Note: Descriptions are shown in the official language in which they were submitted.
8ackground of the Invention
1. Field of the Invention.
The present invention deals with wood pulping and in pdrticular,
with the thermo-meçhanical pulping of wood.
2. Descript~on of the Prior Art.
In the production of pulp from wood for the manufacture of newsprint
and the like wood is conventionally chipped and then introduced into a refi-
ner. Usually this refiner will be the first of two refiners altllouyh single
refiner and three refiner systems are known in the art. In the first refiner
the chips are moved between a rotatiny disk and a statiorlary disc or betweell
double counter rotating discs in a pressuri~ed environment to form a partially
reduced fibrous material which will often be in the fornl of bundles or groups
of separate fibers. In a two refiner system this partially reduced fibrous
material will then he discharged fronl the first refiner and introduced to a
second refiner where it will be further reduced, often to its individual
fibers. This further reduced fibrous material is then discharged froln the
second refiner and after it undergoes latency and cleaning procedures it is
screened to separate pulped material which is acceptable for further treat-
ment known as accept", from that material9 known as "reject" wllich is not
sufficiently reduced and thus unacceptable for further treatment. Generally
about 8Q percent of the mater~al recovered from the second refiner is classi-
fied as accept. Conventionally it has been the practice to provide still
another refiner for the treatment of this reject fibrous ma~eridl. 1~ will be
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appreciated, however, that the use o~ this third refiner is expensive in terms
of capital costs and plant space. It is, there~ore, the object o~ the present
invention to provide an improved me~ns for processing the dbove described
reject ~ibrous materi~l, reducing equip~ent and improving the overall energy
efficiency of the paper mill.
Summary of the Invention
In the present invention wood is first reduced to chips. The wood
chips are then introduced to a first refiner to reduce the chips to a
partially reduced fibrous material. The partially reduced fibrous material is
then discharged from the f~rst refiner and introduced into a second refiner to
further reduce it to a more completely reduced fibrous material. This more
completely reduced fibrous material from the second refining is separated into
accept fibrous materials and reject fibrous material. The second refiner is
pressurized with steam to a pressure of from about 15 p.s.i. to about 75
p.s.i. and is heated to about saturation temperature. The re;ect fibrous
material is reintroduced into the second refiner so that the reject fibrous
material is further reduced and then discharged from the second refiner.
In the alternative, the wood chips are first introduced to a refiner
to reduce the chips to a substantially completely reduced fibrous material and
the reduced fibrous material is discharged from the refiner, separated into
accept fibrous material and reject fibrous material. The refin~r is
pressurized with steam to a pressure of from about 15 p.s.i. to about 75
p.s.i. and heated to about saturation temperature. After the reject fibrous
material has been separated, it is reintroduced into the refiner to be further
reduced and subsequently discharged.
In another alternative, the wood chips are introduced into a first
refiner to reduce the chips to a partially reduced fibrous material which is
discharged from the first refiner and successively introduced lnto and
discharged from at least one more refiner. Then the accept fibrous material
is separated from the re;ect fibrous material. One of the refiners is
pressurized with steam to a pressure of from about 15 p.s.i. to about 75
p.s.i. and heated to about saturation temperature and the r~ject fibrous
msterial is reintroduced into the pressurized refiner so that the reject
fibrous material is further reduced.
Preferably the means for reintroducing the reject fibrous material
includes a plug screw feeder.
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Brief Description of the Drawin~
The accompanying drawing is a schematic illustration of the apparatus
by which a preferred ennbodiment of the metho~ of the present invention may be
carried out.
Detailed Descriptlon
Referring to the dr~wing, wood chips are introduced by nneans of a
feed conveyor 10 to a retention bin 12. The wood chips are discharged from
the retention bin to a pluy screw feeder 14 by means of which they are ~rans-
ported to a steaming tube 16 ~also known as a digester) where they are treated
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with steam. From the base 18 of the steaming tube they are transported by
screw 20 to a conventional first refiner appaxatus 22 where the wood chips
are treated under steam pressure of about 15-75 p.s.i. greater than
atmospheric pressure and at saturation temperature and, as is conventional,
are run between a rotating and a stationary disc or between double counter
rotating discs. Such refiners are well known in the art and are available,
for example, from the Sprout-Waldron Division of Koppers Company, Inc.,
located at Muncy, Pennsylvania. Saturation temperatures for particular steam
pressures are published in Steam Tables by Keenan, Reyes, Hill and Moore
(John Wiley & Sons, 1969). The partially reduced fibrous material discharged
from the first refiner is then removed by means of line 24 to cyclone 26 in
which pressurized steam moves upwardly and is then removed in steam line 28
and in which fibrous material moves downwardly to fiber conveyor 30 which
introduces the fibrous material into a second re~iner 32. The pressurized
steam removed in line 28 can be used to supplement steam requirement in the
drying section of the paper mill. In this second refiner the fibrous material
is preferably under steam pressure of from 15-75 p.s.i. greater than
atmospheric pressure and saturation temperature and is also run between a
stationary and rotating disc. A portion of the steam generated in the second
refiner is removed from the second refiner in line 34 and then line 28 and
fibrous material along with the balance of the generated steam is removed in
steam and fiber line 36 to a second cyclone 38. In this cyclone steam rises
to be removed through steam lines 40 and 28. The fibrous material falls
and is transported to a device 42 which can maintain pressure within the
cyclone while removing fibrous material to an area at atmospheric pressure.
This device 42 may be a swept orifice disc charger, a rotary valve, a plug
screw
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feeder or a high density stock pump. Line 44 transports fi~rous materidl ~o d
conventiondl latency tdnk 48. After the Fibrous mdterial undergoes latency
treatment it is remove~ Vid line 50 to conventiondl cleanintJ and separatiny
appdratus 52 in which dccept fibrous materidl is separdted from reject fibrous
mdteridl. Accept fibrous mdterial is removed in line 54. Reject fibrous
material, on the other hand, is transported in d slurry Vid reject line 56 to
reject press 5~ where water is pressed from it before entering plug screw
feeder 60, After pdsslng through this plug screw feeder the reject fibrous
nlaterial is trans~orted by fiber conveyor 3U alony with other fi~rous nldteridlo being discharged from cyclone 26 to the second refiner where it undergoes the
same treatment in that refiner dS WdS described above. It will be apprecidted
tha~ pressurized stearll production will be proportionally increased with the
addition~l work being done o~ the reject stream in the pressurized secondary
refiner. The reject fibrous Inateridl is then discharged from the secor,d reFi-ner alony with stealll anrd the fibrous materidl oryinally processed in line 36
dnd is then separated from steam in cyclone 3~ and is further processed in
latency tank 48 and cleaning and separating apparatus 52 in the manner descri-
bed above.
It will be appreciated thdt a method and apparatus for the thermo-me-
chanical pulping of wood has been described in which reject fibers can be pro-
cessed at relatively low plant equipment and energy costs has been described,
and that this me~hod also affords a way of recovering a yreater proportion of
the refining ener~lv in the form of pressurized steam. Although -the invention
has been described with a certain degree o-F particularity, it is to be under-
stood that the present disclosure has been made only dS dll exdlll~le and that
the scope of the invention is defined by what is hereafter claimed. In pdrti-
cular, it should be understood that the method and apparatus of the present
inven~ion may to adapted for use with d single reFiner system. That is, after
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wood has been chipped and tredted in the slngle refiner until it is substdn-
tially completely reduced, reject fibrous materials can then be sep~rated and
returned to the sinyle refiner for further reduction dnd additional processing
dS iS described above. It will be understood that the present invention also
encolnpasses the return o-f reject fibrous material to the first refiner in a
two refiner system instead of to the second refiner. Those skilled in the art
will recognize that the reintroduction of the reject fibrous nldteridl into the
~irst refiner could under certain circumstances, result in an over-process~
ing of the nlateridl. Under other circulnstdnces however it will be apprecia--
0 ted that it would be possible to reintroduce reject fibrous material into thefirst refiner for further reduction. Theredfter it would be renloved along
with fibrous material undergoing initial refining~ to the second refiner where
it will be still further reduced and then discharged for further ~rocessing in
the manner described above. Additionally, in a multiple refiner system having
three or Inore refiners it would also be within the scope of the present inven-
tion to reduce wood chips in a first refiner and then further reduce the re-
sultiny partially reduced fibrous nlateridl in the relnainin(J two or nlore other
successively arranged refiners and then separaté accept fronl reject fibrous
nlaterial and -findlly reintroduce the reject fibrous nlaterial into any one o-fsaid refiners. At least the first refiner and preferably the other refiners
in such a three or Inore refiller systenl would be pressurized with steam to a
pressure of from about 15 p.s.i. to about 75 p.s.i. yreater than atmospheric
~ressure and be heated to about saturation temperdture. An appdrdtus -for
carrying out the above described three or more refiner process which includes
a nleans for reintroducing reject fibrous n1ateridl to one oF the refirlers fromthe m~ns for separating accept fibrous material from reject fibrous material
is also within the scope of the present invention, and preferably this rein-
~troduction ans will ~nclude a plug screw feeder.
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