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U . S. Department of Agriculture, Forest Service
57
FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsin
MADISON, WISCONSIN
FACTORS INFLUENCING THE VALU E
OF PULPWOOD
By SIDNEY D . WELLS
Engineer in Forest Products
Approved Copy Filed
11-20-17
FACTORS INFI7JENCING THE VALUE OF PULPWOO D
Observations on the Storage of pulpwood for the Manufactur e
of Sulphate Pull)
By Sidney D . Wells
Engineer in Forest Products, Forest Products laberatery ,
Madison, Wisconsi n
During the last year ; the writer was in elo _e, t;.•e .
with a sulphate pulp mill in the southern States and had oc- ;
casion to observe the relation of the condition of the pulp wood to the pulp output of the mill .
The matter carne-.%M
consequence of a marked decrease in the yield of pulp!
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digester at the beginning of summer .
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Investigation of the
amount of wood charged per digester, species and age of ther.s .trees used, amount and composition of the cooking liquor, an d
pressure and time of cooking together with the pressure curve s
on the recording gauge charts for each cook, showed that n o
noticeable change had been made . The source of the trouble
evidently must have been in the condition of the wood . It
happened that careful records had been made throughout th e
preceding year of the number of digesters blown, the amoun t
{ ~f wood used, and the tons. of pulp delivered .
On summarizing
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and studying these records, it was found that . through con- :
s iderab le periods t hz pulp delivered per digester was fairly
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constant but that the average for the different periods var d considerably . The cause" of this seemed to be that th e
time the wood was held in storage varied considerably fo r
different seasons of the year on account of the 'location o f
the mill and the policy of wood buying . The wood used was
the various species of pine growing in that locality and included ; Loblolly pine (Pinus taeda) 'locally known as loblolly ,
old field,
and spruce pine ; scrub pine (Pinus virginiana) ,
locally known as scru!) and, short shucks pine ; and' short lea f
pine (Pinus echinata), -locally known as short leaf ana bul l
pine . .
The mill was situated on tide water • and ' the pulp wood supply was obtained on the banks of three navigabl e
rivers and their estuaries and towed to the mill on lighters .
During the winter there were times when the . upper r-eaches o-f
these rivers were frozen and most 'of the wood was taken fro m
storage in the mill yard Or on tracts located nearby . During
the spring the cauntry ;-was so wet that most of the wood.
came from the higher and well drained tracts and s ince' they
usually were quite accessible the time the wood lay in
was comparatively short ..
piles "
During the summer and fall the.
more inaccessible tracts became accessible so that these
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tracts furnished a la ~ .ge portion off- tlire wood used at that
season . Some of the wood on these tracts had laid in pi le s
as long as three years . The quality of wood used was similarly dependent upon the condition of the min i s tug boat .
When the tug was in use, wood could be supplie-d from a con ... . i I I
siderab le distance , but when it was out ' of co
gas-a;
o line 1
depende .d on for towing tbe 1ig hrs and,
owing 1 -6 strong tide , light'e-rs : could only .be towed from
f, fir
nearby tracts rapidly enough to keep the- mill supplied .
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The following divisions of the year represent .
periods of variation in average yield* of pulp per dig-6st,ex.1,,-,
the source of wood beings-hown for each period :
Fall . Wood stored in piles in the woods or on . landing
two and three years .
Winter . Wood stored in mill yard or nearbPI:andings
one to two years .
rin
Wood from nearby landings stored o.e and two
years .
Early summer . Wood from more remote landings - store d
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two and three ye'ars .
.
Midsummer . Tug boat e-ng
i_gr
nearby landings stored one and two years
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One week summer) .
Tj-iunches unable to
bring
in wood ,
Wood from remote - corner of yard near rotten slabs .' Store d
and three ycara .
T,w3eers (summer .)
and three yepa
WoodI1
.., 'baC.'vni.th
.
remote landings, store d
. .-Ois ibly infected Tw- kit'id• . ,
arrrunt ing to between 25 an . ,511• Per Gwent',; : col led .
one day (early summer) .
-
, :f7 f
:mot
,eislg.ly Sut wood .
In the . accomp=any, ing table a !.e., given average amount s
of wood charged per ,d1gesster, air-dry
alp
delivered per d i
gester and air-dry•pulp deiive-red . .per . .eord of wood
for'f .•t
:1Zi
of the periods named,
Cords
Perio d
;Time
:stored
:years
Fal l
Winter
Sprin g
Early summe r
Mid, summe r
one week (summer )
Two weeks (summer)
:2 and 3
and 2
:1 and 2
:2 and 3
:1 and 2
:2 and 3
: 2 and
(sorted)
one day (early summer) : gree n
'wood
:charged
: per
:digester
: 6 .2 2
:
6 .29
:
6 .50
6 .41
:
;
6 .40
6 .20
:
6 .49
6 .75
:Tons air :
:dry pulp :Tons ai r
:deliver- :dry pulp
: ea per :per cord
:digester :of wood
.
.4 1
2 ,57 :
.4 6
2 .-9 0 ;
3 .11 :
.48
2 .72 ;
.42
2,0'7 :
.48
2 .61 ;
.4 2
.5 1
3 .31 :
3 62
,54
On analysis of the table it is evident that th e
more nearly green the wood is used the larger the charge o f
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wood per digester, the greater the yield of pulp per digeste r
and
t,tee
greater the yield , of pulp per t cord of wo .od'.Exam-
, :ot i on of the chips and the wood before chipping showed tha t
o
he older the wood the
lighter it was when brought , to a
bone-dry condition, even though it may have weighed more be -
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fore the moisture had been removed . In the old'wood als o
marry of the chips ha* ho les through them, cans e-d by insec t
attack, and the presence on a considertibe portion of the '
sticks. of fruiting bodies of vari'ousfungt showed that deca y
was already we 11 under, way, The loss in pulp production -was
evidently due to the loss of wood substance from the ravages '
of insects, wood-,destroying fungi
and
bacteria .
The loss i?i the case of wood attacked by insect s
is the result of the excavation of burrows . or galleries by
beetles, round and flat-headed borers, and timber :worms .
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While there are differences in the manner in which each bin d
of insect proceeds about its work OA destruction, a description of the habits of one species of round-headed be ers , th e
southern pine , Sawyer (Monohanmus titillator)
will ;c.rve t o
illustrate the made of attack . The female adult d .ge as
egg pit in the bark of cut or fallen timber, in which sh e
deposits, her eggs . In about five days these eggs hatch and
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the larvae . feeding upon the soft inner bark, work thei r
way through it, making it-e ular galleries next to the wood .
Within thiry days, in which time they have attained considerable growth, they commence scoring the surface of the
sapwood, and finally burrow tunnels Into the wood, packin g
the borings between the bark and wood . During these opera =
tions, the larva excavates a chamber in which to pupate ,
and remains in this chamber during its t ra ps it ien to the
adult stage .
It then emerges and the cycle is . completed .
The period for laying eggs extends from the firs t
of march to the middle of ()etcher .
:n order to avoid injury
from attack from these insects, wood felled in this peri.od ,
if not to be converted into pulp within a few weeks, shoul d
be barked at once to remove the food supply o the youn g
larvae . Wood cut at other seasons,
if not converter int o
pulp, should be barked or piled in open pilee se ' hat it ma y
become well dried before the borer season arrives ,
The habit of borers of burrowing between the bar k
and wood has been used to advantage by certain pulp ry a l is
for facilitating the removal of the bark, The cu .bee .luerit
tunneling of the wood, however, not
only en-aile a less o f
wood but means that the digester charge Bent a ; ns less woo d
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and the level of liquor in the digester is lowered, whic h
increases the difficulty of properly immersing the chip s
du7 r_p cooking, to e ecu :ce uniform pulp .
While the loss from insects was serious and ver y
e-- .dente ; the most serious loss was due to the destructio n
of the wood substance by fungus or mould, even, though not
an easily detected . The average observer does not recogniz e
decay in wood until the attack has so far advanced tha t
certain portions are punky or dozy . Often long before this
s'- age has been reached, however, a considerable portion o f
the wood substance has been consumed, and the bone-dr y
weight of the piece greatly 'reduced ,
Wood becomes infected with fungi from contact wit h
other infected wood, from contact with ground infected wit h
fungi, or from spores carried by the air from fruiting bodies
on decaying wood in the vicinity .
If the conditions ar e
favorable, the infection grows, spreading throughout the woo d
in the form of threadlike filaments called mycelia . The mycelium is a living plant and must have food, a suit ab le amoun t
of moiature, a favorable temperature, and
a
small supply o f
air ; its food is the wood substance which is broken down t o
forms readily assimilable by enzymes or ferments secrete d
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by the mycelium . Thus the fibers,. are penetrated and absorbed until only a skel4ton of their former self remains and
their value for pulp is greatly reduced .
From the standpoint of the pulpmaker, the harmful effects are rendered worse from the fact that many fung i
break down the cellulose constituents of the wood to a
greater extent than the lignin constituents, and thereby th e
yield of pulp is diminished more than the amount of constituents that must be dissolved by the cooking liquor .
Thi s
is probably the reason why the same quantity of cookin g
chemical per charge of old wood was required as for gree n
wood, even though with ■ the latter considerably more woo d
substance was in the charge .
The liability of wood to infection and attack b y
fungi is influenced by the amount of moisture present in the
wood and by the temperature . When in the air-dry state ,
such as is-•pes&stble in dry weather, when piled in open pile s
where the air has opportunity to circulate freely, wood wil l
:net- ordinarily be afflicted .
when piled closely,
In damp weather, however, and
in the shade, or surrounded with shrub-
bery, vines, etc,, so that the air cannot freely circulate ,
it retains
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its
moisture, and serious fungous
infection is
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almost certain .
The temperature at which fungi thrive bes t
varies with the species, but it may be said to be usually
between /5 and 90 degrees Fahrenheit . Although growth is
possible below the lower of these
limits, the lower the tem-
perature, the more it is retarded . The effect of temperature s
above the optimum is more marked, a rise of from 4 to 8 degrees causing death in some species ., Although air is necessary for the growth of the fungi, the amount is very smal l
and asufficient quantity is to be found almost anywhere tha t
pulpwood is liable to be placed . Wood immersed in water ,
with the cell cavities completely filled, will, however ,
resist decay indefinitely .
The external evidence, before wood has become punk y
or dozy, that it is infected is either the presence ' of myceli a
or mould on its surface or the formation of fruiting bodies .
The latter is another means by which fungi are propagated, The fruiting bodies give off spores in enormous
numbers, which are carried by the wind, and infect any woo d
on which they may lodge under favorable conditions, By th e
time fruiting bodies appear on wood it is thoroughly infecte d
in their vicinity,- -even though it may appear sound, and the
yield of pulp obt .cable has usually been seriously curtailed .
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A certain amount of the decay of pulpwood may b e
due to bacteria . Although their action in the destructio n
of wood is not well known at the present time, the method s
used in combating fungi have been found effective agains t
them also .
The susceptibility of wood to decay varies greatl y
with the species, as is known to every farmer, who will us e
black locust or red cedar fence posts whenever they are available .
The writer knows of no data showing the relativ e
resistance of various pulpwoods to decay when piled unde r
average conditions . ''he following table, however, give s
the average life of fence posts of various species used fo r
pulpwood,- as observed in a considerable number of trials by
-the U . . "S . Forest
Durability is dependent upon the
service .
Redwood
Chestnut
Longleaf pine
Douglas fir
Western yellow pine
Spruce
Years
1410
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8
7
6
:
Tamarack
Hemlock
Aspen or poplaZ
Lodgepole pine
Balsam fir_
Loblolly pine
Red Gum
Years
6
5
J J
4
4
3
5
lire'portion of sapwood to heartwood, as well as upon species ,
but since pulpwood, " as well as fence posts, is usually take n
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657
from smaller trees with a relatively large proportion o f
sapwood, the comparison
will
shed a certain amount of light
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on its relativerdurability .
By the 'life of fence posts is meant the time necessary for them to decay to the point where they will 'no longe r
support themselves and the wire . Ipng before this point is
reached they would be too seriously attac+'ked to be fit for
conversion to pulp .
Bearing in mind the causes of decay and deterioration in wood aS
otit 1ihed ; the Odnd.Itinb at the mil l
under cons .ideration aapear to be very
- bad . In the firs t
place the species of wood used have a very large proportio n
of sapwood and are extremely susceptible to decay . The
loe
cation on tide water in the southern States means that th e
conditions= of moisture and tempera-twee are such that insec t
and fungus attack will be extreme
active .
Furthermore ,
the local custom of storing the wood closely piled near the
water is edge often on decaying litter, shaded 'by trees and
overrun with shrubbery, vines, and weeds, .contributes greatly
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t-o its de-ow . .
=The rei dy for this situ-ation would seem to
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govern the cutting of the wood by t.he•'= daily c~:eia►ics Qf the
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mill and only accumulate enough reserve to keep the mil l
running over periods when the lighters can not be operated ,
or when, owing to u:ifavorab le weather, planting, harvesting ,
br other reasons, the supply of labor for woods operation s
is limited .
The woods
operations should be so governe d
that all wood can be converted to pulp as nearly freshly
cut as possible and none should be allowed to stand over
Gix
months . Whatever reserve is necessary for the winte r
6hould be cut and moved after the middle of October, an d
all
of this reserve should. be converted to pulp before th e
first of march . By following this procedure, the attack o f
insects on the wood is greatly reduced, since between Octobe r
and march very few eggs are laid .
i,t
Moreover, the attac k
from fungi is reduced to a minimum, since during these month s
the temperature is such that their growth is greatly retarded ,
The gain by following this procedure at a mil l
' that has been J .n the habit of using old wood is enormous ,
not so much in the saving of wood as in the increased ca pacity with the same overhead, labor, and consumption o f
other raw materials . The gain at the mill where these dat a
were obtained is a concrete example .
The production of the mill was governed by th e
capacity of the diffuser department to wash the pulp, the
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recovery and causticizing departments to convert the blac k
liquor into cooking liquor, and the boiler room to supply
steam . The other departments were of greater capacity tha n
that at which they were usually called upon to operate .
The recovery and eaueticising rooms had capacity sufficien t
to provide cooking liquor fer ten digester charges per da y
and this number would tax the diffuser room and boiler room
to their utmost, It was therefore apparent that the onl y
method of increasing the capacity of the mill without ne w
equipment was increasing the yield of pulp per digeste r
without increasing the liquor charge, difficulty in washing ,
or steam consumption ,
The gain in production by using green wood ove r
that obtained in using old wood showed how this could b e
accomplished to a surprising degree . In the early summe r
the average charge per digester using wood stored two an d
three years was 6,41 cords, and the average yield of pulp
per digester was 2,72 tons air-dry or ,42 tons a cold, o n
the day using green wood, also in early summer, the averag e
charge per digester was 6 .75 cords of wood, and the averag e
yield of pulp per digester was 3 .62 tons air dry or .54 tons
per cord . The charge of wood increased one-third of a cord ,
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owing to the more compact manher in which green chips pac k
in comparison with chips from old wood . The amount o f
liquor and steam us ::d per cook was the same in both cs.s es .
The yield of pulp obtained from green wood showed an increase, however, over that obtained from old wood, of . 9
of at on or 33 percent, whereas the time necessary to was h
the cooks from green instead of old wood showed no notice -
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able increase . The daily production, when making tell . cooks
using ,old wood, was • 27,2 tons air-dry pulp ; the pro Fduet ion
obtained from the same number of cools by changing to gz
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et , :,
wood was 36 .2 tons, or an increase of nine toms . This garzl
of nine tons was .obtaired without any increase in the dail y
cost of production more than that of the4;dditlonal'3 .3J
cords of wood, with ~ .he possible exception of half a dog dn ,
laborers added to the force to remove bark, and two -or thre e
men to kandle the increased number of laps - of pulp . The
pulp at that time was selling in the, ne-ighborhood of $1010
a ton, to that the daily increase in profit to the mill by
changing to green wood was between $800 and $900 . Whil e
price received for pulp at that time may be eor <c ?r•ed ab ton would
normal, the increased profit when selling at $50
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be between $400 and $450 a day - surely worth' cons idering,,
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The use of green wood would greatly increase the cost o f
barking . the wood by hand, but this difficulty could be,over1
come by the investment of between $15,000 and $20,000 i n
barking drums, and equipment which would reduce the cost o f
barking the wood to below 25 cents a cord, much below wha t
it is costing at present .
The deterioration of the pulpwood mentioned i n
this article undoubtedly is extreme on account of the specie s
used, climate, location of the mill, and the prevailin g
method of purchasing and handling the wood . It seem probable ,
however, that these conditions prevail to
a
greater or les s
extent in many mills, and proper attention to this, the firs t
step in the manufacture of pulp, will yield ample returns t o
even the best regulated pulp mills .
For illustrations and more complete discussion of los s
by decay see "Timber storage Conditions in the Eastern an d
ilthern states with Reference to Decay probi.ems," by C . J.
Humphrey, Bulletin No . 510, U, S. Dept . of Agriculture ,
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