Method for processing black liquor in pulp production

Abstract

A method for processing black liquor includes operations of: (A1) ultrafiltering the black liquor; (A2) mixing the ultrafiltration concentrate with carbon dioxide and/or sulfuric acid to precipitate lignin in the ultrafiltration concentrate, and obtaining a first inorganic aqueous solution; (A3) mixing the first inorganic aqueous solution with the ultrafiltration permeate to obtain a mixture, and nanofiltering the mixture; (A4) mixing the nanofiltration concentrate with carbon dioxide and/or sulfuric acid to precipitate lignin in the nanofiltration concentrate, and obtaining a second inorganic aqueous solution; (A5) performing a first electrodialysis treatment or reverse osmosis treatment on the second inorganic aqueous solution, and obtaining a remaining inorganic aqueous solution; (A6) mixing the remaining inorganic aqueous solution with the lignin obtained from operation (A2) and/or operation (A4) to obtain a first fuel liquid; and (A7) processing the first fuel liquid to produce sodium sulfide, sodium carbonate, carbon dioxide, and steam.

What is claimed is: 
     
         1 . A method for processing black liquor in pulp production, the method comprising operations of:
 (A1) ultrafiltering black liquor generated in pulp production to obtain an ultrafiltration permeate and an ultrafiltration concentrate, wherein the black liquor comprises at least lignin, sodium hydroxide, sodium sulfide, sodium sulfate, sodium sulfite, sodium carbonate, and water;   (A2) mixing the ultrafiltration concentrate with carbon dioxide and/or sulfuric acid to precipitate lignin in the ultrafiltration concentrate and obtain a first inorganic aqueous solution, wherein the ultrafiltration concentrate reacts with carbon dioxide and/or sulfuric acid to produce sodium carbonate and/or sodium sulfate dissolved in the first inorganic aqueous solution;   (A3) mixing the first inorganic aqueous solution with the ultrafiltration permeate to obtain a mixture, and nanofiltering the mixture to obtain a sodium hydroxide aqueous solution as a permeate and a nanofiltration concentrate as a retentate;   (A4) mixing the nanofiltration concentrate with carbon dioxide and/or sulfuric acid to precipitate lignin in the nanofiltration concentrate and obtain a second inorganic aqueous solution, wherein the nanofiltration concentrate reacts with carbon dioxide and/or sulfuric acid to produce sodium carbonate and/or sodium sulfate dissolved in the second inorganic aqueous solution;   (A5) subjecting the second inorganic aqueous solution to a first electrodialysis treatment or a reverse osmosis treatment, wherein:   while the first electrodialysis treatment is performed, sodium carbonate in the second inorganic aqueous solution is electrolyzed to produce sodium hydroxide, and a sodium hydroxide aqueous solution is obtained at a cathode of the first electrodialysis treatment, and a remaining inorganic aqueous solution is obtained at an anode of the first electrodialysis treatment;   while the reverse osmosis treatment is performed, water is obtained as a permeate and a remaining inorganic aqueous solution is obtained as a retentate;   (A6) mixing the remaining inorganic aqueous solution with a portion of the lignin obtained from operation (A2) and/or operation (A4) to obtain a first fuel liquid; and   (A7) processing the first fuel liquid to produce sodium sulfide, sodium carbonate, carbon dioxide, and steam.   
     
     
         2 . The method according to  claim 1 , wherein operation (A7) comprises the acts of:
 (A7-1) evaporating a portion of water in the first fuel liquid to obtain a concentrated fuel liquid and steam;   (A7-2) mixing the concentrated fuel liquid with a portion of the lignin obtained from operation (A2) and/or operation (A4) to obtain a second fuel liquid; and   (A7-3) combusting the second fuel liquid to generate sodium sulfide, sodium carbonate, carbon dioxide, and steam.   
     
     
         3 . The method according to  claim 1 , wherein
 operation (A2) comprises mixing the ultrafiltration concentrate with carbon dioxide produced from operation (A7); and/or   operation (A4) comprises mixing the nanofiltration concentrate with carbon dioxide produced from operation (A7).   
     
     
         4 . The method according to  claim 1 , after operation (A7), further comprising operations of:
 (A8) mixing water with sodium sulfide and sodium carbonate produced from operation (A7) to obtain a green liquor; and   (A9) subjecting the green liquor to a second electrodialysis treatment, electrolyzing the sodium carbonate in the green liquor to produce sodium hydroxide, wherein a sodium hydroxide aqueous solution is obtained at a cathode of the second electrodialysis treatment, and a sulfuric acid aqueous solution is obtained at an anode of the second electrodialysis treatment.   
     
     
         5 . The method according to  claim 4 , further comprising operations of:
 (A10) mixing sodium sulfide with the sodium hydroxide aqueous solution obtained from operation (A9), the sodium hydroxide aqueous solution obtained from operation (A3), and the sodium hydroxide aqueous solution obtained from operation (A5) to obtain a white liquor; and   (A11) applying the white liquor to the pulp production;   wherein operation (A5) comprises performing the first electrodialysis treatment.   
     
     
         6 . The method according to  claim 1 , after operation (A7), further comprising operations of:
 (A8) mixing water with sodium sulfide and sodium carbonate produced from operation (A7) to obtain a green liquor; and   (A12) subjecting the green liquor to a causticizing reaction with calcium oxide to obtain an aqueous solution comprising sodium hydroxide and sodium sulfide.   
     
     
         7 . A method for processing black liquor in pulp production, the method comprising operations of:
 (B1) ultrafiltering black liquor generated in pulp production to obtain an ultrafiltration permeate and an ultrafiltration concentrate, wherein the black liquor comprises at least lignin, sodium hydroxide, sodium sulfide, sodium sulfate, sodium sulfite, sodium carbonate, and water;   (B2) nanofiltering the ultrafiltration permeate to obtain a sodium hydroxide aqueous solution as a permeate and a nanofiltration concentrate as a retentate, and mixing the ultrafiltration concentrate with the nanofiltration concentrate to obtain a concentrated black liquor;   (B3) mixing the concentrated black liquor with carbon dioxide and/or sulfuric acid to precipitate lignin in the concentrated black liquor and obtain an inorganic aqueous solution, wherein the concentrated black liquor reacts with carbon dioxide and/or sulfuric acid to produce sodium carbonate and/or sodium sulfate dissolved in the inorganic aqueous solution;   (B4) subjecting the inorganic aqueous solution to a first electrodialysis treatment or a reverse osmosis treatment, wherein:   while the first electrodialysis treatment is performed, sodium carbonate in the inorganic aqueous solution is electrolyzed to produce sodium hydroxide, a sodium hydroxide aqueous solution is obtained at a cathode of the first electrodialysis treatment, and a remaining inorganic aqueous solution is obtained at an anode of the first electrodialysis treatment;   while the reverse osmosis treatment is performed, water is obtained as a permeate and a remaining inorganic aqueous solution is obtained as a retentate;   (B5) mixing the remaining inorganic aqueous solution with a portion of the lignin obtained from operation (B3) to obtain a first fuel liquid; and   (B6) processing the first fuel liquid to produce sodium sulfide, sodium carbonate, carbon dioxide, and steam.   
     
     
         8 . The method according to  claim 7 , wherein operation (B6) comprises acts of:
 (B6-1) evaporating a portion of water in the first fuel liquid to obtain a concentrated fuel liquid and steam;   (B6-2) mixing the concentrated fuel liquid with a portion of the lignin obtained from operation (B3) to obtain a second fuel liquid;   (B6-3) combusting the second fuel liquid to produce sodium sulfide, sodium carbonate, carbon dioxide, and steam.   
     
     
         9 . The method according to  claim 7 , wherein operation (B3) comprises mixing the concentrated black liquor with the carbon dioxide produced from operation (B6). 
     
     
         10 . The method according to  claim 7 , after operation (B6), further comprising operations of:
 (B7) mixing water with sodium sulfide and sodium carbonate produced from operation (B6) to obtain a green liquor; and   (B8) subjecting the green liquor to a second electrodialysis treatment, electrolyzing the sodium carbonate in the green liquor to produce sodium hydroxide, wherein a sodium hydroxide aqueous solution is obtained at a cathode of the second electrodialysis treatment, and a sulfuric acid aqueous solution is obtained at an anode of the second electrodialysis treatment.   
     
     
         11 . The method according to  claim 10 , further comprising operations of:
 (B9) mixing sodium sulfide with the sodium hydroxide aqueous solution obtained from operation (B8) and the sodium hydroxide aqueous solution obtained from operation (B2) and the sodium hydroxide aqueous solution obtained from operation (B4) to obtain a white liquor; and   (B10) applying the white liquor to the pulp production;   wherein operation (B4) comprises performing the first electrodialysis treatment.   
     
     
         12 . The method according to  claim 7 , after operation (B6), further comprising operations of:
 (B7) mixing water with sodium sulfide and sodium carbonate produced from operation (B6) to obtain a green liquor; and   (B11) subjecting the green liquor to a causticizing reaction with calcium oxide to obtain an aqueous solution comprising sodium hydroxide and sodium sulfide.   
     
     
         13 . A method for processing black liquor in pulp production, the method comprising operations of:
 (C1) ultrafiltering black liquor generated in pulp production to obtain an ultrafiltration permeate and an ultrafiltration concentrate, wherein the black liquor comprises at least lignin, sodium hydroxide, sodium sulfide, sodium sulfate, sodium sulfite, sodium carbonate, and water;   (C2) distributing the ultrafiltration concentrate into a first ultrafiltration concentrate and a second ultrafiltration concentrate;   (C3) mixing the first ultrafiltration concentrate with carbon dioxide and/or sulfuric acid to precipitate lignin in the first ultrafiltration concentrate and obtain a first inorganic aqueous solution, wherein the first ultrafiltration concentrate reacts with carbon dioxide and/or sulfuric acid to produce sodium carbonate and/or sodium sulfate dissolved in the first inorganic aqueous solution;   (C4) mixing the first inorganic aqueous solution with the ultrafiltration permeate to obtain a mixture, and nanofiltering the mixture to obtain a sodium hydroxide aqueous solution as a permeate and a nanofiltration concentrate as a retentate;   (C5) mixing the nanofiltration concentrate with carbon dioxide and/or sulfuric acid to precipitate lignin in the nanofiltration concentrate and obtain a second inorganic aqueous solution, wherein the nanofiltration concentrate reacts with carbon dioxide and/or sulfuric acid to produce sodium carbonate and/or sodium sulfate dissolved in the second inorganic aqueous solution;   (C6) subjecting the second inorganic aqueous solution to a first electrodialysis treatment or a reverse osmosis treatment, wherein:   while the first electrodialysis treatment is performed, sodium carbonate in the second inorganic aqueous solution is electrolyzed to produce sodium hydroxide, and a sodium hydroxide aqueous solution is obtained at a cathode of the first electrodialysis treatment, and a remaining inorganic aqueous solution is obtained at an anode of the first electrodialysis treatment;   while the reverse osmosis treatment is performed, water is obtained as a permeate and a remaining inorganic aqueous solution is obtained as a retentate;   (C7) mixing the remaining inorganic aqueous solution, the second ultrafiltration concentrate obtained from operation (C2), and a portion of the lignin obtained from operation (C3) and/or operation (C5) to obtain a first fuel liquid; and   (C8) processing the first fuel liquid to produce sodium sulfide, sodium carbonate, carbon dioxide, and steam.   
     
     
         14 . The method according to  claim 13 , wherein operation (C8) comprises acts of:
 (C8-1) evaporating a portion of water in the first fuel liquid to obtain a concentrated fuel liquid and steam;   (C8-2) mixing the concentrated fuel liquid with a portion of the lignin obtained from operation (C3) and/or operation (C5) to obtain a second fuel liquid;   (C8-3) combusting the second fuel liquid to produce sodium sulfide, sodium carbonate, carbon dioxide, and steam.   
     
     
         15 . The method according to  claim 13 , wherein:
 operation (C3) comprises mixing the ultrafiltration concentrate with the carbon dioxide produced from operation (C8); and/or   operation (C5) comprises mixing the nanofiltration concentrate with the carbon dioxide produced from operation (C8).   
     
     
         16 . The method according to  claim 13 , after operation (C8), further comprising operations of:
 (C9) mixing water with the sodium sulfide and sodium carbonate produced from operation (C8) to obtain a green liquor; and   (C10) subjecting the green liquor to a second electrodialysis treatment, electrolyzing the sodium carbonate in the green liquor to form sodium hydroxide, wherein a sodium hydroxide aqueous solution is obtained at a cathode of the second electrodialysis treatment, and a sulfuric acid aqueous solution is obtained at an anode of the second electrodialysis treatment.   
     
     
         17 . The method according to  claim 16 , further comprising operations of:
 (C11) mixing sodium sulfide with the sodium hydroxide aqueous solution obtained from operation (C10) and the sodium hydroxide aqueous solution obtained from operation (C4) and the sodium hydroxide aqueous solution obtained from operation (C6) to obtain a white liquor; and   (C12) applying the white liquor to the pulp production;   wherein operation (C6) comprises performing the first electrodialysis treatment.   
     
     
         18 . The method according to  claim 13 , after operation (C8), further comprising operations of:
 (C9) mixing water with the sodium sulfide and sodium carbonate produced from operation (C8) to obtain a green liquor; and   (C13) subjecting the green liquor to a causticizing reaction with calcium oxide to obtain an aqueous solution comprising sodium hydroxide and sodium sulfide.