Apparatus for measuring the particle size range in a suspension

The particle size range of a paper pulp suspension is determined by flowing the suspension up a measuring tube having a filter at the bottom thereof. When a plug of suspended material has formed, the inlet of the measuring tube is closed off. A liquid is then fed to a member which forms a gap in the plug of material and passes up through a measured portion of the suspension. The time taken for the liquid to pass through the plug to a given height is indicative of the mean particle size of the suspension.

The present invention relates to apparatus for measuring the particle size 
range in a suspension. The suspension which most readily comes to mind is 
paper pulp which is normally manufactured in one place and then supplied 
to a paper manufacturer. The paper pulp contains cellulose fibers which 
may be obtained either through a sulphite process or through a sulphate 
process. The cellulose fibers are then whole. Cellulose fibers or parts 
thereof can be produced by a milling process. In the latter case the 
fibers may be of different sizes and may also form groups together. When a 
paper pulp containing fibers or fiber fragments is manufactured 
mechanically it is essential to know the size range of the cellulose 
particles so that when the supplier receives the paper pulp he is well 
aware that, when manufacturing paper, he will obtain the correct quality 
in the paper produced. In order to determine the size range of 
mechanically produced cellulose particles in a suspension, i.e. in the 
present case in a paper pulp, the paper pulp is allowed to pass through a 
vertical through-flow tube, the upper end of which consitutes a spillway. 
In the through-flow passage, a tube is placed which is also provided at 
its upper end with a spillway, but located higher than the spillway for 
the through-flow passage. A stationary column of paper pulp is thus formed 
in the tube. To the latter tube, between its ends, is connected one end of 
a measuring tube which becomes vertical towards the other end. Between the 
ends of the tube is a filter which allows the suspension liquid, i.e. the 
paper pulp liquid to pass through. The liquid passing through the filter 
rises into the vertical part of the measuring tube which contains two 
indicators located at different levels. The two indicators determine the 
rate of drainage in the suspension which is retarded in front of the 
filter. If the particles in the suspension are small, it will take longer 
for the suspension liquid to penetrate through the filter than if the 
particles in the suspension are larger. 
A plug is formed of the suspension particles in front of the filter 
described above. In reality, therefore, what is measured is the rate of 
drainage of said plug. However, it is desirable to be able to measure the 
drainage rate of a plug which is more similar to the layer of paper pulp 
on a wire cloth. 
The present invention aims at fulfilling this object by placing a 
separating member in front of said filter which cuts off said plug so that 
a layer is obtained in front of the filter and so that the end of the 
layer facing the filter is opposite a passage or gap which can receive 
liquid which may only pass through the separated layer and the filter. The 
liquid in this case has a predetermined pressure which may be set by 
suitable means and is between 0.1 and 1.0 bar. The layer corresponds to a 
layer on a wire cloth. 
The actual separating of the layer is performed by means of the same liquid 
jet which is used for through-flow through the layer. 
To ensure that the liquid intended to flow through the layer will only flow 
therethrough, the inlet end of the measuring tube must be sealed. 
The part of the measuring tube connected to the inlet end of the filter is 
so inclined, according to the invention, that the suspension can only be 
retained in this part if it is subjected to pressure. 
With the inclination of the measuring tube on the inlet side of the filter, 
it is advantageous according to the invention to have a vertical 
through-flow passage which is divided into two parts by an inner wall, one 
part having a spillway which is on a lower level than that of the other 
part. A stationary suspension will thus accumulate in the other part and 
the inlet part of the measuring tube is connected to this part. 
Three indicators are arranged at three different levels in the vertical 
part of the measuring tube and these supply information to a calculating 
device connected to an indicator. 
The filter and separating member can be adjusted to different positions, 
i.e. to positions between a vertical position and a horizontal position 
and therebetween. The adjustment can be performed by means of a setting 
member or by placing them in different positions. Another method is to 
have an intermediate unit in the measuring tube, which is exchangeable, 
each unit containing a filter with the desired inclination. 
Further characteristics of the present invention are clear from the 
following description.

In the drawings, 1 is a vertical through-flow passage, preferably in the 
form of a tube provided with a bottom closure 2. A partition or separating 
wall 3 is arranged in the tube, which does not reach to the bottom of the 
through-flow passage but which protrudes outside the lefthand upper edge 
of the passage 1. The righthand upper edge of the passage is located at 
the same level as the upper edge of the partition. A lefthand space 4 and 
a righthand space 5 are thus formed. Both spaces are in the form of a 
tube, the edge of the lefthand space forming a spillway 6 and the upper 
edge of the righthand space, which are connected, forming a spillway 7. 
The openings 4 and 5 of the two spaces open into a collecting vessel 8 
with outlet 9. The collecting vessel 8 has an inspection hole 30. At the 
bottom of the through-flow passage 1, below the inlet opening of the space 
5, is an inlet tube 10 passing transversely through the vertical passage. 
This tube 10 is closed at its righthand end and is provided with a number 
of outflow openings 11. A measuring tube 12 protrudes into the space 5 and 
has such inclination that liquid cannot be retained in the tube. The 
lefthand end of the tube is so directed that its opening surface is 
perpendicular to the axis of the through-flow passage. In front of the 
opening is a valve 13 which, with the aid of the control member 14, can 
either close or open the lefthand end of the measuring tube 12. To the 
righthand part of the measuring tube 12 is screwed an exchangeable unit 15 
containing a filter 16 which forms a certain angle to the vertical plane. 
The filter 16 is such that it allows through only liquid but not suspended 
particles. Below the filter 16 is a unit 17 which has the task of cutting 
off a layer 33 of suspension particles collected in front of the filter 
16. The layer 33 of known dimensions is cut off with the help of liquid 
from a liquid supplier 18 through a conduit 19. The liquid supplier 18 can 
be set so that the liquid emitted has the desired pressure of between 0.1 
and 1.0 bar. The liquid is supplied to the separating member 17 which is 
provided with a space surrounding the layer formed, and one or more 
openings 31 which guide the liquid jets so that a gap 32 is formed. On the 
lefthand side of the gap 32 the remaining suspension 34 is collected. The 
described unit 15 comprising filter 16 and separating member 17 can be 
replaced by other units in which the angle of inclination of the filter is 
different. It is also feasible to arrange a mechanism which can adjust the 
filter 16 with its separating member 17 to the desired angle in the 
existing unit. 
A vertical extension tube 20, sealed at the upper end with a plug 21, is 
screwed into the unit 15. Said plug contains three electrodes 22, 23 and 
24, the lower ends of which reach the levels A, B and C. The electrodes 
22, 23 and 24 are connected to an evaluation means 25 by wires 26, 27 and 
28. The evaluation means 25 is connected to an indicator 29. The 
electrodes 22 and 23 measure the flow time between levels A and B and 
electrodes 23 and 24 measure the flow time between levels B and C, which 
is stored in the respective memories. Data from the two memories is 
processed and stored in a third memory. All the memories are to be found 
in the means 25. The device is calibrated to correlate flow time with mean 
particle size in the suspension, and the information obtained in the 
indicator 29 can be used to alter the size range of the particles in the 
suspension. 
The extension tube 20 is provided at its upper end with a valve unit 35 
which, via a wire 36, is connected to a switching unit 37. This unit 37 
can either connect the valve 35 with a compressed air unit 39 or with a 
conduit 38 in communication with the surrounding atmosphere and thus 
ensures that the ambient atmospheric pressure can be supplied to the valve 
unit. 
The apparatus described above functions as follows: It is assumed that a 
suspension such as in the present case, paper pulp, prior to delivery is 
allowed to pass continuously through the vertical through-flow passage 1, 
through the space 4, to flow over the spillway 6 into the collecting 
vessel 8 and then leave the vessel 8 through the outlet 9 for delivery. 
While the paper pulp is flowing up through the space 4 it will also flow 
up in the space 5. Since the spillway 7 is located on a higher level than 
the spillway 6, a stationary pillar of paper pulp will be formed in the 
space 5. The paper pulp flowing in the space 5 also flows up in the 
measuring tube 12 through its lefthand end when the valve 13 is open. When 
so much paper pulp has flowed up through the measuring tube 12 that a plug 
consisting of the parts 33 and 34 has been formed by the suspended 
material, the lefthand end of the measuring tube 12 is closed by means of 
the valve 13. In this situation, it is possible that a certain amount of 
liquid may have flowed through the filter 16. If so, the levels A, B and C 
are above the liquid level for the liquid 40 which has passed through the 
filter 16. 
When the lefthand end of the measuring tube 12 is closed, liquid is 
supplied to the cutting member 17 at the desired pressure from the liquid 
supplier 18. The liquid is allowed to pass through openings 31 so that a 
gap 32 is formed. When the gap has been formed, the liquid can be supplied 
at the same pressure or some other desired pressure to the cutting member 
17, the liquid supplied being forced to pass through the upper plug or 
layer 33. The three electrodes 22, 23, and 24 will then measure the times 
when the liquid from the liquid supplier 18 reaches the various levels A, 
B and C. The indications from the electrodes 22, 23 and 24 are processed 
in the evaluation means 25 as described in the following. The result of 
the evaluation performed in the evaluation means 25 is supplied to the 
indicator 29. 
When the evaluation means 25 has obtained its three indications, the aim is 
to prepare the measuring tube 12 for the next measurement. For this 
purpose, the valve 13 is opened. Compressed air is then supplied from the 
conduit 39 to the valve unit 35 via the conduit 36' and switching member 
37. The valve unit 35 was previously supplied with air at atmospheric 
pressure via the conduit 38. The valve 35 is so designed that air is 
introduced to the extension tube 20 so that it moves helically along the 
inner surface of the tube in order to clean the extension tube 20 and to 
press liquid out of the extension tube as well as pressing liquid and 
suspension out of the measuring tube 12. Compressed air and liquid will 
thus flow out of the lefthand end of the measuring tube 12 and the space 5 
will thus be emptied of its contents via the spillway 7 so that it can 
again be filled from below with fresh paper pulp and another measurement 
can be performed. 
It should be obvious that the measuring tube 12 may be provided at the top 
with a valve unit 35 if desired, to facilitate cleaning. 
It should also be obvious that the arrangement with varying angles of the 
filter 16 is not only limited to the apparatus described. The same applies 
to the three electrodes 22, 23 and 24 and the separating member 17. 
Neither is the design and arrangement of the measuring tube 12 limited to 
the apparatus described. 
The division of the through-flow passage 1 as in the present apparatus may 
also have its uses in other types of apparatus. 
The great advantage with three electrodes is that with different paper pulp 
concentrations it is possible to determine whether the particle size range 
is the same or different.