WO2000007806A1

WO2000007806A1 - Method and apparatus for feeding a mass of particulate or fibrous material

Info

Publication number: WO2000007806A1
Application number: PCT/CA1999/000679
Authority: WO
Inventors: Murray Burke; Dennis D'agostino; John Macquarrie; Andrew Richard
Original assignee: Stake Technology Ltd.
Priority date: 1998-08-03
Filing date: 1999-07-26
Publication date: 2000-02-17
Also published as: AU5022099A; CN1168596C; HK1039766B; HK1039766A1; CN1309602A; CA2339002C; CA2339002A1

Abstract

A method for feeding a mass of material comprising at least 90 % alpha cellulose to a reactor which operates at a pressure greater than atmospheric pressure and in which all of the mass of material is activated by an activation agent is disclosed.

Description

METHOD AND APPARATUS FOR FEEDING A MASS OF PARTICULATE OR FIBROUS MATERIAL

FIELD OF THE INVENTION

The present invention relates to an apparatus for conveying a mass of particulate material from an apparatus for transporting bulk material, such as a feeding hopper, to a region of processing of the bulk material. The apparatus may be used to convey the mass of material to a reactor which is operating at a pressure greater than atmospheric pressure.

BACKGROUND OF THE INVENTION

United States Patent No. 4,186,658, which was assigned to the present applicant, discloses an apparatus for feeding a mass of particulate and /or fibrous material to a digester which is at an elevated pressure. The apparatus disclosed in this patent comprises a screw conveyor mounted in a conduit and a reciprocating annular piston which is coaxial with, and partially surrounds, the screw conveyor. A first drives means is operatively associated with the screw conveyor means for rotating the screw and transporting the bulk material to a collecting chamber. A second drive means is operatively associated with the annular piston for reciprocating the piston coaxially with the axis of the screw conveyor means and compacting the material in the collecting chamber. The device of this patent presented a substantial breakthrough in the art of feeding particulate or fibrous material into devices such as pressurized reactors (e.g. digesters) since, by using this apparatus, fibrous material of low fibre shear strength could be compacted to an extremely high compactness to form a virtually solid plug through which a pressurized medium from the processing stage located downstream of the apparatus could not penetrate. In United States Patent No. 4,119,025, which was also assigned to the present applicant, a method of operating the device was taught and in United States Patent No. 4,412,485, the use of such an apparatus to dewater a fibrous or the like mass was disclosed.

In general terms, the apparatus as set forth in these patents has a annular piston which surrounds an auger disposed within a conduit. The auger may be operatively associated with a hopper to which fibrous material (e.g. wood chips) may be loaded. The auger feeds the material to a chamber and, in doing so, commences to compact the mass of material. The annular piston further compacts the mass of material in the chamber through its reciprocating action and advances the mass of material through a downstream conduit to a processing stage, for instance, a digester. The reciprocating annular piston causes the mass of material to become a highly compacted mass which may be pushed through a conduit to a high pressure vessel.

The inventions protected by the above United States patents represented a significant advance in the art which was achieved by combining the annular shape of a reciprocating piston with the action of a regular screw conveyor. Thus, material, such as fibrous material which had a low shear strength, could be compacted to a mass which could be fed into a vessel operating at a substantially elevated pressure (e.g. 450 psi).

In United States Patent No. 4,947,743, which was also assigned to the present applicant, improvements to the apparatus of United States Patent No. 4,186,658 were taught. These improvements increased the overall mechanical and energy efficiency of the apparatus.

Combined auger/piston feeders such as that disclosed in United States Patent No. 4,186,658 are well suited for feeding material to a reactor at an elevated pressure and/or temperature. For example, such an apparatus could be used for a continuous pulp preparation process to feed wood chips to a pulper or to feed coal dust to a furnace. Further, as stated at column 2, line 62-68 of United States Patent No, 4,186,658, the device may be used "for maintaining the material conveyed throughout the entire system in a continuous mass which is highly desirable, particularly when applying the present invention in the art of feeding pressurized vessels such as digesters with organic fibrous material, e.g. straw, bagasse, etc.". Straw, bagasse and the like contain cellulose hemicellulose_and lignin and may be processed in a digester to make feed for ruminant animals or pulp for paper production.

High purity cellulose (i.e. cellulose with an alpha cellulose content of about 90% or greater) may also be used in the production of many cellulose derivative end products including films, such as cellulose and photographic films, fibres, such as for use in clothing, abd rheological modifiers such as methyl cellulose and carboxymethyl cellulose. In order to prepare cellulose for such uses, it is generally desirable to "activate" the cellulose. By such a process, the cellulose is contacted with a chemical (generally referred to as a "activation agent"), which breaks hydrogen bonds within the cellulose molecule. By breaking these bonds, or at least some of them, additional reaction sites are provided thus increasing the reactivity of the cellulose for downstream derivization. Different activation processes have been developed. One of these process uses steam as the activation agent. By contacting cellulose at an elevated temperature (e.g. from about 100°C to about 350°C) and pressure (e.g. from about 10 to about 250 atmospheres), hydrogen bonds within the cellulose molecule are broken thus creating more reaction cites.

More recently, ammonia has been taught as an activation agent. See for example United States Patent No. 4,634,470. Using ammonia, cellulose may be activated at a temperature from about 50°C to about 60°C and at a pressure from about 300 to about 350 psig. As these processes operate under substantial pressures, problems have been encountered in developing efficient activation process. One particular problem has been to feed the cellulose to the process vessel (i.e. the digester) when the digester is at steady state conditions. In a continuous process for the activation of cellulose, the cellulose must be fed to a reactor at a substantial elevated pressure. Therefore, some processes are operated as batch processes whereby the cellulose is fed to the digester and the digester is then brought up to operating conditions. However, these processes are not operated commercially operated and, further, they do not operate at low pressures.

While the activation processes are relatively efficient at their steady state conditions, a problem has developed in feeding the cellulose to the reactors at their steady state conditions so as to create an overall process which is still efficient. While other feeders might be used to feed cellulose to a continuously operating digester, none of these could feed over the entire operating pressure range of a digester. As an alternate to these feeders, the applicant tried to use the combined auger/piston apparatus as described in the preceding United States patents to feed high purity cellulose (i.e. cellulose with an alpha cellulose content of about 90% or greater) to a high pressure digester. Surprisingly, it was found that only about 99% of the cellulose was activated after being fed by such an apparatus to a digester where it was subjected to an activation agent at steady state conditions. The remaining 1% remained unreacted thereby complicating downstream processing of the activated cellulose stream. This is not acceptable for commercial production. Therefore, while the combined auger/piston apparatus has proved useful for various applications in the past, it has been problematic for feeding cellulose to a reactor for activation of the cellulose.

SUMMARY OF THE PRESENT INVENTION It has surprisingly been found by the applicant that the failure of the cellulose to be activated in a digester arises from hornification of the cellulose as it passes through the combined auger/piston feeding apparatus. The hornification of the material creates a hardened material which cannot be fully activated upon contact with the activation agent.

More surprisingly, the applicant was able to determine that the hornification occurred in the outer annular band of the mass of material as it passes longitudinally through the apparatus. Figure 1 shows the radial variation of plug density across the centre of the compression tube of a combined auger/piston feeder along the line 1-1 in Figure 2. As shown in this graph, the density of the plug varies substantially from the centre of the feeder to the outer annular periphery of the tube. This is particularly surprising given that in United States Patent No. 4,947,743, the applicant taught that the leading face of the piston may have a tapered portion which would direct a portion of the material radially inwardly (see column 8, lines 11-15 and Figure 7). The present invention provides a method to feed cellulose to a digester so that effectively all of the cellulose may be activated by an activation agent.

In accordance with the present invention there is provided a method for feeding a mass of material comprising at least 90% alpha cellulose to a reactor which operates at a pressure greater than atmospheric pressure and in which the mass of material is exposed to an activation agent which comprises the step of subjecting the mass of material to pressures and temperatures sufficient to deliver the mass of material to the reactor and below the pressure and temperature at which hornification of the mass of material occurs.

In accordance with the present invention there is also provided a method for feeding a mass of material comprising at least 90% alpha cellulose to a reactor which operates at a pressure greater than atmospheric pressure and in which the mass of material is exposed to an activation agent which comprises the step of relieving the pressure of the mass of material as it passes downstream through the feeder to prevent sintering of the mass of material in the feeder. In accordance with the present invention there is also provided a method for producing an activated cellulose comprising the steps of:

(a) introducing a mass of material comprising cellulose into a feeder;

(b) subjecting the mass of material to pressures and temperatures sufficient to deliver the mass of material to a reactor which operates at a pressure greater than atmospheric pressure while maintaining the mass of material below the pressure and temperature at which hornification of the mass of material occurs;

(c) activating the cellulose in the mass of material in the reactor in the presence of an activation agent to form an activated cellulose; and, (d) discharging the activated cellulose from the digester.

In one embodiment, the mass of material is maintained below its sintering temperature to prevent hornification of the mass of material. The mass of material may be maintained at a temperature below its sintering temperature by cooling at least a portion of the surfaces of the feeder which are in contact with the mass of material.

Alternately, the mass of material may be maintained at a temperature below its sintering temperature by cooling at least a portion of the surfaces of the feeder at which the mass of material is initially compacted. In one embodiment, the feeder may comprise a first conduit provided with a screw conveyor, a reciprocating annular piston coaxial with and disposed in the first conduit, and a second conduit extending from the first conduit towards the digester. The mass of material may be maintained at a temperature below its sintering temperature by cooling one or more of the first conduit, the screw conveyor, the piston and at least the upstream end of the second conduit. In another embodiment, the feeder may comprise a first conduit provided with a screw conveyor and having a discharge end, an intermediate chamber at the discharge end of the first conduit, a reciprocating annular piston coaxial with and disposed in the intermediate chamber, and a second conduit extending from the intermediate chamber towards the digester. The mass of material may be maintained at a temperature below its sintering temperature by cooling one or more of the first conduit, the intermediate chamber, the screw conveyor, the piston and at least the upstream end of the second conduit.

In a further embodiment, the feeder may have a longitudinally extending conduit and the method comprises the step of passing the mass of material through the conduit while subjecting the mass of material to compressional forces to form a continuous, compacted plug approximating in cross section the cross section of the conduit, and maintaining the density of the outer annular section of the plug below a density at which the outer annular section of the plug will sinter. Preferably, the outer annular section of the plug is maintained below 120 lb/ft³, more preferably below 95 lb/ft³, and most preferably below 80 lb /ft³.

The method of the instant invention may be operated by using an apparatus defining a longitudinally extending passage and a longitudinal axis for feeding a mass of material comprised of solid particles and /or fibres to a reactor which operates at a pressure greater than atmospheric pressure in which the mass of material is contacted with an activation agent to activate the cellulose and which comprises: (a) a first conduit having a screw conveyor, the first conduit having an outer wall with an inner surface defining a portion of the passage;

(b) an intermediate chamber at the discharge end of the screw conveyor the intermediate chamber having an outer wall with an inner surface defining a portion of the passage; (c) a reciprocating annular piston coaxial with and disposed in the intermediate chamber, the piston having a forward face;

(d) a second conduit extending downstream from the intermediate chamber towards the reactor, the second conduit having an upstream section extending downstream from the intermediate chamber, a downstream section positioned downstream of the upstream section and an outer wall with an inner surface defining a portion of the passage; and, at least one member selected from the group consisting of:

(e) at least one of the screw conveyor, the intermediate chamber and the upstream section of the second conduit having a heat exchanger having a heat exchange surface for cooling the mass of material;

(f) at least one of the inner surface of the intermediate chamber and the inner surface of the second conduit being relieved radially outwardly thereby reducing the compressive forces on the portion of the mass of material in contact with the relieved surface; and,

(g) all of the forward face of the piston configured not to impart an outward momentum to the mass of material thereby directing the mass of material away from the inner surface of the intermediate chamber, whereby the at least one member is selected to maintain the pressure and temperature of the mass of material below the pressure and temperature at which hornification of the mass of material occurs to thereby permit the mass of material to be activated by its passage through the reactor. In one embodiment, all of the forward face is configured to impart a forward momentum to the mass of material. In another embodiment, the forward face comprises a frustoconical angled surface coaxial with the longitudinal axis and convergent in a direction upstream of the intermediate chamber. The frustoconical angled surface may have an apex angle of 178 to 90°, more preferably 160 to 120° and most preferably 160 to 140°.

In another embodiment, the apparatus may have a temperature sensor to monitor the temperature of the heat exchange surface, and a temperature adjustment member to adjust the temperature of the cooling fluid in the heat exchanger to prevent the mass of material from dropping below its freezing point.

In another embodiment, the interior of the conveyor screw is hollow to define a passageway for a cooling fluid to pass therethrough while the feeder is in operation.

In another embodiment, the intermediate chamber may be provided with a cooling jacket on the exterior surface thereof, the cooling jacket defining a passageway for a cooling fluid to pass therethrough while the feeder is in operation. In an alternate embodiment, or in addition thereto, the second conduit may be provided with a cooling jacket on the exterior surface thereof, the cooling jacket defining a passageway for a cooling fluid to pass therethrough while the feeder is in operation. One or both of the cooling jackets may define a spiral passage through which the cooling fluid passes.

In another embodiment, the inner surface of the second conduit adjacent the intermediate chamber has a diameter greater than the diameter of the inner surface of the intermediate chamber adjacent the second conduit thereby reducing the compressive forces on the portion of the mass of material as it passes from the intermediate chamber to the second conduit. In another embodiment, the inner surface of the intermediate chamber is tapered radially outwardly from its upstream end to its downstream end. In another embodiment, the inner surface of the second conduit is tapered radially outwardly from its upstream end to its downstream end.

In another embodiment, the apparatus also has an insert member extending between the downstream end of the second conduit and the reactor, the insert member having an inner surface, the inner surface of the insert member adjacent the second conduit having a diameter greater than the diameter of the inner surface of the second conduit adjacent the insert member thereby reducing the compressive forces on the portion of the mass of material as it passes from the second conduit to the insert member.

In another embodiment, at least one member selected from the group consisting of:

(a) the inner surface of the intermediate chamber is relieved radially outwardly;

(b) the inner surface of the second conduit is relieved radially outwardly; and,

(c) all of the forward face of the piston is configured not to impart an outward momentum to the mass of material, to allow the mass of material to expand radially outwardly due to the Poisson effect while reducing the frictional forces between the mass of material and the inner surfaces to maintain the mass of material below the sintering temperature as the mass of material passes through the feeder. In accordance with the instant invention, there is also provided an apparatus defining a longitudinally extending passage and a longitudinal axis for feeding a mass of material comprised of solid particles and /or fibres to a reactor which operates at a pressure greater than atmospheric pressure and which comprises: (a) a first conduit having a screw conveyor, the first conduit having an outer wall with an inner surface defining a portion of the passage; (b) an intermediate chamber at the discharge end of the screw conveyor the intermediate chamber having an outer wall with an inner surface defining a portion of the passage; (c) a reciprocating annular piston coaxial with and disposed in the intermediate chamber, the piston having a forward face;

(e) at least one of the screw conveyor, the intermediate chamber and the upstream section of the second conduit having a heat exchange surface for cooling the mass of material; (f) the inner surface of the second conduit adjacent the intermediate chamber having a diameter greater than the diameter of the inner surface of the intermediate chamber adjacent the second conduit thereby reducing the compressive forces on the portion of the mass of material as it passes from the intermediate chamber to the second conduit; and,

(g) all of the forward face of the piston configured not to impart an outward momentum to the mass of material thereby directing the mass of material away from the inner surface of the intermediate chamber.

In combination with one or more of the embodiments set out above, or in lieu thereof, the interior of the piston screw is hollow to define a passageway for a cooling fluid to pass therethrough while the feeder is in operation.

One advantage of the instant invention is that a material which contains 90% or more alpha cellulose may be efficiently fed by a combined auger/piston feeding apparatus to a digester at an elevated pressure where all, or effectively all, of the alpha cellulose may be activated. Accordingly, the advantages and reliability of the combined auger/piston feeding apparatus may now be used in a process of the activation of cellulose.

DESCRIPTION OF THE DRAWING FIGURES

These and other advantages of the instant invention will be more fully and particularly described in accordance with the following description of a preferred embodiment of the invention in which:

Figure 1 is a graph of the radial variation of plug density across the centre of a compression tube;

Figure 2 is a partial, sectional view of an embodiment of a combined auger /piston feeder as connected to a reactor; Figure 3 is a plan view of the feeder of Figure 2;

Figure 4 is a side elevation view of the feeder of Figure 2;

Figure 5 is a simplified hydraulic diagram showing an embodiment of a drive means for the compacting pistons of the combined screw /auger feeder; Figure 6 is a sectional view of a feeder according to the instant invention taken along the centre line of the apparatus;

Figure 7 is an enlargement of a portion of Figure 6; and,

Figure 8 is a sectional view of the embodiment of Figure 6 showing additional features.

DESCRIPTION OF PREFERRED EMBODIMENT The instant invention relates to improvements in combined auger/piston feeders which are known in the art. Such devices have been previously disclosed in United States Patent Nos. 4,186,658; 4,199,025 and 4,947,743, all of which are incorporated herein by reference. The following is a brief description of a standard combined auger/piston feeder as disclosed therein.

In a combined auger/piston feeder, screw 2 is designed to transport a selected mass of material from an apparatus which supplies the mass of material to the combined auger /piston feeder, such as a hopper (not shown), to a discharge end downstream of the hopper.

Turning now to Figure 2, reference numeral 1 designates the bottom outlet 1 of a hopper (not shown) preferably located above one end of an axially extending screw 2 of the conveyor, the screw having a continuous helix 3 extending along the screw. As best seen from Figures 3 and 4, the screw 2 may be fixedly secured to one end of a shaft 4 which is supported, e.g., by bearings mounted in bearing housings 5, 6 which are fixedly secured, e.g., to a base frame 7. The opposite end of shaft 4 may terminate in a gear box 8, whose input in driven, e.g., by a V-belt drive 9 (Figure 4) operatively associated with a drive motor 10.

The opposite end of the screw 2 terminates in proximity to an inlet portion 11 (Figure 2) of a conduit 12, the outlet portion 13 of conduit 12 terminating at a reactor such as a pressurized digester 14. It will be appreciated from Figure 2, that the conduit 12 is maintained in permanent communication with the interior of reactor 14. The term, "permanent communication" in this context means that the combined auger/piston feeder does not constitute any valve or the like separating the outlet 13 of the conduit from the hopper.

The conveyor screw 2 is mounted for rotation within a tubular section 15 whose interior may be provided with four axially elongated ribs 16 which are normally maintained in sliding contact with the periphery of the helix 3 as shown in Figure 2. The exterior of tubular section 15 slidably receives an axially elongated, annular piston 17 which is mounted to move in the axial direction back and forth on the outer side of tubular section 15.

The end of piston 17 is provided with an annular ring 18. Annular ring 18 may be mounted to piston 17 by, e.g., screws 18a. The interior of ring 18, together with the adjacent portion of the interior of piston 17 form an intermediate chamber 19 downstream of tubular section 15. Intermediate chamber 19 is located between the end of the conveyor screw 2 and the inlet 11 of the conduit 12. It will be appreciate from the above that, in general terms, the screw conveyor (2, 3, 15, 16,) is arranged for advancing a mass of material in an generally axial direction away from the region of the outlet of a hopper towards inlet 11 of tubular conduit 12. The outlet of conduit 12 is in a permanent communication with a reactor or the like at a pressure greater than atmospheric pressure, such as a reactor 14. It is clearly seen from Figures 2, 3 and 4 that the conduit 12 extends generally coaxially with the screw conveyor. The foregoing description also shows, with reference to Figure 2, an intermediate chamber 19 at the discharge end of the screw conveyor. Chamber 19 is also generally coaxial with the screw conveyor and is located between the screw conveyor and conduit 12. The chamber 19 is normally in communication with the screw conveyor and also with conduit 12.

Annular ring 18 forms the forward face of the annular piston 17 turned towards the reactor 14. In general terms, the reciprocating piston (17, 18) has a forward face disposed at the intermediate chamber 19 for a reciprocating movement generally coaxially with the screw conveyor with the forward face of said piston means being turned towards the reactor 14.

The assembly of the shaft 4, of the gear box 8, drive 9 and the motor 10 are also referred to as "first drive means for rotating the screw conveyor". Turning now to Figure 3, fixedly secured to the exterior of piston 17 and extending horizontally radially from each side thereof is a boss 20, the radially outside end of each of the bosses 20 being fixedly secured to a portion of a rod 21 slidably received in a housing 22, which is fixedly secured, e.g., to base frame 7. Each of the bosses 20 protrudes through a horizontally elongated slot 23 (bottom of Figure 3) provided in the side of the tubular section 15 housing the piston 17. One end of each of the rods 21 is connected, over a flexible joint 24, with a piston rod 25 of a hydraulic cylinder 26, the opposite end of each of cylinders 26 being pivotally secured to a bracket 27 fixed, e.g., to the base frame 7.

Referring now to the diagrammatic drawing of Figure 5, the cylinder 26 is provide with a piston 28. One end of the interior of the cylinder 26 communicates with a line 29, the opposite end of the cylinder 26 communicating with a line 30. The opposite ends of lines 29, 30 are connected to the output end of a control valve 31. The opposite end of the control valve 31 is connected to a further line 32 which, in turn, communicates with a safety discharge branch 33 and with a drive branch 34. The branch 34 is divided into a low volume, high pressure line 35 and a high volume, low pressure line 36, the lines 35 and 36 communicating with a high pressure, low volume pump 37 and with a low pressure, high volume pump 38, respectively. The line 36 is provided with a check valve 39. A discharge conduit 40 provided with a pilot valve 41 communicates a portion of line 36 between the check valve 39 and the pump 38 with a sump 42. The pilot valve 41 is operatively connected with a pilot line 43 which is in communication with the line 32 referred to above. The control valve 31 is selectively adjustable to communicate line 32 with the sump 42. the system of each of the cylinders 26 and of the associated hydraulic system as referred to in Figure 5, can also be referred to in general terms as "second drive means for reciprocating the piston". The operation of the described portions of this embodiment of the combined auger/piston feeder apparatus is as follows.

A switch (not shown) of the motor 10 is actuated to activate the motor 10 simultaneously with the drive of pumps 38 and 37. The pilot valve 41 is now closed. The fluid delivered by pumps 37, 38 flows via line 32 to the control valve 31 and back into sump 42. On actuation of the control valve 31, the flow is directed from line 32 to line 29, while line 30 now communicates with sump 42. The pressurized fluid drives piston 28 to the right-hand side. Once the piston reaches its position opposite to that shown in Figure 5, the control valve 31 is reversed to communicate line 32 with line 30 and line 20 with sump 42. Accordingly, the pressurized fluid delivered by pump 37 and 38 now drives the piston 28 from the right-hand side to the left-hand side, as viewed in Figure 5. The frequency of the reciprocating motion of the piston 28 and thus of the hollow piston 17 may be in the range of approximately one stroke per second.

Accordingly, with the first and second drive means being actuated, the screw 2 rotates to deliver the material from the outlet 1 of the hopper towards the chamber 19 at the outlet end of the conveyor screw 2. The material, while conveyed by the screw, is simultaneously compacted by the action of the screw and accumulates in the region of chamber 19, to further advance to the right of Figure 2 into the inlet 11 of the conduit 12. The material eventually fills in the entire cross- section of the conduit 12 and is further advanced by the reciprocating motion of the hollow piston 17 whose end ring 18 axially pushes the accumulated mass towards the reactor 14. The advancing action of the piston further compacts the material which, eventually, forms a plug whose density is considerably increased in comparison with the density present at the chamber 19 at which the material leaves the screw conveyor area. It will thus be appreciated that the advancement of the compacted mass through the conduit 12 is effected solely by the action of reciprocating hollow piston 17, while the screw conveyor 2 continuously delivers further material to be compacted by the hollow piston. Reactor 14 may be at a substantially elevated pressure, e.g., 750 psig. The combined action of screw 2 and piston 17 is sufficient to form a plug which may be moved downstream into reactor 14, overcoming the upstream pressure exerted on the plug by the elevated pressure in reactor 14 while preventing any release of pressure (e.g. a blow back) through chamber 19.

It will be appreciated that in general terms, the degree of compacting of said mass by the action of the screw 2 may also be referred to as "a first degree of compactness." In general terms, the mass of the conveyed material may be said to be discharged from a discharge area of the screw conveyor (chamber 19) into a second region (inlet 11) which is axially spaced downstream of the first region (i.e. chamber 19). Furthermore, in general terms, the portion of the conveyed mass located in the second region, or at inlet 11, is subjected to an intermittent force (generated by the hollow piston) which is directed to further advance the mass away from the first region (i.e. from chamber 19) in a direction generally coaxial with the centre line of the screw conveyor.

It is also apparent from the above description that the piston exerts a force on the mass located downstream of the inlet 11 (also referred as "the second region") to overcome the pressure exerted by the conditions in reactor 14 on the plug at outlet 13. Due to these opposed pressures, the plug is subjected to a force frictionally retarding the surface of the mass relative to the intermittent force to assist in the compacting of the mass. This frictional force acts at the interior wall of the conduit 12. Thus, the mass advancing through conduit 12 is compacted by the action of the piston 17 to a second degree of compacting which is in excess of the first degree of compacting effected solely by the action of screw conveyor. It will be appreciated that the second degree of compacting does not subject the conveyor screw 2 to any stress additional to that necessary for conveying and precompacting the material delivered to the chamber 19. Accordingly, the overall assembly of the screw conveyor does not have to be unnecessary bulky. Furthermore, the mechanism of the screw conveyor is not subject to an excessive wear during the operation.

Referring to Figure 6, reactor 14 may have incorporated therein choke cone 50 which is mounted on shaft 52. Insert 54 may be positioned between conduit 12 and reactor 14. Choke cone 50 may extend from reactor 14 into insert 54. Insert 54 has a recess which is adapted to receive therein choke cone 50 when choke cone 50 is fully inserted into recess 54 (such as is shown in Figure 6). In this position, choke cone 50 completely seals reactor 14 from conduit 12.

Shaft 52 is axially movably mounted in reactor 14 so to be able to move from the fully extended position (as shown in Figure 6) to a retracted position in which insert 54 is in communication with reactor 14. To this end, shaft 52 may extend through member 56 which seals reactor 14 and defines an axially extending conduit to guide shaft 52. Distal end 58 of shaft 52 is mounted in housing 60 which may be moved by means known in the art (not shown) from the position shown in Figure 6 to a retracted position denoted by the dotted outline in Figure 6 denoted 60'.

Accordingly, when housing 60 is in the position denoted 60' in Figure 6, choke cone 50 may extend only part way into insert 54. The plug encounters choke cone 50 as it passes through the feeder apparatus into reactor 14. Choke cone 50 thus assists in breaking up plug 50 as it enters reactor 14.

During a stroke, the piston exerts substantial force on the fibres to compress the fibres as annular ring 18 moves from the position shown in solid line in Figure 2 to the position shown in dotted line in Figure 2. Additional force is imparted to overcome the resistance to the flow of the plug along conduit 12. This comprises the work to overcome dynamic friction (i.e. between the plug and the wall of conduit 12), the work to overcome the pressure from reactor 14 which is exerted on the end of the plug at outlet 13 and the work to overcome the resistance to the flow of the plug by choke cone 50. Accordingly, a substantial amount of the force which is imparted by piston 17 onto the mass of material is required to perform the actual compression of the fibres.

As discussed above, combined auger /piston feeders have been used to transport particulate and /or fibrous material. However, when such feeders were tested with reactors for producing an activated cellulose, it was noted that not all of the cellulose was activated during the passage through a reactor. In the best trials which were conducted by the applicant, only up to 99% of the cellulose was activated. While this is a very high yield, in cellulose activation processes, it is important that no significant quantities of cellulose remain in an inactivated state so that an activated cellulose may be prepared for further processing.

The mass of material which is fed to a reactor for cellulose activation comprises a large proportion of cellulose bearing material and a minor proportion of impurities. In particular, the mass of material which is fed to a reactor may comprise at least 89% alpha cellulose, based upon the weight of the total mass of the solid material fed to a reactor 14, more preferably greater than 90% and, most preferably greater than 92%.

The water content of the material which is fed to a reactor for cellulose activation will vary depending upon the process. For example, if steam is the activation agent, then the mass of material may have a water content from about 10 to about 80, more preferably from about 30 to about 70, and most preferably from about 40 to about 60 weight percent water based upon the weight of the total mass and water fed to the reactor. If, on the other hand, the activation agent is ammonia, then the mass of material may have a water content from about 4 to about 15, more preferably from about 5 to about 10, and most preferably from about 6 to about 9 weight percent, based upon the total weight of the water and the mass of material which is fed to the reactor.

Processes for the preparation of suitable cellulose for feeding to a digester are known are known in the art. Typically, the classic acidic sulfite process or pre-hydrolyzed kraft process are used. These are described in Wood: Chemistry, Ultrastructure, Reactions, D. Fengel and G. Wegener, Walter de Gruyter, Berlin, 1989 at pages 414- 481 which is incorparated herein by reference. In research conducted by the applicant, it has been determined that undue hardening of the alpha cellulose as it passes through the feeder apparatus causes a change in the cellulose which prevents the cellulose from being activated when contacted by the activation agent. This hardening or hornification, may be caused by the cellulose being subjected to excessive pressures or excessive temperatures, or combinations thereof, as the feed material is transported through the feeder apparatus. When the feed material is subjected to a temperature and/or pressure which is too high (the "hornification point"), the cellulose in the feed material becomes hardened and not capable of being activated in the reactor.

The exact pressure and temperature at which hornification will occur varies depending upon the water content of the material delivered to the apparatus and the manner in which the material is prepared for feeding (i.e. the cutting/shredding method, the particle size of the material and the like). Without being limited by theory, the applicant believes that the greater the pressure, the lower the temperature at which hornification may occur. Conversely, the greater the temperature, the lower the pressure at which hornification may occur. Therefore, in accordance with one embodiment of the instant invention, the internal shape of the feeder apparatus is reconfigured so as to limit the maximum temperature to which the feed material is subjected to as it travels through the apparatus. In particular, it has surprisingly been found that the hornification occurs in the radially outer annular band of the mass of material as it passes axially through the feeder. This is the mass of material which is closest to the inner wall of conduit 12. Therefore, the internal configuration of chamber 19, conduit 12, insert 54 and /or annular ring 18, as well as the position of choke cone 50, may be modified to relieve the pressure on the mass of material as it passes downstream through the feeder. Preferably, the radially outer annular section of the plug is maintained at a density below 120 lbs /ft³, more preferably below about 95 lbs /ft³, and most preferably, below about 80 lbs /ft³.

The temperature of the plug varies as it passes through the feeder apparatus. The plug is heated by several phenomena including kinetic energy from the physical force of compaction, friction between the plug and the inner wall of chamber 19, conduit 12 and insert 54, and conduction and /or convection as heat is transmitted from reactor 14 into the plug and the feeder apparatus. If the temperature of the cellulose exceeds the sintering temperature (i.e. the temperature at which the alpha cellulose commences to degrade), then all of the cellulose will not be able to be activated in reactor 14. The temperature of the plug may therefore vary greatly between the axial centre line of the feeder and the radially outward portion of the feeder and, in addition, between inlet 11 and outlet 13. It has been found that by maintaining the temperature of the plug (i.e. the mass of material) below its sintering temperature and, more preferably, below its sintering temperature and at a density less than 120 lbs/ft³, more preferably less than 95 lbs/ft³, and most preferably below 80 lbs/ft³, the alpha cellulose will not be subjected to hornification.

In one embodiment, the plug of material is maintained at a temperature below its sintering temperature by cooling at least a portion of the surfaces of the feeder which are in contact with the mass of material as it passes downstream through the feeder to form the plug to enter reactor 14. In another embodiment, at least a portion of the surfaces of the feeder at which the mass of material is initially compacted are cooled. This may be achieved by cooling one or more of tubular section 15, screw 2, piston 17, chamber 19 and at least the upstream end of conduit 12 (i.e. that portion adjacent inlet 11) or combinations thereof.

Referring to Figure 8, tubular section 15 is shown as being in flow communication with conduit 12. While section 15 and conduit 12 may be integrally formed, it is preferred that they are each separate units that are connected together. To that end, section 15 is provided with flanges 62 and conduit 12 is provided with flanges 64. Flanges 62 and 64 have openings therethrough (not shown) for receiving bolt 66. Bolt 66 has a head 68 which abuts against flange 62. The opposed end of bolt 66 has a threaded end for receiving a nut 70. Engagement of nut 70 on the end of bolt 66 secures tubular section 15 to conduit 12. It will be appreciated by those skilled in the art that other methods of connecting the screw section with the conduit 12 may be utilized.

In the preferred embodiment, the apparatus also includes a reactor insert 54 that is a separate unit to conduit 12. It is to be appreciated that the function of insert 54 may be incorporated into conduit 12. Reactor insert 54 may be secured to conduit 12 and reactor 14 by any means known in the art. As shown in Figures 7 and 9, the downstream end of conduit 12 may be provided with flanges 90. The upstream end of reactor insert 54 may be provided with flanges 52. A bolt, such as bolt 66 which is used to connect tubular section 15 to conduit 12, may be used to secure flanges 90 and 92 together (not shown). The downstream end of reactor insert 54 may be affixed to reactor 14 by any means known in the art, and preferably, it is removably attached thereto such as by means of screws and the like.

Cooling may be provided to screw 2 by providing a hollow section 72 therein (see Figure 8) through which a cooling fluid, such as water and the like, may be circulated. Accordingly, any of the feed material which is in contact with the surface of screw 2 and helix 3 may be cooled.

Cooling may also be provided to the mass of material in tubular section 15 by providing an annular cooling jacket which surrounds a portion, and preferably substantially all of, the exterior surface of tubular section 15. Referring to Figures 7-9, cooling jacket 74 may be provided on the exterior surface of tubular section 15. This cooling jacket will provide cooling, in particular, to the portion of the mass of material which is in contact with inner surface 15a of tubular section 15.

As shown in Figure 2, piston 17 is positioned immediately radially outward of tubular section 15. In such a case, cooling jacket 74 may terminates adjacent the position marking the rearward most travel of piston 17. To provide additional cooling to the material which undergoes compaction by screw 2, piston 17 may be provided with a hollow section similar to hollow section 72 of screw 2. Alternately, if piston 17 is positioned sufficiently radially outwardly from tubular section 15, cooling jacket 74 may extend upstream to a position adjacent the rearward most position of travel of annular ring 18 (not shown).

The material which has been compacted by screw 2 is further compacted in intermediate chamber 19 by means of piston 17. The action of piston 17 may produce substantial heating. Accordingly, cooling may be provided in this area by means of a cooling jacket 76 which may be positioned immediately radially outwardly from intermediate chamber 19.

Cooling may be provided to conduit 12 by positioning a cooling jacket 78 radially outwardly thereof. Each of the cooling jackets 74, 76 and 78 may be of any type known in the art. Such cooling jackets have at least one inlet port and at least one outlet port and, they may have a plurality of inlet ports and outlet ports. Further, the cooling fluid (which may be a liquid or a gas and is preferably cooled water), may flow in an upstream direction or a downstream direction with respect to the plug which is fed through the feeder apparatus. For example, referring to Figure 8, cooling jacket 78 may have inlet port 80 and outlet port 82 which is positioned in the downstream direction from inlet port 80. The cooling fluid enters inlet port 80 and travels through cooling jacket 78 to outlet port 82. Due to the high level of compaction which is associated with the formation of the plug adjacent inlet 11 of conduit 12, inlet 80 is preferably positioned adjacent inlet 80 so as to provide the maximum cooling adjacent chamber 19.

As the cooling fluid passes through the cooling jackets, the cooling fluid may have the tendency to bypass a portion of the cooling jacket. Therefore, to ensure proper cooling, it is preferred that the cooling jacket is baffled (such as by helical member 84 of cooling jacket 78) to direct the cooling fluid to pass sequentially longitudinally through the cooling jacket.

If the cellulose is exposed to a low temperature for an extended period of time, then the cellulose may also undergo a change whereby it will not be activated by an activation agent in reactor 14. Therefore, temperature sensors may be provided at various locations in the feeder apparatus to prevent the cooling jacket from excessively cooling the mass of material which is being fed to reactor 14. The temperature sensors may monitor the temperature of the heat exchange surface and adjust the temperature of the cooling fluid in the heat exchanger if the sensors detect that the heat exchange surface is becoming either too hot (i.e. it is approaching a point at which the cellulose may become sintered) or too low (i.e. it is approaching a temperature at which the cellulose may become difficult to activate). The temperature of the heat exchange surface may be moderated by, for example, adjusting the temperature of the input stream to the heat exchanger and /or changing the rate of flow of cooling fluid through the heat exchanger. The pressure to which the mass of material is subjected as it passes through the feeder apparatus may be decreased by at least one of inner surface 19a of chamber 19, inner surface 12a of conduit 12 and inner surface 94 of insert 54 being relieved radially outwardly and/or all of the forward face of annular ring 18 being configured not to impart an outward momentum to the mass of material thereby directing the mass of material away from inner surface 19a of intermediate chamber 19.

Referring to Figure 7, it can been seen that forward face 18b of annular ring 18 is configured so as to direct the mass of material forwardly and inwardly. Forward face 18b may comprise a frustoconical angled surface which is coaxial with longitudinal axis

"A" of the feeder apparatus. The apex angle α may vary from about 178 to about 90°, more preferably from about 160 to about 120° and, most preferably, from about 140 to about 120°.

In United States Patent No. 4,947,743, which is also owned by the applicant, the applicant taught that the inner portion of the forward face of the piston may have a section which is angled inwardly. In experiments which were conducted by the applicant, it was surprisingly found that even with the radially inner portion of the forward face of the piston being angled, hornification of the cellulose still occurred. It has been found that by extending the angled surface to the entire forward face of the piston, that the alpha cellulose is not subjected to hornification. Therefore, in one preferred embodiment of this invention, all of the forward face of the piston is angled. In an alternate embodiment, at least the outer portion forward face 18b is so configured.

In one embodiment, inner surface 19a of intermediate chamber 19 is tapered radially outwardly from its upstream end to its downstream end adjacent inlet 11 of conduit 12. As shown in Figure 7, inner surface 19a extends downstream at an angle β to line B which extends parallel to axis A of the feeder apparatus. Angle β is relatively small and may be from about 1 to about 90 minutes, more preferably from about 10 to about 70 minutes and, most preferably, from about 20 to about 50 minutes. The slight downstream taper in inner surface 19a allows the mass of material to expand slightly outwardly as the plug is formed by the compacting action of piston 17. In one embodiment, piston face 18 may be of any particular configuration as is know in the art and inner surface 19a is tapered at an angle β. Alternately, in a more preferred embodiment, front face 18b of annular ring 18 is angled as taught herein and, in addition, inner surface 19a is tapered at an angle β.

In a similar fashion, inner surface 12a may be at an angle β' to line C which is parallel to axis A of the feeder apparatus. As the plug passes downstream through conduit 12, the radially outward taper of inner surface 12a allows the plug to expand outwardly due to the compressive forces which are applied to the plug as it passes through conduit 12. Angle β' may be from about 1 to about 90 minutes, more preferably from about 15 to about 70 minutes and, most preferably, from about 30 to about 50 minutes. As with the taper of inner surface 19a, in one embodiment, inner surface 12a is tapered at an angle β'. Alternately, or at the same time, one or more of inner surface 19a may be tapered an angle β and front face 18b may be angled as taught herein.

Reactor insert 54 has an inner surface 94. Inner surface 94 may also be configured so as to allow the plug to expand outwardly as it passes downstream from inner conduit 12 to reactor 14. Therefore, inner surface 94 of insert 54 may be at an angle to line which is parallel to axis A of the feeder apparatus (not shown). This angle may be from about 1 to about 90 minutes, more preferably from about 15 to about 70 minutes and, most preferably, from about 30 to about 50 minutes. As with the taper of inner surface 19a, in one embodiment, inner surface 94 is tapered at an angle. Alternately, or at the same time, one or more of inner surfaces 19a may be tapered, inner surfaces 12a may be tapered and front face 18b may be angled as taught herein. In a further alternate embodiment, inner surface 12a of conduit 12 adjacent chamber 19 may have a diameter greater than the diameter of inner surface 19a of chamber 19. Referring in particular to Figure 7, the portion of inner surface 12a immediately adjacent chamber 19 is denoted by reference numeral 86. Surface 86 extends relatively sharply radially outwardly so as to provide, in effect, a sudden radial step 88 outwardly from inner surface 19a of chamber 19. This radially outwardly step has been found to have a substantial effect upon the pressure exerted to the outer annular band of a plug as it passes from chamber 19 to conduit 12 without allowing a blow back from reactor 14.

In the embodiment shown in Figure 7, radial step out 88 is provided adjacent inlet 11 so that inner surface 19a and surface 86 define a smooth transition from chamber 19 to conduit 12 and surface 86 merges smoothly with tapered inner surface 12a. In an alternate embodiment, one or more of the inner surfaces 12a and 19a may not be tapered.

As shown in Figures 7 and 9, inner surface 94 of insert 54 may also have a radial diameter greater than the diameter of inner surface 12a adjacent the downstream end of conduit 12 thus creating a radial step out. This radial step out may be shaped in the same manner as for step out 88. Alternately, as shown, inner surface 94 is not curved as is inner surface 86. Instead, there is a radial discontinuity between inner surface 12a and inner surface 94. It will be appreciated that inner surface 94 may have a curved section, akin to inner surface 86. Alternately, or in addition, there may be a radial discontinuity between inner surface 19a and inner surface 12a so that the interface between the inner surfaces of chambers 19 and 12 has a similar profile as compared to the interface of the inner surfaces of conduit 12 and reactor insert 54.

The extent to which one or more of these features may be used to prevent hornification depends upon a number of factors including the amount of taper which is provided (eg. angles β and β'), the degree of the angle of front face 18b (i.e. the size of angle ), the downstream compressive force which is exerted by piston 17 on the mass of material as the plug is formed, the upstream pressure which is exerted on the plug adjacent outlet 13 due to the elevated pressure in reactor 14 and the type and extent of the radial outward step. Preferably, the configuration of front face 18b and/or the inner surface of one or more of chamber 19, conduit 12 and reactor insert 54 are selected to allow the mass of material to expand radially outwardly due to the Poisson effect while reducing the frictional forces between the mass of material and the inner surfaces of the feeder apparatus.

By allowing the plug to expand outwardly due to the compressive forces which are exerted upon it, the frictional forces between the plug and inner surfaces 19a, 12a and 94 are reduced. This reduction in pressure prevents or, in combination with the temperature moderation, assists in preventing, the hornification of the alpha cellulose as it passes downstream through the feeder apparatus to reactor 14. If the step outs are too large and/or the inner surfaces are tapered at too great an angle, then the plug may not expand all the way to the inner surfaces. If the plug does not contact a sufficient portion of inner surfaces 19a, 12a and/or 94, then the pressure in reactor 14 may be able to expand upstream through the feeder apparatus causing a blow out. Further, if the reactor is at an elevated temperature such as above about 80°, then there may be insufficient cooling of the plug due to the gap between the outer surface of the plug and inner surfaces 19a, 12a and/or 94. This may cause the temperature of the plug to increase past the hornification point. Accordingly, the degree of cooling and the relief of pressure must be balanced to ensure that reactor 14 does not suffer from a blow back or other pressure loss while ensuring that the cellulose does not exceed its hornification point.

It will be appreciated by those skilled in the art that the various modifications may be made to the feeder apparatus and all are within the scope of this invention. In particular, it is noted that, for example, inner surface 12a at a position intermediate inlet 11 and outlet 13, may be provided with a step out. Similarly inner surface 54 may be provided with a step out at an intermediate portion thereof. Further only a portion of one or more of the inner surfaces 12a, 19a and 94 may be tapered.

Claims

WE CLAIM

1. A method for feeding a mass of material comprising at least 90% alpha cellulose to a reactor which operates at a pressure greater than atmospheric pressure and in which the mass of material is exposed to an activation agent comprising the step of subjecting the mass of material to pressures and temperatures sufficient to deliver the mass of material to the reactor and below the pressure and temperature at which hornification of the mass of material occurs.

2. The method of claim 1 wherein the temperature of the mass of material is maintained below its sintering temperature to prevent hornification of the mass of material.

3. The method of claim 2 wherein the mass of material is maintained at a temperature below its sintering temperature by cooling at least a portion of the surfaces of the feeder which are in contact with the mass of material.

4. The method of claim 1 wherein the mass of material is maintained at a temperature below its sintering temperature by cooling at least a portion of the surfaces of the feeder at which the mass of material is initially compacted.

5. The method of claim 4 wherein the feeder comprises a first conduit provided with a screw conveyor, a reciprocating annular piston coaxial with and disposed in the first conduit, and a second conduit extending from the first conduit towards the digester, the method comprising the step of cooling one or more of the first conduit, the screw conveyor, the piston and at least the upstream end of the second conduit.

6. The method of claim 4 wherein the feeder comprises a first conduit provided with a screw conveyor and having a discharge end, an intermediate chamber at the discharge end of the first conduit, a reciprocating annular piston coaxial with and disposed in the intermediate chamber, and a second conduit extending from the intermediate chamber towards the digester, the method comprising the step of cooling one or more of the first conduit, the intermediate chamber, the screw conveyor, the piston and at least the upstream end of the second conduit.

7. The method of claim 1 wherein the feeder has a longitudinally extending conduit, the method comprising the step of passing the mass of material through the conduit while subjecting the mass of material to compressional forces to form a continuous, compacted plug approximating in cross section the cross section of the conduit, and maintaining the density of the outer annular section of the plug below a density at which the outer annular section of the plug will sinter.

8. The method of claim 7 wherein the outer annular section of the plug is maintained below 95 lb/ft³.

9. A method for feeding a mass of material comprising at least 90% alpha cellulose to a reactor which operates at a pressure greater than atmospheric pressure and in which the mass of material is exposed to an activation agent comprising the step of relieving the pressure of the mass of material as it passes downstream through the feeder to prevent sintering of the mass of material in the feeder.

10. The method of claim 9 wherein the feeder has a longitudinally extending conduit, the method comprising the step of passing the mass of material through the conduit while subjecting the mass of material to compressional forces to form a continuous, compacted plug approximating in cross section the cross section of the conduit, and maintaining the density of the outer annular section of the plug below a density at which the outer annular section of the plug will sinter.

11. The method of claim 10 wherein the outer annular section of the plug is maintained below 95 lb/ft³.

12. A method for producing an activated cellulose comprising the steps of:

(a) introducing a mass of material comprising cellulose into a feeder;

(b) subjecting the mass of material to pressures and temperatures sufficient to deliver the mass of material to a reactor which operates at a pressure greater than atmospheric pressure while maintaining the mass of material below the pressure and temperature at which hornification of the mass of material occurs; (c) activating the cellulose in the mass of material in the reactor in the presence of an activation agent to form an activated cellulose; and, (d) discharging the activated cellulose from the digester.

13. The method of claim 12 wherein the mass of material is maintained at a temperature below its sintering temperature by cooling at least a portion of the surfaces of the feeder which are in contact with the mass of material.

14. The method of claim 12 wherein the mass of material is maintained at a temperature below its sintering temperature by cooling at least a portion of the surfaces of the feeder at which the mass of material is initially compacted.

15. The method of claim 13 wherein the feeder comprises a first conduit provided with a screw conveyor, a reciprocating annular piston coaxial with and disposed in the first conduit, and a second conduit extending from the first conduit towards the digester, the method comprising the step of cooling one or more of the first conduit, the screw conveyor, the piston and at least the upstream end of the second conduit.

16. The method of claim 13 wherein the feeder comprises a first conduit provided with a screw conveyor and having a discharge end, an intermediate chamber at the discharge end of the first conduit, a reciprocating annular piston coaxial with and disposed in the intermediate chamber, and a second conduit extending from the intermediate chamber towards the digester, the method comprising the step of cooling one or more of the first conduit, the intermediate chamber, the screw conveyor, the piston and at least the upstream end of the second conduit.

17. The method of claim 12 wherein the feeder has a longitudinally extending conduit, the method comprising the step of passing the mass of material through the conduit while subjecting the mass of material to compressional forces to form a continuous, compacted plug approximating in cross section the cross section of the conduit, and maintaining the density of the outer annular section of the plug below a density at which the outer annular section of the plug will sinter.

18. The method of claim 17 wherein the outer annular section of the plug is maintained below 95 lb/ft³.

19. An apparatus defining a longitudinally extending passage and a longitudinal axis for feeding a mass of material comprised of solid particles and/or fibres to a reactor which operates at a pressure greater than atmospheric pressure in which the mass of material is contacted with an activation agent to activate the cellulose comprising:

(a) a first conduit having a screw conveyor, the first conduit having an outer wall with an inner surface defining a portion of the passage; (b) an intermediate chamber at the discharge end of the screw conveyor the intermediate chamber having an outer wall with an inner surface defining a portion of the passage;

(c) a reciprocating annular piston coaxial with and disposed in the intermediate chamber, the piston having a forward face;

(d) a second conduit extending downstream from the intermediate chamber towards the reactor, the second conduit having an upstream section extending downstream from the intermediate chamber, a downstream section positioned downstream of the upstream section and an outer wall with an inner surface defining a portion of the passage; and, at least one member selected from the group consisting of: (e) at least one of the screw conveyor, the intermediate chamber and the upstream section of the second conduit having a heat exchanger having a heat exchange surface for cooling the mass of material; (f) at least one of the inner surface of the intermediate chamber and the inner surface of the second conduit being relieved radially outwardly thereby reducing the compressive forces on the portion of the mass of material in contact with the relieved surface; and, (g) all of the forward face of the piston configured not to impart an outward momentum to the mass of material thereby directing the mass of material away from the inner surface of the intermediate chamber, whereby the at least one member is selected to maintain the pressure and temperature of the mass of material below the pressure and temperature at which hornification of the mass of material occurs to thereby permit the mass of material to be activated by its passage through the reactor.

20. The apparatus as claimed in claim 19 wherein all of the forward face is configured to impart a forward momentum to the mass of material.

21. The apparatus as claimed in claim 19 wherein the forward face comprises a frustoconical angled surface coaxial with the longitudinal axis, convergent in a direction upstream of the intermediate chamber.

22. The apparatus as claimed in claim 19 further comprising a temperature sensor to monitor the temperature of the heat exchange surface, and a temperature adjustment member to adjust the temperature of the cooling fluid in the heat exchanger to prevent the mass of material from dropping below its freezing point.

23. The apparatus as claimed in claim 19 further comprising an insert member extending between the downstream end of the second conduit and the reactor, the insert member having an inner surface, the inner surface of the insert member adjacent the second conduit having a diameter greater than the diameter of the inner surface of the second conduit adjacent the insert member thereby reducing the compressive forces on the portion of the mass of material as it passes from the second conduit to the insert member.

24. An apparatus defining a longitudinally extending passage and a longitudinal axis for feeding a mass of material comprised of solid particles and /or fibres to a reactor which operates at a pressure greater than atmospheric pressure comprising:

(a) a first conduit having a screw conveyor, the first conduit having an outer wall with an inner surface defining a portion of the passage;

(b) an intermediate chamber at the discharge end of the screw conveyor the intermediate chamber having an outer wall with an inner surface defining a portion of the passage;

(e) at least one of the screw conveyor, the intermediate chamber and the upstream section of the second conduit having a heat exchange surface for cooling the mass of material;

(f) the inner surface of the second conduit adjacent the intermediate chamber having a diameter greater than the diameter of the inner surface of the intermediate chamber adjacent the second conduit thereby reducing the compressive forces on the portion of the mass of material as it passes from the intermediate chamber to the second 5 conduit; and,

(g) all of the forward face of the piston configured not to impart an outward momentum to the mass of material thereby directing the mass of material away from the inner surface of the intermediate chamber. 10