Note: Descriptions are shown in the official language in which they were submitted.
CA 02345762 2001-05-O1
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FEEDING COMMINUTED FIBROUS MATERIAL
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of application Serial
Number 091063,429 filed ,4pril 21, 1998, now Patent No. ~~~ ~0!~a,~~
which in turn is a continuation-in-part of Serial No. 08/738.239 filed
October 25, 1996, now U.S. Patent No. 5,753.075.
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a method and system for feeding
comminuted cellulosic fibrous material to a treatment vessel, such as a
continuous digester. The invention simplifies and dramatically reduces
the number of components needed when compared to the existing art.
U.S. patents 5,476,572, 5,622,598 and 5,635,025 and 5,766,418
introduced the first real breakthroughs in the art of feeding comminuted
cellulosic fibrous material to a treatment vessel in over forty years. These
patents and the application disclose several embodiments, collectively
marketed under the trademark Lo-Level~ feed system by Ahlstrom
Machinery lnc. of Glens Falls, NY, for feeding a digester using a slurry
pump, among other components. As described in these patents and
application, using such a pump to teed a slurry to a high-pressure
transfer device dramatically reduces the complexity and physical size of
the system needed, and increases the ease of operability and
maintainability. The prior art systems employing a high-pressure transfer
device, for example a High-Pressure Feeder as sold by Ahlstrom
Machinery Inc., but without such a pump, are essentially unchanged from
the systems sold and built since the 1940s and 1950s.
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2
The present invention relates to an even more dramatic
improvement to the methods and systems disclosed in the above-
mentioned patent and applications. The present invention actually
eliminates the need for transfer devices, such as a High-Pressure Feeder,
by using high-pressure pumping devices to transfer a slurry of
comminuted cellulosic fibrous material directly to a digester.
The reaction of pulping chemicals with comminuted cellulosic
fibrous material to produce a chemical pulp requires temperatures ranging
between 140-180°C. Since the aqueous chemicals used to treat the
material would boil at such temperatures, commercial chemical pulping is
typically performed in a pressure-resistant vessel under pressures of at
least about 10 bars gauge (approximately 150 psi gauge). In order to
maintain this pressure, especially when performing a continuous pulping
process, special accommodations must be made to ensure that the
pressure is not lost when introducing material to the pressure vessel. In
the prior art this was accommodated by what is known in the art as a
"High-Pressure Feeder". This feeder is a specially-designed device
containing a pocketed rotor which acts as a means for transferring a slurry
of material from a low pressure to a high pressure while also acting as a
valve for preventing loss of pressure. This complicated and expensive
device has long been recognized as an essential component for
introducing slurries of comminuted cellulosic material to pressurized
vessels, typically at elevated temperatures, especially to continuous
digesters.
According to the invention a system which replaces the High-
Pressure Feeder -- which has been recognized for over forty years as
being essential to continuous digesting -- is provided, greatly simplifying
construction of a pulp mill.
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According to one aspect, a system for producing chemical cellulose
pulp from comminuted fibrous cellulose material, such as wood chips,
comprises the following components: A steaming vessel in which
comminuted fibrous cellulose material is steamed to remove the air
therefrom. A superatmospheric pressure vertical treatment vessel having
an inlet for a slurry of comminuted cellulose fibrous material at a top
portion thereof and an outlet at a bottom portion thereof. And,
pressurizing transfer means for pressurizing a slurry of material from the
steaming vessel and transferring it to the treatment vessel inlet, the
pressurizing transfer means consisting of one or more high pressure
slurry pumps located below the top portion of the treatment vessel.
The one or more pumps preferably comprises first and second high
pressure slurry pumps connected in series and each having a pressure
rating, an inlet and an outlet, the first pump inlet operatively connected to
the steaming vessel, the first pump outlet operatively connected to the
second pump inlet, and the second pump having a higher pressure rating
than the first pump. The slurry pumps may be helical screw centrifugal
pumps, double-piston solids pumps, or other similar conventional pumping
devices that are capable of pressurizing a slurry having a relatively high
percentage of solids to (in one or more stages) a pressure of at least
about 5 bar gauge. The pressurizing and transferring may also be
effected by an one or more eductors, of conventional construction, driven
by a pressurized fluid supply, such as supplied by conventional centrifugal
pump.
One typical unit of measure that indicates the relative amount of
solids in a slurry containing solids and liquid is the "liquid-to-solids
ratio".
In this application, this ratio is the ratio of the volume of liquid being
transferred to the volume of cellulose, or wood, material being transferred.
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Typical conventional centrifugal liquid pumps are limited to pumping liquid
having a solids content of at most 3%. This 3% solids content
corresponds to a liquid-to-solids ratio of about 33. In the slurry pumps of
this invention, the liquid-to-solids ratio of the slurry being pumped is
typically between 2 and 10, preferably between 3 and 7, and most
preferably between 3 and 6. In other words, the slurry pumps of this
invention transfer slurries having a much greater solids content than can
be handled by a conventional pump.
A liquid return line may be provided from the top portion of the
treatment vessel, containing liquid separated from the slurry at the top of
the treatment vessel (preferably a continuous digester). The return line
may be operatively connected to an inlet or outlet of one of the slurry
pumps, either directly or indirectly. Preferably the liquid return line is
connected to a pressure reduction means for reducing the pressure of
liquid in the return line before the liquid passes to the inlet or outlet of
the
slurry pump. The pressure reduction means may take a variety of forms,
such as a flash tank and/or a pressure control valve in the return line, or
other conventional structures for effectively reducing the pressure of liquid
in a line while not adversely affecting the liquid. Where a flash tank is
utilized the liquid outlet from the flash tank is connected to the inlet to
the
first slurry pump, and the steam produced by the flash tank may be used
in the steaming vessel.
Alternatively, the pressure reduction may be effected, or even
avoided, by using an eductor which uses the pressurized return line liquor
as its source of pressurized fluid. An eductor may be used in place of or
in conjunction with one or more of the slurry pumps, or other devices, to
transfer slurry to the digester.
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A conventional chute, as well as other optional components, is
preferably connected between the steaming vessel and the at least one
slurry pump, the steaming vessel being located above the chute and the
chute above the at least one slurry pump. The at least one slurry pump is
5 typically located a distance at least 30 feet (about 10 meters) below the
top of the digester, and typically more than about 50 feet (about 15
meters) below.
When the high pressure transfer device is eliminated it is desirable
to utilize other mechanisms to retain one of the functions of the high
pressure transfer device, namely providing pressure relief prevention
should an aberrant condition occur, the high pressure transfer device
typically preventing backflow of liquid from the digester into the feed
system. Pressure relief preventing means according to the present
invention are preferably distinct from the at least one slurry pump,
although under some circumstances the inlets to or outlets from the slurry
pumps may be constructed in a manner so as to provide pressure relief
prevention. The pressure relief preventing means may comprise an
automatic isolation valve in each of the slurry conduits transferring slurry
from the pumps to the top of the treatment vessel and the return line from
the treatment vessel, a conventional controller being provided connected
to the isolation valves and operating the isolation valves in response to
the pressure sensed by a pressure sensor associated with the slurry
conduit feeding slurry to the top of the treatment vessel. The pressure
relief preventing means may also comprise a check valve in the slurry
conduit, and/or a variety of other valves, tanks, sensors, controllers, or
like
fluidic, mechanical, or electrical components which can perform the
pressure relief preventing function.
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The system may also comprise means for augmenting the flow of
liquid to the inlet to the second slurry pump, or to any pump or transfer
device, such as a liquid line having liquid at a pressure below the pressure
at the second slurry pGmp inlet, a conduit bet4veen the liquid line and the
inlet, and a liquid pump in the conduit. The liquid line may be the return
line from the treatment vessel, and the conduit may be connected directly
to the return line. The liquid return line may be connected to a flash tank
as described above, and the conduit may be connected to the flash tank
liquid outlet.
According to another aspect, a method of feeding comminuted
cellufosic fibrous material to the top of a treatment vessel is provided. The
method comprises the steps of: (a) Steaming the material to remove air
therefrom and to heat the material. (b) Slurrying the material with a
cooking liquor to produce a slurry of liquid and material. And, (c)
pressurizing the slurry to a pressure of at least about 5 bar gauge at a
location below the top of the treatment vessel (e.g. at least thirty feet
below, preferably at least fifty feet below), and transferring pressurized
material to the top of the treatment vessel, the pressurizing step
consisting of acting on the slurry with one or more high pressure slurry
pumps.
The method may comprise the further steps of: (d) returning liquid
separated from the slurry at the top of the treatment vessel to the at (east
one pump: and (e) sensing the pressure of the slurry while being
transferred to the top of the treatment vessel, and shutting off the flow of
slurry to the top of the treatment vessel and the return of liquid from the
top of the vessel if the sensed pressure drops below a predetermined
value. There also may be the step (f) of flashing the liquid while returning
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in the practice of step (d) to produce steam, and using the steam in the
practice of step (a).
In an additional embodiment, the concept of transferring a slurry of
chips is extended back to the point where chips are introduced to the mill,
that is, the Woodyard. Conventional pulp mills receive their supply of
ceiluiose material, typically hardwood and softwood but other forms of
cellulose material as described above may be handled, in various forms.
These include as sawdust, as chip, as logs, as long de-limbed trees (that
is, "long wood"), or even as complete trees (that is, "whole trees").
Depending upon the source of cellulose of the "wood supply", the wood is
typically reduced to chip form so that it can be handled and treated in a
pulping process. For example, devices known as "chippers" reduce the
long-wood or logs to chips that are typically stored in open chip piles or
chip silos. This receipt, handling, and storage of the chips is performed in
an area of the pulp mill referred to as the "woodyard". From the
Woodyard the chips are typically transferred to the pulp mill proper to
initiate the pulping process.
In conventional Woodyards, the chips are stored in silos from which
the chips are discharged, typically by means of a rotating or vibrating silo
discharge device, to a conveyor. This conveyor is typically a belt-type
conveyor which receives the chips and transfers them to the pulping
treatment vessels. Since the Woodyard is typically at a distance from the
pulping vessels, this conveyor is typically long. Such conveyors may have
a length of up to one-half mile. In addition, treatment systems that do not
employ the Lo-LevelT"" feeding system, as marketed by Ahlstrom
Machinery and described in US patents 5,476,572, 5,622,598, 5,635,025
and 5,766,416, require that the conveyor be elevated, typically to a height
of at least 100 feet, in order to feed the chips to the inlet of the first
pulping
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vessel. These conveyers, and the structures that support them, are very
expensive and contribute a significant cost to the cost of a digester feed
system.
In another embodiment, the concept of transferring a slurry of ct-~ips
is extended back to the Woodyard. A preferred embodiment of this
invention consists of a method of transferring comminuted cellulosic
fibrous material to a pulping process, consisting of the following steps: (a)
Introducing untreated chips to a first vessel. (b) Introducing slurrying
liquid to the first vessel to create a slurry of material and liquid. (c)
Discharging the slurry from the vessel to the inlet of at least one
pressurizing and transferring device. (d) Pressurizing the slurry in the
pressurizing and sfurrying device and transferring the slurry to a treatment
vessel.
The first vessel is typically a chip storage silo or bin. This bin
preferably has a discharge having one-dimensional convergence without
agitation or vibration, such as a DIAMONDBACK~ bin as described in US
patent #5,000,083, though agitation or vibration may be used. This bin
may also have two or more outlets which feed two or more transfer
devices. This vessel may also be operated at superatmospheric
pressure, for example at 0.1 to 5 bar. If the vessel is operated at
superatmospheric pressure some form of pressure isolation device must
be located at the inlet of the vessel to prevent the release of pressure.
This device may be a star-type isolation device, such as a Low-pressure
Feeder or Air-lock Feeder as sold by Ahlstrom Machinery, or a screw-type
feeder having a sealing capacity as described in U.S. patent 5,766,416.
The slurrying liquid may be any source of liquid available in the
pulp mill, including fresh water, steam condensate, kraft white, black, or
green liquor or sulfite liquor or any other pulping-related liquid. This
liquid
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may be a heated fluid, for example, hot water or steam, having a
temperature of between 50 and 100°C. If the vessel is a pressurized
vessel, liquid temperatures of over 100°C may be used. Though not
essential, this liquid may contain at least some active pulping chemical,
for example, sodium hydroxide (NaOH), sodium sulfide (Na2S),
polysulfide, anthraquinone or their equivalents or derivatives or
surfactants, enzymes or chelates, or combinations thereof.
The pressurizing and transferring device of steps (c) and (d) is
preferably a slurry pump, or pumps, but many other pressurizing and
transferring devices may be used such as the piston-type solids pump or
a high-pressure eductor. Preferably, more than one pressurizing and
slurrying pump is used to transfer the slurry. These may be two or more
slurry pumps, or any combination of slurry pump, piston-type pump, or
eductor. This transfer system may also include one or more storage or
surge tanks as well as transfer devices. Preferably, the one or more
transfer devices include at least one device having de-gassing capability
so that undesirable air or other gases may be removed from the slurry.
Also, during transfer, the chips may be exposed to some form of
treatment, for example, de-aeration or impregnation with a liquid,
preferably a liquid containing pulping chemicals, such as those described
above. The slurry may also be exposed to at least one pressure change
or fluctuation during transfer, for example, such that the pressure of the
slurry is varied from a first pressure to a second, higher pressure, and
then optionally to a third pressure which is lower than the second
pressure. As described in US patents 4,057,461 and 4,743,338 varying
the pressure of a slurry of chips and liquor improves the impregnation of
the chips by the liquor. This pressure pulsation may be achieved by
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varying the outlet pressure of a set of transfer devices in series, or by
controlled depressurization of the slurry between pumping.
In another embodiment, the material need not encounter liquid in
the vessel, but may have liquid firs introduced to it by means of an
5 eductor located in or below the outlet of the vessel. This liquid is
preferably pressurized so that the material and liquid form a pressurized
slurry of material and liquid.
The treatment vessel of step (d) may typically be a steaming
vessel as described above, preferably a DIAMONDBACK~ steaming
10 vessel. The vessel may also be a storage or surge tank in which the
material may be stored prior to treatment. Since the transfer process may
require excess liquor that is not needed during treatment or storage, some
form of de-watering device may be located between the transfer device
and the treatment vessel. One preferred dewatering device is a Top
Separator, as sold by Ahlstrom Machinery. This Top Separator may be a
standard type or an "inverted" Top Separator. This device may be an
external stand-alone-type unit or one that is mounted directly onto the
treatment vessel. An In-line Drainer, also sold by Ahlstrom Machinery,
may also be used for the dewatering device. Preferably, the liquid
removed from the slurry by means of the de-watering device is returned to
the first vessel or to the transfer devices to act as the slurring liquid.
This
liquid may also be used where ever needed in the pulp mill. This liquid
may be heated or cooled as desired. For example, this liquid may be
heated by passing it in indirect heat exchange relationship with any
heated liquid stream, for example, a waste liquid stream having a
temperatures greater than 50°C . This liquid will also typically be
pressurized using one or more conventional centrifugal liquid pumps.
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In one preferred embodiment the treatment vessel of step (d) is a
steaming vessel which feeds one or more transfer devices as described
above. Though this system is preferably used in conjunction with a feed
system not having a conventional High-pressure Feeder, this system may
also be used with a feed system having a High-pressure Feeder.
The method and apparatus for feeding chips from a distant
location, for example, a Woodyard, to a pulping process is not limited to
chemical pulping processes, but may be used in any pulping process in
which comminuted ceilulosic fibrous material is conveyed from one
location to another. The pulping processes that this invention is
applicable to include all chemical pulping processes, all mechanical
pulping processes, and all chemi-mechanical pulping or thermal-
mechanical pulping processes, for either batch or continuous treatment.
According to another aspect there is provided a method of feeding
wood chips to the top of a treatment vessel comprising the steps of: (a)
Steaming the wood chips to remove air therefrom and to heat the
material. (b) Slurrying the wood chips with a cooking liquor to produce a
slurry of liquid and material. (c) Pressurizing the slurry to a pressure of at
least about 5 bar gauge at a location at least thirty feet below the top of
the treatment vessel and transferring pressurized wood chips to the top of
the treatment vessel, the pressurizing step consisting essentially of acting
on the slurry with one or more high pressure slurry pumps. And, (d)
during the practice of the transferring step (c), treating the wood chips with
polysulfide, anthraquinone or their equivalents or derivatives, surfactants,
enzymes, chelants, or combinations thereof.
Where the treatment vessel is upstream of a continuous or batch
digester, step (c) is typically practiced downstream of the treatment
vessel. There may also be the further step (e), before the continuous or
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batch digester and substantially immediately after steps (a) and (b), of
pressurizing the slurry at a location at least 30 feet below the top of the
digester, and transferring pressurized wood chips to the top of the
digester, the pressurizing step consisting of acting on the slurry with one
or more high pressure slurry pumps. There may also be the step of
returning liquid removed from the digester to the treatment vessel, and
adjusting the temperature of the liquid while returning it to the treatment
vessel. The step of removing liquid from the treatment vessel typically
takes place at the top of the treatment vessel.
The method may also comprise the further step of returning liquid
from downstream of the treatment vessel to the treatment vessel, and
adjusting the temperature of the liquid, and the step of adjusting the
temperature of the liquid may take place by passing the liquid through an
indirect heat exchanger. The method may also comprise the further step
of returning liquid separated from the slurry at the tap of the digester to
the one or more slurry pumps, pressurizing the slurry to transfer it to the
digester, and adjusting the temperature of the removed liquid during
recirculation.
The system and method herein not only reduce the size and cost of
the system for transferring comminuted cellulosic fibrous material, but if
the comminuted cellulosic fibrous material is treated during transfer, the
number and size of the formal treatment vessels may be reduced. For
example, this system may eliminate the need for conventional
pretreatment or impregnation vessels prior to the digester. This system
also has the potential for improving the over-all energy economy of the
pulp mill. This and other aspects of the invention will become manifest
upon review of the detailed description and figure below.
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According to another aspect a method of treating comminuted
cellulosic fibrous material using at least first and second series connected
pumps, and at least first and second in series stations each with a
solidslliquid separator is provided. The method comprises the steps of:
(a) Pumping a slurry of comminuted cellulosic fibrous material using the
series connected pumps. (b) Separating some liquid from the slurry at
each station to substantially isolate liquor circulations and streams, and to
recirculate removed liquid from at least one of the stations to upstream of
one of the pumps. And (c) adding chemicals to the slurry upstream of
each of the pumps, the chemicals including at least some chemical
selected from tf ie group consisting essentially of sodium hydroxide,
sodium sulfate; polysulfide, anthraquinone, or their equivalents or
derivatives; surfactants, enzymes, or chelants; or combinations thereof; so
that pre-treatment of the material occurs during transfer of the material
from each pump to each station.
There may be the further step of degassing the slurry at at least
one of the stations. At least first, second and third series connected
pumps and stations may be provided; and there may also be the further
steps of: (d) Circulating liquid removed from the third station to a location
upstream of the second pump, and (e) circulating liquid removed form the
second station to a location upstream of the first pump (step (d) may be
practiced downstream of the first station). There may also be the further
step of passing the removed liquid, during the practice of at least one of
steps (d) and (e), through a heat exchanger to change the temperature
thereof. For example, the temperature of the removed liquid may be
increased or decreased by from about 1 to about 10°C, depending upon
the volume of the liquid and the amount of heating or cooling available.
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Step (c) may be practiced by adding a different chemical, or
combination of chemicals, upstream of each pump, so that significantly
different treatments of the material of the slurry take place during transfer
of the slurry from each pump to its associated station. Step (a) may be
practiced to pressurize the slurry to a pressure of at least 5 bar. Also,
there may be the further step of removing liquid from at least one of the
stations through an eductor (also known as an ejector) instead of a flash
tank and/or control valve.
According to another aspect of this invention, one treatment that
can be used during the transfer of comminuted cellulosic fibrous material
is the removal of metal ions. It is recognized in the art that the presence
of certain metallic compounds or ions, for example, those containing iron,
calcium, manganese, and others, can interfere with pulping and bleaching
reactions or can precipitate as undesirable "scale" on the treatment
equipment. It is also known the metal content of the cellulose material
can be reduced by exposing the material to acidic liquids which can
dissolve metal compounds or ions or to acidic to slightly alkaline
conditions in the presence of a chelating agent (also known as a
sequestering agent) which combine with certain metals and make them
more easily isolated and removed, for example, by washing. According to
the present invention, these deleterious metal-containing compounds and
ions are removed from the cellulose material prior to the cooking process
and bleaching process so that these metals do not interfere with these
processes nor form scale on the equipment used to effect these
processes.
According to this aspect of the invention, there is provided a
method of treating a slurry of comminuted cellulosic fibrous material using
at least first and second series connected pumps, and at least first and
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second in-series stations, each with a solidslliquid separator, in which the
metal content of the material is reduced. The method comprises: (a)
Pumping a slurry of comminuted cellulosic fibrous material using the
series connected pumps. (b) Separating some liquid from the slurry at
5 each station to substantially isolate liquor circulations and streams, and
to
recirculate removed liquid from at least one of the stations to upstream of
one of the pumps. And (c) adding chemicals which dissolve or sequester
metal containing compounds to the slurry at or upstream of at least one of
the pumps, the chemicals including at least one chemical selected from
10 the group consisting essentially of acids, chelating agents, and
combinations thereof, so that at least some of the deleterious metals (e.g.
at least about 10%, preferably about 20%-80%) present in the material
prior to treatment are removed from the material.
There may further be (d) removing at least some of the liquid from
15 the slurry during (a) or (b) to purge at least some (e.g. at least about
10%,
preferably about 20%-80%) of the metal containing compounds from the
liquor circulations. This liquid may be removed in a liquor separating
device, for example, a conventional Top Separator or In-line drainer, or
the liquid may simply be removed via a branch conduit in the circulation
line. Also (d) may also be practiced at substantially the same time as and
using substantially the same equipment in which (b) is practiced. There
may also further be (e) introducing liquid to the circulation to substantially
replace the liquid removed in (d}. The liquid introducing procedure (e)
may be practiced substantially immediately downstream of where (d) is
practiced or elsewhere in the system. Also (e) may be practiced
substantially in conjunction with (c) so that replacement liquid is
introduced substantially with the treatment chemical.
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16
This invention is preferably practiced before a further procedure (f)
of treating the material with an alkaline liquid and (g) digesting the
material in an alkaline digestion process; preferably (a)-(e) are practiced
substantially immediately prior to (f) and (g). The alkaline liquid may
comprise, for example, kraft white, green, or black liquor (which may
contain yield or strength enhancing additives as described above). Thus,
in a preferred embodiment of the invention, the chemical used to effect (c)
is introduced at or upstream of the first pump and the chemical used to
effect (f) is introduced at or upstream of the second pump.
According to another aspect a method of treating comminuted
cellulosic fibrous material is provided comprising the steps of: (a)
Pumping a slurry of comminuted cellulosic fibrous material using the at
least first and second series connected pumps. (b) Separating some
liquid from the slurry at each station to substantially isolate liquor
circulations and streams, and to recirculate removed liquid from at Feast
one of the stations to upstream of one of the pumps. (c) Adding treatment
chemical to the slurry upstream of at least one of the pumps so that pre-
treatment of the material occurs during transfer of the material from that
pump to its associated station. And (d) circulating liquid removed form the
second station to a location upstream of the first pump. Where at least
first, second and third pumps and stations are provided, there is the
further step (e) of circulating liquid removed from the third station to a
location upstream of the second pump. The details of the steps, or
additional steps, may be as set forth above.
According to one aspect of the invention there is provided a system
for producing chemical cellulose pulp from comminuted fibrous cellulose
material, comprising: A steaming vessel in which comminuted fibrous
cellulose material is steamed to remove the air therefrom. A
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superatmospheric pressure vertical treatment vessel having an inlet for a
slurry of comminuted cellulose fibrous material at a top portion thereof and
an outlet at a bottom portion thereof. Pressurizing transfer means for
pressurizing a slurry of material from the steaming vessel and transferring
it to the treatment vessel inlet, the pressurizing transfer means consisting
of one or more high pressure slurry pumps, each having an inlet and
outlet, located below the top portion of the treatment vessel. And means
for circulating liquid from the outlet of at least one the high pressure
slurry
pump to the inlet thereof.
The recirculation means may be conduits and associated
connections to other components, although any conventional structures
which allow or provide this recirculation may be utilized including valves
(in or apart from the conduits), tanks, ejectors, pumps, ducts, heat
exchangers, or the like.
The system preferably further comprises a liquid return line from
the top portion of the treatment vessel, the return line operatively
connected to an inlet or outlet of one of the slurry pumps.
The system may also comprise a heat exchanger located in the
return line, which preferably is a liquid-to-liquid indirect heat exchanger.
While the heat exchanger may be used for cooling or heating liquid in a
return line preferably it is connected to a source of cool liquid and cools
the liquid in the return line, so that it is below the point where it will
flash in
the system.
The system may further comprise a slurrying vessel having an inlet
operatively connected to the steaming vessel and an outlet operatively
connected to the inlet of the one or more slurry pumps; the system may
still further comprise a liquid return line from the top portion of the
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treatment vessel, the return line operatively connected to the slurry
vessel, and the heat exchanger in the return line.
Preferably the at least one pump comprises at least two pumps,
and each of the pumps has a recirculation means as described above.
The recirculation means may comprise a first valve in a recirculation
conduit, and a second valve between the pump outlet and the treatment
vessel, and preferably each of the pumps has a recirculation means as
described above associated therewith.
The treatment vessel may be a first treatment vessel, and the
i 0 system may further comprise a second treatment vessel. The main
conduit is connected to the outlet of the pump (or the last in a series of
pumps), and a flow sputter is provided having an inlet and at least two
outlets. The main conduit is connected to the flow splitter inlet, and one of
the flow splitter outlets is connected to the first treatment vessel, and
another outlet to the second treatment vessel. The first treatment vessel
may also include two or more inlets and the at least two or more outlets of
the flow splitter may be connected to the two or more inlets of the first
vessel. The flow splitter may comprise a chamber having a substantially
triangular shaped static baffle plate arrangement with a triangle apex
substantially aligned with the inlet.
According to another aspect of the invention there is provided a
method of feeding ceilulosic material to the top of a treatment vessel
comprising the steps of: (a) Steaming the material to remove air
therefrom and to heat the material. (b) Slurrying the material with a
cooking liquor to produce a slurry of liquid and material. And (c)
pressurizing the slurry at a location at least thirty feet below the top of
the
treatment vessel and transferring pressurized material to the top of the
CA 02345762 2001-05-O1
19
treatment vessel. the pressurizing step consisting of acting on the slurry
with two or more high pressure slurry pumps.
The method may also comprise (d) establishing a recirculation loop
between each pump outlet and inlet during startup. For example, there
may be a first valve in the recirculation loop and a second valve between
each pump outlet and the treatment vessel, in which case (d) is practiced
to open the first valve and at least partially (e.g. completely) close the
second valve during startup. Then the method may further comprise (e)
after startup closing the first valve and opening the second valve. The
method may also further comprise returning the liquid from the treatment
vessel to one of the pump inlets (preferably a first in-series pump) and
partially cooling the cooling liquid (e.g. with an indirect liquid-to-liquid
heat
exchanger) so that the returning liquid has a temperature below the point
it will flash during handling.
The method may be practiced further utilizing at least a second
treatment vessel or a first treatment vessel having two or more inlets, and
may further comprise statically splitting the flow of slurry from the outlet
of
the last of the pumps to direct part of the flow to each treatment vessel or
the inlets of the first treatment vessel.
According to another aspect of the present invention there is
provided a method of feeding comminuted ceilulosic fibrous material to
the top of a treatment vessel, comprising: (a) Steaming the material to
remove air therefrom and to heat the material. (b) Slurrying the material
with a cooking liquor to produce a slurry of liquid and material; (c)
Pressurizing the slurry at a location at least thirty feet below the top of
the
treatment vessel and transferring pressurized material to the top of the
treatment vessel, said pressurizing step consisting of acting on the slurry
with one or more high pressure slurry pumps. And (d) establishing a
CA 02345762 2001-05-O1
recirculation loop between the pump outlet and inlet during startup. A first
valve may be provided in the recirculation loop and a second valve
between the pump outlet and the treatment vessel; and (d) may be
practiced to open the first valve and at least partially close the second
5 valve during startup; and the method may further comprise (e) after
startup closing the first valve and opening the second valve. Cooling and
returning liquid, and flow splitting, may also be practiced, as described
above.
According to another aspect of the present invention there is
10 provided a static flow splitter comprising: A static chamber. An inlet and
at least two outlets connected to the chamber. And a substantially
triangular shaped static baffle plate arrangement may be located within
the chamber and have a triangle apex substantially aligned with the inlet.
It is the primary object of the present invention to provide a simple
15 and effective system and method for feeding cellulose slurry to a
treatment vessel, and also while achieving enhanced operability and
maintainability. This and other objects of the invention will become clear
from an inspection of the detailed description of the invention and from
the appended claims.
20 BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 illustrates a typical prior art system for feeding a slurry
of comminuted cellulosic fibrous material to a continuous digester;
FIGURE 2 illustrates another prior at system for feeding a slurry of
comminuted cellulosic fibrous material to a continuous digester;
CA 02345762 2001-05-O1
21
FIGURE 3 illustrates one typical embodiment of a system for
feeding a slurry of comminuted cellulosic fibrous material to a continuous
digester according to this invention;
FIGURES 4 and 5 illustrate two other embodiments of systems
according to the invention;
FIGURE 6 is a schematic representation of another system that
may be used for practicing a method according to the invention;
FIGURE 7 is a schematic illustration of another typical system for
feeding a slurry of comminuted cellulosic fibrous material to a digester,
according to the invention;
FIGURE 8 is a side view, with a portion of the near wall of the flow
chamber cut away so as to illustrate the interior thereof, of an exemplary
flow splitter according to the present invention; and
FIGURES 9 and 10 are top and end views of the flow splitter of
FIGURE 8.
DETAILED DESCRIPTION OF THE DRAWINGS
Though the systems shown and described in FIGURES 1-3 are
continuous digester systems, it is understood that the method and system
of the present invention can also be used to feed one or more batch
digesters, or an impregnation vessel connected to a continuous digester.
The continuous digesters shown and which may be used with this
invention are preferably KAMYR~ continuous digesters, and may be used
for kraft (i.e., sulfate) pulping, sulfite pulping, soda pulping or equivalent
CA 02345762 2001-05-O1
22
processes. Specific cooking methods and equipment that may be utilized
include the MCC~, EMCC~, and Lo-Solids~ processes and digesters
marketed by Ahlstrom Machinery Inc. Strength or yield retaining additives
such as anthraquinone, polysulfide, or their equivalents or derivatives may
also be used in the cooking methods utilizing the present invention.
FIGURE 1 illustrates one typical prior art system 10 for feeding a
slurry of comminuted cellulosic fibrous material, for example, softwood
chips, to the top of a continuous digester 11. Digester 11 typically
includes one liquor removal screen 12 at the inlet of the digester 13 for
removing excess liquor form the slurry and returning it to feed system 10.
Digester 11 also includes at least one liquor removal screen 14 for
removing spent cooking liquor during or after the pulping process.
Digester 11 also typically includes one or more additional liquor removal
screens (not shown) which may be associated with cooking liquor
circulation, such as an MCC~, EMCC~ digester cooking circulation, or a
Lo-Solids~ digester circulation having a liquor removal conduit and a
dilution liquor addition conduit. Cooking liquor, for example, kraft white,
black, or green liquor, may be added to these circulations. Digester 11
also includes an outlet 15 for discharging the chemical pulp produced
which may be passed on to further treatment such as washing or
bleaching.
In the prior art feed system 10 shown in FIGURE 1, comminuted
cellulosic fibrous material 20 is introduced to chip bin 21. Typically, the
material 20 is softwood or hardwood chips but any form of comminuted
cellulosic fibrous material, such as sawdust, grasses, straw, bagasse,
kenaf, or other forms of agricultural waste or a combination thereof, may
be used. Though the term "chips" is used in the following discussion to
refer to the comrninuted cellulosic fibrous material, it is to be understood
CA 02345762 2001-05-O1
23
that the term is not limited to wood chips but refers to any form of the
comminuted cellulosic fibrous materials listed above, or the like.
The chip bin 21 may be a conventional bin with vibratory discharge
or a DIAMONDBACK~ steaming vessel, as described in U.S. patent
5,500,083 and sold by Ahlstrom Machinery Inc., having no vibratory
discharge but having an outlet exhibiting one-dimensional convergence
and side relief. The bin 21 may include an airlock device at its inlet and a
means for monitoring and controlling the level of chips in the bin and a
vent with an appropriate mechanism for controlling the pressure within the
bin. Steam, either fresh or steam produced from the evaporation of waste
liquor (i.e., flashed steam), is typically added to bin 21 via one or more
conduits 22.
The bin 21 typically discharges to a metering device, 23, for
example a Chip Meter sold by Ahlstrom Machinery, but other forms of
devices may be used, such as a screw-type metering device. The
metering device 23 discharges to a pressure isolation device 24, such as
a Low-Pressure Feeder sold by Ahlstrom Machinery. The pressure
isolation device 24 isolates the pressurized horizontal treatment vessel 25
from the essentially atmospheric pressure that exists above device 24.
Vessel 25 is used to treat the material with pressurized steam, for
example steam at approximately 10-20 psig. The vessel 25 may include a
screw-type conveyor such as a Steaming Vessel sold by Ahlstrom
Machinery. Clean or flashed steam is added to the vessel 25 via one or
more conduits 28.
After treatment in vessel 25, the material is transferred to a high-
pressure transfer device 27, such as a High-Pressure Feeder sold by
Ahlstrom Machinery. Typically, the steamed material is transferred to the
feeder 27 by means of a conduit or chute 26, such as a Chip Chute sold
by Ahlstrom Machinery. Heated cooking liquor, for example, a
CA 02345762 2001-05-O1
24
combination of spent kraft black liquor and white liquor, is typically added
to chute 26 via conduit 29 so that a slurry of material and liquor is
produced in chute 26.
if the prior art system of FIGURE 1 does employ a
DIAMONDBACK~ steaming vessel as disclosed in U.S. patent 5,000,083,
which produces improved steaming under atmospheric conditions, the
pressurized treatment vessel 25 and the pressure isolation device 24 may
be omitted.
The conventional High-Pressure Feeder 27 contains a low
pressure inlet connected to chute 26. a low pressure outlet connected to
conduit 30, a high-pressure inlet connected to conduit 33, a high-pressure
outlet connected to conduit 34, and a pocketed rotor driven by a variable-
speed electric motor and speed reducer (not shown). The low pressure
inlet accepts the heated slurry of chips from chute 26 into a pocket of the
rotor. A screen in the outlet, at 30, of the feeder 27 retains the chips in
the rotor but allows the liquor in the slurry to pass through the rotor to be
removed via conduit 30 and pump 31. As the rotor turns the chips that
are retained within the rotor are exposed to high pressure liquid from
pump 32 via conduit 33. This high-pressure liquor slurries the chips out of
the feeder and passes them to the top of digester 11 via conduit 34. Upon
reaching the inlet of digester 11 some of the excess liquor used to slurry
the chips in conduit 34 is removed from the slurry via screen 12. The
excess liquor removed via screen 12 is returned to the inlet of pump 32
via conduit 35. The liquor in conduit 35, to which fresh cooking liquor may
be added, is pressurized in pump 32 and passed in conduit 33 for use in
slurrying the chips out of feeder 27. The chips that are retained by the
screen 12 pass downwardly in the digester 11 for further treatment.
The liquor removed from feeder 27 via conduit 30 and pump 31 is
recirculated to the chute 26 above the feeder 27 via conduit 36, sand
CA 02345762 2001-05-O1
separator 37, conduit 38, in-line drainer 39 and conduit 29. Sand
separator 37 is a cyclone-type separator for removing sand and debris
from the liquor. In-line drainer 39 is a static screening device which
removes excess liquor from conduit 38 and passes it through conduit 39'
5 and stores it in level tank 40. Liquor stored in tank 40 is returned to the
top of the digester via conduit 41, pump 42 (i.e., the Make-up Liquor
Pump), and conduit 43. Fresh cooking liquor may also be added to
conduits 41 or 43.
FIGURE 2 illustrates another prior art system 110 for feeding chips
10 to a digester. This system uses processes and equipment described in
U.S. patents 5,476,572, 5,622.598 and 5,635,025. This equipment and
the processes they are used to effect are collectively marketed under the
trademark Lo-LevelT"~ by Ahlstrom Machinery. The components in
FIGURE 2 which are identical to those that appear in FIGURE.1 are
15 identified by the same reference numbers. Those components which are
similar or which perform similar functions to those that appear in FIGURE
1 have their reference numbers that appear in FIGURE 1 prefaced by the
numeral "1 ".
Similar to the system of FIGURE i, chips 20 are introduced to
20 steaming vessel 121 where they are exposed to steam introduced via
conduit 22. The vessel 121 discharges to metering device 123, and then
to conduit 126, which is preferably a Chip Tube as sold by Ahlstrom
Machinery. Cooking liquor is typically introduced to tube 126 via conduit
55, similar to conduit 29 of FIGURE 1. Since the vessel 121 is preferably
25 a DIAMONDBACKS steaming vessel as described in U.S. patent
5,000,083, no pressure isolation device, 24 in FIGURE 1, or pressurized
steaming vessel 25 in FIGURE 1, are needed in this prior art system. As
disclosed in US patent 5,476,572 instead of discharging the slurry of chips
and liquor directly to feeder 27, a high-pressure slurry pump 51 fed by
CA 02345762 2001-05-O1
26
conduit 50 is used to transport the chips to the feeder 27 via conduit 52.
The pump 51 is preferably a Hidrostal pump as supplied by Wemco, or
similar pump supplied by the Lawrence company. The chips that are
passed via pump 51 are transported to digester 11 by feeder 27 in a
manner similar to what was shown and described with respect to FIGURE
1.
In addition to using the pump 51 to pass the slurry to the feeder 27,
the system of FIGURE 2 does not require the pump 31 of FIGURE 1.
Pump 51 supplies the motive force for passing liquor through the feeder
27, through conduit 30, sand separator 37 , in-line drainer 39, and conduit
129 to liquor level tank 53.
The function of level tank 53 is disclosed in pending application
081428,302, filed on April 25, 1995. The tank 53 ensures a sufficient
supply of liquor to the inlet of the pump 51, via conduit 54. This tank may
also supply liquor to tube 126 via conduit 55. This liquor tank 53 also
allows the operator to vary the liquor level in the feed system such that, if
desired, the liquor level may be elevated to the metering device 123 or
even to the bin 121. This option is also described in pending application
08/354,005, filed on December 5, 1994.
FIGURE 3 illustrates one preferred embodiment of a feed system
210 that simplifies even further the prior art feeding systems shown in
FIGURES 1 and 2. In the preferred embodiment shown in FIGURE 3, the
high-pressure transfer device, component 27 of FIGURES 1 and 2, has
been eliminated. Instead of transferring chips to the feeder 27 by means
of gravity in chute 26 of FIGURE 1 or via pump 57 in FIGURE 2, at least
one, preferably two, high-pressure slurry pumps 251, 251' are used to
transport the slurry to the inlet of the digester 11. The components in
FIGURE 3 which are essentially identical to those that appear in
FIGURES 1 and 2 are identified by the same reference numbers. Those
CA 02345762 2001-05-O1
2?
components which are similar or which perform similar functions to those
that appear in FIGURES 1 and 2 have their reference numbers that
appear in FIGURES 1 and 2 prefaced by the numeral "2".
Similar to the procedure in FIGURES 1 and 2, according to the
embodiment of FIGURE 3, chips 20 are introduced to steaming vessel
221. The chips are preferably introduced by means of a sealed horizontal
conveyor as disclosed in pending application 08/713,431, filed on
September 13, 1996. Also, the steaming vessel 221 is preferably a
DIAMONDBACK~ steaming vessel as described in U.S. patent 5,000.083
to which steam is added via one or more conduits 22. The steaming
vessel 221 typically includes conventional level monitoring and controls as
well as a pressure-relief device (not shown). Vessel 221 discharges
steamed chips to metering device 223, which, as described above, may
be a pocketed rotor-type device such as a Chip Meter or a screw-type
device.
In one embodiment the metering device 223 discharges directly to
conduit or chute 226. However, in an optional embodiment, a pressure
isolating device, such as a pocketed rotor-type isolation device, shown in
dotted line at 224, for example a conventional Low-pressure Feeder, may
be located between metering device 223 and chute 226. Though without
the pressure-isolation device 224 the pressure in chute 226 is essentially
atmospheric, with a pressure isolation device 224 the pressure in chute
226 may range from 1 to 50 psig, but is preferably between 5 to 25 psig,
and most preferably between about 10 to 20 psig. Cooking liquor, as
described above, is added to chute 226 (see line 226' in FIGURE 3) so
that a slurry of chips and liquor is produced in chute 226 having a
detectable level (not shown). The slurry in chute 226 is discharged via
radiused outlet 250 to the inlet of pump 251. The introduction of slurry to
the inlet of pump 251 is typically augmented by liquor flow from liquor tank
CA 02345762 2001-05-O1
28
253 via conduit 254 as described in pending application serial no.
08/428, 302.
Pump 251 is preferably a centrifugal high-pressure, helical screw,
slurry pump, such as a "Hidrostal" pump supplied by Wemco of Salt Lake
City, Utah. The pump 251 may alternatively be a slurry pump supplied by
the Lawrence Company of Lawrence, Massachusetts. The pressure at
the inlet to pump 251 may vary from atmospheric to 50 psig depending
upon whether a pressure isolation device 224 is used.
In the preferred embodiment illustrated in FIGURE 3, the outlet of
pump 251 discharges to the inlet of pump 251'. Pump 251' is preferably
the same type of pump as pump 251 but with the same or a higher
pressure rating. If two pumps are used, the pressure produced in the
outlet of pump 251' typically ranges from 150 to 400 psig (i.e., 345-920
feet of water, gauge), but is preferably between about 200 and 300 psig
(i.e., 460-690 feet). If necessary, the liquor in the slurry in conduit 252
may be augmented by liquor from tank 253 via conduit 56 and liquid pump
57.
Though the embodiment illustrated in FIGURE 3 includes two
pumps, only one pump, or even three or more pumps, in series or parallel,
may alternatively be used. In these cases, the discharge pressure from
the one pump, or from the last pump, is preferably the same as the
discharge pressure from pump 251' above.
The pressurized, typically heated, slurry is discharged from pump
251' to conduit 234. Conduit 234 passes the slurry to the inlet of
continuous digester 11. Excess liquor in the slurry is removed via screen
12 as is conventional. The excess liquor is returned to the feed system
210 via conduit 235, preferably to liquor tank 253 for use in slurrying in
conduit 250 via conduit 254. The liquor in conduit 235 may be passed
through a sand separator 237 if desired. This sand separator 237 may be
CA 02345762 2001-05-O1
29
designed for pressurized or unpressurized operation depending upon the
mode of operation desired.
Unlike the prior art systems employing a High-Pressure Feeder (27
in FIGURES 1 and 2) which uses the pressure of the liquor returned via
conduit 35 as an integral part of the method of slurrying from the High-
Pressure Feeder to the digester 11, it is not essential for the operation of
the present invention that the pressurized recirculation 235 be returned to
the inlet of the pumps 251, 251'. The energy available in the pressure of
the flow in line 235 may be used wherever necessary in the pulp mill.
However, in a preferred embodiment, the present invention does utilize
the pressure available in conduit 235 to minimize the energy requirements
of pumps 251 and 251' as much as possible.
How the pressure in return line 235, typically about 150 to 400 psig
is used depends upon the mode of operation of the feed system 210. If
vessel 226 is operated in an unpressurized - essentially atmospheric -
mode, the pressurized liquor returned in conduit 235 must be returned to
essentially atmospheric pressure before being introduced to conduit 250.
One means of doing this is to use a pressure control valve 58 and a
pressure indicator 59 in conduit 235. The opening in valve 58 is
controlled such that a predetermined reduced pressure exists in line 23~~
downstream of valve 58. In addition, the liquor tank 253 may be designcc
so that it acts as a "flash tank" so that the hot pressurized liquor in
cond~.it
235 is rapidly evaporated to produce a source of steam in vessel 253.
This steam can be used, among other places, in vessel 221 via conduit
60. However, instead, in a preferred embodiment, the pressurized liquor
in conduit 235 is used to augment the flow out of pump 251', for example
via conduit 61 and pump 62. The pressure in conduit 235 may also be
used to augment the flow between pumps 251 and 251' in conduit 252 via
conduit 63, with or without pump 64 (a check valve rnay in some cases be
CA 02345762 2001-05-O1
used in place of or in addition to each of pumps 62, 64). By re-using
some of the pressure available in line 235, some of the energy
requirements of pumps 251 and 251' may be reduced.
Also, the heat of the liquor in line 235 can also be passed in heat
s exchange-relationship with one or more other liquids in the pulp mill that
need to be heated.
The pressurizing and transferring of pumps 251 and 251' may
instead by effected by a conventional eductor, for example, an eductor
manufactured by Fox Valve Development Corporation. Or pumps 251,
10 251' may be used in conjunction with an eductor for increasing the
pressure in the inlet or outlet of the pumps. An eductor may also be used
as a means of introducing liquid to the chips. For example, an eductor
may be located in the outlet of or beneath vessel 226 and liquid first
introduced to the chips by means of this eductor. The eductor may
15 comprise a venturi-type orifice in one or more conduits 250, 252, and 234
into which a pressurized stream of liquid is introduced. This pressurized
liquid may be obtained from any available source but is preferably
obtained from conduit 235, upstream of valve 58. An exemplary eductor
is shown schematically at 70 in FIGURE 3.
20 The pumps 251 and 2~1' need not be centrifugal pumps but may
be any other form of slurry transfer device that can directly act on to
pressurize and transfer a slurry of chips and liquor from the outlet of
vessel 226 to the inlet of digester 11. For instance, a solids pump as
typically used in the mining industry may be used; for example, a double-
25 piston solids pump such as the KOS solids pump sold by Putzmeister, or
any other similar conventional pumping device may be used.
One function of the prior High-Pressure Feeder 27 of FIGURES 1
and 2 is to act as a shut-off valve to prevent possible escape of the
pressure in the equipment and transfer conduits, for example, conduits 34
CA 02345762 2001-05-O1
31
and 35 of FIGURE 1, should any of the feed components malfunction or
fail: In the feed system 210 according to the present invention, alternative
means are provided to prevent such release of pressure due to
malfunction or failure. For example, FIGURE 3 illustrates a one-way
(check) valve 65 in conduit 234 to prevent pressurized flow from returning
to pump 251 or 251'. In addition, conventional automatic (e.g. solenoid
operated) isolation valves 66 and 67 are located in conduits 234 and 235,
respectively, to isolate the pressurized conduits 234, 235 from the rest of
the feed system 210. In one preferred mode of operation, a conventional
pressure switch 68 is located downstream of pump 251' in conduit 234.
The switch 68 is used to monitor the pressure in line 234 so that should
the pressure deviate from a predetermined value, the conventional
controller 69 will automatically isolate digester 11 from feed system 210
by automatically closing valves 66 and 67. These valves may also be
automatically closed when a flow direction sensor detects a reversal of
flow in conduit 234.
While the pressure release preventing means 65-69 described
above is preferred, other arrangements of valves, sensors, indicators,
alarms, or the like may comprise the pressure release preventing means
as long as such arrangements adequately perform the function of
preventing significant depressurization of the digester 11.
While the system 210 is preferably used with a continuous digester
11, it also may be used with other vertical superatmospheric (typically a
pressure of at least about 10 bar gauge) treatment vessels having a top
inlet, such as an impregnation.vessel or a batch digester.
FIGURE 4 illustrates a further embodiment in which the concept of
transferring chips is extended from the feed system of a digester to the
Woodyard of a pulp mill. FIGURE 4 illustrates a system 510 for feeding
comminuted cellulosic fibrous material to a pulping process. It consists of
CA 02345762 2001-05-O1
32
a subsystem 410 for introducing chips from the Woodyard to system 510
and a subsystem 310 for treating and feeding chips to digester 11.
Subsystem 310 is essentially identical to the system 210 shown in
FIGURE 3.
Again, the components in FIGURE 4 which are identical to those
that appear in FIGURES 1-3 are identified by the same reference
numbers. Those components which are similar or which perform similar
functions to those that appear in FIGURE 1-3 have their reference
numbers that appear in FIGURE 1 prefaced by the numeral "3".
The Woodyards of conventional pulp mills receive their wood
supply in various forms as described above. Typically, the wood, or other
comminuted cellulosic fibrous material, is converted to chip like form and
stored either in open chip piles or in chip storage silos. In FIGURE 4 the
chip supply is shown as chip pile 80. In a preferred embodiment of this
invention the chips from pile 80 or some other storage vessel are
conveyed by conventional means, e.g., a conveyor or front-end loader
(not shown), and introduced 20 to vessel 81. This vessel may be a
DIAMONDBACK~ vessel or any other conventional storage vessel.
Vessel 81 may be operated at superatmospheric pressure, for example at
0.1 to 5 bar. If the vessel is operated at superatmospheric pressure,
some form of pressure isolation device (not shown) may be located at the
inlet of the vessel to prevent the release of pressure. This device may be
a star-type isolation device, such as a Low-pressure Feeder or Air-lock
Feeder as sold by Ahlstrom Machinery, or a screw-type feeder having a
sealing capacity as described in co-pending application 081713,431.
Liquid, for example fresh water, steam, liquids containing cooking
chemicals is introduced to vessel 81 via one or more conduits 82 to
produce a slurry of liquid and chips and to provide a detectable liquid
level in vessel 81. Means for monitoring and controlling the level of the
CA 02345762 2001-05-O1
33
liquid, and the level of the chips, in vessel 81 may be provided. This liquid
may be a heated liquid, for example, hot water or steam, having a
temperature of between 50 and 100°C. If the vessel is a pressurized
vessel, liquid temperatures of over 100°C may be used. Preferably,
though not essentially, this liquid may contain at least some active pulping
chemical, for example, sodium hydroxide (NaOH), sodium sulfide (Na2S),
polysulfide, anthraquinone or their equivalents or derivatives or
surfactants, enzymes or chelants, or combinations thereof.
From vessel 81, the slurry is discharged to the inlet of slurry pump
85 via conduit 84. The discharge from vessel 81 may be aided by a
discharge device 83 (probably not necessary if a DIAMONDBACK
discharge is used). The flow of slurry in conduit 84 may also be aided by
the addition of liquid via conduit 82'. The conduit 82' may be the only
mechanism for introducing liquid, so that a liquid level is present in conduit
84 or not in vessel 81. Pump 85 may be any type of slurry pump
discussed above, for example, a Wemco or Lawrence pump or their
equivalents, any other type of solids or slurry transfer device. Though
only one pump 85 is shown, more than one pump or similar devices may
be used to transfer the slurry via conduit 86 to vessel 321. The slurry
transfer via conduit 86 may include one or more storage or surge tanks
(not shown). Preferably, the one or more pumps 85 include at least one
device having de-gassing capability so that undesirable air or other gases
may be removed from the slurry.
The slurry discharged from pump 85 is transferred via conduit 86
to subsystem 810. Subsystem 810 may be located adjacent subsystem
710, that is, within about 30 feet of subsystem 710, or may be spaced an
appreciable distance from subsystem 710, for example one-half mile or
more away, depending upon the layout of the pulp mill. Hence, conduit 86
CA 02345762 2001-05-O1
34
is broken to indicate an undetermined distance between subsystem 710
and subsystem 810.
The pressure in conduit 86 is dependent upon the number of
pumps and other transfer devices used and the height and distance that
the slurry must be transferred. The pressure in conduit 86 may vary from
about 5 psig to over 500 psig.
Also, during transfer, the chips may be exposed to some form of
treatment, for example, de-aeration or impregnation with a liquid,
preferably a liquid containing pulping chemicals, such as those described
above. The slurry may also be exposed to at least one pressure
fluctuation during transfer, such that the pressure of the slurry is varied
from a first pressure to a second, higher pressure, and then to a third
pressure which is lower than the second pressure. As described in US
patents 4,057,461 and 4,743,338 varying the pressure of a slurry of chips
and liquor improves the impregnation of the chips with the liquor. This
pressure pulsation may be achieved via varying the outlet pressure of a
set of transfer devices in series, or by controlled depressurization of the
slurry between pumping.
The slurry in conduit 86 is introduced to the inlet of vessel 321.
Though the vessel shown is a treatment, i.e., steaming, vessel, it may
also be a storage vessel, an impregnation vessel, or even a digester.
Since the transfer in conduit 86 typically requires that at least some
excess Liquid, that is not needed during treatment or storage, some form
of de-watering device 87 may be located between the transfer device and
the treatment vessel. One preferred dewatering device is a Top
Separator, as sold by Ahlstrom Machinery. This Top Separator may be a
standard type or an "inverted" Top Separator. This device may be an
external stand-alone-type unit or one that is mounted directly onto the
treatment vessel, as shown. Preferably, the liquid removed from the
CA 02345762 2001-05-O1
slurry by means of de-watering device 87 is returned to vessel 82 or to the
inlet of the pump, or pumps, 85 via conduit 88 to aid in slurrying the chips.
This liquid removed via device 87 may also be used where ever needed in
the pulp mill. This liquid in conduit 88 may be heated or cooled as desired
5 in a heat exchanger 90 and may be pressurized using one or more
conventional centrifugal liquid pumps, 89. The liquid in conduit 88 may be
introduced to vessel 81 via conduit 82 and to conduit 84 via conduit 82'.
The treatment vessel 321 shown is a steaming vessel similar to
vessel 221 shown in FIGURE 3, for example a DIAMONDBACK~
10 steaming vessel. The feed system 310 is otherwise similar to the system
210 shown in FIGURE 3. For example, chip feeding system 410, feeds
digester feed system 310, which feeds digester 11. Note that system 310
of FIGURE 4 is simply one subsystem in the over-all system which feeds
chips from the chip pile 80 to the digester 11. This system may include
15 one or more subsystems 310 for feeding to digester 11.
FIGURE 5 illustrates a further embodiment 610 that is an extension
of the system 510 shown in FIGURE 4. The system 610 is a combination
of three subsystems 710, 810 and 910. Subsystem 710 is similar to the
system 410 of FIGURE 4. Items in FIGURE 5 that are essentially identic~!
20 to those found in FIGURES 1 through 4 are identified by the same
numbers.
Wood chips 20, or some other comminuted cellulosic fibrous
material, from chip pile 80 are introduced with or without pressure
isolation to vessel 81. The chips in vessel 81 may be treated with a gas,
25 such as steam or hydrogen sulfide, or a liquid, such as water or a liquid
containing cooking chemical, introduced by way of one or more conduits
82. Vessel 81 may be any type of vessel, but is preferably a
DIAMONDBACK~ bin, as described above. The treated chips are
discharged from vessel 81 into conduit 84. Though any type of
CA 02345762 2001-05-O1
36
discharging mechanism can be used, the discharge of chips from vessel
81 is preferably performed without the aid of mechanical agitation or
vibration, as is characteristic of DIAMONDBACK~ chips bins. Conduit 84
may be any type of pipe or chute but is preferably a curved Chip Tube as
described above.
Conduit 84 introduces the chips to the inlet of slurry pump 85,
which may be of the type supplied by Wemco or Lawrence, as described
above. Typically, slurrying liquid is preferably first introduced to the chips
in conduit 84, for example, using the conduit 82', to produce a level of
liquid in vessel 81 or conduit 84. The liquid introduced via conduit 82',
may be water or a liquid containing treatment chemicals such as kraft
liquors, with or without strength or yield enhancing additives. Make-up
liquor, for example, liquor containing these chemicals, is typically added
via conduit 782.
The slurry in conduit 86 is introduced to subsystem 810 via liquor
separating device 887, which is similar in operation to device 87 shown in
FIGURE 4. The liquid removed via separator 887 can be returned to
subsystem 710 via conduit 88 or can be used elsewhere in the pulp mill
via conduit 888. If returned to subsystem 710 via conduit 88 the liquor
may be augmented with additional liquid or chemical via conduit 788,
heated via indirect heat exchanger 90 via conduit 790 and pressurized by
pump 89 prior to being re-introduced to vessel 8i via conduit 82 or to
conduit 84 via conduit 82'. Subsystem 710 may also include a liquor
storage tank similar to tank 353 shown in FIGURE 4. Thus by the use of
heater 90 and chemical addition 782 or 788, the slurry of material
transferred from subsystem 710 to subsystem 810 via conduit 86 may be
heated to any desirable temperature while being treated with chemicals.
For example, if the slurry in conduit 86 is heated to about 90°C
or above
in the presence of alkali or sulfide, some pretreatment of the will occur
CA 02345762 2001-05-O1
z
37
during the retention time in conduit 86 prior to introduction of the slurry
into subsystem 810. Of course, lower temperatures and other chemicals
may also be used in conduit 86.
The chips retained by separator 887 are passed to vessel 821.
Vessel 821 may be a vessel similar to vessel 81, but is preferably a tall
cylindrical vessel, for example, 20 to 50 feet tall, in which a liquid level
823
is maintained. A gas space 824 may be maintained above level 823.
Vessel 821 may be maintained at atmospheric pressure or at super-
atmospheric pressure, for example, at 0.2 to 10 bar gauge pressure (e.g.
about 5 bar), depending on the treatment performed in vessel 821. The
temperature in vessel 821 may vary from 50 to 300°C, but is typically
between about 50 and 150°C. Liquid may be introduced to vessel 821 via
one or more conduits 822 or 860. This liquid may contain cooking
chemicals or additives as discussed above. These cooking chemicals or
additives may be the same as those introduced in subsystem 710 or they
may be different. For example, kraft cooking liquor containing a high
concentration of sulfide ion or sulfidity may be introduced to subsystem
710 and kraft cooking chemical containing a lower concentration of sulfide
ion or sulfidity may be introduce to the chips in subsystem 810. In another
example, a polysulfide-type additive may be introduced to the chips in
subsystem 710 and an anthraquinone-type additive may be introduced in
subsystem 810.
The pressure within the vessel 821 may be monitored and
controlled via pressure indicator and controller 825. Excess pressure may
be released via conduit 826, for example, to a conventional non-
condensable gas (NCG) treatment system or to vessel 81 for
pretreatment. In addition, the pressure controller 825 can be used to
regulate the pressure in vessel 821 to vary the pressure to effect pressure
CA 02345762 2001-05-O1
38
pulsation impregnation as described in US patents 4,057,461 and
4,743,338.
The slurry is discharged from vessel 821 to conduit 850. This
discharge may be effected without agitation or vibration as in a
DIAMONDBACKS chip bin, or it may be effected by agitation or vibration
as is conventional. Conduit 850 introduces the slurry to the inlet of pump
851, which may be similar to pump 85, but typically will have a higher
pressure rating. Additional liquid may be introduced to conduit 850 via
conduit 854 to aid in introducing the slurry to the pump 851. The slurry
discharged from pump 851 is passed to subsystem 910 via conduit 886.
The slurry in conduit 886 is introduced to subsystem 910 using the
liquor separating device 987. The separator 987 is similar to devices 887
and 87 {of FIGURE 4). The liquor removed from device 987 may be
returned by conduit 911 to subsystem 810 or may be used elsewhere in
the pulp mill via conduit 988. (f returned to subsystem 810 via conduit
911, the liquor may be augmented with additional liquid or chemical via
conduit 912, heated via indirect heat exchanger 890 via conduit 891 and
pressurized by pump 889 prior to being re-introduced to vessel 821 via
conduit 822 or 860 to conduit 850 via conduit 854. The liquor in conduit
911 may also be introduced to subsystem 710, for example, via a
common connection with conduit 88 or 82. Subsystem 810 may also
include a liquor storage tank similar to tank 353 shown in FIGURE 4.
Thus by using heater 890 and chemical addition 912, the slurry of material
transferred from subsystem 810 to subsystem 910 via conduit 886 may be
heated to any desirable temperature while being treated with chemicals.
For example, if the slurry in conduit 886 is heated to about 90°C
or above
in the presence of alkali or sulfide, some pretreatment of the material will
occur during the retention time in conduit 886 prior to introduction of the
CA 02345762 2001-05-O1
39
slurry into subsystem 910. Of course, lower temperatures and other
chemicals may also be used in conduit 886.
The chips retained by separator 987 are passed to vessel 921,
which may be a vessel similar to vessels 81, or a tail vessel similar to
vessel 821, or a vessel similar to vessel 321 of FIGURE 4. Vessel 921
may be maintained at atmospheric pressure, or at super-atmospheric
pressure [for example, at 0.2 to 10 bar gauge, preferably 0.5 to 5 bar
gauge pressure] depending on the treatment performed in vessel 921
The temperature in vessel 921 may vary from 50 to 300°C, but is
typically
between about 50 and 150°C, preferably between about 80 and
120°C;.
Liquid may be introduced to vessel 921 via one or more conduits 922 or
960. The introduced liquid may contain cooking chemicals or additives as
discussed above. These cooking chemicals or additives may be the same
as those introduced in subsystem 710 or 810 or they may be different.
For example, kraft cooking liquor containing a high concentration of
sulfide ion or sulfidity may be introduced to subsystem 810 and kraft
cooking chemical containing a lower concentration of sulfide ion or
sulfidity may be introduced to the chips in subsystem 910. fn another
example, a polysulfide-type additive may be introduced to the chips in
subsystem 710 and an anthraquinone-type additive may be introduced in
subsystem 810, and kraft white liquor may be introduced to the chips in
subsystem 910. Each or these liquors can be isolated from each other by
the liquor separators 887 and 987.
The slurry is discharged from vessel 921 to conduit 950. This
discharge may be effected without agitation or vibration using a discharge
as in a DIAMONDBACK~ chips bin, or it may be aided by agitation or
vibration as is conventional. Conduit 950 introduces the slurry to the inlet
of pump 951, which may be similar to pumps 85 and 851, but typically will
have a higher pressure rating. Additional liquid may be introduced to
CA 02345762 2001-05-O1
conduit 950 via conduit 960 to aid in introducing the slurry to the pump
951. The slurry discharged from pump 951 is passed to further treatment
via conduit 986, for example, to a digester ( that is, a continuous or batch
digester), or to furthertreatment in a subsystem similar to subsystems 810
5 or 910, or subsystem 310 of FIGURE 4. However, the treatment effected
in subsystems 710, 8i 0 and 910 may be sufficient to produce an
essentially fully-cooked pulp slurry in conduit 950 such that no further
"pulping" need be performed. The pulp in conduit 950 may be passed
directly to washing andlor bleaching.
10 As in subsystems 310, 810, and 910, excess liquor may be
returned to subsystem 910 via conduit 913. The liquor may be augmented
with additional liquid or chemical via conduit 914, heated via indirect heat
exchanger 990 via conduit 991 and pressurized by pump 989 prior to
being re-introduced to vessel 921 via conduit 922 or to conduit 950 via
15 conduit 960. The liquor in conduit 913 may also be introduced to
subsystem 710 or 810, for example, via a common connection with
conduit 88 or 82 (not shown) or a common connection with conduits 911
or 822, or similar conduits. Subsystem 910 may also include a liquor
storage tank similar to tank 353 shown in FIGURE 4.
20 Thus, using heater 990 and chemical addition 914, the slurry of
material transferred from subsystem 910 to the subsequent subsystem or
digester via conduit 986 may be heated to any desirable temperature
while being treated with chemicals. For example, it the slurry in conduit
986 is heated to about 90°C or above in the presence of alkali or
sulfide,
25 some pretreatment of the chips will occur during the retention time in
conduit 986 prior to introduction of the slurry into the subsequent
treatment device, for example to digester 11 of FIGURES 1 and 2. Of
course, lower or higher temperatures and other chemicals may also be
used in conduit 986.
CA 02345762 2001-05-O1
41
Also, though indirect heat exchangers 90, 890, and 990 may each
be supplied by their own separate source of heat, for example, separate
sources of steam or hot water or hot effluent that would normally be
discharged, heat exchangers 90, 890 and 990 may also be supplied with
a common source of heat 915. The source of heat 915 may be, for
example, hot effluent or steam (low, medium or high pressure steam), and
may be introduced to heat exchanger 990 and the residual heat
transferred to heat exchanger 890 via conduit 992. The residual heat
from heat exchanger 890 may be passed to heat exchanger 90 via
conduit 892. Any residual heat remaining in conduit 92 may be used as
needed in systems 710, 810 or 910 or elsewhere in the mill, or it may be
discarded. For example, the liquid in conduit 92, and any residual heat it
may contain, may be introduced to vessel 81 or 821 via conduits 82 or
822 to recover and re-use as much of the available energy as possible.
Using a system 610 as shown in FIGURE 5, a counter-current flow
of treatment liquids can be established between each subsystem. For
example, the liquid from upstream treatment can be returned to
subsystem 910 via conduit 913; the liquid from subsystem 910 can be
returned to subsystem 810 via conduit 911; and the liquid from subsystem
810 can be returned to subsystem 710 via conduit 88. In addition some or
all of these liquors can be removed and used elsewhere via conduits 888
and 988.
The chemical addition at 788, 912 , and 914 is preferably sodium
hydro~ade, sodium sulfide; polysulfide, anthraquinone or their equivalents
or derivatives; surfactants, enzymes, or chelants; or combinations thereof.
For example, different treatment chemicals could be added at each of
788, 912, and 914, so that different treatments take place in each of the
sections 710, 810, and 910. For example, polysulfide may be added at
788, anthraquinone at 912, and chelants and enzymes at 914. The
CA 02345762 2001-05-O1
42
conduits at 788, 912, 914 need not be provided where illustrated in
FIGURE 5, but may be provided at any convenient location which
facilitates impregnation, or other pretreatment, simultaneously with
transport. For example, lines 788, 912, 914 may be added to the lines
790, 891, 991 before the heater exchangers 90, 890, 990, respectively.
In one preferred embodiment, the slurry is treated in the system of
FIGURE 5 to remove undesirable metal-containing compounds or metal
ions from the cellulose material. For example, in this embodiment the
chemical added to the slurry is an acid and/or chelating agent. The acid is
preferably sulfuric acid, sulfur dioxide, acetic acid, formic acid, oxalic
acid,
peroxy acids, Caro's acid, or their equivalents, or combinations thereof.
Acidic bleach plant filtrates can also be used as the source of acid. The
pH of the liquid during acid treatment typically varies from a pH of about 1
to a pH of about 7, but is preferably between a pH of about 2 and about 4.
The temperature of the acid treatment may vary from about 0 to about
150°C, but is preferably between about 60 and about 90°C. The
duration
of the acid treatment may be 10 minutes to 6 hours, but is preferably
about 30 to 120 minutes. The acid treatment may be followed by the
addition of magnesium salts, for example, magnesium sulfate, to replenish
the magnesium content of the material which under certain conditions has
been found to be beneficial.
The chelating agent, that is, a solution containing polydendate
ligand molecules, is preferably EDTA, DTPA, DTMPA, or their
equivalents, or combinations thereof. The chelate charge is typically at
most about 2 kg per ton of pulp but may range from about 0.5 to 5 kg per
ton of pulp. During chelate treatment, the pH of the treatment liquid
typically varies from a pH of about 2 to about 10, but is preferably
between a pH of about 4 and about 8. The temperature of the chelate
treatment may vary from 0 to 150°C, but is preferably between about 60
CA 02345762 2001-05-O1
43
and 110 °C. The duration of the chelate treatment may be 10 minutes to
6 hours, but is preferably between about 30 to about 90 minutes.
The chelation stages (Q) and the acid stages (A) are not mutually
exclusive; both types of treatments may be used, for example, in
succession (in either order) and repeatedly, during the transfer of the
slurry of ceilulosic material. Either treatment may also be practiced
repeatedly. The successive treatments may or may not include a purge or
washing stage between successive treatments. For example, some of the
treatment sequences that may be practiced according to this invention
include, but are not limited to, the following sequences: AA, QQ, AQA,
QAQ, AAQ, QQA, AQQ, QAA, AAA, QQQ, AAQQ, QQAA. Repetition or
extension of these treatment sequences, as would be readily understood
by those in the art, is also within the scope of this invention. Again, these
sequences may or may not include a washing or purge between
successive treatments.
In the embodiment shown in FIGURE 5, the acid or chelating agent
can be introduced via conduit 782, 788, 912, and/or 914, but the acid or
chelate is preferably introduced to subsystem 710 via conduit 782 or to
subsystem 810 via conduit 912. If the acid or chelant is added to
subsystem 810, the metal removal treatment can be followed immediately
by alkaline treatment in subsystem 910 prior to alkaline digestion in, for
example, a digester (not shown) fed by conduit 986, with or without the
use of a conventional high-pressure feeder.
For example, after treatment or transport in subsystem 710, acid ar
chelant can be introduced to subsystem 810 via conduit 912, 854, 860, or
882. The acidified/chelated slurry is pressurized by pump 851 and
passed to liquor separator 987 via conduit 886. The treatment liquor can
be removed via separator 987 and returned upstream of the inlet of pump
851 or, preferably, removed from the system via conduit 988. The metal-
CA 02345762 2001-05-O1
44
laden stream removed via conduit 988 can be passed to other treatment
in the pulp mill or to disposal or to any suitable form of conventional metal
recovery process. The liquid removed via conduit 988 may be removed
simply through a branch conduit from conduit 911 or via a liquor
separator, such as an In-line Drainer (not shown). The liquid in conduit
988 may also be removed directly from separator 987. The volume of
liquid removed via conduit 988 can be replaced, or "made up", by liquid
introduced via conduits 912, 854, 860 and/or 822, for example, water,
washer filtrate, black liquor, or bleach plant effluent, among other
available liquids. Make-up acid or chelate may also be introduced, with or
without make-up liquid, via one or more of the conduits 912, 854, 860,
and/or 822.
In addition, according to this invention, the acid or chelant can also
be introduced via conduit 782 or conduit 788 so that the metal removal
treatment is practiced in the subsystem 710 and a second treatment is
practiced in subsystem 810 prior to alkaline treatment in subsystem 910.
The second treatment in subsystem 810 may be a second acid or a
second chelate treatment, or, if the treatment in subsystem 710 is an acid
treatment, the treatment in subsystem 810 may be a chelate treatment, or
vice versa.
Furthermore, since the pH of the acid or chelate treatment will
typically be distinctly different from the pH of the alkaline treatment (for
example, the alkaline treatment is typically practiced at a pH greater than
8, often greater than 10), in order to avoid excessive consumption of acid,
chelate, and/or alkali, in one embodiment of the invention, the acid or
chelate treatment in a first stage is followed by a wash or neutralization
treatment in a following second stage, prior to the subsequent treatment,
for example, prior to the introduction of alkaline liquids in a third stage.
In
the system shown in FIGURE 5, the acid or chelate treatment can be
CA 02345762 2001-05-O1
practiced in subsystem 710, a somewhat neutral wash or soaking of the
material can be practiced in subsystem 810 and an alkaline treatment can
be practiced in subsystem 910.
For example, acid or chelant can be introduced via conduit 782 and
5 the acidified/chelated slurry is pressurized by pump 85 and passed to
liquor separator 887 via conduit 86. The treatment liquor can be removed
via separator 887 and returned to the inlet of pump 85 or, preferably,
removed from the system via conduit 888. The metal-laden stream
removed via conduit 888 can be passed to other treatment in the pulp mill
10 or to disposal or to a suitable conventional metal recovery process. The
liquid removed via conduit 888 may be removed simply through a branch
conduit from conduit 88 or via liquor separator, such as a conventional In-
line Drainer (not shown). The liquid in conduit 888 may also be removed
directly from separator 887. The volume of liquid removed via conduit 888
15 can be replaced, or "made up", by Liquid introduced via conduits 788
and/or 782, for example, water, washer filtrate, black liquor, or bleach
plant effluent, among other available liquids. Make-up acid or chelate
may also be introduced, with or without make-up liquid, via conduits 788
or 788 or both.
20 After acid or chelate treatment in subsystem 710, subsystem 810
can be used to wash or neutralize the slurry prior to introducing the slur; _~
to alkaline treatment in subsystem 910. For example, essentially neu.-.ra'
to alkaline, preferably metal-free, liquid can be introduced to the slurry via
conduit 912 or conduits 854, 860, or 822 , to wash or increase the pH of
25 the slurry during passage through vessel 821 and through conduits 850
and 886 prior to introducing the slurry to separator 987. The neutralized
or pH-adjusted liquid is removed from the slurry via separator 987 and the
liquid can be returned to upstream of pump 851 via conduit 911 or
removed via conduit 988. Again, the liquid removed via conduit 988 may
CA 02345762 2001-05-O1
46
be removed via a simple branch conduit, via a liquor separator (e.g., a
conventional In-line Drainer) or directly from separator 987.
After metal removal in subsystem 710 and washing or
neutralization in subsystem 810, the cellulose material can be treated
with alkaline cooking chemical, for example, kraft white, green, or black
liquor (with or without additives as discussed above) in subsystem 9i 0
prior to digestion with minimal excess use of chemical due to consumption
of acids and/or chelants by alkali.
FIGURE 6 schematically illustrates other desirable apparatus for
practicing a desirable method according to the invention. Utilizing the
system of FIGURE 6 a slurry of comminuted cellulosic fibrous material
(typically at a consistency of about 5-20%) is transported within a pulp mill
at any locations within a fiber line, such as from the wood yard to a
digester, with intermittent booster pumps in series. Each pump is
associated with a station (treatment vessel) and a solids/ liquid separator
is associated with each station (typically a conventional solid/liquid
separator at the top of the station), to isolate liquor streams or
circulations.
Impregnation, or other pretreatment, is performed simultaneously during
transit of the material, in the circulation lines (that is from one pump to
its
associated station), and the lines can be made very long (e.g. more than
100 yards, up to about a half a mile) to facilitate that pretreatment and
impregnation. Preferably heat exchangers are utilized on the return lines,
and degassing may be provided at one, more than one, or all of the
transfer stations. Also, an eductor (ejector) can be used in place a flash
tank and/or control valves through which liquor is removed and pressure
reduced. Further, pressurized pulsation action may be associated with
the configuration of pumps and stations, the pumps pressurizing the slurry
to at least 5 bar (typically at least about 10 bar). Also, a wide variety of
treatment chemicals may be utilized preferably added upstream of the
CA 02345762 2001-05-O1
47
pumps, including sodium hydroxide, sodium sulfide; polysulfide,
anthraquinone or their equivalents or derivatives; surfactants, enzymes, or
chelants; or combinations thereof.
The chip slurry 1000 is formed in any conventional manner
(including by heat steam slurrying), and first, second and third booster
pumps i 001, 1002, and 1003 are connected in series. The pumps 1001-
1003 are associated with stations (vessels) 1004, 1005, 1006,
respectively. Preferably each of the stations 1004-1006 has a liquid/solid
separator associated therewith. In the embodiment illustrated in FIGURE
6 separators 1007, 1008, 1009 are shown mounted at the top of each of
the stations (treatment vessels) 1004-1006, although the separator could
be at another location, including the bottom.
Preferably chemical is added to the slurry at a number of different
locations in the system, such as upstream at each of the pumps 1001-
1003. This is schematically illustrated by chemical addition at points
1010, 1011, and 1012 in FIGURE 6. The same, or different, chemicals
can be added at each of 1010-1012. Preferably at least some of the
chemical includes sodium hydroxide, sodium sulfide; polysulfide,
anthraquinone or their equivalents or derivatives; surfactants, enzymes, or
chelants; or combinations thereof. In the embodiment actually illustrated
in FIGURE 6, the chemical addition 1012 includes AQ laden white liquor
(e.g. vessel 1006 is a continuous digester).
Instead of establishing circulation lines such as illustrated in
FIGURE 5, circulation is provided in the FIGURE 6 embodiment, in the
preferred form, so as to cause pseudo counter-current flow of the
comminuted cellulosic fibrous material and liquid. While FIGURE 6
illustrates three stations, any number of stations may be provided. In the
embodiment in FIGURE 6, the liquid removed from the separator 1007 in
line 1013, is used elsewhere in the mill, or treated for reuse. The liquid
CA 02345762 2001-05-O1
48
removed from separator 1008 passes in line 1014 to a point upstream of
the pump 1001 (e.g. it is diverted by the valve 1015 either to the slurrying
station 1000, or to the infeed to the pump 1001 ) while liquid separated by
the third separator 1009 is circulated in line 1016 to upstream of the pump
1002, e.g. diverted by the valve 1017 to the first station 1004, andlor to
just upstream of the pump 1002. Fresh liquor, from source 1012, is added
to the bottom of the vessel 1005, or the intake of the pump 1003.
In the return lines 1014, 1016, conventional indirect heat
exchangers 1018, 1019 may be provided which change the temperature
of the liquid therein by at least 5°C. In the embodiment illustrated,
the
liquor is heated, but in some circumstances the liquid could be cooled
instead of heated. A indirect heat exchanger 1020 may be also be
associated with the chemical addition 1012.
Liquor can be passed from the third station 1006 (which may be a
digester -- e.g. black liquor) through a conventional eductor (ejector) 1022,
rather than a flash tank and/or control valves. Each of the pumps 1001-
1003 preferably pressurizes the slurry to a pressure of at least 5 bar
(typically at least about 10 bar).
Degassing may also be associated with one, more than one, or all
of the stations 1004. This is schematically illustrated by the gas removal
lines 1023-1025 in FIGURE 6. Degassing may be accomplished using
any conventional degassing equipment, associated with the separator
1007-1009, the inlet line, or the like.
FIGURE 7 schematically illustrates a continuous digester feed
system similarto the system illustrated in FIGURE 3. Some of the
significant differences between the system of FIGURE 7, and the method
practiced thereby, and the system of FIGURE 3, and the method practiced
thereby, are the provision of a cooling heat exchanger and a return line
from the digester to one or more pumps, a return conduit for introducing
CA 02345762 2001-05-O1
49
liquor directly into the chip tube (by bypassing the surge tank), and a
recirculation conduit from the outlet of one or each slurry pump (including
the first pump) ultimately to the inlet thereof (e.g. connected between the
surge tank and the chip tube for the first pump) to establish a recirculation
flow that is particularly desirable during the startup operation.
It is to be understood that though a continuous digester is
illustrated in FIGURE 7, the present invention is also applicable to a batch
digester system. The system shown in FIGURE 7 includes a feed system
1110 feeding a digester 1111. The feed system 1110 includes an air-lock
chip feed screw 1112, for accepting wood chips 20, and chip bin 1121.
Feed screw 11 i2 is preferably the device disclosed in U.S. patent
5,766,418 and bin 1121 is marketed under the name Diamondback~
Steaming Vessel or Bin as discussed above. Other types of conventional
steaming vessels, for example, horizontal screw conveyors or VibraBin
vessels having a vibrating discharge, may also be used in place of a
Diamondback Bin.
Similar to the system shown in FIGURE 3, the system shown in
FIGURE 7 includes a metering device 1123, such as a Chip Meter, a
vertical conduit 1126, such as a Chip Tube, and a liquor storage vessel
1153, such as Liquor Surge Tank. Also, as shown in FIGURE 3, the
system of FIGURE 7 includes a first pump, or pumping device, 1151 and
a second pump, or pumping device, 1151', which again, may be any type
of pump or pumping device for pressurizing and transferring a slurry of
comminuted cellulosic fibrous material and liquid. One preferred pumping
device is a Hidrostal screw-feed-type pump provided by Wemco Pump of
Salt Lake City, Utah, [http://www.wemcopump.com/Productslhidrostall
details.html] or a pump provided by Lawrence Pumps Inc. of Lawrence,
Massachusetts [http://www.lawrencepumps.coml]. Similar to the system
shown in FIGURE 3, the inlet of pump 1151 is in operative communication
CA 02345762 2001-05-O1
or is connected directly to the outlet of vertical conduit 1126 and the outlet
of pump 1151 is in operative communication with or is connected to the
inlet of pump 1151'. The outlet of pump 1151' is operative communication
with the inlet of digester 1111 via conduit 1134. Excess liquor is returned
5 from the digester 1111 to the feed system 1110 from the inlet of the
digester, or from any other available source of liquid associated with the
digester, via conduit 1135.
Though not shown in FIGURE 7, it would be recognized by those
familiar with the art, that the present invention may also be practiced by
10 having the one or more pumps 1151 feed two or more pumps 1151' for
feeding one or more digesters 1111. This mode of operation may be
particularly suitable for feeding a plurality of batch digesters, but may also
be applicable to feeding two or more continuous digesters. One device
that can be used to split the flow from one conduit to two or more conduits
15 is shown in FIGURE 8. It is also recognized that the present invention
may also incorporate the features of the inventions disclosed in U.S.
patent 5,795,438, the disclosure of which is incorporated in its entirety by
reference herein.
Liquor in conduit 1135 is returned to various locations in the feed
20 system 1110. The liquor in conduit 1135 is preferably returned to Chip
Tube i 126 via conduit 1182 or to tank 1153 via conduit 1183 or to vessel
1121 via conduit 1184. Since the liquor in conduit 1135 will typically have
a temperature greater than 100°C and the Chip Tube 1126 and vessel
1153 may operate at approximately atmospheric pressure, that is, -1 to 1
25 bar gage (that is, 0 to 2 bar absolute), to avoid undesirable rapid
evaporation (that is, "flashing"), some form of cooling device 1136 is
provided. This cooling device is preferably an indirect liquor-to-liquor
cooling heat exchanger, and cools the liquid being returned to below the
temperature at which it will flash. The cooling medium provided in conduit
CA 02345762 2001-05-O1
51
1137 is typically any available cool liquid stream in the pulp mill. One
preferred cooling medium is fresh water which is introduced via conduit
1137 to heat exchanger 1136 at one temperature and removed via
conduit 1138 at a higher temperature. Cooking liquids, for example, kraft
white, green, or black liquor (for example, via conduit 1150) may also be
used as the cooling medium in heat exchanger 1136. A bypass conduit
1135' may also be used to divert liquor around heat exchanger 1136 when
the heat exchanger is not needed or when it is being serviced.
The level of liquid in tank 1153 is typically controlled by a level
control mechanism, for example, a level control mechanism using a d-p
cell level indicator or a gamma radiation level indicator (not shown). The
level in tank 1 i 53 is typically controlled by varying the flow of liquid out
of
branch conduit 1181 which feeds pump 1160, that is, the Make-up Liquor
pump. Pump 1160 pressurizes and introduces this excess liquor to the
top of the digester 1111 via conduit 1161.
Liquor in conduit 1135 may also be introduced, with or with heating
or cooling, upstream of pump 1151 via conduit 1163. Conduit 1163 may
have a valve F. The benefit of introducing pressurized liquid from conduit
1135 upstream of pump 1151 is discussed above in the description of
Figure 3. The present invention also preferably includes a conduit 1156
between the outlet of pump 1151 and conduit 1154 which may have a
valve E, so that liquor may flow from line 1156 to line 1154.
Liquor may also be introduced to conduits 1134 and 1135 via
conduits 1144 and 1145 during normal operation or during shutdown or
startup of the system. For example, weak black liquor or "cold blow"
liquor from pump 1140 may be introduced to conduits 1134 and 1135 to
flush the lines during shutdown or to introduce additional liquor to the lines
as needed, for example, for liquor-to-wood ratio control or black liquor
pretreatment, during normal operation. Cooking liquor, for example, kraft
CA 02345762 2001-05-O1
52
white liquor, green liquor, black liquor, orange liquor, or liquor containing
strength or yield enhancing additives, such as anthraquinone, polysulfide,
chelants, surfactants, sulfur, or their derivatives and equivalents, may be
added to feed system 1110 via conduit 1150 and pump 1152. The liquor
in conduit 1150 is preferably added to Chip Tube i 126 as shown, but can
also be added to conduits 1134 or 1135.
The system shown in FIGURE 7 also includes several valves,
either automatically controlled or manual, which isolate the flow of liquids
and their pressures from each other. Valve A isolates the outlet of pump
1151 from the inlet of pump 1151'. Valve B isolates the outlet of pump
1151' from the digester 1111. Valve C in conduit 1134 isolates the feed
conduit to the digester 1111 from the digester and valve D in conduit 1135
isolates the return conduit 1135 from the digester 1111. These valves are
especially important during upset conditions to isolate the hot pressurized
liquids associated with the digester 1111 from the lower pressure feed
system 1110 and from the surrounding personnel and adjacent
machinery.
The valves A-F, along with selected other valves, can also be used
to isolate liquor circulations to aid in start-up and shutdown procedures.
For example, when valve A is closed and valve E in conduit 1156 is open,
pump 1151 can be started and a closed circulation about pump 1151 can
be established via conduit 1156. Similarly, when valve A is closed and
valves C, D, and F are opened and pump 1151' is started, a circulation
about pump 1151' can be provided via conduit 1134, the top of digester
111, conduit 1135, and conduit 1163. (It is also possible to isolate the
circulation about pump 1151 from the digester 1111 by inserting a conduit
1170, with an appropriate valve G, in conduit 1170 between conduits 1134
and 1135.)
CA 02345762 2001-05-O1
53
The conduits 1156, 1154 (and preferably the isolating Valves A and
E), and associated connections to other components, comprise means for
circulating liquid from the pump 1151 outlet back to its inlet. While
conduits are shown as such means it is to be understood that any
conventional structures which provide this recirculation may be utilized,
including tanks, ejectors, pumps, valves, ducts, heat exchangers, or the
like.
Isolation of these circulations is especially advantageous during
start-up and shutdown conditions when these isolations can be separately
maintained. For example, during start-up, before the introduction of wood
chips, the two pumps 1151, 1151' can be operated to establish one
circulation about pump 1151 via conduit 1156 and a second circulation
about pump 1151' passing through the digester top and conduits 1134
and 1135. By so doing, the proper operation of each pump 1151, 1151'
can be verified and also the pressures and temperatures of each
circulation can be isolated. For example, the temperature and pressure of
the liquid in the circulation in conduits 1134 and 1135 can be raised to
digester operating conduits, for example, 7-15 bar gage at 100-160°C,
while the temperature of the circulation associated with pump 1 i 51 and
conduit 1156 can be maintained at lower conditions, for example, 1-3 bar
gage at 60-120°C. Then when the conditions in each circulation agree,
for example, the liquor in conduits 1134 and 1156 are both at about 10 bar
gage and 120°C, valve A can be gradually opened while valve E is
gradually closed and chips can be introduced to feed system 1110. A
similar situation can occur during shutdown or when the digester 1111
and/or feed system 1110 need to be isolated for servicing.
Feed system 1110 may also include a centrifugal separator for
removing sand and debris, for example, a Sand Separator; a liquor/chips
separator, for example, an In-line drainer; or a liquor storage vessel, for
CA 02345762 2001-05-O1
54
example, a Level Tank, if needed, as found in conventional systems. One
or all of these devices may also be omitted from the embodiment shown in
FIGURE 7.
Feed system 1110 may also include an integral Chip Tube and
Surge Tank, as well as other simplifications to a feed system, as disclosed
in co-pending application 09/520,761 filed on March 7, 2000 (attorney ref.
10-1302), the disclosure of which is incorporated by reference in its
entirely herein.
FIGURES 8-10 illustrate another embodiment of the present
invention for dividing the flow of slurry in a pipe line. FIGURE 8 illustrates
an elevation view, FIGURE 9 a top view, and FIGURE 10 a right-hand
elevation view. The device 1200 shown in FIGURES 8-10, which is
referred to as a static "flow divider" or "flow splitter", can, for example,
be
inserted in conduit 34 of FIGURES 1 and 2, conduit 252 or 234 of
FIGURE 3, conduit 86 and 886 of FIGURES 4 and 5, or corresponding
conduits in FIGURE 6, or conduit 1134 in FIGURE 7.
The static flow splitter 1200 includes an inlet 1201 for a flow of a
slurry of comminuted cellulosic fibrous material and liquid and two or more
outlets 1202, 1203. The inlet and outlets are preferably circular in cross
section, but may be non-circular depending upon the needs of the
installation, including elliptical, rectangular, square, or even triangular.
The device 1200 includes a chamber 1204 for receiving the slurry from
the inlet 1201 and discharging the slurry to the two or more outlets 1203,
1204. The chamber 1204 can have any appropriate cross sectional
shape, including round, elliptical, rectangular, square, or triangular, but
the
shape of the chamber preferably limits the areas in which material in the
slurry can stagnate, for example, sharp corners are avoided. As shown in
FIGURE 8, one preferred shape of chamber 1204 is substantially
triangular in which the outlets 1202, 1203 have centerlines that diverge
CA 02345762 2001-05-O1
from the centerline of the inlet 1201 by between about 30 and 60°, for
example, by about 45°.
The chamber 1204 may also include one or more internal baffle
plates 1210, 1211 (shown in phantom) in FIGURE 8 to aid in directing the
5 flow of slurry to the two or more outlets 1202, 1203. These baffle plates
1210, 1211 may define a triangle with the wall 1212, positioned opposite
the inlet 1201 of device 1200. The ends of the plates 1210, 1211 may be
welded or otherwise attached to the walls 1213, 1214 of the chamber
1204. In the embodiment illustrated in FIGURE 8 the apex 1215 of the
10 substantially triangular baffle plate arrangement 1210, 1211 is
substantially aligned with the inlet 1201. The flow splitter 1200 is static,
i.e. has no moving parts (although the position of the baffle plate
arrangement i 210, 1211 may be made adjustable).
The dimensions of device 1200 will vary depending upon the given
15 or desired dimensions and production rate of the system in which it is
used. The dimension, for example diameter, of the inlet 1201, and the
outlets 1202, 1203, may range from 2 inches to 10 feet. For example, the
inside diameter of the inlet and outlets is about 10 inches. The
dimensions of the chamber 1204 will be essentially dictated by the
20 dimensions of the inlet and outlet, an may also vary from about 2 inches
to about 10 feet, for example, the chamber 1204 shown in FIGURES 8-10
has a width of about 13 inches.
Device 1200 is typically made of any appropriate material that can
withstand the hot (for example, 400°F or hotter), pressurized (for
example.
25 300 psig or greater), corrosive (either acidic or alkaline) slurries that
are
typically handled in a pulp and paper mill, including metals and high-
performance plastics. However, the device is preferably made of metal, in
particular steel, and is preferably made from weldable stainless steel, for
CA 02345762 2001-05-O1
56
example 304L (having an ASTM designation ASTM-A240-304L), or its
equivalents, or better.
In use, the inlet 1201 is connected to the conduit 34, 252, 234, 86,
856, 1134, and one outlet 1202 is connected to the same conduit while
the other outlet 1203 is connected to a conduit leading to the same or
another digester (batch or continuous). Where only two outlets 1202,
1203 are provided preferably about one-half the inlet flow goes to each,
although the plates 1202, 1203 may be dimensioned or positioned, so that
a higher volume flow goes through one outlet 1202, 1203 than the other.
In the broadest aspect of this invention, a system and method are
provided for the multistage transport and treatment of comminuted
cellulosic fibrous material with the economical recovery and re-use of
energy, including thermal energy.
While the invention has been described in connection with what is
presently considered to be the most practical and preferred embodiment,
it is to be understood that the invention is not to be limited to the
disclosed
embodiment, but on the contrary, is intended to cover various
modifications and equivalent arrangements included within the spirit and
scope of the appended claims.
