EP2027337B1

EP2027337B1 - Device and method relating to fibre moulding

Info

Publication number: EP2027337B1
Application number: EP07716109A
Authority: EP
Inventors: Torbjörn Hansson; Björn Nilsson; Per Thomas Järnmark
Original assignee: SIG Technology AG
Current assignee: SIG Combibloc Services AG
Priority date: 2006-03-10
Filing date: 2007-03-09
Publication date: 2013-01-16
Anticipated expiration: 2027-03-09
Also published as: PL2027337T3; ES2403344T3; SE530340C8; EP2027337A4; SE530340C2; EP2027337A1; WO2007106026A1; ZA200808638B; SE0600542L

Description

FIELD OF THE INVENTION

The invention relates to the production of fibre products from stock and especially to three-dimensional objects such as claim shells, and other packaging products but also to objects such as drinking cups for beverages or trays, e.g. food trays; like it is known for example from WO 97/22755 .

BACKGROUND OF THE INVENTION

Flocculation is one of the essential phenomena in a moulded board process. It affects both the runability of the machine and the quality of the final product and the control of the formation, which is one of the most important goals of the process of manufacture. Flocculation is understood as gathering of fibres, fines and fillers present in a slurry into flocks. The phenomenon of flocculation can be divided into two separate phenomena, of which one is flocculation of mainly small particles, i.e. wood-based and mineral-based fines, chemicals, impurities such as resins, and occasional fibres are aggregated in smaller groups. Flocculation of small particles usually requires an auxiliary agent, such as a retention chemical, whose effect is based on electrostatic interactions. The second phenomena relates to aggregation of larger groups and is mainly a mechanical flocculation of fibres is based on the dimensions of the suspended fibres and on the consistency of the suspension. However, the second phenomenon is undesirable, i.e. the flocculation of larger groups; and it is often prevented by keeping the slurry at a constant flow.
The first phenomenon, on the contrary, is desirable. Flocculation of smaller particles affects the retention of smaller particles and, further, the quality factors of the process and the product dependent on said retention. Retention of smaller particles prevents clogging of the formation tools; it is also reduces these particles in the white water since they stuck to the fibre web. Further, the raw material is used more efficiently if more of it adheres to the fibre web. Further, smaller fines remaining in the white water increases growth of micro organisms, and having smaller particles flowing around in the system may lead to problems such as formation of slime, clogging, as well as impaired production and product qualities. The quality of recycled process water tends always to be gradually impaired at increased "closing" or re-use (degree of recycling) in the production facility due to such small residues describes above. In turn, this leads to a gradual quality impairing effect, both on the actual production process and on the product produced in the production facility. This is a central problem.
The invention concerns how to improve the first phenomena, flocculation of mainly small particles, described above.
Further, ozone has been used previously to kill microbiological cultures, to decompose pollutants comprising COD and BOD, to bleach substances in the end product.
US patent No. 4083749 discloses a method of making a sized paper where an aqueous pulp slurry containing a cationic neutral sizing agent or a wet sheet prepared therefrom is treated with an oxidizing agent, e.g. ozone.
FI 110683B discloses a method using ozone to kill micro-organisms in the internal process water in paper mill.
However, in the prior art, ozone gas has not been used as a retention additive or as a catalyst for other retention additives.
It is an object of the invention to provide a device and a method where the white water and/or the pulp slurry are subjected to ozone gas, where the ozone gas functions as a retention agent and as an catalyst for conventional retention agents rendering the flocculation more effective by improving flocculation primarily according to the first phenomenon. Accordingly the ozone gas simultaneous operates as a bleaching agent, and further lowering BOD and COD content as wells killing micro-organisms.

SUMMARY OF THE INVENTION

According to the invention a method according to claim 1 is provided. The production facility further comprises a drying section following the forming section and where condensed water from the drying process of the drying section is supplied to the white water tank.
Further retention agents are added to the pulp slurry in at least one of the following positions: 1) the stock preparation section 2) the forming tank.
According to an embodiment of the invention ozone gas is mixed-in in a position prior to the addition of the retention agents. According to a further embodiment of the invention ozone gas is mixed-in in a position following the addition of the retention agents and/or in conjunction with the retention agents.
According to a further embodiment of the invention sizing agents are added to the pulp slurry and the ozone gas is mixed-in in a position prior to the addition of the sizing agents.
Further, according to the invention a production facility according to claim 8 is provided.
According to further embodiments of the invention ozone gas adding means are additionally provided in at least one of the following positions 4) the stock preparation section 5) the forming tank.

DESCRIPTION OF THE DRAWINGS

The invention will be described in the following in closer details by means of various embodiments thereof with reference to the accompanying drawings wherein identical numeral references have been used in the various drawing figures to denote corresponding components.

Fig. 1: illustrates schematically the material and water flows in the production of moulded three-dimensional pulp objects, and
Fig. 2: shows an embodiment of the mixing-in of ozone gas in a tank containing fluid, and
Fig. 3a: shows a diagram over the substances in the white water where ozone gas and retention chemicals have been added to the pulp slurry prior to a forming step,
Fig. 3b: shows a diagram over the substances in the white water where ozone gas and retention chemicals have been added to the pulp slurry prior to a forming step.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates schematically the material and water flows in the production of moulded three-dimensional pulp objects. To the left in FIG. 1, a stock preparation section 1 is indicated where a pulp slurry is mixed from pulp and water in one ore more steps and where different chemical additives are added, the pulp slurry from the stock preparation section 1 is supplied to the formation section 3 producing a three dimensional moulded board product, which product is dried in the following drying section 4, where after the dried product may be subjected to after treatments.
In more detail, the stock preparation step 1, pulp 6 and water, supplied through the first white water line 8 from the white water tank 5, are mixed in the pulper 19 to form a pulp slurry, e.g. the pulp slurry having a pulp concentration of 4% by weight. Preferably the pulp is provided through pulp bales which are disintegrated and dissolved in water. The pulp used is preferably chemithermo-mechanical pulp (CTMP) but also other pulp that CTMP can be contemplated. CTMP is a preferred pulp in this context since it is relatively easy to dewater a pulp slurry based on CTMP. The mixed pulp slurry is subsequently passed to the storage tank 10 through a first supply line 9. Fresh water 7 may be used to clean the pulper 19 which thereafter is supplied to storage tank 10 diluting the pulp slurry further, e.g. to a pulp concentration of 3% by weight. In the storage tank 10, the pulp slurry can be kept in motion by a stirrer to avoid flocculation according to the second phenomena, i.e. the aggregation of larger groups. The pulp slurry is thereafter passed to the machine tank 14 of through the second supply line 12. White water through the second white water line 11 from the white water tank 5 is also supplied to the second supply line 12 to further dilute the pulp slurry, e.g. to a pulp concentration of 1,5% by weight. In the machine tank 14, the pulp slurry can be kept in motion by a stirrer to avoid flocculation according to the second phenomena. The pulp slurry is thereafter passed to the forming tank 16 of the forming section 2 through the third supply line 15. White water from through the third white water line 13 the white water tank 5 is also supplied to the third supply line 15 to further dilute the pulp slurry, e.g. to a pulp concentration of 0,5% by weight.
A first tool of the forming unit 20 is immersed in the pulp slurry in the forming tank 16 and an embryonic fibre product is formed on the first tool by applying suction through the first tool. The first tool is then removed from the stock and the first tool is brought against a second tool such that the formed fibre product is sandwiched between the first and the second tool. The formed fibre product is heated by the second tool such that at least a part of the water in the formed fibre product is vaporized, which vaporised water is evacuated through suction. This process can be repeated in several heating and pressing steps and when the fibre product has reached a desirable dry solid content, preferably of at least 70%, it may be subjected to final drying by microwaves in the drying section 4, by the microwave oven(s) 23. Prior to final drying by microwaves, the fibre product can be subjected to steam in order to achieve a more evenly distributed moisture content. The dried fibre product leaving the drying section could subsequently be ready to use or be subjected to after treatment such as e.g. laminating.
The water evacuated from the forming unit 20, by suction through the tools, is recycled to the white water tank 5 through the forth white water line 18. From the drying section condensed water can be recycled to the white water tank 5 through the fifth white water line 22.
In the white water tank 5, the white water can be kept in motion by a stirrer. If needed fresh water could be supplied to the white water tank 5. Further white water could also be evacuated from the white water tank 5 possibly to an external purification section.
Chemical additives such as sizing agents, wet strength agents, retention agents, colour chemicals, fixing agents could be added to the pulp slurry at any appropriate position from the pulper 19 to the forming tank 16, the pulper 19 and the forming tank 16 included.
According to the preferred embodiment of the invention the white water tank 5 is configured with an ozone gas adding and mixing equipment as shown in figure 2. Ozone decays rapidly, because ozone is an instable compound with a relatively short half-life. Ozone decays partly in reactive OH-radicals. Therefore, the assessment of an ozone process always involves the reactions of two species: ozone and OH-radicals. The ozone as well as the OH-radicals may react with substances in the water as well as the water it self. The white water is being "charged" and becomes chemically active. As the white water is supplied to the pulper 19, the second supply line 12 or the third supply line 15, the "charged" white water promotes the aggregation of the finer particles and enhances the effects of the retention agents by acting as a type of catalyst for polarization between, particles, substances and additives suspended in the water.
I.e. the ozone gas provides the advantages of 1) acting as an retention agent promoting the aggregation of finer substances to form small groups, whereby more substances are stuck in the fibre web which increases the yield of the input materials, reduces clogging of the forming tools, increases dewatering capacity which provides for higher production quality and/or reducing drying and dewatering energy consumption 2) enhancing the effects of other chemicals in particular conventional retention agents reducing the amount of needed retention chemicals. Further using ozone gas additional advantages are achieved: 3) micro organisms are killed which reduces foam, slime and other effects of micro organisms reducing water consumption and enabling the water system to be more closed 4) BOD and COD content are lowered which also reducing water consumption and enabling the water system to be more closed and if some of the water is outlet to a sewer less or no further purification is needed 5) impurities are bleached reducing discolouring of the products.
Preferably between ozone gas in the amount of 3-30 g/m³ white water is added to the white water tank 5, more preferably 4-20 g/m³. The amount of supplied ozone gas 31 is depending on factors such as, amount of substances in the fluid, desired bleaching effects, economical factors etc.
One embodiment example of the mixing-in of ozone is shown in FIG. 2. A fluid 33, e.g. fibre slurry or white water, is pumped into the tank 24. For instance the storage tank 10, the machine tank 14 and/or the white water tank 5 could be configured in a similar manner as tank 24. As shown in the figure the fluid 33 enters the tank 24 through an fluid inlet 26 at the top of the tank 24. The fluid 33 can be evacuated through the outlet 30 and the vault 28 at the bottom of the tank 24. Ozone gas 31 is injected, through the ozone injection nozzles 25, into the tank 24 in the form of small bubbles, in order thereby to increase the contact surfaces with the fluid 33 and therein contained particles and chemicals. The ozone gas 31 is preferably generated by an ozone generator. Preferably, a stirrer 27 is positioned inside the tank 24, in order to stir the fluid 33 to further increase the possibilities for the ozone gas bubbles 31 to react with the substances in the fluid 33, as well as to prevent the aggregations of larger groups, i.e. flocculation according to the second phenomenon. Appropriately, other stirring means for the fluid 33 can be used. The top of the tank 24 is provided with outlet pipes 29, 34 for evacuation of remaining ozone gas 31 that has passed the fluid 33 without having reacted. Also other gases could be evacuated through the outlets 29, 34. The remaining ozone gas 31 can either be led via pipe 29 to an ozone-destroyer, or it can be returned to the ozone generator via pipe 34, for re-use in order thereafter to be recycled to the tank 24.
It is preferred to provide a contact time between the ozone gas 31 and the fluid 33 which is as long as possible, enabling the ozone gas 31 to react with the fluid 33 and therein contained substances. The tank 24 facilitates this, but the ozone gas 31 could also by supplied in a pipe in where the ozone gas 31 is mixed with the flowing fluid 33, A combination of a tank 24 with a stirrer 27 and a pipe with a static mixer, is also possible. The flow through rate of the fluid in the tank 24 as well as through a static mixer affects the amount of ozone gas 31 needed in order to achieve the desirable reactions. A high flow through rate can be compensated by a higher concentration of ozone gas 31.
FIG. 3a and FIG 3b shows the effect on the substances in the white water using ozone gas and retention agents according to an experiment performed at a paper mill. The retention agents and the ozone gas where added to the pulp slurry in a step prior to the formation. In FIG. 3a retention agents where added between the times: t=3,3 and t=19,6; between t = 12,7 and t= 19,6 ozone gas was also mixed in. The time t in hours. As can be seen the retention agents alone provided for a reduction of substances of 0,9 g/L. The combination of ozone gas and retention agents provided for a further reduction of substances of 0,6 g/L. In FIG. 3b ozone gas was mixed in between the times: t=3,0 and t=17,5; between t = 11,7 and t= 17,5 retention agents where also added. The time t in hours. As can be seen the ozone gas alone provided for a reduction of substances of 0,4 g/L. The combination of ozone gas and retention agents provided for a further reduction of substances of 1,1 g/L. As is also evident from the figures is that there is a combination effect of the retention agents and the ozone gas, the combination effect approximately of 0,2 g/L. Thus during this experiment retention agents provided for ~60% of the reduction of substances, while ozone provided for ~27% and the combination for ~13%. In both experiments the temperature of the pulp slurry and the white water was ~45°C and PH -6, 5-7,0. The pulp slurry was supplied ozone gas in an amount of 5 g/m³ pulp slurry which corresponded to a -0,4-0,5 kg O₃ per tonnes of produced fibre product. The retention agent supplied was PAM+Bentonite. The amount of supplied Betonite was 7kg Betonite per tonnes of produced fibre product. The amount of supplied PAM was 0,5 kg Pam per tonnes of produced fibre product. In the experiments, when using ozone gas and retention agents in combination, the production rate was increased by 5%, but was prevented to increase further due to mechanical limits of the apparatuses. Instead the effect was used to increase the dewatering and the drying energy was reduced by 25-30%.
Whereas the invention has been shown and described in connection with the preferred embodiment thereof it will be understood that many modifications, substitutions, and additions may be made which are within the intended broad scope of the following claims. From the foregoing, it can be seen that the present invention accomplishes at least one of the stated objectives.
The mixing-in of ozone gas 31 can also be facilitated via a mixing-in pump such as a type of turbine pump, or by adding the ozone gas 31 into a pipe by aid of a so called ejector or by a dosing lance as well as other mixing means.
Further, ozone gas 31 could also be mixed-in at the first, second, third, forth and fifth white water lines 8, 11, 13, 18, 22 respectively, preferably by using a static mixer. Further, ozone gas 31 could also be mixed-in at the first, second and third supply line 9, 12, 15 respectively, preferably by using a static mixer. Further ozone gas 31 could also be mixed-in in the pulper 19, the storage tank 10 and/or the machine tank 14. The above mentioned ozone mixed-in positions could be used as stand alones or in combination with other oxone mixed.in positions.
Further, the ozone gas 31 may be added prior to the addition of sizing agents.
Of course other dryers than microwave dryers 23 could be used in the drying section 4.

Claims

A method for the production of three dimensional fibre based moulded board products, the products produced in a production facility comprising a stock preparation section (1) comprising a pulper (19) for preparing a pulp slurry, the pulper (19) connected to a forming section (3), the forming section (3) comprising a forming tank (16) and a forming unit (20), and a white water tank (5) recycling white water from the forming unit (20) to the stock preparation section (1), wherein a first tool of the forming unit (20) is being immersed in the pulp slurry in the forming tank (16) characterised in that a retention agent is being mixed-in, said retention agent being ozone gas (31), in order to render the flocculation more effective through increased aggregation of finer particles, in at least one of the following positions: 1) the white water tank (5) 2) between the white water tank (5) and stock preparation section (1) 3) the stock preparation section (1), 4) the forming tank (16) and 5) between the forming unit (20) and the white water tank (5).
Method according to claim 1 wherein the production facility further comprises a drying section (4) following the forming section (3) and where condensed water from the drying process of the drying section (4) is supplied to the white water tank (5).
Method according to any claim above wherein further retention agents are added to the pulp slurry in at least one of the following positions: 1) the stock preparation section (1) 2) the forming tank (16).
Method according to claim 3 wherein ozone gas is mixed-in in a position prior to the addition of the retention agents.
Method according to claim 3 or 4 wherein ozone gas is mixed-in in a position following the addition of the retention agents.
Method according to any of claim 3 to 5 wherein ozone gas is mixed-in in conjunction with the retention agents.
A method according to claim1 wherein sizing agents are added to the pulp slurry and where ozone gas is mixed-in in a position prior to the addition of the sizing agents.
A production facility comprising a stock preparation section (1) comprising a pulper (19) for preparing a pulp slurry, the pulper (19) connected to a forming section (3), the forming section (3) comprising a forming tank (16) and a forming unit (20), and a white water tank (5) arranged to recycle white water from the forming unit (20) to the stock preparation section (1) wherein a first tool of the forming unit (20) is immersed in the pulp slurry in the forming tank (16), characterized in that retention agent adding means are provided in at least one of the following positions: 1) the white water tank 2) between the white water tank (5) and stock preparation section (1) and 3) between the forming unit (20) and the white water tank (5), said retention agent being ozone gas.
A production facility according to claim 8 wherein ozone gas adding means are additionally provided in at least one of the following positions 4) the stock preparation section (1) 5) the forming tank (16).