Process distributing fluffed pulp into a static bed reactor for gaseous treatment

A process and apparatus for treating and particularly bleaching pulp contacts a pulp with a gaseous reaction medium in a reactor tower. The pulp is fluffed and refined before being added to the pulp bed and then homogeneously permeated with the gaseous reaction medium to produce a uniformly treated pulp. A distribution device is included in the reactor to uniformly distribute the pulp in the reactor and form a homogenous pulp bed having a substantially even upper surface and uniform bed depth.

FIELD OF THE INVENTION 
The present invention is directed to a process and apparatus for the 
treatment of various types of pulps, preferably high-consistency pulps, 
using a gaseous reaction medium. More particularly, the present invention 
is directed to a process and apparatus for the uniform bleaching of pulps 
and particularly high consistency pulp using ozone. 
BACKGROUND OF THE INVENTION 
In the field of pulp treatment using a gaseous reaction medium, bleaching 
is of particular interest. In the past few years, a bleaching process was 
developed using an ozone step in combination with an oxygen bleaching 
step. A particularly beneficial variant of this process is 
high-consistency ozone bleaching. Consequently, various different 
processes for treatment of pulps are previously known. One of these 
processes is described in U.S. Pat. No. 3,814,664 and U.S. Pat. No. 
3,964,962 to Carlsmith. Other processes for ozone bleaching of pulp are 
disclosed in U.S. Pat. No. 4,278,496 and U.S. Pat. No. 4,279,694 to 
Fritzvold. In these processes, pulp is placed in a tower and permeated by 
a gaseous medium such as oxygen or ozone. These processes, however, have 
not received general acceptance, primarily due to the random and poor 
bleaching results achieved. 
In an effort to improve the bleaching results, various tests were conducted 
using a horizontal dynamic reactor upstream of the static bleaching tower 
in order to achieve more thorough mixing of the pulp with the oxygen or 
ozone bleaching agent. Examples of this type of process are described in 
EP 0 106 460 and U.S. Pat. No. 5,174,861. These processes and devices, 
however, also did not provide satisfactory bleaching results. In 
particular, the abovenoted processes result in non-homogenous bleaching of 
the pulp as reported in "Importance of Reactor Design in High Consistency 
Ozone Bleaching" by White, Gandek, Pikulin and Friend (79th Annual Meeting 
CPPA). 
SUMMARY OF THE INVENTION 
A primary objective of the invention is to provide a process and apparatus 
for homogeneously and uniformly bleaching pulp without degrading or 
destroying the pulp fibers. 
A further object of the invention is to provide a process and apparatus for 
treating pulp with a gaseous reaction medium by fluffing or refining the 
pulp before introducing to the pulp bed and thereafter homogeneously 
permeating the pulp bed with the gaseous reaction medium. 
Another object of the invention is to provide a process and apparatus for 
uniformly and homogeneously bleaching pulp with ozone in a static bed of 
fluffed or refined pulp. 
Still another object of the invention is to provide a process and apparatus 
for uniformly bleaching pulp with ozone in an efficient and economical 
manner. 
The objects of the invention are basically attained by providing a process 
for treating pulp with a gaseous reaction medium comprising the steps of 
feeding a gaseous reaction medium and a pulp to a fluffer and passing said 
gaseous reaction medium and pulp in admixture through a fluffing zone in 
said reactor to produce a partially reacted fluffed pulp, discharging said 
fluffed pulp into a pulp static bed reactor and distributing said pulp 
substantially uniformly in said reactor to form a pulp bed having a 
substantially uniform and homogeneous upper surface and bed depth, said 
reactor having a distribution means for distributing said fluffed pulp 
substantially uniformly across the entire diameter of said reactor and 
upper surface of said pulp bed, and passing a gaseous reaction medium 
uniformly through the pulp bed. 
The objects of the invention are further attained by an apparatus for 
treating pulp with a gaseous reaction medium, comprising a fluffer having 
a pulp inlet and a comminuting zone for receiving a mixture of pulp and a 
gaseous reaction medium and for fluffing and refining the pulp in the 
presence of said gaseous reaction medium to produce a partially reacted 
pulp, a pulp static bed reactor having an inlet positioned below the 
fluffer for receiving the fluffed and refined pulp and gaseous reaction 
medium directly from the fluffer, said reactor having a pulp outlet at a 
lower end thereof, distribution means disposed in the reactor and spaced 
below the inlet for substantially uniformly distributing the pulp across 
the diameter of the reactor and forming a substantially uniform and 
homogeneous pulp bed having a substantially uniform upper surface and bed 
height, and means for introducing a gaseous reaction medium into the 
reactor and passing the gaseous reaction medium through the pulp bed. 
Other objects, advantages and salient features of the invention will become 
apparent from the following detailed description which, taken in 
conjunction with the annexed drawings, disclose preferred embodiments of 
the invention.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is directed to a process and apparatus for uniformly 
treating a pulp with a gaseous reaction medium. The invention is further 
directed to a process and apparatus for producing a uniformly bleached 
pulp using ozone as the reaction medium. The uniform bleaching and 
treatment of the pulp is basically attained by passing the pulp through a 
fluffer to produce a fluffed pulp, forming a uniform pulp bed from the 
fluffed pulp and passing the gaseous reaction medium through the pulp bed. 
In embodiments of the invention, the pulp is refined to single fibers. As 
shown in FIG. 1, the apparatus 10 comprises a fluffer or refiner 12, a 
reactor 14 in the form of a reaction tower and a distribution device 16 
for distributing the pulp substantially uniformly across the diameter of 
the reactor to form a uniform bed height and depth in reactor 14. The pulp 
being treated by the process can be a chemical, mechanical or waste paper 
pulp. 
The fluffer 12 is a defibrator having a pair of opposing grinding plates 
located within a comminution chamber. The fluffer 12 can be a defibrator 
having a structure similar to that disclosed in U.S. Pat. No. 4,913,358 to 
Sbaschnigg et al. and U.S. Pat. No. 5,314,583 to Kappel, which are hereby 
incorporated by reference. The fluffer 12 includes a fixed grinding plate 
18 and a rotating grinding plate 20 which is driven by a motor 22. The 
fixed grinding plate 18 is movable in a direction toward the rotating 
grinding plate 20 to selectively adjust the space in the comminuting 
chamber. The fluffer 12 can be cooled or heated by means of a fluid on the 
stationary and rotating grinding plates. In embodiments, the fluffer is 
cooled by introducing a cooling fluid such as water through cooling 
chambers in the housing. The fluffer 12 fluffs and refines the fiber 
bundles to single fibers. 
In preferred embodiments as shown in FIG. 1, the grinding plates 18, 20 are 
oriented vertically so that the pulp passing through the fluffer 12 is 
directed radially outward from the plates and downward into the reactor 
14. In alternative embodiments, the grinding plates can be oriented 
horizontally. The vertical orientation of the grinding plates as shown is 
generally preferred when the fluffer 12 can be positioned directly above 
the reactor 14 since the pulp exiting the fluffer 12 can be directed 
downwardly into the reactor 14 without the need for a carrier gas to 
convey the fluffed pulp. 
A screw feeder 24 is coupled to the fluffer 12 to feed the pulp 
continuously to the fluffer 12. The pulp is supplied to the screw feeder 
24 through a chute 26. In preferred embodiments, the screw feeder 24 
includes an inlet port 28 to supply the gaseous reaction medium to the 
pulp in the screw feeder. 
Referring to FIG. 1B, the fluffer 12 according to a preferred embodiment of 
the invention is illustrated in cross-section showing screw feeder 24 and 
grinding plates 18, 20. As shown, the screw feeder 24 includes a double 
walled barrel 25 defining an annular space 27 around the screw 29. The 
annular space 27 terminates at the exit end 35 of the barrel 25 between 
the grinding plates 18, 20. The structure and operation of this fluffer is 
disclosed in WO 94/27713 which is incorporated by reference. The pulp is 
fed through screw feeder 24 coaxially with respect to the axis of the 
rotating grinding plate 20. The gaseous reaction medium, such as ozone, is 
fed through inlet port 28, passes through the annular space 27 and exits 
at 35 adjacent the fixed grinding plate 18 at the upstream end of the 
fluffing zone 31. As shown, the opposing surfaces of the grinding plates 
18, 20 define a fluffing and comminuting zone 31. The pulp and reaction 
medium are contacted and mixed together as they enter the fluffing and 
comminuting zone 31. The barrel 25 includes a conical shaped collar 37 to 
direct the reaction medium radially outwardly through the comminuting 
zone. In this fashion, the pulp and reaction medium are contacted with 
each other and fed simultaneously through the fluffing and comminuting 
zone 31 to produce a fluffed, refined and partially reacted pulp. In this 
embodiment, little or no reaction takes place in the screw feeder. 
In alternative embodiments, the inlet port 28 is positioned at the upstream 
end of the screw feeder 24 adjacent the pulp inlet 30 to enable the pulp 
to mix with the reaction medium as both are conveyed co-currently to the 
feed inlet of the fluffer 12. The position of the inlet port 28 is 
coordinated with the length of the screw feeder 24, the type of pulp, and 
the reaction medium to promote proper reaction conditions and reaction 
times in the screw feeder. The residence time in the screw feeder is 
sufficient to initiate the reaction without over bleaching the outer 
surface of the pulp particles. In preferred embodiments, the gaseous 
reaction medium is added with the pulp at an inlet of the fluffer so that 
the pulp and reaction medium are fed together co-currently to the 
comminuting chamber of the fluffer 12. When the reaction medium is ozone, 
the rate of reaction is very high so that the ozone is added with the pulp 
28 to mix with the pulp and initiate the bleaching reaction on the pulp 
particles as the pulp enters the fluffing zone. Reactants which have a 
rate of reaction less than ozone can be mixed with the pulp in the screw 
feeder. Generally, ozone is not mixed with the pulp for long periods of 
time before entering the fluffer to avoid non-uniform bleaching of the 
pulp. 
In the process of the invention, the pulp is supplied to the screw feeder 
24 while the reaction medium is introduced through the inlet port 28 where 
it is directed to the fluffer. The pulp and reaction medium are then fed 
together co-currently to the inlet of the fluffing zone of the fluffer 12 
where pulp is comminuted and fluffed while in continuous contact with the 
reaction medium to produce a partially treated or reacted pulp. The 
fluffed pulp and reaction medium are dispensed to the reactor 14 and 
distribution device 16 to form a uniform bed height where the gaseous 
reaction medium then passes uniformly through the bed 32. 
Referring to FIG. 1, a gas reaction medium, such as oxygen or an oxygen and 
ozone mix, also can be fed in further embodiments into this fluffer 12 
through an inlet 38 in the housing of the fluffer. In this embodiment, the 
reaction gas can be added near the grinding plates 18, 20 and mixed into 
the pulp as the pulp is being separated into single fibers. The pulp 
mixture, consisting of separated fibers and a reaction gas medium, in 
which part of the reaction between the gas and the surface of the fibers 
has already taken place, is then directly fed into the pulp reactor 14 or 
bleaching tower. 
The reactor 14 has the shape of a cylindrical tower having a height and 
width sufficient to treat a suitable volume of pulp as known in the art. 
The reactor 14 includes a pulp inlet 30 in the upper portion thereof and a 
pulp outlet 52 at the bottom. As shown in FIG. 1, the pulp inlet 30 is 
positioned in the center of the reactor and spaced vertically above the 
distribution device 16. A chute 54 extends from the fluffer 12 to the 
inlet 30 to guide the pulp from the fluffer into the reactor. 
The pulp exiting the fluffer 12 drops downwardly onto a rotating 
distribution disc 40 of distribution device 16, which, as shown, is on an 
incline. The pulp strikes the disc 40 and is distributed from there onto 
the surface of the pulp bed 32. The fluffed pulp striking the rotating 
disc 40 is distributed substantially uniformly across the diameter of the 
reactor 14 and the upper surface 76 of the pulp bed 32. The loose 
distribution of the pulp and the separated fibers result in a pulp bed 32 
having good permeability to ensure efficient gas contact with the pulp and 
prevent channeling of the gas through the pulp bed. The rotating 
distribution disc 40 prevents a cone shape from forming in the pulp bed 32 
as shown by phantom line 33 in FIG. 1, and the resulting disadvantages of 
uneven permeation of the pulp material by the gaseous reaction medium. The 
gas permeates the uniform bed of pulp material evenly and reacts evenly 
with the surface of the individual fibers so that a uniform bleaching 
reaction is obtained without individual fibers being destroyed or 
overreacted due to excessive contact with the bleaching agent. The 
residual gas is collected in a double casing 42 of the reactor 16 and is 
removed through the outlet port 44. Any remaining gas withdrawn from the 
reactor 14 is destroyed and the residual oxygen recycled to produce 
additional ozone if desired. In further embodiments, the ozone removed 
from the reactor 14 is recycled directly to the inlet 28 of the screw 
feeder 24. The ozone or other gaseous reaction agent can be cooled to 
40.degree. C. or less before recycling to cool the pulp and the screw 
feeder or fluffer. 
The reacted and treated pulp is discharged at the bottom end of the reactor 
14 or bleach tower by a discharge device 46. In embodiments, dilution 
water is added through inlet 47 to the outlet to dilute the pulp 
suspension to a low or medium consistency of approximately 3-15 wt %. This 
resulting pulp suspension is fed to a further treatment stage of the pulp 
process by a pump 48 as known in the art. 
The distribution device 16 includes a vertically oriented shaft 56 which is 
preferably centered in the reactor and directly below the pulp inlet 30. 
The shaft 56 is coupled to the rotating discharge device 46 so that the 
shaft 56 rotates with the discharge device 46. Discharge device 46 
includes a plurality of vanes 59 spaced from the bottom wall of the 
reactor 14 to sweep the pulp to the outlet 52. A motor 61 drives the 
discharge device 46 and the shaft 56 at a selected speed to attain the 
desired discharge rate and residence time of the pulp in the reactor. The 
screw feeder 24 and fluffer 12 are operated at a speed complementing the 
speed of the discharge device 46 to maintain a constant pulp level in the 
reactor 14. 
In the embodiment of FIGS. 1 and 1A, distribution device 16 is a 
disc-shaped device 40 mounted on the upper end of the shaft 56. The disc 
40 is fixed at an incline below the inlet 30 to distribute the pulp around 
the pulp bed 32. The angle of the disc 40 with respect to the shaft 56 is 
selected in relation to the pulp being processed, the speed of rotation of 
the disc 40 and the dimension of the reactor 14. In the embodiment shown 
in FIGS. 1 and 1A, disc 40 is positioned at about 30.degree. to the 
horizontal. The actual dimension of the disc 40 is selected to uniformly 
distribute the pulp across the diameter of the reactor 14. In the 
embodiment shown, the disc 40 is a circular shaped disc having a diameter 
about one-half the diameter of reactor 14 and pulp bed 32. 
The fluffed pulp exiting the fluffer 12 essentially free-falls through an 
atmosphere of the gaseous reaction medium in the chute 54 and reactor 14 
above the distribution device 16 to ensure contact of the pulp fibers with 
the gaseous reaction medium. The fluffed pulp then strikes the rotating 
distribution device 16 and is deflected radially around surface 76 of the 
pulp bed 32. The gaseous reaction medium is generally introduced a short 
distance upstream of the fluffer or directly into the fluffer and flows 
downwardly through the pulp bed 32 as shown by arrows 58. In further 
embodiments, additional reaction medium can be introduced to reactor 14 
through an inlet 60 at the upper end or inlet 62 at the lower end when a 
counter-current gas flow through the reactor 14 is desired. 
The reactor 14 is a static bed reactor such that the pulp bed moves 
downwardly through the reactor as the pulp is discharged from the bottom. 
Preferably, the reactor includes no agitation device to reform, mix or 
alter the pulp bed after it is formed. 
In preferred embodiments of the invention, the permeability of the pulp bed 
32 in the pulp reactor 14 corresponds to an approximate pressure loss of 
less than 0.02 bar per meter of height of the pulp, preferably less than 
0.001 bar per meter, and most preferably less than 0.0002 bar per meter of 
pulp height. Maintaining a high permeability by a suitable fluffer allows 
the gaseous reaction medium to flow readily through the pulp bed without 
high energy consumption and without undesirable channeling of the reaction 
medium through the pulp bed. 
The bulk density of the fluffed and refined pulp 32 in the pulp reactor 14 
is typically between 30 and 170 kg per m.sup.3, preferably between 50 and 
150 kg per m.sup.3. In one embodiment, the bulk density is about 120 kg 
per m.sup.3. The low bulk density of the pulp provides sufficient space 
between the individual fibers to allow the gaseous reaction medium, such 
as ozone, to flow between the fibers, thus providing homogeneous 
permeation of the pulp fibers by the gaseous reaction medium. 
The gaseous reaction medium is passed through the pulp bed 32 at a speed of 
between 5 and 500 mm per second in relation to the overall cross section, 
and preferably between 10 and 100 mm per second. The permeation speed of 
the gaseous reaction medium provides an optimum contact period between the 
gaseous medium and the pulp, as well as a suitable retention time in the 
reactor 14. 
The fluffed and refined pulp entering the reactor 14 is distributed evenly 
over the surface of the pulp bed 32 in the reactor. The substantially 
uniform distribution of the pulp provides a uniform flow resistance of the 
pulp bed 32 and avoids undesirable channeling of the gaseous reaction 
medium through the bed. The uniform distribution also prevents some fibers 
from not contacting the gaseous medium, while preventing others from being 
damaged by excessive contact with the gaseous medium. The uniform 
distribution of the fluffed pulp on the pulp bed 32 ensures a uniform 
contact of the pulp fibers by the gaseous reaction medium and a uniformly 
treated pulp. 
The uniform treatment of the pulp bed 32 by the gaseous reaction medium is 
provided by maintaining a substantially uniform height or depth across the 
entire width of the pulp bed. In preferred embodiments, the center 34 or 
the highest point of the pulp bed 32 is no more than 0.2 times higher than 
the depth at the outer radius 36 or lower point of the surface of the pulp 
bed 32. The best results are achieved with the height difference of the 
pulp bed layer within this range. 
It is generally preferred that the pulp be a high consistency pulp having a 
consistency between about 20 and about 60 wt %. Pulp consistency within 
this range provides a high efficiency process. 
The pulp preferably has the Kappa number being between 1 and 20 when the 
pulp enters the screw feeder 24 and fluffer 12. A kraft pulp has an 
initial Kappa number of about 3-20, and preferably about 7-12. A sulfite 
pulp has a Kappa number of about 2-8, while a waste paper pulp has a Kappa 
number of about 1-10. In some instances, such as a dissolved pulp, the 
initial Kappa No. can be as low as 1. The Kappa No. of the pulp discharged 
from the reactor 14 decreases 1-15 and preferably 3-10 units from the 
starting Kappa No. Approximately 50% of the Kappa reduction occurs in the 
fluffer with the remaining reduction occurring in the reactor 14. 
The pulp entering the screw feeder and fluffer 12 preferably has a 
brightness between about 35 and 80% ISO or more, preferably about 45-60% 
ISO. Generally, brightness values are about 40-65% ISO for kraft pulp, 
about 60-80% ISO for sulphite pulp, and about 50-80% ISO for waste paper. 
The brightness of the pulp upon leaving the reactor 14 is usually 
increased 2-30%, and preferably 5-20% compared with brightness of the 
incoming pulp. Typically, about 50% of the increase in brightness occurs 
in the screw feeder and fluffer with the remaining increase occurring in 
the reactor 14. The actual increase in brightness depends on various 
factors including the initial brightness and ozone concentration. 
Generally, the brightness of the pulp increases about 1-15% ISO and 
preferably 2-10% ISO in the fluffer. 
The viscosity of the pulp is preferably as high as possible since the 
viscosity is a means of estimating the length of the cellulose fibers. A 
decrease in viscosity is usually a good indication of degradation of the 
cellulose fibers. Degradation can occur during pulp digestion, oxygen 
delignification and ozone bleaching. It is important to minimize the fiber 
degradation in the process and apparatus of the invention. In preferred 
embodiments of the invention, the pulp being fed to the fluffer has a 
viscosity of about 900 to 1500 dm.sup.3 /g (SCAN) for softwoods and about 
700 to 1400 dm.sup.3 /g (SCAN) for hardwoods. The viscosity generally 
drops about 50 to 300 dm.sup.3 /g in the ozone stage depending on the 
initial viscosity. Generally, the higher the initial viscosity, the 
greater the drop in the ozone stage. 
The pH of the pulp is preferably maintained low since ozone is unstable at 
high pH. Since a very low pH may also attack the fibers, the pH is 
maintained in the range of about 2-6, and preferably about 2-4 during the 
ozone treatment. 
The gaseous reaction medium is preferably mixed with the pulp in the 
fluffer 12 before the reactor 14. In this manner, the gaseous reaction 
medium reacts immediately with the fiber surfaces as the pulp is being 
fluffed, thus achieving a homogenous reaction. The gaseous reaction medium 
further can be added to the pulp bed in the reactor into the gas area 
above or below the pulp bed. When additional gaseous reaction medium is 
added to the reactor, the gaseous medium can be added in a counter-current 
or co-current manner. 
The gaseous reaction medium in preferred embodiments is ozone in a suitable 
carrier gas such as air or oxygen. The ozone concentration in the carrier 
gas is generally about 3-5% by volume to provide effective pulp bleaching. 
In further embodiments, the gaseous reaction medium can be hydrogen 
peroxide, oxygen, nitrogen oxides or other known reaction agents at 
standard concentrations. 
The height or depth of the pulp bed to the diameter of the pulp bed 
generally has a ratio of more than 0.5, preferably more than 1. This ratio 
of the height to the diameter ensures an optimum permeability cross 
section with suitable retention times for the gaseous reaction medium and 
the pulp. The reactor 14 is dimensioned to accommodate the bed height and 
diameter. 
The reactor 14 also includes a distribution device 16 to ensure uniform 
feed and distribution of the pulp onto the pulp bed 32 and to provide an 
even and uniform pulp bed surface. The distribution device 16 provides a 
uniform pulp bed height and prevents the fiber bundles which are broken 
down in the fluffer 12 from agglomerating and forming large fiber bundles. 
The uniform pulp bed permits homogeneous permeation and treatment of the 
pulp by the gaseous medium. 
A further feature of the invention is the distribution device connected to 
the discharge device of the reactor, and rotating along with the discharge 
device. Thus, there is no need for an additional drive, and the rotating 
movement of the distribution device is coordinated with the discharge rate 
of the pulp. 
FIG. 2 shows an alternative embodiment of the distribution device in the 
reactor. The reactor is essentially the same as the reactor of FIG. 1, so 
that like elements are identified by the same reference number. A fluffer 
(not shown) and an inlet 31 for the pulp and gaseous reaction medium as in 
the embodiment of FIG. 1 are included. The distribution device as shown is 
attached to the rotating shaft 56 extending upwardly from the discharge 
device and rotates simultaneously with the shaft. The distribution device 
is in the form of an inclined chute 64 having a bottom wall 66 and side 
walls 68 to direct the pulp outwardly as the device rotates. As shown in 
FIG. 2A, the chute has an outer edge 70 extending diagonally between the 
side walls 68. The diagonal outer edge 70 promotes a uniform radial 
distribution of the fluffed pulp across the diameter of the upper surface 
76 of the pulp bed 32 as shown by the arrows 71. 
The angle of incline, size and rotational speed of the chute 64 are 
tailored for the type of pulp being treated. Factors which are taken into 
consideration in selecting the chute include, for example, the pulp 
density, viscosity, consistency and whether the pulp is a chemical, 
mechanical, or waste paper pulp. In addition, the height and width of the 
reactor and the pulp bed affect the design of the distribution device to 
obtain a uniform bed height of the pulp bed. 
FIGS. 3 and 3A show a further embodiment of the distribution device in the 
reactor 14. A fluffer and reaction medium inlet (not shown) are provided 
in a similar manner to the embodiment of FIG. 1. As in the previous 
embodiments, the distribution device is coupled to the vertical shaft 56 
which is coupled to the discharge device 46. In this embodiment, the 
distribution device 16 includes at least one and preferably two arms 72 
and 74 extending horizontally outward from the shaft 56. In the embodiment 
shown, the two arms 72, 74 are spaced axially along the shaft 56 and are 
positioned substantially perpendicular to each other. The arms 72, 74 have 
a width and length complementing the dimensions of the reactor 14 to rake 
the pulp outwardly and produce a pulp bed having a substantially uniform 
height. Arms 72, 74 have a length about 60% to 80% of the radius of the 
reactor 14. The width of the arms generally increases the smoothing effect 
on the pulp bed, but increases power consumption required to rotate the 
arms. The pulp is introduced to the reactor 14 through the inlet 30 at the 
upper end and falls downwardly onto the distribution device. In the 
absence of the distribution device, the pulp normally falls to form a cone 
shape 33 as shown in phantom lines. The distribution device rakes the pulp 
to a substantially level surface 76 as shown in FIG. 3. 
In preferred embodiments, the upper arm 72 is positioned at the desired 
pulp height, while the lower arm 74 is positioned below the surface 76. 
The arms 72, 74, as shown, are coupled to the shaft 56 by bolts 78 so that 
the position of the arms 72, 74 on the shaft 56 can be adjusted. In this 
manner, the height of the arms 72, 74 and the spacing between the arm can 
be selected. The arms are rotated at a speed to maintain a smooth upper 
surface and uniform pulp bed depth. For example, a rotation speed is 
generally about 0.2 to 2 rpm for a high consistency pulp and about 3 to 10 
rpm for a medium consistency pulp. 
FIGS. 4 and 4A show a further embodiment of the distribution device in the 
pulp reactor. A fluffer (not shown) and reaction medium and pulp inlet 30 
are provided in a similar manner to the embodiment of FIG. 1. In this 
embodiment, the distribution device is a cross beam 80 having a central 
hub 82. The shaft 56 extending upward from the discharge device 46 passes 
through the hub 82 so that hub 82 and cross beam 80 are slidable on the 
shaft 56. A flexible coupling device 84 extends from the upper end 86 of 
the shaft 56 and is coupled to the cross beam 80. The cross beam 80 is 
supported by the flexible device 84 which can be, for example, chains or 
cables. As the shaft 56 rotates, the resistance of the cross beam 80 on 
the pulp material 88 causes the flexible device 84 to twist around the 
shaft 56 and raise the height of the cross beam 80 with respect to the 
shaft 56 and the pulp material 88. In this manner, the height of the cross 
beam 80 changes with changes in the pulp bed height. As in the previous 
embodiments, the cross beam 80 rakes the pulp to produce a substantially 
uniform pulp height. The weight and dimension of the beam 80 and the 
attachment point of the flexible coupling device determine the efficiency 
of the smoothing effect on the pulp bed. 
The apparatus according to the invention ensures a uniform pulp bed, and 
the fluffed and refined pulp enables the treating gas to effectively and 
uniformly contact the surfaces of the fibers and produce a uniformly 
treated pulp. The uniformity of treatment and gas contact is particularly 
important in the bleaching of pulp with oxygen, ozone or other bleaching 
agents. 
While various embodiments have been selected to illustrate the invention, 
it will be understood by those skilled in the art that various changes and 
modifications can be made therein without departing from the scope of the 
invention as defined in the appended claims.