NL1037826C2

NL1037826C2 - Method for treating a quantity of material containing asbestos particles.

Info

Publication number: NL1037826C2
Application number: NL1037826A
Authority: NL
Inventors: Robin Marco Smit; Arend Mulder; Mark Hendrikus Aloysius Leerkotte
Original assignee: A & G Milieutechniek B V
Priority date: 2010-03-24
Filing date: 2010-03-24
Publication date: 2011-09-27

Description

Title: Method for treating a quantity of material containing asbestos particles

The invention relates to a method for treating a quantity of material in which asbestos particles and other particles of the same order of magnitude as the asbestos particles are present, in order to separate the asbestos particles from the other particles.

5 It is a known fact that asbestos is considered a dangerous material. Still, it can be found in many buildings, and also in rubble paths, for example.

In the field of waste processing, materials like rubble, soil and gravel containing asbestos particles cannot be handled (reused) according to standard procedures if the percentage of asbestos is higher than a predetermined maximum, 10 which is often the case in practice. In view of this fact, there is a great need for methods which are suitable to be used for separating asbestos particles from the other particles in the material. Conventionally, sieving techniques are used for separating particles having different dimensions from each other. The problem with materials like rubble, soil and gravel containing asbestos particles is that the 15 dimensions of the asbestos particles are often not significantly different from the dimensions of other particles. Hence, using a standard sieving technique cannot result in a separation of an asbestos fraction from the rest of the material.

It is an object of the invention to provide a method for separating asbestos particles from a quantity of material, which is suitable for realizing an effective 20 separation of the asbestos particles from other particles which are contained by the quantity of material, even in cases where the dimensions of the asbestos particles are in the same order of magnitude as the dimensions of the other particles.

The object of the invention is achieved by a method in which a bar sieve is applied, in particular a bar sieve which has bars at at least two different levels, 25 wherein the bars of the different levels have mutually shifted positions, seen in a direction perpendicular to a direction in which the bars are extending, and parallel to tangent planes of the bars at each of the different levels, and wherein the quantity of material is led over the bar sieve.

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The present invention is based on the insight that the asbestos particles are normally shaped like a plate, whereas the other particles are not. By using a bar sieve as mentioned, i.e. a bar sieve having bars at at least two different levels, wherein the bars of the different levels have mutually shifted positions, it is achieved 5 that the asbestos particles can be separated from the other particles. The reason is that the asbestos particles can be made to tilt and thereby pass through an opening between two bars of two different levels, like a letter through an opening of a mailbox, as it were, while the other particles, which are not shaped like a plate and which do not have a relatively small dimension in one direction, cannot pass through 10 the opening as mentioned, provided that the size of the opening is chosen properly.

In particular, the opening should be large enough to allow the plate-shaped asbestos particles to pass in a particular tilted condition, and small enough to block the particles having a shape which is more sphere-like than plate-like, in which all dimensions are larger than the relatively small dimension of the plate-shape, even if 15 the overall dimension of the particle is in the same order of magnitude than the overall dimension of the plate-shaped particle.

In order to ensure that the asbestos plates will perform the tilting movement which is necessary for passing between the bars of two different levels, it is preferred if the bar sieve is vibrated. Due to the vibration, all particles are made to move over 20 the bar sieve. In the process, the asbestos plates jump on bars which are located at a highest level in the sieve. As soon as it occurs that a portion of an asbestos plate is protruding with respect to a bar and is not supported by another bar, a tilting movement takes place, as a result of which the plate slips between bars of two different levels.

25 Preferably, in order to stimulate movement of the particles over the bar sieve, the bar sieve is oriented such as to be at an angle with the horizontal.

In a practical embodiment of the bar sieve which is applied in the method according to the invention, an imaginary connection line between two bars of successive levels, which are located next to each other, is at an angle with the 30 tangent planes of the bars in each of the levels concerned which is in an order of magnitude of 30 degrees. Tests which have been performed in the context of the invention have proven such an embodiment of the bar sieve to be effective, wherein it is very well possible to actually have the tilting movement of the asbestos plates which is needed for letting those plates pass the sieve.

3

Taking into account common dimensions of asbestos particles and other particles in a quantity of material, which may be rubble from a rubble path, for example, a suitable distance between two bars of successive levels, located directly next to each other, is a distance in a range of 0.6 cm to 2.0 cm. Tests which were 5 performed in the context of the invention have proven that 1.8 cm is a practical possibility within this range.

When the method according to the invention is carried out, it is achieved that asbestos particles pass the bar sieve which is used in the process, while particles of the same order of magnitude stay behind. When relatively small particles are present 10 in the quantity of material, these particles pass the bar sieve as well. In order to separate the particles which have passed the bar sieve from the asbestos particles, it is advantageous to use an additional sieve, which is positioned underneath the bar sieve. The sieve may be a conventional sieve having a plurality of square or rectangular openings, or circular openings, for example. In any case, the sieve may 15 be designed such that a largest internal dimension of the openings is in an order of magnitude of a distance between two bars of successive levels of the bar sieve, located directly next to each other, wherein it is possible for the largest internal dimension of the openings to be a few millimeters larger than the distance as mentioned. On the basis of such dimensioning of the openings of the additional 20 sieve, it is achieved that the asbestos particles cannot pass the sieve, as the dimensions of their main body surfaces, i.e. surfaces which can be denoted as constituting a top surface and a bottom surface of the plate-shape, are too large, whereas the other particles can. In this way, the asbestos particles are separated from all the other particles of the quantity of material, including the relatively small 25 particles. For sake of completeness, it is noted that there is a maximum to the size of the openings of the additional sieve, which is determined by the fact that the additional sieve should be capable of allowing only other particles than asbestos particles to pass.

It follows from the foregoing that the invention provides a practical way of 30 separating asbestos particles from a quantity of material. The invention is especially applicable in situations in which the separating process cannot simply be performed by using conventional sieves and making a distinction between particles on the basis of differences in size. The invention proposes to use a sieve which is a bar sieve, and which has bars at different levels and with a shifted positioning, so that the 4 asbestos particles can pass through the sieve on the basis of being plate-shaped and being capable of sliding between bars of different levels when performing a suitable tilting movement.

In practical applications of the present invention, it is advantageous if the 5 treatment of the asbestos-containing material takes place under conditions of underpressure.

The invention will be further explained on the basis of the following description of a bar sieve which is suitable to be used in a process of separating asbestos r 10 particles from a quantity of material, with reference to the drawing, in which equal reference signs indicate equal or similar components, and in which: figure 1 shows a number of bars of the bar sieve; and figures 2-4 illustrate the way in which an asbestos particle is made to pass the bar sieve.

15

Figure 1 shows a number of bars 10 of a bar sieve 1 which is suitable to be used for the purpose of carrying out the method according to the invention, which is aimed at processing a quantity of material containing both asbestos particles and particles of the same order of magnitude as the asbestos particles, in such a way that 20 a separation is made between the asbestos particles and the other particles which are contained by the quantity of material.

The shown example of the bar sieve 1 has particulars as described in the following. The bars 10 of the bar sieve 1 are arranged at two levels. In figure 1, the levels of the tangent planes associated with the two levels are indicated by means of 25 dashed lines and reference signs 11 and I2, wherein the reference sign 11 is used to indicate the level of the highest tangent plane, and wherein the reference sign I2 is used to indicate the level of the lowest tangent plane. For sake of clarity, it is noted that in this text, the tangent plane of an arrangement of bars 10 at a particular level is an imaginary plane touching all the bars 10 of that level at a top side.

30 Figure 1 clearly shows that the bars 10 are extending substantially parallel with respect to each other, in a regular pattern. This is not essential within the scope of the present invention, yet it is practical. Furthermore, the patterns in which the bars 10 are arranged at the different levels are shifted with respect to each other, seen in a direction perpendicular to longitudinal axes of the bars 10, and parallel to 5 the tangent planes. In the shown example, a bar 10 of one level is arranged halfway between two bars 10 of another level.

In figure 1, the distance between two bars 10 at the same level is indicated by reference sign d1, and the distance between two bars 10 of different levels, which 5 are located directly next to each other, is indicated by reference sign d2. In the following, for sake of clarity, the first distance will be referred to as bar interspace distance, and the second distance will be referred to as bar interlevel distance.

A practical value of the bar interlevel distance is 1.8 cm. Furthermore, a practical value of an angle a between an imaginary line connecting two bars of 10 different levels, located directly next to each other, which line is diagrammatically depicted as a dashed line i in figure 1, and the tangent planes is 30 degrees. Hence, in the embodiment as described, the value of the bar interspace distance equals 2 * cos(30°) * 1.8 cm = 3.12 cm.

On the basis of the foregoing, it is clear that a first dimension of openings in 15 the bar sieve 1 for letting pass particles is 1.8 cm, and that a second dimension of the openings equals the length of the bars 10, which may be any suitable dimension for having a bar sieve which is capable of handling a quantity of material such as rubble or a mixture of soil and gravel, for example, a dimension in an order of magnitude of a meter.

20 An example of a quantity of material containing asbestos is rubble taken from certain rubble paths. In such a case, an overall size of the particles of the rubble, including the asbestos particles, is about 5 to 6 centimeters. By applying the bar sieve 1 as described in the foregoing, the asbestos particles can be separated from the other particles, wherein it is possible to obtain clean rubble in which the content 25 of asbestos is below 100 milligram per kilogram of rubble.

According to the invention, the asbestos particles are separated from other particles on the basis of their plate-like shape. Figures 2-4 illustrate the process which takes place when a quantity of material such as rubble is made to move over the bar sieve 1. At a certain moment in the process, an asbestos plate 20 ends up in 30 a position in which it is possible for the plate 20 to tilt about a bar 10 of the highest level. This position, which is a position in which an end portion of the plate 20 is not supported by any of the bars 10, is shown in figure 2.

Initially, the asbestos plate 20 has an orientation which is most stable, i.e. an orientation in which the plate 20 has a flat position on the bar sieve 1, as illustrated in 6 figure 2. When the asbestos plate 20 tilts around one of the bars 10, the plate 20 is capable of passing underneath an adjacent bar 10 of the highest level and passing above a nearest bar 10 of the lowest level. The asbestos plate 20 is thinner than 1.8 cm, and therefore, it is possible for the plate 20 to pass the sieve 1 in a tilted 5 condition. Figure 3 shows how the asbestos plate 20 is tilted, and figure 4 shows how the asbestos plate 20 actually falls through the bar sieve 1.

The sieving process is performed very well when a bar sieve 1 as described in the foregoing is applied and vibrated, so that the particles continuously jump up and down on the sieve 1, and continuously assume random positions on the sieve 1. In 10 this way, it is achieved that every asbestos plate 20 reaches a position for tilting at some point. Advantageously, the design of the sieve 1 is such that the positioning of the bars 10 allows for a smooth passage of the asbestos plates 20, while blocking a large amount of other particles. In fact, only the asbestos plates 20 and particles having a diameter which is smaller than 1.8 cm are capable of moving from a top 15 side of the bar sieve 1 to a bottom side.

It is desirable to separate the asbestos particles from the relatively small particles which have fallen through the bar sieve 1 as well. In view of this fact, it is advantageous to apply an additional sieve (not shown), which is arranged underneath the bar sieve 1, and which has openings adapted to allow the particles 20 which could pass the bar sieve 1 along with the asbestos particles 20 to pass. To that end, the openings have a diameter which is approximately the same as the small dimension (i.e. 1.8 cm) of the openings of the bar sieve 1, or which is slightly larger. The additional sieve does not need to be a bar sieve, but can be a sieve having circular openings, or square openings, for example. In any case, the asbestos 25 particles 20 cannot pass such a sieve as long as there is no configuration of elements in the sieve which might cause a tilting movement of the particles 20, and even if there would be such configuration, a width and/or length dimension of the main body surfaces of the particles 20 would be too large. The asbestos particles 20 rest like discs in a flat position on the sieve surface of such an additional sieve, and 30 stay behind, while the other particles fall through. On the basis of this effect, the asbestos particles 20 are isolated, and can be separately processed further.

For sake of completeness, it is noted once again that the dimensions and other details of the bar sieve 1 mentioned in the foregoing are not essential. It is important that the sieve 1 is adapted for causing the asbestos plates 20 to tilt and for 7 allowing the asbestos plates 20 to reach an opening in their tilted position, which opening is large enough for letting pass the asbestos plates 20 when these plates 20 are supplied with a sideward movement, wherein the relatively small thickness of the plates 20 is the determining factor.

5 Different applications of the bar sieve 1 may require different distances between the bars 10. Adapting the design of the bar sieve 1 in view of another application may involve placing the bars 10 closer to each other or further away from each other, but it may also be practical to only increase or decrease the diameter of the bars 10. As long as a centre-to-centre distance between the bars 10 at the 10 highest level remains the same, the dimensions of a zone in which asbestos plates can be made to tilt remain the same as well. In this way, it is possible to decrease the distance between the bars 10, for example, thereby blocking larger particles, and still allow all asbestos plates to pass. If the centre-to-centre distance between the bars 10 at the highest level would be decreased, there would be a risk that the 15 largest asbestos plates would not be able to pass the bar sieve 1 any more, namely when the decreased centre-to-centre distance results in a continuous support of such plates by the bars 10 as mentioned during a movement of the plates over the bar sieve 1.

In practical situations, the bar sieve 1 can be composed of two identical 20 sieves, wherein one sieve is arranged underneath another, and wherein the sieves are shifted with respect to each other, seen in the direction perpendicular to the longitudinal axes of the bars 10, and parallel to the sieve surfaces of the sieves. When two sieves are used for composing a sieve with bars 10 at two levels, it is possible to have an adjustable positioning of the sieves, so that it is possible to adapt 25 the configuration of the composed sieve and to meet various requirements of actual situations of treatment of a quantity of material such as a mixture of soil and gravel.

In particular, the extent to which the sieves are shifted with respect to each other can be adjustable and/or the mutual distance of the sieves can be adjustable, so that the size of the openings between bars 10 at different levels can be varied.

30

It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims.

8

The present invention can be carried out in respect of various types of material containing asbestos particles, i.e. asbestos-contaminated material. Examples include rubble, soil and gravel as mentioned, and also a mixture of soil and gravel as mentioned, or, in general terms, a coarse soil fraction.

5 -

The invention can be summarized as follows. In a process of separating asbestos particles 20 from other particles in a quantity of material, a bar sieve 1 is applied. A particular aspect of this bar sieve 1 is that the bars 10 are arranged at at least two levels, wherein the bars 10 of the different levels are shifted with respect to 10 each other in a direction perpendicular to the longitudinal axes of the bars 10, and parallel to the tangent planes of the bars 10 at each of the different levels. On the basis of this configuration of the bar sieve 1, and the fact that the asbestos particles 20 are plate-shaped, it is achieved that the asbestos particles 20 are tilted and are made to pass between the bars 10 of successive levels of bars 10. Hence, the 15 asbestos particles 20 are passed through the sieve 1 in an orientation which is at an angle with respect to the vertical, wherein the asbestos particles 20 are moving in a direction more or less parallel to a direction in which their main body surfaces are extending. In fact, the relatively small thickness of the asbestos particles 20 is used as a discrimination factor for separating the asbestos particles 20 from other 20 particles which are of approximately the same size of the asbestos particles 20, but which do not have the relatively small dimension.

For the purpose of separating the asbestos particles 20 from relatively small particles which have fallen through the bar sieve 1 along with the asbestos particles 20, an additional sieve is applied, which is designed such as to be capable of 25 allowing the relatively small particles to pass, while blocking the asbestos particles 20 on the basis of the dimensions of their relatively large main body surface. Hence, in the additional sieve, it is the difference between the diameter of the non-asbestos particles and the dimensions of the main body surfaces of the asbestos particles 20 which causes a separation between the two types of particles.

1037826

Claims

A method for treating an amount of material containing asbestos particles (20) and other particles of the same order of magnitude as the asbestos particles (20), in particular separating the asbestos particles (20) from the other particles, wherein a rod sieve (1) is used, in particular a rod sieve (1) which has rods (10) on at least two different levels, the rods (10) of the different levels having positions shifted relative to each other, seen in a direction perpendicular to a direction in which the rods (10) extend, and parallel to interfaces of the rods (10) at each of the different levels, and wherein the amount of material is passed over the rod-screen (1).

Method according to claim 1, wherein the rod sieve (1) is made to vibrate.

Method according to claim 1 or 2, wherein the rod sieve (1) is held at an angle to the horizontal.

4. Method according to any of claims 1-3, wherein a rod sieve (1) is used in which an imaginary connecting line (i) between two directly adjacent rods (10) of successive levels, an angle (a) in an order size of 30 degrees with the interfaces of the rods (10) at the respective levels.

5. Method according to any of claims 1-4, wherein a rod screen (1) is used in which a distance (d2) between two directly adjacent rods (10) of successive levels in a range of 0.6 cm up to 2.0 cm.

6. Method according to claim 5, wherein a rod sieve (1) is used in which there is a distance (d2) of an order of 1.8 cm between two directly adjacent rods (10) of successive levels. 1037826

Method according to any of claims 1-6, wherein a rod sieve (1) is used which is composed of at least two rod sieves, each of which has rods (10) on a single level, and which are movable relative to each other in order to vary the configuration of the assembled rod screen (1).

A method according to any one of claims 1-7, wherein an additional screen is used, which is held below the rod screen (1), and which has openings whose largest internal dimension is in an order of magnitude of a distance (d2) between two directly adjacent rods (10) of successive levels of the rod sieve (1) are located.

9. Method according to any of claims 1-7, wherein an additional screen is used, which is held under the rod screen (1), and which has openings 15 whose largest internal dimension is at most a few millimeters greater than a distance (d2) between two directly adjacent rods (10) of successive levels of the rod sieve (1).

10. Use of a rod screen (1) for treating an amount of material containing asbestos particles (20) and other particles of the same order of magnitude as the asbestos particles (20), in particular separating the asbestos particles (20) of the other particles, which rod screen (1) has rods (10) on at least two different levels, the rods (10) of the different levels having positions shifted relative to each other, viewed in a direction perpendicular to a direction in which the rods (10) extend, and parallel to interfaces of the rods (10) at each of the different levels. 1037826