PGW Pressurized Ground Wood System

The recent purchase of a complete WOOD ROOM and PGW “Pressurized Ground Wood” System has presented an abundance of available equipment.

System Picture

PGW Fiber Department

Pressurized groundwood (PGW) fiber is the primary source of fiber used for producing coated groundwood paper.

Woodyard and Woodroom

Wood Room Equipment

Local aspen wood was formerly delivered by truck to an on-site 7 area Woodyard that has the capacity to hold 20,000 cords of wood.  The wood was then processed in the Woodroom (building 113) where it was debarked and cut into 4 foot lengths at a rate of 19 cords per hour.  A delivery system processed and fed the resulting bark and wood waste to the boilerhouse where it was burned as fuel.

PGW Pulpmill

The shortened and debarked lengths of aspen from the Woodroom were conveyed to the pulpmill 100 cord capacity storage bin for storage (building 101).  The wood was then fed to the main Pulmill’s (building 100) four 7000 hp pressurized grinders where it’s ground to pulp at a rate of 280 tons per day (70 tpd per grinder).  Next, the pulp was thickened and pumped to the screening and bleaching area located near the paper machines

PGW Screenroom and Bleach Plant

Final PGW fiber processing was accomplished in the Screenroom (building 95) and Bleach Plant (building 15), both were located in the main mill area near the paper machines.  Here the pulp was screened through numerous very fine slotted screens where only the proper size fibers were accepted for making paper.  The rejected fibers were thickened and refined down to a more acceptable size before being screened again.  The final low brightness screened pulp was then pumped to the bleach plant where it was bleached using a two stage alkaline peroxide bleaching process that both brightened and improved the pulps’ strength properties.

PGW Fiber Department process details

Woodyard

●    Constructed in 1998

●    Encompassed 7 acres

●    Capacity to store up to 20,000 cords of logs

●    Wood was harvested primarily within a 150 mile radius of the mill

●    Approximately 125,000 cords of aspen are received each year

●    The yard is open Monday through Friday

●    Almost all wood is received by truck

●    Wood inventory is managed on a first-in-first-out (FIFO) system

●    Older wood is retrieved from one lot, while fresh wood is decked in the other

●    One operator on shift Monday through Friday

Woodroom

●    The log debarking and cutting system was installed in 1998 with start-up on December 20, 1998

●    The process was supplied by Andritz Kone wood

●    The woodroom is rated at 19 cords per hour

●    Pulp is supplied to the pressurized Groundwood plant

●    Two operators per shift

Log Loading Deck – capacity 15 cords

Deicing Chamber – capacity 7.5 cords

Compact Wave Feeder – new in 2006

Two Debarkers

– one on-line and one off-line

– rated at 20 logs per minute

Nicholson A5A - Manitowoc DeBarker

Slasher Deck – logs cut to 50″ lengths

Slasher Deck on Woodroom Log Cutter

Pulpmill

●    The pressurized groundwood pulpmill started up on February 15, 1990

●    Pulp is produced on four Tampella 7000 hp pressurized grinders

●    Each grinder is rated at 70 tons per day or 280 tons per day total

●    The log delivery system is supplied by Kone wood

 ●   Three operators per shift

Process…

●    100 cord peeled log storage bin of aspen

●    Kone wood log conveying and feed system

●    Four Tampella grinders, Model T1812, each driven by a 7000 hp motor and rated at 70 ton per day

–   35 psi grinder pressure

–   196 degrees F shower water temperature

–   230 degrees F discharge stock temperature

●    Pressurized disc thickener supplied by Hedemora

●    12 ton stock chest

●    Grinder stones supplied by Norton

      -Bolt through design is used

      -Stone life of approximately three years

●    Roberts stone grinding systems – pattern is 6 x 28 at a depth of 0.030

●    Specific energy Consumption (SEC) is controlled at 65  resulting in a unscreened pulp at:

      -180 Canadian Std. Freeness

      -59 to 60 brightness

      -3.17% pulmac shive count which includes refiner rejects

●    Tamsec distributed control system controls the Kone log feed system and the grinders

●    Bailey Infi 90 distributed control system is used to control the stock system

Pressurized Groundwood Screening

Process…

●    Six ton screen supply chest

●    Two primary course screens, P1, Bird 400 with 0.032 profile screen baskets

●    Four primary screens, P2, Hooper PSV 400 with 0.005 low profile wedge wire baskets

●    One secondary screen (S1) processing the rejects from the P1’s – Ahlstrom F2 with a 0.032”             profile screen, accepts are fed forward to the P2’s

●    One secondary screen (S2) processing the rejects from the P2’s

      -Tap 200 with a 0.004” slotted screen

      -Accepts are fed forward to the decker

●    Cleaners

      PRIMARY

      -First stage             64-5” celleco 350

      -Second stage        40-5” celleco 350

      -Third stage             16-5” celleco 350

      -Fourth stage          6-5” celleco 350

      -Fifth stage             1-5” celleco 300

      SECONDARY

      -First stage             22-celleco 270

      -Second stage        6-celleco 270

      -Third stage             2-celleco 270

●    Thickener

      -One Hedemora and one Dorr Oliver disc filter, feed consistency 0.5 to 0.8% discharge consistency

       Approximately 8%

      -5 ton storage chest

●    Screened reject system

      -DSM Screen for thickening

      -2 SL4S Thune screw presses

      -2 reject refiners, one on stand-by 20 HPDT

      -Screened reject rate approximately 40%

●    Screened unbleached pulp storage

      -100 ton stock storage chest

      – 60 ton stock storage chest

      -5 ton stock storage chest

      -12 ton bleach supply chest

●    Screen unbleached pulp properties

      -120-135 Canadian standard freeness

      -62 brightness

      -98.3 opacity

      -6.85 tensile

      -21.54 burst

      -0.57 pulmac

●    Post refining

      -Two 42” sprout twin flow refiners, 1000 HP and 1500 HP

      -Approximately 0.9 – 1.2 HPDT

●    One operator per shift

Groundwood Bleaching

●    The mill uses a two stage alkaline peroxide bleachery to brighten the groundwood pulp as well as develop pulp strength properties

●    Brightness target out of the 1^st stage is 68 and 2^nd stage is 83-84

●    Current bleaching and delivery systems provide two different brightness mechanical pulps for the paper machines

High Brightness System

Presses for bleach feed

●    One 2.6 meter Andritz twin wire press, 25% discharge consistency with 145 TPD

●    One 2.6 meter Andritz twin wire press, 32% discharge consistency with 135 TPD

Chemical addition system

●    There are two chemical feed systems

●    No. 1 chemical system for #3 press

●    No. 2 chemical system for #4 press

●    Peroxide, caustic and sodium silicate are injected into static mixers for each feed system along with chemical carrier water from the washer seal box

●    No. 1 and No. 2 chemical system adds the bleach liquor to the pulp at a double shafted pin mixer for each press

●    The chemical feed rate

      -Peroxide = 66 lbs./ton

      -Caustic = 65 lbs./ton

      -Silicate = 15 lbs./ton

●    Bleaching takes place in the bleach tower at 15 to 22% consistency

●    The temperature in the bleach tower ranges from 120 to 150 degrees F

●    The pH feeding the presses is 5.6 and in the tower during bleaching it is 9.5

●    Bleach tower

      -40 ton capacity

      -Retention time of 2-4 hours

●    The system has two Impco drum washers, each with four shower headers

●    The filtrate is used for tower dilution, washer feed dilution, chemical carrier water and wasting to the anaerobic treatment plant

●    The consisgtency feeding the washers is approximately 2.0% and the discharge is at 4.5%

Medium Brightness System

●    1st stage Alkaline peroxide bleaching takes place in the standpipe to the medium brightness high density tank

●    The chemical feed rate is:

      -Chelant      3 lbs./ton

      -Caustic      20 lbs./ton

      -Peroxide    12 lbs./ton

      The pulp consistency at the point of addition is 5.5%

●    The pH is 5.6 and the stock temperature at this point in the process varies from 135 to 150 degrees F

Bleached Pulp Storage

●    Total bleaching capacity

      -Medium bright system:       150 TPD

      -High bright system:                222 TPD

●    Storage

      -Medium bright system:       80 Tons

      -High bright system:               20 Tons

Bleached Pulp Properties

●    High Bright

      -CSF           78

      -Brightness 82-84

      -Opacity      94

      -Pulmac      0.13

      -Porosity     71.9

      -Bulk           2.5

      -tTensle       8.8

      -Scott bond            100

      -Burst         28.8

      -Tear           0.42

●    Medium bright

      -CSF           92

      -Brightness 68

      -Opacity      96

      -Pulmac      0.17

      -Porosity     99

      -Bulk           2.8

      -Tensle        8.0

      -Scott bond            77

      -Burst         25.3

      -Tear           0.39

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