SE545465C2 - Method and arrangement for adding treatment liquors to cellulose raw material in a continuous process using down flow vessels - Google Patents

Abstract

The present inVention relates to an arrangement for adding a treatment liquor to comminuted cellulose material, preferably Wood chips, during the manufacture of chemical pulp in a continuous process using a down-flow Vessel (13) Where chips are descending down the Vessel in a plug flow and Where treated chips are continuously fed out at the bottom of the Vessel, Wherein the treatment liquor is supplied from a common source Via piping to at least 3 side mounted heat and treatment liquor distributors (8) each of Which comprising a first end (80) arranged outside said Vessel (13) and an open second end (81) arranged to extend through a Vessel Wall (130) and into the interior of said Vessel (13). The inVention also relates to a method for adding a treatment liquor to comminuted cellulose material.

Description

METHOD AND ARRANGEMENT FOR ADDING TREATMENT LIQUORS TO CELLULOSE RAW MATERIAL IN A CONTINUOUS PROCESS USING DOWN FLOW VESSELS TECHNICAL FIELD The present invention relates to a method and an arrangement for adding a treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process using a down-flow vessel where chips are descending down the vessel in a plug flow and where treated chips are continuously fed out at the bottom of the vessel.

BACKGROUND In old conventional Prior Art used cooking of chemical cellulose pulp with continuous digesters it was common to use a pre-treatment arrangement with a chip bin, steaming vessel and an impregnating chip chute, before the cooking process is established in the digester. Steaming has been carried out in one or several steps in the chip bin, prior to the subsequent formation of a slurry of the chips in an impregnation fluid or a transport fluid. The steaming has been considered to be absolutely necessary in order to be certain of expelling the air and water that is bound in the chips, such that the impregnation fluid can fully penetrate the chips, and such that air is not drawn into the system. Today a technique with a common treatment vessel for steaming and impregnation at substantially atmospheric conditions often is used.

During the last few years the design capacity of new digester systems has been significantly increased, from typically 500-2000 ADt/24h to production rates over 5000 ADt/24h. As the design production rate increases the combined chip steaming and impregnation vessel diameter increases as well. The fact that the diameter of the vessel increases and in combination with using prior art technology, the added treatment liquor may not be evenly distributed over the entire cross-sectional area of the vessel resulting in a chemical concentration gradient. The above-mentioned disadvantages with prior art addition of treatment liquors are made more obvious as sizes of these steaming and impregnation vessels becomes bigger. The diameter of a typical cylindrical treatment vessel for a digester system with capacity over 5000 ADT per day is well over 9 meters.

Other disadvantages with prior art techniques can be chip and liquor channeling, steam channeling around pipes and diff1culties to completely distribute the treatment liquors from the shell of the vessel to the center of the vessel. All these disadvantages may cause an uneven treatment of the chips such that quite varying pulp quality is produced.

The document WO 2011021968 (A1) discloses a method and arrangement for adding treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process. Said process using a down-flow vessel where chips are descending down the vessel in a plug flow and where treated chips are continuously fed out at the bottom of the vessel. By arranging more than two parallel pipes offset from the center of the vessel could a better distribution of treatment liquor be obtained.

Prior art technique still has disadvantages to achieve an even/smooth chip plug flow and an even distribution of treatment liquor.

SUMMARY OF THE INVENTION The principle object of the invention is to obtain an improved arrangement for the addition of treatment liquors to chips during the manufacture of chemical pulp in a continuous process using a down-flow vessel where chips are descending down the vessel in a plug flow, which arrangement does not demonstrate the disadvantages that are associated with other known solutions as described above. This principal objective becomes more important in high-capacity processes, with capacities of producing well over 4000 and as much as 6000 ADT/pulp per day, and where treatment vessels becomes huge and having diameters well over 9 meters.

Thus, the invention relates to an arrangement for adding a treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process using a down-flow vessel where chips are descending down the vessel in a plug flow and Where treated chips are continuously fed out at the bottom of the vessel, Wherein the treatment liquor is supplied from a common source via piping to at least three side mounted heat and treatment liquor distributors each of Which comprising a first end arranged outside said vessel and an open second end arranged to extend through a vessel Wall and into the interior of said vessel. Thereby, a better spread of the treatment liquor is obtained through over the plug floW area and it is possible to secure the position for the addition of the treatment liquor.

According to an aspect of the invention the heat and treatment liquor distributors are arranged at the vessel in the steaming zone, thereby it is possible to save material and it becomes energy efficient since the treatment liquor does not need to be transported as high as in prior art Where it is supplied at the top of the vessel.

According to the invention, the heat and treatment liquor distributor comprises an outer support pipe, an insert pipe and a first connection, the first connection is arranged at said first end, thereby it is possible to add treatment liquor at the first connection outside the vessel, the treatment liquor passes through the insert pipe and into the chip plug.

According to still another aspect of the invention, the heat and treatment liquor distributor is arranged in a Way that said support pipe and said insert pipe are arranged at an angle from a vertical plane and said angle is preferably l0-90°, more preferred 20- 70° and most preferred 30-45°, thereby it is possible to control the heat profile both diametrically and vertically.

According to yet another aspect of the invention the heat and treatment liquor distributor comprises an upper stiffener and a lower stiffener that contributes to Withstand the forces from the chip plug.

According to another aspect of the invention the lower stiffener is tapered doWnWards parallel to the chip plug floW direction giving advantages such that the frictional forces decreases, and the chip plug coalesces When it has passed the heat and treatment liquor distributor and thus avoids areas With less Well packed chips.

According to still another aspect of the inVention the insert pipe is arranged to be exchangeable, thereby it is possible to change length of the insert pipe and a desired distribution of the treatrnent liquor can be obtained.

Additional benefits and advantages of the inVention will become readily apparent to the person skilled in the art in View of the detailed description below.

DRAWINGS The invention will now be described in more detail with reference to the appended drawings, wherein Fig. l discloses a schematic View of an arrangement for adding treatment liquor according to the prior art; Fig. 2 discloses a schematic View of an arrangement for adding treatment liquor according to the present inVention; Fig. 3 discloses a cross sectional View according to line A-A in Fig. 2, according to the present inVention; Fig. 4 discloses a cross sectional View of a heat and treatment liquor distributor according to the inVention; and Fig. 5 discloses a cross sectional View according to line D-D in Fig. 4, according to the inVention.

DETAILED DESCRIPTION During the following description the terrn "treatment liquor" will be used, and by this is meant one kind of treatment liquor that is intended to be added eVenly to the entire chip flow in the treatment Vessel. This treatment liquor could comprise only of spent cooking liquor, i.e. black liquor, from a subsequent digester or the treatrnent Vessel itself, but could also be a mixture of two or more of following liquids; ° black liquor, ° fresh cooking chemicals such as white liquor (and additives e.g. antraquinon), ° dilution liquids from subsequent wash stage (i.e. wash filtrate from such wash stages), ° steam (added directly in order to heat the treatment liquor).

The terrn "treatment liquid" can also be used, and by this is meant the treatment liquid established in or Withdrawn from the vessel, Which besides partially used treatment liquor also contains chip moisture or any other organic or inorganic content dissolved from the chips.

The term "treatment vessel" Will also be used, and by this is meant any kind of treatment vessel used for treating chips in either form of delignification or impregnation state, i.e. the vessel could be an atrnospheric combined steaming and treatment vessel like IMPBIN, or a pressurized digester.

The term "comminuted cellulose material" Will be used, Which preferably could be in form of Wood chips, but also more fragmented Wood material such as saWdust or pin chips, all obtained from either hardWood or softWood.

Fig. l shoWs an arrangement for adding treatment liquor to comminuted cellulose material during the manufacture of chemical pulp in a continuous process according to prior art. The arrangement comprises an essentially cylindrical impregnation vessel 30 arranged vertically and into Which unsteamed chips are continuously fed into the top of the impregnation vessel via feed means, for example in the form of a small chip buffer l and a chute feed 2. The chips that are fed into the vessel are thus unheated chips that norrnally have the same temperature as the ambient surroundings. The pressure in the vessel can be adjusted as necessary through a control valve 31 arranged in a valve line 4 at the top of the impregnation vessel, possibly also in combination With control of the steam via input lines 5. When atmospheric pressure is to be established, this valve line can open out directly to the atmosphere. It is preferable that a pressure is established at the level of atmospheric pressure, or a slight def1cit pressure by the outlet 4 of magnitude -0.5 bar (-50 kPa), or a slight excess pressure of magnitude up to 0.5 bar (50 kPa). Input of a ventilating floW, SW_AIR (sWeep air), can be applied at the top as necessary, Which ensures the removal of any gases present or brought into the vessel by the in feed of comminuted cellulosic material. The impregnated chips are continuously fed out via output means, here in the form of an Outlet 10, possibly also in combination with bottom scrapers (not shown), at the bottom of the impregnation vessel The level of the chips, CH LEV, above the level of the liquid, LIQ_LEV, should preferably be at least 2 meters and more preferred at least 5 meters when impregnating wood chips. In the case of pulping raw material of low density, a corresponding increase in the height of the column of chips over the surface of the fluid is preferably established. This height is important in order to provide an optimal passage of the chips in an even plug flow through the vessel. When impregnating primarily easily cooked types of wood, such as eucalyptus and other annual plants, steaming with fresh steam can be essentially avoided. Fresh steam is thus not necessarily added to the chips that lie on top of the fluid level established by the impregnation fluid during normal steady- state operation.

When treating primarily wood raw material that is difficult to cook, especially softwood having less density, and in operational cases with extremely low temperature of the chips, (such as during the winter), the chips that lie above the fluid level established by the impregnation fluid can be heated by the addition to the impregnation vessel of extemal steam ST such that a temperature of the chips approach 100 °C in the chip pile before the chips reach the fluid level that has been established by the treatment liquor.

The treatment liquor BL is supplied from a common source via piping 7 to a common header 7c and more than two vertical pipes 7b are connected with their upper end to the common header 7C and having their open second ends inserted in the chip plug flow. The vertical pipes 7b are arranged at a radial position in the treatment vessel being smaller than the radius of the treatment vessel at the height of the open second end of the vertical pipes. A single valve CV is arranged in the piping 7 outside of the treatment vessel 30 and close to or at the exterior wall of the vessel. By such location could the pressure of the treatment liquor be maintained in the piping system up and until the wall of the treatment vessel, and any pressure reduction is only induced in piping located inside of the treatment vessel. The treatment liquor BL can also be established as a mixture from totally separate sources, that is, not from one common flow of black liquor. For example, the treatment liquor may also contain a wash f1ltrate. The treatment liquor added can also be a mixture of black liquor and an additive amount of fresh Cooking Chemicals, i.e. white liquor, with the object of establishing alkali profiles that are necessary for the process. In particular if the residual alkali in the black liquor is low. A rapid initial consumption of alkali norrnally takes place, simply in order to neutralize the wood acidity, while it is desired to keep the final residual alkali after the impregnation stage at a certain level. The needed amount of additional alkali is mostly dependent on the level of wood acidity being released during steaming in the chip volume above the liquid level, and thus dependent on type of wood being treated (softwood or hardwood).

The vessel may be equipped without or with extraction screens to allow liquid extraction (REC) early in the process.

The hot treatment liquor BL being added according to the wet-steaming process where the temperature of the treatment liquor BL added via the pipes 7b at the position of the outlets exceeds the boiling temperature at the prevailing pressure close to the outlets, such that a flashing effect is obtained in the chip volume being located above the fluid level in the vessel.

Fig. 2 discloses a schematic view of a preferred arrangement for adding treatment liquor according to the present invention, with emphasis on the improvements made in relation to the prior art in Fig. 1. Fig. 2 is a cross sectional view seen from the side. Here is shown an arrangement for adding treatment liquor BL to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process. Said process using a down-flow vessel 13 where comminuted cellulose material is descending down the vessel in a plug flow and where treated comminuted cellulose material is continuously fed out at the bottom of the vessel, similar to what is intended in Fig. 1. The improvement here is that the treatment liquor BL is supplied from a common source BL via piping (not shown) to a first end 80 of at least three side mounted heat and treatment liquor distributors 8 arranged in the wall 130 of the vessel 13. The first end 80 of the heat and treatment liquor distributor 8 is arranged outside the Vessel 13 and an open second end 81 of the heat distributor 8 are arranged inside the vessel 13 inserted in the chip plug flow.

Fig. 3 discloses a cross sectional View according to line A-A in Fig. 2. Here is seen that the arrangement for adding treatment liquor in this embodiment comprises five heat and treatment liquor distributors 8 arranged 72° apart.

Fig. 4 shows a cross sectional View of a heat and treatrnent liquor distributor 8 according to the inVention. The heat and treatrnent liquor distributor 8 comprises an outer support pipe 82, an insert pipe 83 and at least a first connection 84. The heat and treatment liquor distributor 8 is arranged in a way that the first coupling 84 is arranged at the first end 80 of the heat and treatrnent liquor distributor 8 and outside the Vessel. The second open end 81 of the heat and treatment liquor distributor 8 is arranged inside the Vessel 13 inserted in the chip plug flow. The joint between the support pipe 82 and the insert pipe 83 in the first end is sealed in a suitable way for example by a gasket 88. The heat and treatment liquor distributor 8 penetrates the wall 130 of the Vessel 13 and to reinforce the wall 130 in that area the heat and treatment liquor distributor 8 also comprises a pad plate 85 which is welded to an inside 131 of the wall of the Vessel. The pad plate 85 act as reinforcement such that the heat and treatment liquor distributorcan withstand forces from the chip plug.

The heat and treatment liquor distributor 8 further comprises an upper stiffener 86 and a lower stiffener 87. The upper stiffener 86 is preferably a plate welded against the pad plate 85 and an upper side 82a of the support pipe 82 with a slope of approximately 45° between an upper 86a and a lower 86b end of said plate. The upper stiffener 86 extends substantially parallel to the chip plug flow direction. The upper stiffener 86 acts like a knife edge such that the chip plug is cleaved which reduces friction between the chip plug and the heat and treatment liquor distributor 8 when the chip plug flow passes.

Thanks to this solution a smooth chip plug flow is achieved.

The lower stiffener 87 comprises a first stiffener plate 87a and a second stiffener plate 87b. The first stiffener plate 87a and the second stiffener plate 87b have the shapes of triangles with a first edge A, a second edge B and a third edge C. The first edge A of the first and the second stiffener plates 87a, 87b are welded, With a distance X in between (see Fig. 5), against the pad plate 85. The second edge B of the first stiffener plate 87a and the second stiffener plate 87b are welded against a lower side 82b of the support pipe 82. The first stiffener plate 87a and the second stiffener plate 87b are arranged to run towards each other and be joined together in their lowest part 87c, see the cross- sectional view in Fig. 5. The lower stiffener 87 is tapered downwards substantially parallel to the chip plug flow, creating a space S in between in this described example. The skilled person realize that the lower stiffener may be arranged in other ways for example it may be a massive piece. The distance X between the first stiffener plate 87a and the second stiffener plate 87b is preferably as close as the diameter of the support pipe 82. This design of the lower stiffener 87 gives advantages such that the chip plug coalesces under the lower stiffener 87 and thus avoids areas with less well packed chips that could form channels for the added treatment liquor that can be a disadvantage with prior art. This design of the heat and treatment liquor distributor 8 with the lower stiffener 87 also contributes to achieve a smooth chip plug flow. The lower stiffener 87 also contributes to strengthen up and helps to withstand the forces from the chip plug flow.

The heat and treatment liquor distributor 8 is preferably arranged such that the support pipe 82 and the insert pipe 83 are arranged at an angle ot of l0-90° from a vertical plane (see Fig. 4), more preferred at an angle ot of 20-70° and most preferred at an angle ot of 30-45°. Thanks to the fact that the heat and treatment liquor distributor 8 is arranged at an angle ot, the heat profile can be adjusted both vertically and diametrically which gives increased flexibility for how the heat profile can be controlled in the steaming zone. The insert pipe 83 is arranged to be exchangeable and depending on the choice of length of the insert pipe 83 a desired distribution of the treatment liquor can be obtained. The skilled person realize that it is also possible to have different length of the insert pipes 83 if a specific spread is to be obtained. The combination of the choice of the angle ot and the length of the insert pipe/pipes 83 provides many opportunities to control the spread of heat/treatrnent liquor. The heat and treatment liquor distributor 8 is preferably arranged so the second open end 8l is at least a distance Y (see Fig. 4) from the inside l3l of the wall of the vessel. The distance Y is preferably at least 50 mm, more preferred at least 100 mm and most preferred at least 200 mm which provides a more even distribution of the treatrnent liquor over the entire cross-sectional area of the vessel. An alternative embodiment (not shown) is to arrange the insert pipe 83 to be movable, then it becomes even easier to control the heat dissipation as desired.

Treatment liquor is supplied via the first connection 84, passing through the insert pipe 83 into the wood chips in an even distribution through the chip plug. An altemative embodiment of a heat and treatment liquor distributor 8 according to the invention comprises a second connection (not shown) arranged on an upper part 82c of the support pipe 82 outside the wall of the vessel (see Fig. 4). Through this second connection, it is possible to boost the heat supply by supplying treatrnent liquor via the annular space 83a between the support pipe 82 and the insert pipe 83 into the chip plug flow. Through this second coupling it is possible to supply heat temporarily or perrnanently in a fixed position.

The inventive idea for the arrangement for adding treatment liquors also includes the combination of heat and treatrnent liquor distributors 8 as described above with a central vertical pipe (not shown) with its lower open end inserted in the chip plug flow approximately in the same height as the heat distributors 8 are arranged.

The arrangement for adding treatrnent liquors as shown thus provides a method for adding a treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process using a down-flow vessel where chips are descending down the vessel in a plug flow and where treated chips are continuously fed out at the bottom of the vessel and where the addition of the treatment liquor is made via 3 or more heat and treatment liquor distributors 8, thus distributing the treatment liquor in an even distribution through over the plug flow area and reducing interference of the plug flow to a minimum.

According the inventive method it is preferred during steady state operations (i.e. excluding start and stop or occasional disturbances) that the fluid level in the vessel is established such that it lies under the level of the chips in the vessel l3 and that thesecond open ends 8l of the heat and treatment liquor distributors 8 are located above the fluid level but below the level of the chips in the treatment vessel 13. The inventive method utilizes the wet steaming process Where the temperature of the treatment liquor added via the 3 or more heat and treatment liquor distributors 8 at the position of the second open ends 8l exceeds the boiling temperature at the prevailing pressure close to the open second ends 8l, such that a flashing effect is obtained in the chip volume being located above the fluid level in the vessel. There is thus no need to use any flash tanks for flashing of steam and pressure from the black liquor WithdraWn from the digester and the black liquor is instead flashed inside of the chip pile Where the heating is required, and at no energy losses.

Claims (1)

1.Claims An arrangement for adding a treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process, the arrangement comprises a down-flow vessel (13) where chips are descending down the vessel in a plug flow and where treated chips are continuously fed out at the bottom of the vessel, at least three side mounted treatment liquor distributors (8) arranged for supplying treatrnent liquor from a common source via piping, each treatment liquor distributor (8) comprises a first end (80) arranged outside said vessel (13) and an open second end (81) arranged to extend through a vessel wall (130) and into the interior of said vessel (13), characterized in that said treatrnent liquor distributor (8) comprises an outer support pipe (82), an insert pipe (83) inserted into said outer support pipe (82) and a first coupling (84), the first coupling (84) is arranged at said first end (80), such that treatment liquor via piping can be supplied to the first end (80). An arrangement for adding a treatrnent liquor according to claim 1, characterized in that said treatrnent liquor distributors (8) are arranged such that said open second end (81) are located, above a level of the liquid (LIQ_LEV) but below a level of the chips in the vessel (13). . An arrangement for adding a treatment liquor according to claim 1 or 2, characterized in that said treatment liquor distributor (8) is arranged in a way that said support pipe (82) and said insert pipe (83) are arranged at an angle (ot) from a vertical plane and said angle (u) is preferably 10-90°, more preferred 20-70° and most preferred 30-45°. An arrangement for adding a treatment liquor according to any of claims 1-3, characterized in that said treatment liquor distributor (8) comprises an upper stiffener (86) and a lower stiffener (87) both arranged inside the vessel (13). An arrangement for adding a treatrnent liquor according to claim 4, characterized in that said lower stiffener (87) is tapered downwards substantially parallel to chip plug flow direction. An arrangement for adding a treatment liquor according to claim 4, characterized in that said upper stiffener (86) comprises a plate that extends substantially parallel to the chip plug flow direction. An arrangement for adding a treatment liquor according to any of claims 1-6, characterized in that said insert pipe (83) is arranged to be exchangeable. An arrangement for adding a treatment liquor according to any of claims 1-7, characterized in that said open second end (81) is arranged a distance (Y) from an inside (131) of the vessel wall (130), said distance (Y) is preferably at least 50 mm, more preferred at least 100 mm and most preferred at least 200 mm. A method for adding a treatment liquor to comminuted cellulose material, preferably wood chips, during the manufacture of chemical pulp in a continuous process using a down-flow vessel (13) where chips are descending down the vessel (13) in a plug flow and where treated chips are continuously fed out at the bottom of the vessel, the addition of the treatment liquor is made via three or more treatment liquor distributors (8) arranged in a vessel wall (130) of said vessel (13) and the treatment liquor is supplied via a first coupling (84), arranged outside the vessel (13) and on a first end (80) of said treatment liquor distributor (8), the treatment liquor is further passing through an insert pipe (83) comprising a second open end (81) that is arranged inside the vessel (13) inserted into the wood chips, thus distributing the treatment liquor in an even distribution through over the plug flow area, characterized in that a fluid level in the vessel (13) is established such that it lies under the level of the chips in the vessel (13) and that the second open ends (81) of the treatment liquor distributors (8) are located above the fluid level but below the level of the chips in the treatment vessel (13). A method for adding a treatment liquor according to claim 9, characterized in that the temperature of the treatment liquor added via the 3 or more treatment liquor distributors (8) at the position of the second open ends (81) exceeds the boiling temperature at the prevailing pressure close to the open second ends (81), such that a flashing effect is obtained in the chip volume being located above the fluid level in the vessel (13).