CA1233059A - Method and apparatus for refining lignocellulose containing material - Google Patents

Abstract

ABSTRACT

A method and apparatus is disclosed for refining lignocellulose containing material in which a gaseous medium is present. In accordance with this method and apparatus, the lignocellulose material is refined between a pair of opposed inner and outer refining surfaces by rotating the refining surfaces in opposite directions along a common axis. Gaseous flow paths are provided along the inner refining surface to provide for sufficiently uniform gaseous flow therealong during refining to avoid a stoppage of gaseous flow to an extent which would result in deleteriously affecting the material being treated. The refining surfaces are angularly disposed relative to the common axis such that, during refining, the material being treated is urged by centrifugal force against the outer refining surface to affect simultaneously the desired refining of the material and the flow of gaseous medium along the flow paths to avoid deleteriously affecting the material.

Description

The present invention relates in general to a method and apparatus adapted for refining fibrous material and, more particularly, to such method andapparatus for refining lignocellulose containing material such as wood chips.
In the refining industry for refining fibrous material, for example, lignocellulose containing material, disc refiners are often used which are constructed of two opposed refining discs or members which are rotated relative to one another within an enclosed housing. The refining discs may be rotated in opposite directions (commonly referred to as counter rotating or double disc refiners), or one disc may be rotated while the other disc remains stationary (commonly referred to as single disc refiners. The refining discs are provided with grinding or refining surfaces in the form of refining segments having refining means usually constructed of ridges spaced apart by intermediategrooves. Between the opposed refining surfaces a radially arranged refining zone or gap is formed in which the lignocellulose containing material is processed by the ridges of the refining surfaces when such material is passed radially outward under the influence of centrifugal force developed during relative rotation of the refining discs. The material is supplied to the refining gap provided between the refining discs through openings arranged in communication therewith in one of the refining discs.
Durillg the processing of the lignocellulose containing material, which material normally consists of wood chips, large amounts of steam or other gaseous medium usually develops from the liquid included along with the lignocellulose containing material, or from liquid added directly into the disc refiner during its operation. Also, steam or other gaseous medium may be supplied directly to the disc during the refining operation as desired. The supplied liquid is required for insuring that the lignocellulose containing material ~331)~ii9 flows through the refining zone without disruption and in order to prevent the refining operation from elevating the temperature of the processed material to a temperature which could give rise to discoloration of the material. However, the steam causes problems in that it disturbs the material flow through the refining gap. More particularly, the steam flows both with the material outward in the refining gap and inward against the feed direction of the material, The outward flowing part of the steam can assume a very high speed and thereby has a disturbing effect on the material flow. Further, the steam may flow out in a jerky manner, whereby the stability of the refining gap is lo affected so that the material flow will be nonuniform. This can result in deterioration of the pulp quality.
In counter rotating disc refiners of the conventional type, the individual particles in the material are affected during their passage through the refining gap by centrifugal force produced by the refining disc in the grooves of which the particles are located. Owing to the countercurrent rotation of the refining discs the particles located in the space between the two refining discs in principle stand still and are subjected only to a rolling uncontrolled processing, so that the steam is not permitted to pass freely outward through the refining gap. This results in a nonhomogeneous treatment of the material, with varying uncontrolled temperatures and staying or dwell times for the material. Thus, the quality of the product manufactured is thereby deleteriously affected.
In United States Patent No. 4,221,631, it is suggested to lead away the steam from the refining gap through passageways extending transversely through the refining segments, whereby the disturbing effect of the steam on the refining operation can be reduced. However, new problems arise owing to ~L2~3~

the clogging of these passageways, so that the original problem remains to be solved, In United States Patent Noah, there is provided a feed passage for the wood chips in one of the counter-rotating discs and a steam escape passage in the other one. United States Patent Nos. 4J059l237~
4~219J166 and 4J082,233 also relate to this problem. In United States Patent No. 4,059,237 to Mainstream this problem in a double-disc refiner is solved by the use of a separate removal channel connected to the material inlet passage adjacent the rotating feed-in disc. In the double-disc refiner disclosed in United States Patent No. 4,219,166 to Norma Circa et at, 10 provision is made for the steam to escape through the feed screw in counter current flow to the incoming material. In the single-disc type refiner disclosed in United States Patent No. 4,082,233 to Roil Renewal, special steam separating means rotate along with the rotating disc in the feed-in opening to separate excessive high pressure steam from the pulp material, allowing it to escape through a separate channel in the feed screw shaft.
Thus, each of these solutions involves diverting of the steam to paths other than through the refining gap or zone.
Because of increasing demand for large capacity refining equipment with adequate refining efficiency, it has also proved to be a problem in the 20 industry to properly control the radial passage of the lignocellulose material between the opposed refining disc, particularly in the peripheral portion thereof, so as to obtain maximum performance. More particularly, as the material progresses radially through the refining zone, it is desirable to have it alternate between the refining surfaces on the opposing discs, so that more work is performed on the material in a single pass. It has been found in practice, however, that unless the flow is properly retarded, the movement of LOWE dew the pulp becomes too rapid, as explained herein, and the refining action is minimized. Heretofore, attempts have been made to retard the passage of the material through the refining gap by arranging the ridges and grooves in the refining segments so that they can serve additionally as flow retarders.
Such attempts are exemplified by United States Patents Nos. 3,674,217;
3,040,997j 3,125,306 and 1,091,654. The provision of flow retarders, however, has resulted in clogging of the refining surfaces. In single disc type refiners in which the refining surface of the stationary disc has become clogged, the effect has been to minimize the effectiveness of the flow retarders such that the dwell time, and thereby the efficiency of the refiner, is reduced.
When flow retarders are introduced in double disc refiners, they tend to compound the problem inherent in same of inhibiting steam flow which occurs when the material stands still due to the countercurrent rotation of the refining discs.
Another attempt to solve the problem of controlling the flow in a single disc-type refining apparatus is exemplified by United States Patent Noah dated May 23, 1978, to By A. Aureole. The primary object of that patent is to solve the problem created by the high pressure steam in the peripheral zone of the grinding space. in order to prevent the partly refined material from being blown out from the peripheral grinding zone by the high velocity steam, Aureole utilizes the centrifugal force to separate the steam and to open up an escape passage for the steam while retaining the steam-liberated material between the opposed refining surfaces. However, this still has resulted in clogging of the stationary-outer refining surface, which in turn has had the effect of reducing the efficiency of the refining operation.
Further, this arrangement of Aureole has also resulted in a reduction of the ~LZ33()~ii9 dwell time of the material being treated which also affects the refining efficiency.
It is thus an object of the present invention to overcome the above-noted disadvantages of the prior art while providing an efficient refining operation resulting in a uniform and consistent treatment of the lignocellulose material.
In accordance with the present invention, there is provided a method and apparatus for refining lingnocellulose containing material in which a gaseous medium is present.

The method of the invention comprises the steps of refining the material between a pair of opposed inner and outer refining surfaces by rotating the refining surfaces in opposite directions along a common axis, providing for gaseous flow paths along the inner refining surface to provide for sufficiently uniform gaseous flow thrilling during refining to avoid a stoppage of gaseous flow to an extent which would result in deleteriously affecting the material being treated, and angularly disposing the refining surfaces relative Jo the common axis such that, during refining, the material being treated is urged by centrifugal force against the outer refining surface and away from the inner refining surface to effect simultaneously the desired refining of the material and the flow of gaseous medium along the flow paths to avoid deleteriously affecting the material.
The apparatus in accordance with the present invention comprises a pair of opposed refining members rotatable about a common axis and defining inner and outer refining surfaces arranged in opposing relationship. Means are provided for rotating the refining members in opposite directions along the common axis. Also, means associated with the inner and outer refining isles surfaces are provided which define gaseous flow paths along the inner refining surface to provide uniform gaseous flow there along during refining material sufficient to avoid a stoppage of gaseous flow to an extent which would otherwise result in deleteriously affecting the material being treated.
The refining surfaces are angularly disposed relative to the common axis such that, during refining, the material being treated is urged by centrifugal force against the outer refining surface and away from the inner refining surface to effect simultaneously the desired refining of the material and the flow of gaseous material along the gaseous flow path.
With such a method and apparatus, problems of the deleterious effects of the gaseous medium in the refining zone are minimized. Specifically, by providing gaseous flow paths along the inner refining surface, together with the provision of angular orientation of the inner and outer refining surfaces to provide for centrifugal force on the material being treated, there will be a separation of the gaseous medium from the material being treated and a transport of the gaseous medium along the flow paths to avoid ; deleteriously affecting the material. Additionally, the material being treated will be urged against the outer refining surface and away from the inner refining surface to effect the desired refining in a uniform and consistent manner. This thus permits the flow of steam or other gaseous medium outward through the refining zone without disturbing or adversely affecting the material flow and/or the stability of the refining zone. Consequently, a more uniform flow of material, and thus improved pulp quality, will be achieved.
Further, because the material is urged against the outer refining surface and away from the inner refining surface, problems of clogging of the material on the outer surface will be minimized since the outer refining surface is 1~33~)5i~g rotated What is, particles of lignocellulose in the outer refining surface will be subjected to centrifugal force due to rotation of the outer refining member, thereby insuring that the material will be urged past the flow restrictions in the outer refining surface and thus through the refining zone so that they are subjected to the desired refining action.
Still further, in accordance with the present invention, the pressure and temperature of the material to be treated may be controlled quite easily and efficiently by simply controlling the pressure and temperature of the gaseous medium in the housing surrounding the refining members. More particularly, because a substantially unrestricted flow of gaseous medium is provided through the refining zone, a relatively small pressure drop and temperature reduction of the gaseous medium during passage through the refining zone is provided, thereby assuring more effective control of the pressure and temperature of the gaseous medium in the refining zone, and thus of the material to be treated during the passage through the refining zone.
In accordance with a presently preferred embodiment of the present I: invention, the gaseous flow paths are provided along the inner refining surface by means of a series of grooves which extend along the inner refining surface throughout the radial extent of the refining zone. More preferably, the grooves yin the inner refining surface are substantially free of flow restriction, thereby insuring a substantially unimpeded or uninterrupted flow of gaseous medium out of the refining zone.
Still further, in accordance with another preferred embodiment, the refining surfaces are substantially conical in shape, and the angle of the refining surfaces along the radial extent of the refining zone is preferably between 15 and 75 with respect to a plane normal to the common axis of ~23~

rotation. Alternatively, the refining surfaces may be spherical in shape so that the angle of the refining zone through the radial extent thereof increases from a first predetermined angle relative to the plane normal to the common axis to a second predetermined angle relative to the plane normal to the common axis. With this latter embodiment, the first predetermined angle preferably is greater than or equal to 5 and the second predetermined angle is greater than 15 and less than or equal to 85.
The above description, as well as further objects, features and advantages of the present invention, will be more fully understood by reference to the following detailed description of presently preferred but nonetheless illustrative methods and apparatuses for refining lingo cellulose containing material in accordance with the present invention, when taken in conjunction with the accompanying drawings wherein:-Figure 1 is a partial cross-sectional elevation of a refiner ; constructed in accordance with the present invention having opposed refining members;
figure 2 is an enlarged cross-sectional elevation of a portion of the refining members as shown in figure 1;
17igure 3 is an axial section of a portion of the refining surface of the inner refining member;
Figure is an axial section of a portion of the refining surface of the outer refining member.
Figure 5 is a cross-sectional elevation through a portion of the refining zone formed between the refining members; and Figure 6 is a partial cross-sectional elevation of a refiner constructed in accordance with another embodiment of the present invention.

~3305~

Referring generally to the drawings, the method and apparatus for refining lignocellulose containing material, e.g. wood chips, in accordance with the present invention will be described in greater detail. Referring first to Figures 1 and 2J the refiner apparatus of the present invention is constructed from a pressure-proof housing 1 which encloses two rotatable refining members, namely an inner refining member 2 and an outer refining member 3. The refining members 2, 3 are, respectively, mounted on axles or shafts 4, 5, which axles are respectively supported in bearings 6, 7. The refining members 2, 3 are mounted for rotation in opposite directions to one another within the housing 1 about a common axis which coincides with the axis of the axles I, 5. The lignocellulose containing material to be refined is supplied to the space formed between the refining members 2, 3 through openings 10 in the outer refining member 3 by means of a screw feed 8 provided in a charging funnel 9.
The refining members 2, 3 are each provided with refining surfaces in the form of detachable refining segments 11, 12. As shown in Figures 3 and I, the refining surfaces of the refining segments 11, 12 are respectively provided with ridges 13, I and intermediate grooves 15, 16. The refining segments 11, 12 on the inner and outer refining members 2, 3 define there between a refining zone or gap 17 which extends radially relative to the rotational axis of the refining members 2J 3 as shown in Figure 2. The refining zone 17 forms an angle, i.e., the refining angle I, with a radial plane which is normal to the rotational axis of the refining members 2, 3. In accordance with the preferred embodiment of the present invention, the refining angle is suitably selected in the range of approximately 15 to 75, and more preferably between 20 and 60. It will be noted that portions of the inner - g US

refining surface along the refining zone 17 are located radially inward relative to respective portions of the outer refining surface at the same location along the refining zone 17. In the refining zone 17, the lingo-cellulose containing material is refined as such material passes outward there through by centrifugal force acting upon such material during rotation of the refining members I 3, the refining operation being effected by the ridges 13, 14 of the refining segments if, 12.
In the preferred embodiment, the grooves 15 in the refining segment 11 of the inner refining member 2 are substantially free of flow restrictions in order to permit the transport of steam or other gaseous medium along the grooves in a radially outward direction. Such steam, as described above, either is generated from liquid included with the lignocellulose containing material or is separately added to the refiner. It will also be appreciated that, because of the presence of the steam, the environment in the housing is pressurized, i.e., is at a pressure above atmospheric pressure. As is well ; known, refining of lignocellulose material in such a pressurized environment may be advantageous for certain purposes.
In contrast to the grooves 15 in segment 11, the grooves 16 in the refining segment 12 of the outer refining member 3 are provided with a number of slow restrictions or obstructions 18 which force upward the lignocellulose containing material moving outwardly along the grooves 16 to insure that such material is subjected to refining treatment between the ridges 13, 14 on the refining segments if, 12. By means of a nozzle lo, diluting liquid, for example water, is supplied in a controlled manner in order to maintain the concentration of lignocellulose containing material at a desired level. The refined material and pressurized gaseous medium is discharged from the housing 1~33~3S~

; 1 in a conventional manner, such as by means of a blow valve (not shown), which may be connected to an outlet opening at the top of the housing 1.
In the operation of the refiner of the present invention (as illustrated in Figure 1) the lignocellulose containing material is fed into the space formed between the two rotating refining members 2, 3, which members are provided with refining surfaces constructed of ridges 13~ I and inter-mediate grooves 15, 16 and which surfaces are arranged to define a refining zone 17 for treatment of the material. Usually, steam is developed simultaneously during the refining operation due to the included liquid, but, steam can also be supplied separately thereto. The lignocellulose containing material passes radially outward through the refining zone 17 and is thereby influenced by action of the centrifugal force created by rotation of the refining members 2, 3 and enters the enclosed housing 1. More particularly, due to the centrifugal force created by the rotation of the refining members 2, 3 about their common axis, the lignocellulose containing material is maintained substantially in contact with the refining surface of the outer refining member 3, thereby permitting steam to be transported radially outward along the grooves 15 in the refining surface of the inner refining member 2. The grooves 16 in the refining surface of the outer refining member 3 are provided with below restrictions or obstructions 18 which force the lignocellulose containing material upward and out of the grooves 16 in order to bring about an efficient processing between the ridges 13, 15 of the two refining surfaces of the inner and outer refining members 2, 3.
The refining members 2, 3 are preferably formed with the refining surfaces of the refining segments 11~ 12 provided in conical arrangement such that the refining zone 17 constantly inclines relative to a radial plane ; - 11 -3L233~

which is normal to the rotational axis of the refiner. This inclination, -I it toe refining angle, as previously noted is preferably selected in a range ox between 15 and 75, and preferably between 20 and 60. The magnitude of the refining angle is determined in view of many factors such as the rotation speed of the refining members 2, 3, the desired dwell time for the lignocellulose containing material in the refining zone 17, the diameter of the refining members 2, 3, the appearance and construction of the refining surfaces, and the desired refining effect and refining capacity.
The refining members 2, 3, alternatively, can be formed with several conically arranged refining surfaces with different angles, or with refining surfaces which, as seen in an axial plane, are curved and preferably spherical.
This implies that the component of the centrifugal force driving the lingo-cellulose containing material in the direction of the refining zone 17 is relatively smaller the further radially outward the material moves. Such effect can be an advantage because the centrifugal force increases with the distance from the common rotational axis of the refining members 2, 3. The dwell time of the lignocellulose containing material in the refining zone 17 can be extended in this way. Due to the above-described inclination of the refining zone 17, the refining will be extended and the length of the refining zone 17 will be greater for a certain diameter of the refining members

2, 3 than in the case of a planar refining zone, such as in conventional disc refiners.
Another embodiment of the present invention is illustrated in Figure 6 and differs from the embodiment shown in Figure 1 substantially only by the inclination of its refining zone 20. The refining segments 21, 22 which define the refining zone 20 are constructed and arranged to have spherical ~2339~

surfaces. The center of such spherical surfaces is located on the common ; rotational axis of the refining members 2, 3. Thus, it will be appreciated that the refining angle increases successively with the radial distance from the common rotational axis. Accordingly, during operation, that part of the centrifugal force acting upon the lignocellulose material in the direction of the refining zone 20 will decrease as the material moves further radially outward from the center of the common rotational axis. Thus, a more uniform feeding of the lignocellulose containing material through the refining zone 20 can be obtained. The spherical surfaces in accordance with this embodiment of the present invention are preferably designed such that the refining angle at the entrance to the refining zone 20 is greater than approximately 5, and the refining angle of the exit from the refining zone is at least 15 and less than or equal to 85. This condition applies also when the refining surfaces are defined by several different conical surfaces.
Further, in accordance with the method of operation of the refiner in accordance with the embodiments disclosed in figures 1 and 6, the lignocellulose containing material intended to be refined, preferably wood chips, is fed by the screw 8 to the other refining member 3 and through the openings 10. Thereafter, the material is moved outward through the refining zone 17, 20 by action of centrifugal force Due to the inclination of the refining zone 17, 20, the centrifugal force simultaneously moves the lingo-cellulose containing material against the refining surface of the outer refining member 3 so that the grooves 15 in the refining surface of the inner refining member 2 are rendered substantially void or free from such material.
Thereby, a relatively free and open passage is formed through which the devil-owed or supplied gaseous medium can be transported radially outward along such ~:33()~

grooves 15. By adjusting the pressure in the enclosed housing 1, the gaseous transport can be adjusted such that the temperature within the refining zone 17, 20 can be controlled.
The lignocellulose containing material is thus treated by the ridges 13, 14 of the refining surfaces which act upon the material by compression and shearing forces. The greatest compression force arises when the lignocellulose containing material is clamped between the edges of the ridges 13, 14, while the shearing forces are greatest when the material is rubbed between the surfaces of the ridges 13, 14. The flow restrictions or obstructions 18 located in the grooves 16 in the refining surface of the outer refining member 3 force the material outward and out of the grooves 16.
The lignocellulose containing material is thereby subjected to a homogeneous and uniform refining by the ridges 13, 14, without being disturbed by interference from the steam passing through the refining zone 17, 20. The refining operation in accordance with the present invention has resulted in an increase in the proportion of long fibers in the refined material and a decrease in the shrives content. This results in an improvement in the quality ; of the refined lignocellulose containing material.
According to the present invention, the rotational speed of the running members 2, 3 can be chosen according to the refining angle at which the refining zone 17, 20 is inclined relative to the rotational axis in order to achieve the desired separation of the gaseous medium from the material being refined and to achieve the desired refining action on the material. Thus, the refining process may be controlled by changing the refining angle and the ; speed of rotation ox the refining members 2, aye well as by varying other variables normally associated with the refining process, such as different :

~L~33~

species of raw material, moisture content, length and width of the refining zone 17, 20 and the efficiency of the energy transfer. Most of these variables can be controlled by adjusting the axial load or refining pressure in the refining zone 17, 20. Also, in this manner, the heat of the escaping steam or other gaseous medium can be effectively utilized to control the pressure and temperature of the lignocellulose material in the refining zone 17, 20, in contrast to the waste of energy resulting from the explosive character of the steam discharge at the periphery of conventional disc refiners.
While the segment patterns shown in Figures 2 - 5 have proved advantageous, both for efficient refining of the pulp material and for the separation of steam or other gaseous medium generated in or supplied to the refining zone 17, 20, it should be understood that the invention is not ; restricted to these segment patterns. Thus, the refining segments 11, 12 may incorporate patterns of various designs, which provide adequate refining of the material and evacuation of steam or other gaseous medium from the refining zone during the refining process, in accordance with the invention as described herein.
In this regard, the grooves 15 in the preferred embodiment are substantially free Ox restrictions or obstructions so as to provide a substantially unimpeded flow of gaseous medium thrilling during operation.
In accordance with another preferred embodiment, minor restrictions or obstructions may be provided in the grooves lo and the advantageous benefits of separation of the gaseous medium from the material being refined and the transport of the gaseous medium out ox the refining zone 17, 20 still achieved.
For instance, the grooves 15 could be provided with transverse ridges (not shown) similar to the obstructions 18 in the grooves 16 of the refining member :LZ3;~0Si~

3, but which transverse ridges are of a height less than the height of the ; ridges 13 in the refining surface of the inner refining member 2, In fact, such transverse ridges could have a height equal to that of the ridges 13 and still achieve adequate separation and transport of the gaseous medium from the refining zone 17, 20 during a refining operation.
Further, it will be appreciated that an important feature of the invention is the splitting of the centrifugal force generated by the rotational movement of the refining members 2, 3 to create one vector force sufficient to deflect the pulp material toward the refining surface of the outwore refining member 3 and create an escape passage for the steam or other gaseous medium along the refining surface of the inner refining member 2, and another vector force sufficient to propel the material through the refining zone 17, 20 with optimum refining efficiency.
The purpose of the grinding or refining process is to fibrous the raw material with minimum damage to the fibers and to achieve the quality required for the specific end use. In this connection, it is of great importance to have a refiner with the highest possible capacity and lowest energy consumption. The invention disclosed herein provides a refiner by which the refining process can easily be regulated for optimum results in response to the several variables associated with the refiner process, as explained herein. or example, this can be achieved by changing the angle of inclination of the refining zone relative to a radial plane normal to the axis of rotation thereof) according to the energy demands of the refining process to thereby control the effect of the centrifugal force so as to separate excess high pressure steam or other gaseous medium, and so as to ' propel the gaseous medium-liberated material at a controlled rate while ~2330~i~

utilizing the liberated gaseous medium to regulate the temperature and pressure in the refining zone. The invention disclosed herein thus presents a novel concept for the refining of lignocellulose containing material, and the system embodying the invention provides a highly efficient and flexible means of influencing the refining result.
It will be appreciated that the refining equipment to which the invention is applicable usually includes conventional instruments which are monitored during operation of the equipment for information as to the state of the refining process, such as load and refining pressure, temperature, rate of material consumption, need of cooling water and other variables influencing the refining process, so that fairly rapid adjustments can be made to meet these variables by the use of the invention described herein.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and application of the present invention. It is further to be understood that numerous modifications may be made in the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of refining lignocellulose containing material in which a gaseous medium is present, comprising, in combination, the steps of refining the material between a pair of opposed inner and outer refining surfaces by rotating the refining surfaces in opposite directions along a common axis, said refining surfaces defining a refining zone therebetween extending radially outward relative to said common axis, portions of said inner refining surface along said refining zone being located radially inward of respective portions of said outer refining surface at the same location along said refining zone;
providing in the construction of the inner and outer refining surfaces for gaseous flow paths along the inner refining surface to induce sufficiently uniform gaseous flow therealong during refining to avoid a stoppage of gaseous flow to an extent which would result in deleteriously affecting the material being treated; and angularly disposing the refining surfaces relative to said common axis such that, during refining, the material being treated is urged by centrifugal force against the outer refining surface and away from the inner refining surface to effect simultaneously the desired refining of the material and the flow of the gaseous medium along said paths whereby to avoid deleter-iously affecting the material.

2. The method of claim 1, wherein said refining step comprises refining in a pressurized atmosphere.

3. The method of claim 1, wherein said step of providing gaseous flow paths comprises providing a series of grooves along said inner refining surface throughout the radial extent of said refining zone.

4. The method of claim 3, wherein said grooves in said inner refining surface are substantially free of flow restrictions therealong throughout the radial extent of said refining zone.

5. The method of claim 1, wherein said refining step comprises refining between a pair of refining surfaces in which at least a portion of the refining surfaces along said refining zone are substantially conical in shape.

6. The method of claim 5, wherein said step of angularly disposing the refining surfaces comprises disposing said refining surfaces so that the angle of said refining surfaces along the radial extent of said refining zone is between 15 and 75 degrees with respect to a plane normal to said common axis.

7. The method of claim 1, wherein said refining step comprises refining between a pair of refining surfaces in which at least a portion of the refining surfaces along said refining zone are spherical in shape so that the angle of said refining zone along the radial extent thereof increases from a first predetermined angle relative to a plane normal to said common axis to a second predetermined angle relative to said plane normal to said common axis.

8. The method Of claim 7, wherein said first predetermined angle is greater than or equal to 5 degrees and said second predetermined angle is greater than 15 degrees and less than or equal to 85 degrees.

9. Apparatus for refining lignocellulose containing material in which a gaseous medium is present, said apparatus comprising a pair of opposed refining members rotatable about a common axis, one of said refining members having an inner refining surface and the other of said refining members having an outer refining surface, said inner and outer refining surfaces defining a refining zone therebetween extending radially outward relative to said common axis, portions of said inner refining surface along said refining zone being located radially inward of respective portions of said outer refining surface at the same location along said refining zone; means for rotating said refining members in opposite directions along said common axis; means associated with said inner and outer refining surfaces defining gaseous flow paths along said inner refining surface to provide uniform gaseous flow therealong during refining of material sufficient to avoid a stoppage of gaseous flow to an extent which would result in deleteriously affecting the material being treated; and wherein said refining surfaces are angularly disposed relative to said common axis such that, during refining, the material being treated is urged by centrifugal force against said outer refining surface and away from said inner refining surface to effect simultaneously the desired refining of the material and the flow of gaseous medium along said gaseous flow paths to avoid deleteriously affecting the material.

10. The apparatus of claim 9, further including means for providing a pressurized atmosphere during operation of said apparatus.

11. The apparatus of claim 9, wherein said outer refining surface including a series of ridges and intermediate grooves therein; said grooves including flow restriction means therein; and wherein said means defining said gaseous flow paths comprise a series of grooves along said inner refining surface throughout the radial extent of said refining zone.

12. The apparatus of claim 11, wherein said grooves in said inner refining surface are substantially free of flow restrictions throughout the radial extent of said repining zone.

13. The apparatus of claim 9, wherein said inner and outer refining surfaces along said refining zone are substantially conical in shape.

14. The apparatus of claim 13, wherein said refining surfaces along the radial extent of said refining zone are at an angle of between 15 and 75 degrees with respect to a plane normal to said common axis.

15. The apparatus of claim 9, wherein said inner and outer refining surfaces along said refining zone and spherical in shape so that the angle of said refining zone along the radial extent thereof increases from a first predetermined angle relative to a plane normal to said common axis to a second predetermined angle relative to said plane normal to said common axis.

16. The apparatus of claim 15, wherein said first predetermined angle is greater than or equal to 5 degrees and said second predetermined angle is greater than 15 degrees and less than or equal to 85 degrees.