FIELD OF THE INVENTION The present invention relates to a method and an apparatus for pneumatic supply and discharge of liquid filled hollow pulp fibers. The method aims in particular at preconditioning pulp fibers for a pass through a venturi throat or a venturi tube, which is used to decompose bundles of fibers into individual fibers or to split individual hollow fibers in their longitudinal direction by opening their lumen along the weakest part of the cylindrical fiber wall. The invention includes embodiments comprising such decomposing or splitting steps singly or in sequence, a first venturi tube decomposing fiber bundles and a second downstream venturi tube splitting the individual fibers.

BACKGROUND OF THE INVENTION Fiber morphology

In the pulp and paper industry all processing apparatuses and methods are influenced by the pulp characteristics, which derive particularly from fiber morphology, population, length, coarseness, coarseness to length ratio, wall thick- ness and diameter, and fiber types to list the most important ones.

Fiber morphology is the key element that influences the pulp characteristics. Up to now the paper industry has not given fiber morphology full consideration as regards pulp processing and papermaking.

Among the most important aspects that affect the morphology of the fibers are the species of the trees or non-wood plants that are processed into pulp.

Another major aspect of fibrous pulp is coarseness, a measure of how much fiber wall material there is in a fiber per unit-length of that fiber.

The relationship of fiber diameter and wall thickness affects the tendency of the fiber to collapse. Pulp fines are generally considered to be detrimental to pulp properties because they don't contribute significantly to sheet strength and they displace longer fibers, they lower freeness and impede the drainage on the paper machine, they aren't easily retained on the paper machine wire, they tend to pro- duce paper surfaces prone to picking and dusting, and they have a high specific surface area that attracts a disproportionate amount of additives.

There is another category of fines, called secondary fines that are fragments of fibers and fiber walls. Secondary fines result from fiber damage in wood chip production and transport, pulping, mixing and refining. Secondary fines, within some reasonable limits, are generally considered beneficial for sheet strength, opacity and surface properties.

Regarding non-wood pulps, cotton linters pulps are nearly pure cellulose fibers produced from second-cut cotton linters. From a strength potential perspective, the nearly pure cellulose severely limits hydration and bonding potential. As a consequence refining has little influence on strength development and, while these pulps are quite durable and stable, they are not used to make strong papers without being combined with other fibers and/or bonding additives.

Three other non-wood pulps belong to the category of pulps with very uneven fiber length distribution and quite different fiber types. Bamboo, kenaf and ba- gasse pulps have very similar fiber length, but their coarseness values cover a fairly broad range. All three pulps have at least two very distinct fiber types, namely a long, relatively thick-walled fiber much like softwood latewood fiber, and a large diameter thin-walled short fiber.

Wood cell structure Major difference between softwoods and hardwoods is that softwoods are dominated by one fiber type, the tracheid, while hardwoods have fiber trache- ids and vessel elements. The vessel elements specialize in vertical transportation of water in the tree trunk. Each vessel consists of vessel elements that are cylindrical cells with open ends. They are connected longitudinally to form pipe structures. All hardwoods have vessels in the range of 10% to 50% of their volume, depending on species. Vessel elements of some hardwood species are extremely large in diameter compared to their fibers. In addition to having more fiber types, the volume that the fiber types occupy, and their size and shape, is more varied in hardwoods. In softwoods the tracheids are 90+% of the wood volume and 94+% of the pulp mass. In contrast, the hardwood fiber tracheid volume ranges from 40 to 70%, while the vessel elements occupy 10 to 40% of the wood.

There is a third group of small cells, namely the ray tracheids in softwoods and the ray and axial parenchyma in hardwoods. Ray cells constitute less than 10% of the volume of softwoods, but the parenchyma cells in hardwoods can be up to 40% of the wood volume and more than 20% of the mass of a market pulp. These very small cells are commonly referred to as primary fines.

Pulping The major types of fibrous pulps produced today are chemical pulps made by digesting, thermomechanical pulps (TMP) made by heat and mechanical defibrillation and chemi-mechanical and chemi-thermomechanical pulps (CMP and CTMP) made by mechanical refining with use of heat and/or chemicals. Chemical pulping has a low yield and the pulps are rather expensive. Mechanical pulps are rather weak and yield lower-quality although cheaper paper products compared with chemical pulps. Ultra-high-yield chemi-mechanical (CMP) pulps and chemi-thermo-mechanical (CTMP) pulps represent alternatives, which combine high yield, low cost, and fewer pollution problems while achieving good mechanical properties. The only major drawback of CMP/CTMP pulps is their relatively high defibrillation energy.

Steam explosion pulping (SEP) was suggested as an alternative to CMP/CTMP processes in the early 1990s because of the reduced refining energy required for the SEP pulp. A much higher temperature is used (180- 210°C) as compared with that used in conventional CMP/CTMP processes (120-150 °C) and a shorter time. Moreover, the cook is terminated by a sudden pressure release.

Paper recycling is the process of recovering waste paper, pulping the paper and turning it into new paper products. There are three categories of paper that can be used as feed stocks for making recycled paper, namely mill broke, pre-consumer waste, and post-consumer waste. Mill broke is paper trimmings and other paper scrap from the manufacture of paper, and is recycled internally in a paper mill. Pre-consumer waste is material which left the paper mill but was discarded before it was ready for consumer use. Post-consumer waste is material discarded after consumer use, such as corrugated containers, magazines, newspapers, office paper, telephone directories etc.

Pulp processing

The most usual processes for the fibrous wood or non-wood pulps are wash- ing, bleaching, chemical treatments of the pulp, refining, drying, and pa- permaking. Recycled fibrous wood or non-wood pulps are subjected to dein- king, bleaching, refining and papermaking.

Pulp washing aims at the removal of residual digesting or bleaching liquor from the pulp. All washing methods displace spent liquor only from the space out- side and between the pulp fibers, but leave practically all spent liquor inside the fiber lumen. Some leaching of the inside bound liquor happens during the dilution/extraction stages between multiple washing steps in series. However, a substantial amount of spent liquor, typically 1 .5-2 times the weight of the fibers, is still carried over inside the hollow fiber lumen to the next processing stage.

Bleaching of pulp fibers is done with chemicals in gaseous or liquid form. One or more bleaching stages are required to achieve desired result. Each bleaching stage is accomplished at a preferred pulp consistency, temperature, pressure, time duration, and chemical concentration. Each bleaching stage is followed by a washing stage to remove the dissolved organic matter and the bleaching chemicals to minimize the carry-over to the next bleaching stage. In bleaching typically only one washing step is used per stage. Again, the wash leaves a substantial amount of already dissolved organic matter and bleaching chemicals inside the fiber lumen. This carry-over consumes and thereby wastes some of the newly added chemicals in the next bleaching stage.

The industrial process of removing printing ink from paper fibers of recycled paper to make deinked pulp is called deinking. Many newsprint, toilet paper and facial tissue grades commonly contain 100% deinked pulp and in many other grades, such as lightweight coated for offset and printing and writing papers for office and home use, deinked pulp makes up a substantial proportion of the furnish. In the fast-growing digital printing market, a noteworthy development is the introduction of commercial inkjet web presses for on-demand newspapers and various publications and business forms. However, inkjet inks are generally not de-inkable and are, therefore, incompatible with paper recovery and recycling. Ten percent is a reasonable estimate for the percentage of inkjet-printed paper that a mill can tolerate.

Very small and hydrophilic ink pigments are generally easily dislodged from the fiber surface during pulping. The mechanical action imparted to the pulp in a repulper, however, causes the small ink pigments to enter into the lumen via pit apertures where they deposit irreversibly on the surface of fiber lumen.

Some end products in chemical pulping require additional chemical treatment after the conventional bleaching stages. For instance, mercerized pulps are produced by post-treatment of steeping a bleached pulp in caustic to swell the fibers, to remove hemicelluloses and to render the pulp inert as far as strength development from refining is concerned. Market pulps are used to produce cellulose derivatives including sodium carboxyl methyl cellulose (CMC), hydroxyl ethyl cellulose (HEC), methyl ethyl cellulose (MEC) and cellulose diacetate. Dissolving pulps having uniform intrinsic viscosity, also measured as degree of polymerization, undergo a process that reduces it to syrup that can be further processed into cellophane film and fibers for rayon, acetate and other man- made fibers.

Refining or beating of chemical pulps is the mechanical treatment and modification of fibers so that they can be formed into paper or board of the desired properties. The main target of refining is to improve the bonding ability of fibers so that they form strong and smooth paper sheet with good printing properties. Refining affects fibers by cutting and shortening of fibers, fines production, removal of parts from fiber walls, external fibrillation, delamination, internal fibrillation, swelling, curling, creating kinks etc., and dissolving or leaching out colloidal material into the external liquor. As a result of the above effects, fibers after refining are collapsed (flattened) and made more flexible, and their bonding surface area is increased.

Production of market pulp as well as various types of paper and board products requires drying of the final product. Most market pulp is air dried (90% fiber, 10% water) and compressed into bales or in some cases the pulp mat is split and rewound into rolls. Two basic systems are employed in the production of dry market pulp: the conventional system, and the flash-drying system.

The conventional system of producing dry market pulp parallels conventional papermaking: a thick pulp mat is formed with a Fourdrinier wet end, most re- maining free water between the fibers is removed mechanically in the press section, and evaporative drying is employed with either a steam-heated cylinder dryer or an air-float dryer section.

Flash or spray drying refers to the process whereby the fibrous material is introduced as a spray or an analogous form into a stream of hot gases. The high-temperature heat content of the gas stream causes flashing of moisture to vapor.

However, the entrapped water in the lumen immediately turns to steam (one cc of water becoming 1700 cc of steam), creating an internal explosion. The water in the fiber's wall and interior lumen evaporates, causing the fiber to shrink and contract. Each fiber reacts to this explosion in varying ways, depending on the structural weaknesses along the length of the fiber. These inherent weaknesses create knuckles in the fibers' shape. Along with the knuckles the fibers develop a characteristic curly shape and become convoluted. These misshapen fibers have made flash-dried pulps recognized as being ideally suited to the needs of those mills producing filter papers and latex-saturated paper and board.

In drying a sheet of paper two basic physical processes are involved, heat transfer and mass transfer. Heat is transferred from some source such as steam to the wet sheet in order to provide the energy required to drive the moisture from the sheet. The moisture evaporates and is then transferred from the sheet to the surrounding atmosphere by the mass transfer process. Multi- cylinder drying is the most common way in the paper and paperboard industry.

Venturi tubes in pulp processing

A specific teaching of use of a venturi tube in connection with pulp processing is found from US patent 5,785,810. According to this prior art publication washed and dewatered pulp is delivered to a pressure chamber and then, together with an added bleaching agent, is moved through a discharge passageway to a subsequent bleaching location. The discharge passageway in- eludes a venturi tube for accelerating the pulp and for shredding the pulp into smaller particles. Such shredding mainly involves shattering of bundles of fibers into smaller fiber groups or individual fibers, thus increasing the number of individual solid fibrous particles, but does not affect the tubular hollow structure of the individual fibers.

Furthermore, the applicant ^' s previous international application PCT/FI291 1 /051 123, still secret at the filing date of the present application, describes use of a venturi tube for splitting individual hollow fibers in their longitudinal direction, which opens the lumen of the fibers like a pea pod, thereby releasing the liquid contents of the lumen for easy removal and increasing the free surface area of the fibers readily available for further treatments, but does not break the individual fibers into pieces and, as distinguished from the teaching of US 5,785,810 does not increase the number of separate particles in the process. As noted, wood as well as non-wood fibers comprise tracheids, having a cylindrical shell surrounding a hollow lumen and closed ends. Only small bordered pit holes along a longitudinal line in the tracheids allow passage of liquids in and out of the fiber lumen. In softwoods the tracheids are 90+% of the wood volume and 94+% of the pulp mass, whereas hardwood fiber tracheid volume ranges from 40 to 70%, while the vessel elements occupy 10 to 40% of the wood.

The tracheids remain closed through all the present technology processing steps in the pulp and paper industry from digesting through washing, bleaching and drying. Only in mechanical refining of chemical pulp, for improving paper sheet formation and its strength characteristics, some fiber cell walls are opened, but due to concomitant cutting of the fibers refining is used only to a limited extent leaving most of the tracheids closed.

The closed tracheids create a number of problems to a broad range of the present-day pulp and paper industry processes. For pulp washing, only the free liquid outside between the fiber cells is washable to recover the dissolved organic matter and chemicals in the spent cooking liquor, or to remove the dissolved organic matter and spent bleaching chemicals from the pulp before the next bleaching or final drying stage. For pulp bleaching, all bound liquid inside the closed fiber lumen carries already dissolved organic matter and spent cooking or bleaching chemicals into the next stage. This carry-over consumes fresh bleaching chemicals leaving less for further bleaching reactions in the cell wall. Also, the closed cylindrical fiber wall allows the bleaching chemicals access to the desired organic matter, mainly lignin, and in specialty pulps also the hemicelluloses, in the cell wall only through the outside wall surface. The miniscule open area of the bordered pit holes does not allow practically any transfer of bleaching chemicals into the fiber lumen and simultaneously transfer of any dissolved organic matter out of the same holes.

All bound liquid inside the closed fiber lumen, after the unbleached pulp wash- er or after the last bleach plant washer, carries already dissolved organic matter, spent cooking liquor, or bleaching chemicals into the market pulp or paper mill pulp storage chest. There some of the bound liquid has time to leach out from the fiber lumen into the free wash liquid of the last washing stage surrounding the fibers. In case of market pulp drying the wet end filtrate from the sheet formation before the pulp dryer carries a large COD load, the leached amount, into the pulp mill effluent system. Any dissolved organic matter and chemicals that were not leached out of the fibers will be carried with the market pulp to the customers mill, where it eventually will add to that mill's COD load after repulpers and the refining action free most of the remaining carry-over to the mill's effluent system.

For recycled paper, there are a variety of undesirable materials bound inside the fibers, such as ink particles, paper filler materials, glue, dissolved organic matter, digesting and bleaching chemicals etc. All these undesirable materials are carried over in the bound liquid inside the fiber lumen to the final end products.

For drying, the closed fiber structure with lumen filled with liquid retards and increases the burden of removing the liquid from pulp or paper mechanically or by evaporation. This bound liquid is a major factor behind the massive press- ing and drying sections of the present-day paper and board machines, and the high energy consumption for obtaining the final dried product. SUMMARY OF THE INVENTION

The specific problems due to the closed lumen of the fibers as discussed in the previous chapters above are solved by the invention described and claimed in PCT/FI291 1 /051 123, which is incorporated by reference as part of the present specification. As noted above, the teaching of the reference is splitting of individual hollow fibers as they pass through a venturi tube, the pressure drop at the venturi throat causing longitudinal splitting of the fiber along the weakest line in the cylindrical fiber wall but keeping the fiber as one piece, i.e. not shredding or cutting it into smaller particles. The reference includes a number of embodiments, in which the splitting of fibers serves as a useful pretreatment for subsequent pulp processing steps such as washing, bleaching, drying, chemical reacting, deinking, cleaning and papermaking, all of which as applicable are incorporated by reference in the present specification.

A remaining problem, which applies to the venturi tube treatments of fibrous pulp, shredding or disintegrating of bundles of fibers into smaller fiber groups as described in US 5,785,810 as well as splitting of individual fibers according to the teachings of PCT/FI291 1 /051 123, is how to best precondition the pulp or fibers so as to achieve their pass through the venturi throat in a controlled manner. According to US 5,785,810 washed pulp is supplied as a mat on a conveyor belt and lifted with the aid of a doctor ^' s blade and gas blow to a housing, from where it is blown to the discharge passageway provided with the venturi throat. The matted pulp has an irregular constitution, which is not fully equalized by shredding at the venturi throat, and for the splitting of individual hollow fibers such known preparatory steps are wholly unsuitable and are not meant for such either.

The present invention solves the above problem by providing a method of pneumatic supply and discharge of liquid filled hollow pulp fibers, which is suitable for disintegrating bundles of fibers into individual fibers and also for splitting individual hollow fibers by opening their lumen in the longitudinal direction as the fibers are passed through a venturi tube. According to the invention the method comprises the steps of (i) supplying liquid filled hollow pulp fibers into a feed chamber through a feed chamber inlet by means of gas, (ii) packing the liquid filled hollow pulp fibers in the feed chamber by letting gas pass through a permeable wall of said feed chamber to a gas outlet, (iii) closing said gas outlet after said packing step, (iv) pressurizing the gas surrounding the liquid filled hollow pulp fibers in the feed chamber to substantially above atmospheric pressure, (v) discharging the liquid filled hollow pulp fibers and the surrounding pressurized gas from the feed chamber through an outlet, and (vi) passing the discharged liquid filled hollow pulp fibers through a venturi tube. In the invention wet fibrous pulp, in which the lumen of the individual hollow fibers is full of liquid, is preferably dispersed in a gas flow and carried by the same to the feed chamber, where the fibers, individually or as minor bundles, are deposited against a permeable wall, which retains the fibers but lets the gas flow through to the gas outlet. In this way controlled packing of the fibers is achieved, with gas surrounding the liquid-containing fibers. After the packing the pressure in the feed chamber is increased, and the packed fibers are then released for discharge through another outlet leading to the venturi throat, which according to the condition of the fibers either disintegrates bundles of fibers into smaller fiber groups or individual fibers or causes longitudinal splitting of individual fibers. To a degree both phenomena may occur simultaneously, and a number of venturi throats may be arranged in series to achieve stepwise disintegration of bundles into separate fibers and further splitting of the individual fibers.

According to an embodiment of the invention the liquid filled hollow pulp fibers and the surrounding gas discharged from the feed chamber enter a bypassing gas flow carrying said pulp fibers to said venturi tube. Preferably the bypassing gas flow, which may be e.g. air or steam vapor, is at a pressure substantially above atmospheric pressure but lower than the pressure in the feed chamber.

According to another embodiment of the invention the liquid filled hollow pulp fibers and the surrounding pressurized gas are discharged from the feed chamber through a first venturi tube into a lower pressure and are then passed through a second venturi tube into a yet lower pressure. The first venturi tube will cause a sudden velocity change in the flow of fiber bundles, resulting in separation of individual fibers from the fiber bundles. The second venturi tube is then adapted to split individual fibers in their longitudinal direction by opening their lumen along the weakest part of their fiber wall. Preferably a bypassing gas flow tube, for instance with air or steam vapor, is arranged to receive the fibers from the first venturi tube and carry them to the second venturi tube. If desired, the number of subsequent venturi tubes may be even larger. The pressure in the feed chamber may be maintained with compressed air, other gas or steam vapor during the discharge blow until the feed chamber is empty.

During the supply of pulp fibers to the feed chamber and deposition and pack- ing of the fibers against the feed chamber inner wall the gas passage through the permeable wall to the gas outlet may be sustained and enhanced by means of vacuum suction. The gas surrounding the liquid filled hollow pulp fibers in the feed chamber is preferably air.

According to a further embodiment of the invention the liquid filled hollow pulp fibers are supplied to the feed chamber at a consistency in the range of 15^15 %, preferably 20-35 %.

The gas surrounding the liquid filled hollow pulp fibers in the feed chamber typically is at a pressure in the range of 6-15 bar, preferably 8-12 bar. The pressure of the gas surrounding the liquid filled hollow pulp fibers in the bypassing gas flow may be at a pressure in the range of 5-14 bar, preferably 6-10 bar. The volume of the gas surrounding the liquid filled hollow pulp fibers in the feed chamber and/or said bypassing gas flow may be 5-15-fold, preferably 8- 12-fold, to the volume of the liquid filled hollow fibers.

According to a still further embodiment of the invention the liquid filled hollow pulp fibers and the surrounding gas is discharged out of the feed chamber by means of a pressurized steam vapor flow through the feed chamber.

The invention also provides an apparatus for pneumatic supply and discharge of liquid filled hollow pulp fibers, which is adaptable and useful for carrying out the method according to the invention as discussed above. The apparatus ac- cording to the invention comprises (i) a feed chamber, (ii) a feed chamber inlet for liquid filled hollow pulp fibers, (iii) at least one inlet for gas, to pack and pre- pressurize the liquid filled hollow pulp fibers in the feed chamber, (iv) a wall of said feed chamber permeable to a gas flow but impermeable to the liquid filled hollow pulp fibers in the feed chamber, (v) a gas outlet for gas flow passing said permeable wall of the feed chamber, and (vi) a fiber outlet for discharging the liquid filled hollow pulp fibers and the surrounding gas from the feed chamber to a lower pressure outside of the feed chamber. A specifically advantageous embodiment of the invention is formed by an apparatus, which comprises a number of parallel feed chambers connected to a common pressurized bypass flow channel. This will enable discharge of liquid filled hollow pulp fibers and surrounding gas from one feed chamber while an- other feed chamber is being supplied with liquid filled hollow pulp fibers and yet another feed chamber is pressurized with gas. The arrangement allows continuous discharge of fibers by alternating the feed chambers, one chamber being discharged while the others proceed through the preparatory stages. For effective disintegration of bundles of fibers at the first discharge stage and splitting of individual fibers at the second stage each feed chamber preferably has a first downstream venturi tube of its own, whereas the bypass flow channel issues into a second venturi tube, which is common to all of said parallel feed chambers.

Other useful embodiments of the apparatus according to the invention are found in the claims. Their function may be understood from the previous discussion on the corresponding method claims or from the following detailed description and drawings of preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an assembly diagram of the apparatus of the first embodiment of the present invention showing reference numbers for general description of the apparatus.

FIG. 2 is a cross-section A-A of FIG. 1 .

FIG. 3 is a cross-section B-B of FIG. 1 . FIG. 4 is an assembly diagram of the apparatus of the second embodiment of the present invention showing reference numbers for general description of the apparatus.

FIG. 5 is a cross-section A-A of FIG. 4. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It is believed that a clearer understanding of the present invention will be obtained by first describing briefly the main components of the apparatus of the first embodiment of the present invention, followed by a more detailed descrip- tion of the apparatus of the first embodiment of the present invention. After this, there will be a brief description of the overall operation of the first embodiment of the present invention. Then there will be descriptions of further embodiments.

(a) Main components of the apparatus of the first embodiment of the pre- sent invention

With reference to FIG. 1 , the apparatus of the first embodiment of the present invention comprises one or more cyclone chambers for receiving dewatered or wetted liquid filled hollow pulp fibers at a desired consistency, one or more rotary valves to ration out the pulp fibers from the cyclone chambers while main- taining a good air lock condition, one or more tubular elongate feed chambers or vessels ("feed tubes") to pre-pressurize the pulp fibers, an air blower system to enhance the flow and packing of pulp fibers into the feed tubes, a permeable false bottom in each feed tube to hold the pulp fibers above the discharge nozzle but to allow passage of air through to the suction side of the air blower system to assist supplying and packing of the pulp fibers into the feed tube with vertical air flow, a discharge valve and a first venturi tube section through which to discharge the fiber-air-gas mixture from the feed tubes, a pressurized flow chamber channel pipe assembly to receive the pre-pressurized pulp fibers during discharge from the feed tubes, a blow valve and a second venturi tube section and blow valve through which to discharge the fiber-air-gas-steam mixture from the pressurized flow chamber channel pipe assembly, means to pre- pressurize the feed tubes with steam vapor, compressed air or other gas, and means to pre-pressurize the pressurized flow chamber channel pipe assembly with compressed air, other gas or steam vapor, and means to maintain the de- sired pressure in both the feed tubes and the pressurized flow chamber channel with compressed air, other gas or steam vapor during the discharge blow of the pulp fiber-air-gas-steam mixture from the feed tubes. FIG. 1 shows three cyclone chambers and feed tubes, but one or any plurality of cyclone chambers and feed tubes can be used to process any desired amount of pulp fibers.

The individual cyclone chambers are fed on a continuous basis but the feed tubes are filled, pre-pressurized and discharged as a batch process.

The individual cyclone chambers can also be fed with more than one pulp grade to process simultaneously a desired mix of fibers.

(b) Detailed description of the apparatus of the first embodiment of the present invention The apparatus 10 of the first embodiment of the present invention is shown with reference to FIG. 1 . The apparatus 10 of the present invention comprises three elongate feed tubes 12, 14 and 16 being supplied with liquid filled hollow pulp fibers 18, which are rationed out with rotary valves 21 from cyclone chambers 22, 24 and 26. The rotary valves 21 maintain a good air lock condi- tion between the cyclone chambers and the feed tubes. All three feed tubes 12, 14 and 16 have an upper end 13 and lower end 15.

There are two nozzle connections at the upper end 13. Valve 28 controls the steam pressure in a header tube 29a and valve 30 the compressed air or other gas pressure in a header tube 31 a which are connected to each feed tube with individual shut-off valves 29 and 31 respectively. Air circulation nozzle through valve 32 enables scavenging of the fiber feed valve 40 at the top of the feed tubes from pulp fibers before its closure and also scavenging of steam vapors from the feed tube through valve 44 at the end of the fiber discharge phase of the operation. An air circulation header tube 33a is connected to each feed tube with individual shut-off valves 33.

The lower end 15 comprises a permeable wall formed by a false bottom 34 to hold the pulp fibers above an outlet comprising a discharge nozzle 36 but to allow passage of air from the feed tube through a gas outlet comprising a valve 38 to the suction side of an air blower 42 and out through valve 39 into the cy- clone chamber 22. The air blower 42 is used to assist supplying and packing of the pulp fibers into the feed tube with vertical air flow. Valve 44 at the end of a suction side header tube 46 to the air blower 42 is used to provide air through valve 32 for scavenging of steam vapors from the feed tube at the end of the fiber discharge phase of the operation as well as for scavenging the pulp fibers from the fiber feed valve 40 before its closure.

The apparatus 10 can be considered as having three main operating sections that cooperate with one another to accomplish the major functions of the pre- sent invention. First, there are the above described three cyclone chambers 22, 24 and 26, second, there are the three elongate feed tubes 12, 14 and 16, and third, there is a pressurized flow chamber channel 48. The pressurized flow chamber channel 48 has two main sections: (i) a pipe assembly 50 to receive the pulp fibers 18 alternatively through three first venturi tube sections 52 and respective valves 54 through the discharge nozzles 36 from the three elongate feed tubes 12, 14 and 16, and (ii) a second venturi tube section 56.

An inlet end 58 of the pipe assembly 50 is connected to a feed valve 60 for pressurizing the pressurized flow chamber 48 with compressed air, other gas or steam vapors. The discharge end 62 of the pipe assembly 50 is connected to a blow valve 64 to discharge the fiber-air-gas-steam mixture from the pressurized flow chamber 48 through the venturi tube section 56.

Depending on what kind of pulp fibers are being processed with the apparatus of the present invention, the processed split fiber pulp in a high density storage tank 72 will be diluted and pumped out either through line 78 to a rewasher, line 80 to screen room, line 82 to bleach plant, line 84 to refiners, or line 86 to a paper machine.

The apparatus 10 is supplied with liquid filled hollow pulp fibers typically at 20 to 35 percent consistency. In some instances there may be advantages to use lower feed consistencies, such as 15 to 20 percent or higher consistencies, such as 35 to 45 percent. Pulp fibers at the desired consistency from either a dewatering or wetting line are typically delivered with a pneumatic conveying system 88 through air blowers 90 into the cyclone chambers 22, 24 and 26.

(c) Brief description of the overall operation of the first embodiment of the present invention With the foregoing detailed description of the apparatus in mind, there will now be a brief description of the overall operation of the first embodiment of present invention. Initially, liquid filled hollow pulp fibers at the desired consistency, typically at 20 to 35 percent consistency, from either a dewatering or wetting line, are typically delivered with a pneumatic conveying system 88 through air blowers 90 into the cyclone chambers 22, 24 and 26. Rotary valves 21 ration the pulp fibers at desired rate through the open feed valves 40 into the feed tubes 12, 14 and 16. Valves 38 and 39 are open and valves 28, 29, 30, 31 , 32, 33, 44, 54, 60, and 64 are closed. Air blower 42 creates a down draft in the feed tubes to enhance the filling supply and packing of the pulp fibers.

Once a feed tube, say number 12, has the desired amount of pulp fibers as de- termined by an infrared light cell or other instrument, valve 39 is closed and valves 32, 44 and 33 (in tube 12) are opened to let air blower 42 deliver a scavenging air blow through feed valve 40 in the feed tube 12 to clear it from pulp fibers before closing. Then valves 33, 38, and 40 in feed tube 12 are closed and valve 39 opened. Now feed tube 12 is ready for pre-pressurizing to desired operating pressure. Valve 31 in the feed tube 12 is opened and the automatic, compressed air or other gas or steam vapor, control valve 30 brings the gas pressure in the feed tube 12 to pre-set level. Simultaneously opening the automatic steam control valve 60 at the inlet end 58 of the pipe assembly 50 brings the steam pressure in the pressurized flow chamber channel 48 to pre-set level somewhat lower than the pressure in the feed tube 12.

Now the feed tube 12 is ready for discharge. Valve 29 in the feed tube 12 is opened simultaneously with valve 54 and the blow valve 64. The automatic steam control valve 28 maintains the pressure in the feed tube 12 at pre-set level somewhat higher than the pressure in the pressurized flow chamber channel 48 during the duration of the discharge blow until the feed tube is empty of pulp fibers. Simultaneously the automatic steam control valve 60 maintains the pressure in the pressurized flow chamber channel 48 at pre-set level somewhat below the pressure in the feed tube 12. The first venturi tube section 52 causes a sudden velocity change in the flow of the fiber bundles from the feed tube 12 into the pressurized flow channel 48 resulting in individual fibers' separation from the fiber bundles, and thus enhancing the opening of the hollow lumen of the individual fibers in their passage through the second venturi tube section 56 at the end of the gaseous flow channel. When an infrared light cell or other instrument determines the feed tube 12 to be empty of pulp fibers, then valves 33 and 54 in the feed tube 12 simultaneously with the blow valve 64 will be closed. Valve 38 at the bottom of feed tube 12 and valve 44 are opened to release any remaining pressure from the feed tube 12 and opening of valves 33 and 40 will scavenge any steam vapors left in the feed tube. Opening of valve 39 and closing of valve 44 will allow feed tube 12 to be filled again with a new batch of pulp fibers from cyclone chamber 22.

All valve openings and closings are controlled automatically by a computer program which ensures that any plurality of feed tubes can be operated simultaneously to ensure practically a continuous supply and discharge flow of split liquid filled hollow fibers into the high density storage tank 72 through the apparatus of the present invention without any valves being out of sync.

The preferred range of the operating pressure in the pre-pressurized feed tube is typically 6 to 10 bars. In some instances there may be advantages to use lower pressures, such as 3 to 6 bars, or higher pressures, such as 10 to 15 bars. The pressure in the pressurized flow chamber is maintained at a somewhat lower pressure than the pressure in the pre-pressurized feed tube to control a desired pulp fiber flow rate through the first discharge venturi throat 52. (d) General description of the apparatus of the second embodiment of the present invention

The apparatus 10a of the second embodiment of the present invention is shown in FIG. 2. This second embodiment is substantially the same as the first embodiment, except that the rotary valves 21 under the cyclone chambers 22, 24 and 26 in the first embodiment are eliminated and the permeable false bottom 34 is replaced with one or more permeable tubular sections 35 in the feed tube(s) or vessel(s). The permeable tubular section 35 is enclosed within an outer cylindrical shell 35a and upper and lower ring-shaped end plates 35u and 35I, which together form an annular shape chamber 37. The suction side of air blower 42 is connected to each annular shape chamber 37 with a suction pipe 37a to assist supplying and packing of the pulp fibers into the feed tube with vertical air flow. Valves 37b in each suction pipe 37a are opened and closed in a consecutive order starting from the lower end 15 and progressing upwards as the vertical height of the pulp fiber column increases inside the feed tube(s) or vessel(s). The discharge nozzle 36 as shown in the first embodiment is replaced with a pipe elbow section 36a connecting to the lower end 15 of the feed tube(s) or vessel(s) with a pipe reducer 36b.

The prepressurizing of the feed tube(s) or vessel(s) can also be done in a dif- ferent manner than the one used in the first embodiment of FIG. 1 . Instead of feeding compressed air or other gas or steam vapor with valve 31 into the upper end 13 of the feed tube 12, valve 31 can be installed to feed the suction side header of the air blower 42 through valve(s) 42b while keeping valve 42a closed. (e) Brief description of the overall operation of the second embodiment of the present invention

The operation of this second embodiment is substantially the same as the first embodiment, except that the pneumatic conveying system 88 delivers the liquid filled hollow pulp fibers through air blowers 90 directly into the feed tubes 12, 14 and 16 through the open feed valves 40. Air blower 42 still creates a down draft in the feed tubes, but now through the permeable tubular sections 35 to enhance the supply and packing of the pulp fibers. Valves 37b in each suction pipe 37a are opened and closed in a consecutive order starting from the lower end 15 and progressing upwards as the vertical height of the pulp fi- ber column increases inside the feed tube(s) or vessel(s). This time no scavenging of the feed valves 40 is required.

The prepressurizing of the feed tube(s) can also be done in a different manner than the one used in the first embodiment of FIG. 1 . Instead of feeding compressed air or other gas or steam vapor with valve 31 into the upper end 13 of the feed tube 12, valve 31 can be installed to feed the suction side header of the air blower 42 through valve(s) 42b while keeping valve 42a closed.

When an infrared light cell or other instrument determines the feed tube 12 to be empty of pulp fibers, then valves 33 and 60 will be closed but valves 54 in the feed tube 12 and the blow valve 64 at the end of the pressurized flow channel 48 will be left open until the pressure in the feed tube 12 and in the pressurized flow chamber 48 has dropped down to atmospheric pressure.

It is to be recognized that the above embodiments of the method and apparatus according to the present invention are only given by way of example, and yet other possible methods, apparatuses, and modifications could be made without departing from the basic teachings of the present invention.

All benefits of the fiber spitting operation as described in connection with the inventor's previous invention in patent application PCT/FI291 1 /051 123, includ- ing method and apparatus for the splitting of cellulosic fibers, methods for the treatment of fibrous pulps for a papermaking process, and methods for paper drying and paper products with split fibers, apply also to the present invention.