The present invention relates to a method of measuring the drainage properties of different materials when subjected to compression. The method is unique insofar as it includes measurement of material resilience, i.e. springback, properties. As examples of material may be mentioned liquid-containing bark, lignocellulose fibres, peat and sludge. The method may also be used for measuring how different chemicals affect material drainage properties, as well as for studying how such as different fourdrinier wires, filters and chemicals affect material drainage properties.

PRIOR ART

On the market there is much equipment for measuring the spontaneous dewatering taking place in fibre suspen- sions over the fourdrinier wire sections of pulp and paper-making machines. This type of dewatering is measured according to standardized methods and is stated in grinding degree or freeness. However, there lack instruments that intelligently and simply measure drainage properties during compression in well-defined conditions. The only known method measuring anything approaching drainage properties under compression is the so-called WRV-method (water retention value method) , which measures the ability to retain liquid in such as pulp during centrifuging that subjects the material to large G-forces causing the liquid to be urged from the material.

None of the known methods and equipments measure the expansion different materials demonstrate after com¬ pression at relatively high pressures.

DISCLOSURE OF THE INVENTION Technical problems

In many processes it is of essential importance to press out as much liquid as possible from different materials, such as paper pulp, peat, bark, sludge and slurry. For the manufacture of dewatering equipment it is also of interest to find the right implementations that lead to maximum capacity and effect. In addition, it is of interest,,for fourdrinier wire and/or filter manufacturers and chemical suppliers to find optimum drainage properties for their specific products. In combustion it is of great importance to reduce moisture content to a minimum level, since every such reduction substantially increases the value of the material as fuel. A classical problem in reducing moisture content to a low level depends, inter alia, on the fact that it is very difficult and complicated to evaluate optimum conditions for pressing liquid out of different mate- rials.

The usual methods, used today for measuring drainage properties pertaining to such as lignocellulose mate¬ rial, only give a relative measure for the spontaneous dewatering and thickening, which take place in watery pulp suspensions over the fourdrinier wire sections in a paper-making machine. For such measurement there are thus so-called grinding degree and freeness testers that are used in accordance with standardized methods. There are also apparatus operating discontinuously, which measure grinding degree and freeness. It should be emphasized that there is poor relationship between the spontaneous dewatering indicated in the analysis and the forced drainage occurring in the pressure section of a paper-making machine. One problem is that there is no instrument, which can be used readily and in a reproducable way for measuring the drainage pro-

perties of liquid-containing material subjected to compression.

Technical solution

Many problems associated with the known art may be solved by using the present invention.

The invention relates to a method signifying that liquid-containing material is subjected to mechanical pressure forcing liquid therefrom via compression. The device is also provided with sensors continuously measuring a) the material volume under compression and b) the inherent resilience of the material after com- pression is released.

Characteristic for the method is that pressure applied to the material is well controlled with the aid of a computer program. In additon, the method is charac- terized by automatic measurement of both volume of compressed material and volume of liquid urged there¬ from. In a preferred embodiment of the invention mea¬ surement values are recorded by a computer and results written out on a printer connected to it. Material subjected to pressure is juxtaposed a perforated plate or a synthetic material, such as a fourdrinier wire used in the pulp and paper industry and through which liquid urged from the material can pass. This plate or fourdrinier wire rests in turn on a steel structure provided with ducts. In order to prevent loss of so- called zero fibres or other fine material, a relatively close mesh fourdrinier wire or a filter of suitable material may be placed on the perforated plate.

Since it is known that different fourdrinier wires and filters affect drainage, it is within the scope of the invention to test them.

The materials that can be tested with respect to their drainage properties are inter alia lignocellulose products, such as paper pulp, or peat, sludge, sugar beet residue and waste products. The method may also be utilized for measuring the ability of material to retain liquid under mechanically applied pressure, as well as for measuring the liquid reabsorption proper¬ ties of different materials. In the latter case, press¬ ure on the material can be reduced so that it can expand and to a certain extent return to its original volume. During this expansion the material can reabsorb moisture previously urged out of it. This volume in- crese (and rewatering) also constitutes a measure of the material's resilience or springback ability.

The method in accordance with the invention will now be explained in more detail and with reference to Fig. 1.

Material 1, being one of several having different properties, is placed in a cylinder 2 and juxtaposed to the bottom 3 thereof, the bottom usually being provided with a removable steel fourdrinier wire 4 (this may be replaced, e.g. by a plastics one) . A synthetic four¬ drinier wire 5 or a filter 5• of some kind may be placed on the wire 4. If the material contains a rela¬ tively large volume of liquid, some self-drainage occurs, resulting in that liquid will migrate through the mentioned wires and/or filter. In accordance with the invention, the portion of solids in the material shall be at least 4% and preferably at least 10% of the total weight of material including liquid.

After passage through the wire section 4, 5, 5• the liquid 13 is led out from the bottom of the cylinder via ducts 6, and into a container 7 placed on weighing means 8. The liquid volume, or rather its weight is

automatically registered by a computer 9 connected to the means 8.

The liquid run-off described may be called spontaneous drainage, and varies greatly, depending on initial material properties and of course on its liquid con¬ tent. This spontaneous drainage may also be regarded as measure of the drainage to expect, e.g. the fourdrinier wire section of a paper-making machine. In accordance with the invention, it is desirable, but not necessary, to measure and record spontaneous drainage.

In accordance with a preferred embodiment of the in¬ vention, the liquid-containing material is subjected to mechanical pressure, resulting in compression, which urges liquid out from the material. The modus operandi is as follows. A piston 10 is placed against the upper part 11 of the material, and is urged by hydraulic pressure against the material such that its engagement with the material is continous. Furthermore, the rate at which the piston 10 is driven may be regulated with the aid of a computer 9 in communication 12 with the drainage means.

With the aid of a program controlling the computer the piston 10 may be retained in a given position and at a given pressure. For enabling measurement of rewatering and resiliency of the material, piston pressure may be reduced, which permits expansion of the material. The volume (or weight) of liquid pressed out by the piston 10 is collected in a container 7 and registered by the computer 9. Characteristic for the invention is that registration is continuous, thus enabling write-out of both tables and graphs by the computer, which is also connected to a weighing means 8. In addition to the mentioned pressures and volumes, material temperature may also be measured, most easily by providing a cylin-

der 2, coacting with the piston, with such as a thermo¬ element.

A further characteristic of the invention is that it enables measuring the expansion or elastic properties of the material after releasing pressure against it. Expansion is registered continuously and may be measur¬ ed for several hours, if so desired. Normally, it is sufficient to measure resiliency or springback for some period up to a maximum of 30 minutes.

The method is preferably used for testing and develop¬ ment work on a laboratory scale, but may of course be integrated as a method in a mill, factory or the like for continuously monitoring drainage.

The invention will now be clarified in more detail with the aid of some embodiment examples.

Embodiment example 1

Thickened, unbleached, chemical, mechanical pulp was taken from a pulp mill. From a total weight of pulp and water the dry pulp weight was 24,3%, i.e. the pulp had a dry pulp content of 24,3%.

At the same time unbleached sulphite pulp with a dry pulp content of 22,6% was taken.

The drainage properties of the pulps taken were ana¬ lysed in accordance with the well-established freeness method having the standard denotation, SCAN-C 21:65. Results are collected in table 1. It may be mentioned that the higher freeness is, the more easy dewatering the pulp is considered to be.

100 g absolutely dry weight samples were taken from the respective pulps, i.e. a weight of 416,7 g chemical- mechanical pulp including water, and 454,5 g sulphite pulp including water. The samples were placed individu- ally in turn in the cylinder 2. It was noted that no spontaneous dewatering occurred with either sample.

Forcing water from the pulp was performed by driving the piston 10 with successively increasing pressure against the pulp 11. Water 13 urged out was collected in the container 7 and its weight registered by the computer 9. The weight of water and pulp dry content at different pressures are illustrated in table 1. The dry content is obtained continuously with the aid of the (unique) computer program.

Table 1

CHEMICAL-MECHANICAL SULPHITE PULP MASS

Absolutely dry content before compression, % 24,3 22,6

Freeness as

SCAN-C 21:65*, ml 675 605

Compression, kP/cm ² 15 40 80 15 40 80

Water forced out, ml (g) 118 160 193 161 225 255

Dry content, % 33,5 38,9 44,6 34,1 43,6 50,1

*Canadian Standard Freeness

As will be seen from the results, it has surprisingly been found that achieving high dry content is easier with sulphite than with chemical-mechanical pulp.

This is particularly surprising, since the freeness values clearly indicated that on compression the chemi¬ cal-mechanical pulp should be easier to drain than the sulphite pulp. The embodiment example has thus shown that existing measuring apparatus for suspensions do not indicate in a relevant manner how drainage can take place, when materials are compressed.

Embodiment example 2

Since unexpected and surprising results were obtained for the embodiment example 1, new, but different tests were carried out on the same types of pulp used in this example. The pulps were therefore ground in a so-called PFI mill. Grinding was performed so that the pulps were given different grinding degrees, which were measured according to the standardized SCAN-C method 19:65. The grinding degree method is fairly similar to freeness measurement, and the only practical difference is that resulting measurements are given in different units.

After grinding, the pulp suspension was thickened in a centrifuge to a dry content of 24-28%. For obtaining a dry content of 24% water was mixed with samples having a greater dry content than 24%. The grinding degrees of the samples were then measured according to the stan¬ dard method and the drainage properties in accordance with the invention. In these tests the samples were subjected to a constant pressure of 40 kP/cm ² in the drainage tester. The results are arranged in table 2.

Table 2

Dry content, %, after compression at 40 kP/cm ²

Chemical-mechanical Sulphite pul pulp

Grinding degree,

°SR 13 (not ground) 38,4 43,6

15 36,3 39,2

20 33,1 32,4

25 30,5 28,5

30 29,8 26,1

As will be seen, it has completely surprisingly been found that grinding makes the sulphite pulp more diffi¬ cult to dewater than the chemical-mechanical pulp. This is particularly surprising, since the results are opposite to those obtained in embodiment example 1.

It may thus be established that there is an essential difference between known measuring methods (grinding degree and freeness) relating to so-called spontaneous dewatering, and the drainage that can be read off with the aid of the present invention.

Embodiment example 3

To demonstrate the possibility of measuring the resili¬ ence or springback of pulps, tests were made on the same type of pulps as in the preceding tests. In this case samples containing 100 g absolutely dry substance (dry content 26%) were subjected to a compression of 50 kp/cm ² . This pressure was maintained for 2 minutes and subsequently totally released, so that only the weight of the piston 10 acted on the sample 11. The volume of the sample was read off immediately prior to pressure release. After 5 minutes free expansion of the sample

the height of the piston in the cylinder was read off, whereat the programmed computer quickly calculated how much the sample had expanded subsequent to the release of maximum pressure (50 kP/cm ² ) . The results are pre¬ sented in table 3.

Table 3

Pulp type Chemical- Sulphite mechanical

Pulp volume before compresso ₍ cπr 450 372

Pulp volume after 2 min at max pressure, cm ³ 350 300

Pulp volume after 5 min expansion, cm ³ 425 325

Expansion calculated as relative, % 21,4 8,3

As will be seen, the method shows very clearly that springback ability is considerably greater with the chemical-mechanical than with the sulphite pulp.

Embodiment example 4

In this fouth test mutually equivalent plastics four¬ drinier wires obtained from different manufacturers were tested. In separate tests, each wire was placed on the steel wire 4 at the bottom of the cylinder 2. Test samples with 100 g absolutely dry weight of sulphite pulp with a dry content of 24,5% were used. Each sample was placed in the cylinder 2 and a pressure of 40 kp/cm ² was applied to the sample. The time taken to reach this pressure was 30 seconds and maximum pressure was maintained for 2 minutes. Dry content directly on

reaching maximum pressure and at 2 minutes after reach¬ ing it are presented in table 4.

Table 4

Wire manufacturer A B

Dry content directly on reaching max pressure, % 43,2 45,3 41,9 Dry content after 2 min at max pressure 45,6 45,7 44,9

It is surprising that the differences were so great between the wires with respect to drainage rate direct- ly after reaching maximum pressure, thus showing the importance of being able to measure the effect of a wire of drainage. As will be seen from the values in table 4, the differences in dry content between the three wires had levelled off. This is less interesting, since in practice rapid and dynamic processes are required.

Advantages

A number of advantages is obtained in applying the measuring method in accordance with the invention. Drainage properties of different materials may be readily and rapidly measured in well-defined and repro- duceable conditions. The method also permits great flexibility without relinquishing measuring accuracy. A big advantge is that it is possible to perform relevant measurements on small sample quantities, which sub¬ stantially facilitates measuring with accompanying and clearly discernable test cost.

The method has great importance from the environmental aspect, since it will be easier to find the best condi-

tions for optimally and maximally reducing moisture content in different materials. Since moisture content can be reduced to a lower level, less energy will be required, e.g. for drying pulp and paper. With lower moisture content in the material there are obtained several positive effects in its combustion, since besides better energy exchange there is obtained less discharge of injurious gases.

The described device may naturally also be used to advantage for measuring fatigue properties relating to material elasticity. Examples of materials here are rubber and synthetic polymer material, e.g. polyure- thane.