Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to the gaseous reaction --
- of material and more specifically to apparatus and processes
particularly suited for the gas phase treatment of fibrous
material such as, by way of specific example, the bleaching ---
5 or delignification of lignin-containing cellulose pulp. ---
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Wood pulp may vary in their content of lignin or other
non-cellulosic material. The amount of lignin in a particu-
lar pulp may be determined by appropriate convertional tests --
and a Rappa number assigned to the pulp which indicates the .-
10 amount of lignin. The higher the Kappa number, the more ---
lignin in the pulp. -
. When wood pulp is to be bleached the amount of deligni- -
- fication is indicated by a Kappa reduction. The higher the
Kappa reduction, the higher the amount of delignification.
:
The reaction between lignin and oxygen is exothermic
and the heat generated is proportional to the amount o~ -
lignin removed. In a reactor without substantial venting or
other mean8 ~or controlling the pulp temperature, the accum~
ulated heat will result in a substantial temperature ---
20 increase ~rom top to bottom in a pulp bed. It is usually -
desired to keep the temperature at tbe top of the bed at -~
95 -100 C to obtain a reaction rate sufficient to complete --
the deligniEication in 20-30 minutes. On the other hand, --
there is a risk of pulp degra~ation if the pulp temperature -
25 exceeds 120-125 C. Thus it is important that the gas ---
which reacts with the lignin of the pulp is controlled so
that the temperature at the top of the pulp bed is kept
within the 95-100 C range but the temperature at no point
in the bed exceeds the 120-125 C temperature.
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Currently known reactor systems for reacting a gaseous
material with a gas permeable material include (1) flowing -_
the reaction gas co-currently with the pulp flow and (2)
flowing the gaseous material counter-currently to the pulp ~ -
flow. Bither system will work satisfactorily with low
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amounts of delignification of a Kappa reduction of 20, or
less. For Kappa reductions of more than 20, it is necessary ---
to have special arrangements in the reactor system for ---
cooling or controlling the temperature in the pulp bed.
With either co-current flow or counter-current flow,
recycled cooled gas works satisfactorily for a
delignification equivalent to a Rappa reduction of up to 30. ---
However, neither system works well enough for a -_
delignification equal to a Rappa reduction of more than 30.
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Thus, if one wants to obtain a delignification reduc~
tion of Kappa 20 or less, this can be done effectively with
currently known co-current and counter-current systems. If
one wants to obtain a delignification of from 20 to 30 ---
Kappa, it can be done with the provision o~ special arrange~
.
1~ ments added to the conventional reactor. The special
arrangements would include a means for recycling the reactor
gas with the gas being cooled in the recycling means. ~ow- --
ever, neither prior art system will work e~fectively if one
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desire~ to obtain a delignification reduction o~ more than ~~
20 Kappa 30-
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The trend in the pulp Dleaching industry is to expand
oxygen bleachings to higher and higher Kappa number reduc- --
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tion. Thus, a pulp bleaching system which will permit the _
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delignification of pulp equivalent to a Kappa number reduc- ----
25 tion of 30 or more is highly desirable. This invention -
provides the industry with such a system.
Briefly described the new reactor includes a generally -
vertical vessel. Material supply means are connected to the
upper end of the vessel. The material to be treated flows
30 through the vessel from ~he top to the bottom in the form of ---
a gas permeable bed and is discharged from the lower end of -----
the vessel. An upper gas inlet is provided in the upper end --
of the vessel~ Gas is supplied ~hrough this gas inlet and
flows co-currently with the flow of the gas permeable bed -~
35 but at a much higher velocity. A lower gas inlet is pro- --
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vided in the lower end of the vessel through which gas is
- supplied and flows counter-currently to the flow of the pulp
bed. Gas outlet means are provided on the vessel between
--the upper and lower gas supply inlets. An upper gas recir~
culation conduit means connects the gas outlet means with
-the upper end of the vessel for recirculating gas back into
the upper end of the vessel. A lower gas recircultion
-conduit means connect~ the gas outlet means with the lower
end of the vessel for recirculating gas back into the lower
10 en~ o~ the vessel~
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Bxiefly described my new me~hod o~ performing an exo~ -
-thermic reaction of a gas with a sui able material comprises ---
the steps of supplying ga~ to the upper part of a retention
vess~l at a controlled rate and flowing the gas downwardly
15 through the gas permeable bed at a velocity greater than --
that of the downward movement o~ the gas permeable bed. The
unreacted gas is removed from the vessel at a point above ---
the bottom of the gas permeable bed. Simultaneously gas is
supplied to the lower part of the retention ve~sel at a --
20 controlled rate at a temperature below the temperature o~ --
the gas supplied to the upper part of the retention ve~sel. -
The gas flows upwardly through the gas permeable bed. The --
unreacted gas is removed from the vessel at a point above
the bottom of the gas permeable bed. The temperature and --
25 rate of the gas supplied to the upper part of the retention --
vessel is such that the gas permeable bed is rapidly heated
to the minimum reaction temperature. The temperature and --
rate of the gas supplied to the lower part of the retention --
vessel is such that the temperature of the gas permeable bed ---
30 will not exceed the maximum allowable temperature~ -
.
~he invention as we}l as its many advantages may be --~-
~urt~el unaerst~o~ by re~erence t~ t~e ~ win~ aetai~e~ --
description ~nd drawings in which~
Figv 1 is a graph showin~ calculated temperature pro~
35 files for a Kappa reduction of 50 in a pulp be~ using prior
_4_ 1219733 8526-IR-PA
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art co-current recirculation with the recirculating gas
cooled to 100 C. ---
.. -.--
Fig. 2 is a graph showing calculated temperature pro- -
files for a ~appa reduction of 50 in a pulp bed using prior --~
5 art counter-current circulation with the recirculating gas -
cooled to 100 C. ~~~~
_...
Fig. 3 i8 a view schematically illustrating one
preferred embodiment constructed in accordance with the ----
present invention; and _-
. _
10Fig. 4 is a graph showing a calculated temperature
profile for a 50 Kappa reduction in a pulp bed using the -~
embodiment of Pig. 3.
. . .
Referring to the drawings and, more particularly, to
Fig. 1, the graph shows calculated temperature profiles at
15 different gas flow rates for a pulp bed height of 6 meters.
The pulp enters the retention vessel at 90o C; the
co-current recirculating gas is cooled to 100 C, and the
delignification Kappa number is 50. ~rhe Fig. 1 gra~h i8 a
typical graph for a prior art co-current recirculation
20 oxygen bleaching of pulp system. With such a prior art
system the gas is flowed through the pulp bed downwardly at
a velocity higher than the moving pulp. Near the bottom of
the reactor the unreacted gas is separated from the pulp and
recirculated back to the top of the reactor. The temper-
25 ature near the top of the pulp bed should quickly rise toabove 95 C to obtain a reaction rate sufficient to complete
the delignification in 20 to 30 minutes retention time.
However, the temperature at any point in the pulp bed must
not be allowed to exceed around 120 C. If the temperature
30 exceeds 120 C degradation of the pulp is likely to occur.
.. .
The graph of Fig. 1 shows the temperature profiles in a
co-current recirculation gas cooled system for gas flow
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rates of .5 kilogram of oxygen per kilogram of pulp; 1.0
kilogram of oxygen per kilogram of pulp; and 2.0 kilograms --
of oxygen per kilogram of pulp. A recirculation rate of 1 --
or more kilogram of oxygen per kilogram of pulp will give --
5 the desired temperature control. However, this corresponds -
to a relative gas velocity of 18 or more feet per minute. --
Gas flows of this magnitude cannot be handled in a ---
co-current system without excessiv~ pressure arop and pulp ---
compaction in a porous pulp bed of 6 meters height. For ---
10 effective bleaching of the pulp excessive pulp compaction in
the porous pulp bed must be avoided. It is necessary that
the pulp in the pulp bed be fluffy and sufficiently gas -~
permeable to perform he bleaching operation~ Therefore, a
co-current recirculating gas system even with the gas being ~--
15 cooled before it is recirculated back to the top of the
retention vessel is not effective for high Kappa reduction
delignification. ----
. .
Fig. 2 is a graph showing calculated temperature pro~
files at differen~ gas flow rate~ for a pulp bed height of 6 --
20 meter~. The pulp enters the retention vessel at 90 C; the --
counter-current recirculating gas is cooled at 100 C; and
the delignificatipn l~appa number is 50. In a counter- -
current system, the gas flows counter current to the flow o~ --
the pulp pile or bed. The circulating gas is removed from -
25 the top of the reactor and re-enters at the bottom after
~lowing through a cooler. The graph of Fig. 2 shows gas -
flow rates of .5 kilograms oxygen per kilogram o~ pulp, 1.0 :::
kilogram of oxygen per kilogram of pulp, 2.0 kilograms o~ -
oxygen per kilogram of pulp, and 3.0 kilograms o~ oxygen per ---
30 kilogram of pulp. It can clearly be seen ~rom the graph of --_
Fig. 2 that a gas recirculation flow rate of 3 kilograms or
more of oyxgen per kilogram of pulp must be maintainea in ~--
the reactor in order to make certain that at no point in the ---
reactor the pulp temperature exceeds 120 C. Such a high
35 rate of gas recirculation against the pulp flow is highly
undesirable, High rates of gas recirculation ayainst the
pulp flow can prevent the pulp from flowing ~ownward in the `-
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reactor and cause a Uhang-upu~ especially in the upper
portion of the bed where the pulp is only lightly compacte~
Al~o, the pulp entering into the top of a reactor is fluffy -~
and consists of fibers. Gas removal at this point is not -
desirable becausP of the large amounts of fine fibers float-
ing in the gas stream. Therefore, conventional counter~
current recirculating systems also cannot be used effec~
tively for high delignification. --:--
-,
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The preferred embodiment of the invention shown in Fig. --
10 3 includes a reaction vessel 10. The reaction vessel 10 has -- -
an upper portion 12, an adjoining middle portion 14, and an
adjvining bottom or lower portion 16. The upper portion 12
of the vessel 10 is formed of horizontal cross-section or --
cross-sectional area substantially less than that of the --
15 communicating middle portion 14. The lower part 20 of the ---
upper portion 12 extends partially into the middle portion -
14 to provide a first gas receiving chamber 18 define~ by
lower part 20 of the upper portion 12, the upper outer -
periphery 21 of the middle portion 14, and the upwardly
20 tapering annular closure wall 22 interconnecting the middle ---
portion 14 and the upper portion 12. --
. .
The upp~r end of the chamber 18 is closed by the --
annular closure wall 22; however, below the closure wall 22, -
a gas discharge outlet 24 is connected to the chamber 18 for --
25 discharging gas from the latter.
-. .~
The middle portion 14 of the vessel 10 is formed o~ -
horizontal cross-section or cross-sectional area substan- -
tially lesæ than that of the communicating lower portion 16.
The lower part 26 of the middle portion 14 extends partially --
30 into the lower portion 16 to provide a second gas receiving
chamber 28 defined by lower part 26, the upwardly tapering
annular enclosure 30 and the upper outer periphery 31 of the `-
lower portion 16.
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The upper end of the chamber 28 is closed by the
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upwardly tapering annular closure wall 30; however, below ~.
the closure wall 30 a gas inlet 32 is connected to the ---
chamber 30 which receives gas fed into the lower portion 16.
_
, ....
The upper end of the vessel upper portion 12 is pro~
5 vided with at least one gas inlet 34 which communicates such ...
upper portion 12 with a gas make-up conduit 36 controlled by ... -
valve 37. The upper end of the vessel upper portion 12 is
further provided with a material inlet or inlet conduit 38 .-.-
which is connected to such upper end generally centrally of ....
10 the vessel 10. The inlet conduit 3B contains a feed screw
40, mounted on a supporting shaft 42 rotatably driven by a
driving motor (not shown) which is adapted for dow~wardly _.
feeding material into the vessel upper portion 12. The -
inlet conduit 38 is connected to a material supply conduit ~~-
15 44. ....
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The upper end of the vessel upper portion 1~ contains -.
means particularly adapted for disintegrating, breaking up,
and fluffing the material supplied to the inlet conduit 38.
Such means also spreads the disintegrated, broken up, and
20 fluffed material across the cross-section of the vessel --.-
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up~er ~ortion 12. As illustrated, such means are of the ---
type described in US Patent Number 3,785,577, and comprises ... -
an inner annulus or ring 46 of arcuately spaced apart rotary
pins connected to the shaft 42 for driven rotation therewith --
-
25 and a coaxial, radially spaced, outer annulus or ring 48 of ---.-
arcuately spaced apart stationary pins. During operation of -`
the apparatus, the annulus 46 of rotary pins is continuously .. ~
rotatably driven relative to the annulus 48 of stationary --.. -----
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pins; and material supplied through the inlet conduit 38 is _.
30 disintegrated or fluffed b~ the relative motion of the pins -
and then is discharged outwardly through the spaces between .---
t~e adjacent ones of the pins to be resultantly spread in ~
fluffed, disentegrated, or broken up condition across the ---
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cross-section of the vessel 10. -.
The lower end of the vessel 10 is provided ~lith
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discharge means for discharging material from the vessel 10,
such discharge means being illustrated as comprising a pulp
outlet conduit 50 connected to the vessel lower end, and a
scraper 52 in the vessel lower end adjacent the outlet 50
adapted to be rotatably driven by a driving motor (not
shown~ through a driving shaft 54. A dilution supply
conduit 56 supplies dilution liquor to the lower end of the
vessel. However, it will be understood the discharge means
. of the apparatus can be of other suitable construction.
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10The apparatus further includes means for redistributing
heat in the reaction ves~el 10 during the reaction process
~o control the temperature therein. More specifically, a
; recirculation conduit 60, external to the vessel 10, is
connected at opposite ends to the gas outlet 2~ and the gas
15 inlet 34 for recirculating a portion of the gas discharged
through the gas conduit 62 back through the gas inlet 34
into the upper end of the vessel. The recirculating conduit
60 controlled by valve 61 moreover is provided with a con~
ventional centrifugal blower 64 adapted for blowing the
20 recirculated gas through the recirculation conduit 60 ~o the
gas inlet 34; and as illustrated the gas make-up conduit 36
is connected to the gas inlet 34 througn the recirculation
conduit 60 whereby the recirculated gas and the gas supplied
by the conduit 36 are supplied intermixed through the inlet
34.
A portion of the gas flowing through conduit 62 from
outlet 24 is recirculated through a recirculation conduit 70
controlled by valve 72. The reGirculation conduit 70,
external to the vessel 10, is connected to the gas inlet 32
30 for recirculating the gas discharged through conduit 70 back
through ~he gas inlet 32 into the lower end of the vessel.
T~e recirculating conduit 70 is provided with a conventional
centrifugal blower 74 adapted for blowing the recirculated
gas through the recirculating conduit 70 to the gas inlet
35 32. The gas circulating through recirculation conduit 70 is
passed through a gas cooler 76 where it is cooled before the
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gas is recircula ed back to the gas inlet 32. .~
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A description of the operation of the before described
apparatus and the oxysen delignification o~ ~ellulose pulp .-
hereinafter follows, it being unders~oo~ that the maximum .--.. ---
5 temperature in the vessel 10 during such reaction must be .. -.
maintained below about 120-125 C to prevent degradation of
the pulp.
:....
. .
Throughout such operation the shafts 42 and 54 are con~
tinuously rotatably driven to provide continuous rotation of .~
10 the screws 40, the annulus 46 of the rotary pins and the ..
bottom scraper 52. Pulp being reacte~ is retaine~ in the ---
vessel 10 at a reactor pressure of approximately 100 psi for
the period of 20 to 30 minutes suitable or desirable for the -.
reaction in a porous, gas permeable bed or plug of fluffed ~.
15 pulp, which bed has its upper end generally as indicated by -_
the re~erence numeral 78 and spaced below the upper end of -_
the vessel upper portion by a gas space 80. The pulp move~ _
progressively downwardly in the porous plug form as reacted ---
pulp is ~ischarged from the bottom of the plug through the ---
20 outlet 50. -
..- ..:
.. -
The feed screw 40 continuously receives pulp from the
conduit 44 and feeds the pulp downwardly to the therebelow -
annuli 46, 48 of relatively rotating pins. Such pins, due
to their relative rotation, disintegrate and fluff the pulp ---
25 to a condition suitable for the reaction and the formation ---
in the vessel 10 of the before described porous, gas perme- ..
able pulp plug. ~he annuli 46, 48 of pins, furthermore,
discharges the pulp in a radially outwardly flow between -.-
adjacent ones of the pins whereby the pulp showers down- ---
30 wardly hrough the space 80 onto the upper end 78 of the
therebelow pul p plug.
Simultaneously, reaction gas or oxygen is continuously
supplied at a controlled rate and temperature through the -.
gas inlet 34 into the space 80 into the pulp showering down~
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wardly therethrough~ Hencel the pulp during its downwardly
showering is exposed to the introduced reaction gas and a ..
small portion of the reaction gas reacts with the pulp at
this timeO The unreacted gas continues downwardly through --
the porous pulp plug at a velocity which is substantially
greater than that of the downward movement of the pulp. An.-~
additional volume of the recirculation gas reacts with the-._
pulp during downward flow, and the remaining gas passes --.
upwardly through the gas discharge chamber 24 and into the ... -.
10 outlet conduit 62. A port,on of the gas flowing through .---
outlet conduit 62 is fed through valve 61, through the gas .-
recirculation conduit 60 by the blower 64, and into the -~
upper end of the vessel upper portion 12. The recirculated -
gas i5 supplied into the gas space 80 through the gas inlet
15 34 intermixed with gas from the gas supply conduit 36. The ~
major portion o~ the heat contained in the recirculated gas .--=-
is in the form of water vapor due to evaporation of water --
from the hot pulp. The recirculated gas entering the gas .--
space 80 has a higher temperature than the entering pulp
20 and, due to the high turbulence in the gas space 80, and the .. -.-
large exposed surface area of the pulp showering downwardly
therethrough, heat transfer from the recirculated gas to
such pulp by condensation of the water vapor containe~ in -
the recirculated gas occurs almost instantaneouslyO There~
25 fore, substantiallyr equalized temperature of the recir~
culated gas and the fluffed pulp is attained prior to the ..
deposit of pulp on the upper level 78 of the pulp bed. The -.-.
amount of this heat transfer from the recirculated gas to ----
the pulp is, of course, dependent upon the rate and temper- ... -.
30 ature of gas recirculated. -
Simultaneously, a portion of the gas from conduit 62 is ---
fed through the recirculating conduit 70 controlled by valve -.~
7~, the gas cooler 76, and then recirculated back through _--
the lower gas inlet 32 into gas chamber 28, and upwardly
35 through the middle portion 14 of the vessel 10, through the `.`-
gas chamber 18, and out of gas outlet 62. :~
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2~9733
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The temperature and rate of the gas supplied to the
upper part 12 of the retention vessel 10 must be such that
: the gas permeable bed is rapidly heated to the minimum
reaction temperature. Also, the temperature and rate of gas
supplied to the lower part of the retention vessel must be
such that the temperature of the gas permeable bed will not
exceed the maximum allowable temperature of 120 C to 125
C. This is particularly important for the delignification
of pulp in high amounts such as a reduction in Rappa equal
10 to 30 or more~ ,
..,~
If the wood pulp be~ height is approximately 6 meters --
- and it is desired to provide a Rappa reduction of 30 Kappa
- or more, less than 1 kilogram of oxygen per kilogram of pulp
is to be recirculated to the upper part of the retention --
15 vessel and at least 2 kilograms of oxygen per kilogram of --
pulp cooled to 100 C is recirculated counter-currently to
tbe movement of pulp to the lower part of the retention
vessel. -.-
The delignification reduction of a pulp equal to 50 -
20 Kappa reduction is illustrated in Fig. 4 which is a graph -~
with the bottom recirculation. The hot gas iæ cooled to 100 ---
C before re-entering. This will prevent the pulp from -
exceeding the maximum allowable temperature. As can be seen ---
from the more specific example of the 50 Kappa reduction
~5 shown in Fig. 4, the amount of pulp recirculated to the
upper part of the retention vessel is .5 kilograms o~ oxygen
per kilogram of pulp and the amount of oxygen recirculated -
to the lower part of the retention vessel is 2 kilograms
oxygen per kilogram of pulp. -
Co-current recirculation at the top of the reactor has --
the following advantages: --
1~ Pulp is only lightly compacted in top layers. There is ---
only a minimal resistance to the gas flow. ~-
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2. Co-current flow in the top layers will prevent pulp
=- -.-
hang up. -
....
3. ~ot gas from the reactor is used to heat up the incom-
ing pulp, thus saving steam. ..
.,,
4~ Pulp will heat up quickly to the minimum rea tion
temperature because of the fast heat transfer between the
hot gas and the fluffed pulp. --
.-. .
50 Large amounts of fine fibers are floating in the ga~ ....
stream surrounding the fluffer. Co-current ga~ flow forces
10 these fibers to settle in the pulp bed.
Counter-current recirculation in the bottom layers of
the pulp bed has the following advantages~
.. ..
...
lo Counter current flow will prevent excessive compaction
in the bottom layers, thus keeping the flow resistence to a .~
15 minimum. ,.. ~
2. ~eat is efficiently removed, thus preve.nting the pulp -.
Erom exceeding the maximum allowable temperature and avoid- ...
ing pulp degradation. ..
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