Briquetting of wood waste


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Briquetting of wood waste
Physical Description:
Forest Products Laboratory (U.S.)
University of Wisconsin
U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory ( Madison, Wis )
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aleph - 29615885
oclc - 288960924
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Full Text

U, S. *v a VN OF I LIR;,


Ievised May 1945


No. I S42

Madison, Wisconsin
In Coopeation with the Univ eity of Wimecnst

S 4 -


A Survey of Wood Waste Briquetting and the
Conditions :;cessary for Successful
Manufacture and Sale of Briquets

The utilization of sawdust, shavings, spent tanbark, chemical bark, and chips
in the manufacture of fuel in the form of briquets has been successfully car-
ried on in several European countries for many years. During the past 30 to
40 years wood briquetting operations have been conducted more or less sporad-
ically in this country, but only recently have they achieved any considerable
degree of financial success.

Wood waste briquets c-.n be profitably made in America only under exceptionally
favorable conditions of mn-ufacture and sale. Other forms of fuel are rela-
tively cheap in most parts of the United States, and wood briquets cannot
usually be cold in competition with them on the basis of heat units delivered
per dollar of cost.

The requisites for success in wood waste briquetting operations are (1) a
large and continuous supply of suitable raw mater als, (2) low production
costs, and (3) a ready- sale for the finished product at fair prices. On ac-
count of the bulkiness and low value of the materials used in r.*irng briquets
the stock must be obtained locally-; for the same reasons, the principal
market for the briquets must be found in the general region of production.
Because of special properties some briquets will, however, find sale in
distant localities, especially in the larger cities.

Manufacturing Processes

In general, the wood waste briquet is made by compressing previously dried
sawdust, shavings, or shredded wood in a heavy press. The hardness of the
briquet depends upon the process used and upon the pressure applied.

In systems which utilize the refuse of resinous woods, the resinous material
in the wood waste serves as a binder to hold the briquet together, and a very
heavy pressure produces a very firm and hard briquet. In other systems, some
sort of binder is mixed in before compressing, this binder often being coal-
tar pitch, petroleum refuse, or waste liquors resulting from the manufacture
of wood pulp by the sulfite process. Shill other systems rely entirely upon
mechanical binders; one uses a wire tie which encircles the briquet; another
uses a tarred jut,' cort. which runs throughout the length of the briquet.
Briquetting of wood waste using added binders, rope, or metal ties to hold
the briquet together is chiefly of historical interest in this country, since
briquotting methods employingg such binders have not been used here for many
years. The latest t:y of equipment for wood waste briquctting and the method
exclusively employed in current commercial briquetting operations in this

R.pcrt No. R1'L--


country dIevelop prevures so great that, in the formation of tnhe briquet, the
elasticity of the wood is destr-..'ed and.1 no added binder is c-q. hired to g
stablbe )r o duct.

he relm'nar Or"ying f the sawdust or other wood waste for bri .etig is
a nece".ar, .. ep, s:nce it is practically imlnossible to make wet wood stock
cohere oro perly,. :e problem of dryrin has been a stumbling block of serious
nroportions in nore t'an one installation. >i- actual drying of small &antti-
:es 'f' w- ae s simple matter, but t:ie design of mechanism or he
ctinnou ri of large quantities has rresexted difficulties. I, former
y-' rs, ether live or exhaust steam was used almost exclu ;ively in the drying
ooerationw;, the material rassing over oteam-heatc 'i T)ate" or floors or 'eIng
carrie along in a stream of air which has been heated by forcing it th ough
"team-heated coils of riipe. In present-day briquetting operations, "..'*at for
I.... : s lar-gely supplied by- flue ?.-"-s from sawmill and factory stacks. If
a binder i" to be emr'loyed in .'..:k." t.he briquet, it is usually mixed in
mechanically just before the final heatin.-. takes place, the mixture beir.n, fed
into t'. machine through steam-heated hoppers and pipes.

Althour 7he varJous preo;es for makin; briquets differ greatly in their de-
tails of cosrucbion, most of them work on the cylin .er and plunger prin-
ciple, th (:) being driven by miearns of crank and connecting rod or '
some to;le.joint rnystem of levers so designed hat it is capable of exerti.t presura at the end of the stroke. Practically all of the pres-es are
automa ixllr fed, the only attention required beinr4 to provide a supply of
raw materials and to rc-ive the finished briquet. In systems in which
binders ro-.c: as pitch are used, and in those in which the resins of thu. wood
nerv, %c*r binders, it is necessary to provide a lor. cooling trough for t'he
finisho' briquoto. -nese troughs are sometimes as mruch as 150 feet in length.
In syst.:.i, using :mccrnical binders cooling troughs arc un,,ecessary.,

Several :, .",pean briquetting methods employ some kind of binder mixed with
th.- wood waete or rely upon the resinu.u- material in the wood to hold t'.,
briqu.-to toet er. In this country-r, cohesion of particles in briquets is ob-
tained by !oyi rresrures sufficiently hi : to dCstr,,C" the elastic ty
of the wood, '"h result s in high stability of the fin]r'.d -)roduct. Cur-
rently, all c mnercial ,ood waste bri "ts, as far as is 'nown., are made by
one t-pe o 'c in.

he r''w, :etoril u", i:n this nmc'inc ir c'hiefl." savin's from dry lumber.
It r! f-th' driC, u-r.all; y flue gases, to 6 percent moisture content.
- ..~ r c'i grod to ;'iform *i zu 'inS u'i in a-nncirarce to pro-c okri
oatmeal, and in tha con-'ition is d livc" I to rve mold. Pressure exerted on
th.e maerial in th -old r1. between 1!5,00 pound" u'd 0O,OCO pounds per
square inch. -he o ini Iin, ':riquet i, 12 i1hu iand 4 11 in ii.etr
and weigs 8 punds ru:uo <\ 'it;- of the :riquet is ab-out 1.3. -hese
'riquets :iil .lou>utt 1 8,250 British ;.er-al tunits rcr pound of m 21terial.
- 'o '-'t7 of the briquetting m:vc:.i:<.. is ab;;ut 11 tons o;r cwa'a of 24 )'o5rs.

i:rt 1o- . 1

Of the 55 or more machines operating in the United States, all but two are
located in the Pacific Coast states, Idaho, and northwestern Montana. The
annual production is about 200,000 tons. The price to the consumer ranges from
S7.50 to '9.00 per ton, delivered, at points of manufacture.

A methodof briquetting in which sawdust only is used as raw material has been
devised.-L By this method, green sawdust is preheated in a retort to an end
temperature of 2750 C. (527 F.) which requires about 40 minutes. Heating is
discontinued just before full distillation of the wood begins. In the pre-
heatinr, the wood loses its elasticity and can be readily compressed into
stable briquets under a pressure of 6,500 pounds per square inch. The pre-
heated sawdust is allowed to cool to 1000 C. (212* F.) at which temperature
it is ready for briquetting. The density of the finished briquet is about
0.90. The loss in weight in prehes-;ing is about 35 percent of the original
weight of the sawdust used, and consists largely of water. The British
thermal unit yield of the briquets is about 10,400 per pound.

A method of producing charcoal from pine sawdust has recently been announced.-
The charcoal obtained is reported to be highly dense, with a specific gravity
of 0.51.

The briquetting of wood waste is generally considered profitable only with
large-scale operations. Small-scale production of briquets has rarely, if
ever, ) en successful. A possible reason for lack of success in briquetting
in a small way is the lack of suitable equipment for such operations. If
some feasible method could be devised, it would result in the salvaging of
considerable amounts of sawdust and shavings for local fuel use. It could
also make possible the production of special briquets, such as those impreg-
nated wvrith chemicals to yield colored flames, for which higher prices are
received. A type of briquet that produces colored flames is quite common
on the market during the Christmas season.

Fuel Value and Burning Qualities of Briquets

There seems to be a wide range of opinion concernin--- the fuel value and burn-
ing qualities of wood waste briquets. Some ardent enthusiasts claim all the
virtues for them and others, equally sincere, declare them unsuitable under
many conditions. Certain German-made briquets are reported as unsuited for
use in the tight porcelain stoves, so common in that country, on account of
rapid combustion. Rapidity of combustion is also claimed to be a distinct
disadvantage in places There it is desireJ to bank a fire over night.

-Basore, C. A. "';- Briquettes from Southern Pine Sawdust," Bul. :o. 1,
Sineeriu7 Experimernt Station, Alabama Polytechnic Institute, Auburn,
-Basore, C. A. "The Production of Lump Charcoal from Pine Sawdust V.ithout a
Binder," Bul. 'No. 14, Engineering Experiment Station, Alabama Polytechnic
Inst-itute, Auburn, Ala.

Report r,. RPI 2


It seems reasonable to suppose that the more loosely formed briquets v:ill
burn more rapidly than those formed under greater pressure or with firmer
binding material; and it is believed that it miy be possible to regulate the
speed of combustion to a certain extent by varying the conditions under which
the bri~u.?ts are made. It is pointed out by one of the manufacturers of
briquebtin- machinery that briquets made by his machine can be used for kin-
dli-.- wood by brekrLn,- the binder. This bears out the deduction just drawn,
since kindling must make a quick, hot fire to be satisfactory.

The fact remains, however, that notwithstandin- the failure of a number of
both foreign and domestic wood briquetting plants, there are certain condi-
tions under which the industry appears to flourish, and it should not be
difficult to find out, in a general way, what those conditions are.

Before analyzing outside conditions which may have a bearing uron the success
or failure of a briquetting plant it will be well to look at the briquet it-
self, and study its fuel value,

It seems rather peculiar that it has been found necessary heretofore to lay
especial emphasis on the fuel value of briquets. It is quite logical to
suppose that since the bricuet is merely wood, 1 pound of briquet should have
as many heat units stored in it as 1 pound of the same species of wood, mois-
ture conditions being equal. As a matter of fact, data at hand uphold this
view entirely. Another fact concernr>- wood, which is borne out by tests
made by the Forest Products Laboratory, is that, disregi-rdinr the heat value
of the resins which appear abundantly in various species, a pound of absolutely
dry wood has a very nearly constant fuel value (heat units) irrespective of

It is probably true, therefore, that thoroughly dry wood briquets will also
have a nearly constant fuel value, weight for weight, regardless of the kind
of wood used. Well-seasoned wood has a fuel value of about ,000O British
thermal units per pound. Briquets of the same moisture content probably have
the same fuel value as wood. If the wood contains resins the same result may
be expected on account of the high heat value of the resins.

In compari.i- briquets with cordwood or stove wood it must be remembered that
the briquet is usually much dryer, therefore will generate more heat per
pound of mate-ial than wood.

Conditions Necessary for Successful Manufacture and Sale

Certain coQi;tions are needed for the successful sale of briquets because of
their heatir-. and other properties.

In the first place, the fuel value -r nound_ is much less for wood than for
coal, so that to obtain the same amount of heat much more wood (dry) than coal
must be used. If the wood is green instead of dry, still more must be used,
because all the water in the wood is useless from a hcat-v,- standpoint, and
some of the heat of the wood is used up in convertinr.- this water to steam during

Report No. R-42'

This means that, if one is buying primarily on a heat unit basis, he can
afford to pay much more for coal than for wood or wjood briquets -- usually
from one and a half to two times as much for coal as for wood when both are
dry. If the wood is green, it is quite possible that the coal will have three
or four times the effective heating value of the wood.

If the kindling, appearance, cleanliness, burning qualities, and other special
properties of the briquet are of value, as in domestic use, the price obtain-
altle will be proportionately higher.

In the second place, the cost of manufacturing briquets is considerable, con-
servative estimates placing the figure at not less than $5 or `6 a ton.

In the third race, the bulkiness of the fuel prevents its general shipment
for long dis-,cuces. This applies to the finished briquet and to the raw
materials a]ik4e.

It is believed that the ultimate consumer will have to pay at least $7.50 a
ton for the -que ts to assure profitable mnnufacturej and on that basis it
can rditly .t-unined unde- nornaJ co2. itions what the minimum price
of coaj. mus'm to alloww c.crmper ition, .l-, for convenience; that the coal
under oonsiko':atic.:1 is bituminous, posS:sr," one and one-half times the heat
value of the '.riqu,-',. That ccal must sell for at least ,ll.25 a ton before
the briquet at $7,5') can offer the same heat value for the same price. V.'ood
briquets are currently selling at ':' to $15 per ton to the consumer in
Pacific Coast states.

The main market for briquets will probably be for domestic uset so that the
cleanliness and easy kindling qualities of the briquet will be an asset, and
it might be able to compete with coal at a somewhat lower rrice, the house-
wife being willing to pay a little more for the same he3t value on account of
other desirable properties. The small percentage of ash and the absolute
absence of clinkers are great advantages in favor of briquets or wood over
coal. The small volume of smoke is also pointed out as an advantage.

In competing with cordwood the briquet has certain advantages, such as less
labor in pre-rAring for the fire, less moisture and therefore more wood per
pound, and less need for kindling wood.

In conclusion, it may be stated that the best chances for the success of the
wood waste or sawdust briquet are in those regions where suitable wood waste
is abundant and coal is expensive. The region fulfilling those conditions
best in this country is the Pacific Coast; and it is a significant fact that
companies that have attempted to establish the industry in America- are
chiefly in that part of the country.

Report. ":o. R,'I'--


RE ZR-_U 3

"Wood Waste Makes Fuel Briquettes." Published in the American Lumberman,
Chicaso,- Ill., Tiy 15, 1943.

" "ood '":r;te Marie. Published in American Forests, "Washington, D. C.,
S'. tnembor 1940.

"Fir Sawdust Briquettes." Published in The Timberman, Portland, Oreg.,
Oct. 1>3,.

"WVood rriquuttes." Fubli:hed in the W'st Coast Lumberman, Seattle, 7'.ash.,
Oct. 1931.

"Profitable Utilization of Wood Waste," by H. A. Porter. Published in
The Timberman, Portland, Oreg., June 1927.

"New Fuil Developed from Wood wastee : Carbon Briquette Made from Mill Waste
Looks Promising." Published in The Timbcrman, Portland, Oreg., Feb. 1923.

"Wood Briquetting Machine," by R. B. Coleman. Published in the West
Coast Lumberman, Seattle, Wash., May 1, 1920.

"Briquettes," by A. L. Stillman. Published by the Chemical Publishing
Comp':,y, E,.-:ton, Pa., 1923.

Report "o. R.,12

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