Apparatus for pressurized refining of lignocellulose material

A multi-stage process, and apparatus for carrying out the process, are provided for refining lignocellulose containing material at high consistency. The lignocellulose material is pretreated to form a mixture of the lignocellulose material and pressurized steam conveyed via the pressure of the pressurized steam to a first refiner, wherein the lignocellulose material is conveyed mechanically into a first refining zone within the first refiner while causing the pressurized steam in the mixture to pass in reverse direction to the lignocellulose to a steam venting outlet to vent the steam from the first refiner. The lignocellulose material fed into the first refining zone is subjected to refining action thereby producing a mixture of partially refined lignocellulose material and pressurized steam developed during the refining action. This mixture of partially refined lignocellulose material and pressurized steam is conveyed via the pressure of the pressurized steam to a second refiner, wherein the partially refined lignocellulose material in the mixture is conveyed mechanically into a second refining zone in said second refiner while causing the pressurized steam in said mixture to pass in reverse direction to the lignocellulose material to a steam venting outlet to vent the steam from the second refiner. The lignocellulose material fed into the second refining zone is subjected to refining action thereby producing a mixture of further refined lignocellulose material and steam developed during said refining action. The further refined lignocellulose material is discharged from the second refiner and separated from the steam developed during the refining action.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the refining of lignocellulose 
material, such as wood chips, in a pressurized environment, and more 
particularly, to a multi-stage method for refining lignocellulose 
material, and an apparatus for carrying out the method, wherein the 
lignocellulose material is refined at pressure in at least an upstream 
stage refining zone and a downstream stage refining zone with the 
lignocellulose material being pneumatically transported between stages by 
the steam generated in the upstream stage refining zone. The method may be 
advantageously carried out by using disc-type refiners and, most 
advantageously, utilizing disc-type refiners incorporating high speed 
shaft driven ribbon feeders. 
It is well known in the art to stage, that is to place in series, a 
plurality of refining zones, typically two, to produce mechanical or 
chemi-mechanical or thermomechanical pulp from lignocellulose material, 
most commonly wood chips. In such conventional systems, it is the common 
practice to pass the lignocellulose material at a high consistency through 
a first pressurized refining zone to produce a semi-refined pulp entrained 
in steam generated within the first refining zone. The semi-refined pulp 
entrained in the steam generated in the first refining zone is passed 
directly to a steam separating device, most commonly a cyclone, wherein 
the steam is separated from the semi-refined pulp and the semi-refined 
pulp is then conveyed, most typically by a screw feeder, to a second stage 
refining zone. The semi-refined pulp is further refined in the second 
refining zone to produce a fully refined pulp again entrained in steam 
generated within the refining zone. The fully refined pulp and steam 
mixture generated in the second refining zone is discharged directly to a 
second steam separating cyclone wherein the steam is separated from the 
pulp and the fully refined pulp recovered. 
Typically, such multi-stage, high consistency refining is carried out 
utilizing in combination a first stage refiner, followed by a steam 
separating cyclone, followed by pulp conveyor means, followed by a second 
stage refiner. One such system is shown in U.S. Pat. No. 3,661,328 wherein 
the wood chips to be refined are first pretreated and then passed to a 
first stage refiner comprising a pressurized double rotating disc refiner 
wherein the chips are initially refined to produce a partially refined 
pulp. The partially refined pulp is conveyed in steam generated in the 
pressurizing refiner zone within the double rotating disc refiner directly 
to a steam separating cyclone wherein the partially refined pulp is 
separated from the steam and recovered. The partially refined pulp is then 
fed from the discharge of the steam separating cyclone by a screw conveyor 
directly to a second refiner comprising an atmospheric double rotating 
disc refiner. 
Another method and apparatus for the multi-stage, high consistency refining 
of wood chips and other lignocellulose material through staged independent 
refiners is disclosed in U.S. Pat. No. 4,298,425. As shown therein, the 
wood chips are first subjected to a grinding operation in the refining 
zone of a pressurized rotating disc type defibrator to produce a partially 
refined pulp consisting of a flocculent mass of initially separated and 
freed fibers entrained in steam generated within the first stage refiner, 
such steam typically having a temperature of 110.degree. to 140.degree. C. 
The partially refined pulp is conveyed in the steam generated within the 
first stage refiner directly from the discharge of the first stage refiner 
to a steam separating cyclone wherein the partially refined pulp is 
separated from the steam and the steam is recovered. The separated 
partially refined pulp is then passed from the discharge of the steam 
recovery cyclone through a screw conveyor to a second stage refiner which 
again is a rotating disc defibrator wherein the pulp material is further 
refined to product the final product pulp. 
Such conventional multi-stage, high consistency refining of lignocellulose 
material may also be carried out using a single machine incorporating two 
refining zones such as shown in U.S. Pat. No. 4,700,900. As disclosed 
therein, the high consistency refining is accomplished using a refiner 
which has two virtually identical but separate refining zones defined in a 
single machine. The wood chips to be processed are first fed by means of a 
screw conveyor to the first stage refining zone and subjected to 
defibrating therein to form a partially refined pulp entrained in steam 
generated within the refining zone. The partially refined pulp entrained 
in the steam generated in the first refining zone is discharged therefrom 
directly to a steam separating cyclone disposed interstage between the 
first stage refining zone and the second stage refining zone. The 
partially refined pulp is separated from the steam generated within the 
first refining zone and discharged from the steam separating cyclone 
directly to a screw conveyor which feeds the partially refined pulp to the 
second stage refining zone within the machine wherein the partially 
refined pulp is further refined to produce the final fully refined pulp 
product. 
It would be advantageous if the partially refined pulp could be discharged 
from the first stage of the refining zone and conveyed in the steam 
generated within the first refining zone directly into a ribbon feeder for 
conveying the partially refined pulp to second refining zone and 
separating the steam therefrom without the use of an interstage cyclone. 
Heretofore, the direct transfer of partially refined pulp from a first 
refining stage to a second refining stage has been limited to low 
consistency pulping operations wherein steam is not generated within the 
refining zone. In low consistency pulping systems, that is systems wherein 
the pulp is processed in an aqueous slurry having a solids content of less 
than about 4% by weight, steam is not generated in the refining step due 
to the fact that there is sufficient liquid in the aqueous pulp slurry to 
absorb the heat generated during the refining step without the formation 
of steam. For example, as shown in U.S. Pat. Nos. 2,864,562 and 3,323,731, 
two pairs of grinding discs disposed within the same machine are operated 
in series with the outlet of the first refining zone connected by a 
substantially U-shaped conduit directly to the inlet of the second 
refining zone. After the pulp fed to the first refining zone between the 
first set of grinding discs is subjected to a grinding treatment therein, 
the partially refined pulp resulting therefrom is conveyed directly to the 
inlet to the second refining zone between the second pair of grinding 
discs wherein further grinding treatment is carried out to produce the 
final product pulp. 
It is an object of the present invention to provide a high consistency 
pressurized multi-stage refining method, and an apparatus for carrying out 
the method, wherein the lignocellulose material is refined under high 
consistency pressurized conditions in at least an upstream refining zone 
and a downstream refining zone with the lignocellulose material being 
conveyed directly from the outlet of the first refining zone to a ribbon 
feeder feeding the second refining zone in the steam generated in the 
upstream stage refining zone. In high consistency refining, that is 
refining wherein the pulp is processed in a gaseous slurry having a solids 
content of 15% by weight or greater, and generally a solids content of 20% 
to 50% by weight, there is insufficient liquid in the pulp slurry to 
absorb the heat generated during the refining step without the formation 
of steam. Naturally, the higher the solids content, i.e. the consistency, 
of the pulp slurry, the greater the amount of steam generated during the 
refining step. 
SUMMARY OF THE INVENTION 
In accordance with the method aspect of the present invention, there is 
provided a multi-stage process, and apparatus for carrying out the 
process, for refining lignocellulose containing material comprising the 
steps of pretreating the lignocellulose material to form a mixture of the 
lignocellulose material and pressurized steam, conveying said mixture of 
lignocellulose material and pressurized steam via the pressure of the 
pressurized steam to a first refining means, mechanically conveying the 
lignocellulose material in the mixture into a refining zone between a pair 
of opposed refining discs of the first refining means while causing the 
pressurized steam in the mixture to pass in reverse direction to the 
lignocellulose to a steam venting outlet to vent the steam from the first 
refining means, subjecting the lignocellulose material fed into the 
refining zone of the first refining means to refining action between a 
pair of relatively rotating opposed refining discs thereby producing a 
mixture of partially refined lignocellulose material and pressurized steam 
developed during the refining action, conveying the mixture of partially 
refined lignocellulose material and pressurized steam via the pressure of 
the pressurized steam to a second refining means, mechanically conveying 
the partially refined lignocellulose material in the mixture into a 
refining zone between a pair of opposed refining discs in said second 
refining means while causing the pressurized steam in said mixture to pass 
in reverse direction to the lignocellulose material to a steam venting 
outlet to vent the steam from the second refining means, subjecting the 
lignocellulose material fed into the refining zone of the second refining 
means to refining action between the relatively rotating refining disc 
thereby producing a mixture of further refined lignocellulose material and 
steam developed during said refining action. The further refined 
lignocellulose material discharged from the second refining means is 
separated from the steam developed during the refining action in the 
second refiner means thereby recovering the further refined lignocellulose 
material.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawing, FIGS. 1 and 2 and V FIGS. 3 and 4 illustrate 
schematically alternate embodiments and the method of the present 
invention wherein the lignocellulose material to be refined is processed 
through two distinct refining stages with the material being transported 
from the first refining zone, i.e., the upstream refining stage, directly 
to a ribbon feeder feeding the second refining zone, i.e., the downstream 
refining stage, via the pressurized steam generated in the first refining 
zone. Although the method of the present invention will hereinafter be 
described with reference to wood chips, it is to be understood that the 
method of the present invention may be applied to refine other forms of 
lignocellulose containing material. 
In the embodiment of the multi-stage method of the present invention 
illustrated in FIGS. 1 and 2, the refining is carried out using a pair of 
disc refiners 10,110 disposed in series with respect to the flow of 
lignocellulose material. Each of the disc refiners 10,110 is the type 
commonly known as a TWIN refiner, such as disclosed in U.S. Pat. Nos. 
3,847,359 or 3,893,631, adapted to carry out the method of the present 
invention. A TWIN refiner has two separate refining zones defined in a 
single refiner apparatus, one refining zone on each side of a central 
rotating disc having attrition plates mounted on each side and flanked on 
each side by an opposed attrition plate which is rotationally fixed 
relative to the central rotating disc. A preferred embodiment of a twin 
refiner adapted for use in the method of the present invention is shown in 
FIG. 5. It is to be understood, however, that a pair of single disc 
refiners may be arranged in series to carry out the method of the present 
invention. 
In the embodiment of the multi-stage method of the present invention 
illustrated in FIGS. 3 and 4, the refining is carried out using a single 
refiner 210 of the type hereinbefore mentioned. The TWIN refiner 
illustrated in FIG. 5 is also adaptable to carry out this embodiment of 
the method of the present invention. When such a refiner is employed to 
carry out the embodiment of the method of the present invention 
illustrated in FIGS. 3 and 4, one side of the refiner serves as the first 
stage or upstream refining zone, while the other side of the refiner 
serves as the second stage or downstream refining zone. Again, the 
material being refined is transported directly from the first stage 
refining zone to a ribbon feeder feeding the second stage refining zone 
via the pressurized steam generated in the first refining zone. 
In the embodiment of the multi-stage pressurized refining process of the 
present invention illustrated in FIGS. 1 and 2, the cellulosic material to 
be refined, which typically comprises low content wood chips, is stored in 
a bin 20 and drops from the hopper 22 thereof into feeder 24, typically a 
screw feeder. From the feeder 24, the wood chip stock is conveyed at a 
controlled rate to and drops through chute 26 into the pretreatment 
apparatus 30 wherein the wood chip stock is mixed with an aqueous solution 
which may simply comprise water without any chemical additives or may 
comprise water having dissolved therein various well known pulp treatment 
chemicals. In any case, the wood chips are mixed with the aqueous solution 
to form a high consistency slurry, that is a slurry having a solids 
content of at least 15% by weight, and typically in the range of 20 to 50% 
by weight, depending on the type of refining apparatus through which the 
infeed stock is to be later refined. The infeed stock slurry then passes 
from the inlet chamber of the pretreatment apparatus 30 to the chip 
fractionator portion 32 thereof wherein the wood chips in the stock slurry 
are subjected to an initial grinding action which fractionates the chips 
to separate long fibers therefrom. In the chip fractionation process 
carried out in the conventional chip fractionator 32 of the pretreatment 
apparatus 30, the heat generated in the steam and cellulosic fiber 
mixture. 
In accordance with one aspect of the present invention, the fiber and steam 
mixture discharging from the pretreatment apparatus 30 is passed through 
feed conduits 34 to the inlet of the first stage refining apparatus 10, 
the cellulosic fiber and steam mixture being conveyed from the discharge 
of the pretreatment apparatus 30 through the conduits 34 to the inlet of 
the refining apparatus 10 via the pressure of the steam in the mixture. 
The infeed stock mixture, comprising the fractionated wood chips entrained 
in steam generated in the chip fractionator passes from the feed conduits 
into the inlet conduits to the refiner 10 which are arranged to direct the 
stock mixture tangentially into the ribbon conveyors 40a,40b in the 
direction of rotation of the ribbon conveyors. As the tangentially 
directed stock mixture is received by the ribbon conveyors 40a,40b, it is 
advanced by the ribbon conveyors 40a,40b to the throat of the refining 
zones on each side of the central rotating disc, the centrifugal forces 
which act upon the fiber portion of the stock mixture due to the high 
speed operation of the ribbon conveyors 40a,40b hold the fiber stock 
around the periphery of the feeder housing thereby permitting the steam to 
flow back through the open central region of the ribbon conveyors 40a,40b 
to the outer end of the feeder housing and through the steam discharge 
passages of the refiner 10 to be vented or preferably, passed to a heat 
recovery system. The fractionated fiber stock is delivered axially by the 
ribbon conveyors 40a,40b to the throat of the refining zones on opposite 
sides of the central rotating disc and is driven by centrifugal force of 
the rotating disc through the refining zones formed between the stationary 
plates into the peripheral region of the refiner casing and out through 
the refiner outlets as a partially refined pulp 13 entrained in steam 
generated within the refining zone when the heat generated during the 
refining process evaporates water present in the infeed stock 11. 
The mixture of partially refined pulp and steam generated 13 is conveyed 
through the transfer conduits 62a,62b which respectively interconnect the 
discharge outlets 16a,16b of the first and second refining zones of the 
refiner 10 to the inlet conduits 114a,114b to the downstream refiner 110. 
The partially refined pulp and steam mixture received through the infeed 
conduits 114a,114b is directed tangentially into the ribbon conveyors and 
advanced by the ribbon conveyors 140a,140b towards the refining zones on 
each side of the central rotating disc of the downstream refiner 110. Due 
to the high speed operation of the ribbon conveyors 140a,140b the 
partially refined pulp stock is held around the peripheral of the feeder 
housing about the ribbon conveyors 140a,140b while the steam in the infeed 
mixture flows back through the open central region of the ribbon conveyors 
140a,140b along the ribbon drive shaft to the steam discharge outlets of 
the downstream refiner 110 disposed at the outer ends of the housing 
surrounding the ribbon conveyors 140a, 140b. The partially refined pulp 
stock is delivered axially by the ribbon conveyors 140a,140b through the 
throats of the refining zones on opposite sides of the central rotating 
disc and is driven by centrifugal force through the refining zones between 
the refining plates into the peripheral region of the casing of the 
downstream refiner 110 and thence through the refiner outlet 134 as a 
refined product pulp 113 entrained in steam generated by evaporation of 
water present in the partially refined pulp by the refining heat generated 
during the grinding operation carried out in the refining zones of the 
downstream refiner 110. 
The refined pulp stock and steam mixture 113 is discharged from the 
downstream refiner 110 through the exhaust conduit 90 to a steam 
separating means 50, most commonly a cyclone separator wherein the steam 
in the mixture is separated from the refined pulp stock. The steam 55 
separated from the mixture of refined pulp stock and steam 113 discharged 
from the secondary refiner 110 may be vented to atmosphere or, preferably, 
passed to a heat recovery system together with the steam 15 and 115 vented 
from the upstream and downstream refiners through the ribbon conveyors 
40a,40b,140a,140b. The refined pulp stock separated from the mixture 113 
in the separation means 50 is discharged therefrom and collected in a 
latency chest as the refined product pulp. 
In the embodiment of the process of the present invention illustrated in 
FIGS. 3 and 4, the infeed stock mixture 11, comprising the fractionated 
wood chips entrained in steam generated in the chip fractionator passes 
through a single feed conduit into the first inlet conduit 314a to the 
refiner 310 and is directed via the first inlet conduit 314a tangentially 
into the ribbon conveyor in the direction of rotation of the ribbon 
conveyor. As the stock mixture is advanced by the ribbon conveyor 340a to 
the throat of the first refining zone on the upstream side of the central 
rotating disc, the centrifugal forces which act upon the fiber portion of 
the stock mixture due to the high speed operation of the ribbon conveyor 
340a hold the fiber stock around the periphery of the feeder housing 
thereby permitting the steam to flow back through the open central region 
of the ribbon conveyor 340a to the outer end of the feeder housing and 
through the steam discharge passage of the refiner 310 to be vented or 
preferably, passed to a heat recovery system. The fractionated fiber stock 
is delivered axially by the ribbon conveyor 340a to the throat of the 
first refining zone on the upstream side of the central rotating disc and 
is driven by centrifugal force of the rotating disc through the first 
refining zone into the peripheral region of the refiner casing and out 
through the first refiner outlet 316a as a partially refined pulp 13 
entrained in steam generated within the refining zone when the heat 
generated during the refining process evaporates water present in the 
infeed stock 11. 
The mixture of partially refined pulp and steam generated 13 is conveyed 
through the transfer conduit 362 which interconnects the discharge outlet 
316a of the first refining zone of the refiner 310 to the second inlet 
conduit 314b to the second refining zone of the refiner 310. The partially 
refined pulp and steam mixture is directed through the second inlet 
conduit 314b tangentially into the ribbon conveyor 340b and is advanced by 
the ribbon conveyor 340b towards the second refining zone on the opposite 
side of the central rotating disc of the refiner 310. Due to the high 
speed operation of the ribbon conveyor 340b the partially refined pulp 
stock is held around the periphery of the feeder housing about the ribbon 
conveyor 340b while the steam in the infeed mixture flows back through the 
open central region of the ribbon conveyor 340b along the ribbon drive 
shaft to the steam discharge outlet of the refiner 310 disposed at the 
outer end of the housing surrounding the ribbon conveyor 340b. The 
partially refined pulp stock is delivered axially by the ribbon conveyor 
340b through the throat of the second refining zone and is driven by 
centrifugal force through the second refining zone and thence through the 
refiner outlet 334 as a refined product pulp 113 entrained in steam 
generated by evaporation of water present in the partially refined pulp by 
the refining heat generated during the grinding operation carried out in 
the refining zones of the refiner 310. 
The refined pulp stock and steam mixture 113 is discharged from the refiner 
310 through the exhaust conduit 90 to the steam separating means 50, most 
commonly a cyclone separator wherein the steam in the mixture is separated 
from the refined pulp stock. The steam 55 separated from the mixture of 
refined pulp stock and steam 113 discharged from the secondary refiner 310 
may be vented to atmosphere or, preferably, passed to a heat recovery 
system together with the steam 15 and 115 vented from the upstream and 
downstream 10 refining zones through the ribbon conveyors 340a and 340b. 
The refined pulp stock separated from the mixture 113 in the separation 
means 50 is discharged therefrom and collected in a latency chest as the 
refined product pulp. 
Referring now to FIG. 5 of the drawings, there is depicted therein a 
refining apparatus, commonly referred to as a Twin refiner, adapted for 
carrying out the process of the present invention either in the embodiment 
illustrated in FIGS. 1 and 2 or the embodiment illustrated in FIGS. 3 and 
4. The refiner 200 comprises a base 212 supporting spaced separable casing 
sections 214,216 and a central casing section 218 which is removably 
secured between the sections 214,216 to provide access to the refining 
zones to permit maintenance of the apparatus and replacement of the 
refiner plates. Bearing support housings 222,224 extend outwardly from the 
casing sections 214,216, respectively, to house bearing assemblies 
223,225, respectively, which rotatably support the refiner drive shaft 226 
which extends between the bearing assemblies through the casing sections. 
Drive means (not shown) for rotating the rotor shaft 226 typically 
comprises a motor mounted on an adjustable motor base independent from the 
refiner base and connected to the rotor shaft 226 either via a direct gear 
coupling or by a belt drive. 
The casing sections 214,216 respectively include non-rotating annularly 
shaped heads 234,236 which are disposed perpendicularly to the axis of the 
drive shaft 226 and extend circumferentially about the drive shaft 226 in 
spaced relationship between the casings 214,216 within the annular central 
casing 218 mounted therebetween. The heads are secured to their respective 
casings and have mounted thereto refiner plate assemblies 242,244, 
respectively, on the opposed facing surfaces of the heads 234,236. The 
refining plate assemblies each comprise a conventional array of refining 
plate elements well known in the art, such as those in U.S. Pat. No. 
3,473,745. 
A radially extending rotor disc 250 is centrally mounted on the rotor shaft 
226 within the central casing 218 intermediate the spaced non-rotating 
heads 234,236 and is keyed to the rotor shaft 226 for rotation therewith. 
Sets of refining plates 252,254 of conventional construction are mounted 
to the opposite faces of the central rotor disc 250 to face the axially 
juxtaposed refiner plates 242 and 244 and define a first refining zone 260 
between the spaced refiner plates 242 and 252 and a second refining zone 
270 between the spaced refiner plates 244 and 254. 
In order to defibrate lignocellulose material at high consistency in 
accordance with the process of the present invention, the refiner 200 is 
equipped with two separate and distinct feeder means, the first feeder 
means disposed within the refiner casing section 214 in operative 
association with the first refining zone 260 and the second feeder means 
disposed within the refiner casing section 216 in operative association 
with the second refining zone 270. In the refiner apparatus of the present 
invention, at least of the feeder means, generally the downstream feeder 
means, and preferably, both of the first and second feeder means are 
adapted to directly receive a mixture of lignocellulose material and 
superatmospheric pressure steam from an upstream refining zone or 
pretreatment stage, thereby avoiding the necessity of innerstage 
separation of the lignocellulose material from the steam as required in 
conventional refiners operating a high consistency. The first and second 
feeder means embodied in the Twin refiner illustrated in FIG. 5 are both 
adapted as hereinafter described to receive a mixture of lignocellulose 
material and steam and for conveying the lignocellulose into its 
associated refining zone while passing the steam in the opposite direction 
to the flow of lignocellulose material and away from the refining zone to 
a steam vent. 
Referring now to FIGS. 5 and 6, inlet conduits 202 and 204 are respectively 
mounted to and open into the casing sections 214 and 216 for directing the 
lignocellulose material to be processed tangentially into the ribbon 
conveyors feeding the first and second refining zones 260 and 270, 
respectively. The longitudinally elongated conveyor housings 220a,220b 
extend coaxially with the rotor shaft 226 on each side of the central 
rotor disc 250, one extending within the refiner casing section 214 and 
having a discharge outlet opening to the throat of the first refining zone 
260, and the other extending within the refiner casing section 216 and 
having a discharge outlet opening to the throat of the second refining 
zone 270. As best seen in FIG. 6, the inlet conduits 202, 204 extend 
exteriorly respectively of the refiner casing sections 214 and 216 and 
open respectively to the conveyor housings 220a,220b to direct the mixture 
of lignocellulose material and steam from a supply conduit tangentially 
into the conveyor housings 220a,220b. Ribbon conveyors 240a and 240b are 
mounted respectively within the conveyor housings 220a and 220b and are 
keyed to the rotor shaft 226 for rotation therewith. The ribbon conveyors 
are 240a and 240b are essentially identical aside from the opposite pitch 
of the spiral ribbon elements mounted about the conveyor shaft whereby 
material is fed in opposite directions toward the central rotor disc 250 
from rotation of the shaft 226. The ribbon conveyor illustrated in U.S. 
Pat. No. 3,441,227, the disclosure of which is hereby incorporated herein 
by reference, may be utilized, as well as thereof, as the ribbon conveyors 
240a and 240b. 
As noted hereinbefore, upon rotation of the ribbon conveyors 240a and 240b, 
the lignocellulose material is separated from the steam in which it has 
been conveyed into the conveyor housing. The centrifugal forces generated 
by the high speed rotation of the ribbon conveyors throw and hold the 
lignocellulose material around the periphery of their conveyor housings 
while permitting the steam to flow in reverse direction through the 
central open portion of each ribbon conveyor. Steam vents 290a and 290b, 
mounted respectively to the refiner casing sections 214 and 216, open to 
the conveyor housings 220a,220b, respectively, and extend therefrom 
exteriorly of the refiner casing sections 214 and 216 to provide a flow 
conduit for venting the separated steam from the conveyor housings. The 
steam vents are disposed so as to open into that end of each conveyor 
housing which is axially remote from the central rotor disc 250. As the 
ribbon conveyors 240a and 240b rotate, the lignocellulose material is 
advanced along the axis of the conveyor housings into the first and second 
refining zones, respectively, while the steam separated from the received 
mixture passes axially outwardly through the open central portion of each 
ribbon conveyor oppositely to flow of lignocellulose material to and 
through the steam vents 290. 
A discharge conduit means 298, mounted to the center refiner casing section 
218, communicates with the annular chamber therein for providing a 
discharge conduit for passage of refined and/or partially refined material 
from the refiner. If the output materials discharged from the first and 
second refining zones are to be passed to a common receptacle, then the 
discharge conduit means 298 may comprise a single outlet passage opening 
through the center refiner casing section 218 to receive material 
discharged from both the first and second refining zones. If the output 
materials discharged from the first and second refining zones are to be 
passed to different receptacles, then the discharge conduit means 298 
comprises a pair of independent outlet passages, both opening through the 
center refiner casing section 218, but with one outlet passage arranged to 
receive only material discharged from the first refining zone and with the 
other outlet passage arranged to receive only material discharged from the 
second refining zone. 
Although the refiner apparatus illustrated in FIG. 5 is of type commonly 
referred to as a Twin refiner wherein two separate and distinct refining 
zones are housed in the same refiner casing, it is to be understood that a 
single-disc type refiner apparatus, such as disclosed in U.S. Pat. No. 
3,441,227, may be adapted to carry-out the process of the present 
invention by equipping the refiner apparatus with a feeder means adapted 
as hereinbefore described to receive a mixture of lignocellulose material 
and steam and convey the lignocellulose material into the refining zone 
while passing the steam in the opposite direction to the flow of 
lignocellulose material and away from the refining zone to a steam vent. 
For example, the single disc refiner apparatus disclosed in U.S. Pat. No. 
3,441,227, may be modified to directly receive a mixture of lignocellulose 
material and superatmospheric pressure steam, rather than lignocellulose 
material from which the steam has previously been removed via a cyclone 
separator or the like, by providing an inlet conduit which passes through 
the refiner casing and opens to the housing of the feeder means at a 
location intermediate the refining zone and the steam vent so as to direct 
the lignocellulose material and steam mixture tangentially into the ribbon 
conveyor in the same direction as the rotation of the ribbon conveyor. 
The feeder means embodied in the refiner apparatus of the present invention 
illustrated in FIGS. 5 and 6, may also be utilized as a stand alone steam 
separator 300 as shown in FIG. 7. The steam separator 300 comprises an 
axially elongated housing 320 having a lignocellulose discharge outlet 330 
opening therefrom at one axial end thereof and a steam vent 390 opening 
therefrom at the other axial end thereof for venting steam from the 
separator. Conveyor means 340, most advantageously a ribbon conveyor, is 
mounted within the housing 320 about a rotatable drive shaft 326 disposed 
along the axis of the housing 320 and adapted for rotation about its axis 
by conventional motorized drive means (not shown). The conveyor means 340 
is keyed to the drive shaft 326 so as to rotate therewith. An inlet 
conduit 304 opens to the housing 320 at a location intermediate the 
lignocellulose material discharge outlet 330 and the steam vent 390 to 
receive a mixture of lignocellulose material and superatmospheric pressure 
steam and direct the received mixture tangentially into the ribbon 
conveyor means 340 in the direction of the rotation of the conveyor means. 
Upon rotation of the ribbon conveyor means 340 at high speed, the 
lignocellulose material is separated from the steam in which it has been 
conveyed into the conveyor housing. The centrifugal forces generated by 
the high speed rotation of the ribbon conveyor throws and holds the 
lignocellulose material around the periphery of the conveyor housing while 
the lignocellulose material is conveyed to the discharge outlet 330 and 
the steam is permitted to flow in reverse direction through the central 
open portion of the ribbon conveyor to the steam vent 390. 
The method of the present invention, and the systems disclosed herein for 
carry out said method, wherein the lignocellulose material being refined 
is transported between stages pneumatically by the steam generated during 
the processing rather than mechanically transported, allows for the 
optimization of pulp quality and steam recovery at maximum pressure. 
Transport of the lignocellulose in the steam generated during processing 
as taught herein permits up to a fifty percent reduction in dwell time of 
the pulp at pressure and therefore allows operation and steam recovery at 
higher pressure without the undesirable excessive darkening of the pulp 
experienced when the pulp is exposed to a pressurized environment for 
longer periods. The use of process steam transport also eliminates the 
need for interstage mechanical equipment, including screw conveyors and 
interstage cyclone separators for steam removal, thereby substantially 
reducing capital expenditures, reducing maintenance costs, reducing system 
complexity, and improving reliability.