WO2010043766A1

WO2010043766A1 - Pulp processing method and system

Info

Publication number: WO2010043766A1
Application number: PCT/FI2009/050824
Authority: WO
Inventors: Matti-Paavo SARÉN; Tuomo KÄLKÄJÄ
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2008-10-13
Filing date: 2009-10-13
Publication date: 2010-04-22
Anticipated expiration: 2011-04-13
Also published as: FI20085964L; AT509358A3; FI122771B; AT509358B1; FI20085964A0; AT509358A2; DE112009002297T5

Abstract

A processing system for wood-fibre pulp comprises a separator (102), a treating process (112) and a return device (100). The separator (102) separates vessels (126) from the wood-fibre pulp (120, 122) for the treating process (112), which breaks the structure of the vessels (126). The return device (100) feeds the vessels (128) broken by the treating process (112) into the wood-fibre pulp (120, 122, 204).

Description

PULP PROCESSING METHOD AND SYSTEM

FIELD

[0001] The invention relates to a processing method and system for wood-fibre pulp.

BACKGROUND

[0002] There are vessel cells, i.e. vessels, in all deciduous trees. Their size and shape depend on wood species and habitat, but, in particular, vessels occur in tropical deciduous trees, such as eucalyptus, acacia etc. In papermaking and in utilisation of finished paper the vessels cause problems. In papermaking the vessels cause, for instance, fluffing and in printing on paper there occurs a "vessel picking" problem, in which a vessel detaches from the surface of paper and leaves a white spot thereon.

[0003] Studies have been published on vessels and attempts have been made to find solutions to the problems caused by them. The vessels have been removed from wood-fibre pulp and conveyed to a discharge duct. Removal of vessels from the stock flow reduces the yield, however, and it is not feasible either.

BRIEF DESCRIPTION

[0004] The object of the invention is to provide an improved method and a system implementing the method. This is achieved by a method for processing wood-fibre pulp. The method further comprises: separating the vessels from the wood-fibre pulp for a treating process; breaking the structure of the vessels in the treating process; feeding the broken vessels from the treating process into the wood-fibre pulp.

[0005] The invention also relates to a processing system for wood- fibre pulp. The processing system comprises a separator, a treating process and a return device; the separator is arranged to separate the vessels from the wood-fibre pulp for the treating process; the treating process is arranged to break the structure of the vessels; the return device is arranged to feed the vessels broken by the treating process into the wood-fibre pulp.

[0006] Preferred embodiments of the invention are disclosed in the dependent claims.

[0007] Several advantages are achieved by the method and the system of the invention. Vessels are no longer removed from a stock flow, but they are utilized in the manufacture of a product without deterioration in printing properties, for instance.

LIST OF DRAWINGS

[0008] The invention will be described now in greater detail in connection with preferred embodiments with reference to the attached drawings, in which

Figure 1 shows a processing system with feedback for wood-fibre pulp,

Figure 2A shows a processing system with feedforward for wood- fibre pulp,

Figure 2B shows a separator process,

Figure 3 shows a meter,

Figure 4 shows an aperture in the meter,

Figure 5 illustrates pulp with a whole vessel therein,

Figure 6 illustrates pulp with a broken vessel therein, and

Figure 7 is a flow chart of the method.

DESCRIPTION OF EMBODIMENTS

[0009] The processing system of wood-fibre pulp is first examined by means of Figure 1. Bold arrows represent wood-fibre pulp 120, 122, 124, 204, 206 flowing in a tube and a suspension of vessels 126 having unbroken structure and a suspension of vessels 128 having broken structure. Thin arrows represent measurement signalling. The processing system for wood-fibre pulp comprises a separator 102, a treating process 112 and a return device 100. The separator 102 separates the vessels 126 from the wood-fibre pulp 122 for the treating process 112, which breaks the structure of the vessels. The vessels may be separated from the wood-fibre pulp either before a pulp drying machine or, alternatively, on a paper machine, depending on the treatment, end-product and need. Once the vessels have been treated to a desired degree in the treating process 112, the broken vessels 128 may be returned to the wood-fibre pulp 122 by means of the return device 100 upstream of the separator 102. Wood-fibre pulp 124 containing broken vessels with the vessels removed may be fed from the separator 102 onwards onto a paper machine, for instance.

[0010] Figure 1 shows a form of operation with feedback return. Figure 2A shows a form of operation, in which return of vessels is carried out by feedforward supply. In that case the operation is similar to that in Figure 1 , but the return is carried out after the separator 102. In general, the treated fraction may be returned either back to the input of the first step of centrifugal cleaning or to the accept of the first step, depending on the behaviour of refined vessels in the centrifugal cleaning.

[0011] The separator 102 may be, for instance, a vortex cleaner, a classifier or a sifter. The return device 100 may be a tube connection.

[0012] In the treating process 112 vessels may be modified with metal refiner blades, for instance. Appropriate refining allows large part of the vessels to be disintegrated such that they cause less trouble. Therefore the refined vessels may be recycled back to the stock flow.

[0013] Alternatively or additionally, it is possible to modify vessels chemically in the treating process 112. A form of operation employs carboxyl methyl cellulose (CMC) or the like for breaking the structure of the vessels.

[0014] Treatment of vessel cells, i.e. vessels, is now examined in greater detail by means of Figure 2B. Each separator 250 to 260 may be a centrifugal cleaner, a sifter or a classifier. In the sifter and/or classifier the separation of vessels may be carried out by means of one or more sifters or classifiers, or sifter or classifier surfaces. The centrifugal cleaner, in turn, separates vessels from other fibre material on the basis of their lower specific weight, i.e. higher density. The shape of vessels, which is a short stump, acts in the same direction, i.e. on separation to the reject of centrifugal cleaning. Centrifugal cleaning is the most commonly used solution for vessel separation. In an embodiment one single separator 250 is employed for vessel separation. However, separating devices may be added in cascade. In cascade connection the accept pulp A of a separating device is returned to serve as input pulp for a preceding separating device. In Figure 2B the separating devices 250, 256 to 260 are connected in cascade.

[0015] For instance, when two separating devices are used connected in cascade, the reject R from a first separating device 250 is fed into a second separating device 256. The second separating device 256 processes the reject R from the first separating device 250 and a concentrated vessel cell fraction is obtained as a reject fraction R from the second separating device 256. Correspondingly, it is possible to connect a plurality of separating devices 250, 256 to 260 as shown in Figure 2B. In this manner the vessels will be con- centrated to a higher proportion in the reject fraction R of cleaning, i.e. separation.

[0016] In general, to be able to separate as large part as possible of the vessel cells into the reject fraction, it may require that a plurality of separating devices 250 to 254 be connected in series such that an accepted fraction, i.e. the accept, from a preceding separating device is conveyed to a subsequent separating device 252, whereby each stage provides separation of more vessel cells in the reject fraction. There may be a plurality of these separating devices connected in series. When there is no need to concentrate the proportion of vessel cells to a particularly large proportion for refining, vessel- containing pulp obtained as reject fractions from the separating devices 250 to 254 may be left untreated with at least one individual separating device 256 to 260 treating separator reject.

[0017] Vessels are typically shorter in size than other lignocellulose fibres, but of the same order in diameter or larger in relation thereto. When sufficiently small slot or mesh size is used in classifying, the vessels, i.e. vessel cells, are concentrated as rigid and sliver-like fibres in the reject pulp, whereas fines and other small-size elastic fibre material and a filler, for instance, permeates the sifter surface in sifting and passes into the accept pulp. It has been found that the higher the mass-to-reject ratio of the classification or sifting performed, the larger the proportion of vessels separated into the reject pulp. Thus the proportion of reject of the fed pulp may be 10 to 30% higher than in typical classification use. Separation of vessels from the pulp to be classified may thus be implemented by performing the classification using at least 20% mass-to-reject ratio. Because the separation is enhanced as the mass-to-reject ratio increases, the separation may also be performed using at least 30% mass-to-reject ratio, for instance.

[0018] After the separation of vessels and before refining them it may be necessary to thicken the vessels in order to enhance refining. The refining may be performed efficiently if the vessel-containing pulp is concentrated to thickness of 3 to 30% prior to conveying the pulp to refining. It is possible to use a disc filter, a drum thickener and/or a screw press, for instance, for thickening.

[0019] Vessels can be broken by refining them between the refining surfaces of a refiner. Breakage may be performed in a desired manner and to a desired degree, so that broken vessels may be returned in a suitable form into the process. The refining surfaces of the refiner may be metal surfaces comprising blade edges, for instance, or refining surfaces intended for grinding refining or wet beating. The refining surfaces intended for grinding or refining wet-beaten pulp may consist of a basalt blade surface, for instance, comprising a concrete surface with holes therein, or they may be fabricated of metal refiner surface bases that are coated, for instance, with grits made of aluminium oxide and constituting the refining surface. Further, the refining surface may be provided as a combination of at least two above-mentioned refining surfaces, for instance, such that a metallic surface comprising blade edges constitutes one refining surface and a grinding-type refiner surface constitutes the second refining surface. Additionally or alternatively, the opposing refiner surfaces may be manufactured of two or more different grinding-type refiner surfaces. The refiner surfaces set forth are refiner surfaces known per se, and therefore they are not presented in any greater detail.

[0020] Irrespective of the type of the treating process 112, the purpose of the treating process 112 is to break the structure of the vessels, because the binding area of a broken vessel is larger and the binding capability is better than those of a whole vessel. After the treating process 112 the vessels are good for papermaking. Breaking of the vessel structure also improves the quality of finished paper, for instance, in view of printing and appearance.

[0021] The treating process 112 may be carried out in a predetermined manner without measuring the wood-fibre pulp or the vessels. But, as shown in Figures 1 and 2A, in the processing system it is also possible to perform several measurings that may be utilized in a manual or automatic adjustment of the processing system for wood-fibre pulp.

[0022] The processing system may comprise a signal processing unit 108, which may receive data on the state of the processing system from at least one meter 104, 106, 110, 114, 118, 200, 202 and control the vessel treating process 112 on the basis of the data received from each meter 104, 106, 110, 114, 116, 118. The signal processing unit 108 may comprise a processor, a memory and one or more appropriate computer programs for signal processing and/or controlling.

[0023] The processing system may comprise at least one meter 104, 116, 118, 200, 202 for measuring vessels in the wood-fibre pulp 120, 122, 124, 204, 206. In that case the signal processing unit 108 may control the vessel treating process 112 on the basis of the measurement of at least one meter 104, 116, 118, 200, 202. The meter 116 may measure the amount and/or quality of the vessels in untreated wood-fibre pulp 120. The meter 104 may measure the amount and/or quality of the vessels in treated wood-fibre pulp 122 containing both treated and non-treated vessels.

[0024] The meters 116 and 104 may measure the variation in concentration of vessels potentially causing most problems in the wood-fibre stock flow. This also enables adjustment of the reject ratio of the separator 102 on the basis of said measurement.

[0025] The meters 118, 202 may measure the amount and/or quality of vessels in the treated wood-fibre pulp 124, 206, from which the non- treated vessels are removed and into which the treated vessels are fed. The meter 200 may measure the wood-fibre pulp 204, from which the (non-treated) vessels are removed, but to which non-treated vessels are not added.

[0026] The signal processing unit 108 may also act as a controller and control the separator 102 to adjust vessel separation in the wood-fibre pulp 122 on the basis of the measurement. If the amount of whole vessels increases, according to the meter 202, in the treated wood-fibre pulp 124 downstream of the separator 102, it is possible to enhance the operation of the separator 102 so as to involve as many vessels as possible in the treating process 112. Enhancement may refer to a prolonged transit time of wood-fibre pulp through the separator 102, an increased rotating speed of a centrifugal cleaner or the like. Correspondingly, if the amount of whole vessels decreases in the treated wood-fibre pulp 124 downstream of the separator 102, it is possible to reduce the performance of the separator 102 or to keep it unchanged. It is possible to increase (decrease) the performance of the separator 102, if the amount of vessels increases (decreases) in the untreated wood-fibre pulp 120 or in the wood-fibre pulp 122 between the return device 100 and the separator 102.

[0027] The processing system may comprise a meter 110 for measuring vessels to be fed into the treating process. In that case the signal processing unit 108 may control the treating process 112 so as to adjust the breakage of vessel structure on the basis of the measurement. If vessels 126 abound, i.e. the vessel flux is large according to the measurement by the meter 110, it is possible to enhance the treating process 112. Correspondingly, if on the basis of the meter 110 the quality of the vessels 126 is such that it requires more efficient treatment than before, the treating process 112 may be en- hanced. Enhancement of the treating process 112 may refer to a prolonged treatment time, increased forces exerted on the vessels, increased amount of a chemical treating agent and/or addition of a chemical agent for breaking the structure of the vessels more efficiently.

[0028] The processing system may comprise a meter 114 to measure vessels in the treating process 112. In that case the signal processing unit 108 may control the treating process 112 so as to adjust the breakage of vessel structure on the basis of the measurement. When an amount of vessels exceeding a threshold value is found broken, the vessels may be returned back to the wood-fibre pulp. If the meter 114 finds that the vessels are better broken than what was predetermined, it is possible to reduce the efficiency of the treating process 112. Correspondingly, if it is found, on the basis of the meter 114, that the vessels are broken in a predetermined manner or more poorly than that, it is possible to enhance the treating process 112.

[0029] The processing system may comprise a meter 106 for measuring vessels emerging from the treating process 112. In that case the signal processing unit 108 may control the treating process 112 so as to adjust the vessel structure on the basis of the measurement. If the meter 106 finds that the vessels are better disintegrated than what was predetermined, it is possible to reduce the efficiency of the treating process 112. Correspondingly, if it is found, on the basis of the meter 106, that the vessels are broken in a predetermined manner or more poorly than that, it is possible to enhance the treating process 112.

[0030] On the basis of data from the meters 106, 110 and 114 it is possible to adjust the treating process 112 and to obtain information on how the separation of vessels has succeeded. In addition, by comparison of measurements carried out before and after the treating process 112 it is possible to assess how well the vessel refining succeeded.

[0031] Figure 3 shows a meter 104, 106, 110, 114, 116, 118, 200, 202, which may comprise a source of radiation 300 and a detector 302. The source of radiation 300 directs radiation to an object 304 to be measured, which may comprise wood-fibre pulp 120, 122, 124, 204, 206 or untreated vessels 126 before the treating process 112 or treated vessels 128 after the treating process 112. The object to be measured 304 may be a suspension, which contains water as a medium and wood fibres and/or vessels as dry matter particles. The suspension may flow, for instance, in a tube 306 transparent to radiation used in the measurement. The vessels in the object to be measured 304 scatter and/or absorb radiation directed thereto. In this application the scattering also includes reflection. The detector 302 may detect radiation passing through the object to be measured directly from the source of radiation or radiation scattered from the object to be measured, whereby an image is formed on the object to be measured 304. The detector 302 converts the received image produced by radiation into an electric image signal that may be an analogue or a digital signal. The signal processing unit, which may comprise a convertor for converting an analogue signal to a digital one, may process the image signal with an appropriate image processing program. Vessel separation with the separator 102 from the wood-fibre pulp, evaluation of the treating process 112 in the signal processing unit 108 and optional control of the treating process 112 may be based on shape recognition of vessels. This solution is suitable for continuous online fibre measurement. The image of each meter may be analysed for the amount of vessels and the breakage of their structure. Separation of whole and broken vessels may be carried out either by conventional technology (dimensional criteria) or, for instance, by learning classifiers, such as a neural network or PLS (Partial Least Squares) classifier.

[0032] Each meter may also comprise an imaging element 308 that produces for the detector 302 an image of the object to be measured 304. In addition, it is possible that the meter comprises a focusing element 310, wherewith the radiation is enhanced to focus on the object to be measured 304. If the detector 302 detects radiation passing through the object to be measured directly from the source of radiation, the treated and/or non-treated vessels appear on the image provided by the detector as dark objects against a bright background. If the detector 302 detects radiation scattered from the particles of the object to be measured 304, the particles, such as treated and/or non-treated vessels, appear on the image provided by the detector as bright objects against a dark background.

[0033] The source of radiation 300 may be an optical source of radiation and both the imaging element 308 and the focusing element 310 may include optical components, such as lenses or mirrors. The source of radiation 300 may include one or more LEDs that emit visible light or infrared radiation.

[0034] When optical radiation is directed to the detector 302 directly from the source of radiation 300, it is possible to improve the quality of the im- age by means of the arrangement of Figure 4. The imaging element 308 may comprise an optical element 400 focusing the radiation emitted from the object to be measured 304, such as a lens or a mirror, which focuses the optical radiation to a small aperture 404 in a opaque piece 402, the diameter of the aperture being less than 5 mm, for instance. Generally, the diameter of the aperture 402 is 1 mm, only 0.1 mm or even less. The radiation coming from the aperture 402, in turn, may be imaged with the optical element 406, such as a lens or a mirror, for the detector 302.

[0035] The detector 302 may be a black-and-white or colour digital camera having a detecting element including a semiconductor pixel matrix.

[0036] The source of radiation 300 may also be an X-ray source, in which case the detector 302 is a semiconductor pixel matrix sensitive to X- radiation. Further, the source of radiation 300 may be a source of ultrasound radiation, in which case the detector 302 is an ultrasound detector sensitive to acoustic radiation.

[0037] Figure 5 shows an image provided by the meter, where one can see a vessel 500 having an unbroken structure. Also a fibre 502 appears in the image.

[0038] Figure 6 shows an image provided by the meter, where one can see a vessel 600 which has a broken structure and which the signal processing unit 108 does not define as a (whole) vessel 126, 500. Also a fibre 502 appears in the image.

[0039] Figure 7 shows the flow chart of the method. In step 700 the vessels are separated from the wood-fibre pulp for the treating process 112. In step 702 the structure of the vessels is broken in the treating process. In step 704 the vessels are supplied from the treating process 112 into the wood-fibre pulp 120, 122.

[0040] The signal processing unit 108 may be implemented by a processor, a memory and computer programs and the control of the treating process 112 may be implemented as a computer program. Alternatively, the signal processing unit 108 may be implemented as a hardware structure by means of separate logic components, one or more integrated circuits or one or more application-specific integrated circuits (ASIC). A hybrid of these various implementations is also possible.

[0041] The computer program, in turn, may be placed in the distribution means of the computer program for the distribution thereof. The distribu- tion means of the computer program is readable by a data processing device and it encodes the computer program commands for controlling the treating process 112.

[0042] The distribution means may be a solution known per se for distributing the computer program, for instance, a medium readable by a data processing device, a program storage media, a memory readable by a data processing device, a software distribution package readable by a data processing device, a signal readable by the data processing device, a telecommunication signal readable by the data processing device or a compressed software package readable by the data processing device.

[0043] Even though the invention is described in the above with reference to the examples of the attached drawings, it is obvious that the invention is not limited thereto, but it may be modified in various ways within the scope of the attached claims.

Claims

1. A method for processing wood-fibre pulp, characterized by separating (700) vessels (126, 500) from the wood-fibre pulp (120,

122) for a treating process (112); breaking (702) the structure of the vessels (126, 500) in the treating process (112); feeding (704) the broken vessels (128, 600) from the treating process (112) into the wood-fibre pulp (120, 122, 204).

2. The method of claim ^ characterized by measuring the vessels (126, 500) in the wood-fibre pulp (120, 122, 124, 204, 206) and controlling the breakage of the structure of vessels (126, 500) on the basis of the measurement.

3. The method of claim 1, characterized by measuring the vessels (126, 500) in the wood-fibre pulp (120, 122, 124, 204, 206) and controlling the separation of vessels (126, 500) from the wood-fibre pulp (120) on the basis of the measurement.

4. The method of claim 3, characterized by controlling the treating process (112) of the vessels (126, 500) on the basis of the measurement.

5. The method of claim 1, characterized by measuring the vessels (126, 500) to be fed to the treating process (112) and controlling the treating process (112) of the vessels (126, 500) on the basis of the measurement.

6. The method of claim ^ characterized by measuring the vessels (126, 500) in the treating process (112) and controlling the treating process (112) of the vessels (126, 500) on the basis of the measurement.

7. The method of claim 1, characterized by measuring vessels (126, 500) emerging from the treating process (112) and controlling the treating process (112) on the basis of the measurement.

8. A system for processing wood-fibre pulp, characterized in that the processing system comprises a separator (102), a treating process (112) and a return device (100), the separator (102) is arranged to separate vessels (126, 500) from the wood-fibre pulp (120, 122) for the treating process (112), the treating process (112) is arranged to break the structure of the vessels (126, 500), the return device (100) is arranged to feed the vessels (128, 600) broken by the treating process (112) into the wood-fibre pulp (120, 122, 204).

9. The processing system of claim 8, characterized in that the processing system comprises a signal processing unit (108) and the signal processing unit (108) is arranged to receive data on the state of the processing system and to control the treating process (112) of the vessels (126, 500) on the basis of the received data.

10. The processing system of claim 9, characterized in that the processing system comprises at least one meter (104, 116, 118) for measuring vessels (126, 500) in the wood-fibre pulp (120, 122, 124, 204, 206) and the signal processing unit (108) is arranged to control the treating process (112) of the vessels (126, 500) on the basis of the measurement of each meter (104, 116,118).

11. The processing system of claim 10, characterized in that the signal processing unit (108) is arranged to control the separator (102) to adjust the separation of the vessels (126, 500) from the wood-fibre pulp (120, 122) on the basis of the measurement.

12. The processing system of claim 9, characterized in that the processing system comprises a meter (110) for measuring the vessels (126, 500) to be fed into the treating process (112) and the signal processing unit (108) is arranged to control the treating process (112) so as to adjust the breakage of the structure of vessels (126, 500) on the basis of the measurement.

13. The processing system of claim 9, characterized in that the processing system comprises a meter (106) for measuring broken vessels (128, 600) emerging from the treating process (112) and the signal processing unit (108) is arranged to control the treating process (112) so as to adjust the breakage of the structure of the vessels (126, 500) on the basis of the measurement.

14. The processing system of claim 9, characterized in that the processing system comprises a meter (114) for measuring vessels (126, 500) in the treating process (112) and the signal processing unit (108) is arranged to control the treating process (112) so as to adjust the breakage of the structure of vessels (126, 500) on the basis of the measurement.