Vol. 13 No. 2 1991

- NEW ZEALAND

PULP CHIP QUALITY FROM IN-WOODS CHIPPERSCOUPLED WITH CHAIN FLAIL DELIMBERS-DEBARKERS:

DOES IT MATCH CONVENTIONAL WOODYARD QUALITY?

W. F. Watson, Professor, Department of Forestry, Mississippi State University, U.S.A.A. A. Twaddle, Scientist, Harvest Planning, Forest Research Institute

B. J. Stokes, Research Engineer, USDA Forest Service, Auburn, Alabama, U.S.A.

ABSTRACT

Chain flail delimber-debarkers have gained adegree of acceptance in the Southern USA,especially for processing thinnings from pineplantations. TIzis Technical Release com-pares the quality of chips produced by in-woods chippers teamed with chain flaildelimber-debarkers, with chips produced inconventional large-scale woodyards, to g&e aguideline as to what may occur with similarprocessing of radiata pine in New ZealandPine chips from the chain flail and in-woodsdisc chipper compared favourably with pinechips produced ffom drum debarker and discchippers in woodyards. These in-woods chipswere similar in bark content and in heproduction of chips of an acceptable size.The flails, however, were less effective indebarking hardwood stems than were thedrums in the woodyards.

INTRODUCTION

Chain flails teamed with in-wood chippershave become a significant source of chipsfor pulp mills, particularly in the Southeastregion of the U.S.A. Currently, a total of90 chain flail units have been manufacturedby the three commercial firms supplyingthese units - Manitowoc, Peterson Pacificand ForestPRO (Twaddle et al, 1989) -with over 50 of these operating in theSouth. Other firms have recently.begun tooffer brands of flails (for example, Chipar-vestor has just introduced an integral flail-chipper unit). Each flail-chipper pair iscapable of producing 60,000 tonnes of chips

annually; thus, the 75 units in place inNorth America will probably produceabout 4.5 million tonnes of chips for use inthe manufacture of pulp.

The typical chain flail operation in theSouth consists of :

(1) Feller-btmchers for felling the trees

(2) Grapple skidders which move thetrees with the tops intact to a process-ing area

(3) A knuckleboom loader .to feed thetrees into the flail

(4) A chain flail delimber-debarkerwhich removes the limbs and the bark

(5) An in-woods chipper which receivesthe delimbed and debarked stemsand converts the stems to chips, and

(6) Haul units with chip vans to transportthe chips to the pulp mill

The total cost of one of these in-woodsoperations is 1 to 1.5 million dollars (U.S.)when all of the support equipment is in-cluded.

The commercially available chain flailshave two drums mounted either horizon-tally or vertically. The chains are attachedto these drums, and the drums turn at arate of about 500 r-pm when in operation.

The flails were designed to carry 36-39chains on each drum with the chains beingarranged in six rows along the drums. MostSouthern contractors, however, are nowdoubling the numbers of chains to improvedebarking quality. The chains currentlyused were designed for skidder tyres andhave an average life of 1,300 tonnes in asingle configuration to 2,500 tonnes in ad o u b l e c h a i n c o n f i g u r a t i o n w h e ndelimbing-debarking pine (Car;, et al,1990).

The in-woods chippers preferred in theSouth are Trelan 23 and Chiparvestor 23models. These have the capacity to handlestems up to 58 cm in diameter. Both aredisc chippers and have 400 to 550 kilowattdiesel-powered plants. The chippers wereequipped with separators in all of the trialsreported in this Technical Release. Most ofthe material rejected by the chipperseparator consists of slivers of wood, up to10 cm long.

since the first commercial flail was intro-duced in the Southern U.S.A. in December1986. The monitoring of the operations:including utilisation and wood recoverystudies, has been reported elsewhere(Stokes and Watson, 1990).

These, and other data (Stokes and Wat-son, 1989; Carte et al, 1989) are presentedhere to give the New Zealand forest in-dustry some guidelines as to what may beexpected from similar in-woods processingof radiata pine, and how the output fromthese systems compares to conventionaldrum debarking and disc chipping at awood yard.

ACMVOWLEDGEMENTS

The authors wish to thank Price IndustriesMonticello, Arkansas, for their support i;providing a chip classifier for use in thisstudy. The assistance of the many loggiigcontractors is also appreciated The USAforestry jirms listed below gave enormoussupport in the various in-woods phases of

research : Champion International, Scotter Company, Stone Container, Union

Westvaco, and Weyerhauser.

Figure I - Large fied chippers operating inconventional woodyards, such as this295cm-12 knife unit, are more like& to be

well maintained than mobile in-woodschippers

The risers of the chips are usually moreconcerned with the quality of those chipsproduced outside the mill gates, as com-pared to the quali ty of those chipsproduced in the more controlled environ-ments of the woodyards. To assess thequality of the woods-produced chips in theSouthern U.S.A., the Forestry Departmentat Mississippi State University and theForest Engineering Project at the USDAForest Service at Auburn, Alabama, haveco-operated in monitoring these operations

the past four years chip samples havecollected from the operations of

hip contractors who utilised ‘1chain flails. Over 400 chip samples havebeen collected in seven different Statesand six different species are included in thiStudies (see Tables 1, 2, and 3 for a sum-mar-y of the sources of these data).

The chips were collected at the end of theblower sgout. A thick-walled PVC pipewith a 90 elbow glued to the end was usedto catch the chips as they were being blowninto a chip van. The chip samples were col-lected in a bucket and then- transferred toplastic bags to be transported back to alaboratory for analysis.

Classifiers available for analysing the chihave varied over the life of the study. d

se

chip samples collected prior to 1990 wereclassified on a Universal vibrator screen.During most of this period, classification

w

-4-

was carried out on length of chips only. Thechip samples collected in 1990 have beenanalysed with the use of a Price Chip Clas-sifier provided by Price Industries of Mon-ticello, Arkansas. The use of the Price,which classifies primarily by thickness, al-lowed a direct comparison of flaildelimbed-debarked in-woods chips with thechips gathered and analysed by Twaddle(1990) in his South-wide woodyard surveyas this latter study also used a Price clas-sifier. Direct comparisons of chip dimen-sions can only be made using identical clas-sifiers with the same sample sizes andscreen retention times.

The Price Classifier defines pin chips asthose less than Zrnm thick but not able topass through a Smm-round hole. Fines areable to pass through.

Pins and fines are both generally un-desirable in the pulping process. Pins canplug digestor screens and refiner plateswhile fines, because of their small size, canrestrict liquor circulation and return littleuseful pulp fibre.

Oversize chips also cause considerableproblems in the pulping process, and al-most always are screened from the chipflow and rechipped or sliced._^

Figure 2 - In-woods chippers processingchain flailed pine are capable of producing ahigh quality pulp chip matching those from a

conventional woodyard.

ANALYSIS

Bark Content

The results of the bark content of thesamples taken prior to 1990 (Table 1) showevidence of the work that was ongoing inthe refinement of operational strategies in

debarking with flails. The first three studiesreported in Table 1 were experimentaloperations, and bark contents ranged ashigh as 3.4%. By 1989 when the chain tri-als were conducted (Table 2), the contrac-tors and equipment manufacturers haddeveloped strategies for using the flailswhich. would maintain the bark content atless than 1% for the pine stems and at 3%for the soft hardwood species. In controltests where no flails were used, the barkcontent of chips produced from whole-treeloblolly pine was 10% and chips producedfrom whole-tree soft hardwoods was 12%.Thus, the flails are now reducing the barkcontent of the chips by 90% in the loblollypine and 70% in the soft hardwoods.

The bark contents observed in the chainwear tests (Table 2) can be considered asrepresentative of debarking that is cur-rently attainable for operations using chainflails for debarking. Comparing these ob-servations to those obtained by woodyardsurvey, we find that the debarkingcapability of the flails is equivalent towoodyard drum debarking for pine stems,but the flails are not as effective as drumsin debarking hardwoods.

Analyses of the bark content in the earlystudies (Table 1) showed that debarkingwith the chain flails was most difficult inthe winter months. A one-way analysis ofvariance of the pine bark content datashowed that month of year was significantin accounting for differences (Fp,156 =12.65). However,onIy January (winter inthe U.S.A.) was significantly different fromthe remaining months. The contractorsusing the flails now double the numbers ofchains and are able to overcome this dif-ficulty.

When chip samples were taken during autilisation study, the average diameter atbreast height (DBH) of the stems beingprocessed was recorded. These data wereavailable for a total of 52 loblolly pinesamples that were collected prior to 1989.The bark content in these samples was sig-nificantly related to the diameter of thestems being processed, with chip bark con-tent increasing as stem diameter decreased.This shows the flails are not as efficient indelimbing when several small stems are fedat once into the unit.

Chip Size

The samples collected in 1990 (Table 3)were analysed using a Price Classifier andtherefore could be compared directly withthe information gathered by Twaddle(1990) in his Southern woodyard survey asidentical classification techniques wereused. A possible confounding problem wasthat these latter data were collected in theauturrm and the flail data were collected inthe spring, so additional matching measure-ments of the flail were made in the autumnof 1990.

All of the in-woods chippers working withpine in the 1990 spring and autumn studieswere set up to produce a 22nu-nlong chip.Thus, all woodyards sampled which weremanufacturing pine chips and whose chip-pers were set up to produce 22mm chipswere selected to compare with the in-woods chippers. Altogether 15 chippers inconventional pulpmill woodyards wereidentified for this comparison.

Chip analyses for the three groups are com-

pared in Table 4. Note that the percent-ages of pins and fines were significantlylower for the in-woods chippers. Thereason for this could be related to thefreshness of the wood. The in-woods chip-pers were producing a significantly higherpercentage of overs. While chip thicknessincreases with increasing moisture content(Hartler, 1962), the higher overs produc-tion is probably also related to the inex-perience of the contractors and theirlimited knowledge of chipper maintenancecompared to their woodyard counterparts.

CONCLUSIONS

Southern U.S.A. experience is that chainflail delimber-debarkers teamed with in-woods chippers can produce pine chipscomparable in quality to those produced inthe woodyards, although inexperiencedcontractors can produce poor quality chips.The bark content of in-woods pine chipscurrently being produced with flail debark-ing is similar to the bark content of chipsfrom the survey of wood yards (0.6% barkfor in-woods chips as compared to 0.8%bark for woodyard chips). Although the

Table 4 - Comparison of dimensions of chips produced from pine stems at a woodyard with chipsproduced with jlail delimbers-debarkers and in-woods chippers

Woodyard chips(Autumn)

In-woods chips(Spring)

In-woods chippers(Autumn)

F Significance

Number of samples 45 51 95

Over.3 (%) 19.2 25.5 29.0 9.97 0.05

Accepts (%) 75.3 73.0 68.0 665 NS

Pins (%I 3.7 1.7 1.8 40.50 0.0 1

Fines (%) 1.8 0.8 1.1 28.38 0.01

Definitions:

Overs retained on an 8 mm slotaccepts retained on 2 mm slot, pass an 8 mm slotpins pass 2 mm slot, retain on a 5 mm round holefines pass 2 mm slot, pass 5 mm round hole

Figures 3 and 4 - A @picai Southern in-woods pulp chip operation consists of a loader feeding theflail where the stems pass straight through into a chipper. Chips are blown into the rear of the

trailer. In thi.s example tile clzairz flail is a Matritowoc brand, und tile chipper is a Trelan.

flails were less effective in debarking sys-tems in the winter months, the debarkingquality has been improved in current usageby doubling the chains. The in-woods chipscontained a s-jgnificantly lower percentageof pins and hnes than were found in thewoodyard chips, bu! the percentage ofovers was significantly higher in the in-woods chips.

The chain flail units did not debarkhardwoods as well as the drum debarkersin the woodyards. The average bark con-tent of the chain flail debarked hardwoodchips was a full percentage higher for thein-woods chips (3.1%) than for the woodyard chips (1.9%).

These data on southern pine would indi-cate that providing radiata pine will delimbsatisfactorily in chain flails, and if chip con-tractors attend to chipper maintenance,high quality pulp chip should be able to bemanufactured in the forest in NewZealand.

REFERENCES

Twaddle, A.A., Stokes, B.J. and W.F. Wat-son (1989) : “Chain Flail Processing : ANew Look at an Old Idea”, LIRA Techni-cal Release, Vol. 11 No. 2.

Carte, C., Watson, W.F. and B.J. Stokes(1990) : “The Effects of In-Woods FlailDebarking on Debarking Chain Wear”.Proceedings of Annual Council on ForestEngineering Meeting, Kill Devil Hills,August 12-16 (In Press).

Stokes, B.J. and W.F. Watson (1990) :“Wood Recovery with In-Woods Flailingand Chipping”. Proceedings 1990 TAPPIPulping Conference (In Press).

Stokes B.J. and W.F. Watson (1989) : FieldEvaluation of In-Woods Flails in theSouthern United States”. Proceedings ofIEA/BA Task VI, Activity 2 Workshop 30-31 May, New Orleans (Eds. Hudson JiTwaddle) Aberdeen University ForestryResearch Paper 1989 : 3.

Carte C., Watson W.F. and B.J. Stokes(1989) : Factors Impacting Chip Qualit)from Flail Debarked Stems”. ASAE PaperNo. 89-7S93, 12-15 December.

Twaddle, A.A. (1990) : “Roundwood Chip-ping facilities in the Southern U.S. : “A Sur-vey of Equipment and Chip Quality”. Un-published Master’s Thesis, MississippiState University.

Hartler, N. (1962) : “The Effect of SpoutAngle as Studied on an ExperimentalChipper”. Svensk Papperstidning, Vol. 65w

This Techicol Release is the work of the authors andis not the result of LIRA project work. LIRA pub-lishes it in the interests of wider dissehlation ofknowledge in the &dust?. LIR.4 takes no respon-sibility for tile accurucy of jigures nor does it neces-san’ly support or disugree with the opinions and con-clusiolis shown.

fo r fu r ther mformclfmn contc~ctN 2 LOGGING INDUSTRY RESEARCH ASSOC INC