WO1998043065A1

WO1998043065A1 - Apparatus for measuring the permeability of crystal particles suspended in a slurry

Info

Publication number: WO1998043065A1
Application number: PCT/NL1998/000162
Authority: WO
Inventors: Paul Jos Diepen; Viktor Peter Charles Vreeken
Original assignee: Technische Universiteit Delft
Priority date: 1997-03-21
Filing date: 1998-03-23
Publication date: 1998-10-01
Also published as: NL1005595C2

Abstract

The invention relates to an apparatus for measuring the permeability of crystal particles suspended in a slurry, comprising a filtering element (3) and driving means (4, 5, 6) for driving the slurry into the filtering element. The filtering element is connected with discharge means (8, 9) for the filtrate and a measuring instrument (10) for determining the flow rate of the filtrate. The filter element is a pipe, in which the lumen between its two ends is covered by a filter medium provided therein. The filtrate-supply side of the pipe is equiped for receiving the slurry.

Description

Apparatus for measuring the permeability of crystal particles suspended in a slurry

The invention relates to an apparatus for measuring the permeability of crystal particles suspended in a slurry, comprising a filtering element and driving means for driving the slurry into the filtering element, to which filtering element discharge means are connected for the filtrate and a measuring instrument for determining the flow rate of the filtrate.

From US-A-4, 891, 098 a filtration simulator is known for determining the interaction and the effect on a liquid stream when additives are incorporated into a feed line for a paper mill. This know apparatus comprises a slurry tank for receiving the feed for the papermaking machine, as well as filtering means comprising a permeable filter, wherein the feed side of the filter is in fluid communication with the slurry tank, and the discharge side of the filter is in fluid communication with the same slurry tank. Means are provided for measuring the pressure and the volume flow of the aqueous paper stream feed being conducted from the slurry tank through the filtering means. In contrast, the present apparatus relates to the measuring of the permeability of crystal particles suspended in a slurry.

The above-mentioned permeability is an indirect measure for the size of the crystal particles. There is a need for an apparatus providing a quick and accurate manner for determining said permeability.

To feed the known apparatus, a sample is taken from the slurry which is present in an apparatus or which is part of a process stream. The problem with this method is the representativity of the sample taken and the logistics which have to be furnished for moving the sample to the laboratory where the apparatus for processing the sample is housed. It is the objective of the invention to provide an apparatus by means of which locally and in a relatively short measuring time the permeability of crystal particles suspended in a slurry can be determined in a manner which meets the standard of accuracy normally given for such measuring parameters .

This is achieved according to the invention by the fact that the filter element is a pipe, in which the lumen between its two ends is covered by a filter medium provided therein, and the filtrate-supply side of the pipe is equipped for receiving the slurry. This surprisingly simple measure provides an accurate manner for a quick measurement of the permeability of the crystal particles present in the slurry, at very low cost.

The invention is based on the realization that when taking a sample, the filter cake initially builds up on the filter medium in the pipe, with the resistance of the filter cake increasing correspondingly. As the pipe is finite, the filter cake builds up until the end of the pipe is reached at the side where the pipe is receivingly coupled or can be coupled with a receptacle containing the slurry. From that moment the filter cake grows on three dimensionally, while the cake's resistance does not, or only slightly increase further. The pipe may have any shape and may, for instance, taper toward either end. However, best results are obtained if the pipe is substantially cylindrical . The three dimensional growth of the filter cake is spherical. Practice has shown that the resistance of the filter cake in the spherical portion is negligibly small with respect to the cake's resistance in the cylindrical pipe. This realization is the basis for the quick and relatively accurate measurement by means of the apparatus according to the invention. In an advantageous embodiment the apparatus according to the invention is characterized in that the pipe is substantially cylindrical, forming a funnel at the side of the discharge means and running into a discharge connection, and that the driving means comprise a vacuum pump which is connected to the discharge connection. In this application the term vacuum pump also includes a water jet pump or vacuum ejector, or generally any device with which a vacuum can be created at the side of the discharge connection. Of course, such a vacuum pump is not necessary if there is an overpressure in the slurry.

It is useful to provide a filtrate receptacle after the discharge connection. This filtrate receptacle will then collect the filtrate that has passed the pipe and the device measuring the flow rate .

It is desirable that the filtrate's flow direction in the pipe be reversible. This has the advantage that after measuring, the filtrate collected in the filtrate receptacle can be fed through the pipe in reversed direction so that the filter cake accumulated there, can be flushed back to the slurry. For one thing, this provides the advantage that after a measurement is carried out, the filter pipe is cleaned and also, that after com- pletion of a measurement the concentration of the slurry is not influenced by this measurement .

Another advantageous embodiment of the apparatus according to the invention is characterized in that at the discharge side of the pipe and the filtrate receptacle a buffer reservoir is provided to which the vacuum pump is connected.

A preferred embodiment of the apparatus is characterized in that the driving means used is a pump with a reversible fixed delivery and that both at the feed side and the discharge side of the pump a pipe is installed which is provided with a filter medium. In such an embodiment the lift or pressure difference over the pump can be measured in order to determine the moment when it no longer exhibits any significant change. The value then reached is a measure for the resistance produced by the filter cake that has developed in the inlet pipe . By reversing the pump, the respective pipe is flushed clean and a further measurement can take place with the other pipe. The invention is further embodied in the separate filter element that is suitable to be applied in the apparatus for measuring the permeability of crystal particles according to the invention. The invention will now be further elucidated with reference to the drawing, in which

Fig. 1 shows an apparatus for measuring the permeability of crystal particles according to the invention; Fig. 2 shows a typical course of a measurement signal obtained with the apparatus according to the invention;

Fig. 3 shows a separate filter element according to the invention; and Fig. 4 shows an alternative embodiment of the apparatus for measuring the permeability of crystal particles according to the invention.

Identical reference numbers used in the figures refer to the same parts . Fig. 1 shows the apparatus for measuring the permeability of crystal particles suspended in a slurry. This apparatus is generally indicated by reference number 1 and comprises a filter element 3 and driving means 4, 5, 6 for driving slurry from a receptacle 2 into the filter element 3.

In Fig. 3 the filter element 3 is shown in more detail. It is formed as a pipe, in which the lumen between its two ends A, B is covered by a filter medium 7 provided therein. To the one end B of the pipe 3 discharge means 8, 9 are connected, as well as a measuring instrument 10 for determining the flow rate of the filtrate. The other end A of the pipe 3 is receivingly coupled with or can be coupled with the slurry container 2.

Preferably the pipe 3 is substantially cylindrical as shown in Fig. 3, forming a funnel at the side of the discharge means 8, 9 and running into a discharge connection 11. Further, the driving means 4, 5, 6 for the filtrate comprise a vacuum pump 4 which via a buffer reservoir 5, a pipe 6, a filtrate receptacle 9 serving to collect filtrate drawn from the container 2, and a pipe 8, is connected to the filter element 3.

The apparatus is used as follows .

The filter element 3 is introduced into the slurry in the container 2. In the buffer reservoir 5 an underpressure is created by means of the vacuum pump 4. To this end valve 12 is closed and valve 13 is open. When there is an adequate underpressure in the buffer reservoir 5, the vacuum pump 4 is stopped and valve 13 is closed. The pipe 6 comprises also a three-way tap 14 which is adjusted such that the filtrate receptacle 9 is in communication with the pipe 6. Then valve 12 is opened, resulting in an underpressure in filtrate receptacle 9, so that slurry is being sucked from the container 2 through the filter element 3. The filtrate volume then registered by the flow meter 10 is shown in Fig. 2. Initially this filtrate volume increases by a value which is determined solely by the resistance of the filter medium 7. However, immediately thereafter filter cake build-up occurs on the filter medium 7, causing the filtrate flow to decrease until the filtrate flow has reached a constant value at the moment t = t_x. This constant value corresponds with the maximum resistance of the filter cake build-up in the pipe-like filter element 3. The subsequent spherical further growth of filter cake does not significantly alter the filtrate flow as is shown in Fig. 2 for t > t_x. The thus drawn in filtrate is collected in the filtrate receptacle 9 until the above-mentioned constant filtrate flow value is reached. At that moment the three-way tap 14 is adjusted such that an atmospheric pressure or possibly overpressure is created in the filtrate receptacle 9, causing the filtrate in the filtrate receptacle 9 to return in reverse flow direction through the filter element 3 to the receptacle 2. In this manner the filter cake together with the filtrate is flushed back to the slurry in the receptacle 2. The registered filtrate flow value, preferably its constant portion, is processed and serves as measure for the permeability of the crystal particles from the slurry. Various modifications to the embodiments discussed above are conceivable, which are all within the scope of the appended claims. For instance, the vacuum pump 4 may be omitted if the slurry in the receptacle 2 is under pressure. Of course, in that case, a sufficient overpressure with regard to the pressure of the slurry is required in order to flush back the filtrate accumulated in the filtrate receptacle 9.

In an alternative embodiment shown in Fig. 4, which is deemed to be very practical, the apparatus according to the invention is provided with a pump 4 which has a reversible but in any case fixed delivery and that both the feed side and the discharge side of the pump 4 are provided with a filter element 3 which, according to the invention, takes the shape of a pipe provided in its lumen with a filter medium. Both filter elements 3 are introduced in the receptacle 2 containing the slurry comprising the suspended crystal particles. The pressure build-up over the pump is measured by means of a measuring device 15. This pressure build-up reflects the resistance over the drawn- in filter element 3 which pressure increases during measurement and by which the permeability of the crystal particles suspended in the slurry in the receptacle 2 can be determined. When with said measurement the pressure has become constant, the per- meability of the crystal particles can be derived therefrom. If the pump is then switched over, the filter element 3 will be flushed clean while simultaneously a next measurement can be carried out with the filter element 3 located at the other side of the pump 4.

Claims

1. An apparatus for measuring the permeability of crystal particles suspended in a slurry, comprising a filtering element and driving means for driving the slurry into the filtering element, to which filtering element discharge means are connected for the filtrate and a measuring instrument for determining the flow rate of the filtrate, characterized in that the filter element is a pipe, in which the lumen between its two ends is covered by a filter medium provided therein, and the filtrate- supply side of the pipe is equipped for receiving the slurry.

2. An apparatus according to claim 1, characterized in that the pipe is substantially cylindrical.

3. An apparatus according to claim 1 or 2 , characterized in that the pipe is substantially cylindrical, forming a funnel at the side of the discharge means and running into a discharge connection, and that the driving means comprise a vacuum pump which is connected to the discharge connection.

4. An apparatus according to claim 3, characterized in that a filtrate receptacle is provided after the discharge connection.

5. An apparatus according to one of the preceding claims, characterized in that the filtrate's flow direction in the pipe is reversible.

6. An apparatus according to one of claims 1-5, characterized in that at the discharge side of the pipe and the filtrate receptacle a buffer reservoir is provided to which the vacuum pump is connected.

7. An apparatus according to one of claims 1-3, characterized in that the driving means comprise a pump with a reversible fixed delivery and that both at the feed side and the discharge side of the pump a pipe is installed which is provided with a filter medium.

8. A filter element for separating a filtrate and crystal particles from a slurry, characterized in that the filter element is a pipe, in which the lumen between its two ends is covered by a filter medium provided therein.

9. A filter element according to claim 8, characterized in that the pipe is substantially I cylindrical.