CA2163368C - Production of white liquor - Google Patents
Production of white liquor Download PDFInfo
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- CA2163368C CA2163368C CA002163368A CA2163368A CA2163368C CA 2163368 C CA2163368 C CA 2163368C CA 002163368 A CA002163368 A CA 002163368A CA 2163368 A CA2163368 A CA 2163368A CA 2163368 C CA2163368 C CA 2163368C
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- liquor
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- sulphidity
- white liquor
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Abstract
A method of producing white liquor having enhanced and/or reduced sulphidity in the recovery of chemicals in a sulphate pulp process is described. In the method one starts from a calcium sulphide rich smelt of inorganic chemicals, which has been obtained by simultaneous combustion of black liquor and processing of lime sludge. This smelt is treated with an aqueous solution, whereupon the calcium sulphide in the smelt is present in a solid form and the rest of the chemicals are in solution. Thereupon the solid calcium sulphide is separated and the obtained solution is processed as a green liquor in per se known manner to a white liquor having reduced sulphidity, whereupon optionally the separated solid calcium sulphide is mixed with the required amount of white liquor to a white liquor having enhanced sulphidity.
Description
PRODUCTION OF WHITE LIQUOR
The present invention relates to the production of white liquor in the recovery of chemicals in a sulphate pulp process.. More precisely, the invention relates to the production of white liquor having enhanced and/or reduced sulphidity starting from a calcium sulphide rich smelt of inorganic chemicals, wl-lich has been obtained by simultaneous combustion of black liquor and processing of lime sludge.
The production of a calcium sulphide rich smelt of inorganic chemicals in connection with simultaneous combustion of black liquor and processing of lime sludge has been described in the simultaneously filed patent application having the title "Combustion of black liquor".
Backgy~,und In the production of pulp according to the sulphate pulp method _.
wood, in the form of chips, is delignified in an alkaline solution, which mainly consists of NaOH and NaHS, in a pressurized cooking process, which in the final stage normally has.a temperature in the range of 150-175°C. The ratio of hydroxide ions [OH ] to [HS-] is normally within the .range: of 25-40% sulphide (2HS ], calculated on the sum of the cont~=nts of sulphide ions and hydroxide ions.
An increased content of sulphide ions in relation to hydroxide ions in the cooking liquor increases the yield of pulp and, normally, improves the important properties of the final product. In the beginning of the cooking process, the so called impregnation stage, an increased proportion of sulphide ions forms the bases of a more efficient release of lignin during the actual cooking process. A simultanE=ous reduction of the contents of hydroxide ions decreases the degradation of cellulose, which results in an increasE:d yield and higher quality of the final product.
Summarv of the invention The present invention provides a white liqucr having enhanced sulphidity, which can be utilized in the above mentioned cooking process.
Further, the invention provides white liquor having reduced sulphidity. White liquor having reduce~~
sulphidity may e.g. be used as a chemical in the produtltion of bleached wood pulp.
In one aspect, the invention provides a method of producing two types of white liquor in the recovery of chemicals in a sulphate pulp process, a first type having enhanced sulphidity and a second type having reduced sulphidity, comprising the steps of: a) providing a calcium sulphide rich smelt of inorganic chemicals resulting from simultaneous combustion of black liquor and processing of lime sludge; b) treating said calcium sulphide rich smelt with an aqueous solution to yield a mixture wherein the calcium sulphide is in solid form and the rest of the chemicals are in solution; c) separating the solid calcium sulphide from the mixture to yield a solution; d) processing the solution as green liquor by causticization according to the reaction formula:
2a Ca(OH)Z~s~+[CO32-]-~CaC03~s~+[2 OH]
followed by separation of the solid CaC03~s~, the lime sludge, to yield said first type of white liquor having reduced sulphidity; e) mixing the solid calcium sulphide (CaS;
obtained in step c) with a required amount of white 1__quor to react to [OH-] of the white liquor with the CaS according to the reaction formula:
CaS~s~+[H20]+[2 OH-]-~Ca(OH)2~5~+[HS-]+[OH ]; and f) separating the solid Ca(OH)Z from the mixture obtained in step e) to yield the second type of white liquor having enhanced sulphidity.
Description of the invention The present invention provides a method of producing white liquor having enhanced and/or reduced sulphidity in the recovery of chemicals in a sulphate pulp process. The method implies that a calcium sulphide rich smelt of inorganic chemicals, which has been obtained by simultaneous combustion of black liquor and processing of lime sludge, is treated with an aqueous solution, whereupon the calcium sulphide in the smelt is present in solid form and the rest of the chemicals are present in solution, after which the solid calcium sulphide is separated, and a) the obtained solution is processed as a green liquor in a per se known manner to a white liquor having reduced sulphidity, whereupon optionally b) the separated solid calcium sulphide (CaS) is mixed with a required amount of white liquor, the [OH ] of the white liquor reacting with CaS according to the reaction formula CaS ~8~ + H20 + [20H ] ------> Ca (OH) z ~8~ + [HS ] + [OH ]
to a white liquor having enhanced sulphidity and solid Ca(OH)2, which is separated.
As initially indicated a calcium sulphide rich smelt of inorganic chemicals may be obtained when combustion of black liquor and processing of lime sludge are performed simultaneously, which is described in a patent application having the title "Combustion of black liquor" which is filed simultaneously with the present application.
The combustion may have taken place in a liquor combustion plant, which can be a conventional recovery boiler, but can also be a liquor gasification plant.
By the expression "the obtained solution is processed as a green liquor in ~ ~ known manner to a white liquor having reduced sulphidity" is meant in the specification and the appended claims that the obtained solution is processed in the same way as is known for processing of green liquor to white liquor. By "enhanced sulphidity" and "reduced sulphidity" is intended a comparison with the sulphidity of white liquor that has been previously produced in a conventional manner.
t In one embodiment of the method according to the invention the solid Ca(OH)2 separated in the method is further processed by addition thereof, after separation of the solid sulphide, to the obtained solution, and this is processed by causticizing according to the reaction formula WQ 94/29516 ~ ~ ~ ~ . q. PCT/SE94/00537 Ca (OH) 2 ~8~ + [C032 ] ------> CaC03 ts~ + [20H ]
and the solid CaC03~s~, the lime sludge, is separated, whereby white liquor having reduced sulphidity is obtained.
In another embodiment of the invention the aqueous solution used in the method is water. According to still another embodiment the aqueous solution is weak liquor. Weak liquor is a weakly alkaline solution which has been obtained e.g. in the washing of separated lime sludge (CaC03) in conventional causticizing.
According to yet another embodiment of the invention the solid sulphide is separated by filtration.
~y use of the invention In a sulphate pulp process the main part of the cooking chemicals are found together with organic materials dissolved from wood in the black liquor (recycled liquor), which after evaporation to combustible dry solids content is burnt in a liquor combustion plant, which normally is a recovery boiler, but which also can be a liquor gasification plant.
In the liquor combustion process the main part of the cooking chemicals are recovered from a smelt which is formed by the combustion and which then is transported to a dissolver for dissolution in a weakly alkaline solution (weak liquor). (The weak liquor has normally been obtained from the washing of lime sludge (CaC03), which has been separated in the~causticizing plant ) .
WO 94/29516 216 ~ 3 ~? ~
PCTlSE94/00537 The alkaline solution (green liquor) which is obtained in the soda dissolver mainly contains sodium compounds, the available sulphide being to 90-95% in the form of NaHS, and the remaining amount sodium being mainly in the form of Na2C03.
i The green liquor is usually cleaned from solid process substances and is thereafter added to the causticizing process, where burnt lime (Ca0) is added in such an amount that 80-85% of Na2C03 is converted to NaOH according to the formula:
Na2C03~1~ + H20 + CaO~s~ ~__'- 2NaOHtl~ + CaC03ts~
After separation of the solid CaC03 (lime sludge) is formed, a strong alkaline solution (white liquor) is obtained, the active chemicals for the cooking process of which are NaHS and NaOH.
The sulphidity of the white liquor, i.e. the ratio between 'sulphide ions and hydroxide ions, is mainly determined by the ratio S/Na2 in the dissolved smelt of inorganic chemicals from the liquor combustion plant.
In certain liquor evaporation processes the combustion will occur in such a way that the sulphide is mainly obtained in the gaseous phase as hydrogen sulphide (H2S) and is separated in a gas cleaning plant by scrubbing with an alkaline solution, so that the cleaned gas contains low contents of sulphide prior to combustion in the gas furnace. The alkaline solution to the scrubber can either consist of hydroxide or carbonate, and in either case the need of burnt lime (Ca0) is increased more than would be needed if NaSH was obtained in conventional manner from Na2S in a smelt of chemicals from a recovery boiler. The increase in the need of burnt lime is related to the amount of HZS that is taken up by the scrubber liquid.
WO 94/29516 2 ~ ~ 3 ~ ~ ~ 6 PCT/SE94/00537 Scrubbing:
HAS ~g~ + OH ~=s HS + HBO Or H2S ~g~ + CO32 ~_--' HS + HC03 Slaking:
Ca0 ~S~ + H20 ~_~ Ca (OH) a ~s~
Neutralizing:
Ca (OH) z ~s~ + 2HC03 ~_= CaC03 ~8~ + C032 + 2H20 Causticizing:
Ca (OH) 2~8~ + CO32 ~_~ Ca (C03ts~ + 2OH
The calcium sulphide rich smelt of inorganic chemicals which is used in the present invention derives from simultaneous combustion of black liquor and processing of lime sludge ( CaC03 ) .
Irrespective of whether this has occurred in a recovery boiler or a liquor evaporator the inorganic chemicals are obtained in melted form, where the following reactions occur in the presence of CaC03:
1. CaC03 + Na2S ---> CaS + Na2C03 > 600C
2. CaS + Na2C03 ---> Ca0 + NazS + > 800C
COZ
3. Ca0 + Na2S ---> CaS + Na20 < 800C
The indicated temperatures are very approximate and may, depending on different circumstances, vary by e.g. ~70°C.
i W094/29516 ~ 163368 '7 PCT/SE94/00537 In a liquor evaporator which works in a temperature range where the sulphide normally leaves the evaporator in the form of H2S
and the rest of the inorganic chemicals in solid form, the sulphide will be obtained in the form of CaS if CaC03 is supplied to the black liquor in the molar ratio of S/Ca = 1, and the CaS leaves the evaporator in solid form like the rest of the inorganic chemicals. In the liquor evaporator the reaction will occur according to the formula 1 above.
If weak liquor is used as aqueous solution in the treatment of calcium sulphide rich smelt according to the invention the CaS
will be in solid form, if the content of [OH ] in the solution is so high that CaS will be converted to NaHS or NazS in the dissolver, which is not the case if the content of NazS in the smelt of chemical from the combustion plant is low or if the solid CaS is separated before it is converted to NazS.
If the aqueous solution that is used in the present invention for treatment of the calcium sulphide rich smelt is water the solution will indeed be slightly alkaline, but the risk of CaS
being converted to NazS before it is separated in solid form is considerably reduced or totally eliminated.
CaS is separated, e.g. by filtration, and the purified, Na2C03 rich solution is transported to the causticizing plant, where a white liquor having reduced (low) content of [HS ] is obtained.
The separated CaS is mixed with a required amount of the white liquor produced or another white liquor, e.g. in a reaction vessel, whereby the [OH ] of the white liquor reacts with CaS
according to the formula:
The present invention relates to the production of white liquor in the recovery of chemicals in a sulphate pulp process.. More precisely, the invention relates to the production of white liquor having enhanced and/or reduced sulphidity starting from a calcium sulphide rich smelt of inorganic chemicals, wl-lich has been obtained by simultaneous combustion of black liquor and processing of lime sludge.
The production of a calcium sulphide rich smelt of inorganic chemicals in connection with simultaneous combustion of black liquor and processing of lime sludge has been described in the simultaneously filed patent application having the title "Combustion of black liquor".
Backgy~,und In the production of pulp according to the sulphate pulp method _.
wood, in the form of chips, is delignified in an alkaline solution, which mainly consists of NaOH and NaHS, in a pressurized cooking process, which in the final stage normally has.a temperature in the range of 150-175°C. The ratio of hydroxide ions [OH ] to [HS-] is normally within the .range: of 25-40% sulphide (2HS ], calculated on the sum of the cont~=nts of sulphide ions and hydroxide ions.
An increased content of sulphide ions in relation to hydroxide ions in the cooking liquor increases the yield of pulp and, normally, improves the important properties of the final product. In the beginning of the cooking process, the so called impregnation stage, an increased proportion of sulphide ions forms the bases of a more efficient release of lignin during the actual cooking process. A simultanE=ous reduction of the contents of hydroxide ions decreases the degradation of cellulose, which results in an increasE:d yield and higher quality of the final product.
Summarv of the invention The present invention provides a white liqucr having enhanced sulphidity, which can be utilized in the above mentioned cooking process.
Further, the invention provides white liquor having reduced sulphidity. White liquor having reduce~~
sulphidity may e.g. be used as a chemical in the produtltion of bleached wood pulp.
In one aspect, the invention provides a method of producing two types of white liquor in the recovery of chemicals in a sulphate pulp process, a first type having enhanced sulphidity and a second type having reduced sulphidity, comprising the steps of: a) providing a calcium sulphide rich smelt of inorganic chemicals resulting from simultaneous combustion of black liquor and processing of lime sludge; b) treating said calcium sulphide rich smelt with an aqueous solution to yield a mixture wherein the calcium sulphide is in solid form and the rest of the chemicals are in solution; c) separating the solid calcium sulphide from the mixture to yield a solution; d) processing the solution as green liquor by causticization according to the reaction formula:
2a Ca(OH)Z~s~+[CO32-]-~CaC03~s~+[2 OH]
followed by separation of the solid CaC03~s~, the lime sludge, to yield said first type of white liquor having reduced sulphidity; e) mixing the solid calcium sulphide (CaS;
obtained in step c) with a required amount of white 1__quor to react to [OH-] of the white liquor with the CaS according to the reaction formula:
CaS~s~+[H20]+[2 OH-]-~Ca(OH)2~5~+[HS-]+[OH ]; and f) separating the solid Ca(OH)Z from the mixture obtained in step e) to yield the second type of white liquor having enhanced sulphidity.
Description of the invention The present invention provides a method of producing white liquor having enhanced and/or reduced sulphidity in the recovery of chemicals in a sulphate pulp process. The method implies that a calcium sulphide rich smelt of inorganic chemicals, which has been obtained by simultaneous combustion of black liquor and processing of lime sludge, is treated with an aqueous solution, whereupon the calcium sulphide in the smelt is present in solid form and the rest of the chemicals are present in solution, after which the solid calcium sulphide is separated, and a) the obtained solution is processed as a green liquor in a per se known manner to a white liquor having reduced sulphidity, whereupon optionally b) the separated solid calcium sulphide (CaS) is mixed with a required amount of white liquor, the [OH ] of the white liquor reacting with CaS according to the reaction formula CaS ~8~ + H20 + [20H ] ------> Ca (OH) z ~8~ + [HS ] + [OH ]
to a white liquor having enhanced sulphidity and solid Ca(OH)2, which is separated.
As initially indicated a calcium sulphide rich smelt of inorganic chemicals may be obtained when combustion of black liquor and processing of lime sludge are performed simultaneously, which is described in a patent application having the title "Combustion of black liquor" which is filed simultaneously with the present application.
The combustion may have taken place in a liquor combustion plant, which can be a conventional recovery boiler, but can also be a liquor gasification plant.
By the expression "the obtained solution is processed as a green liquor in ~ ~ known manner to a white liquor having reduced sulphidity" is meant in the specification and the appended claims that the obtained solution is processed in the same way as is known for processing of green liquor to white liquor. By "enhanced sulphidity" and "reduced sulphidity" is intended a comparison with the sulphidity of white liquor that has been previously produced in a conventional manner.
t In one embodiment of the method according to the invention the solid Ca(OH)2 separated in the method is further processed by addition thereof, after separation of the solid sulphide, to the obtained solution, and this is processed by causticizing according to the reaction formula WQ 94/29516 ~ ~ ~ ~ . q. PCT/SE94/00537 Ca (OH) 2 ~8~ + [C032 ] ------> CaC03 ts~ + [20H ]
and the solid CaC03~s~, the lime sludge, is separated, whereby white liquor having reduced sulphidity is obtained.
In another embodiment of the invention the aqueous solution used in the method is water. According to still another embodiment the aqueous solution is weak liquor. Weak liquor is a weakly alkaline solution which has been obtained e.g. in the washing of separated lime sludge (CaC03) in conventional causticizing.
According to yet another embodiment of the invention the solid sulphide is separated by filtration.
~y use of the invention In a sulphate pulp process the main part of the cooking chemicals are found together with organic materials dissolved from wood in the black liquor (recycled liquor), which after evaporation to combustible dry solids content is burnt in a liquor combustion plant, which normally is a recovery boiler, but which also can be a liquor gasification plant.
In the liquor combustion process the main part of the cooking chemicals are recovered from a smelt which is formed by the combustion and which then is transported to a dissolver for dissolution in a weakly alkaline solution (weak liquor). (The weak liquor has normally been obtained from the washing of lime sludge (CaC03), which has been separated in the~causticizing plant ) .
WO 94/29516 216 ~ 3 ~? ~
PCTlSE94/00537 The alkaline solution (green liquor) which is obtained in the soda dissolver mainly contains sodium compounds, the available sulphide being to 90-95% in the form of NaHS, and the remaining amount sodium being mainly in the form of Na2C03.
i The green liquor is usually cleaned from solid process substances and is thereafter added to the causticizing process, where burnt lime (Ca0) is added in such an amount that 80-85% of Na2C03 is converted to NaOH according to the formula:
Na2C03~1~ + H20 + CaO~s~ ~__'- 2NaOHtl~ + CaC03ts~
After separation of the solid CaC03 (lime sludge) is formed, a strong alkaline solution (white liquor) is obtained, the active chemicals for the cooking process of which are NaHS and NaOH.
The sulphidity of the white liquor, i.e. the ratio between 'sulphide ions and hydroxide ions, is mainly determined by the ratio S/Na2 in the dissolved smelt of inorganic chemicals from the liquor combustion plant.
In certain liquor evaporation processes the combustion will occur in such a way that the sulphide is mainly obtained in the gaseous phase as hydrogen sulphide (H2S) and is separated in a gas cleaning plant by scrubbing with an alkaline solution, so that the cleaned gas contains low contents of sulphide prior to combustion in the gas furnace. The alkaline solution to the scrubber can either consist of hydroxide or carbonate, and in either case the need of burnt lime (Ca0) is increased more than would be needed if NaSH was obtained in conventional manner from Na2S in a smelt of chemicals from a recovery boiler. The increase in the need of burnt lime is related to the amount of HZS that is taken up by the scrubber liquid.
WO 94/29516 2 ~ ~ 3 ~ ~ ~ 6 PCT/SE94/00537 Scrubbing:
HAS ~g~ + OH ~=s HS + HBO Or H2S ~g~ + CO32 ~_--' HS + HC03 Slaking:
Ca0 ~S~ + H20 ~_~ Ca (OH) a ~s~
Neutralizing:
Ca (OH) z ~s~ + 2HC03 ~_= CaC03 ~8~ + C032 + 2H20 Causticizing:
Ca (OH) 2~8~ + CO32 ~_~ Ca (C03ts~ + 2OH
The calcium sulphide rich smelt of inorganic chemicals which is used in the present invention derives from simultaneous combustion of black liquor and processing of lime sludge ( CaC03 ) .
Irrespective of whether this has occurred in a recovery boiler or a liquor evaporator the inorganic chemicals are obtained in melted form, where the following reactions occur in the presence of CaC03:
1. CaC03 + Na2S ---> CaS + Na2C03 > 600C
2. CaS + Na2C03 ---> Ca0 + NazS + > 800C
COZ
3. Ca0 + Na2S ---> CaS + Na20 < 800C
The indicated temperatures are very approximate and may, depending on different circumstances, vary by e.g. ~70°C.
i W094/29516 ~ 163368 '7 PCT/SE94/00537 In a liquor evaporator which works in a temperature range where the sulphide normally leaves the evaporator in the form of H2S
and the rest of the inorganic chemicals in solid form, the sulphide will be obtained in the form of CaS if CaC03 is supplied to the black liquor in the molar ratio of S/Ca = 1, and the CaS leaves the evaporator in solid form like the rest of the inorganic chemicals. In the liquor evaporator the reaction will occur according to the formula 1 above.
If weak liquor is used as aqueous solution in the treatment of calcium sulphide rich smelt according to the invention the CaS
will be in solid form, if the content of [OH ] in the solution is so high that CaS will be converted to NaHS or NazS in the dissolver, which is not the case if the content of NazS in the smelt of chemical from the combustion plant is low or if the solid CaS is separated before it is converted to NazS.
If the aqueous solution that is used in the present invention for treatment of the calcium sulphide rich smelt is water the solution will indeed be slightly alkaline, but the risk of CaS
being converted to NazS before it is separated in solid form is considerably reduced or totally eliminated.
CaS is separated, e.g. by filtration, and the purified, Na2C03 rich solution is transported to the causticizing plant, where a white liquor having reduced (low) content of [HS ] is obtained.
The separated CaS is mixed with a required amount of the white liquor produced or another white liquor, e.g. in a reaction vessel, whereby the [OH ] of the white liquor reacts with CaS
according to the formula:
4. CaS~s~ + HZO + [20H ] ---> Ca (OH) z~s~ + [HS ] + [OH ]
WO 94/29516 ~ ~f. ~ ~$ PCT/SE94/00537 The solid phase (Ca(OH)2) is separated e.g. by filtration, whereby a white liquor having enhanced thigh) sulphidity is obtained.
The separated solid phase, Ca(OH)z, may then be recycled to a green liquor and causticized according to the formula:
WO 94/29516 ~ ~f. ~ ~$ PCT/SE94/00537 The solid phase (Ca(OH)2) is separated e.g. by filtration, whereby a white liquor having enhanced thigh) sulphidity is obtained.
The separated solid phase, Ca(OH)z, may then be recycled to a green liquor and causticized according to the formula:
5 . Ca (OH) 2~8~ + [C032 ] ---> CaC03~8~ + (20H ]
The solid lime sludge (CaC03) which thereby arises is separated, e.g. in a filtration plant, and may be recycled, after washing, to the combustion plant, where it may be burnt together with black liquor. Upon separation of the lime sludge, a white liquor having reduced (low) content of [HS ] is obtained.
From the formula S above, it is evident that [OH ], which has been consumed in the production of white liquor having enhanced sulphidity according to the invention, formula 4, has been re-created by the causticizing, without any need of additional burnt lime (Ca0). Thus, the production of white liquor having enhanced and/or reduced sulphidity can be produced without an increase in the amount of burnt lime.
r i
The solid lime sludge (CaC03) which thereby arises is separated, e.g. in a filtration plant, and may be recycled, after washing, to the combustion plant, where it may be burnt together with black liquor. Upon separation of the lime sludge, a white liquor having reduced (low) content of [HS ] is obtained.
From the formula S above, it is evident that [OH ], which has been consumed in the production of white liquor having enhanced sulphidity according to the invention, formula 4, has been re-created by the causticizing, without any need of additional burnt lime (Ca0). Thus, the production of white liquor having enhanced and/or reduced sulphidity can be produced without an increase in the amount of burnt lime.
r i
Claims (5)
1. ~~A method of producing two types of white liquor in the recovery of chemicals in a sulphate pulp process, a first type having enhanced sulphidity and a second type having reduced sulphidity, comprising the steps of:
a) providing a calcium sulphide rich smelt of inorganic chemicals resulting from simultaneous combustion of black liquor and processing of lime sludge;
b) treating said calcium sulphide rich smelt with an aqueous solution to yield a mixture wherein the calcium sulphide is in solid form and the rest of the chemicals are in solution;
c) separating the solid calcium sulphide from the mixture to yield a solution;
d) processing the solution as green liquor by causticization according to the reaction formula:
Ca(OH)2(S)+[Co3 2-].fwdarw.CaCO3(S)+[2 OH]
followed by separation of the solid CaCO3(S), the lime sludge, to yield said first type of white liquor having reduced sulphidity;
e) mixing the solid calcium sulphide (CaS) obtained in step c) with a required amount of white liquor to react to [OH-] of the white liquor with the CaS according to the reaction formula:
CaS(S)+[H2O]+[2 OH-].fwdarw.Ca(OH)2(S)+[HS-]+[OH-]; and f) separating the solid Ca(OH)2 from the mixture obtained in step e) to yield the second type of white liquor having enhanced sulphidity.
a) providing a calcium sulphide rich smelt of inorganic chemicals resulting from simultaneous combustion of black liquor and processing of lime sludge;
b) treating said calcium sulphide rich smelt with an aqueous solution to yield a mixture wherein the calcium sulphide is in solid form and the rest of the chemicals are in solution;
c) separating the solid calcium sulphide from the mixture to yield a solution;
d) processing the solution as green liquor by causticization according to the reaction formula:
Ca(OH)2(S)+[Co3 2-].fwdarw.CaCO3(S)+[2 OH]
followed by separation of the solid CaCO3(S), the lime sludge, to yield said first type of white liquor having reduced sulphidity;
e) mixing the solid calcium sulphide (CaS) obtained in step c) with a required amount of white liquor to react to [OH-] of the white liquor with the CaS according to the reaction formula:
CaS(S)+[H2O]+[2 OH-].fwdarw.Ca(OH)2(S)+[HS-]+[OH-]; and f) separating the solid Ca(OH)2 from the mixture obtained in step e) to yield the second type of white liquor having enhanced sulphidity.
2. ~The method according to claim 1, wherein the solid Ca(OH)2 obtained in step f) is added in the step d) to the solution for processing.
3. ~The method according to claim 1 or 2, wherein the aqueous solution in step b) is water.
4. ~The method according to claim 1 or 2, wherein the aqueous solution in step b) is weak liquor.
5. ~The method according to any one of claims 1 to 4, wherein the separation in step c) of the solid calcium sulphide is performed by filtration.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9301921A SE501347C2 (en) | 1993-06-04 | 1993-06-04 | Preparation of white liquor with elevated and / or reduced sulphidity |
| SE9301921-4 | 1993-06-04 | ||
| PCT/SE1994/000537 WO1994029516A1 (en) | 1993-06-04 | 1994-06-03 | Production of white liquor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2163368A1 CA2163368A1 (en) | 1994-12-22 |
| CA2163368C true CA2163368C (en) | 2006-02-07 |
Family
ID=35890341
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002163368A Expired - Fee Related CA2163368C (en) | 1993-06-04 | 1994-06-03 | Production of white liquor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2163368C (en) |
-
1994
- 1994-06-03 CA CA002163368A patent/CA2163368C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2163368A1 (en) | 1994-12-22 |
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