GB2170441A

GB2170441A - Method for extrusion processing of cellulose-bearing materials

Info

Publication number: GB2170441A
Application number: GB08601521A
Authority: GB
Inventors: Gordon Ray Huber; Bobbie Wayne Hauck
Original assignee: Wenger Manufacturing LLC
Current assignee: Wenger Manufacturing LLC
Priority date: 1982-11-26
Filing date: 1986-01-22
Publication date: 1986-08-06
Also published as: GB2131342A; GB8601521D0; DE3342812A1; GB2170441B; GB8331235D0; JPS59150190A; GB2131342B

Abstract

A defiberated product is produced by extruding coarse wood or wood derived materials having a moisture content of 5 to 75 percent by weight, by conveying it by a screw (32) through a barrel 27 in which the material is subjected to increasing shear and compression forces, at a temperature of 212 DEG F to 650 DEG F and pressure of 200 to 5,000 p.s.c., and is extruded through a restricted die orifice (106). The pressure of the material in the barrel is sensed by a sensor (84) which controls the supply of hydraulic fluid to die chambers (112,114), so that successive sensed high or low pressure respectively causes a die piston head (78) to be displaced conically, to increase or decrease the size of orifice (106) and produce a corresponding reduction or increase in the barrel pressure. <IMAGE>

Description

1 GB 2 170 441 A 1 SPECIFICATION process wood chips or other cellulose-

orfiber bearing materials. Theo retica I ly,.the advantages of Method for extrusion processing of cellulose- extrusion processing of these materials are man bearing materials ifest, particularly from the stand-point of energy 70 consumption. However, severe problems are en The present invention is broadly concerned with an countered in practice, stemming principally from the extrusion method designed to efficiently handle and great difficulty in smoothly and efficiently extruding extrude material heretofore preventing extreme pro- rough, coarse materials such as wood chips. Typical cessing problems such as wood chips, sawdust and ly, attempts to extrude wood chips result either in other woody residues, municipal solid waste, and 75 excessive surging and blowing or other signs of crop residues. More particularly, it is concerned with uneven operation, or perhaps more often complete such a device and method which makes use of a plugging of the machine, necessitating a break down transition screw section within the barrel which and clean-up of the machine. In view of these serves to even out material flow and assist in problems, it is believed that no commercially suc build-up of relatively high pressures and tempera- 80 cessful extrusion apparatus or process has hereto tures; moreoverr the overall extrusion apparatus fore been developed which can effectively restruc preferably includes an adjustable die which further ture and definrate cellulose or fiber-bearing mate facilitates the extrusion operation. rials.

A number of processes and devices have been The present invention overcomes the problems proposed in the past for the purpose of restructuring 85 noted above and provides an extrusion method cellulose or fibre-bearing materials to produce a which is specifically designed to handle, without the comminuted or defibrated product. To give but one usual problems, materials such as wood chips, example, clefibrated wood is used in the production sawdust and other woody residues, including muni of so-called fiber board. The clefibrated wood can be cipal solid waste and crop rsidues (e.g., wheat straw, produced by a technique known as "gun puffing" 90 corn stover, bagasse). In addition, the extruder wherein wood chips are treated with high pressure hereof has been used to process and texturize whole steam in a large vessel followed by a sudden release soybeans having the usual high fat content.

of pressure to separate and restructure the wood Broadly speaking, he method of the present inven chips into fibers and thus obtain the defibrated tion utilises and extruder including an elongated product. Another type of process to achieve this 95 barrel presenting a material inlet and a matrial outlet result involves disc refining of wood chips wherein, adjacent opposed ends thereof, with an elongated, after an initial pressure treatment, the wood chips axially rotatable screw within the barrel which are conveyed to a large multiple disc refiner which is serves to advance the material from the inlet end to likewise operated under pressure. Large commercial the outlet end thereof. The screw is especially units of this type are capable of refining wood chips 100 designed for smoothing out material flow in the down to essentially single fiber size, butfor this machine so as to minimize formation of an unman pupose require a very large motor, e.g., two ageable plug of material. This feature, coupled with thousand horsepower. One significant problems die means adjacent the outlet end of the barrel which with disc refiners is maintenance and parts replace- is variable to alterthe effective dimensions of the die ment costs. These units are prone to wear out critical 105 opening during operation of the extruder, has been operating components at a rather considerable rate, - found to materially facilitate processing of materials and are therefore deficient. of the type described.

Treatment of municipal solid waste has also been Accordingly,. the invention provides a method of practiced in the past in orderto renclerthis material producing a defibrated product suitable forthe uniform and usable as a fuel. One technique for 110 manufacture of fiber board or the like, said method treatment of municipal solid waste is known as comprising the steps of: providing a quantity of hydropulping. In this process, a slurry of the waste rough, coarse material selected from the group and water is introduced into a large kettle having a consisting of wood and wood-derived materials and perforated bottom. A rotating scraper blade is situ- having a moisture content of from 5 to 75 percent by ated adjacent the perforated bottom, and serves to 115 weight; passing said material into an elongated reduce and restructure the solids passing through barrel of an extruder, and axially rotating the extrud the kettle bottom. er screw to convey said material along the length of Generally speaking, all of the processes men- the barrel, said conveying step including the steps of tioned above are deficient in one important respect, gradually increasing the shear and compression i.e., they consume large amounts of energy. For 120 forces exerted on said material as the material example, the disc refining process for wood chips, passes along the length of said barrel, developing a although effective for producing the desired defi- temperature within said extruder barrel of from brated wood, can be almost prohibitively expensive 212'F. to 650'F., developing a pressure within said from an energy requirement standpoint. This stems barrel of from 200-5000 psi; and extruding the not onlyfrorn the inherent electrical power con- 125 mateiral through a restricted orifice, including the sumption of the large driving motor and steam used steps of adjusting the effective dimensions of said in treatment of woodchips, but also from the fact restricted orifice in response to pressure conditions that large volumes of water must be pumped and within said barrel, so as to produce said defibrated handled along with wood chips. product. Preferably also, said moisture content is Attempts have been made in the past to extrusion 130from 30 to 50% by weight. Preferably also, said 2 GB 2 170 441 A 2 pressure is from 750-1500 psi. Preferably, the presents a frustoconical bore therethrough, Finally, method further includes the step of passing the it will be observed that the assembly 30 is affixed to material through an elongated compression zone of the outlet end of head 48 for receiving material decreasing cross-sectional area along the length therefrom (see Figure 4).

thereof and having a rotatable element located 70 The screw 32 is likewise made up of sections, therein, while simultaneously rotating said element. which can broadly be referred to as an inlet feed Preferably also, said material is retained in said section 50, a transition screw section 52, and a barrel for a period of time is form 15-200 seconds. compression screw section 54. The inlet screw Figure 1 is a side elevation view of extrusion section 50 comprises a single flighted screw mem- apparatus in accordance with the invention; 75 ber 56 situated within tubular head 38 and serving to Figure 2 is an end elevational view of the appar- convey material forn inlet 28 along the length of the atus illustrated in Figure 1; barrel 27 to the transition section.

Figure 3 is an enlarged, fragmentary vertical The transition screws section 52 is in the form of a sectional view taken along line 3-3 of Figure 2 and specialized screw member 58 which is situated illustrating the inlet, transition and compression 80 downstream of the screw member 56 and is coupled screw sections of the extruder screw; thereto. As best seen in Figure 3, a steamlock die 74 Figure 4 is an enlarged, fragmentary vertical is interposed between the screw members 56,58.

sectional view at the outlet end of the extruder (This steamlock is preferred, but not essential in the apparatus, and depicting the preferred adjustable extrusion apparatus.) The screw member 58 making die structure; 85 up the transition screw section is advantageously in Figure 5 is a side elevational view of the preferred the form of an elongated body presenting a general transition screw section and illustrating the gradual ly cylindrical outer face 60 and a constant or and progressive increase in flight depth of the first decreasing root diameter (of course, it would also be screw flight thereof; and possible to employ a variable root diameter screw).

Figure 6 is a vertical sectional view of the section 90 Structure is provided which defines respective, axial depicted in Figure 5. ly spaced apart first and second flight means 62, 64 Turning now to the drawings, an overall extrusion on the body which extend outwardly from theface apparatus 10 is illustrated in Figure 1 and 2 which 60 and generally helically along the length of the includes a primary feed hopper 12 provided with an screw body. As illustrated in Figures 5 and 6, the first inclined delivery auger 14, a secondary hopper 16 95 and second flight means 62, 64 in effect present a provided with a twin screw feeder mechanism 18, pair of continuous helical portions extending co and an extruder assembly broadly referred to by the extensively along the screw axis. Moreover, it will be numeral 20. The hopper 12 is of conventional observed that the depth (i.e. , the distance from the construction and includes the usual supports 22. The face 62 to the outer surface of the flight) of the first auger 14 is oriented obliquely within the confines of 100 flight means 62 is less than that of the second flight hopper 12 and extends upwardlythrough the open means 64. In the illustrated embodiment, the first top thereof. A delivery chute 24 serves to convey flight means 62 starts at essentially zero depth and material augered from the confined of hopper 12 gradually and progressively increases, during a into secondary hopper 16. The hopper 16 is likewise period of about one and one-quarter revolutions of of known construction and includes supports 26 and 105 the flight means, until the depth of the firstflight an open top for delivery of material from chute 24. means 62 equals that of the second flight means 64.

Both of the hoppers 12 and 16 are preferably This gradual increase in flight depth is best seen in provided with rotating scrapers adjacent the bottom Figures 5 and 6, whereas the starting or zero depth thereof, so that agglomeration of material therein is point 66 of the first f light means 62 is depicted in prevented. 110 Figure 3.

The extruder assembly 20 includes an elongated As will be explained in more detail hereinafter, the multiple section tubular barrel 27 having a material purpose of transition screw section 52 is to smooth inlet 28 in communication with twin screw feeder 18, out the flow of rough, coarse material passing as well as adjustable die structure 30 positioned through the extruder assembly to prevent plugging adjacent the opposite outlet end of the barrel. 115 of the machine.

The assembly 20 further includes an elongated, The compression screw section 54 in effect occu multiple section auger screw generally referred to by pies the remainder of the length of the extruder the numeral 32 which is situated within the barrel 27 barrel 27, i.e., this section 54 is disposed within and is axially rotatable therein through the medium heads 40-48. The compression screw section in- of motor34and drive assembly 36. The screw 32 120 cludes one or more double flighted screw members serves to advance material from inlet 28 along the such as th screw members 68 and 70 respectively length of barrel 27 and finally through the die illustrated in Figures 3 and 4. Also, this section 54 opening presented by adjustable die structure 30; in includes the conical screw member 72 positioned addition, the screw serves to subject the material to within head 48 (see Figure 4). if desired, respective shearforces and imparts heatto the material in the 125 steamlock dies 74 can be situated between the mannerto be described hereinafter. respective screw members making up the overall In the embodiment shown, barrel 27 is provided compression screw section 54.

with a total of five axially aligned, interconnected, Itwill be understood by those skilled in the artthat tubular heads 38-46, as well as somewhat shorter, the described screw members are of essentially internally spirally ribbed compression head 48 which 130 tubular, sectionalized configuration and include a 3 GB 2 170 441 A 3 central bore. The overall extruder is typically equip- bolted to the outlet end of compression head 48 as ped with a central, powered, rotatable splined shaft depicted. The innermost face of member 108 is of which receives the screw members making up the smooth, circular configuration and is provided with a overall screw 32, as well as the steamlock dies. The circular recess receiving a seal 110. The member 108 tubular nature of screw member 58 is illustrated in 70 is configured to define, in conjunction with the Figure 6 as at 76. surfaces 102, 104 and the structure 100, first and The die structure 30 includes an elongated, tubu- second hydraulic fluid chambers 112,114. A pair of lar, axially shiftable piston head 78, an elongated, bores, 116, 118, are provided through the member axially rotatable bullet element 80 located partially 108 and respectively communicate with the cham- within piston head 78, hydraulic means 82 operative- 75 bers 112, 114. Schematically illustrated hydraulic ly coupled to head 78 for selective axial shifting of fluid lines 120, 122 are operatively coupled to the the latter in either axial direction, pressure sensing respective bores 116, 118 as illustrated.

means 84 operatively disposed within barrel 27 for The hydraulic means 82 is of conventional con sensing the pressure conditions therewithin, and struction and has been illustrated only in schematic complete means 86 operatively coupling the press- 80 form. Those skilled in the art will appreciate, howev ure sensing means 84 and hydraulic means 82. er, that the purpose of hydraulic means 82 is to direct In more detail, head 78 includes a sidewall 86 and hydraulic fluid under pressure to either of the bores inner, bore-defining wall portions which cooper- 112, 114, depending upon the pressure conditions atively define a continuous bore 88 through the within barrel 27, as sensed by the sensor 84. To this length of piston head 78. In particular, a first 85 end, the hydraulic means 82 includes the usual frustoconical wall portion 90 is provided which hydraulic fluid reservoir, hydraulic pump, and sole extends inwardly in a converging manner from the noid operated valves.

extrerne input end of piston head 78. A second The sensor 84 is preferably in the form of a frustoconical wall portion 92 having a largest diapressure transclicer which is operatively disposed meter end 94 and a smallest diameter end 96 is also 90 within an appropriate bore provided through the provided, along with a third wall portion 98 of sidewall of compression head 48. Thus, the sensor is cylindrical configuration which extends from the operable to detect the pressure conditions within the smallest diameter end 96 of wall portion 92. barrel 27 adjacent the inlet to the die structure 30. In The wall portions 90 and 92 cooperatively define a the event that excessive pressure conditions are frustoconical input end bore section, whereas wall 95 sensed within the barrel 27, hydraulic fluid is portion 98 defnes a cylindrical, substantially condirected to chamber 112 which has the eff ect of stant diameter output end bore section. It will further shifting piston head 78 rightwardly as viewed in be observed that the diameter of the output end bore Figure 4, to thereby increase the effective transverse section is substantially equal to the diameter of the dimensions of the extrusion opening 106, with the smallest end 96 of portion 92, and that it is free of 100 result that the pressure conditions are reduced. On any obstructions to material flow therethrough. the other hand, if a low pressure condition is sensed, The outer surface of piston head 78 is of irregular hydraulic fluid is directed to the chamber 114, so that construction and includes four circurnferentially piston head 78 is shifted leftwardly as viewed in spaced, peripheral recesses (not shown) adjacent Figure 4 to decrease the effective dimensions of the the output end of the head, and an annular, outward- 105 opening 106 and increase barrel temperature.

ly projecting structure 100 between the input and The die structure 30 described above is fully output ends of the head 78. respective, smooth, depicted and described in Application for U.S.

cylindrical bearing surfaces 102,104 extend in Letters Patent, Serial No. 06/210,684, filed November opposite direction from the opposed ends of the 26,1980, now abandoned. The disclosure of this structure 100 for purposes which will be made clear. 110 application is hereby incorporated by reference The bullet 80 is of elongated, frustoconical con- herein.

figuration and is cleined by a smooth, converging In addition, external hydraulic piston and cylinder sidewall and a circular front wall. The largest dia- assembly may be employed in lieu of or to assist the meter end of the bullet 80 extends from the smallest internal structure described for shifting of piston diameter end of the conical screw member 72, and in 115 head 78.

effect forms an extension of the latter. Thus, the It has been discovered that extrusion of materials bullet 80 rotates with the screw 72 during operating such as wood chips, wood-derived materials, paper, of the extrusion apparatus. preferably, the bullet 80 municipal solid wastes, crop residues and whole or is integral with the screw member 72. ground soybeans can be materially enhanced Referring specifically to Figure 4, it will be seen 120 through use of the described apparatus. Broadly thatthe converging sidewall of bullet 80 is com- speaking, the effect of the transition screw section, in plementally configured relative to the wall portion conjunction with the adjustable die structure 30, is to 92, to thereby define an annular extrusion orifice or even out flow of the material within the extruder opening 106 between the bullet sidewall and wall barrel so as to avoid plugging. The transition screw portion 92. It will also be obseved that the effective 125 section has been found to gradually increase the transverse dimensions of the opening 106 can be shearforces on the material between the low shear varied by axial shifting of head 78, in the mannerto inlet section to the high compression section, where be explained. as the adjustable die maintains good continuity of The overall adjustable die structure 30 includes an operation by correlating the size of the die opening annular, apertured, stationary member 108 which is 130 with the quantity of incoming material and the shear 4 GB 2 170 441 A 4 and working conditions imposed thereon. These pressure setting for the die structure is usually components greatly facilitate the sometimes around 1,000 psi.

troublesome extrusion of the rough, coarse mate

Claims

rials described above. Indeed, actual tests using CLAIMS conventional

extrusion apparatus to extrude wood 70 chips resulted in plugging or inefficient operation, 1. A method of producing a defibrated poduct whereas an extruder in accordance with the inven- suitable for the manufacture of fiber board orthe tion handles the same feedstock without difficulty. like, said method comprising the steps of:

In the extrusion of cellulose- orfiber-bearing providing a quantity of rough, coarse material materials, it is preferable to add moistureto the 75 selected from the group consisting of wood and matrial prior to or during the extrusion process in wood-derived materials and having a moisture con order to achieve a total moisture content (i.e., native tent of from 5 to 75 percent by weight; moisture plus added moisture) of from about 5 to 75 passing said material into an elongated barrel of percent by weight, and more preferablyfrom about an extruder, and axially rotating the extruder screw 30 to 50 percent by weight. During the extrusion, the 80 to convey said material along the length of the temperature should be maintained within the ex- barrel, truder barrel at a level of from about 212 to 650 said conveying step including the steps of gradual - degrees Fahrenheit, and more preferably from about ly increasing the shear and compression forces 300 to 400 degrees Fahrenheit. Likewise, the pressexerted on said material as the material passes ure conditions within the barrel should be above 85 along the length of said barrel, developing a temper about 200 psi, more preferablyfrom about 200 to ature within said extruder barrel of from 212'F. to 5,000 psi, and most preferably from about 750 to 650'F., developing a pressure within said barrel of 1,500 psi. from 200-5000 psi; and The material during the extrusion should be extruding the material through a restricted orifice, retained within the barrel 27 for a period of from 90 including the steps of adjusting the effective dimen about 15 to 200 seconds, and more preferably for a sions of said restricted orifice in response to press period of from about 30 to 60 seconds. This is ure conditions within said barrel, so as to produce achieved not only by adjusting the rotational speed said defibrated product.

of the screw 32, but also by adjustment of the 2. A method as setforth in Claim 1, further effective clearance of the extrusion opening 106 95 including the step of passing the material through an between the bullet 80 and wall portion 92 (e.g., elongated compression zone of decreasing cross between about.001 inch to.500 inch, preferably.010 sectional area along the length thereof and having a inch to.200 inch). As noted above, such adjustment rotatable element located therein, while simul is most advantageously effected in response to taneously rotating said element.

pressure conditions within the barrel. 100 3. A method as setforth in Claim 1 orClaim 2, In the extrusion of wood chips to produce a said moisture content being from 30 to 50% by defibrated product useful for the production of weight.

fiberboard, wood chips of appropriate average 4. Amethod as setforth in anyof Claims 1,2or3 dimension (e.g., one inch) are taken on an as is basis or wherein said pressure is from 750-1500 psi.

without any presoaking or premoisturizing and are 105 5. A method asset forth in any preceding claim passed into the barrel of extruder assembly 20. wherein said material is retained in said barrel for a However, it could prove advantageous in some period of time is from 15- 200 seconds.

types of wood to premoisten the wood. The wood 6. A method as setforth in Claim 5, said time can be virtually any type, such as hardwoods and period being from 30-60 seconds.

softwoods. Exemplary woods include gum, aspen, 110 7. A method of producing a defibrated product poplar, pine or walnut, and will typically have a substantially as hereinbefore described.

moisture content of from 20-60% byweight. The extruder would normally be operated at an rpm level Amendments to the claims have been filed, and of 75 to 600, preferably 150 to 300 rpm. have the following effect:

During the initial startup, the machine will typically 115 Claim 1 to 5 above have been deleted ortextually experience surging and blowing, and such is control- amended.

led by varying the effective dimensions of the die New or textually amended claims have been filed opening until this opening effectively correlates with as fol lows:

the feed rate of wood chips to the machine. When continuous operations have been established, the 120 CLAIMS die assembly 30 is set to adjust the die opening when the pressure conditions within barrel 27 vary 1. A method of producing a defibrated product significantly from e.g., 1,000 psi. This setting level suitable for the manufacture of fiber board or the can be varied over a considerable range, depending like, said method comprising the steps of:

upon the type of final product desired, such as 125 providing a quantity of cellulose or fiber-bearing smaller or larger particle size. material having a moisture content of from 5 to 75 The extrusion of municipal solid waste and crop percent by weight; residues is essentially similar to that outlined above. passing said material into an elongated barrel of Typically, the total moisture content of such feed- an extruder, and axially rotating the extruder screw stocks should average about 40% by weight, and the 130 to convey said material along the length of the 3 GB 2 170 441 A 5 barrel, said conveying step including the steps of gradually increasing the shear and compression forces exerted on said material as the material passes along the length of said barrel, developing a temperature within said extruder barrel of from 212T. to 650T. (1 00T to 343T), developing a pressure within said barrel of from 200-5000 psi (1.38x 1 06-3.45x 107 N M-2); and extruding the material through a restricted orifice, including the steps of adjusting the effective dimensions of said restricted orifice in response to pressure conditions within said barrel such that said dimensions are increased in response to a high pressure condition and reduced in response to a low pressure condition, so as to produce said defibrated product.
2. A method asset forth in Claim 1, wherein said orifice is defined by a die structure having an elongated compression zone of decreasing crosssectional area along the length thereof and having a rotatable element located therein.
3. A method assetforth in Claim 1 orClaim 2, said moisture content being from 30 to 50 percent by weight.
4. A method assetforth in anyof Claims 1,2 of---3 wherein said pressure is from 750-1500 psi (5.17x 106 to 1.03x 107 N M-2).
5. A method asset forth in any preceding claim wherein said material is retained in said barrel for a period of time from 15-200 seconds.

Printed in the UK for HMSO, D8818935,6186,7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.