1. Unit Processes and Optimization Opportunities in the Pulp & Paper Mill
Brad S. Carlberg, P.E.
Senior Controls & Instrumentation Engineer
Waste Treatment Plant
Bechtel National Inc.
Richland, WA

2. Brad S. Carlberg, P.E. (Control Systems)
My Pulp & Paper career began with my 3rd grade science project in 1965 – who knew?
Over twenty years experience in Process Engineering and Process Control specifically with Distributed Control Systems and Programmable Logic Controllers combining extensive experience with both Hardware and Software Design, Programming, Implementation and Startup, including Advanced Continuous and Batch Control Programming.
Currently working (less than an hour drive from where he was born) for Bechtel on the Hanford Vitrification Plant in Richland, Washington

3. Lessons learned:
understand the equipment and the processes in a pulp & paper mill
understand the similarities to other industries
understand specific areas where control system optimization can decrease costs and/or increase production

4. The Typical Pulp & Paper Mill
There are six main “islands” of automation of the mill:
raw material receiving & preparation (the woodyard)
the pulp mill
the powerhouse
the paper mill
converting and finishing
effluent treatment.

5. THE WOODYARD (RAW MATERIAL RECEIVING & PREPARATION)
Debarking Drum is rotates and raw logs pass axially through to remove bark
Bark doesn’t make good paper AT ALL

6. THE WOODYARD Pulpwood logs out of debarking drum to the chippers
Chips are ”classified” (sorted) by size & species

7. THE WOODYARD (RAW MATERIAL RECEIVING & PREPARATION)

8. THE WOODYARD (RAW MATERIAL RECEIVING & PREPARATION)
Chips pneumatically transported from the Woodyard first to the chip bins and then to fill the Digester

9. THE PULP MILL Lime Kiln (the two rotating cylinders) Gas/Oil fired
Dry and Calcine the Lime Mud from the Slaker for reuse in the Causticizer

10. THE POWERHOUSE Multiple stories to house the Kraft Recovery Boiler
Like any industrial boiler, EXCEPT burns Black Liquor
Produces Green Liquor for Pulping
Induced Draft Fan
Multiple (~Fifty) Sootblowers
Electrostatic Precipitators remove particulate from stack gases
Steam feeds Digester, Evaporators, Paper Machine & Turbine-Generator

11. LIQUOR BURNERS IN THE KRAFT RECOVERY BOILER
Multiple (~12) burners per boiler
Strong black liquor 65% solids
Recovers inorganic chemicals as molten smelt that exits the bottom of the boiler into the green liquor dissolving tank to be reused in the digesting (cooking) process

12. % CONSISTENCY (of Wood Pulp Fiber) = 100 x Lbsfiber / (Lbsfiber + LbsWater)
microwave
Blade
Rotating Disk
Can be pumped at 3-5%
Can be stored at 15%

13. BROWN STOCK WASHERS
Rotating Cylinders covered with wire mesh pick up a 2” mat of pulp from the vat
COUNTERCURRENTLY Wash the pulp mat with water to Remove the weak black liquor
Filtrate sucked through the wire mesh by a gravity-formed vacuum into tanks directly below
Washed pulp “doctored” off of the rotating cylinders 180o after pickup

14. BLEACH PLANT TOWERS
Towers provide residence time for Bleaching chemicals to react with and to brighten pulp stock
3-Stage:
D1-Eop-D2
D=Chlorine Dioxide
Eop = Extraction with oxygen & peroxide

15. CHLORINE DIOXIDE GENERATOR
Environmentally friendly alternative to Liquid or Gaseous Chlorine Bleaching Agent
Interlocked to guard against a “puff” (explosion)
A great case for MPC control to control Cl O2 density ( g/l )

16. BLEACH PLANT WASHERS
Used to remove residual bleaching chemicals from the pulp

17. PULP HIGH-DENSITY STORAGE CHESTS
That’s A LOT of pulp
Enough for a couple of shifts in case the pulp mill goes down – the paper machine can still run

18. THE PAPER MILL – STOCK PREP
The refiners condition the pulp stock when cooking in the digesters is stopped early

19. THE PAPER MILL – STOCK PREP
The two plates cut & brush up the fibers
Optimize Power/Ton

20. STOCK PREP CLEANERS Centrifugal force separates lights from heavies
Remove contaminants or non-uniform sized fibers

21. THE PAPER MILL – WET END
Headbox at the far end feeds the Fourdrinier wire
Vacuum to remove water

22. PAPER MACHINE – DRY END LOOKING TO WET WET END
~100 yards long
Forming section
Press section
Dryer section
Finishing section

23. CONVERTING AND FINISHING
Cut the big rolls of paper into transportation-size rolls
Rewind the big rolls of paper into transportation-size rolls

24. EFFLUENT TREATMENT Just like a municipal waste treatment plant
Aeration Basin
Clarifiers
Settling ponds

25. OPTIMIZATION OPPORTUNITIES IN THE PULP & PAPER MILL
RECOVERY BOILER SOOTBLOWING
BLACK LIQUOR EVAPORATORS
CAUSTICIZING
BATCH AND CONTINUOUS DIGESTERS
SCREENING AND REFINING
WASHING
BLEACHING
LIME KILN
PULP STOCK PREPARATION, CLEANING, REFINING, AND BLENDING
PAPER PAPERMAKING, PRESSING AND DRYING SECTIONS OF THE PAPER MILL

26. PULP & PAPER PROCESS OVERVIEW
Woodyard
Digester
Washer
Bleach
Plant
Weak
Black Liq
Pulp Mill Hot Buttons
Wood Supply
Causticizing operation
Digester/Washer
Production
Air Pollution
Water Pollution
Pulp Quality
Chemical and Energy use
Maintenance
White
Liquor
Evaporator
Paper
Mill
Strong
Black Liq
Causticizing
Green
Liquor
Dissolving
Tank
Recovery
Boiler
Shipping
Lime Kiln

27. RECOVERY BOILER DCS GRAPHIC

28. RECOVERY BOILER ROTARY SOOTBLOWER
Uses high-pressure steam to blow soot off of boiler tubes to improve heat transfer between furnace gases and boiler water
Sequence the individual sootblower operation for optimal steam usage
Low Temp & High Diff Press signal which sections to blow

29. LIME KILN PROCESS
Big energy savings possible here!

30. LIME KILN DCS GRAPHIC
Long Deadtime means Good case for Multivariable Predictive Controller
CV – Temps
MV – ID Fan ASD
DV – Production Rate

31. RECAUSTICIZING – traditional control
Big chemical savings possible here!
Long Deadtime means Good case for Multivariable Predictive Controller
CV – Conductivity
MV – Green Liquor & Lime feeder ASDs
DV – White Liquor Production Rate

32. RECAUSTICIZING – new sensors
Big chemical savings possible here!

33. RECAUSTICIZING DCS GRAPHIC

34. BLACK LIQUOR EVAPORATOR
Fouling reduces efficiency
Automate boilout when fouling decreases heat transfer from steam to liquor

35. EVAPORATOR DCS GRAPHIC

36. BROWN STOCK WASHERS DCS GRAPHIC
An Optimum Dilution Factor of 1.0 means that the Lbs wash water equals the lbs pulp stock
Less wash water reduces the load on the evaporators i.e. steam usage

37. CONTINUOUS DIGESTER DCS GRAPHIC
Kappa Number is the amount of delignification of the pulp fiber
For example, brown board will have a higher Kappa Number than bleached pulp
White Liquor Analyzer to sense residual chemical
Kappa Analyzer to sense fiber delignification

38. BATCH DIGESTERS DCS GRAPHIC
Batch Scheduling - Steam Leveling smoothes boiler operation
Chip Qualities – uniform moisture
Batch digesters- liquor analyzer
Better Kappa control
Reduce white liquor usage
Batch digesters- Kappa analyzer

39. PAPER MACHINE SCANNER
Multiple sensors across width machine width measure:
Moisture
Basis Weight
Caliper (Thickness)

40. PAPER MACHINE SCANNER

41. PAPER MACHINE DRYERS
Paper sheet rolls over the steam-heated dryer cylinders to evaporate moisture
Optimize Steam Usage to save energy costs

42. IN CONCLUSION
After reading this paper and seeing this presentation you now have a better understanding of the equipment and the processes in a pulp & paper mill, you can see the similarities to other industries
You have an idea of several specific areas where control system optimization can decrease costs and/or increase production

43. ACKNOWLEDGEMENTS
First and foremost, I would not be here today (literally and figuratively) had my Father not spent his entire career with the same pulp & paper manufacturer and, in fact, gave me the raw materials and the technical background for my 3rd science project
I likely would not be in instrumentation & controls had (ISA PUPID Life Fellow) John Lavigne written the book “An Introduction To Paper Industry Instrumentation” which I read immediately following graduation
I must thank the pulp & paper mill workers in mills scattered throughout North America from whom I gained the immeasurable experience to write this paper

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