CA1267255A - Method for increasing the efficiency of a causticizing process - Google Patents
Method for increasing the efficiency of a causticizing processInfo
- Publication number
- CA1267255A CA1267255A CA000544206A CA544206A CA1267255A CA 1267255 A CA1267255 A CA 1267255A CA 000544206 A CA000544206 A CA 000544206A CA 544206 A CA544206 A CA 544206A CA 1267255 A CA1267255 A CA 1267255A
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- Canada
- Prior art keywords
- lime
- white liquor
- lime mud
- causticity
- causticizing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/40—Production or processing of lime, e.g. limestone regeneration of lime in pulp and sugar mills
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- Paper (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A METHOD FOR INCREASING THE EFFICIENCY
OF A CAUSTICIZING PROCESS
A method for increasing the efficiency of the causticizing process which comprises: a) adding to a green liquor between 78 and 82% of the stoichiometric amount of lime necessary to react with the amount of Na2C03 present in the green liquor to obtain a white liquor containing NaOH and lime mud. The white liquor is then clarified by extracting the lime mud present to obtain a white liquor having a total solid concentration of about 10-60 grams/liter. The supernatant liquid of the white liquor is treated with an additional amount of lime to increase the causticity to about 87%, then allowing further causticizing reaction between the lime and Na2CO3. The remaining lime mud present is removed to obtain a white liquor which has the causticity of about 87%. One is thus able to raise the causticity of partially clarified white liquor following the normal causticizing process, the mud present being sufficient to increase causticity without substantially decreasing settling rate.
A METHOD FOR INCREASING THE EFFICIENCY
OF A CAUSTICIZING PROCESS
A method for increasing the efficiency of the causticizing process which comprises: a) adding to a green liquor between 78 and 82% of the stoichiometric amount of lime necessary to react with the amount of Na2C03 present in the green liquor to obtain a white liquor containing NaOH and lime mud. The white liquor is then clarified by extracting the lime mud present to obtain a white liquor having a total solid concentration of about 10-60 grams/liter. The supernatant liquid of the white liquor is treated with an additional amount of lime to increase the causticity to about 87%, then allowing further causticizing reaction between the lime and Na2CO3. The remaining lime mud present is removed to obtain a white liquor which has the causticity of about 87%. One is thus able to raise the causticity of partially clarified white liquor following the normal causticizing process, the mud present being sufficient to increase causticity without substantially decreasing settling rate.
Description
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This invention relates to a method of increasing the e~ficiency o~ the causticizing process related to the maXing of white liquor from green liquor in a pulping operation in adding lime by steps.
BACKGROUND OF THE INVENTION
In the manufacture of alkaline-process of making pulps, the wood is cooked with white liquor comprising NaOH, sodium carbonate, and sulfur salts of sodium such as sodium sulfate, sulfide, thiosulfide. ~ter cooking, the liquor is 10 evaporated, the organic materials burned and the inorganic materials are dissolved to obtain the green liquor. This green liquor is generally discharged in a slaker together with lime. The lime produaes calclum hydroxide which is further reacted in reactors mounted in series call~d 15 causticizars, and following the causticizars, the lime mud (CaCO3) is ~iltered such as with rotating drums. Thus, this process generates white li~uor by converting the Na2C03 to cau~tic soda (NaOH) and lime mud CaCO3, CaO
This invention relates to a method of increasing the e~ficiency o~ the causticizing process related to the maXing of white liquor from green liquor in a pulping operation in adding lime by steps.
BACKGROUND OF THE INVENTION
In the manufacture of alkaline-process of making pulps, the wood is cooked with white liquor comprising NaOH, sodium carbonate, and sulfur salts of sodium such as sodium sulfate, sulfide, thiosulfide. ~ter cooking, the liquor is 10 evaporated, the organic materials burned and the inorganic materials are dissolved to obtain the green liquor. This green liquor is generally discharged in a slaker together with lime. The lime produaes calclum hydroxide which is further reacted in reactors mounted in series call~d 15 causticizars, and following the causticizars, the lime mud (CaCO3) is ~iltered such as with rotating drums. Thus, this process generates white li~uor by converting the Na2C03 to cau~tic soda (NaOH) and lime mud CaCO3, CaO
2 ~ Ca(OH)2 ~ Na2C~3 ~ 2NaOH + CaCo3~. The 20 process is illustrated for instance in U.S.P. 4,536,236 dated August 20, 1985 as invented by BertelsenO
; THE INVENTION
A method has now been found to increa~e the eficiency of a causticizing process which comprises:
25 a) adding to a green liquor between 78 and 82~ o~ the ~ stoichiomekric amount o~ lime necessary to react with the ; amount of Na2C03 present in the green liquor to obtain a cau~ticized white liquor containing NaOH and lime mud, ; b) partially clarifying said white liquor by extracting 30 the lime mud present to obtain a white liquor having a total , ~ : ' "; `,.," ~
.,.
~.
~ ~7~55
; THE INVENTION
A method has now been found to increa~e the eficiency of a causticizing process which comprises:
25 a) adding to a green liquor between 78 and 82~ o~ the ~ stoichiomekric amount o~ lime necessary to react with the ; amount of Na2C03 present in the green liquor to obtain a cau~ticized white liquor containing NaOH and lime mud, ; b) partially clarifying said white liquor by extracting 30 the lime mud present to obtain a white liquor having a total , ~ : ' "; `,.," ~
.,.
~.
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lime mud solid concentration of about 10-60 grams/liter, preferably 20-40 and most preferably 20 grams/liter, c) taking said white li~uor containing about 10-60 grams/liter, preferably 20-40 and most preferably 20 grams/liter of total solid concentration and adding an additional amount of lime to increase the causticity to about 87~, d) allowing further causticizing reaction between the lime and sodium carbonate, and e) removing the remaining lime mud present to obtain a white liquor which has the causticity of about 87%.
In accordanc~ with the present invention by having step c), one is abl~ to raise the causticity of partially clarified white li~uor following the normal causticizing process.
The white liquor is partially clarified before adding the extra lime. By so doing, it has been found that:
the lime mud must be present to accelerate the caus ticizing reaction, 2- using only part of the lime mud initially present to ensure yood settling rate at high causticity. This settling rate is not affected much by excess lime and high causticity compared to high solids concentration as seen hareinbelow.
DETAILED DESCRIPTION OF THE DRAWINGS
In th~ drawings which illustrate a particular embodiment of the invention.
Figure 1 is a diagramatic view of the various apparatus components and piping illustrating the flow of the green liquor transformed into a white liquor of high causticity.
Figure 2 is a 3-dimensional graph illu~trating the ~ ~ ' ' ~725.~
effect of lime mud concentration on causticity wherein the abscissa is indicative of the initial concentration of lime mud in grams per liter (g/l), the ordinate is indicative of % causticity and the 3rd dimension is indicative of the time in minut~s.
DETAILED DESCRIPTION O~ THE INVENTION
In order to condu~t step a) a convenient way is to add in a slaker 4 as shown in Figure 1, between 78 82% of the stoichiometric amount of lime necessary to be fed via line 6 to react with the amount of Na2CO3 present in the green liquor fed via line 8, and allowing the lime to produce calcium hydroxide. These two reactants are then fed via line 12 into causticizers, such as for example, illustrated ~; at 14, 16 and 18 that are mounted in series via lines 20 and 22. These causticizers are provided with agitators for instance, mechanical stirrers 26, 28 and 30 in order to well mix the reactants and maintain them in state of uniform solution. The residence tims in the causticizers is, for sake of example, of the order of an hour and a hal~ to two.
The last o~ these cau~ticizers hown at 18 is connected to a clari~ier 19 via line 27 for ~eeding thereto the white liquor. The clarifier allows settling of the lime mud by gravity whlch can be removed via line 31 which may lead into line 44 or be independent. Other means setting density ~- 25 gradient may be used if desired. The supernatant solution in the clarifier having about 20 g~l o~ solids is then ~ed via line 32 to anothex causticizer 34 where lime is ~urther ~; added via line 36 joining line 6.
This further causticizing at 34 is carried out to achieve a causticity of about 87% during a time period of ,~
:
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about a quarter o~ an hour to an hour. It may proceed during a period of 40 to 50 minutes, or 40 to 55 minutes when the white liquor contains about 20 g/l of lime mud solid. When the white li~uor contains about 60 g/l of lime mud solid, the causticizing can proceed in less than 30 minutes.
The causticizer i~ also provided with a mechanical stirrer 38 to homogeneously mix the reactant after which it is displaced via line 35 to be filtered at 40. The white liquor is collected at 42 for further use, while the lime mud is collected via line 44 leading into joining line 31.
The stoichiometric amount of lime necessary to react with the amount of Na~C03 present in the green liquor can be determined by titration or conductivity as is well known in the art, such as described by R.G. MacDonald and Franklin in Pulp & Paper Manufacture, published by McGraw-Hill Book Company.
EXAMPLES
The following examples will serve to illustrate particular embodiments of the invention.
~ SAMPLE A
: A 760 ml of filtered white li~uor containing about 115 gJl Total Titrable Alkalies (~TA) and 23~ sulphidity was causticized with 46 g o~ fresh lime. The initial causticity of the white liquor was 80.1% and within a reaction time of 30:mins it increased to 82.6P6 (Figure 2). It further : : increased to 84.6 in 60 mins. However, the e~uilibrium : causticity o~ 88.6% was achieved after 20 hrs. This finding ; indicated that in accordance with prior art, the causticizing of white liquor is a ~low process and the : :
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12~;i725~, equilibrium causticity could not be achieved within a reasonable time.
During test starting with green liquorl a ~aster reaction rate was observed when fresh lime was added to the causticized li~uor containing lime mud. It was there~ore suspected that lime mud had some "catalytic ef~ect" on the causticixing of white liquor. Further experiments were therefore conducted to confirm the observation.
The following experiments were conducted in order to determine the causticity versus lime mud concentration and reactlon time.
Such as i8 described in Pulp and Paper Manufacture already mentioned (2nd Edition) under 9~59, page 563 to 566.
The causticizing reaction was carried out in a reactor having a lid to prevent evaporation and a port for sampling the slurry. The reactor contained a known volume of liquid and a known weight o~ lime mud, at a known constant temperature measured with a thermocouple and a thsrmometer.
The stirrer was turned on while heating the slurry to the desired temperature, at which point the quantity o~ lime re~uired to bring the liquor causticity to equilibrium was added. A stopwatch was started when the lime was added and the slurry was sampled every 15 minutes. A sample of the slurry was also collected before adding the lime. These samples were immediately ~iltered to stop further reaction between the lime and sodium carbonate. The filtrate was then analysed: One may, i~ desired use the ABC titration, to determine sodium ~ydroxide, sodium carbonate, and sodium sulphide, or use any instrument to that e~fect. The ABC
' ' ' ' ~' ` ' ' . ' .
` ` ' ' ` ' ` ' , ' .
~.2~ 5 titration involves the determination of sodium hydroxide, sodium sulphide and sodium carbonate.
S~MPLE B (without lime mud) Time mins. Causticity_~
0 77.81 78.81 32 79.14 79.22 79.15 The settling rate was determined as follows:
Five hundred ml of the slurry samples which had been causticized for 60 mins were vigorously stirred, transferred to 500 ml graduated cylinders and allowed to settle. A stop-~ watch was started when the slurry was trans~erred to the ; 15 beaker. Then the extent o~ the settling, i.e. the level of the interface between the clarified liquor and the ~ettling mass, was noted at regular intervals.
The settling rate was determined to be 3.24 cm/minute.
: The re~ults were plotted as shown in Figure 2.
E~AMPLE 2 The following results were obtained with a green liquor having a lime mud concentration of 20 g/l.
~Qmyg~3~g~ C Time mins~.Causti~ y %
82.0 0 78.6 : 25 84.1 15 7g.9 84 d 2 30 80.8 : 84.~ 45 82.~
; ~ ~4.4 6~ 83.1 The r~sults are plotted in Figure 2.
The settling rate was determined and ~ound to be 1.36
lime mud solid concentration of about 10-60 grams/liter, preferably 20-40 and most preferably 20 grams/liter, c) taking said white li~uor containing about 10-60 grams/liter, preferably 20-40 and most preferably 20 grams/liter of total solid concentration and adding an additional amount of lime to increase the causticity to about 87~, d) allowing further causticizing reaction between the lime and sodium carbonate, and e) removing the remaining lime mud present to obtain a white liquor which has the causticity of about 87%.
In accordanc~ with the present invention by having step c), one is abl~ to raise the causticity of partially clarified white li~uor following the normal causticizing process.
The white liquor is partially clarified before adding the extra lime. By so doing, it has been found that:
the lime mud must be present to accelerate the caus ticizing reaction, 2- using only part of the lime mud initially present to ensure yood settling rate at high causticity. This settling rate is not affected much by excess lime and high causticity compared to high solids concentration as seen hareinbelow.
DETAILED DESCRIPTION OF THE DRAWINGS
In th~ drawings which illustrate a particular embodiment of the invention.
Figure 1 is a diagramatic view of the various apparatus components and piping illustrating the flow of the green liquor transformed into a white liquor of high causticity.
Figure 2 is a 3-dimensional graph illu~trating the ~ ~ ' ' ~725.~
effect of lime mud concentration on causticity wherein the abscissa is indicative of the initial concentration of lime mud in grams per liter (g/l), the ordinate is indicative of % causticity and the 3rd dimension is indicative of the time in minut~s.
DETAILED DESCRIPTION O~ THE INVENTION
In order to condu~t step a) a convenient way is to add in a slaker 4 as shown in Figure 1, between 78 82% of the stoichiometric amount of lime necessary to be fed via line 6 to react with the amount of Na2CO3 present in the green liquor fed via line 8, and allowing the lime to produce calcium hydroxide. These two reactants are then fed via line 12 into causticizers, such as for example, illustrated ~; at 14, 16 and 18 that are mounted in series via lines 20 and 22. These causticizers are provided with agitators for instance, mechanical stirrers 26, 28 and 30 in order to well mix the reactants and maintain them in state of uniform solution. The residence tims in the causticizers is, for sake of example, of the order of an hour and a hal~ to two.
The last o~ these cau~ticizers hown at 18 is connected to a clari~ier 19 via line 27 for ~eeding thereto the white liquor. The clarifier allows settling of the lime mud by gravity whlch can be removed via line 31 which may lead into line 44 or be independent. Other means setting density ~- 25 gradient may be used if desired. The supernatant solution in the clarifier having about 20 g~l o~ solids is then ~ed via line 32 to anothex causticizer 34 where lime is ~urther ~; added via line 36 joining line 6.
This further causticizing at 34 is carried out to achieve a causticity of about 87% during a time period of ,~
:
., ''~ ' . ',,~ :
.. ..
~2~7'~:5.~
about a quarter o~ an hour to an hour. It may proceed during a period of 40 to 50 minutes, or 40 to 55 minutes when the white liquor contains about 20 g/l of lime mud solid. When the white li~uor contains about 60 g/l of lime mud solid, the causticizing can proceed in less than 30 minutes.
The causticizer i~ also provided with a mechanical stirrer 38 to homogeneously mix the reactant after which it is displaced via line 35 to be filtered at 40. The white liquor is collected at 42 for further use, while the lime mud is collected via line 44 leading into joining line 31.
The stoichiometric amount of lime necessary to react with the amount of Na~C03 present in the green liquor can be determined by titration or conductivity as is well known in the art, such as described by R.G. MacDonald and Franklin in Pulp & Paper Manufacture, published by McGraw-Hill Book Company.
EXAMPLES
The following examples will serve to illustrate particular embodiments of the invention.
~ SAMPLE A
: A 760 ml of filtered white li~uor containing about 115 gJl Total Titrable Alkalies (~TA) and 23~ sulphidity was causticized with 46 g o~ fresh lime. The initial causticity of the white liquor was 80.1% and within a reaction time of 30:mins it increased to 82.6P6 (Figure 2). It further : : increased to 84.6 in 60 mins. However, the e~uilibrium : causticity o~ 88.6% was achieved after 20 hrs. This finding ; indicated that in accordance with prior art, the causticizing of white liquor is a ~low process and the : :
., .
; ~ , : ' ''~. .
~ , '`":: ~`':
12~;i725~, equilibrium causticity could not be achieved within a reasonable time.
During test starting with green liquorl a ~aster reaction rate was observed when fresh lime was added to the causticized li~uor containing lime mud. It was there~ore suspected that lime mud had some "catalytic ef~ect" on the causticixing of white liquor. Further experiments were therefore conducted to confirm the observation.
The following experiments were conducted in order to determine the causticity versus lime mud concentration and reactlon time.
Such as i8 described in Pulp and Paper Manufacture already mentioned (2nd Edition) under 9~59, page 563 to 566.
The causticizing reaction was carried out in a reactor having a lid to prevent evaporation and a port for sampling the slurry. The reactor contained a known volume of liquid and a known weight o~ lime mud, at a known constant temperature measured with a thermocouple and a thsrmometer.
The stirrer was turned on while heating the slurry to the desired temperature, at which point the quantity o~ lime re~uired to bring the liquor causticity to equilibrium was added. A stopwatch was started when the lime was added and the slurry was sampled every 15 minutes. A sample of the slurry was also collected before adding the lime. These samples were immediately ~iltered to stop further reaction between the lime and sodium carbonate. The filtrate was then analysed: One may, i~ desired use the ABC titration, to determine sodium ~ydroxide, sodium carbonate, and sodium sulphide, or use any instrument to that e~fect. The ABC
' ' ' ' ~' ` ' ' . ' .
` ` ' ' ` ' ` ' , ' .
~.2~ 5 titration involves the determination of sodium hydroxide, sodium sulphide and sodium carbonate.
S~MPLE B (without lime mud) Time mins. Causticity_~
0 77.81 78.81 32 79.14 79.22 79.15 The settling rate was determined as follows:
Five hundred ml of the slurry samples which had been causticized for 60 mins were vigorously stirred, transferred to 500 ml graduated cylinders and allowed to settle. A stop-~ watch was started when the slurry was trans~erred to the ; 15 beaker. Then the extent o~ the settling, i.e. the level of the interface between the clarified liquor and the ~ettling mass, was noted at regular intervals.
The settling rate was determined to be 3.24 cm/minute.
: The re~ults were plotted as shown in Figure 2.
E~AMPLE 2 The following results were obtained with a green liquor having a lime mud concentration of 20 g/l.
~Qmyg~3~g~ C Time mins~.Causti~ y %
82.0 0 78.6 : 25 84.1 15 7g.9 84 d 2 30 80.8 : 84.~ 45 82.~
; ~ ~4.4 6~ 83.1 The r~sults are plotted in Figure 2.
The settling rate was determined and ~ound to be 1.36
4~' ` ::
.
.:.
cm/minute~
The ~ollowing results were obtained with a green li~uor having a lime mud concentration of 40 g/1.
Temperature CTime mins.Causticity %
81.9 0 78.0 84.0 15 80.9 ~4.1 30 82.0 : 84,0 45 83.2 84.1 60 83.3 The results are plotted in Figure 2.
The settling rate was also determined and found to be ; 0.36 cm/minute.
The following results were obtained with a green li~uor ha~ing a lime mud concentration o~ 60 g/l.
Temperature C Ta~ ia~ Causticity ;: 82.4 o 7~.0 84.4 15 ~1.5 : 20 84.5 30 83.0 ~. ~
84.5 45 83.4 .~ 84.5 60 ~3.8 The results were plotted as shown in Figure 2.
;: The settling rate was datermined and found to be 0.32 ; 25 :cm/minute.
The following results were obtained with a green liquor ~ havlng a lime mud concentration o~ 80 g/l.
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.~ ~3 ~ r ~r~
Tem~erature CTime mins. Causticity %
82.0 ~ 78.0 84.~ 15 ~0.7 8~.2 30 81.~
584.9 45 82.2 84.9 60 83.0 These results were then plotted as shown in Figure 2.
The settling rate was determined and found to be O .27 cm/minute, DISCUSSION FROM THE EXAMPLES
As can be easily seen, a plot of white liquor .; causticity versus lime mud concentration at di~ferent ; reaction times, indicates an optimum level of lime concentration (~igure 2). The causticity levels off around 15 40 g/l then decrease after 60 g/l, especially at high reaction times (more than 45 mins). At 60 mins rea~tion ,~ time, the white liquor causticity is 83.1~ at 20 g/l compared to 83.3% at 40 g/l, 83.8~ at 60 g/l and 83.0~ at 80 ~: g/l. However, at low reaction times (less than 30 mins) the : 20 causticity increased almost linearly up to the optimum level of 60 g~l. These results indicate that, in practice, lime mud concentrations as low as 20 g/l can be used to improve the white liquor causticity if adequate reaction time (more khan 45 mins) can be provided. However, if sufficient reaction time cannot be provided (less than 30 mins) then lime mud concentration as high as 60 g/l should be used.
As can be seen when the normal level of lime mud in ~: white liquor is above 60 as is generally encountered after a .~ ; sPt of causticizers in series, say 80 g/l, from the above Figure ~ it is clear that the lime mud has to be signifi-:
.: :
~ ' ` :
cantly reduced befoxe fresh lime is added to maximize the causticity without adversely af~ecting the settling rate.
In combining the results of both the causticizing and settling tests initial lime mud concentration o~ 20 g/l corresponding to 3.5% solids in the final slurry appears to b~ the opkimum. ~he causticity levels off at initial lime mud concentration of 20 g/l and the settling rate for this sample at room temperature at l.36 cm/minute is exp~cted to be within the range of l.5 to 3.0 cm/minute which is the acceptable range within the industry at 90C.
If desired, the lime mud may be separated from the white liquor in the lask separation unit (pressure filter 40) and recycled to the slaker 4. This permits excess lime to be added in the last causticizer and thereby achieve causticity close to the e~uilibrium within a reasonable period of timeO
Having de~cribed the invention, particularly preferred embodiments thereo~, modificatlons will be evident to those skilled in the art without departing from the spirit of the invention as defined in the appended claims.
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:
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cm/minute~
The ~ollowing results were obtained with a green li~uor having a lime mud concentration of 40 g/1.
Temperature CTime mins.Causticity %
81.9 0 78.0 84.0 15 80.9 ~4.1 30 82.0 : 84,0 45 83.2 84.1 60 83.3 The results are plotted in Figure 2.
The settling rate was also determined and found to be ; 0.36 cm/minute.
The following results were obtained with a green li~uor ha~ing a lime mud concentration o~ 60 g/l.
Temperature C Ta~ ia~ Causticity ;: 82.4 o 7~.0 84.4 15 ~1.5 : 20 84.5 30 83.0 ~. ~
84.5 45 83.4 .~ 84.5 60 ~3.8 The results were plotted as shown in Figure 2.
;: The settling rate was datermined and found to be 0.32 ; 25 :cm/minute.
The following results were obtained with a green liquor ~ havlng a lime mud concentration o~ 80 g/l.
:' :A
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, .~ . .
.~ ~3 ~ r ~r~
Tem~erature CTime mins. Causticity %
82.0 ~ 78.0 84.~ 15 ~0.7 8~.2 30 81.~
584.9 45 82.2 84.9 60 83.0 These results were then plotted as shown in Figure 2.
The settling rate was determined and found to be O .27 cm/minute, DISCUSSION FROM THE EXAMPLES
As can be easily seen, a plot of white liquor .; causticity versus lime mud concentration at di~ferent ; reaction times, indicates an optimum level of lime concentration (~igure 2). The causticity levels off around 15 40 g/l then decrease after 60 g/l, especially at high reaction times (more than 45 mins). At 60 mins rea~tion ,~ time, the white liquor causticity is 83.1~ at 20 g/l compared to 83.3% at 40 g/l, 83.8~ at 60 g/l and 83.0~ at 80 ~: g/l. However, at low reaction times (less than 30 mins) the : 20 causticity increased almost linearly up to the optimum level of 60 g~l. These results indicate that, in practice, lime mud concentrations as low as 20 g/l can be used to improve the white liquor causticity if adequate reaction time (more khan 45 mins) can be provided. However, if sufficient reaction time cannot be provided (less than 30 mins) then lime mud concentration as high as 60 g/l should be used.
As can be seen when the normal level of lime mud in ~: white liquor is above 60 as is generally encountered after a .~ ; sPt of causticizers in series, say 80 g/l, from the above Figure ~ it is clear that the lime mud has to be signifi-:
.: :
~ ' ` :
cantly reduced befoxe fresh lime is added to maximize the causticity without adversely af~ecting the settling rate.
In combining the results of both the causticizing and settling tests initial lime mud concentration o~ 20 g/l corresponding to 3.5% solids in the final slurry appears to b~ the opkimum. ~he causticity levels off at initial lime mud concentration of 20 g/l and the settling rate for this sample at room temperature at l.36 cm/minute is exp~cted to be within the range of l.5 to 3.0 cm/minute which is the acceptable range within the industry at 90C.
If desired, the lime mud may be separated from the white liquor in the lask separation unit (pressure filter 40) and recycled to the slaker 4. This permits excess lime to be added in the last causticizer and thereby achieve causticity close to the e~uilibrium within a reasonable period of timeO
Having de~cribed the invention, particularly preferred embodiments thereo~, modificatlons will be evident to those skilled in the art without departing from the spirit of the invention as defined in the appended claims.
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Claims (14)
1. A method to increase the efficiency of a causticizing process which comprises:
a) adding to a green liquor between 78 and 82% of the stoichiometric amount of lime necessary to react with the amount of Na2CO3 present in the green liquor to obtain a causticized white liquor containing NaOH and lime mud, b) partially clarifying said white liquor by extracting the lime mud present to obtain a white liquor having a total lime mud solid concentration of about 10-60 grams/liter, c) taking said white liquor containing about 10-60 grams/liter of solid and adding an additional amount of lime to increase the causticity to about 87%, d) allowing further causticizing reaction between the lime and Na2C03, and e) removing the remaining lime mud present to obtain a white liquor which has the causticity of about 87%.
a) adding to a green liquor between 78 and 82% of the stoichiometric amount of lime necessary to react with the amount of Na2CO3 present in the green liquor to obtain a causticized white liquor containing NaOH and lime mud, b) partially clarifying said white liquor by extracting the lime mud present to obtain a white liquor having a total lime mud solid concentration of about 10-60 grams/liter, c) taking said white liquor containing about 10-60 grams/liter of solid and adding an additional amount of lime to increase the causticity to about 87%, d) allowing further causticizing reaction between the lime and Na2C03, and e) removing the remaining lime mud present to obtain a white liquor which has the causticity of about 87%.
2. The method as defined in claim 1 wherein in step b) the white liquor is clarified to obtain a total lime mud solid concentration of about 20 40 grams/liter.
3. The method as defined in claim 1 wherein in step b) the white liquor is clarified to obtain a total lime mud solid concentration of about 20 grams/liter.
4. The method as defined in claim 1, 2 or 3 wherein in step d) said further causticizing reaction is allowed for a period of about a quarter of an hour to an hour.
5. A method to increase the efficiency of a causticizing process which comprises:
a) adding to a green liquor in a slaker, between 78 and 82% of the stoichiometric amount of lime necessary to react with the amount of Na2CO3 present in the green liquor, said lime in the presence of said green liquor producing calcium hydroxide, and allowing the calcium hydroxide to react with the Na2CO3 in causticizers mounted in series to obtain a causticized white liquor containing NaOH and lime mud, b) feeding into a clarifier said white liquor from the last causticizer mounted in series and extracting a portion of the lime mud present to obtain a white liquor having a total lime mud solid concentration of between 10 and 60 grams/liter, c) taking said white liquor containing between 10 and 60 grams/liter of lime mud solid and feeding it to a further causticizer with an additional amount of lime to increase the causticity to about 87%, d) allowing further causticizing reaction under agitation between the lime and Na2CO3, and e) removing the remaining lime mud present to obtain a white liquor which has the causticity of about 87%.
a) adding to a green liquor in a slaker, between 78 and 82% of the stoichiometric amount of lime necessary to react with the amount of Na2CO3 present in the green liquor, said lime in the presence of said green liquor producing calcium hydroxide, and allowing the calcium hydroxide to react with the Na2CO3 in causticizers mounted in series to obtain a causticized white liquor containing NaOH and lime mud, b) feeding into a clarifier said white liquor from the last causticizer mounted in series and extracting a portion of the lime mud present to obtain a white liquor having a total lime mud solid concentration of between 10 and 60 grams/liter, c) taking said white liquor containing between 10 and 60 grams/liter of lime mud solid and feeding it to a further causticizer with an additional amount of lime to increase the causticity to about 87%, d) allowing further causticizing reaction under agitation between the lime and Na2CO3, and e) removing the remaining lime mud present to obtain a white liquor which has the causticity of about 87%.
6. The method according to claim 5 wherein in step b) said clarifier has a top and bottom portion, extracting at said bottom portion said portion of lime mud present to obtain from said top portion said white liquor having a total lime mud solid concentration of between 10 and 60 grams/liter,
7. The method according to claim 6 wherein step e) is conducted by filtration.
8. The method according to claim 5, 6 or 7 wherein in step d) the causticizing reaction is allowed to proceed during a period of about a quarter of an hour to an hour.
9. The method according to claim 5, 6 or 7 wherein in step d) the causticizing reaction is allowed to proceed during a period of about 40 to 50 minutes.
10. The method according to claim 5, 6 or 7 wherein in step c) said white liquor contains about 20 grams of total lime mud solid and in step d) the causticizing is allowed to proceed about 40 to 55 minutes.
11. The method according to claim 5, 6 or 7 wherein in step c) said white liquor contains about 60 grams of total lime mud solid and in step d) the causticizing is allowed to proceed less than 30 minutes.
12. The method according to claim 5, 6 or 7 wherein in step a) in the causticizers the calcium hydroxide and Na2CO3 reside for a period of about 1-1/2 to 2 hours, and wherein in step d) the causticizing reaction is allowed to proceed during a period of about a quarter of an hour to an hour.
13. The method according to claim 1, 5 or 6 wherein after step e) said lime mud is recycled by being reused in step a).
14. The method according to claim 5, 6 or 7 wherein steps a) to e) are allowed to proceed continuously, and wherein in step d) the causticizing reaction is allowed to proceed during a period of about a quarter of an hour to an hour.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000544206A CA1267255A (en) | 1987-08-11 | 1987-08-11 | Method for increasing the efficiency of a causticizing process |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000544206A CA1267255A (en) | 1987-08-11 | 1987-08-11 | Method for increasing the efficiency of a causticizing process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1267255A true CA1267255A (en) | 1990-04-03 |
Family
ID=4136240
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000544206A Expired - Fee Related CA1267255A (en) | 1987-08-11 | 1987-08-11 | Method for increasing the efficiency of a causticizing process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1267255A (en) |
-
1987
- 1987-08-11 CA CA000544206A patent/CA1267255A/en not_active Expired - Fee Related
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