Basics of Kraft Pulping & Recovery Process. Art J. Ragauskas Institute of Paper Science and Technology Georgia Institute of Technology

Transcription

1 Basics of Kraft Pulping & Recovery Process Art J. Ragauskas Institute of Paper Science and Technology Georgia Institute of Technology

2 Outline History Goals Process Overview Kraft Pulping Process Kraft Recovery Power Plant Caustic Plant

3 History Soda pulping process patented, Soda recovery via incineration patented, First successful soda mill, Kraft pulping process patented by Dahl, First commercially viable kraft mill, Sweden, Kraft recovery furnace, 1930 s.

4 Kraft Pulping and Recovery: Overall Objectives Chemical convert wood into cellulosic pulp High quality, strong pulp for papermaking Operate safely Minimize impacts on air and water Satisfy customer needs Maximum product quality Minimize cost

5 Kraft Pulping Objectives Use chemicals, heat, pressure to liberate fibers. Operate safely. Minimize impacts on air and water. Satisfy customer needs - maximum product quality. Minimize cost.

6 Kraft Recovery Objective Concentrate and burn black liquor. Provide energy produced from organics. Provide partially reconstituted pulping chemicals. Operate safely. Minimize impacts on air and water. Satisfy customer needs, product quality. Minimize cost.

7 Kraft Caustic Plant Objective Final step in reconstituting pulping chemicals. Provides fresh cooking liquor. Regenerates lime from lime mud. Operate safely. Minimize impacts on air and water. Satisfy customer needs, product quality. Minimize cost.

8 The Kraft Pulping and Recovery Process Process overview. Dale Proctor, 2003

9 Dale Proctor, 2003

10 The Kraft Pulping and Recovery Process Flow Diagram Pulp Mill White Liquor Black Liquor Caustic Plant Power Plant Green Liquor

11 The Kraft Pulping and Recovery Basic Process Flow White Liquor NaOH Na 2 S Pulp Pulp Mill Mill Cooking Washing Dale Proctor, 2003 Black Liquor Turpentine pulp

12 Raw Material

13 Structure of Wood Fibers P S 1 S 2 S 3 Lumen Middle Lamella

14 Chemical Structure of Fibers H HO H O HO H H OH H H HO H O HO H H OH H O O HO O OH HO H H OH H H H HO O HO H H OH H H H HO O % n % O HO O OH O HO OH O O HO O OH HO O OH O O-Xylan OH n: HO Substituted with O OH H 3 CO HO 2 C O O OH O CH 2 OH HO H 3 CO H 3 CO OH O CH 3 OH CH 2 CH H 3 CO O O OH Extractives 2 8 % CH 2 OH H 3 CO O OH H 3 CO O OH OCH %

15 Physical Structure of Fibers Cellulose embedded in lignin hemicellulose matrix.

16 Kraft Yields Lignin Cellulose Hemicellulose Extractives Pine Wood 30 kg 45 kg 20 kg 5 kg 50% Yield Kraft 5 kg 40 kg 2.5 kg 0 kg

17 Chip Quality Hardwood vs. Softwood Wood Density Roundwood vs. Chips SMC Thinnings Mature Juvenile (8 12)

18 Chip Storage Manage Chip Pile By-Products Acid Hydrolysis Yield

19 Chip Preparation Chips Roundwood Longwood Slasher Barking Drum Chipper Chip Storage Chip Screens Rechipper Boiler Magnet Pulp Mill

20 Kraft Pulping White Liquor NaOH + NaSH Pulp Mill Dissolve & Fragment Lignin White Liquor Black Liquor Peeling and Chain Scission of Polysaccharides Caustic Plant Green Liquor Power Plant Dale Proctor, 2003

21 Kraft Chemistry NaOH Na + + OH - Na 2 S 2 Na + + S 2- S 2- + H 2 O SH - + OH - NaOH + Na 2 S + H 2 O 3Na + + 2OH - + SH - Na 2 CO 3

22 Kraft Pulping Digesters Batch and Continuous Reactors Dissolve & Fragment Lignin ºF psi ph Dale Proctor, 2003

23 Kraft Pulping White Liquor Blow Tank Chip Feed System Digester Knotters Screens/Cleaners Washers Evaporators (Recovery)

24 Batch Digesters 20+ ft. Height ft. Diameter Carbon Steel Pressure Vessel

25 Batch Digesters Locking Pin Liquor Top Off Level & Pressure Sensors Chip Chute Capping Valve Gasoff Vent Temperature Probes Blowline White and Black Liquor

26 Continuous Digesters: Chip Feed System Pressurized Feed System

27 Chip Bin Low Pressure Feeder Top Separator Impregnation Zone Steaming Vessel Chip Chute White Liquor High Pressure Feeder Inline Drainers

28 Continuous Digesting System Carbon Steel Pressure Vessel ft Height.

29 Liquor Heaters Heating Zone Screens Flash Tank Flash Steam to SV Extraction Zone Screens Cooking Zone Washing & Cooling Zone Outlet Device Blow Tank Liquor to Evaporators Cold Blow

30 Pulp Preparation Blow Tank Knotters Counter Current Washers Chip Bin Hot Water to Final Washing Stage Shower Liquor from Later Stages to Shower Earlier Liquor from First Stage to Evaporators Screens/Cleaners Pulp Storage

31 Kraft Chemistry Extractives Dissolved Turpentine Tall Oil

32 Extractives Digester Relief Cyclone Separators Condensers Decanter Storage Black Liquor

33 The Kraft Pulping and Recovery Process Flow Diagram Pulp Mill White Liquor Black Liquor Caustic Plant Power Plant Green Liquor

34 Power Plant Kraft Recovery Black Liquor Evaporation Recovery Boiler

35 Kraft Power Plant Black Liquor from Pulp Mill Washer Filtrate & Flash Tank Black Liquor Oxidation?? Green Liquor to Caustic Plant Smelt Dissolving Tank Concentrated Black Liquor Concentrator or Direct Contact Evaporator Recover Boiler

36 Kraft Multiple Effect Evaporators Weak Black Liquor Steam Soap Skimmer Flash Tank Concentrated Liquor Tank

37 The Kraft Recovery Boiler Recovery Boiler Water Evaporation Burns Organics Steam Reduces Oxidized Sulfur Compounds Recovers Inorganics as Smelt

38 Kraft Recovery Boiler Green Liquor Na 2 CO 3 Na 2 S White Liquor Pulp Mill Black Liquor Caustic Plant Power Plant Green Liquor Dale Proctor, 2003

39 The Kraft Recovery Boiler Precipitator Concentrated BL from Concentrator Salt Cake Black Liquor Mix Tank Steam Liquor Heater Dissolving Tank

40 Precipitator Economizers Flue Gas Superheater and Screen Waterwalls Boiler Bank Forced Air Fan Secondary Air Air Heaters Black Liquor Smelt Spouts Primary Air Smelt Dissolving Tank

41 The Kraft Recovery Boiler Precipitator Boiler Feed Water Hot Combustion Gas Economizer Boiler Section Superheater Furnace Wall Screen Turbines

42 The Kraft Recovery Boiler Oxidation Na 2 S + 3/2 O 2 + CO 2 Na 2 CO 3 + SO 2 Oxidizing Pyrolysis Na 2 S+ H 2 O+ CO 2 Na 2 CO 3 + H 2 S Drying Reduction Reduction Na 2 SO + 2C 4 Na 2 S + 2CO 2 Na 2 SO 4 + 4C Na 2 S + 4CO

43 The Kraft Pulping and Recovery Process Flow Diagram Pulp Mill White Liquor Black Liquor Caustic Plant Power Plant Green Liquor

44 The Kraft Pulping and Recovery Process Flow Diagram

45 The Kraft Chemical Recovery Process Flow Diagram CaO (Lime) Smelt - Na 2 CO 3 Slaker CaO + H 2 O Ca(OH) 2 (Slaked Lime) Na 2 CO 3 + Ca(OH) 2 NaOH (Caustic) + CaCO 3 (Lime Mud) Pulp Mill

46 The Kraft Caustic Plant Process Flow Diagram Green Liquor Clarifier Slaker Causticizers White Liquor Clarifier Dregs Washer or Filter Lime Silo Filter Mud Washer Kiln

47 Safety Pulp Mill - Acid Cleaning Digester, Liquor Heaters, Inline Drainers Power Plant - Smelt Water Explosions Caustic Plant - Gas in Kiln

48 Environmental Concerns Water Air Acid Cleaning Liquor Spills Stacks

49

50 Thank You!