Technical deliverables ECOTARGET 500345

2005-02-03 Page 1 (9)

Contract no.: 500345 (NMP2-CT-2004-500345) Project acronym: ECOTARGET

Project title: New and innovative processes for radical

changes in the European pulp & paper industry

Instrument: Integrated Project

Thematic Priority: NMP

D1.2.5 Shear and compression behaviour of fibre beds formed by spruce and pine fibres

Due date of deliverable: 9.6.2006 Actual submission date: 9.6.2006

Start date of project: 01 November 2004 Duration: 48 months Organisation name of lead contractor for this deliverable: University of Oulu Revision: [1] Dissemination Level PU Public X RE Restricted to a group specified by the consortium (including the

Commission Services)

CO Confidential, only for members of the consortium (including the Commission Services)

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SHEAR AND COMPRESSION BEHAVIOUR OF FIBRE BEDS

FORMED BY SPRUCE AND PINE FIBRES The method and preliminary results

Mirja Illikainen University of Oulu

Abstract This paper presents the new device for studying the compression and shearing properties of TMP pulps. With the help of the new device, compressibility of high consistency TMP pulps can be measured in the temperatures up to 180°C and using the compressible pressure from one to eight bars. The disruptive shear stress of compressed pulp pad is measured under the compression. First results showed that the compressibility of pulps is much higher at the temperatures from 120 °C to 170 °C than at the room temperature. The compressibility was not the function of the freeness. In shearing tests, the equipment caused the complete disruption of the pulp pad and the disruptive shear stress was not depended on the thickness of the cake between the needles. Introduction Mechanisms of thermomechanical pulp (TMP) refining have been studied since the beginning of TMP manufacturing. The aim of these studies has been to clarify what happens between the refiner plates: what causes the desired development of fibres and what kind of factors affect the energy consumption in refining. In refiner, wood material is affected by shearing and compressive forces. Studying the refining mechanisms is challenging due to the harsh conditions inside the refiner. Different kind of experimental devices has been developed for studying the mechanisms of refining in laboratory scale. This paper presents the laboratory scale equipment developed for studying the compressibility and disruptive shear stress of high consistency TMP pulps at high temperatures and steam environment. Preliminary results of the compressibility and shearing experiments are also presented. The compressibility of TMP pulps with different freeness values was tested and volume fraction of pulps at different temperatures was studied. The effect of the cake thickness on the torqe was also investigated. Equipment of shear and compression Equipment of shear and compression (ESCO) is presented in Figure 1. Main parts of the ESCO are the cylindrical vessel, the pneumatic press and the rotating bottom of the vessel. The device is connected to the steam line. High pressure steam is used for heating up the pulp. ESCO is connected to the computer. The computer is used for operating of the equipment. To the computer all the measured data is collected and stored: temperatures inside the cylinder, piston position, compressive force and torque. Measuring frequency of 14 1/s is used. Main operational principles of the ESCO are presented in Figure 2. The pulp is put into the cylinder and then the bottom and the top of the cylinder are bolted. Pulp is heated using steam so that steam is flowed through the pulp pad. Temperature of the steam is controlled using

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pressure reducing valve. Temperatures up to 180 degrees are possible. At the bottom of the vessel there is also the valve for condensated water. Pulp is compressed using the piston and the pneumatic press. During compression the upside and the bottom of the cylinder are connected for pressure balancing. The velocity of the piston can be controlled: the minimum velocity is about 1mm/s. Pressures from 1 to 8 bars can be used. ESCO can be assembled using different surfaces on the bottom and the piston plates. Smooth surfaces are used for study of compressibility of the pulps. For studying shearing properties, the bottom and the piston of the cylinder are completed with needles (Figure 3). In shearing test the pulp is first compressed and after the compression the bottom of the vessel is rotated and compressed pulp pad is broken down. The motor is connected to the axis of the bottom plate and it is used for the rotating the bottom of the vessel. Rotational speeds from 5 to 30 rpm are possible. Figures 4 and 5 illustrate the example of output data of compressing and shearing experiments respectively.

Fig.1 Equipment of shear and Fig. 2 Main operational principles of ESCO. compression (ESCO).

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Fig. 3. Needle plates.

Fig 4. Output data in the compressibility Fig 5. Output data in the shearing experiment. experiment. Materials and methods Materials Thermomechanical pulps with different freeness values were produced by using 20 inch pilot refiner. Pulps were produced from Norway spruce chips and from two different kind of Scots pine chips (sawmill and thinning pine). Freeness levels and specific energy consumptions are presented in Table 1.

0

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time [s]

pre

ssu

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ba

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0,43

0,44

0,45

0,46

0,47

0,48

0,49

0,5

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ract

ion

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pre

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-20

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Table 1. Specific energy consumption and freeness levels of produced TMP pulps wood specie refining

stage SEC (MWh/t)

Total SEC (MWh/t) (1st, 2nd, 3rd stages)

CSF (ml)

Norway spruce 1 0.61 0.61 747.5 Norway spruce 2 0.57 1.76 299 Norway spruce 2 1.42 2.61 118 Norway spruce 2 2.14 3.33 65 Sawmill pine 1 0.81 0.81 723 Sawmill pine 2 0.51 1.86 340 Sawmill pine 2 1.48 2.83 156 Sawmill pine 2 2.32 3.67 54 Thinning pine 1 0.79 0.79 719 Thinning pine 2 0.76 1.92 298 Thinning pine 2 1.90 3.06 97.5 Thinning pine 3 1.12 3.99 62 Methods ESCO was used for study the compressibility and shearing of pulps. In compressibility tests 100 g of absolutely dry pulp was loaded into the cylinder at the consistency level of about 30 %. Steam was used for heating up the pulp and heating time of 15 minutes was used. Compressibility experiments were carried out using steam at temperatures of 120, 150 and 170 °C. Before the actual experiments, the effect of the piston velocity on the compressibility was investigated. Experimental points are shown in Table 2. Pressures from 3 to 9 bars and piston velocities from 1 to 15 mm/s were used. Experiments were carried out at the room temperature and pulp was soaked with water. In later experiments the piston velocity of from 1 to 5 mm/s was used. Experimental plan for compressibility tests is presented in Table 3. Pressures 1, 2, 4, 6 and 8 bars were used in all experimental points. After experimetns dry content of the compressed pulp cake was determined. Table 2. Test point for studying the effect of piston velocity on the pulp compressibility. Test point pressure

[bar] piston

velocity [mm/s]

3.1 3 1 3.2 3 4 3.3 3 8 4.1 4 4 4.2 4 6 4.3 4 8 4.4 4 11 6.1 6 8 6.2 6 10 6.3 6 13 6.4 6 15 9.1 6 8

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9.2 9 11 9.3 9 12 9.4 9 14

Table 3. Experimental point for compressibility experiments. Compressive pressures of 1, 2, 4, 6 and 8 bar were used in all the experiments. wood specie CSF

(ml) 15 °C 120 °C 150 °C 170 °C

Norway spruce 747.5 x x x x Norway spruce 299 x Norway spruce 118 x The effect of amount of pulp between the needle plates on the measured torque was studied. The aim of these experiments was to study if the developed needle plates cause the complete disruption of compressed pulp pad. In shearing experiments heating time of 15 minutes was used. After heating pulp was compressed using certain compressive pressure. Compressed pulp pad was broken down and needed torque was measured. The rotational speed of the bottom of the cylinder was 8,4 rpm. Table 4 presents experimental points for shearing experiments. Norway Spruce was used in shearing experiments at the temperature of 150°C. Table 4. Variables in shearing tests pressure (bar)

thickness of the cake

1,8 2.5 1,8 10.8 2,2 2.1 2,2 3.5 3 5.1 3 5.9 3 8

Equation 1 presents the definition of the volume fraction of pulp. The density of fibre cell wall was used for calculating the volume of fibre solid material, which is then compared to the total volume of pulp.

volumetotal

wallfibre

volumetotal

materialfibre

Vρ

m

V

Vε ==

(1)

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Results and discussion The effect of piston velocity The aim of these experiments was to clarify if the velocity of the piston has an effect on the final volume fraction of pulp. Hypothesis before experiments was that high piston velocity would delay the water filtration and thus decrease the final volume fraction of pulp. The results of these experiments are presented in Figure 6. No effect of piston velocity on the final volume fraction of pulp can be observed. In the experiments the velocity of the piston was from 1 to 15 mm/s and pulp was compressed controlling the pressure of the pneumatic cylinder, as stated above. Because the motion of the piston was controlled by pressure, the velocity of the piston was slowed down when pulp pressure was increased. In experiments the final volume fraction of pulp was reached its final value slowly as can be seen in Figure 4. Thus, the velocity of the piston was very slow at the end of the experiment in all the measured cases. The velocity of the piston is not a critical factor studying the compressibility of pulps using ESCO. Fig 6. Volume fraction of spruce TMP at 20 °C. Different piston velocities were used. The effect of freeness Spruce TMP with different freeness values were compressed using different compressive pressures at temperature of 120 °C. Figure 7. illustrates the volume fraction of pulp as a function of compressive pressure of pulps with different freeness. No clear effect of freeness on compressibility can be seen.

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0 2 4 6 8 10 12 14 16Piston velocity [mm/s]

Volu

me

frac

tion

[%]

3 bar 6 bar 9 bar 4 bar

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Fig. 7. Compressibility of pulps with different freeness values. The effect of temperature Figure 8. presents the volume fraction of spruce TMP as a function of the compressive pressure at different temperatures. At the room temperature the volume fraction of 0.33 was found using the maximum pressure while at temperatures from 120 to 170 °C volume fractions increased to the level of 0.43. Pulp was thus more compressible at the higher temperatures than at the room temperature due to the softening of wood. Slight differences between volume fractions can be observed also at the higher temperatures. The higher the temperature the less compressible is the pulp. This result is probalby due to the volume of water since the density of water is the lower the higher is the temperature. Dry contents of cakes after 8 bar compressing are presented in Table 5. Fig. 8. Volume fraction of spruce TMP as a function of the compressive pressure in different temperatures.

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747,5 ml

310 ml

118 ml

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0,35

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Pressure [bar]

Volu

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ctio

n [

]

20 °C

120 °C

120 °C

150 °C

170

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Table .5 Dry content of the cake after the compression Temperature

[°C] Dry content after 8 bar compression [%]

120 46.6 150 55.4 170 55.9

The effect of cake thickness Figure 9. shows the results of shearing experiments. The cake thickness between the needle plates did not affect the disruption of compressed pulp pad which indicates that pulp pad is broken down similarly irrespective of the amount of pulp between the plates. Fig. 9. The effect of the thickness of the cake on the needed torque. Spruce TMP at 150 °C. Equipment testing and preliminary results show that equipment works and repeatability results about compressibility and shearing properties of TMP pulp can be achieved. The equipment has shown to be suitable for study compressing and shearing properties of TMP pulps. Conclusions Testing of the ESCO and preliminary results showed that equipment is suitable for study compressing and shearing properties of TMP pulps. The piston velocity had no effect on the final volume fraction of pulp. In shearing test the amount of pulp did not affect torque that was needed to broken down the compressed pulp pad. Freeness did not have effect on volume fraction of pulp. Pulp was more compressible at high temperatures (120 – 170 °C) than at the room temperature. At high temperatures up to 120 °C the lower the temperature the slightly more compressible was the pulp. This result was probably due to the lower density and higher volume of water at high temperatures.

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Thickness of the cake [mm]

To

rqu

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Nm

]

1,8 bar

3 bar

2,2 bar