Facility for grinding ultrafine mineral material

Abstract

The invention relates, inter alia, to a grinding method for obtaining a fine fraction (12) and an ultrafine fraction (14) from a mineral material (10), the method comprising the following steps: - a mineral material (10) is ground by means of at least one grinder (2), providing a ground material (11); - the ground material (11) is separated into a fine fraction (12) and a coarse fraction (13) by means of the first selector device (3); - at least a portion (12a) of the fine fraction (12) is separated into an ultrafine fraction (14) and a residual fraction (15) by means of a second selector device (4); - at least a portion (15b) of the residual fraction (15) is sent to the grinder (2) in order to be ground, or alternatively at least a portion (15ba) of the residual fraction (15) is mixed with the remainder (12b) of the fine fraction (12).

Description

Ultrafine mineral material grinding plant

[0001] The invention relates to the field of grinding mineral matter, such as that used for the manufacture of binders, for example cement, or blast furnace slag.

[0002] The invention relates more particularly to a grinding process for obtaining a fine fraction and an ultrafine fraction from a mineral material. It also relates to a grinding installation suitable for obtaining such a fine fraction and such an ultrafine fraction.

[0003] Context of the invention

[0004] A plant for grinding mineral material to obtain a fine or ultrafine fraction comprises at least one mill and a particle size selection device, also known as a sorting device. In a grinding cycle, the material ground by the mill is directed to the sorting device, where the ground material is classified to obtain two distinct particle size fractions: a first fraction with a particle size smaller than the cut-off mesh, corresponding to the desired product, and a second fraction with a particle size larger than the cut-off mesh. This second fraction is then returned to the mill for the next cycle.

[0005] To obtain a fine fraction and an ultrafine fraction of a mineral material, two grinding plants or two separation plants are usually used in series. A first grinding plant is initially used to obtain a fine fraction from the ground mineral material. Then, a second plant is used to obtain an ultrafine fraction from the fine fraction produced in the first plant.

[0006] Using two separate grinding facilities to obtain a fine fraction followed by an ultrafine fraction results in significant operating costs.

[0007] Furthermore, the installation used to achieve the desired ultrafine fraction requires a complex configuration. In particular, the fine fraction received by the second installation is already of a very fine particle size, so the grinding performed by the second installation is degraded in terms of both performance and energy cost. The operating stability of the mill is also significantly impacted.

[0008] The invention aims to address these problems and proposes an improved process for obtaining a fine fraction and an ultrafine fraction from a mineral material.

[0009] To this end, the invention relates, according to a first aspect, to a grinding process for obtaining a fine fraction and an ultrafine fraction from a mineral material, implemented in a grinding installation comprising:

[0010] - at least one crusher capable of grinding said mineral material into a granulate, and

[0011] - a first particle size selection device, called the first selector device, capable of separating said crushed material into two fractions, namely a fine fraction and a coarse fraction, said coarse fraction being returned to said crusher,

[0012] - a second particle size selection device, called a second selection device, capable of separating at least part of said fine fraction into two fractions, namely an ultrafine fraction and a residual fraction,

[0013] said process includes the following steps:

[0014] - the said mineral material is ground using at least one crusher, obtaining a ground material,

[0015] - the ground material is separated into the said fine fraction and the said coarse fraction by means of the said first selecting device,

[0016] - at least a portion of said fine fraction is separated into said ultrafine fraction and said residual fraction by means of said second selecting device,

[0017] - at least part of the residual fraction is directed to the crusher to be crushed, and / or at least part of the residual fraction is mixed with the remainder of said fine fraction.

[0018] The fine fraction not directed towards the second separator allows the first finished product to be obtained.

[0019] The ultrafine fraction corresponds to a second finished product.

[0020] Thus, it is possible to supply a first finished product and a second finished product from the same grinding installation simultaneously and continuously.

[0021] The installation allows for adaptation to the required quality of the first and second finished products, as well as to the respective production rates of these finished products.

[0022] The required quality of the first and second finished products refers to the particle size distribution of each finished product. Specifically, with regard to the first finished product, the invention allows for control of the proportion of ultrafines in that finished product.

[0023] For example, if the first finished product requires a significant proportion of ultrafines, then the proportion of the residual fraction sent to the mill will be increased for regrinding, thereby generating more ultrafines. As an illustration of this example, one might expect to produce a first finished product such as ground blast furnace slag intended for use as a reactive additive in cement or concrete production. In this case, a predetermined quantity of ultrafines is required.

[0024] Using two particle size sorting devices in series with the same mill in a single grinding plant reduces the production cost of ultrafine material. Furthermore, regrinding at least part of the residual fraction by mixing it with the mineral material prevents degradation of the mill's efficiency and stability.

[0025] By directing at least part of the residual fraction to the crusher for grinding, and / or by mixing at least part of the residual fraction with the remainder of said fine fraction, it is possible to obtain three configurations of the installation:

[0026] - either a first configuration in which all or part of the residual fraction is directed to the crusher to be crushed, without any part of the residual fraction being mixed with the remainder of said fine fraction,

[0027] - or a second configuration in which all or part of the residual fraction is mixed with the remainder of said fine fraction, without any part of the residual fraction being directed to the crusher to be crushed,

[0028] - or a third configuration in which at least part of the residual fraction is directed to the crusher to be crushed, and the other part of the residual fraction is mixed with the remainder of said fine fraction.

[0029] According to one embodiment of the invention, at least a part of said fine fraction corresponds to a range of values ​​between 10% and 70% of the fine fraction separated by the first selector device, preferably between 40% and 60%.

[0030] It has been found that such ranges of values, preferably between 10% and 70%, and even more preferably between 40% and 60%, allow for the production of between 1% and 30%, and between 2% and 20%, of ultrafines on the total production produced by the installation (including fines and ultrafines), while allowing for energy optimization of the installation compared to the known solution with two grinding installations.

[0031] According to one embodiment of the invention, at least a part of said residual fraction corresponds to a range of values ​​between 0% and 100% of the residual fraction separated by the second selector device, preferably between 40% and 100%, even more preferably between 80% and 100%.

[0032] It has been observed that such a range of values, preferably between 40% and 100%, and even more preferably between 80% and 100%, allows for minimal degradation of the quality of the fines produced by the installation (i.e., the fines, produced as the first finished product, have a proportion of undegraded ultrafines), while optimizing the overall efficiency of the installation.

[0033] According to one embodiment of the invention, in the grinding stage, the mineral material is ground by impact.

[0034] According to one embodiment of the invention, in the grinding step, the mineral material is ground by compression of a bed of material.

[0035] According to a second aspect, the invention relates to a grinding installation for obtaining a fine fraction and an ultrafine fraction from a mineral material comprising:

[0036] - at least one crusher capable of grinding said mineral material into a granulate, and

[0037] - a first particle size selection device, called the first selector device, capable of separating said mineral material into two fractions, namely a fine fraction and a coarse fraction, said coarse fraction being returned to the crusher,

[0038] - a second particle size selection device, called a second selection device, capable of separating at least part of said fine fraction into two fractions, namely an ultrafine fraction and a residual fraction,

[0039] - a first circuit to direct at least part of the fine fraction from the first selector device to the second selector device,

[0040] - a second circuit for steering:

[0041] - at least a portion of the residual fraction from the second selector device, to the first circuit to be mixed with the remainder of said fine fraction; and / or

[0042] - at least part of the residual fraction from the second selector device to the crusher to be crushed.

[0043] The remainder of said fine fraction is understood to mean the fine fraction from the first particle size selection device subtracted from said fine fraction at least a part of the fine fraction intended for the second particle size selection device.

[0044] By providing a second circuit to direct: - at least part of the residual fraction from the second selector device to the first circuit to be mixed with the remainder of said fine fraction; and / or - at least part of the residual fraction from the second selector device to the crusher to be crushed, it is possible to obtain three configurations of the installation:

[0045] - either a first configuration in which all or part of the residual fraction from the second selector device is directed to the crusher to be crushed, without any part of the residual fraction being mixed with the remainder of said fine fraction,

[0046] - either a second configuration in which all or part of the residual fraction is directed to the first circuit to be mixed with the remainder of said fine fraction, without any part of the residual fraction being directed to the crusher to be crushed,

[0047] - or a third configuration in which at least part of the residual fraction is directed to the crusher to be crushed, and the other part of the residual fraction is directed to the first circuit to be mixed with the remainder of said fine fraction.

[0048] According to one embodiment of the invention, the installation includes a control device to direct the fine fraction towards the second selector device and / or towards a material outlet of the first circuit.

[0049] According to one embodiment of the invention, the installation includes a control device to direct the residual fraction towards the crusher and / or towards a material outlet of the first circuit.

[0050] The use of the control device(s) allows the quantity of fine fraction taken and / or the quantity of residual fraction taken to be adjusted according to the type of mineral material to be ground and according to a compromise between the need for concentration of residual fraction and the stability of the grinding of the installation.

[0051] According to one embodiment of the invention, the crusher is a ball mill.

[0052] According to one embodiment of the invention, the crusher is a crusher among: a roller press, a vertical crusher or a horizontal roller crusher.

[0053] According to one embodiment of the invention, the first selector device comprises a dynamic separator.

[0054] According to one embodiment of the invention, the second selector device includes a dynamic separator.

[0055] Advantageously, a dynamic separator includes an envelope comprising:

[0056] - a rotor equipped with blades on its periphery configured to propel a portion of the material contained in the suspended material stream by centrifugal force,

[0057] - a set of blades surrounding the rotor configured to guide a flow of suspended material towards the blades.

[0058] Other features and advantages of the invention will become apparent during the reading of the detailed description that follows, for the understanding of which reference should be made to the attached drawings.

[0059] The diagram represents a schematic view of the grinding installation according to the invention.

[0060] This is a schematic representation of a selector device that can be used for the invention.

[0061] A la, we have represented a grinding installation 1 for obtaining a fine fraction 12 and an ultrafine fraction 14 from a mineral material 10.

[0062] At this point, dashed arrows represent a flow of matter as such, while solid arrows represent a flow of matter in suspension, that is to say a flow of matter mixed with a gas, for example air.

[0063] As shown, the grinding installation 1 comprises at least one grinder 2, a first particle size selection device, called the first selector device 3, and a second particle size selection device, called the second selector device 4.

[0064] The crusher 2 is capable of grinding mineral material 10 into a ground product 11. This mineral material 10 is supplied by a distribution hopper 5. Advantageously, the crusher 2 is a ball mill, but is not limited to this. The crusher 2 can also be selected from: a roller press, a vertical mill, or a horizontal roller mill.

[0065] The grinding circuit C0 includes a gas inlet E0 allowing the introduction of gas into the circuit C0 in order to promote the suspension of the grinding material 11.

[0066] In addition, the grinding circuit C0 includes a gas outlet S0 designed to draw off excess gas present in the circuit C0. The grinding circuit C0 is further connected to the selector device 3 by means of a dedicated duct C0-1.

[0067] The ground material 11 can be introduced into the selector device 3 by gravity from its top, or introduced directly into the duct C0-1, for example using a bucket elevator. When the ground material 11 is introduced directly into the duct C0-1, it mixes with the gas present in the ground material circuit C0, so that the material 11 becomes a suspended substance 11'.

[0068] Alternatively or in a complementary manner, the ground material 11 can be introduced into a ground material circuit C0 in the form of a suspended substance 11', i.e. the ground material 11 mixed with a gas.

[0069] The suspended matter 11' comprising the ground material 11 is then directed towards the selector device 3 using the ground material circuit C0 and enters the selector device 3 through the dedicated sheath C0-1.

[0070] The selector device 3 is intended for carrying out a first separation step in which the said ground material 11, in the form of suspended matter 11', is separated into two fractions 12, 13, i.e. a fine fraction 12 and a coarse fraction 13.

[0071] The said coarse fraction 13 is returned as material to the crusher 2 by means of a return circuit C0', while the said fine fraction 12 is in suspension at the outlet of the selector device 3 in order to subject at least a part 12a of the fine fraction 12 to a second separation stage.

[0072] It will be understood that the particle size of the coarse fraction 13 is greater than the cut-off mesh of the first selector device 3, while the particle size of the fine fraction 12 is less than this cut-off mesh.

[0073] At the outlet of the selection device 3, the suspended fine fraction 12' passes through a filtering means 6, for example a bag filter. The filtering means 6 separates the suspended matter 12' into the fine fraction 12 itself and into a gas.

[0074] A drawing means 7 is provided to draw the gas separated by the filtering means 6 in order to direct this gas towards the outlet S0 common to the grinding circuit C0.

[0075] The fine fraction 12 in the form of matter is directed towards a first circuit C1.

[0076] The first circuit C1 includes a control means C10, here a three-way valve, allowing the fine fraction 12 from the filtering means 6 to be directed to the second selector device 4 and / or to a material outlet S1.

[0077] At least part 12a of the fine fraction 12 is intended to be directed to the second selector device 4, while the remainder 12b of the fine fraction 12 is collected by the material outlet S1 of the first circuit C1.

[0078] Said at least a part 12a of the fine fraction 12 is introduced at the level of a gas inlet duct C3-1 of the third circuit C3. The inlet duct C3-1 is supplied with gas by a gas inlet E3, for example air.

[0079] The inlet duct C3-1 is intended to supply the second selector device 4 with a suspended material 12'' corresponding to said at least a part 12a of the fine fraction 12 mixed with the gas from the gas inlet E3. The unused fine fraction 12 12b (also called the remainder 12b) for this second separation stage is advantageously collected to form a first finished product 16.

[0080] The second selector device 4 is provided for carrying out the second separation step, in which said at least one part 12a of the fine fraction 12 is separated into two fractions 14, 15, i.e. an ultrafine fraction 14 and a residual fraction 15.

[0081] Upon exiting the selection device 4, the suspended ultrafine fraction 14 14' passes through a filtering means 8, for example a bag filter. The filtering means 8 separates the suspended matter 14' into the ultrafine fraction 14 itself and into a gas.

[0082] A drawing means 9 is provided to draw the gas separated by the filtering means 8 in order to direct this gas to an outlet S2 of the second circuit C2.

[0083] The ultrafine fraction 14 is collected and advantageously forms a second finished product 14.

[0084] It will be understood that the particle size of the residual fraction 15 is greater than the cut-off mesh of the second selector device 4, while the particle size of the ultrafine fraction 14 is less than this cut-off mesh.

[0085] Advantageously, the installation 1 includes a second circuit C2 to direct at least a part 15a, 15b of the residual fraction 15 from the second selector device 4 according to the needs of the installation.

[0086] In this case, two combinable configurations are envisaged to allow obtaining the first finished product 16 from installation 1.

[0087] The second circuit C2 includes a control device C20 to direct the residual fraction 15 from the second selector device 4 to the crusher 2 and / or to the material outlet S1 of the first circuit C1.

[0088] Thus, the residual fraction 15 is intended to be reground, or to be mixed with the remainder 12b of the fine fraction 12. Of course, it may be provided that a part 15b of the residual fraction 15 is intended to be reground, and also that another part 15a of the residual fraction 15 is to be mixed with the remainder 12b of the fine fraction 12.

[0089] In a first configuration, the residual fraction 15 is directed to the crusher 2 for grinding. In this case, the residual fraction 15 can be returned directly to the crusher 2, or alternatively introduced directly into the return circuit C0' to be mixed with the coarse fraction 13 returned to the crusher 2.

[0090] This first configuration advantageously allows for the removal of a portion 15b of the residual fraction 15, which includes ultrafines that escaped separation by the second selector device. This enables the re-grinding of this portion 15b of the removed residual fraction 15 without degrading the plant's performance. In other words, returning a predetermined quantity of residual fraction 15 to the mill prevents the first finished product 16 from being depleted of ultrafines.

[0091] In a second configuration, at least a part 15a of the residual fraction 15 is directed to the material outlet S1 of the first circuit C1 to be mixed with the remainder 12b of the fine fraction 12 in order to directly enrich the first finished product 16 with fines after removing the ultrafines.

[0092] This second configuration advantageously allows taking a sufficient quantity of residual fraction 15 to allow reuse of part 15a of the residual fraction 15 in order to form a first finished product 16 further enriched in fines free of ultrafines without degrading the performance of the second separation device 4.

[0093] We will now describe an example of a particle size selection device, called a selector, which can be the first selector device 3 and / or the second selector device 4.

[0094] A particle size selection device allows a stream of particles present in a gas stream to be separated into two fractions, one fine below a determined particle size (called cut-off mesh), the other coarse above said particle size.

[0095] Such a device is also known in the relevant industrial sector as a "Centrifugal Air Selector".

[0096] Separation is achieved using a vertical-axis cylindrical rotor equipped with blades evenly spaced around its periphery. Between these blades, the particles are subjected to opposing forces: on the one hand, the centrifugal force generated by the rotor's rotation, which tends to expel the particles, and on the other hand, the drag force generated by the velocity of a gas drawn towards the center of the rotor, which tends to carry them towards the gas outlet. Thus, the centrifugal force is greater for larger particles and the drag force is greater for smaller particles, thereby achieving particle size separation of the processed materials.

[0097] Materials smaller than a predetermined particle size are carried with the gas towards the outlet as a suspension, while materials larger than this predetermined particle size fall back down and are collected by gravity. Such high-performance separation devices are described in particular in documents FR-2,642,994 or FR-2,658,096, which are incorporated by reference. The materials to be processed can be fed either by gravity from the top, in which case the materials are generally dispersed by a rotating plate attached to the rotor, or as a suspension in the incoming gas, or by combining the two preceding feeding methods.

[0098] A la, we have represented such a particle size selection device 1'. This device 1' includes a casing 6', inside which a rotor 2', equipped with blades 3' on its periphery, can rotate around a vertical axis of rotation.

[0099] A set of blades 7' surrounds the rotor 2', opposite the blades. The blades guide a gas flow towards the blades 3' and the center of the rotor. The blades are equipped with pivots, along a vertical axis, which allow them to move in order to adjust their orientation and adapt the speed of the gas reaching the rotor to the rotor's rotational speed.

[0100] The pivots of all the guide vanes are connected to a single device that allows all the vanes to be oriented simultaneously at the same angle relative to the rotor's peripheral surface. A hopper 10', positioned below the rotor and the vanes of the device, collects the material that has fallen and is ejected by the rotor, while the material carried by the aspirated gases is discharged through outlet 9'. This outlet 9' is immediately followed by a 90' bend to allow the rotor drive to be positioned above this bend. The rotation shaft 21', belonging jointly to the rotor and its drive (not shown), passes through this bend, inside which it is protected by a sleeve 22'. The gas supply to the device is provided by the casing 6' and by a vertical duct 5' extending downwards from said casing 6', encompassing the hopper 10'.

[0101] The materials to be sorted can be suspended in the supplied gas stream, or discharged at the top of the rotor via inlet points 8'. As can be seen in the diagram, according to the prior art, the hopper 10' adds a substantial height to the device and thus contributes to its overall height. The hopper also necessitates positioning the motor above the rotor 2'.

[0102] Although this description refers to specific embodiments, modifications may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments illustrated or mentioned may be combined in additional embodiments. Therefore, the description and drawings should be considered illustrative rather than restrictive.

Claims

A grinding process for obtaining a fine fraction (12) and an ultrafine fraction (14) from a mineral material (10), implemented in a grinding installation (1) comprising: - at least one crusher (2) capable of grinding said mineral material (10) into a ground product (11), and - a first particle size selection device, called the first selection device (3), capable of separating said ground product (11) into two fractions (12, 13), namely a fine fraction (12) and a coarse fraction (13), said coarse fraction (13) being returned to said crusher (2), - a second particle size selection device, called the second selection device (4), capable of separating at least a portion of said fine fraction (12) into two fractions (14, 15), namely an ultrafine fraction (14) and a residual fraction (15), said process comprising the following steps: - said mineral material (10) is ground by means of of at least one crusher (2), obtaining said crushed material (11),- the ground material (11) is separated into said fine fraction (12) and said coarse fraction (13) by means of said first selecting device (3), - at least a portion (12a) of said fine fraction (12) is separated into said ultrafine fraction (14) and said residual fraction (15) by means of said second selecting device (4), - at least a portion (15b) of the residual fraction (15) is directed to the crusher (2) for grinding, and / or at least a portion (15a) of the residual fraction (15) is mixed with the remainder (12b) of said fine fraction (12). Grinding method according to the preceding claim, wherein at least a part (12a) of said fine fraction (12) corresponds to a range of values ​​between 10% and 70% of the fine fraction (12) separated by the first selector device (3), preferably between 40% and 60%. A grinding process according to any one of the preceding claims, wherein at least a part (15b) of said residual fraction (15) corresponds to a range of values ​​between 0% and 100% of the residual fraction (15) separated by the second selector device (4), preferably between 40% and 100%, even more preferably between 80% and 100%. A grinding installation (1) for obtaining a fine fraction (12) and an ultrafine fraction (14) from a mineral material (10) comprising: - at least one crusher (2) capable of grinding said mineral material (10) into a ground product (11); - a first particle size selection device, called the first selection device (3), capable of separating said ground product (11) into two fractions (12, 13), namely a fine fraction (12) and a coarse fraction (13), said coarse fraction (13) being returned to the crusher (2); - a second particle size selection device, called the second selection device (4), capable of separating at least a portion (12a) of said fine fraction (12) into two fractions (14, 15), namely an ultrafine fraction (14) and a residual fraction (15); - a first circuit (C1) for directing at least a portion (12a) of the fine fraction (12) from the first selector device (3) to the second selector device (4),- a second circuit (C2) to direct: - at least a portion (15a) of the residual fraction (15) from the second selector device (4) to the first circuit (C1) to be mixed with the remainder (12b) of said fine fraction (12); and / or - at least a portion (15b) of the residual fraction (15) from the second selector device (4) to the crusher (2) to be crushed, grinding installation (1) according to the preceding claim, wherein the installation (1) includes a control device (C10) for directing the fine fraction (12) to the second selector device (4) and / or to a material outlet (S1) of the first circuit (C1). Grinding installation (1) according to any one of the preceding claims, wherein the installation includes a control device (C20) for directing the residual fraction (15) to the grinder (2) and / or to a material outlet (S1) of the first circuit (C1). Grinding installation (1) according to any one of the preceding claims, wherein the mill (2) is a ball mill or a mill (2) selected from: a roller press, a vertical mill or a horizontal roller mill. Grinding installation (1) according to any one of the preceding claims, wherein the first selector device (3) comprises a dynamic separator. Grinding installation (1) according to any one of the preceding claims, wherein the second selector device (4) comprises a dynamic separator. Crushing installation (1) according to any one of claims 8 or 9, wherein the dynamic separator (3, 4) comprises a casing (6') including: a rotor (2') having blades (3') on its periphery configured to propel part of the material contained in the suspended material stream by centrifugal force, a set of vanes (7) surrounding the rotor (2') configured to guide a suspended material stream towards the blades (3').

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