CA1320067C

CA1320067C - Method of making mechanical and chemi-mechanical papermaking pulp

Info

Publication number: CA1320067C
Application number: CA000598482A
Authority: CA
Inventors: Rune Lennart Pettersson; Borje Nils Svensson; Myat Thoung Htun; Lars-Ake Hammar; Per Ossian Engstrand
Original assignee: STFI Skogsindustrins Tekniska Forskningsinstitut AB
Current assignee: Valmet AB
Priority date: 1988-05-06
Filing date: 1989-05-02
Publication date: 1993-07-13
Anticipated expiration: 2010-07-13
Also published as: FI91787C; SE8801731L; WO1989010998A1; DE68909231D1; JPH03504256A; SE461103B; EP0413736B1; FI91787B; EP0413736A1; SE8801731D0; DE68909231T2; FI905482A0

Abstract

ABSTRACT

The invention relates to a method of manufacturing mechanical and chemi-mechanical papermaking pulp by disintegrating and beating wood material in at least two steps. The material is coarse-disintegrated in a first step at a concentration exceeding 20%, acid groups in the wood material are neutralized, the mater-ial is diluted to a concentration of 1-10% and beaten in one or several steps. Under these conditions the total energy consump-tion is substantially reduced without reducing the yield and deteriorating the properties of the pulp.

Description

1 3200~7 Method of making m ^.~r=~ n~ ^nemi-mechanical papermak-ing pulp This invention relates to a method of making mechanical and chemi-mechanical papermaking pulp by disintegrating and beating wood material in at least two steps.
One object of the invention is to carry out the disinte-gration and beating in such a manner, that the total energy consumption is substantially reduced, as will be be described in the following.
The beating of cellulose-containing material at low pulp concentration is a method, which has been employed since long in order to improve the paperforming propert-ies of the fibres. This applies, however, only to fibres free of lignin or substantially free of lignin, such as fibres pr-oduced according to the sulphate or sulphite methodO As regards pulps ~anufactured mechanically, such as thermomechanical pulp (TJ~IP) or chemi-mechanical pulp (CTMP), beating at low concentration, so-called post--reflning, was not considered applicable other than as a method f~r increasing the light-scattering capacity of the pulps and for reducing slightly the fibre length and thereby improving the formation at the making of paper.
Investigations have been carried out previously to re-beat at lower concentrations a TiilP manufactured at high concen-tration. In Scan Forsk Rapport 409/1984, for example, works are reported concerning energy consumption at re--beating at low concentration compared~with refining at high concentration. The results from this investigation show that the freeness of TMP can be lowered by 10-30 ml without essentially deteriorating the strength properties, and that an energy saving of 50-150 kWh/ton could be achieved. The total energy consumption, however, was , considerable and of the magnitude 1600 to 2300 kWh/ton.
In Pulp and Paper Magazine of Canada, Vol. 81~ No 6, June 19~0, page 72-80 (N.Hartler) experiments are reported to reduce the energy consumption at the refining of chips.
One proposal made here is to change the chemical environ-ment by the addition of chemicals. By adding sodium hydrox-ide the energy consumption could be reduced by 30%, but the total consumption yet amounts to about 1300 kWh/ton~
At these experiments, however, the yield was deteriorated slightly and the ISO-brightness considerably.
In Svensk Papperstidning, 1982, page R 132-139 (P.Axelson and R.Simonson) the effect of sulphite impregnation of the chips on the refining process, a.o. the energy consumption, is discussed. At a certain amount of sulphite taken-up, the energy consumption diagram showed a minimum. Totally, how-ever, the energy consumption was on a high level of 2000 kWh/ton.
Experiments have been carried out previously to treat thermomechanical pulp with fibre-modifying che~icals. It was then found~ that by treating the defibered pulp with ozone prior to the refining in a two-step process the energy consumption could be lowered by up to 30%. This~ however, could be achieved only at the expense of the yield.
According to the present invention it has proved possible to manufacture mechanical papermaking pulp by a substanti-ally reduced energy consumption.
This is achieved according to the invention, in that the wood material in a first step is coarse-disintegrated at a concentration of above 20%. The energy input here shall be at maximum 8oo kWh/ton wood material. The acid groups lncluded in the wood material thereafter shall be neutral-ized entirely or partially, and the material be diluted with water of a temperature corresponding to the softening temperature of the lignin. The dilution water shall have an :~

`-`` 1 320067 -3- 20368-5~9 ion s~rength of at maximum 0.05 mole per l:Ltre. The coarse-disintegrated material then shall be beaten a~ a concentration of 1-10% with an energy inpuk of totally a maximum of 500 kWh~ton material.
Thus, according to one aspect, the invention provides a method of manufacturing mechanical and chemi-mechanical papermaking pulp with low energy input, by disintegrating ancl beating wood material in at least two steps, wherein in the first step the material is coarse-disintegrated at a concentration above about 20~ with an energy input of at maximum about 800 k~h~ton wood material, acid groups in the wood material are neutralized entirely or partially by the addition of NaOH in an amount of at maximum about 9 kg/ton, the material is diluted to a concentration of about 1 to 10% by water witll a temperature corresponcling to the softening temperature of the lignin and with an ion strength of at maximum about 0.05 mole per litre, and then the mate.rial is beaten in one or several further steps with a total energy input at the beating steps of at maximum about 500 kWhiton material.
.20 The present invention is based on the idea that there is a relation between the disintegration of the wood material to fibres and the way, in which the energy pulses are transferrecl to the material, i.e~ whether the energy pulses are transferred in liquid phase or steam phase. Attention also is to be paid to the ~hermal and physical state of;.the wood material when the energy ~ pulses are being transferred.
: ~ One has not been successful previously by beating at low ~ concentration to defibre the wood package in order to reduce the ~.~
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' -3a- 20368-559 erlergy consumption at the manufactl.lre of mechanical pulps. The reason is, -that one did not know how to avoid the clipping of the fibres and thereby ~he much too low tensile and tear index of the resulting mechanical pulp and at the same ~ime to bring about improved binding properties of the pulp.
In order to achieve this, it is i.mpor~ant to accurately control the temperature and chemical environment of the fibre suspension in connection with the beating.
~ or obtaining a low ~otal energy consump~ion, the energy input in the first coarse-defiberiny step must be low. The first high concentration step can be at atmospheric pressure o:r pressurized and be carriecl out by tearing (shredding), chip pressing, plug screwing ~type Impressa-finer or PREX) or by defibering in a refiner.
The final beating then takes place in one or several steps at low pulp concentration, i.e. at a cOnceDtration of 1-10%.
At this beating must be observed~ that the specific edge load is suffi~ciently low, and tha~ the temperature and chemicàl envlronment of the fibre suspension has been ' :

adjusted to the softening and swelling state of the wood polymers This implies according to the invention, that the temperature at the beating shall be at least as high as the softening temperature of the sti~est amorphous wood polymer, that the acid groups of the wood polymers substantially are ionized, and that the ion strength of the process water is sufficiently low.
The invention is described in the follo~ing in greater detail by way of some embodiments and with reference to to the accompanying drawings~ in which Fig. 1 is a flow sheet of an embodiment of the method according to the invention, Figs. 2-4 are diagrams of properties ana energy consumpt-ion of a pulp manufactured according to Fig. 1, Fig. 5 is a flow sheet of a second embodiment of the invention, and Figs. 6-8 show properties and energy consumption a~ the method according to said second embodiment The flow sheet according to Fig. 1 illustrates the manuf-acture of thermomechanical pulp for newsprint.
Chips from spruce were steamed in a first step and preheat-ed. The preheated chips then were disintegrated in a pressurized refiner with an energy consumption of 700 kWh/ton. At this coarse-defibering 3 kg NaOH were added in the beating zone of the refiner for neutralizing acid groups included in the wood material. To the defibered material dilution water with a temperature of 80 C and an ion strength of 2.0~mmole/1 was added in order to obtain a pulp concentration of 3%
At this concentration the pulp then was beaten in five subsequent steps at a speci~ic edge load of 0.3-0.5 ws/m ~
and a total net energy consumption of 150 kh'h/ton pulp , . , ' : 1 320~67 corresponding to a gross energy consumption of 250 kWh/
ton pulp to a freeness of 150 ml CSF and a mean fibre length (PML) of 1.8 mm, i.e about equal to TMP-pulp manufactured in conventional manner with an energy con-sumption of 1750 kWh/ton pulp.
The total energy consumption at the method according to the invention, thus, was reduced from 1750 to 950 kWh/
ton pulp.
The yield amounted to about 97%
A comparison between the properties for a TMP-pulp manu-factured conventionally and one manufactured according to the invention appears from Table 1.
In this connection should be mentioned, that as convention-al TMP-process the refining system was used, which up till now was known as the least energy requiring one, i.e. a pressurized twin-disc refiner:combined with short dwell time at the pressurized preheating.
When bwo-step processes with single-disc refining are used, in most cases more than 2000 kWh/ton are required for obtalning a pulp with 150 m/CSF.
T A B L E
T M P
: conventional Invention Energy consumption,kWh/ton 1750 950 Freeness, ml CSF : 150 150 PML x), mm : : 1.:9 1.9 Shives ccntent,Sommerville % 1.3 : 0 5 Tensile index, kNm/kg . :32.0 -32 0 Tensile stiffness index 3.4 3.4 Stretch at bre~k,~ : 2.0 1 g Tear:index, N~ /kg 6.5 5 5 Dens~ty, kg/m : : 380 380 S, m /kg : : : :58.o 58.0 :ISO-brightness, %~ 0 60 :
) PML = mean particle length measured according to : SI~I pulp measurine~system:

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The manufacture of TMP according to the invention is com-pared in Fig. 2~ 3 and 4 with TM~ manufactured convention-ally with single-step refining in twin-disc refiner, which is the least energy consuming TMP-process existing with the present state of art.
Fig. 2 shows the tensil~ index as a function of the electric energy consumption. It appears clearly from the Figure, that the increase in tensile index at a certain electric energy consumption is considerably greater for TMP manufactured according to the invention.
Fig, 3 shows the tear index as a function of the tensile index for TMP according to the invention and conventional TMP. It appears that the development of the tear index for the respeetive TMP is about the same, i.e. at optim-ation of the low concentration beating according to the invention the fibre cutting and thereby the serious de-crease in tear index are substantially entirely avoided, which cutting and decrease occur usually at conventional low concentration beating of mechanical pulps.
Fig. 4 shows how the light-scattering coefficient (s) deveIops at conventional TMP and TMP manufactured accord-ing to the invention It appears that the s-development requires as low an electric energy input as the tensile index development, l.e. the saving of electric energy to a certain s-value is of equal size as the saving of el-ectric energy to a certain tensile index value.

This example relates to the manu~acture of chemi-mechanic-al pulp (CTMP or CMP) according to the flow sheet shown in Fig. 5.
The treatment with impregnation chemicals, which can be sulphitesg peroxide7 oxygen gas3 ozone and/or liquor, , can take place prior to the first defibering step, after this step but prior to the final beating~ after the final beating, or at combinations of these. In the flow sheet shown the impregnation is carried out prior to the first defibering step.
The first defibering step at high concentration is carried out in the same way as in Example 1.
At the manufacture of chemi-mechanical pulp the washing step is very essential~ so that according to the invention the beating shall take place at low ion strength The washing, therefore, is carried out prior to the final beating. In cases when the chemical kreatment is carried out as the last process step, washing kakes place even after this step.
The final beating takes place in the same way as according to Example 1~ but process temperature and chemical environ-ment must be adjusted to the special properties, which the wood polymers have assumed by treatment with impregnation chemicals, It is essential to pay regard to the number of sulphonic acid groups, which have been introduced by possible sulphite treatment As an increasing amount of sulphonic acid~groups reduces the softening temperature of the lignin, the temperature of the process water can be lower than at the manufacture of TMP-pulp according to Example 1. A sufficiently high temperature at the manufacture of CTMP is ~QC. From a brightness point of view it is advantageous to use the lowest possible temp-erature.~ By sodium sulphite treatment both the sulphonic , acid:groups and the carboxylic acid groups ate ionized :: from the beginnlng.
W~en at;the manufacture of~CTMP it i5 chosen to modify ~: the~wood wlth peroxide, oxygen~.or oz.one, certainly no ~: sulphonic acid~groups are obtàined, but the contenk of ~: khe wc,od material, especially of the lignin, of carboxylic .

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~, acid groups increases considerably~ which implies lower-ing of the softening temperature of the lignin.
In the eaxmple according to Fig. 5 chips from spruce were steamed and impregnated with a sodium sulphite solution-in an amount corresponding to a 2~ charge, whereafter they were preheated at a temperature of 130C
for 3 minutes. The material was then coarse-disintegrated with an energy consumption of about 600 kWh/ton in a pressurized chip refiner at high concentration (about 35%). The resulting yield amounted to about 96%.
The coarse-defibered material obtained was diluted to about 3~ and latency treated at 80C for 20-30 minutes.
The pulp was pressed to a concentration of ~5-50% and again diluted to 3~ at a temperature of 70C. At this concentration the pulp then was beaten with a specific edge load of 0.3-0.5 Ws~m in five subsequent steps with a net energy consumption of 150 kWh/ton correspond-ing to a gross energy consurnption of 250 kWh/ton for obtaining a pulp with a freeness of 250 ml CSF and a mean fibre length ~PML) of 1.7 mm, i.e. as a convention-ally manufactured CTMP-pulp produced in one step with an energy consumption of 1750 kWh/ton.
By the method according to the invention, thus, the en-ergy consumption was reduced from the conventional 1750 kWh/ton to 850 kWh/ton.
The properties of the CTMP-pulp obtained compared with conventional GTMP-pulp are shown in Table 2 , TABLE _ Conventional Invention Energy consumption,kWh/ton 1750 850 CSF ml 250 250 PML, mm - 1.7 Tensile index, kNm/kg 40 40 Tensile stiffness index - 4 6 Stretch at break, ~ 1.9 1.6 Tear index Nm2/kg 6.7 5.5 Density, kg/m3 420 450 S, m /kg 43 45 IS0-brightness, % 60 60 The manufacture of CTMP according to the invention is compared in Figs. 6,7 and 8 with manufacture according to conventional technique.
In Fig. 6 the tensile index is shown as a function of the energy consumption for a CTMP-pulp manufactured accord-ing to the invention and for pulp manufactured conventlon ally. Compared at a certain tensile index, for example 40 kNm/kg, conventional refining consumes about 1750 kWh/
ton pulp while at the method according to the inventlon only about 850 kWh/ton are consumed.
At a comparison of the method according to the invention with conventional method in a relationship with the tear index as a function of the tensile index, it appears that the relationships~are similar, i e. one avoids the fibre cutting, which is usual at low concentration beating and which gives rise to~a~substantially reduced tear index.
Thls appears from the diagram in Fig. 7.
The light-scattering coefficient of the CTMP-pulp manuf-; actured according to the invention as a function of the energy consumption is shown in the diagram in Fig. 8 compared with conventionally manufactured pulp. It shows : :

,, , here that according to the invention the energy consumpt-ion to a certain light-scattering index is substantially lower.

EXAM~.E 3 This example relates to the manufacture of highly sulfon~
ated CTMP or CMP, i,e pulp containing more than 4 g of bound sulphur per kg wood material.
Chips from spruce were impregnated with a sodium sulphite solution containing about 120 g of sodium sulphite per litre in an amount correspondi~g to a charge of` about 12%. The chips were preheated at a temperature of 140C
for 10 minutes, whereafter they were coarse-disintegrated with an energy consumption of about 400 kWh/ton wood.
The defib~ation was carried out in a pressurized chip refiner, and the yield obtained was 93-94~. A~ter a latency treatment at 60C for 20-30 minutes at a pulp concentration of 3%, the pulp was beaten in three steps at an edge load of 0.3 to 0.5 Ws/m and a net energy con-sumption of 100 kWh/ton corresponding to a gross energy consumption of 160 kWh/ton.
The properties of the resulting pulp were determined, and in the following Table 3 the values obtained are stated in comparison with a CTMP manufactured in a conventional way in a one-step process with an energy input of 1500 kWh/ton.
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t 320067 Conventional Invention Energy consumption, kWh/ton 1500 560 CSF, ml 4 4 PML, mm 1.9 1.9 Tensile index, kNm/kg 65 65 Stretch at break, % 2.0 1.8 Tear index, Nm2/kg 8.o 8.o Density, kg/m3 440 450 S, m /kg 34 36 ISO-brightness, % 59 59 This embodiment is an example of how in the first step extruders can be used for coarse-disintegrating wood material. According to the example an extruder of the type Bivis was used.
Spruce chips were steamed in the usual manner at 100 C
for 10 minutes, whereafter they were fed into a Bivis-machine. At the defibration in the machine 2-3% sodium sulphite solution was char~ed so that the sulfonation degree of the material amounted to 1.5 g of sulphur per kg wood. The electric energy consumption was about 400 kWh/ton wood when the material passed through the four compression zones o~ the twin screw. After discharge, the~fibre material was diluted to about 5% pulp concen-tration at about 70C~ whereafter the suspensicn was pumped ~o beating in seven steps in a low concentration refiner. After the fifth beating step, the freeness of the pulp was about 250 ml CSF, the tensile inde~ was 55 kNm/kg, and the tear index 6 Nm /kg;at a net energy consumption~of 150 kWh/ton and a gross energy consumpt-ion of 250 kWh/ton.
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The total energy consumption for the manufacture of chemi-mechanical pulp (CTMP) to a freeness value of 250 ml CSF by the method according to the invention, thus, amounts to 650 kWh/ton, which is to be compared with about 1750 kWh/ton according to the best conventi-onal technique for obtaining the same freeness value~
By beating in seven low concentration steps according to the invention, a freeness value of 50 ml CSF can be obtained, and the resulting CTMP-pulp is suitable for use in magazine and LWC-paper The total energy consumption yet can be kept below about 850 kWh/ton.
Pulp of this lastmentioned type cannot be manufactured with conventional technique,because then a sufficiently good smoothness cannot be achieved.
The invention is not restricted to the embodiments described, but can be varied within the scope of the irven~lon ~dea.

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Claims

1. A method of manufacturing mechanical and chemi-mechani-cal papermaking pulp with low energy input, by disintegrating and beating wood material in at least two steps, wherein in the first step the material is coarse-disintegrated at a concentration above about 20% with an energy input of at maximum about 800 kWh/ton wood material, acid groups in the wood material are neutralized entirely or partially by the addition of NaOH in an amount of at maximum about 9 kg/ton, the material is diluted to a concentration of about 1 to 10% by water with a temperature corresponding to the softening temperature of the lignin and with an ion strength of at maximum about 0.05 mole per litre, and then the material is beaten in one or several further steps with a total energy input at the beating steps of at maximum about 500 kWh/ton material.

2. A method according to claim 1, wherein at least 25% of the total energy input is supplied at the beating.

3. A method according to claim 1, wherein the coarse-disintegrated material after the first step is washed in order to reduce the ion strength.

4. A method according to claim 1, 2 or 3 wherein the energy input in each beating step amounts to about 50-150 kWh/ton pulp.

5. A method according to claim 1, 2 or 3, wherein the coarse-disintegrated material is diluted with water having a temperature of from about 40C to about 95C.