Forest Products Laboratory (U.S.)

Reineke, L. H. (Lester Henry), 1900-

Undetermined

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•BRIQUETS FROM WOOD WASTE'ByL . H . REINEKE, Technologis tForest Products Laboratory,? Forest Servic eU .S . Department of Agricultur eThe art of briquetting is relatively old and widespread in its applica-tions to a great variety of substances . It is applied to the meterin gof uniform quantities (pills), to consolidation of fine material int oconvenient units (sugar cubes, coal dust), to densification of bulkymaterial (metal turnings for remelting, peat), and to improvement o fphysical qualities (powder metallurgy, charcoal) . The equipment, tech-nique, and experience of this broad field are available for guidance i nwood briquetting, since the consolidation, densification, and improve-ment of physical qualities desired for utilization of finely dividedwood refuse apparently parallel the customary briquetting of metalturnings and of coal dust and other fuel stuffs .These more or less general briquetting methods have been used in som eEuropean countries for many years for sawdust, shavings, extracted bark ,and chips. . In this country, because of the cheapness of other fuels andthe plentiful supply of solid firewood, many similar ventures during th elast half century have been financially unsuccessful . As a conservationand stop-loss measure, there remains a strong inducement to convertotherwise waste wood of low value to dense, clean, easily burned bri-quets . It-has been only in the last decade or so that any considerabledegree of financial success has attended wood-briquetting efforts (andthen only under the most favorable circumstances) . This has beenprimarily due to the use of a radically, different method .It has been found that some granular materials require no added binde rbecause they are self-bonding when briquetted at elevated temperatures .Among these is wood . At temperatures above the minimum plastic tempera-ture (325° F . for wood), the elastic strains set up in the material unde rbriquetting pressure are completely relieved and the particle surface scome together into intimate contact . Cohesion of the interfaces ,'This is one of a series of Forest Products Laboratory reports on woo dwaste utilization .?Maintained at Madison, Wis ., in cooperation with the University o fWisconsin .Report No. 1666-13	Revised September 1960Ointerlocking of broomed-out, fibrous parts of the particles, and apossible adhesion of the heat-softened lignin (the natural bonding agen tbetween the wood fibers), all contribute to a binding action that impartssatisfactory strength to briquets after they have cooled under pressure .BriquettingMachinesThis self-bonding feature of wood waste is the basis of the only wood -briquetting process commercially successful in this country at present .Practically all plants based upon this process use one type of machine, -the "Pres-to-log," made by Wood Briquettes, Inc ., Lewiston, Idaho . Thi smachine operates by compressing the waste wood (sawdust, shavings, an dother scrap gound to oatmeal size) into a primary compression chamberby means of a feed screw developing a pressure of approximately 3,000pounds per square inch . At the outlet from this chamber a secondar yhead cuts the compressed material into a spiral ribbon and forces i tinto a mold under a local pressure of 25,000 to 30,000 pounds per squareinch, the friction at this extreme pressure generating sufficient hea tto produce the necessary plasticity for self-bonding . The molds arecylindrical holes 4 inches in diameter spaced at regular intervals inand extending through the rim of a large wheel about 12 inches wide ,with the axes of the molds parallel to the axis of the wheel . Thebottom of the mold cavity is closed by a hydraulically operated piston ,which supplies the necessary resistance during filling and retracts a sthe mold fills . When the mold is filled, the mold wheel revolve sslightly to bring the next mold cavity into line for filling. The moldwheel is water cooled, and the briquets are cooled below their plasti ctemperature by the time it makes a complete revolution. The cooledbriquet is ejected from the mold as the resistance piston enters th emold cavity ahead of it preparatory to its filling .The 4- by 12-inch briquets produced by this machine are suitable fo rhand firing but not for mechanical .stoking . For stoker briquets, adifferent type of machine, which is available from the same company ,extrudes the self-bonded material through a cluster of eight 1-inchround holes to form continuous rods . As these rods emerge from th eextrusion head, they are cut into 1-inch lengths by rotating knive sand yield pellets suitable for mechanical stoking .Extrusion-briquetting is a recent development, and few machines usin gthis principle are in use . A Swiss extrusion machine, the "Glomera,"4for making stoker briquets without binder is also available . It has-These machines are understood to be available in this country only on alease-royalty basis . For use abroad, they are sold outright .Sumner Iron Works, Everett, Wash ., has been licensed to produce th eGlomera Briquettor and auxiliary equipment in the United States .•Report No . 1666-13	-2 -two adjustable tubes, about 3-1/2 inches in diameter, through which thematerial is forced by pistons or rams . The tubes have an adjustabl eslight taper that provides. sufficient resistance to the flow of thematerial to develop high pressure under the pistons, which causes theloose material to be compacted . The cohesion between successive charge sis less than that within each charge, so that the extruded briquet tend sto separate easily into disks about 1/4 to 1/2 inch thick. These aremore conveniently handled for stoking small fires in cook stoves o rshoveling the fuel into a furnace . An automatic head for wrapping ofbriquets with cellophane is available . Newer models of this machinegive greater density and cohesion by precompressing the charges befor ethe pistons force them into the tubes . The horizontally positionedpistons of the Glomera machine are driven by a pulley and compound leverarrangement . In a new German briquet press, the alternate-acting piston sare hydraulically actuated, in a vertical position .A machine operating on the piston principle was developed about 1949by Walter W. Letts of Northville, N .Y . Eight or sixteen extrusion tube sproduce stoker-size briquets 1-1/8 inches in diameter and several inche slong . The pressure face of the piston, or ram, has a dimpled center andscalloped radial grooves, the imprints of which improve the interlockingof successive charges of material, so that there is less tendency forthe briquet to break up into small disks . The Sandy Hill Iron and Bras sWorks, Hudson Falls, N.Y ., was the manufacturer of the machine .A third method for binderless briquetting is used by the CaliforniaPellet Mill Co . of San Francisco . In this process, the material is fe dinto a die cup that has many orifices in its bottom. A roller unde rheavy pressure revolves over the material on the bottom of the die cupand forces the material through the tapering orifices . Rods of densematerial are thus formed that are cut into short lengths by a rotatingknife under the die cup .,-	, • -A production rate of about 2 tons per hour is reported for the pelletize rsystem. Production with the Glomera machine is 1 ton per hour . One mancan tend the machine and pack the product . With the Letts machine, aproduction of 700 to 1,000 pounds per hour could be expected from aneight-tube machine, with one man supervising four machines . Productionwith the log-size Pres-to-log machines, more than 120 of which have beeninstalled, is about 1/2 ton per hour, with 1 man tending 2 machines .The stoker-size Pres-to-log machine produces about 20 tons per 24-hourday .For profitable production, continuous round-the-clock operation isdesirable. For efficient use of labor, some installations have beenmade in pairs or multiples . thereof . Since the daily output of a pair ofmachines is 24 tons, it is apparent that a large and continuous supplyof waste must be available . To compete successfully with other fuels ,costs must be kept at a minimum . Briquetting machinery, therefore, mus tbe located at the source of waste to eliminate expensive handling ofbulky material . Because the large quantities of waste required can b eReport No. 1666-13	-3-obtained in the West and because competing fuels are expensive in thatregion, nearly all of the briquetting plants are located there . Oneeastern plant, in New Jersey, has a luxury market in New York and othe rlarge eastern cities where the cleanliness and convenience of briquet scommand a premium price for fireplace, restaurant, dining-car, and ship -galley use .No accurate cost figures on Pres-to-log briquetting are available, but inthe West, where this product is sold in bulk, the selling price ofstoker briquets, delivered, was $12 per ton, bulk, or $13 per ton ,sacked, in 1950 . A "unit" of 240 log briquets (approximately 1 ton )sold for $13 .35, delivered, or $12 .35 on a cash-and-carry basis. Summerprices were $1 less to encourage picnic use and early stocking fo rwinter use.	-Dry Waste EssentialAt present, waste used for briquetting is chiefly from coniferou sspecies . One southern plant is making log-size briquets from oa ksawdust . Many types of vegetable material, from alfalfa to bark, havqbeen briquetted successfully, and a study by the Michigan College o fMining and Technology. shows that some northern hardwoods, alone or inmixture with eastern hemlock, can be made into briquets . High-qualitybriquets can be made from bark alone, but the large volumes of barkrequired for a briquetting operation usually are available only at plant susing wet debarking methods . Extensive drying thus becomes necessary .To develop the necessary strength and hardness in the briquet, it isessential that waste be used with a moisture content of less than 10 per-cent, preferably 6 percent . Various types of dryers (such as drums ,steam-heated plates, and steam pipes over which the waste is cascaded )may be used to bring the waste to the desired moisture content . A recentdrier installation,_6 the Raymond Flash Dryer, uses a short exposure t ohot gases to reduce the moisture content to the desired level . Flash'dryers are also made by the Glomera manufacturers .Charcoal Briquet sThe production of charcoal briquets may be accomplished either bypreparing the charcoal first and then pressing it, or by preparing woodbriquets to be carbonized after forming . During the war, 85 percent o fthe total production of Pres-to-log briquets was used for charcoa l-Hereford Garland . "Possibilities for the Production of Wood Briquett eStoker Fuel in Northern Michigan." Forest Products Research Division,Michigan College of Mining and Technology, Houghton, Mich .' June 1950 .6The Timberman, 48 :4, p. 48 . February 1947 .Report No . 1666-13 -4-production . Basorel developed a method of making a semicharcoa lbriquet by preheating sawdust until the distillation of pyroligneou sacid ceased, at which point tar_ distillation began and the sawdust wa sbrownish in color . This partly charred sawdust was then cooled to 212° F .moistened with water, and pressed into molds . Basore and Moorelater developed a method! in , which the dry sawdust was heated in molds ,under no pressure except the weight of the mold piston, until partiall ycarbonized .and then placed under a pressure of 350 pounds per squar einch until, carbonization was complete . The resulting briquets were the nfurther heated to drive off smoke-producing volatiles .In the Seaman process of distilling finely subdivided wood, the resultinggranulated charcoal is mixed with wood tar produced in the distillatio nprocess, briquetted, and reheated in a retort . Here the lighter frac -tions of the tar are driven off and recovered, and the remainder under -goes a coking that binds the charcoal particles firmly together . Avery dense briquet results from this process e9 '.Field of Briquet DevelopmentFurther developments in briquetting are possible either in the proces sused or in the type of machinery employed, but prospects for substantia limprovement are not encouraging . A small, inexpensive machine and.simple process that could convert small quantities of green sawdust t obriquets economically would be very useful in salvaging the waste a tsitre7,~ .sawmills, -espeeially .portables, where available waste is not suffi -cient to warrant the installation of the large-capacity machines nowavailable .The many processes and machines so far developed have two characteristic sthat must also be a part of future developments . These are (1) the us eof pressure to reduce the bulk and provide hardness for resistance tohandling and to improve burning qualities and (2) the provision of someagency to bind the small particles together to form the briquet . Pres-sures pmay vary over a wide range that may be as high as 25,000 t o30,000 pounds per square inch, and several types of binding actions ar e.available, s'ome' :of -which have been used with varying success .Binding agents may be .broadly classed as external, such as wrappings o fcloth Or-paper or ties'of cord or,wire, and internal, in which the,-Cleburne A . Basore . "Fuel Briquettes From Southern Pine Sawdust . "Bul . 1, Engin. Expt . Sta ., Alabama Polytechnic Inst ., Auburn,Ala. May 1930 .8C . A. Basore and O . C . Moore. "The Production of Lump Charcoal Fro mPine Sawdust Without a Binder ." Bul . 14, Engin . Expt . Sta., AlabamaPolytechnic Inst ., Auburn, Ala . November 1942 .Nixing tar with charcoal is common practice and not limited to th eSeaman process . Under some briquetting conditions, starch-boun dbriquets are also very dense .Report No . 1.666-13 -	-5- .ti 1binding agent maybe dispersed within the briquet . Internal binders may ,be subgrouped into "additives," such'as glues, cements, wood tar added.to charcoal ; "extractives" from the briquetted material itself, such a sbitumen from soft coal, gums from southern pines, tars from partiall ycarbonized wood ; or "self-bonding," a characteristic of plasticize dmaterial .If :satisfactory .briquets are to be produced economically, binders mus tmeet a number of severe requirements . Overall cost is a primary consid -eration, in which unit cost of material, relative quantity required ,cost of applying, .and effect on production must be analyzed . Secondly ,the binding agency must produce a briquet of sufficient toughness t owithstand exposure and the shocksof transportation, storage, an d' stoking . Exposure to weather must not .cause crumbling or excessivesoftening, and during combustion the exposure to heat must not caus e.- _disintegration and consequent loss of fine pieces•throughthe grates .The binder, .preferably, should not cause smoke nor produce gummy deposits .An objectionable odor, during storage or burning, .should - be avoided ,and dust should not-form in handling . Added binders should have at:least as high a heat value as wood .Additive binders fall into three classes : inorganic materials (such as.cetinent and silicate of soda), organic materials (tar, pitch, resins ,glues), and fiber. Some of these permeate the material to be briquetted ; .others merely surface-coat it . .For wood fuel, cements are objectionabl eand have not-been used because of increased ash, decreased combusti -bility, and disintegration during burning: Organic . binders usuallyincrease the heat value of wood briquets and do not add to their as hcontent, and briquets made with some of these binders -do not soften o rdisintegrate . during combustion. The majority_of the binders mostsuitable from a physical• standpoint . are too expensive to use in theproportions .necessary for'good briquetting .Self-contained extractable binders'are,,ayaiLable in some types o f.materials, chiefly " the' bituminous coals, from which an added nonbindin gsolvent extracts tarry materials that serve to bind the-particle stogether upon • subsequent evaporation of the solvent . Wood has noextractable binders . of . this class (except the resins of a few species )but has a-parallel in the, formation of tars in destructive distillatio nthat can be .added to charcoal for briquetting, binder . The partialcarbonization of wood 'briquets produces a comparable result .Fibrous binders for briquets have receivedlittle study . In briquettingpeat, one process .is assisted by the hydration of fibers during th egrinding, or "mastication," stage of-preparing the material . Varioustypes . of fibrous material might serve as .binding agents, but the cheap -est would be hydrated wood fiber . This can be prepared from wood wast eby grinding it to a high degree of hydration .\ The hydrated fiber coul dthen be added in relatively small proportions .to the material to beprocessed into briquets by a wet method combined with air drying foreconomy .Report No . 1666-13	-6-A new briquet product has recently been introduced that combines sawdus tand coal dust, with added chemicals . The mixture is compressed intologs 4 inches in diameter and 24 inches long, and the individual briquet sare wrapped in paper for cleanliness in handling .The combination of wood with other fuel materials, such as coal, peat ,,and flue dust, or with metal wastes to be reprocessed, may be worthy o fexploration . Such combination may be somewhat restricted because of th e.need for :having two or more materials available in sufficient quantityat the same place ; on the other hand, situations may exist where th equantity of each material, separately, may be inadequate to operate abriquetting plant :but may :be fully adequate if two or more material s.can be combined .	-

Briquets from wood waste

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Briquets from wood waste

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