Device and method for processing solid particles

Abstract

The present invention relates to an installation for processing solid particles, in particular coal particles, comprising at least a first pneumatic conveyor (5) and a first sifter (6) provided with at least one screen capable of separating undersize particles, of dimensions smaller than a threshold, which pass through the screen, from rejected particles, of dimensions greater than the threshold, which remain on the screen and can be redirected towards a reject line (7). The installation is characterised in that the first sifter (6) is fed directly by the first pneumatic conveyor (5) such that the moving air of the first pneumatic conveyor (5) accompanies the undersize particles through the screen. The present invention also relates to a processing method that can be implemented in the installation of the invention.

Description

Device and method for treating solid particles

[0001] The present invention relates to the field of solid particles. It relates more particularly to an installation and a method for the treatment, in particular for the transport, purification, screening and grinding of solid particles, in particular of mineral or vegetable coal or other products rich in carbon and easily flammable.

[0002] Sieving solid particles involves confronting a flow of solid particles with a sieve; the aim is to force particles finer than a certain dimension through the sieve, and to retain particles larger than said dimension. However, it is known that some fine particles do not pass through the sieve, but are retained by the movement of the whole of the particles, and end up following the path of the large particles. There is therefore a need to find a solution so that as many of the fine particles as possible pass through the sieve.

[0003] We also know that coal has a tendency to spontaneously ignite upon contact with air. It is said to be self-igniting. Several treatments exist to prevent such self-ignition. In particular, the coal can be wetted, with the disadvantage that it becomes difficult or even impossible to purify it or carry out other separation operations.

[0004] Alternatively, a non-reactive gas such as nitrogen can be used to prevent ignition, as proposed in CN215755276, for example. This is costly, however, and reduces the risk only as long as the gas is present.

[0005] Document CN209382679 proposes sending fresh, preferably humid, air into a coal stock to prevent it from igniting. In addition to the same disadvantages as above, such a method does not allow the treatment of products with small particle sizes, since forced convection is then not possible.

[0006] Document JP2009079118 proposes pneumatic conveying of coal to bring it to a combustion furnace; it recommends cooling and watering the coal during conveying, to prevent it from igniting before reaching the combustion furnace.

[0007] All these solutions are not satisfactory and do not allow for complete screening, nor easy treatment of solid particles, particularly of coal in terms of purification or separation, and in addition, they only prevent a fire from starting during the treatment.

[0008] Therefore, there is a need for a system and method for treating solid particles, particularly a carbon, which allows purification and separation operations with good separation performance.

[0009] The present invention provides a method and a device for treating solid particles, in particular coal, which improves separation performance while preventing fires during and after treatment.

[0010] To do this, it proposes an installation for treating solid particles, in particular coal, comprising at least a first pneumatic conveyor and a first sieve provided with at least one sieve capable of separating passing particles, of dimensions less than a threshold, which pass through said sieve, from reject particles, of dimensions greater than said threshold, which remain on said sieve and can be redirected towards a reject pipe. This installation is particular in that said first sieve is supplied directly by the first pneumatic conveyor so that the moving air of the first pneumatic conveyor accompanies the passing particles through said sieve.

[0011] Thanks to these provisions, the installation can separate particles of different sizes more efficiently.

[0012] According to other characteristics: the first pneumatic conveyor may have a particle path length before arrival at the first sieve of at least 8 meters, preferably at least 10 meters, thus allowing oxidation of the exposed carbon atoms, which makes the coal non-reactive, and it no longer ignites, even after the end of the treatment, the installation may comprise an ultrasonic vibrator capable of inducing ultrasonic vibration to said sieve, thus making it possible to avoid or at least reduce the frequency of clogging of the sieve, the installation may further comprise a grinder capable of being fed by said reject pipe, and of grinding the reject particles into finer particles, and a second pneumatic conveyor which may or may not have a common part with the first pneumatic conveyor, configured to convey said finer particles to a second sieve, which may or may not be the first sieve,said second sieve being fed directly by the second pneumatic conveyor so that the moving air of the second pneumatic conveyor accompanies the fine particles through at least one sieve of said second sieve; such an arrangement, in addition to the above advantages, makes it possible to optimize the use of all the coal by reducing the particle size below a threshold where it can be used, while avoiding any risk of fire, the second pneumatic conveyor may have a particle path length between the outlet of the crusher and the arrival at the sieve of at least 8 meters, preferably at least 10 meters, thus ensuring the oxidation of the carbon atoms which have become exposed following grinding, and thus avoiding the risk of ignition of the particles obtained, the installation may comprise a densimetric separator, preferably of the zigzag type,configured to separate particles that are being conveyed in the first pneumatic conveyor, thus making it possible to remove foreign bodies, in particular metal, glass or stone.,

[0013] The present invention also relates to a method for treating solid particles, in particular coal, comprising the following steps: pneumatic conveying of the particles towards a first sieve, passage of a portion of the particles through said first sieve, the moving air of the pneumatic conveying passing through said first sieve, recovery of the rejects from the first sieve.

[0014] Thanks to these provisions, the process allows particles of different sizes to be separated more efficiently, while avoiding fires during treatment.

[0015] According to other characteristics: said pneumatic conveying of the particles to a first sieve occurs over a path length of at least 8 meters, preferably at least 10 meters, thus allowing in the case of coal an oxidation of the exposed carbon atoms, which makes the coal non-reactive, and it no longer ignites, even after the end of the treatment, the method may further comprise a densimetric separation step during pneumatic conveying, thus making it possible to remove foreign bodies, in particular metallic, glass or stone, the method may further comprise a step of grinding the rejects from the first sieve into finer particles, then pneumatic conveying of the finer particles to a second sieve, the first and second sieves may, or may not, be the same sieve;such an arrangement, in addition to the above advantages, makes it possible to optimize the use of all the coal by reducing the granulometry below a threshold where it can be used, while avoiding any risk of fire starting.;

[0016] The present invention will be better understood on reading the detailed description which follows, with reference to the appended figure: This is a schematic view of an installation according to a particular embodiment of the invention.

[0017] It represents a solid particle processing facility.

[0018] The invention will be described below considering that said solid particles are coal particles; the coal may be biochar, biocarbon, vegetable coal, mineral coal, graphite, etc. or any other carbon-rich, highly flammable material, such as coal. The invention relates in particular to any installation for treating solid coal particles, in particular light particles, with an apparent density of less than 0.8.

[0019] As described further, an installation according to the invention makes it possible to effectively separate particles of different particle sizes, and to ensure that the particles are neutralized, and thus no longer risk self-igniting; the invention thus applies particularly to the treatment of any carbon-rich and self-igniting material such as coal, such as, for example, biochar, biocarbon, vegetable coal, mineral coal and graphite.

[0020] The installation according to the invention may comprise a coal storage tank 1, for example with a volume of 100 m3. This tank may be equipped with a cooling system, for example by circulating water, to limit the risk of ignition at this stage. But throughout the installation, humidification of the coal particles will be avoided, to maintain their ability to be separated effectively by screening, and to be crushed to reduce their particle size.

[0021] The installation may comprise a conveyor capable of conveying the coal particles to a buffer tank 2, for example a bucket elevator 13.

[0022] The buffer tank 2 may consist, for example, of two tanks of 6 m3 each, which may facilitate the control of the installation; for example, one may wait until one of the two tanks is empty before filling it, while the other tank is used to supply the downstream part of the installation. The buffer tank 2 may be equipped with a honeycomb airlock 3 or any other flow control device at its lower end to control the flow rate of the material outlet from the buffer tank 2.

[0023] The installation may comprise at least one screw conveyor 4, arranged downstream of the buffer tank 2, configured in a known manner to collect the particles of material at the outlet of the buffer tank 2, and convey them to the rest of the installation.

[0024] The installation may comprise a first pneumatic conveyor 5, configured to convey the particles from the screw conveyor 4 and at least to a first sieve 6.

[0025] The first sieve 6 is configured to be fed from above, both by the coal particles, and by the air from the first pneumatic conveyor 5.

[0026] The first sieve 6 comprises at least one sieve, and may comprise several stages of sieves, for example four as in the example shown in. The cut-off dimension of the sieves is smaller as one goes towards the lower stages.

[0027] According to the invention, the first pneumatic conveyor 5 is connected to the first sieve 6, so that the air from the first pneumatic conveyor 5 passes through at least one sieve in the same direction as the passing particles, i.e. finer than the cut-off dimension of said sieve.

[0028] Such an arrangement allows the air from the pneumatic conveyor 5 to carry the finest particles through the sieve. Without this, the finest particles could remain suspended above the sieve and be lost in the atmosphere or leave with the rejects; which would produce a mixture of larger particles and finer particles, and would harm the quality of separation of the particle sizes.

[0029] According to another embodiment, the installation may comprise another type of conveyor, configured to convey the particles from the buffer tank 2 to the first sieve 6; it then comprises a supply of pressurized or moving air configured to produce a movement of air through the sieves in the same direction as the particles which pass through the sieve. According to this embodiment, it is considered in the context of the present invention that such an air supply is assimilated to a pneumatic conveyor effective at least on the movement of the particles upon arrival at the first sieve 6. It produces the same effect of driving the finest particles through a sieve.

[0030] The sieves can be operated by a vibrator, which facilitates the distribution of particles on the sieve, and allows the rejects to be gradually led towards the contours of the sieve, where they can be recovered by a reject pipe 7.

[0031] Said vibrator may for example comprise a vertical component, the function of which is to bounce the rejects on the sieve, and a horizontal component, the function of which is to gradually push the rejects towards the circumference, where the reject pipe 7 is then located. These two components may for example be obtained by two eccentric rollers.

[0032] The screens are preferably horizontal, to facilitate the routing of the rejects towards the reject pipe 7.

[0033] According to a preferred embodiment of the invention, the first sieve 6 may further comprise an ultrasonic vibration device, capable of inducing an ultrasonic vibration in at least one sieve, making it possible to reduce the risks of clogging of said sieve.

[0034] According to a preferred embodiment of the invention, it can be ensured that the particles transported by the first pneumatic conveyor 5 travel a distance of at least 8 meters, preferably at least 10 meters before their arrival in the first sieve 6. Such a distance allows time for the coal particles to undergo neutralization, by oxidation of the exposed carbon atoms. Once these exposed carbon atoms are oxidized, the coal is no longer reactive to air, and therefore no longer risks catching fire; it is neutralized, that is to say that its self-ignition has been treated and controlled.

[0035] In fact, the inventor carried out numerous tests, and he noticed that with lengths of less than 8 meters of pneumatic conveying, a fire could always start, whereas from 8 meters he never observed one. Taking into account the various parameters of pneumatic transport, we can in any case affirm that beyond 10 meters of pneumatic transport, the coal is well neutralized, and there is no longer any risk of fire starting.

[0036] The reject line 7 can be configured to conduct the rejects to a grinder 8, which grinds the reject particles, i.e. those which do not pass through the corresponding sieve, into finer particles.

[0037] A honeycomb airlock 9 or any other device may be placed before the crusher 8 to extract the coal while limiting air loss.

[0038] At the outlet of the crusher 8, a second pneumatic conveyor 5 is provided according to the invention, configured to convey the particles obtained to a second sieve 6. According to a preferred embodiment of the invention, they can be conveyed to the first sieve 6; in this embodiment, the second sieve 6 will be said to be the first sieve 6.

[0039] A portion of the second pneumatic conveyor 5 may consist of a portion of the first pneumatic conveyor 5; the second pneumatic conveyor 5 then simply conveys the particles to an inlet in the first pneumatic conveyor 5.

[0040] It is also possible to provide a simple gravity conduit, or any other solution, which conveys the particles to an inlet of the first pneumatic conveyor 5.

[0041] As shown in the, a screw conveyor 4 can be arranged to recover the particles from one or more grinders 8, and introduce them into the first pneumatic conveyor 5.

[0042] According to another particular embodiment of the invention, it can be ensured that the particles leaving the grinders 8 travel a distance of at least 8 meters, preferably at least 10 meters in the second pneumatic conveyor 5; this condition is respected if the ground particles are recovered at the inlet of the first pneumatic conveyor 5 as illustrated in the, and that the first pneumatic conveyor 5 has a length of at least 8 meters, preferably at least 10 meters.

[0043] This condition can be important because during grinding, the particles are broken into several parts, and new carbon atoms are exposed. Such a distance will again ensure the neutralization of the new particles. Depending on the type of grinding, it will be more or less important to maintain this distance after grinding. In some cases, a shorter distance may be sufficient.

[0044] A densimetric separator 10, preferably zigzag, can be placed in the first pneumatic conveyor 5 to separate the foreign bodies and cause them to fall into a receptacle 11 provided for this purpose.

[0045] Such a densimetric separator 10 may consist of dishes arranged in the enclosure of the first pneumatic conveyor 5, so as to deflect the flow of particles several times, in a zigzag, which promotes the separation of foreign bodies heavier than the coal particles. Most foreign bodies are generally heavier than coal, in particular foreign bodies made of stone, steel and glass, and such a solution generally makes it possible to purify the coal satisfactorily.

[0046] The first sieve 6 may comprise several stages of sieves, the particles passing through the upper sieve being confronted with a second sieve arranged just below. This second sieve also has a reject pipe 7, making it possible to recover the particles which do not pass this sieve.

[0047] Such a reject pipe 7 can then lead the particles to another crusher 8, with finer grinding, or even to a final storage facility, for example a big bag 12, which will collect the particles with a granulometry between the cut-off thresholds of the first two sieves. Here too, a honeycomb airlock 9 or any other device can be used to extract the coal while limiting air loss.

[0048] An installation according to the invention thus makes it possible to obtain an efficient and precise separation of the particles according to their granulometry; for example, on one side, particles with dimensions less than 0.1 mm can be obtained, in another container those with dimensions between 0.1 and 0.3 mm, in yet another, those between 0.3 and 0.6 mm, and in a fourth, those between 0.6 and 1 mm; in such an example, a grinder 8 is provided making it possible to reduce the size of all particles with dimensions greater than 1 mm.

[0049] In the example shown in , three sieves are arranged one below the other; the rejects from the upper sieve, for example of a dimension greater than 1 mm, are sent to a first crusher 8. The crushed particles are then collected by a screw conveyor 4, and conveyed to the pneumatic conveyor 5, which recycles them to the sieve 6.

[0050] The passers-by from the upper sieve arrive at the intermediate sieve; the rejects from the intermediate sieve are collected in a reject pipe 7; from there a diverter can, depending on the treatment objectives, send the particles to a second crusher 8, from where the crushed particles will be conveyed to the sieve 6, by means of the screw conveyor 4 and the pneumatic conveyor 5, or to a big bag 12 storing for example the particles of dimensions between 0.6 and 1 mm.

[0051] The passers-by from the intermediate sieve arrive at the lower sieve; the rejects from the lower sieve are collected in a reject pipe 7; from there a diverter can, depending on the treatment objectives, send the particles to a third crusher 8, from where the crushed particles will be conveyed to the sieve 6, by means of the screw conveyor 4 and the pneumatic conveyor 5, or to a big bag 12 storing for example particles with dimensions between 0.3 and 0.6 mm.

[0052] The crushers 8 may be tooth, roller, ball, attrition, or other techniques, depending on the flow rates, input particle sizes, and output particle sizes targeted or other parameters.

[0053] The particles passing the third sieve of the first sieve 6 can be sent to a filter 14, in which all the remaining particles are collected, and the air is allowed to escape from the pneumatic conveyor. The remaining particles are then directed, for example, to another big bag 12 storing, for example, particles with dimensions less than 0.3 mm, and the supply pipe to this big bag 12 can also be equipped with a honeycomb airlock 9 to limit air losses.

[0054] According to another embodiment, the particles passing the third sieve of the first sieve 6 can be transported to a second sieve 6, which may or may not have several sieve stages, and / or grinders 8; such a second sieve 6 can make it possible to collect other granulometries of coal particles, and thus make it possible to offer a wide variety of different products at the outlet of the installation. The particles passing the last sieve of the second sieve 6 can then be sent to the filter 14. This makes it possible, for example, to collect separately particles with dimensions less than 0.1 mm, and on the other hand those with dimensions between 0.1 and 0.3 mm.

[0055] According to a preferred embodiment of the invention, the entire chain, pneumatic conveyor 5, sieve(s) 6 where applicable on its different stages, the reject pipes 7, where applicable up to their airlock 9, the pipe to a filter 14 and the outlet of the filter 14 can be subjected to a continuous air flow from one end of the chain to the other. There is of course air which escapes, in particular at the airlocks 9, but one or more pumps are adjusted so that there is always an air flow accompanying the passing particles, and sufficient air flow to ensure the transport of the particles.

[0056] Although the above description is based on particular embodiments, it is in no way limiting of the scope of the invention, and modifications may be made, in particular by substitution of technical equivalents or by different combination of all or part of the characteristics developed above. The scope of the invention is defined by the following claims.

Claims

Installation for treating coal particles, comprising at least a first pneumatic conveyor (5) and a first sieve (6) provided with at least one sieve capable of separating passing particles, of dimensions less than a threshold, which pass through said sieve, from refuse particles, of dimensions greater than said threshold, which remain on said sieve and can be redirected towards a refuse pipe (7), characterized in that said first sieve (6) is supplied from above directly by the first pneumatic conveyor (5) so that the moving air of the first pneumatic conveyor (5) accompanies the passing particles through said sieve. Installation according to the preceding claim, in which the first pneumatic conveyor (5) has a path length of the particles before arrival at the first sieve (6) of at least 8 meters, preferably at least 10 meters. Installation according to one of the preceding claims, in which the sieve (6) comprises a vibrator, designed to induce a vibration in the at least one sieve, preferably a vibration having both a vertical component and a horizontal component. Installation according to one of the preceding claims, comprising an ultrasonic vibrator capable of inducing an ultrasonic vibration in said sieve. Installation according to one of the preceding claims, further comprising a grinder (8) capable of being supplied by said reject pipe (7), and of grinding the reject particles into finer particles, and a second pneumatic conveyor (5) which may or may not have a common part with the first pneumatic conveyor (5), configured to convey said finer particles to a second sieve (6), which may or may not be the first sieve (6), said second sieve (6) being supplied directly by the second pneumatic conveyor (5) so that the moving air of the second pneumatic conveyor (5) accompanies the fine particles through at least one sieve of said second sieve (6). Installation according to the preceding claim, in which the second pneumatic conveyor (5) has a particle path length between the outlet of the crusher (8) and the arrival at the second sieve (6) of at least 8 meters, preferably at least 10 meters. Installation according to one of the preceding claims, comprising a densimetric separator (10), preferably of the zigzag type, configured to separate particles which are being conveyed in the first pneumatic conveyor (5). A method of treating coal particles, comprising the following steps: pneumatic conveying of the particles to a first sieve, feeding said first sieve from above, passing a portion of the particles through said first sieve, the moving air of the pneumatic conveying passing through said first sieve, recovery of the rejects from the first sieve. The method of claim 8, wherein said pneumatic conveying of particles to a first sieve occurs over a path length of at least 8 meters, preferably at least 10 meters. Method according to one of claims 8 to 9, further comprising a step of grinding the rejects from the first sieve into finer particles, then pneumatically conveying the finer particles to a second sieve, the first and second sieves possibly being the same sieve or not.

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