JP2004183189A - Method and apparatus for producing chemical pulp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce energy and cost in a method for producing chemical pulp by steaming wood chips with knots in a digester. <P>SOLUTION: The method for producing chemical pulp is to digest wood chips with knots in the digester to produce the chemical pulp and comprises the following steps (a) to (e). In the step (a), a low pressure slurry comprising crushed cellulose-based fiber material is formed by mixing a liquid with the crushed cellulose-based fiber material in a vessel or a pipe practically acting at an atmospheric pressure. In the step (b), the slurry is fed to a low pressure inlet of a slurry-transfer device. In the step (c), a high pressure slurry comprising the crushed cellulose-based material is formed in a transfer device. In the step (d), the high pressure slurry is discharged from the transfer device and fed to the digester. In the step (e), knots are removed from the slurry containing digesting cellulose material with knots at practically atmospheric pressure, subsequently, the removed knots are directly transferred to the vessel, the pipe or down stream of those and are brought to a part of the low pressure slurry fed to the transfer device. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a chemical wood pulping method and apparatus. In particular, the invention relates to a method and apparatus for treating knots (also called "knots") in such a chemical wood pulping process.
[0002]
2. Description of the Related Art
Screw tip meters are commonly used to measure the feed of chips to digesters used in chemical wood pulping processes. Accordingly, chip meters are used to supply undigested wood chips in a controlled manner in downstream pre-pulping and cooking operations, such as chip steaming or impregnation vessels and / or digestion vessels. You. Generally, chip chutes are used to transport undigested wood chips in such downstream operations.
[0003]
Conventionally, knots present in wood chips are generally removed by screening after at least some cooking. Therefore, many pulp mills are provided with a drainer, such as the system proposed in US Pat. No. 3,886,035, to remove knots from the pulp. The entire contents of this patent specification and the contents of each patent specification cited below are expressly incorporated herein by reference thereto.
[0004]
Subsequent refinement or re-digestion of such knots can minimize waste and recover the fiber content present in the waste (US Pat. No. 4,002,528). Book). Conventionally, in the knot collecting technology, the knot separated from the pulp is generally returned to the chip storage, but this requires an expensive recycling apparatus. In some cases, a knot drainer is placed on top of the chip reservoir, but in such a configuration, the entire filtrate is pumped to send the knots recovered after cooking to the chip reservoir for reprocessing. And requires excessive energy.
[0005]
Recently, in U.S. Pat. No. 5,672,245, another knot recycling technique has been proposed, which separates the knots by means of a screen downstream of a pulp digester and separates the separated knots. After processing the black liquor in the knot storage, the knot suspension is pumped to be re-sent to the chip chute upstream of the high-pressure feeder.
[0006]
[Means for Solving the Problems]
In accordance with the present invention, the knots removed by conventional means such as screening in a knotter or screen room are essentially supplied with atmospheric pressure prior to cooking in a cooking step in a chemical wood pulping process. New methods and apparatus are provided that return directly (without pumping) to the system. In particular, a predetermined amount of undigested wood chips is weighed and sent without pumping to a chip container or chip chute upstream of the digestion process. Thus, according to the method and apparatus of the present invention, by providing the knots in a chip handling system operating at essentially atmospheric pressure, unlike the prior art, which returns the knots to an elevated chip reservoir, Including returning the knots to the chip supply system. Most preferably, the knots from the knotter or screen room are returned to the chip supply system via a knot drainer or separator operably coupled to a chip screw or chip chute.
[0007]
Accordingly, the present invention is directed to a new LO-LEVEL Supply System (registered trademark) commercially available from Andritz, Inc., Glens Falls, NY, USA (U.S. Pat. Nos. 5,476,572, 5,700). No. 5,355, 5,968,314, 5,766,418, 6,368,453, 6,436,233).
[0008]
The use of the present invention allows the knot drainer or separator to be placed in a lower location (eg, physically attached to a tip screw or tip chute, rather than in a higher location, such as the top of a tip reservoir), resulting in energy savings. Cost can be reduced. There is no need to pressurize the knots to the pressure of conventional feed systems, further saving energy.
These and other forms and advantages will become more apparent upon careful consideration of the following description of exemplary preferred embodiments.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
As shown in the attached FIG. 1, one particularly preferred system according to the invention comprises a supply system 10, which comprises, for example, ground cellulose such as hardwood chips or softwood chips. The system fiber material is introduced, steamed, slurried, pressurized, and the slurry is fed to a continuous digestion system (not shown). These systems are disclosed in U.S. Pat. Nos. 5,476,572, 5,622,598, 5,635,025, 5,700,355, 5,766,418, 5,968,314. It is disclosed in the specification and is commercially available from Andritz, Inc., Glens Falls, NY, USA under the name LO-LEVEL®.
[0010]
The cellulosic fiber material to be ground can take many forms, including wood chips, grasses such as straw and kenaf, agricultural waste such as bagasse, recycled paper or wood chips, but for simplicity, "chips" Is used to indicate ground cellulosic fiber material. However, any and all of the materials described herein, as well as other materials not described, can be processed by the present invention. Although the following description and FIG. 1 refer to one continuous digester, the present invention is applicable to a case where a plurality of continuous digesters and one or more discontinuous digesters or batch digesters are supplied. Can also be applied.
[0011]
As shown in FIG. 1, the chips 13 are introduced into the system 10 by a separating / weighing device 14 from a chip storage facility such as a wood factory via a conveyor (not shown). For example, FIG. 1 shows a screw-type separation device 14 as described in US Pat. No. 5,766,418. A device 14 driven by an electric motor (not shown) introduces the chips into a chip holding and outflow container 16. While various types of containers are known in the art, container 16 is commercially available from Andritz, Inc. and is disclosed in U.S. Patent Nos. 5,500,083, 5,617,975, 5,628,873. No. 4,958,741 or commercially available from Andritz, Inc. and described in US Pat. No. 6,199,299. Preferably, it is a CHISELBACK (registered trademark) container. Generally, the container has a gamma radiation level sensing system, a regulated exhaust port for exhausting gas accumulated in the container, and one or more steam inlet lines 16 '. The pressure in the vessel 16 may be slightly lower than atmospheric pressure, or slightly higher than atmospheric pressure. That is, the pressure within vessel 16 can vary from about -1 bar to 2 bar gauge (ie, from about 0 bar to 3 bar absolute).
[0012]
During the steaming in the vessel 16, the air normally present in the chips is replaced by the steam and the heating of the chips is started. By removing air from the cavity in the chip, the cooking chemicals can effectively diffuse into the chip and minimize the buoyancy of the chip during subsequent processing.
[0013]
The steamed material is discharged from the bottom of the container 16 to a metering device 17 such as, for example, a star-type metering device or a chip meter sold by Andritz, Inc. However, any other type of metering device may be used. The metering device 17 is driven by an electric motor (not shown), and the rotational speed of the metering device is usually controlled by operator input to define a set introduction speed of the chip into the system. The chips discharged from the metering device 17 are introduced into a vertical line or pipe 18, for example a chip tube sold by Andritz, Inc. Generally, first, cooking agent and other liquids are introduced into the chips in line 18 by one or more lines 19, whereby the level of liquid is reduced to a predetermined level in line 18. At the height, there is a slurry of chips and liquid at the bottom of the conduit 18. The level of this liquid is generally monitored and controlled by a level detector, such as a gamma radiation level detector or "dp" cell. The weighing device 17 does not normally function as a pressure separation device, but may function as a pressure separation device. Also, typically, the pressure in line 18 can vary from 0 bar to 2 bar gauge pressure (ie, 1 bar to 3 bar absolute).
[0014]
The conduit 18 discharges the slurry of the chips and the liquid to the suction port of the slurry pump 21 through the semi-curved region 20. Any slurry pump may be used, but pump 21 may be a Hydrostal® screw centrifugal pump sold by Wemco Pump Company of Salt Lake City, Utah, USA, or Lawrence, Mass., USA Preferably, the pump is provided by Lawrence Pumps, Inc. The slurry pump 21 driven by the electric motor 21 ′ pressurizes the slurry in the pipeline 18 and transports the slurry to the low-pressure inlet 23 of the high-pressure transport device 24 via the pipeline 22. This high-pressure transport device is preferably a high-pressure feeder sold by Andritz, Inc. The high pressure feeder 24 typically has a pocket rotor mounted in a housing having a low pressure inlet 23, a low pressure outlet 25, a high pressure inlet 26 and a high pressure outlet 27. Typically, the low pressure outlet 25 has a screen plate (not shown) to minimize the passage of chips from the low pressure outlet 25 while allowing the liquid in the slurry to pass from the low pressure outlet 25 to the line 28. To the limit. However, the screen at the low pressure outlet of feeder 24 may be omitted, as disclosed in US Pat. No. 6,199,299. The chips held in the feeder by the screen are slurried with high pressure liquid supplied to inlet 26 via line 30 by a pump 29, preferably a top circulation pump (TCP) provided by Andritz, Inc. Be converted to The slurry is discharged from the high pressure outlet 27 into line 31 and to the digester 32 of the digestion system 12 at a gauge pressure of about 5 bar gauge to 15 bar, typically about 7 bar gauge to 12 bar.
[0015]
The digester (not shown) may be a single digester or a digester having multiple vessels. Also, the digester may be a hydraulic digester or a vapor phase digester. Also, the digester may consist of one or more batch digesters, or may include one or more batch digesters. The cellulosic material to which the cooking agent has been added is processed in the digester at a predetermined temperature and pressure, and essentially fully processed chemical cellulose pulp is discharged into a line at the bottom of the digester. While many types of processes may be performed in the digester, preferred processes are described in U.S. Patents 5,489,363, 5,536,366, 5,547,012, 5,575,890. 5,620,562, 5,662,775, 5,824,188, 5,849,150, 5,849,151, 6,086,712, 6,132,556, 6,159,337, 6,280,568, and 6,346,167, and include the process sold under the trademark LO-SOLIDS by ANDRITZ INC. Also, the process performed in the digester is described in U.S. Patent Nos. 5,635,026, 5,779,856 and is commercially available from Andritz, Inc. under the name EAPC (TM) digestion. May be one of the processes in question.
[0016]
As shown in FIG. 1, excess liquid in the slurry in line 31 at the top of the digester is separated from the slurry by a liquid separator and returned to feed system 10 by line 34. The liquid in the pipe 34 is pressurized by a pump 29 driven by an electric motor 29 ′, and is introduced into the high-pressure inlet 26 of the feeder 24 via the pipe 30 as a pressurized slurry liquid. Usually, the feeder 24 is driven by an electric motor (not shown), and its speed is monitored and controlled.
[0017]
As shown in FIG. 1, the liquid discharged from the low-pressure outlet 25 of the high-pressure supply device 24 is sent to a cyclone-type separator 35 via a pipe 28. The separator 35 separates undesired substances and debris such as sand and stone from the liquid in the conduit 28. The separator 35 is preferably a sand separator sold by Andritz, Inc. Liquid containing little or no undesirable material or debris exits separator 35 and passes through line 36 to liquid separator 37. At least some liquid is removed from liquid separator 37, which is preferably an in-line drainer sold by Andritz, Inc., and sent to vessel 39 via line 38. Container 39 is preferably a level tank sold by Andritz, Inc. The liquid is discharged from the container 39 to the line 40 and the pump 41, and is supplied to the digester via the line 42 as a replenisher as necessary. The pump 41 is preferably a make-up liquor pump (MLP) sold by Andritz, Inc. The sand separator 35, the level tank 39, and the in-line drainer 37 can be omitted if they do not interfere with the basic functions of the supply system 10.
[0018]
Before the liquid discharged from the separator 37 into the pipe 43 is introduced into the tank 45, for example, kraft white liquor, green liquor, orange liquor (ie, liquid containing a polysulfide-based additive) or black A cooking agent such as a liquid may be supplied. Tank 45 is preferably a liquor surge tank sold by Andritz, Inc. and described in U.S. Pat. No. 5,622,598. Preferably, the cooking chemical is heated or cooled by a heat exchanger (not shown) as needed. Some liquid in line 43 may bypass tank 45 and be introduced into line 18 via line 19 as described above. The tank 45 communicates with the pipe 18 and the inlet of the pump 21 via the pipes 47 and 20. As disclosed in U.S. Patent No. 6,368,453, tank 45 may include an integral container coaxial with line 18 or may comprise an integral container coaxial with line 18. Is also good.
[0019]
Importantly in the present invention, a knot separator or drainer 50 is provided for feeding the knots via line 52 to line 18 downstream of metering device 17 without a pump or other process equipment. That is. Most preferably, the knot separator 50 is a model KW secondary knotter sold by Andritz, Inc. The knot separator 50 separates the knots from the slurried knot and liquid inlet feed pumped from the primary knot or knot screener introduced through the inlet line 54. In a knot separator 50 (operated essentially at atmospheric pressure), a vertically oriented screw-type conveyor is driven by a motor 55, and the separated knots have enough liquid to allow it to flow. At the same time, it is raised into the discharge chute 56 connected to the pipeline 52. The separated liquid is conveyed to the chamber 60 via the chute 58, and then discharged through the pipe 62. Gas may be exhausted from the chamber 60 via the conduit 64.
[0020]
Thus, the present invention provides for returning knots to the chip supply system 10 by feeding knots directly into the conduit 18 under essentially atmospheric conditions without pumping or other operations. Including.
[0021]
Although the present invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, the present invention is not limited to the disclosed embodiments, but is within the spirit and scope of the appended claims. It goes without saying that various modifications and equivalent configurations are covered. For example, instead of using a high pressure feeder, it is also possible to use a transport device consisting of a pump, such as the transport device disclosed in US Pat. Nos. 5,753,075 and 6,325,890.
[Brief description of the drawings]
FIG. 1 shows one particularly preferred system according to the invention for processing a knot.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Supply system, 12 ... Digestion system, 13 ... Chip, 14 ... Separation / weighing apparatus, 16 ... Chip holding / outflow container, 17 ... Measuring apparatus, 18 ... Vertical pipeline, 20: semi-curved area, 21: slurry pump, 22: pipeline, 23: low pressure inlet, 24: high pressure transfer device, 25: low pressure outlet, 26 ..High-pressure inlet, 27 ... High-pressure outlet, 28 ... Pipe, 29 ... Pump, 30, 31 ... Pipe, 32 ... Peptizer, 34 ... Pipe, 35 ..Separator, 36 ... pipe, 37 ... liquid separator, 39 ... container, 41 ... pump, 40, 42, 43 ... pipe, 45 ... tank, 50 ... Knot separator, 52 ... Pipe, 54 ... Inlet pipe, 55 ... Motor, 56 ... Discharge chute 58 ... shoot, 60 ... chamber, 62, 64 ... line

Claims (18)

A method for producing a chemical pulp by digesting wood chips including a knot in a digester,
(A) forming a low pressure slurry consisting of the ground cellulosic fiber material by mixing the liquid with the ground cellulosic fiber material in a vessel or conduit operating at essentially atmospheric pressure; ,
(B) supplying the slurry to a low pressure inlet of a slurry transport device;
(C) forming a high-pressure slurry made of the pulverized cellulose material in the transfer device;
(D) discharging the high-pressure slurry from the transfer device and supplying the slurry to a digester;
(E) removing knots from the slurry containing the cellulosic material being digested, including knots, essentially at atmospheric pressure, and then transporting the removed knots directly to the vessel or conduit or downstream thereof; And thereby, making said knots a part of the low-pressure slurry supplied to said transport device;
The chemical pulp manufacturing method characterized by including. 2. A high pressure carrier having a low pressure inlet, a low pressure outlet for removing liquid from the slurry, a high pressure inlet for supplying high pressure liquid to the carrier and a high pressure outlet for discharging the high pressure slurry. Chemical pulp manufacturing method. The method for producing a chemical pulp according to claim 1 or 2, wherein the removed knots are directly supplied into the slurry and supplied to a conveying device before the low-pressure inlet. 3. The method of claim 1 or 2, wherein the knot is removed from the slurry of the ground cellulose material during digestion using a knot drainer or a separator. The vessel or conduit has a chip chute and a metering device for discharging a measured amount of the ground cellulosic material to the chip chute, and step (e) introduces the removed knots into the low pressure slurry with the chip chute. The method for producing a chemical pulp according to claim 1, further comprising the step of: The method according to claim 1 or 2, comprising recirculating at least a portion of the liquid removed from the slurry at the low pressure outlet of the transport device to the vessel or conduit. 7. The chemical pulp production method of claim 6, comprising pumping a low pressure slurry containing the removed knots to a low pressure inlet of a transport device. An apparatus for producing chemical pulp from a slurry of cellulosic material containing knots,
(A) a digester for pressure digesting a cellulosic material containing knots;
(B) a vessel or conduit operating at essentially atmospheric pressure to form a low pressure slurry of ground cellulosic fibrous material;
(C) a conveying device having a low-pressure inlet and a high-pressure outlet, wherein the low-pressure inlet receives the low-pressure slurry from the vessel or the conduit, and forms a high-pressure slurry made of the ground cellulose material discharged through the high-pressure outlet;
(D) means for supplying the high-pressure slurry to a digester;
(E) removing the knots from the slurry of the digested cellulosic material containing the knots, essentially at atmospheric pressure, and then transporting the removed knots directly to a vessel or conduit, whereby Knot separator, knot separator or knot drainer to make a part of the low-pressure slurry supplied to the transport device,
A chemical pulp manufacturing apparatus comprising: 9. The chemical pulp manufacturing apparatus of claim 8, wherein the knot separator has a knot drainer for removing knots from a slurry of ground cellulose material being digested. The chemical pulp manufacturing apparatus according to claim 5, wherein a knot drainer or a knot separator is physically attached to the vessel, the pipe or a metering device to the vessel or the pipe. 10. A means including a chip chute and a metering device for discharging a measured amount of ground cellulosic material to the chip chute, wherein means are provided for introducing the removed knots into the low pressure slurry with the chip chute. Or the chemical pulp manufacturing apparatus according to 10. 9. The chemical pulp manufacturing apparatus according to claim 8, wherein the transport device has a low pressure outlet that allows liquid to be removed from the slurry and a high pressure inlet for receiving high pressure liquid into the transport device. 13. The chemical pulp manufacturing apparatus according to claim 12, further comprising a recirculation line for recirculating at least a part of the liquid removed from the slurry at the low pressure outlet of the transfer device to the container or the line. The container has a chip chute and a weighing device for discharging a measured amount of the ground cellulose material to the chip chute, and the knots removed by the knot separator are directly introduced into the chip chute. Item 9. The chemical pulp manufacturing apparatus according to Item 8. The method for producing chemical pulp according to claim 14, further comprising a slurry pump for pumping a low-pressure slurry containing the removed knots to a low-pressure inlet of a transport device. A method for returning removed knots to a chemical wood pulp process, comprising feeding the removed knots directly to an essentially atmospheric pressure chip processing system, downstream of a chip storage tank, especially downstream of a metering device. Method. 17. The method according to claim 16, wherein the removed knots are fed directly to a vessel or line, for example a chip chute, upstream of a digester. 18. The method of claim 16 or 17, wherein the removed knots are supplied to a chip handling system without pumping or other operations.

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