Screening For Quality One mill’s experience

Screening For Quality One mill’s experience

Gary Parobeck Acrowood

gparobeck@acrowood.com

Appvion Roaring Spring, PA

From length screening to thickness screening.

It was a long haul but worth the trip.

Where is Roaring Spring PA

Mill Information

End product - carbonless and security papers.

Five Batch Digesters

Hardwood chips – 80% manufactured on site. 20% saw mill and chip mill supply.

The Screening System Before

Getting There

Testing – Testing – Testing

First investigations in 1999

Chips were sent to various suppliers for screening and overs treatment testing

The end product was sent on for independent cook trials

Close review by mill personnel

Testing

Testing

Results

Thickness screening offered the greatest savings and shortest payback

Cracking was shown to provide the mill the best result for their cooking process

A compromised was reached based on available funds and space

New Thickness Screens

Model 1730 Screw Conveyor

Model 1230 Side Fed Screw

Model 55144 DiamondRoll Thickness Screen

Model 35108 DiamondRoll Fines Screen

Note – the new system was designed to send the overs through a sizer and then recirculate this product back over the screening system.

Side View

Installation Photos – During Demo

Installation Photos

Bucket elevator at left feeds the screw conveyor which in turn feeds the infeed screw distributor.

Installation Photos

Installation Photos

#1 and #2 Accepts Chutes below DTS

DFS #2 Accepts bypass - above DFS fines and accepts - below

Installation Photos

Screen Performance

Design Capacity 100 green tons per hour

Performance Guarantee:

Infeed Chip Quality Chip Quality after Screening ≤10% Overthick (+8mm T) ≤2.0% Overthick (+8mm T) >10% and ≤15% Overthick ≤2.5% Overthick >15% Overthick ≤3.0% Overthick

≤1.5% Fines (-3mm RH) ≤0.5% Fines (-3mm RH) >1.5% and ≤2.5% Fines ≤0.6% Fines >2.5% Fines ≤0.8% Fines

Fines removed by DiamondRoll screen ≤0.5% Accepts loss (+2mm thickness)

Mill Classification

To the Digester – Old System

Over 1 ½” RH – 3 %

Over 8mm T: 11%

1 1/8” RH: 7%

7/8” RH:17%

5/8” RH: 27%

3/8” RH: 27%

Pins (3/16 RH): 7% Dust: 1%

Average Overs 6mm 4mm 2mm P&F Accepts

Summer '12 17.63 28.37 39.14 13.74 1.11 81.26

To the Digester New System

Their new stack was 10mm, 8mm, 6mm, 4mm, 2mm and a 3mm RH

After screen with out the sizer product they saw 96.9% Accepts

What did this mean to the mill

Yield improvement

liquor savings of 12,000 gallons per day.

Overall improvement in Digester operation

Cleaner, Safer Working Environment.

The Perfect Storm

The Perfect Storm

The Sizer product is returned to the infeed for re-screening

A fraction of the returned material contained chunks that were just over 8mm thick and as such were rejected as an over.

These pieces were small enough to also pass the Sizer grate again.

The Perfect Storm

As a result overthick built up to a level which over-ran the sizer capacity

The mill could bypass the Sizer and could continue to run

This of course meant no overs removal and everything but the fines went to the Digester

What to do?

Open up the DiamondRoll Thickness Screen to allow the larger pieces to pass

Or – Install a smaller grate in the Sizer thus reducing the size of the product.

Consequences

If the screen is opened up a higher percentage of overthick will make it to the Digester.

If the Sizer is closed down fines and pins will go up, ultimately greater fiber loss

Action Taken – Step One

The mill has resolved this issue (for now) by revising the screen IRO:

First half (infeed) 7.5mm IRO

Second half – 9.5mm IRO

Last two shafts – 13mm IRO.(Gate)

IRO Change

The IRO is changed by shims between the bearing housings.

IRO Change

Discharge end gate

Results

Accepts to the Digester dropped from 94% to 90% due to allowing more overthick.

But it did solve the problem of the overs build up and Sizer plugging

Action Taken Step Two

They worked with the Sizer Manufacturer to make grate changes

They were able to close the DiamondRoll thickness screen back down to a 7.5 MM IRO – All but the last two that Remain at a 13MM IRO

Automated gate at the discharge end of the thickness screen

Overview

They are happy with the system and it has shown great savings.

Currently accepts to the digester are back in 94% range.

Their target is to bring the accepts to the Digester up to 96% or better. They have calculated that for every 1% at the digester they save $000,000 per year.

Questions ?

Slicers & Crackers

Chip Slicers

Chip Slicer Basics

Gravity Feed

Bottom Discharge

Slices Chips to Thickness

Two Co-Rotating Elements: Anvil Rotor and Knife Ring

Typically 95% Reduction Efficiency

Must be protected from contaminants

The anvils push the chips into the knives, while centrifugal force holds them flat against the knife ring

Chip Slicer Function

123 rpm

369 rpm

Chip Slicer Drive

Single 150 HP, 1200 rpm motor

Belt drive to the gear train

Simple gear box design

Shear Pin Coupling

Wear Parts

There are six main wear part components: Anvils

Knives

Counter knives

Knife carriers

Wear plates

Gauge plates

Knife

Anvil

Knife Carrier

Wear Plate

Counter Knife

Gauge Plate

Gear Assembly

Chip Quality

95% Reduction Efficiency

10-15% Fines and Pin chip production

The thickness control is adjustable

Chip distribution into the slicer is adjustable

Summer & winter chip quality is essentially the same

Chip Slicer Efficiency - Evaluation on Southern Pine

Model 1511i Chip Slicer Configured for 10mm Thickness Control

Sample +10mm T +8mm T +6mm T +4mm T +2mm T +3mm RH Pan

Infeed 66.5% 16.6% 12.9% 3.8% 0.2% -- --

Infeed 69.4% 17.3% 10.7% 2.6% <0.1% -- --

Slicer Product 0.4% 31.7% 29.7% 22.9% 12.9% 1.9% 0.5%

Slicer Product 0.9% 36.1% 29.8% 20.7% 10.1% 1.8% 0.5%

Results*: 99.0% >10mm Overthick Reduction Efficiency 1.9% Pin Chip Generation (<2mm T, >3mm RH) 0.5% Fines Generation (<3mm RH)

Chip Quality

* Results based on the average of both Infeed and Slicer Product Samples

Chip Crackers

Reducers And Drivelines

Two reducers drive the rolls

Large universal joint drivelines connect the rolls and reducers

Swing arms support the rolls

Chip Cracker

• Overthick chips are compressed by two diamond tipped rolls which gently crack the chips

• Cracking allows proper liquor penetration in pulping

• Can adjust performance by changing pressure and/or gap between rolls

Cracker Rolls and Segments

• Square central box

• Machined attachment surfaces

• Integrated register lip that locates individual segments and transfers cracking forces from the segment to the central shaft

Cracker Performance

High overthick treatment efficiency –+95% fissuring effectiveness at 8mm chip thickness control.

Low pins and fines production

Typically <2.5% combined pins and fines (pins <7mm, >3mm RH, fines <3mm RH)

Cracker Pulping Response

More effective overthick treatment results in better pulping response

“Hardwood – Cracked overthick chips produced (3.4 to 3.8%) more absolute wood to pulp yield than rechipped overthick chips. Knots were (85% to 89%) less and Shives (22% to 26%) less with Cracked overthick chips compared to Rechipped overthick chips.” Econotech study in 2006

Cracker Pulping Response

More effective overthick treatment results in better pulping response

“Softwood – Cracked overthick chips produced (2.5 to 2.6%) more absolute wood to pulp yield than rechipped overthick chips. Knots were (71% to 86%) less and Shives (6% to 37%) less with Cracked overthick chips compared to Rechipped overthick chips.” Econotech study in 2006