitation of sodium carbonate monohydrate.
The portion of separated liquor not recycled is 30
discharged to maintain a balance between the mass of
contaminants introduced with the incinerator product
and the mass of contaminants discharged with said liquor.
Enough water should be added to the system to
make up for losses, for example, through hydration of 35
sodium carbonate, evaporation, entrainment of liquor in
the solids and discharge of a portion of the liquor as
described above. This water is optionally introduced
into the system as wash water for the solids separated
from the system. 40
The invention also provides fot carbonating the
mother liquor with a flue gas containing carbon dioxide,
maintaining the liquor at a temperature of about 45· C.,
thereby producing a precipitate containing sodium sesquicarbonate
and separating the precipitate from the 45
mother liquor.
It has been found that nearly half of the sodium carbonate
in solution resulting from the sodium carbonate
monohydrate crystallisation step can be precipitated as
sodium sesquicarbonate (Na2C03' NaHC03.2H20) by 50
sparging with flue gas. This process has the advantage
over our aforementioned co-pending application that
the solution need not be cooled below 3D· C. to precipitate
the decahydrate of sodium carbonate and that pure
carbon dioxide gas need not be used in the carbonation 55
process to precipitate sodium bicarbonate as the only
compound recovered.
Further sodium carbonate can be recovered by carbonating
the mother liquor, after separation of the sodium
sesquicarbonate, with substantially pure carbon 60
dioxide, maintaining the temperature of the liquor at
about 45· C., precipitating sodium bicarbonate and separating
the precipitate from the solution. Sodium carbonate
which dissolves in the monohydrate crystallisation
process is thus recovered by using the abovemen- 65
tioned processes in series. The crystals of sodium sesqui·
carbonate and sodium bicarbonate produced in the car
bonation stages are separated from their mother liquon
4
by settling or filtration or centrifugal separation and the
mother liquors containing the bulk of the contaminants
are discharged from the system.
Although it might be possible to obtain sodium sesquicarbonate
and sodium bicarbonate crystals of acceptable
purity by merely separating the solid crystals
from the solutions in the various stages, it is to be noted
that these solutions contain large proportions of the
dissolved contaminants and that' crystals may occlude
some of this solution. It is therefore desirable to wash
the separated crystals in the filtration or centrifuging
processes.
The recovered sodium carbonate monohydrate with
contaminants at an acceptable level can be dissolved to
produce "green liquor" which is processed further according
to known procedures to produce the "white
liquor" used for example for soda pulping, oxygen pulping,
oxygen bleaching or any bleaching stage requiring
caustic soda.
Similarly the crystals of sodium sesquicarbonate and
sodium bicarbonate may be dissolved and causticised to
product white liquor. However, with the sesquicarbonate
and bicarbonate mixture the causticising would consume
more lime than normally required because the
sodium bicarbonate has to be converted to sodium carbonate
by the lime before the normal causticising reaction
can take place.
Preferably therefore the mixture of sodium sesquicarbonate
and sodium bicarbonate crystals are first decomposed
by heating to convert the mixture to sodium
carbonate, water and carbon dioxide. This carbon dioxide
can be recovered and re-used for carbonation in the
fmal bicarbonate precipitation stage described above.
The decomposition can be carried out in solution or the
crystals can be decomposed in a kiln or fluidised bed
according to known processes. The sodium carbonate
can then be dissolved together with the monohydrate
crystals to produce "green liquor" and the latter processed
to form "white liquor" for use in pulping or
bleaching of vegetable fibres.
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing is a schematic flow sheet
of a soda pulping process embodying a pulping chemical
recovery circuit according to the invention.
DETAILED DESCRIPTION OF THE DRAWING
Referring to the drawing, wood chips are fed by line
1 to a digester 2, wherein the wood chips are digested
by a pulping liquor fed by line 3 and containing sodium
hydroxide as the active pulping chemical in the soda
process.
The resulting pulp and spent pulping liquor are separated
and the pulp is washed with water 8, on brown
stock washer 4. The pulp can be washed with oxygen
bleach plant effiuent fed by the line 5 if desired.
The washed, unbleached pulp is fed by line 6 to an
oxygen bleaching plant 7 and the bleached pulp is
washed by water fed by line 9.
The spent liquor 10 which may also contain substances
derived from the bleaching operation is evaporated
in an evaporator 11.
The concentrated spent liquor 12 is burnt in a fluidised
bed incinerator 13, and the hot granular incinerator
product proceeds- by line 14 to a calciner 15. Th:
incinerator product consists mainly of sodium carbon-ate
containing contaminants such as chlorides, sulphate~
and potassium compounds. The incinerator product
L.C.S
EXAMPLE 1
Incinerator product (S.S.)
Starting liquor (L.S.)
S<?lids separated after first crystallisation (S.C.!)
Liquor separated after first crystallisation (L.C.!)
Solids separated after eight crystallisations (S.C.S)
Liquor separated after eighth cryst8Ilisation (L.C.S)
S.S. L.S. S.C.! L.C.! S.C.S
6
The carbon dioxide gas with water vapour and some
entrained solids from the calciner 15, proceeds by line
44 to the separator 19, where solids are removed by
scrubbing with water 18 and returned by line 4S to the
crystalliser 17.
The gas containing carbon dioxide and water vapours
is passed to the second stage carbonator by line 47, with
a portion of the gas being recycled by line 46 to the
calciner.
Liquor 48 from the separator 41, containing substantially
all the contaminants in solution is discharged from
the system.
In order to illustrate the invention example~ thereof
will now be described.
4,138,312
5
after passing through the calciner goes by line 16 to the
crystalliser 17, together with sodium carbonate produced
in the calciner by decomposition ofsesquicarbonate
and bicarbonate crystals delivered to the calciner 15
by line 43. In the crystalliser the incinerator product is 5
slurried in a solution containing dissolved incinerator
product. The temperature of the slurry is maintained
above 35° C., and sodium carbonate monohydrate is
crystallised. The contaminants dissolve and remain in
solution. The slurry containing newly formed sodium 10
carbonate monohydrate is withdrawn from the crystal·
liser by line 20, to the separator 21. The solids so separated
after washing with water contain substantially
pure sodium carbonate and proceed by line 22 to the
dissolver 23. The separated solution containing the bulk 15
of the contaminants and dissolved sodium carbonate is
recycled by line 31 to the crystalliser with a bleed otTby 4.5 liters of a liquor (L.S.) containing the constituents
line 32 to the carbonator 33. The volume of solution in given in the analysis of liquor (L.S.) below was placed
the crystalliser is kept constant by adding make-up in an agitated vessel and heated to a temperature of 85°
water by line 18 to separator 19 or by adding it directly 20 C. A series of crystallisations were carried out by addto
the crystalliser. ing an incinerator product (S.S.) derived from a soda
The separated solids are dissolved in dissolver 23 cooking process to the liquor in the vessel in the followwith
water or preferably weak white liquor delivered ing manner..For the first crystallisation, 840g of the
by line 24 to the dissolver. The solution called green incinerator product (S.S.) at a temperature of 320° C.
liquor proceeds by line 25 to the causticiser 26, where 25 was added to the liquor in the vessel and the slurry so
sodium carbonate is converted substantially completely formed was agitated for a period in excess of IS minutes
to sodium hydroxide by reaction with lime 27 from lime maintaining the temperature of the slurry at 85° C. At
kiln 28. The. precipitated calcium carbonate mud in the the end of this period 2 liters of slurry were withdrawn
causticiser 26 is separated from the sodium hydroxide 30 from the vessel, filtered under vacuum and the sepasolution
known as strong white liquor and is washed rated solids washed with 400 ml of hot water. The
with water to remove entrained alkali from it. The washed solids (S.C.l.) were analysed. The liquor
resulting wash solution is called weak white liquor and (L.C.l.) separated prior to washing, was analysed and
should preferably be used to dissolve the sodium car- returned to the agitated vessel. The washings were also
bonate in dissolver 23. 35 returned to the vessel.
After washing, the calcium carbonate mud may be Prior to· the second crystallisation, the volume of
returned by line 29 to a lime kiln 28 to be converted to slurry in the agitated vessel was made up to 4.5 liters
calcium oxide. with water and the temperature ofthe slurry adjusted to
The strong white liquor obtained from causticiser 26 85° C.
is recycled via line 30 to provide the pulping liquor fed For the second crystallisation, 840g of incinerator
by line 3 to digester 2. This sodium hydroxide solution 40 product (~.S.) at a temperature of 320° C. w~ added to
can also be used as a source of alkali in the bleach plant the slurry m the vessel and the slurry was agttated for a
7. period in excess of 15 minutes, maintaining the tempera-
In the carbonator 33, the solution introduced via line t~re of the slurry at 8~0 C. At the end of this period, 2
32 is subjected to the carbonation process by reaction hters of slurry were Withdrawn from the vessel fIltered
with carbon dioxide contained in the flue gas from in- 45 under vacuum and the separated ~olids washed with 400
cinerator 13 delivered by line 34. This flue gas should ~ of hot water. Th~ washed sol~ds were analysed. The
first be cooled as the temperature in the carbonator hquor separated pnor to washing was analysed and
should be below 60° C. In the reaction with carbon returned to the agitated vessel. The washings were
dioxide carbonate in solution is converted to bicarbon- 50 retu~ed to the ,:essel. ..
ate and precipitates mainly as sodium sesquicarbonate. . Pnor t~ the third crystalhsatlon the volum~ of sluI!y
The slurry so formed proceeds by line 35 to a separa- m the agttated vessel was made up to 4.5 hters With
tor 36. The solid sodium sesquicarbonate is separated water and the temperature of the slurry adjusted to 85°
from the solution and may be washed with water 37 if C. .. . .
desired. The solution from the separator 36 proceeds by 55 A total of eight. crystalhsatlons were carned .ou~ in
line 38 for the second carbonation stage in carbonator the m:mner descnbed ~or the second cry~talbsatlon
39 where it is subjected to the carbonation process by re<;ychng the separated ~quors and the washings to the
reaction with concentrated carbon dioxide gas deliv- agt~ted v~sel and m~g up the volume of slurry to
ed b 1
· 47 Th b t' 1 t" rt d 4.5 hters With water pnor to each subsequent crystallier
y me . e car ona e m so u Ion IS conve e sat'
to bicarbonate and precipitates mainly as sodium bicar- 60 ~. bonate. . e analYS'IS 0f .the 1c.01o1W'ing products produced'In
Th 1 e s urry so 1c.0rmed'IS dell'vered by II' ne 40 to a thiS example are gtven below: .
separator 41 where the solids are separated from the
solution and may be washed if desired by water 42.
The solids from the separators 36 and 41 proceed by 65
line 43 to the calciner 15 where the heat contained in the
incinerator product calcines them to sodium carbonate,
carbon dioxide and water.
8
then separated from the liquor in a continuous centrifuge.
The liquor at the beginning and end of the carbon~
atipn process was analysed as well as the crystals. The
following results were obtained:
5
Liquor Liquor
before after
Carbonation Carbonation Crystals
Sodium as Na 8.48% 4.16% 20.04%
10 Potassium as K 3.03% 3.18% 0.65%
Carbonate asC03 9.10% 0.90% 3.50%
Bicarbonate as HC03 0.96% 5.40% 54.50%
Sulphate as S04 6.00% 7.23% 1.25%
Chloride as CI 1.16% 1.41% 0.24%
Water 71.27% 77.72% 19.82%
15
Whereas the above examples relate to a batch process, it
will be appreciated that the process of the invention
may be operated batch-wise or on a continuous basis.
We claim:
1. A process for the manufacture of cellulose pulp by
means of a soda process in which spent liquors are concentrated
by evaporation and the concentrated liquors
are incinerated in a fluidized bed incinerator to produce
a granular sodium carbonate incinerator product contaminated
by chlorides, sulphates and potassium compounds,
the incinerator product being dissolved in
water and causticized in known manner to form white
liquor comprising essentially sodium hydroxide, which
white liquor is re-used in the said soda process to provide
a closed system, the improvement comprising:
treating the incinerator product with water to form a
slurry, agitating the slurry so as to dissolve incinerator
product with its contaminants and at the same
time crystallize substantially pure sodium carbonate
monohydrate leaving a major proportion of the
contaminants in solution, separating the substantially
pure sodium carbonate from the liquor containing
the contaminants, and washing the separated
sodium carbonate with water;
converting sodium carbonate remaining with the
contaminants in solution to sodium bicarbonate by
carbonation with carbon dioxide, separating the
precipitate so formed from the mother liquor, and
converting the precipitate thus recovered to substantially
pure sodium carbonate;
utilizing sodium carbonate recovered in the formation
of white liquor; and
discharging the contaminant bearing mother liquor
from the system.
2. The process of claim 1 in which the temperature of
the slurry is maintained above 35° C.
3. The process of claim 2 in which the temperature of
the slurry is maintained at approximately 85° C.
4. The process of claim 1 in which a portion of the
liquor obtained after separation of sodium carbonate
from the slurry is recycled for the formation of slurry
with incoming incinerator product, the solution of further
contaminants and the precipitation of sodium car-
60 bonate monohydrate.
5. The. process of claim 4 in which the portion of
separated liquor not recycled is discharged, after carbonation
with carbon dioxide, to maintain a balance
between the mass of contaminants introduced with the
incinerator product and the mass of contaminants discharged
with said liquor.
6. The process of claim 5 in which make-up water is
added to the slurry to replace losses of water, such
20
45
4,138,312
3.03
6.7
10.9
13.8
1.2
64.3
= 4.03g
= 0.12g
= 3.91g
2.0
0.06
32.7
0.011
22.0
41.4
2.18
6.0
14.9
13.9
0.70
62.5
0.88
0.03
7
33.0
0.004
23.4
42.7
-continued
1.91
4.5
EXAMPLE 2
13.8
15.4
1.58
4.8
0.48 0.51
1.8 63.9
%
% 51.2
%%
%
% 40.1
After the sodium sesquicarbonate crystals had been
removed from it, the liquor was returned to the carbonating
column, the temperature was kept at 49° C. and
the solution was sparged with pure carbon dioxide for 65
11 hours. Thereafter fresh liquor was added periodically
and slurry removed at such a rate as to replace the
contents of the column in 15 hours. The crystals were
Li~uor Liauor
be ore a er
Carbonation Carbonation Crystals
Sodium as Na 11.40% 8.48% 27.08% Potassium as K 2.36% 2.37% 0.34% 50
Carbonate as C03 14.49% 8.41% 26.50%
Bicarbonate as He03 nil 1.42% 18.60%
SUlfchate as S04 5.14% 5.75% 0.38%
Ch oride as CI 1.23% 1.43% 0.17%
Water 65.38% 71.64% 26.9~%
55
Sodium
as Na
Potassium
asK
Carbonate
asC03
Sulphate
asS04
Chloride
asCI
Water
NOTE
No bleed out of liquor was carried oyt between each crystallisation
(~xcept for. material consumed in analysis) as it was deemed that the
hquors were not sufficiently concentrated in contaminants. It will be
noted that the concentration ofcontaminants increased between the first
and the eighth crystallisation. To maintain the cOllcentration of anyone
contaminant in liquor L.C.8 for further crystallisations. it would be
necessary to bleed out liquor in sufficient volume to maintain a balance
between the mass of such contaminant entering the vessel and the mass
of such contaminant leaving in the solids and in the bleed out. For
example. further buildup in the concentration of chloride in the liquor
could be prevented as follows:
Chlorides entering in 840g of incinerator
product at 0.48%
Chlorides removed in the solids at 0.01 1%
(I O6Og of solids from 2 liters of slurry
in the 8th crystallisation)
Hence Chlorides to be removed in the
bleed out
A liquor representing the liquor composition after 30
repeated crystallisations with the same liquor was prepared
for use in pilot plant experiments in order to
precipitate sodium sesquicarbonate from it. The liquor
was kept in a carbonating column at 43° C. and was
sparged with a mixture of air and carbon dioxide con- 35
taining 14% carbon dioxide by volume. Sparging was
continued for 16 hours whilst maintaining the temperature
at 43° C. Thereafter fresh liquor was added periodically
and slurry was withdrawn at such a rate as to
replace the contents of the column in 15 hours. At the 40
end of this period the slurry was withdrawn from the
column and the crystals were separated from the liquor
in a continuous centrifuge. The liquor before and after
carbonation was analysed as well as the crystals. The
results were the following:
The liquor remaining after separation of the sodium
sesquicarbonate crystals was carbonated with pure carbon
dioxide to precipitate sodium bicarbonate. This is
described in the next example.
EXAMPLE 3
At a concentration of 1.2% chloride in the liquor, 25
325.8g of liquor would be bled out prior to the 9th
crystallisation.
4,138,312
10
discharging the contaminant bearing second mother
liquor from the system.
8. The process of claim 7 in which the separated
precipitates obtained after carbonation of the mother
S liquors are heated in known manner to form sodium
carbonate, carbon dioxide and water and the carbon
dioxide so formed is utilised as set out in the process of
claiJJl7 to produce sodium bicarbonate.
9. A process for the manufacture of cellulose pulp by
10 means of a soda process in which spent liquors are concentrated
by evaporation and the concentrated liquors
are incinerated in a fluidized bed incinerator to produce
a granular sodium carbonate incinerator product contaminated
by chlorides, sulphates and potassium com-
IS pounds, the incinerator product being dissolved in
water and causticized in known manner to form white
liquor comprising essentially sodium hydroxide, which
white liquor is re-used in the said soda process to provide
a closed system, the improvement comprising:
treating the incinerator product with water to form a
slurry, agitating the slurry so as to dissolve incinerator
product with its contaminants and at the same
time crystallize substantially pure sodium carbonate
monohydrate leaving a major proportion of the
contaminants in solution, separating the substantially
pure sodium carbonate from the mother liquor
containing the contaminants, and washing the
separated sodium carbonate with water; and
carbonating the mother liquor with a flue gas containing
carbon dioxide, maintaining the liquor at a
temperature of about 45· C. producing a precipitate
consisting mainly of sodium sesquicarbonate,
separating the precipitate from the mother liquor,
and converting the precipitate to substantially pure
sodium carbonate;
utilizing sodium carbonate recovered in the formation
of white liquor; and
discharging the contaminant bearing second mother
liquor from the system. • • • • •
9
make-up water being used for washing of sodium carbonate
after separation from the liquor.
7. A process for the manufacture of cellulose pulp by
means of a soda process in which spent liquors are concentrated
by evaporation and the concentrated liquors
are incincerated in a fluidized bed incinerator to produce
a granular sodium carbonate incinerator product
contaminated by chlorides, sulphates and potassium
compounds, the incinerator product being dissolved in
water and causticized in known manner to form white
liquor comprising essentially sodium hydroxide, which
white liquor is re-used in the said soda process to provide
a closed system, the improvement comprising:
treating the incinerator product with water to form a
slurry, agitating the slurry so as to dissolve incinerator
product with its contaminants and at the same
time crystallize substantially pure sodium carbonate
monohydrate leaving a major proportion of the 20
contaminants in solution, separating the substantially
pure sodium carbonate from'the frrst mother
liquor containing the contaminants, and washing
the separated sodium carbonate with water;
carbonating the frrst mother liquor with a flue gas 2S
containing carbon dioxide, maintaining the liquor
at a temperature of about 45· C. producing a precipitate
consisting mainly of sodium sesquicarbonate,
separating the precipitate from the resulting
second mother liquor, and converting the precipi- 30
tate to substantially pure sodium carbonate;
converting sodium carbonate in the second mother
liquor to sodium bicarbonate by carbonation with
substantially pure carbon dioxide, separating the 3S
sodium bicarbonate precipitate so formed from the
mother liquor, and converting the precipitate thus
recovered to substaIltially pure sodiumcarbonate;
utilizing sodium carbonate recovered in the formation
of white liquor; and 40
4S
SO
SS
60
6S