SE540961C2

SE540961C2 - Method of providing a paper fibre composition by combining chemical and mechanical pulping

Info

Publication number: SE540961C2
Application number: SE1650710A
Authority: SE
Inventors: Claes Jonas Fredrik Johnsson; Erik Lennart Peter Nelsson; Eva Birgitta Svensson Rundlöf; Jan Christer Sandberg
Original assignee: Holmen Ab
Priority date: 2016-05-23
Filing date: 2016-05-23
Publication date: 2019-01-29
Also published as: CA3025476A1; EP3464712A1; WO2017204723A1; US20200318287A1; SE1650710A1

Abstract

The present invention relates to a method of production of a paper fibre composition, comprising the steps of:a) Providing a vessel,b) Providing NaSOin the range of 12-122 kg/bdt combined with NaOH in the range of 0-97 kg/bdt, or NaHSOin the range of 10-100 kg/bdt combined with NaOH in the range of 10-100 kg/bdt to said vessel,c) Providing wood, preferably softwood chips to said vessel for pre-treatment,d) Providing heat and pressure to said vessel in order be able control the vessel to have a temperature T comprised in the range of 160 °C - 184 °C,e) Controlling the retention time t for the wood chips, in relation to the temperature T of the content of the vessel, wherein T is controlled to be within the range of step d) and t is controlled to be in the range of 2-27 min, preferably in the range of 2-25 min, more preferred in the range of 5-20 min,f) Providing a defibration device coupled to the outlet of said vessel, the defibriation device being a refiner, mill, defibrator, fiberizer, or the like,g) Providing the pre-treated wood chips to the defibration device,h) Providing an energy consumption of 75-1000 kWh/bdt in said defibration device.The invention also relates to a paper fibre composition prepared by the method and a paper or paperboard or molded pulp made from the paper fibre composition.

Description

METHOD OF PROVIDING A PAPER FIBRE COMPOSITION BY COMBINING CHEMICAL AND MECHANICAL PULPING The present invention relates to a method according to claim 1, a paper fibre composition according to claim 4 and a paper or paperboard or molded pulp according to claim 5.

PRIOR ART It has been known for a long time how to make pulp and paper products by means of a combination of mechanical and chemical Oethods.

In general mechanical treatment of wood chips such as for example the well-known thermomechanical pulp (TMP) process gives a high yield pulp. Also in general an entirely chemical pulp such as the KRAFT process gives a pulp with considerably lower yield but a product with better strength properties, than a mechanical pulp in general.

In US2323194 it is disclosed a combination of chemical treatment and following mechanical treatment. However it has not been identified how to achieve a strong mechanically treated paper products that also renders a high yield, without processing the fibres mechanically so much that the energy consumption makes the product too expensive for the market.

SHORT DESCRIPTION OF THE INVENTION The objective of the present invention is to achieve a paper fibre composition that will give a strong paper product.

A further objective is to achieve a paper fibre composition that also gives a high yield that is in the range of 85-95%.

A further objective is to achieve a paper fibre composition that does not use excessive amounts of energy or chemicals.

A further objective is to achieve a paper fibre composition with high enough strength that can be used in products where normally only pure chemical pulps is considered.

At least one objective is achieved by a method of production of a paper fibre composition, comprising the steps of: a) Providing a vessel, b) Providing Na2SO3in the range of 50-90 kg/bdt combined with NaOH in the range of 0-97 kg/bdt, or NaHSO3in the range of 40-80 kg/bdt combined with NaOH in the range of 10-100 kg/bdt to said vessel, c) Providing wood, preferably softwood chips to said vessel for pre-treatment, d) Providing heat and pressure to said vessel in order be able control the vessel to have a temperature T comprised in the range of 175 °C - 184 °C, e) Controlling the retention time t for the wood chips, in relation to the temperature T of the content of the vessel, wherein T is controlled to be within the range of step d) and t is controlled to be in the range of 5-9 min; f) Providing a defibration device coupled to the outlet of said vessel, the defibration device being a refiner, mill, defibrator, fiberizer, or the like, g) Providing the pre-treated wood chips to the defibration device, h) Providing an energy consumption of 75-1000 kWh/bdt in said defibration device.

The above method is mechanical pulping process that yields stronger pulp compared to particular energy input for TMP or CTMP, and for particular chemical dosage in CMP or NSSC processes. Among other things it gives higher tensile and burst, and compression strength index.

These amounts give the advantages of keeping the amounts of chemicals low, which is desired for both environmental reasons, as cost reasons.

These amounts have been found particularly advantageous in terms of the desired objects.

In a further aspect of the invention the method according to the above paper test sheets made from the paper fibre composition gives a Tensile index of 18-150 Nm/g, preferably of 25-150 Nm/g, even more preferred of 40-150 Nm/g.

For values of Tensile index above 60-65 Nm/g it should be understood that these values are in general only achieved when measuring on a pure chemical pulp, thus the present invention has the effect that a much higher yield can be achieve without sacrificing strength properties. The reason for this is the much lower yield that pure chemical pulps result in.

According to a further aspect it is suggested a method according to the above wherein the temperature t is comprised in the range 175-184°C.

This range of temperature is preferred as it makes it possible to reduce the chemicals needed and also the preheating time t, and still achieving a final product with even better strength properties. A higher temperature requires a shorter preheating time t.

According to a further aspect it is suggested a method according to the above wherein there is a further step provided i) a further treatment step where further refining is added, in the range of 1-2500 kWh/bdt, to said paper fibre composition.

According to a further aspect a paper fibre composition made according to the method above is suggested.

According to a further aspect there is suggested a paper or paperboard or a molded pulp, comprising a paper fibre composition according to the above.

Paper or paperboard or molded pulp according to the above, wherein the paper fibre composition is directly used in said paper or paperboard or molded pulp.

Paper or paperboard or molded pulp according to the above, wherein the Paper or paperboard or molded pulp comprises the paper fibre composition, but that the paper fibre composition is exposed to further treatment in order to change the properties, wherein said further treatment comprises further mechanical treatment, such that the paper fibre composition has a Tensile index that is higher than 50 Nm/g but lower than 150 Nm/g LIST OF DRAWINGS Figure 1 discloses the process equipment of the invention.

DETAILED DESCRIPTION The present disclosure relates to a process as seen in figure 1. A vessel 1 is provided that is coupled to a fibre defibration device 2. There is an inlet 3 for wood chips and an outlet 4 leading to the defibration device 2. From the defibration device there is an outlet 6.

The vessel 1 is a pressure vessel that is able to sustain pressures where a water suspension can reach temperatures of at least for the ranges that are discussed below that is at least 184 °C, but preferably 190 °C or more such as 200 °C. The inlet 3 is of a suitable dimension for allowing wood chips to enter the vessel 1.

The defibration device 2 can be constituted of a refiner, fiberizer, defibrator, mill or the like. A preferred device is a refiner.

The present disclosure relates to a method for achieving a superior fibre composition that when applied in a product such as Paper or paperboard or molded pulp gives a comparably strong product as to what is previously known for a mechanical or chemithermomechanical processes.

Fibre composition means in general a pulp of fibres that originates from a fibre source. For the present disclosure the preferred fibre source is softwood, in general a larger share of spruce is preferred, if not being the only component. However it is possible to use pine and spruce in mixtures. Also a little amount of hardwood can be used for the present disclosure but the major part of the fibre composition is always has a softwood source. It should be understood that the present disclosure does not relate to a fibre composition made solely from hardwood or in amounts of hardwood that exceeds the content of softwood.

The present disclosure relates to a method with steps a -h).

Step a) a) Providing a vessel, The vessel 1 must be is a pressure vessel. This means that the vessel needs to be able to sustain pressures where a water suspension can reach temperatures of at least 184 °C or more as discussed above. The vessel can be constituted in different ways. A vessel arranged for batch wise operation is of course possible also. That is a vessel that is loaded, closed and then opened and the content is passed on to the next step. However for the present disclosure a vessel that is part of a continuous process is the preferred. Thus the vessel 1 can be equipped with valves at the inlet 3 and the outlet 4 that can control the flow through the vessel 1. It is of course known to the person skilled in the art how to achieve this, for example also incorporating a rotary feeder (valve) or a plug screw at the inlet. At the outlet 4 it is possible to implement a feeding screw. The outlet 6 of the defibration device 2 can have a blow line valve. Pressure is controlled by the heat that can be supplied through a separate inlet 5, by steam etc. in a known manner for the person skilled in the art. The main inlet 3 is of a suitable dimension for allowing wood chips to enter the vessel 1 at a sufficient rate. However the precise configuration is known to the person skilled in the art and the given features of the inlet 3, outlet 4, and outlet 6 are only given as way of example.

Step b): b) Providing Na2SO3in the range of 50-90 kg/bdt combined with NaOH in the range of 0-97 kg/bdt, or NaHSO3in the range of 40-80 kg/bdt combined with NaOH in the range of 10-100 kg/bdt to said vessel, There are different ways to add sulphite (SO3<2>) and hydroxide (OH ) ions to wood, e.g. NaHSO3 together with NaOH or Na2SO3together with a smaller amount of NaOH. Thus NaHSO3when mixed with NaOH forms Na2SO3, but the result remains the same. The important here is the active substance that is the SO3<2">ion in combination with the OH<">ion. The amounts of Na2SO3or NaHSO3and NaOH in step b) in amounts of 50-90 or 40-80 kg/bdt are carefully chosen, in order to not add excessive amounts of chemicals to a high cost, or too little which will not achieve the desired pulp properties, "kg/bdt" means kilo grams of chemical substance per bone dry ton, i.e. dry amount of chemicals per dry fibre mass. The lower limit of the Na2SO3can be altered to 50, 55, 60, 65, 70, 75, 80, 85, 90kg/bdt, the corresponding upper limit can likewise be altered to 50, 55, 60, 65, 70, 75, 80, 85, 90, kg/bdt. The NaOH combined with Na2SO3can have a lower limit altered to, 5,10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, 95 kg/bdt and an upper limit altered to 5,10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 6570, 75, 80, 85, 90, 95 kg/bdt. The NaHSO3can have a lower limit altered to 40, 45, 50, 55, 60, 65, 70, 80, kg/bdt and an upper limit altered to 40, 45, 50, 55, 60, 65, 70, 80, kg/bdt. The NaOH combined with Na2SO3can have a lower limit altered to 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 85, 90, 95, 100 kg/bdt and an upper limit altered to 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 85, 90, 95, 100 kg/bdt Step c) c) Providing wood, preferably softwood, chips to said vessel for pre-treatment, It should be understood that the chips is in general not needed to be added in the order of after the chemicals. The chips can be added before or at the same time as the chemicals of step b). The chemicals can also be added to the chips prior to the chip entering the vessel of step a). Thus the order of addition between chemicals and chips is not essential for the present disclosure. Chips are in general of the ordinary size known for the person skilled in the art. The chips may have been pretreated with steam before entering the vessel.

Step d) d) Providing heat and pressure to said vessel in order be able control the vessel to have a temperature T comprised in the range of 175 °C - 184 °C, This given temperature range is not well explored for mechanical pulps. By controlling the temperature to be within this range, the objective of the invention can be achieved. It should be understood that the temperature is essentially kept the same in the vessel 1 and the defibration device 2.

The upper limit of the range of T could be 183 °C, 182 °C, 181 °C, 180 °C, 179 °C, 178 °C, 177 C°, 176 °C, 175 °C, Step e) e) Controlling the retention time t for the wood chips, in relation to the temperature T of the content of the vessel, wherein T is controlled to be within the range of step d) and t is controlled to be in the range of 5-9 min, The retention time is crucial to achieve the desired objective of the invention. In the narrow range of 5-9 min there objective of the invention is reached. In order to keep the yield high the retention time t cannot be extended outside the given range. The control of the retention time is easily achieved by for example controlling the flow through the vessel 1.

The lower limit of the retention time t can be altered to 5, 6, 7, 8, 9 min. The upper limit of the retention time t can be altered to 5, 6, 7, 8, 9 min.

Step f) f) Providing a defibration device coupled to the outlet of said vessel, the defibration device being a refiner, mill, defibrator, fiberizer, or the like, The core of the invention is to be able to achieve a strong paper product that can compete with lower yield chemical pulps in terms of their strength properties. Therefore the chips after treatment with chemicals and heat are defibrated and refined mechanically. The yield is kept high as most of the lignin content of the original material is not dissolved entirely. A refiner is preferred, however the means for achieving the mechanical treatment can be other means and it is desired to keep the temperature, i.e. pressure within the range of step 175-184°C.

Step g) g) Providing the pre-treated wood chips to the defibration device, Step h) h) Providing an energy consumption of 75-1000 kWh/bdt in said defibration device.

The energy consumption can have a lower range value of 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 525, 550, 575, 600, 625, 650, 675, 700, 725, 750 kWh/bdt.

The energy consumption can have a high range value of 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 525, 550, 575, 600, 625, 650, 675, 700, 725, 750, 775, 800, 825, 850, 875, 900, 925, 950, 975 kWh/bdt In order to not reduce the average fibre length of the pulp too much it is preferable not to exceed the 1000 kWh/bdt. It is also not desired use an energy lower than 75 kWh/bdt as this would not achieve the desired level of defibering.

The order of the steps is of course not crucial, for example the administration of chemicals step b) can be made together with the wood chips step c) or the chips can be added before the chemicals.

It should be understood that the pressure is essentially kept the same in the vessel and the defibration device.

In order to achieve the appropriate product it is possible to measure the paper fibre composition properties by making paper test sheets. These sheets should provide a tensile index of 18-150 Nm/g but preferably 25 or 40- 150 Nm/g which indicates really good strength properties.

This combination of ranges results in desired properties of the paper fibre composition according to the invention. It should be understood that within the specified ranges a lower retention time t requires a higher temperature T in order to achieve the product. We refer to examples below for further understanding.

It is possible to narrow the temperature range to 175-184 °C, to find a well-functioning range for the temperature to be used in the vessel 1 and the defibration device 2.

If a particularly favourable paper product is desired it is possible to at least on further treatment step This further treatment step further adds refining in the range of 1-2500 kWh/bdt, to said paper fibre composition.

By adding step i) a final product with excellent strength properties is achieved.

The added energy consumption in the refining can have the following lower limit 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 2050, 2100, 2150, 2200, 2250, 2300, 2350, 2400, 2450 kwh/bdt.

The added energy consumption in the refining can have the following higher limit 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 2050, 2100, 2150, 2200, 2250, 2300, 2350, 2400, 2450 kwh/bdt.

EXEMPLES The following recipes are part of the invention Softwood being the main part of the treated fibre source: Method: Chips were preheated with steam to 90 °C and was fed continuously through a plug-screw feeder into an impregnator located inside the pressurized reaction vessel. An impregnation solution was simultaneously added to the impregnator containing water sodium bisulfite and sodium hydroxide. The retention time in the reaction vessel was controlled by the level of chips and the temperature was controlled by addition of 12 bar steam. After retention in the reaction vessel, chips were directly fed to the refiner where chips were defibrated with varying specific energies. Pulps were collected from the blow line of the refiner.

EXAMPLE 1 not part of invention kg/bdt NaHSO3; 30 kg/bdt NaOH; t = 10 min; T = 180 °C; Fibre source, Picea abies The defibration device used was a OVP 20" Sunds defibrator The energy input was 260 kWh/bdt Tensile index was measured by: IS05269-2 (Rapid Köthen handsheets), IS01924-2 (Tensile index measurement) Tensile index was measured to be 37.4 Nm/g PQM Fibre length: 2.44 mm Example 1 was repeated with the method, same equipment and fibre source in the following examples 2-7.

EXAMPLE 2 not part of the invention 80 kg/bdt NaHSO3; 56 kg/bdt NaOH; t = 20 min; T = 160 °C; Tensile index: 34.7 Nm/g PQM Fibre length: 2.42 mm Energy: 123 kWh/bdt EXAMPLE 3 not part of the invention 50 kg/bdt NaHSO3; 35 kg/bdt NaOH; t = 20 min; T = 160°C; Tensile index: 34.6 Nm/g PQM Fibre length: 2.43 mm Energy: 255 kWh/bdt EXAMPLE 4 50 kg/bdt NaHSO3; 35 kg/bdt NaOH; t = 10 min; T = 180 °C Tensile index: 28.2 Nm/g PQM Fibre length: 2.36 mm Energy: 169 kWh/bdt EXAMPLE 5 not part of the invention 80 kg/bdt NaHSO3; 28 kg/bdt NaOH; t= 20 min; T = 160 °C Tensile index: 36.8 Nm/g PQM Fibre length: 2.29 mm EXAMPLE 6 not part of the invention 40 kg/bdt NaHSO3; 28 kg/bdt NaOH; t= 20 min; T = 160 °C Tensile index: 39.8 Nm/g PQM Fibre length: 2.22 mm Energy: 647 kWh/bdt EXAMPLE 7 50 kg/bdt NaHSO3; 35 kg/bdt NaOH; t = 5 min; T = 180 °C Tensile index: 33.9 Nm/g PQM Fibre length: 2.22 mm Energy: 396 kWh/bdt From the examples 1- 7 it must be understood that a prior art thermomechanical pulp has a much shorter fibre length in the order of 1,4 mm at a corresponding Tensile index as in examples 1-7 above.

Claims

1. Method of production of a paper fibre composition, comprising the steps of: a) Providing a vessel (1), b) Providing Na2SO3combined with NaOH, or NaHSO3combined with NaOH to said vessel (1), c) Providing wood, preferably softwood chips to said vessel (1) for pre-treatment, d) Providing heat and pressure to said vessel (1) in order be able control the vessel (1) to have a temperature T comprised in the range of 175 °C - 184 °C, e) Controlling the retention time t for the wood chips, in relation to the temperature T of the content of the vessel (1), wherein T is controlled to be within the range of step d) and t is controlled to be in a predetermined range: f) Providing a defibration device (2) coupled to the outlet of said vessel (1), the defibration device (2) being a refiner, mill, defibrator, fiberizer, or the like, g) Providing the pre-treated wood chips to the defibration device (2), h) Providing an energy consumption of 75-1000 kWh/bdt in said defibration device (2), characterized by that the Na2SO3is provided in the range of 50-90 kg/bdt combined with NaOH in the range of 0-97 kg/bdt, or NaHSO3is provided in the range of 40-80 kg/bdt combined with NaOH in the range of 15-80 kg/bdt to said vessel (1), wherein t is controlled to be in the range of 5-9 min.

2. Method according to any of the claims above, wherein paper test sheets made from the paper fibre composition gives a Tensile index of 18-150 Nm/g, preferably of 25-150 Nm/g, even more preferred of 40-150 Nm/g.

3. Method according to any of the claim above wherein there is a further step provided i) a further treatment step where further defibration is added, in the range of 1-2500 kWh/bdt, to said paper fibre composition.

4. Paper fibre composition made according to the method according to any of the claims 1-3.

5. Paper or paperboard or molded pulp, comprising a paper fibre composition according to claim 4.

6. Paper or paperboard or molded pulp according to claim 5, wherein the paper fibre composition is directly used in said paper or paperboard or molded pulp.

7. Paper or paperboard or molded pulp according to claim 5 or 6, wherein the Paper or paperboard or molded pulp comprises the paper fibre composition according to claim 4, but that the paper fibre composition has been exposed to further treatment in order to change the properties, wherein said further treatment comprises further mechanical treatment, such that the paper fibre composition is provided with a Tensile index that is higher than 50 Nm/g but lower than 150 Nm/g.