FI122630B - Continuous digester system and method for operating a continuous cellulose digester - Google Patents

Description

CONTINUOUS COOKING SYSTEM AND METHOD FOR USING CONTINUOUS CELLULOSE COOKER

In the manufacture of pulp from pulverized cellulosic fibrous material by continuous operation, that is to say, 5 teaspoons of pulp from which paper products are made, two types of digesters are used: hydraulic digesters and double-phase or steam-phase digesters. The hydraulic digester is a pressure-resistant vessel completely filled with finely divided cellulosic fibrous material and liquid, where the typical overpressure in the vessel is influenced by the introduction or removal of the liquid into the vessel. The vapor phase cooker is not completely filled with 10 liquids but has pressurized steam at the top. Because this gas zone can be compressed relative to the liquid zone below it, the pressure of the vapor phase cooker is typically determined by the gas pressure at the top of the digester. Prior art steam-phase digesters are described, for example, in U.S. Patents 3,380,883; 3,429,773; 3,532,594; 3,578,554 and 3,802,956.

15

Reactions of the cooking chemicals used to make the chemical pulp with the chopped cellulosic fibrous material require a temperature of 140-180 ° C. Because atmospheric-pressure aqueous chemicals treating the material would boil at these temperatures, in commercial applications, chemical pulping is typically performed in 20 pressure-resistant vessels at a pressure of at least about 5 bar (i.e., at least about 70 psig).

The two types of cookers differ in their function mainly by heating the contents of the kitchens to the desired temperature of 140-180 ° C. In a hydraulic digester 25, a suspension of the pulp cellulosic fibrous material, typically wood chips, and cooking liquor is heated by heated liquid circuits, i.e. by one or more return cycles. The liquid is removed from the digester typically by means of, for example, an annular screen assembly and a pump, the liquid is heated by steam in an indirect heat exchanger and returned to the material by means of a conduit 30 in the center. In a steam-phase digester, the chips are typically heated by exposing the chips to steam. This steam heating typically occurs when the chips are fed into the steam-filled zone at the top of the digester.

2 In addition to the method of heating, the operation of the hydraulic digester and the steam-phase digester differs in the way the level of chips and liquid in the vessel is monitored and adjusted. Since the hydraulic kettle is completely filled with liquid, only the level of its chips needs to be monitored. In a hydraulic digester, the level of the chips is monitored by mechanical blades whose deflection is detected by an electronic load meter or similar device. Two or more, preferably three or more, of these electromechanical devices are placed on the inner wall of the hydraulic digester. The presence or absence of chips at the blade height is determined by how much the chips bend or move the blade. The Mit-10 stacks detect the movement of each pallet and the approximate percentage of chip height in the hydraulic digester is determined by a mathematical algorithm. The machine operator can change the chip height by changing the chip feed to the hydraulic digester or the pulp from the digester.

15 In a steam-phase digester, two surface heights are to be monitored and adjusted: as for a hydraulic digester, and for liquid. Unlike a hydraulic digester, the steam-phase digester is not submerged in liquid at the top of the digester. Due to the nature of the steam phase cooker, where heating of the chip requires direct contact of the chip with the steam, the surface height of the chip in the steam-phase cooker is above the liquid level. The surface height of this non-submerged (exposed) chips is typically detected by a gamma ray transceiver / receiver located on the side of the digester. In a vapor phase digester, the liquid level is detected by a conventional liquid pressure detector, e.g., a "dp cell".

25 Chips are also fed to these two types of digesters by different mechanical devices. Wood chips or other comminuted cellulosic fibrous material is typically fed into a continuous digester inlet through a separate feed system. The feeding system typically includes a device for de-airing the chips, heating the chips, pressurizing and adding cooking liquor before feeding the sus-30 suspension of chips and liquor into the digester. In a hydraulic digester, a suspension of chips and liquor is fed by a downward-facing screw-type conveyor known in the art as a "top separator". Because in the vapor-phase digester, the suspension is fed with its gases, the suspension of chips and liquor is moved upward in a screw-type conveyor from which the chips and liquor flow over the top of the conveyor and fall freely into the space filled with steam. This upward flow and chips and liquid overflow are ideally suited for the steam-5 raftase cooker as it prevents gas from escaping during suspension delivery while providing an overflow type container for excess fluid removal. This device is referred to in the art as the '' inverted peak separator ''. Both devices remove excess liquid from the suspension for return to the feed system (e.g., a conventional high pressure feeder) as a suspension forming fluid. The operation of these devices 10 is similar, but they are both used in connection with a clearly defined type of digester.

Conventionally, the operation and construction of the hydraulic digester and the steam-phase digester are also markedly different. No one of these skilled in the art would operate one of these types of digesters in the same way as another type, at least without making significant modifications to the digester. For example, a steam-phase digester typically does not have the required number of annular sieves or fluid cycles required for heating in a hydraulic digester. The hydraulic digester, on the other hand, does not have the apparatus required by the steam phase digester to detect the chipping surface above the liquid surface. There are also two different types of top-20 inks that are different in structure and function.

The steam-phase digester has several disadvantages compared to a hydraulic digester. For example, direct exposure of wood chips to steam can be detrimental to the chips fibers. Typically, a rapid increase in the temperature of the chips when it comes into contact with the steam can cause uneven handling of the chips. For example, if the chips are not impregnated uniformly with cooking chemicals, the elevated temperature may cause the cooking chemical to react unevenly with the cellulosic and non-cellulosic constituents of the chips. This can be manifested in degraded pulp quality, which can, for example, reduce paper strength or result in uneven removal of lignin. The smoother heating and treatment provided by the fluid-filled hydraulic digester typically results in less uneven handling of the chips because the chips are submerged in liquor.

4 The vapor phase cooker is also sensitive to changes in the level of chips and liquid. Since the heating of the chips to the boiling point in the steam-phase digester is mainly done by keeping the chips exposed to steam, the reduction of this residence time means a reduction in the 5 heating. Therefore, in the steam phase cooker, the chip surface must always remain sufficiently above the liquid level to ensure proper heating. If the residence time of the chips in the steam state is shortened, the chips become less warmed, which results in an increase in the amount of uncooked chips or reject in the pulp produced. For this reason, the user of the steam-phase digester must constantly monitor and adjust the level of the liquid relative to the surface of the chips. This problem does not occur in a fluid-filled hydraulic digester where heating is effected by fluid circulation.

In the vapor-phase digester, the chips stack above the liquid surface promotes an uneven pressure distribution and thus an uneven movement of the chips in the digester, thus affecting the movement of the 15 '' chips column. The weight of the submerged chips is somewhat offset by the lifting power of the liquid. However, the chips pile above the liquid surface presses the chips below, depending on the distribution of the chips in the cross-machine direction. Because the chips are typically fed close to the center line of the digester, the conical chipper presses more on the center of the chuck statue than the part on the walls of the digester. An additional 20 load in the center, along with the friction caused by the walls of the digester, promotes the downward movement of the chips in the center of the digester, called "" channeling ". Due to the uneven movement of the wood chips, the wood chips will be treated unevenly. This is manifested by increased rejection and reduced paper strength, as well as increased consumption of cooking chemicals and poor runnability. In a fluid-filled hydraulic digester, there is less variation in load and uneven movement of the chips column.

However, the ability to increase the downward load if necessary may be an advantage. When the downward movement of the chip stack is limited, the non-submerged chip stack can act as an additional downward load that promotes downward movement of the chip stack 30, for example, when disturbed or otherwise desired. Thus, the ability to vary the surface height of the chip stack relative to the surface level of the liquid in a desired manner may provide the user with greater flexibility in controlling the digester. Conventional hydraulic cookers do not have this capability due to their characteristics. In conventional steam-rafters, the use of this capability is substantially prevented by the critical residence time required by the steam-phase digester in the steam zone. Thus, a machine with such a capability is a new technology.

Also, gamma radiation transmitting / receiving devices that typically monitor and adjust the chip height in steam phase cookers are not desirable. Any type of radiation emitting device is not desirable to the factory for the sake of safety and because its maintenance and servicing requires trained technical personnel. The plant management and maintenance staff prefer a kettle, such as a hydraulic kettle, which does not require such equipment.

The hydraulic digester also achieves a more efficient and smoother chip-warming process. A hydraulic digester with a countercurrent heating cycle has been found to distribute heat and cooking chemicals more efficiently and evenly to the chipping column. For example, a hydraulic cooker using a Lo-Solids® soup, marketed by Andritz and described in U.S. Patent Nos. 5,489,363; 5,547,012 and 5,536,366, can utilize a heated boiling and dilution liquor stream which, when derivatized with respect to a downstream flush, heats the chip column more evenly and distributes the lye more evenly to the chip column. Originally designed as a steam phase digester, the machine can be modified to operate in substantially the same way as a hydraulic digester with a countercurrent heating circuit that replaces and improves the heat and chemical distribution of the original vapor phase structure. Heating the chips directly with steam is not an efficient use of steam energy and not only damages the cellulosic fibers but also adds extra fluid to the system. The additional liquid or steam condensate only dilutes the desired liquid in the chips. This additional moisture is due to the fact that the chips are introduced directly into contact with the steam. Direct exposure to steam in the steam phase digester increases the liquor ratio by 0.1 to 0.3 units compared to a hydraulic digester. This additional liquid does not provide any additional benefit to the cooking process but disadvantages the need for evaporation in the recovery system. In addition, this heating medium, condensed vapor, is lost in the subsequent steps of pulping 6. In indirect steam heating, on the other hand, the heating medium is essentially retained and recycled in the steam cycle and can be used elsewhere as needed or reused for steam production. The present invention avoids this inefficient use of energy and fluid.

5

Thus, the digester of the invention not only has several clear advantages over the vapor-phase digester, but the invention can also be used in modernization or retro-fit installations of existing vapor-phase digesters, whereby the digester is more efficiently operated as a hydraulic digester.

10

Existing steam-phase digesters typically cannot be used as hydraulic digesters because of the distinctly different equipment and operation. Typically, a vapor-phase digester cannot be used like a hydraulic digester, especially since the vapor-phase digesters are based on heating the chips by direct steam treatment before the chips are submerged in the liquid. However, with the present invention, the vapor-phase digester can be modified to function effectively as a hydraulic digester with all operational and operational advantages, while providing the required inexpensive chip heating mechanism.

Vapor phase type operations have some advantages. For example, the gas-filled space above the chips and liquid surfaces 20 may compensate for variations in the liquor flow to the digester used for pressure control. In a hydraulically inflated digester, the internal pressure of the vessel is controlled by adjusting the amount of feed liquor, e.g., the amount of wash filtrate fed through a conventional pressure control valve. Otherwise, under varying conditions, this may result in excessive variation in the pressure-driven flow. However, in a steam-phase cooker, the pressure is controlled by adjusting the gas pressure in the gas-filled state. This is typically done by pressurized gas supplied through a unit in the vicinity of the gas-filled space at the top of the digester. The gas supply to the top of the digester does not interfere with the flow of liquid below or the movement of the statue. Thus, for gases containing vapor or pressurized gas, such variations dampen and provide a smoother liquor flow to the digester.

7

Furthermore, it is advantageous to be able to switch the system from one heating mode to another. For example, in the case of hydraulic heating, if the strainers of the heating circuit become clogged, the user of the cooker designed according to the invention can heat the chips to the cooking temperature by applying steam to the top of the stove when the strainers are inactive or wiped by the chips.

In some prior art steam phase cookers, chips can be treated upstream with cooking liquor. However, these digesters typically undergo "" pre-hydrolysis "prior to kraft-10 cooking. Pre-hydrolysis is the acid treatment of a cellulosic material which is intended to remove hemicellulose components from the cellulose so as to obtain relatively pure cellulose. Such pulps are known as '' viscose pulp '' or '' soluble pulp '', which are used as the basis for the production of rayon fibers and cellulose films, for example cellophane. As disclosed, for example, in U.S. Patent No. 3,380,883, the chips are subjected to hydrolysis in the gas phase of a continuous imaging digester and the chips are then immersed in an alkaline liquid to terminate the acidic hydrolysis reaction and begin the alkaline kraft cooking reaction. This alkaline treatment takes place upstream.

The process for producing viscose pulp is different from the kraft process 20 of the invention (the invention does not relate to the production of viscose pulp). Removal of hemicellulose from kraft pulp is not only disadvantageous (hemicellulose is of great importance for the strength properties of kraft pulp, for example), but also the treatment disclosed in patent 3,380,883, for example, clearly addresses the specific requirements of pre-hydrolysis treatment and subsequent kraft treatment. The flow of alkali liquor upstream is clearly intended to aid in the separation of acidic lye from the 25 alkali liquors.

According to the invention there is provided a digester system and a method for operating a continuous cellulosic digester having a top and a bottom and an inverted hood separator at the top of the digester.

30 8

A preferred embodiment of the invention is a method of using a continuous cellulose digester having a top and bottom, an inverted top separator, and a bottom removal, the method comprising the steps of: a) feeding the pulverized cellulosic fibrous material and , a suspension formed; b) providing a liquid surface above the bottom of the inverted peak separator in the digester; c) providing a surface of the chopped cellulosic fibrous material below the bottom of the peak separator in the digester; d) removing the liquid from the inverted peak separator at at least one point such that substantially all of the free lye is removed from the introduced comminuted cellulosic fibrous material; and e) removing kraft pulp near the bottom of the 10 digesters (e.g., more than about 1000 t / day).

According to the method, step d) may be carried out to provide a flow of liquid upstream of the cellulosic fibrous material close to the peak separator, and / or step d) may further be carried out by removing fibers from the removed liquid by means of a line strainer and / or such that the removed liquid o is cooled to at least 5 ° C and / or step d) can be accomplished by removing lye from a plurality of circumferentially spaced locations, and step b) may be performed such that the machine is substantially hydraulically charged. The inverted Peak 20 may have a perforated screw thread; then the perforated screw in step d) enhances fluid flow. The digester may have a portion having a first diameter of about 3 to about 5 m at its top and a second portion having a diameter of at least about 7 m below the top, wherein the pivoting peak separator is in the portion having a first diameter, and that a portion having a second diameter provides a surface of the material. The kettle can also be operated substantially completely upstream.

Yet another embodiment of the invention is a continuous digester system for producing chemical cellulosic pulp from cellulose chips, the system comprising: a continuous digester having a top and bottom; an inverted separator 30 at the top of the cooking vessel which feeds the chips and liquid into the cooking vessel and separates some liquid from the chips; the liquid surface in the digester above the bottom of the inverted peak separator; 9 a chip surface below the liquid level in said digester; means for hydraulically heating the chips in the digester to the digestion temperature; means for removing liquid from a pivoting top separator and means for removing mass in the vicinity of the bottom of the cooking vessel.

5

The means for removing fluid from the inverted peak separator may comprise at least first and second circumferentially spaced outlet channels for fluid removal and the outlet channels connected to different structures outside the digester. The digester may have a shoulder between portions having a first and a second halo) and a separation screen positioned just below the shoulder in a portion having a second diameter. The system may further include means for hydraulically heating the chips of the digester, such means including an outlet strainer, a recirculation circuit connected to the strainer comprising a pump, an indirect heater and a duct whereby the fluid discharged through the strainer is heated in the heater and returned through the duct. The inverted peak separator may have a perforated screw thread. The outlet means may include at least one channel, and a further in-line fluid outlet member coupled to said channel, and the digester may be substantially hydraulically full, or the liquid surface may be located between the inverted peak separator and the digester cover with

20

These and other features of the invention will be apparent from the following detailed description of the drawings, and from the appended claims.

Figure 1 is a schematic and partially cut away view and a partially vertical view of a typical feed and top of a conventional vapor-phase digester; Fig. 2 shows, as in Fig. 1, a typical feed and top of a conventional hydraulic digester; Fig. 3 shows, as in Figs. 1 and 2, a typical feed and top of a digester according to the invention, in which the method according to the invention is applied in practice; Fig. 4 shows, as in Fig. 3, another embodiment of the digester of the invention; Figure 5 illustrates, as in Figure 4, another embodiment of a digester of the invention in which the method of the invention is put into practice; Fig. 5 shows a continuous machine according to another embodiment, which has many similarities to the embodiment of Fig. 5; and Fig. 7 is a cross-sectional view of the shaft of an exemplary screw embodiment of the inverted peak separator of Figs. 5 and 6, seen from above.

Figures 1 and 2 show the tops of two conventional transmitters. Fig. 1 shows the top of the steam-phase digester 10 and Fig. 2 the hydraulic digester 20. These digesters may be the only digesters in the pulp production system, or they may be the other of two vessels; the system may include, for example, another vessel known as impregnation vessel in prior art systems. These digesters are typically fed with a suspension of chopped cellulose fiber material, typically wood chips, and cooking liquor, e.g., kraft white liquor. Typically, the suspension is first treated with a feed system, e.g., LO-LEVEL®, sold by Andritz Inc., Glens Falls, NY. The vapor phase digester shown in Fig. 1 is typically fed with a suspension of chips and liquor through conduit 11. The suspension is fed to the digester by means of a conventional vertical screw conveyor 12, known in the art as "inverted peak separator". The suspension is transported upwards in the separator 12 and the top end of the separator 12 discharges chips and lye as indicated by arrows 13. As the suspension flows upwards, excess slime is removed by means of a cylindrical screen 14 and the slurry is returned to the feed system through a conduit 15. The chips removed from the separator 12 and the lye 13 fall through the gas-filled zone 16 into the chips pile 17. To further heat the chips by steam, the top surface of the chips pile 17 is held above the surface of the cooking liquor 18 as shown in Figure 1. After heating with steam, the chips are submerged in the cooking liquor below the liquid surface, referred to in Figure 1 as 18, and the cooking process continues.

To improve heat distribution in the chipping column and stack 17, the vapor phase digester 10 typically also includes a lye removal screen 19 and a rotation 21 for suctioning, removing and returning the lye 11 through the centrally located passage 24 to the chipping column. Circulation 21 typically includes a pump 25 and may include a fluid heater 25 '. The liquor removal screen 19 and the associated circulation 21 (including pump 25 and channel 24) are referred to in the prior art as "equalization circulation". Below the Ta-5 sintering screen 19, the cooking process continues with a more even distribution of heat and chemicals.

In the vapor phase digester 10, the surface height of the chip stack 17 is typically monitored by means of a gamma transmitter and receiver, schematically shown in Figures 10 26 and 26 ', respectively, and facing each other in the vicinity of the chip stack 17.

The transmitter / receiver 26, 26 'detects the presence or absence of chips in the pile 17 and the level of the chips can be adjusted either by changing the suspension flow into vessel 10 or by changing the pulp flow out of vessel 10.

15

In addition to the chip height, the vapor phase digester 10 also needs to monitor and adjust the liquor level. The liquor level 18 is typically monitored by a conventional liquor level detecting device, schematically depicted in Figure 1 as 27, such as a "dp" cell or the like, which senses a chip above the surface reference level.

In the vapor phase digester 10, the pressure and temperature of the space occupied by the vapor 16 must also be monitored. The pressure in zone 16 is typically maintained by an air compressor which supplies pressurized air (or other gas which is inert to the chemical processes of digester 10, e.g., almost pure nitrogen gas) to the top of digester 10 when the pressure drops below the reference level. The excess pressure that may be exerted, for example, by the gases supplied with the suspension, is typically discharged by a conventional pressure relief device, schematically shown in Figure 1 as 28. The temperature in zone 16 is monitored and controlled by adding pressurized steam through duct 22 from steam source 23.

12

Similarly to the steam-phase digester 10 of Fig. 1, the conventional hydraulic digester 20 of Fig. 2 is supplied with a suspension of chips and lye from the feed system through channel 60. The suspension is fed to digester 20 via a conventional "peak separator" 61, which is a downward screw conveyor. The liquor fed through the separator 61 is shown in the figure by the double arrow 62, chipped by a simple arrow 63. As the suspension moves down the conveyor 61, the excess liquor is removed from the suspension via a cylindrical sieve 64 and returned to the feed system (e.g., high pressure feeder) .

10 The chips fed by the separator 63 form a chipping surface 66. Since the digester 20 is hydraulically full, the zone 67 above the chipping surface 66 is filled with liquid, so that the digester does not typically have a gas zone. The chip height in the liquid-filled vessel 20 is typically monitored by one or more conventional mechanical blades 68 (such as Andritz Inc., Glens Falls, NY sold under the designation "K-15 1000"), which are positioned on the inside of the digester and connected to electronic load meters. The presence or absence of chips is detected by the movement of the blades 68, and the chip height is calculated as a percentage by a mathematical algorithm. Gam mass irradiation devices (such as 26, 26 'in Figure 1) are not required. As with the steam-phase digester, the chip height in the hydraulic digester 20 is controlled either by changing the feed of the sus-20 pension or by removing the cooked chip.

In contrast to the digester 10 of Fig. 1, the chips at the top of the pile 66 are typically not heated to full cooking temperature but must be heated before the cooking begins. This is typically done using one or more heated cooking circuits 70. The heating may be downstream or countercurrent; the rotation 70 shown in Fig. 2 warms the chips upstream. The chips suspension first flows past the lye removal screen 71, which removes lye from the suspension through channel 78. The liquor removed through the channel 78 may be led to chemical recovery or used to pre-treat the chips prior to the boiler 20. This lye removes the free liquor represented by double arrow 76, 30 upstream of the downstream chip described by simple arrow 77. The heated liquor 76 is obtained in cycle 70. The liquor is first removed from the slurry 13 via a strainer 72, a duct 73 and a pump 79, heated by an indirect steam heater 74 (e.g. to a temperature of 135-170 ° C) and returned via a centrally located return conduit 75. Cooking liquor, e.g., kraft white liquor, is typically added to this cycle. If a Lo-Solids® soup as described in U.S. Pat. 5,547,012; and 5,536,366 and sold by Andritz, part of the liquor removed through channel 73 can be led to chemical recovery and replaced by a low soluble organic matter such as a mixture of cooking liquor and diluent or water.

After the suspension has been heated to boiling temperature by rotation 70, the suspension may be further cooked and further processed below strainer 72.

Figure 3 illustrates a digester 30 employing a preferred embodiment of the invention. The digester 30 may be modified from the digester 10 by removing or disabling the members 26, 26 ', and inserting blades 68 into the system and heater 74 and "equalization rotation" 21 in recirculation 21, perhaps in another location. It is usually not necessary to move the dp cell 27 or to replace it in some way. Alternatively, the machine 30 may be new.

As in the system of Figure 1, a suspension of chips and lye is fed to the upper end of the digester 30 via a passageway 31 and a conventional inverted peak separator 32 such as those sold by Andritz. The suspension is fed to the digester 30 typically at a temperature of 90 to 130 ° C, depending on the chips being treated in the feed system prior to the digester 30. For example, the feed system is a LO-LEVEL® feed system sold by Andritz Inc. of Glens Falls, NY. and in patent application 08 / 428,302, filed April 25, 1995, the suspension is fed to a digester at about 95-100 ° C. When the chips are fed by a conventional feeding system, e.g. one with a pressurized horizontal steaming vessel, the suspension enters the digester at 115-120 ° C. As usual, the peak separator 32 removes excess liquid from the chips while moving the chips upward and exits the chips and liquid from the separator, as shown by arrows 33. The removed liquor is returned to earlier stages of the process, e.g.

14 high-pressure feeders or impregnation vessels such as those sold by Andritz.

Chip 33 is exposed to gas in space 35 before it reaches its lye at level 36 and falls into the ha-5 heap pile 37. Gas space 35 above liquid surface 36 typically contains air or gases entering the digester 30 with a suspension of chips and lye. If desired or necessary, other gases such as steam, nitrogen or any other suitable gas used for treatment or maintaining the desired pressure can be added to this air. In a sulphite cooking system, the gas space 35 is typically filled with 10 sulfur dioxide gas (SO2). The temperature in space 35 is typically maintained below 160 ° C, typically below 140 ° C, and preferably below 130 ° C (and even below 120 ° C) and the pressure reads from 3.5 to 13.8 bar (e). ) (50 to 200 psig), preferably 5.5 to 13.8 bar (e) (80 to 200 psig), e.g. 5.5 to 10.3 bar (e) (80 to 150 psig). To maintain pressure in space 36, as is common in the prior art, pressurized gas may be introduced into the space via duct 38 15 from source 39. Further, prior art may remove excess pressure using conventional pressure relief device 80. At the top of digester 30, chips, which is represented by the double arrow 43 in the same direction.

The fluid level 36 is typically monitored by a conventional level 20 indicating device, e.g., a "dp cell" 27, although other devices may be used. The level of the liquid may be varied by adjusting the amount of liquid entering or leaving the digester 30, e.g., by adjusting the flow in channel 51 or any suitable channel through which the liquid is introduced into or removed from digester 30. The chip height 37 is also individually monitored by one or more conventional mechanical blades 25 and a load meter 68 mounted on the wall of the digester 30 near the chip surface 37. As usual, the chip height 37 can be controlled by increasing or decreasing the flow of chip into the digester 30 or increasing or decreasing from the stove 30.

Since the incoming chips are preferably not exposed to steam in the gas space 35, the chips are preferably heated to the cooking temperature hydraulically, for example by means of one or more heated liquor cycles. One preferred way of handling the chips is to use screen assemblies 40 and 41. The liquor is removed through the screen assembly 41 and the duct 44, typically by means of a conventional pump 53. The removed liquor is indirectly heated by steam in the heat exchanger 45 (e.g., at least about 130 ° C) before being returned through the passage 46 5 in the vicinity of the screen 41. A cooking chemical, e.g., kraft white or black liquor, is added through conduit 47 to circuit 44. Preferably, Lo-Solids® cooking, such as described in U.S. Patent Nos. 5,489,363, is carried out in digester 30; 5,547,012 and 5,536,366 sold by Andritz. If this occurs, a low-dissolved-organic liquid content such as dilution liquor, e.g., 10 wash filtrates, bleach filtrate, or lean black liquor may be added to channel 44 via channel 48.

Preferably, the heated liquor returned to the digester 30 via duct 46, shown by double arrow 49, flows upstream of the downward flowing chip indicated by arrow 50. The flow of liquor 49 upstream is effected by the removal of Lipe-15 through strainer 40 to duct 51. Typically, liquor 49 heats downward flowing chips 50 to a cooking temperature of 140-180 ° C. Although the liquor in Fig. 3 flows upstream, the heated liquor in the same direction may be used instead of or in addition to the upstream. The liquor flowing in the channel 51 may be led to the recovery of chemicals or used to pre-treat the chips before or in the digester 30. The return circuit 52 may also be connected to the system.

After the screen 41, the heated suspension is typically maintained at a temperature at which the cooking process continues or can be further processed in subsequent zones of the digester 30 before being removed from the digester.

25

Due to the low temperature at room 35 (preferably 130 ° C or below), the pulp may be treated with yield and / or strength enhancing additives such as anthraquinone and its derivatives and / or polysulfide and its derivatives and the like before being fed to the container 30 without destroying the additives. . The temperature at 35 must be maintained at 90-110 ° C if the treatment (or further treatment) is with anthraquinone or its derivatives, and at 90-140 ° C if the treatment (or further treatment) is carried out with the polysulfide and 16 with its derivatives or with similar substances. The treatment in space 35 can take from five minutes to two hours, preferably from about ten minutes to an hour, and the desired conditions are maintained by adjusting the temperature and pressure of the steam to be added at 38 in FIG.

5

Figure 4 illustrates another embodiment of the spout system 100 of the present invention, similar to that shown in Figure 3. Many of the items shown in Figure 4 are identical or identical to those shown in Figure 3 and are referred to with the same numbers as in Figure 3, but "1" is added before the numbers. For example, the inverted peak 10 separator 132 in Fig. 4 is similar to the inverted peak separator 32 in Fig. 3.

The system of Figure 4 includes a conduit 131 through which a suspension of chips and liquor is fed to a digester 130. The suspension is fed to a separator 132 which moves the suspension upward in a screw conveyor while liquor exits the suspension through a cylindrical screen, collector and conduit 134. The chips and leaving unexplored the liquor flowing out of the separator, as indicated by 133 by means of the arrow, and will have steam or kaasuillaan 135. The gas or vapor is fed through the channel 138 of the source 139. The chips and the excess liquor will fall in the liquor having a surface height is described numeral 136, and the chips accumulate the chips pile 137 The level of the liquor and chips is typically adjusted as described in connection with the embodiments of Figures 1, 2 and 3.

The digester system 100 differs from the system of Fig. 3 in that the digester 130 of Fig. 4 has a portion (feed portion) 95 having a first diameter which is smaller than the diameter of the second portion (major portion) 98. The diameter of the portion 98 is at least 20% larger (e.g. 25 about 100-300% larger) than the diameter of the portion 95. The portion 95 is advantageous when the material is processed in a high capacity digester, for example in a digester 130 which produces 1000 tons of pulp per day or more. The portion 95 may typically have a diameter of only about 3 to 5 meters while the diameter of the main portion (second portion 98) of the digester 130 may be about 7 to 12 meters or more. This embodiment 30 is not limited to cookers in which the diameter of the feed portion is different from the diameter of the main portion of the container; although the diameters of portions 95 and 98 are the same, the invention is still effective.

17

The difference in diameters of sections 95, 98 shows in particular how the present invention can be incorporated into an existing digester system, in particular a two-stage hydraulic digester system. Such an installation would simply require, as a major change, only the replacement of the existing feeder, i.e. the peak separator, with the inverted peak 5 separator 132 and the feed 131 shown in Figure 4.

The embodiment of Fig. 4 further includes a decalcifier 86 which removes liquor from the peak separator 132 in addition to the liquor removed through the channel 134. Discharge means 134, 86 (as well as other discharge means which may be present in the system) are preferably located in the circumferential direction 10 about 30 to 120 ° apart. This slurry auxiliary drainage means 86 may remove additional slurry from separator 132, in addition to the slurry typically discharged through channel 134, and lead to slurry formation in a feeder, e.g., a High Pressure Feeder or LO-LEVEL feeder such as Andritz Inc, Glens Falls, N.Y. or to the bottom part of a previous treatment vessel, e.g. The flow from duct 86 may be 0.5 to 5 m3 per tonne of pulp produced (i.e., m / tp), but typically is about 1 to 3 m per tonne of pulp produced.

Substantially all free lye can be removed from the feed chips suspension by other methods. For example, the separator 132 itself may be designed to dispense with a suspension having little or no free lye (e.g. typically less than 10%, preferably less than about 5% of the original amount of free lye), such that the separator 132 is e.g. a screw and an outlet screen portion than a conventional or converging screw-type press structure that functions substantially like a plug feeder. Or, more liquid can be removed simply by adding an additional channel 86 'from channel 134 shown in Figure 4 25.

The above method of removing the lye from the inverted peak separator 132 is particularly advantageous in keeping the treatment liquor used during the previous treatment fed through the channel 131 from the liquor below the separator 132 represented by the liquor surface 136. If, for example, in U.S. Patent Application Serial No. 08 / 911,366, filed Aug. 7, 1996, excess cold liquor not removed through channel 134 may be removed through channel 86, wherein little or substantially no colder liquor is fed to the hotter liquor indicated by surface 136. This system is also advantageous when separating other pretreatment liquors from the lye in vessel 130, for example, strength or yield enhancing additives such as anthraquinone or polysulphide or hydrogen sulphide or the like and derivatives containing them. The lye removed through channel 86 can be led to the recovery of chemicals or used elsewhere in the mill as needed, including in the bleaching plant.

Fig. 4 also shows a heating circuit 85 having an outlet screen 87 just below shoulder 99, a duct 88, a pump 89, a duct 90, an indirect steam heater 91, a return duct 92, a liquor manifold 93, and a plurality of feed nozzles 94. to remove, heat and add lye as needed. For example, cooking liquor such as kraft white liquor or black liquor, or other liquors containing soup additives, or dilution liquor having a lower solids content than the corresponding concentration of the filter 87, may be added to the circulation 85 through channel 96. While the lye is added through channel 96, or instead, the lye can be removed through channel 97. The liquor can be removed through the channel 97 without adding the lye through the channel 96, for example, if it is desired to provide a flow of liquor upstream in the upper part of the digester 130. The system of Figure 4 is particularly advantageous in modernization of a two-vessel hydraulic digester system, where existing top rotary screens are used as liquor removal screens 87. Also, single-stage digesters and steam-phase digesters can be fitted with an arrangement according to the invention.

25

Like the digester of Fig. 3, the digester 130 operates by feeding a suspension of chopped cellulosic fibrous material, e.g., softwood chips, from a feed system or a previous treatment, e.g., a soaking vessel, to a top separator 132 rotated through a channel 131 and removing liquor from the separator as well as through channel 134 as usual. Further, as is customary, the screw conveyor of the separator 132 conveys the suspension upward as the 19 lyes exit and the chips and remaining liquor fall over the top of the seal 132 of the separator 132 as shown by arrows 133. The chips leaving the separator 132 fall through the gas / vapor space 135 into the liquor in the vessel 130, referred to as a surface height 136. The chips then descend to the chips pile 137 and subsequently treated as desired, e.g. Lo-5 Solids soup as described in one or more of the 5,489,363; 5,536,366; 5,547,012; 5,575,890; 5,620,562; 5,662,775 etc, or EAPC ™ soup as described in U.S. Patent 5,635,026. However, according to the invention, additional liquor from channel separator 132 may be removed through channel 86. This additional lye removal is preferably performed through channel 131 to limit or substantially eliminate the flow of free (i.e. not chip bound) lye fed (i.e., that only about 10% or less of the free lye remains). Also, additional heating or supply of additional liquor may be effected in the circuit 85 as described above, e.g., by means of a valve in line 96, which is controlled by a level sensing member 136.

15

Preferably, the pressurized gas / vapor is supplied from the subject 139 in the same manner and to provide the same conditions as in the embodiment of Figure 3.

The invention described in connection with Figures 3 and 4 provides a method of treating comminuted cellulosic fibrous material to produce wood pulp or a method for modifying an existing vapor-phase digester to produce kraft pulp which achieves smoother heating and treatment of the chips; which is less prone to channeling; by which the radiation source detecting the chip height can be excluded; and makes the kettle 25 easier to use.

The embodiment of Fig. 5 is a spout system 100A according to the invention, otherwise similar to the embodiment shown in Fig. 4, but the digester 130A is substantially hydraulically filled so that there is no pressurized gas zone above the liquid and chips. In the embodiments of this embodiment, the parts corresponding to those of Figure 4 are denoted by the same reference numerals.

20

Since the cooking vessel 130A is substantially hydraulically filled, it has no liquid surface 136, channel 138, gas source 139, or associated structures of the embodiment of Figure 4. The embodiment of FIG. for retro-fit installations in single-5 or two-pot cooker systems with gas-phase cooker, as these appliances can be omitted. Since the liquor removed through the channels 134, 86, 86 'may contain fibers or be hotter than desired, one or more of the channels 134, 86, 86' may have a device for filtering the fibers or cooling the liquor before being used elsewhere in the pulp mill (e.g. suspension forming fluid at the bottom of the 10 receptacles of the two-vessel system). Such a line-mounted screen 101 in channel 134. Such a line-mounted screen 101 may be, for example, shown in Figure 2 of U.S. Patent 5,401,361, which is incorporated herein by reference, or a conventional indirect heat exchanger for cooling liquor in channel 134 may be provided. e.g. 5 ° C (e.g. 10-30 ° C).

15

5, the liquor is discharged through one or more channels 134, 86, 86 'such that, at the top of the vessel, the liquor flows upstream as shown schematically by arrows 102. The upstream flowing liquor may be heated as shown in FIG. only one of the passageways 86, 86 '134, as shown in Fig. 5 by the circulation 103, and the liquor may be returned to vessel 130A or used to treat cellulosic material with additives such as AQ for strength or yield. Under these conditions, the circulation 85 may not be necessary, but rather the lower circulation 130A heated to the lye.

25

Embodiment 100B of Fig. 6 is substantially similar to Embodiment of Fig. 5 but, instead of being substantially hydraulically full, vessel 130B is filled with lye up to the top of separator 132 as schematically depicted by 104 in Figure 6 and gas can be added to a small gas phase 130B between the lid and the liquid surface 104 as indicated by the pressurized gas source 139.

21

The inner peak separator 132 of the embodiments of Figures 5 and 6 may be operated such that the liquor can flow freely forward and backward. At the top of digester 130A, 130B, the liquor flow may be downstream or upstream, and the flow of cellulosic material (e.g., 5 chips) and the entire digester 130A, 130B may be upstream if desired. Further, in both embodiments, a twisted screw thread 106, such as schematically shown in Figure 7, may be used as a peak separator screw. The screw thread 106 rotates about axis 105 and may have holes of any type or size 107 as long as they promote fluid flow.

10

While the invention has been described and explained above in what is currently considered to be the most preferred embodiment of its practice 11, it is to be understood that it may be varied in many ways without departing from the scope of the invention. 15 methods.

Claims (17)

A method of operating a continuous cellulose pulp cooker (130A, 130B) having a top and bottom, a reverse top screw (132) at the top, a top and a bottom of the reverse top screw (132), and an outlet in the cellulose pulp cooker (132). 30, 130) bottom, characterized in that it comprises the following steps: a) a suspension of finely divided cellulosic fibrous material and lye, including free lye, is fed into the continuous digester (130A, 130B) through the inverted top screw (132); B) a liquid level (104) is established in the digester above the bottom of the inverted top screw (132); c) a level (137) of cellulosic fibrous material is provided in the digester (130A, 130B) below the bottom of the inverted top screw (132); d) lye is withdrawn from the inverted top screw (132) in at least one location for removing substantially all free lye from the loaded suspension of finely divided cellulosic fibrous material; and e) pulp is discharged in the vicinity of the bottom of the boiler (130A, 130B) in an amount of more than about 1000 tons per day. 20 A method according to claim 1, characterized in that step d) is performed to achieve a countercurrent flow of liquid relative to the cellulosic fibrous material adjacent the top screw (132). Method according to Claim 1, characterized in that step d) is further performed to remove fibers from the drawn liquid in an in-line dewaterer (101). Method according to claim 1, characterized in that step d) is further performed to cool the peeled liquid with at least 5 ° C. Method according to claim 1, characterized in that step d) is carried out by extracting liquid at several points located at a distance from each other along the circumference. 6. A process according to claim 1, characterized in that step b) is carried out in order to substantially completely fill the digester (130A) with liquid. 5 Method according to patent 1, characterized in that the inverted top screw (132) is provided with a perforated screw thread (106) and that step d) is carried out to promote the flow of liquid by utilizing the perforated screw thread (106). Method according to claim 1, characterized in that the cooking vessel (130A, 130B) has a portion (95) having a first diameter of about 3-5 meters at its top and a second portion (98) having a second diameter of at least 7 meters below the top portion, and the inverted top screw (132) is located in the portion (95) of the first diameter, and step c) is performed to achieve a material level (137) of the portion (98) of the second diameter. 15 9. A method according to claim 1, characterized in that the digester (130A, 130B) is operated substantially completely and poured countercurrently. A continuous digester system for producing chemical cellulose pulp from cellulose chips, characterized in that it comprises: a continuous digester (130A, 130B) having a top and a bottom; in the top of the boiler, a reverse top screw (132) which feeds chips and liquid into the boiler (130A, 130B) and separates part of the liquid from the chip; a liquid level (104) in the boiler (130A, 130B) above the bottom of the inverted top screw (132); A chip level (137) in the boiler (130A, 130B) below liquid level (104); devices for heating the chips in the boiler (130A, 130B) to boiling temperature with liquid; liquid extraction devices from the inverted top screw (132); and pulp extraction devices in the vicinity of the bottom of the digester (130A, 130B). 30 11. A system according to claim 10, characterized in that the devices for withdrawing liquid from the inverted top screw (132) comprise at least one first and a second withdrawal line (86, 134) for removing liquid located at a distance from one another along the circumference. , which drain lines (86, 134) are connected to structures outside the digester (130A, 130B). System according to claim 11, characterized in that the cooker vessel (130A, 130B) has a shoulder portion (99) between the portion (95) of the first diameter and the portion (98) of the second diameter, and the portion (98) of the second diameter. has a pull-off screen (87) disposed immediately below the shoulder portion (99). System according to claim 10, characterized in that it comprises devices for heating the chips in the digester (130A, 130B) with liquid, which includes a pull-out screen (87), an ether circulation circuit (85) which is connected to the pull-out screen (87) and contains a pump (89), an indirect heating device (91) and a conduit (88), wherein liquid is withdrawn through the screen (87) with the pump (89), the liquid is heated by the heating device (91) and then fed into the digester (130A, 130B) ) through the conduit (92). System according to claim 10, characterized in that the inverted top screw (132) is provided with a perforated screw thread (106). 15. A system according to claim 10, characterized in that the retraction means comprise at least one conduit (134); and a further in-line dewaterer (101) in said conduit. 25 System according to claim 10, characterized in that the digester (130A) is substantially completely filled with liquid. System according to claim 10, characterized in that liquid level (104) is located between the inverted top screw (132) and the top of the boiler (130B) so that a small gas space is formed between the liquid level (104) and the top of the boiler (130B).