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Pulping Technical Services

The Go-To Place for Solutions to Pulping Challenges

The mission of the Pulp and Paper Technical Services program is to support our allied industries with high quality, cost-effective services. From small-scale laboratory testing to pilot-scale production of large quantities of pulp or paper from a variety of sources, we are well-equipped for almost any technical challenge related to pulping and pride ourselves on a total customer focus.

Chemical Pulping

With a large number of digesters, ranging from 0.03-845 gallons (100 ml to 3200 liters), we are well equipped to conduct studies on a variety of materials. Typical activities include furnish studies, pulping optimization, comparison of different processes, and digester additives evaluation.

Pulping studies are conducted on both traditional and alternative wood furnishes. A variety of non-wood raw materials are also studied, including agricultural residues (corn stalk, rice, and wheat straw) and fiber crops (kenaf, hemp, and sisal.)


M&K 2.5-gallon (10-liter) Batch Digesters

Number available: 4

Capacity: up to 1200 grams of dry wood chips per batch


  • basket insert for chips
  • sidearm liquor circulation
  • electric resistance heating in sidearm
  • computer control of heatup and hold times
  • cold blow via liquor expression from digester bottom

NC State 0.8-gallon (3-liter) Pressure Bombs for Cooking or Bleaching

Number available: 6

Construction: 316 SS

Capacity: 200 grams dry chips, 200 grams medium- to high-consistency pulp


  • each bomb has its own top-mounted valve for introduction of gases
  • each bomb has its own thermocouple for monitoring of temperature
  • rotating rack in hot-air oven permits six bombs to be processed at the same time (insures good mixing of chemicals and raw material)
  • two bombs coated with Teflon for maximum brightness development

Process options:

  • digestion
  • oxygen bleaching (high and medium consistency)
  • oxygen- and peroxide-reinforced extraction
  • pressurized peroxide

Paprican-Designed 3-gallon (11.4 liter) Batch Digester with Internal Moving Fingers

Capacity: 1.1 OD lb (500 OD grams) of medium- or high-consistency pulp; 250-400 AD grams of bulky non-wood material

Construction: 316 SS lined with Teflon


  • 150 psig max. pressure
  • can be pressurized with oxygen or other gases
  • internal fingers lift and mix material; variable speed
  • external electrical heating bands

This reactor is well-suited for medium- or high-consistency bleaching of pulp with a variety of agents, including oxygen. The reactor is also an excellent bench-scale digester for nonwood materials. The fingers provide a lifting and turning action similar to a screw-type digester.

Small Pilot-Scale

7.5-gallon (28-liter) Hot-Blow Digester

Capacity: 20 lb (9 kg) dry chips

Construction: 316 SS


  • liquor circulation through sidearm
  • indirect steam heating in circulation line
  • hot blow to blow tank

13-gallon (50-liter) Cold-Blow Batch Digester System

Number available: 4

Construction: electropolished 316 SS


  • liquor circulation through sidearm
  • electrical heating in circulation line
  • basket inserts to hold chips
  • piping configuration permits system to be used for displacement-type cooking (RDH, Enerbatch Superbatch)
  • piston pump permits chemical profiling during cook for emulation of modified cooking

7.5-gallon (28-liter) Direct-Steamed Rotary Batch Digester/Reactor

Capacity: 15 dry pounds chips or 5-6 dry pounds bulky nonwood materials

Construction: 316 SS


  • 250 psig max pressure
  • rotating action insures good mixing of chemicals and raw material
  • heating via direct steam injection
  • can be pressurized with oxygen or other gases

This vessel can be used for cooking or for bleaching at medium or high consistency.

Large Pilot-Scale

40-gallon (150-liter) Vertical, Screw-fed, Continuous Digester with Refiner Discharge

Capacity: up to 3 tons/day on wood; less on bulky non-woods

Construction: 316 SS


  • atmospheric pre-steaming
  • 3:1 volumetric reducing screw and plug former permit continuous feeding into the pressurized digester
  • flooded-zone impregnation box at discharge of plug former permits intense chemical impregnation; lifting screws drain material briefly before falling into vessel
  • up to 30 minutes of retention time
  • 250 psig pressure max.
  • nuclear gauge for accurate level control
  • bottom agitator ensures that material moves into discharge screw
  • 12-inch refiner in discharge line; digester cannot be run without refiner

This unit can be used for continuous production of chemical or semi-chemical pulp, as long as the process permits short retention times and some degree of refining at the discharge. On non-woods, the unit can be made to run like a screw-type digester. The unit has been run successfully on corn stalk, wheat straw, hemp, and kenaf.

Mechanical Pulping

Mechanical pulping trials may include RMP (refiner mechanical pulping), CMP (chemimechanical pulping), TMP (thermomechanical pulping), or CTMP (chemithermomechanical pulping). Semi-chemical pulping may also be carried out.

For small-scale or screening trials, the KRK Pressurized Laboratory Refiner may be used, with batch sizes 1-5 lb (0.5-2 kg.) Large-scale proofing or production trials may be accomplished in the 3-ton/day Sunds CD-300 2-stage pilot plant.

Pulp produced in the pilot plant can be screened, cleaned, washed, and bleached on a continuous basis.

Small Pilot-Scale

KRK Pressurized Laboratory Refiner

Capacity: up to 15 pounds (6.8 kg) dry wood chips per batch; less for bulky non-woods

Construction: 316 SS


  • 7.5-gallon (28-liter) infeed vessel and 11.3-gallon (42-liter) discharge vessel permit batchwise running of TMP, CTMP
  • 150 psig max. pressure
  • direct steaming into infeed vessel
  • chemical prep and preheating system

permits injection of chemicals just prior to refining 12-inch refiner with 60-HP motor running at 3600 rpm adjustable plate gap on-line energy measurement

This unit permits small batches of material to be processed very accurately and quickly, making it perfect for exploratory trials.

Large Pilot-Scale

Sunds CD-300 Mechanical Pulping Pilot Plant

Capacity: up to 3 tons/day continuous feed on wood chips


  • two true, real-time stages of refining
  • atmospheric pre-steaming
  • 3:1 volumetric reducing screw for plug feed into reactor
  • impregnator box for impregnation with chemicals
  • 40-gallon (150-liter) pre-heating vessel with nuclear level control and up to 30 minutes retention, 150 psig max.

primary refiner: 300-HP, 3600 rpm pressurized cyclone permits primary and secondary stages to be run at different pressures secondary refiner: 250-HP, 3600 rpm interstage reactor permits treatment of primary-stage pulp with aqueous or gaseous agents prior to secondary refining, 150 psig max. dedicated process computer with energy consumption monitoring

Pulp Processing

NC State has a flexible array of pilot equipment available for pulp processing and stock preparation. In one facility, pulp can be made down, bleached or otherwise chemically treated, washed or thickened, screened, centrifugally cleaned, and refined. Clients may ship in their own pulp in the form of market pulp, wetlap, drylap, or slurries. Pulps may also be generated on site chemically (using the rotary globe digester), mechanically (using the 3 ton/day Sunds pilot plant), or via recycling. The final product may be formed into paper on the pilot fourdrinier, wet- or dry-lapped on the fourdrinier, or collected in drums or other containers from dewatering on the drum washer or screw press.

Pulping and Stock Makedown

Black Clawson 200-gallon (760-liter) Hydrapulper

This very flexible piece of equipment can be used both for stock-prep. pulping, mild chemical pulping, and low- or medium-consistency bleaching. The ability to inject steam and/or chemicals is particularly attractive.

Capacity: 200 gallons (760-liters), can hold up to 45-90 OD lb (21-40 OD kg) of pulp at a consistency of 3-6 % (Vokes rotor) or up to 150 OD lb (68 OD kg) of pulp at medium consistency (helical rotor)

Construction: epoxy-lined carbon steel


  • Vokes rotor for low-consistency pulping
  • Hi-con helical rotor for high-consistency pulping and bleaching
  • 20-HP motor with variable-speed drive
  • can be pressurized up to 50 psig due to bolted-head construction
  • steam, gases (oxygen, ozone), and/or chemicals can be injected into vortex zone

50-gallon (190-liter) Pilot Pulper

Capacity: 50 gallons (190 liters), up to 17 OD pounds (7.7 OD kg) of pulp at 5 % consistency or 42 OD pounds 19 OD kg) at 12% consistency

Construction: 316 SS


  • 10-HP motor
  • low-consistency (Vokes) and high-consistency (helical) rotors available
  • atmospheric de-inking capability with Lamort-style passive air intake shroud

Washing and Thickening

Bauer Hydrasieve Slanting Screen

Designed to take low-consistency stock and thicken it passively to 3-6 percent.

Construction: 316 SS

Face: 24″

Screen: 0.010 slotted wave plate

Renneberg Pilot Screw Press

Useful for intense dewatering of pulp slurries. Discharge consistencies of up to 40% are possible, depending on the furnish.

Construction: 316 SS


  • 10-HP motor with variable-speed drive
  • 3 feet (1 m) long, 6″ (15-cm) diameter

Filtration Engineers Pilot Rotary Drum Filter Washer

The equipment may be used either for dewatering or intense washing.


  • 3 feet (1 m) diameter, 1 foot (0.3 m) face width
  • separate vacuum headers for vat and mat sections
  • 316 SS wetted parts
  • up to three wash showers available with variable flow
  • rider rolls available for increased dewatering
  • vat agitator
  • discharge consistency 8-15 %
  • capacity 30 gpm (114 lpm)

Centrifugal Screening

Ahlstrom M200 Centrisorter Centrifugal Pressure Screen

This unit has been modified to accept a 100 gpm (380-lpm) feed rate.


  • 50-HP motor, 1200 rpm
  • foil-type (LR) rotor

Baskets available:

  • Slots: 0.010″ (0.25 mm)
  • Holes: 0.063″ (1.6 mm) or 0.008″ (0.20 mm)

Gauld Periflow 140 Centrifugal Pressure Screen


  • 60-HP motor with variable-speed drive
  • taper-shear rotor
  • internal accepts (rotor) shower and rejects nozzle flush

Baskets available:

  • Slots: 0.008″ (0.20 mm) or 0.016″ (0.41 mm)
  • Holes: 0.032″ (0.81 mm), 0.062″ (1.6 mm) or 0.082″ (2.1 mm)

Centrifugal Cleaning

Single bodies of the following centrifugal cleaners are available for flow-through production of cleaned pulp:

  • Beloit Posiflow: This is a forward cleaner with a feed rate of about 70 gpm. A variety of nozzle types are available for optimum cleaning efficiency.
  • Beloit Uniflow: This is a reverse cleaner with a feed rate of about 100 gpm. A variety of reject nozzles and inserts are available.
  • Celleco Low-Density Cleaner: This is a heavyweight contaminant cleaner with a feed rate of about 100 gpm.
  • Noss Horizontal Canister Cleaner (Forward and Reverse): This canister cleaner may be run with either forward, reverse, or forward/reverse modes.


Sprout-Bauer Twin-Flo Stock Prep Refiner

Designed for refining of stock at low consistency.


  • 12″ (30.5 cm) plate size
  • 150-hp motor at 1800 rpm

Pulp Testing

  • Freeness: CSF and Shopper-Riegler
  • Kappa

Viscosity – 0.5 % CED and intrinsic Brightness – ISO and GE Fiber length distribution – Bauer- McNett, Kajaani FS-200, Optest FQA